Co-reporter:Jingfang Sun, Chengyan Ge, Xiaojiang Yao, Weixin Zou, Xi Hong, Changjin Tang, Lin Dong
Applied Surface Science 2017 Volume 426(Volume 426) pp:
Publication Date(Web):31 December 2017
DOI:10.1016/j.apsusc.2017.07.069
•Impregnation modes induced marked difference in physicochemical property and catalytic activity.•The NO conversion exhibited the order of CuCeAl-SI > CuCeAl-CI.•The improvement activity originated from the obtaining of more interfacial interaction between copper oxide species and ceria of CuCeAl-SI.A series of ceria modified CuO/γ-Al2O3 (CuO-CeO2/γ-Al2O3) catalysts were prepared via stepwise impregnation (CuCeAl-SI) and co-impregnation (CuCeAl-CI) method and tested in the model reaction of NO reduction by CO. It was found that the influence of impregnation modes on the catalytic properties of CuCeAl samples mainly lies on the control of ceria particle sizes and modulation of the distribution of various copper species. In both impregnation modes, ceria was mainly spread on γ-Al2O3 as small particles while copper species were highly dispersed. A quantitative estimation of copper species was tentatively provided via a combined surface acid leaching experiment and H2-TPR characterization for the first time. The results showed that for CuCeAl-CI catalyst, about 55% and 25% copper species were dispersed on γ-Al2O3 and nanosized ceria, respectively, while about 20% was migrated into ceria lattice during the calcination process. In contrast, in CuCeAl-SI sample, the corresponding values changed to about 25%, 70% and 5%, respectively. The synergistic effect between copper species and ceria can promote the improvement of catalytic performance, which results in higher activity of CuCeAl-SI than that of CuCeAl-CI catalyst.Download high-res image (127KB)Download full-size image
Co-reporter:Kaili Ma;Weixin Zou;Lei Zhang;Lulu Li;Shuohan Yu;Changjin Tang;Fei Gao
RSC Advances (2011-Present) 2017 vol. 7(Issue 10) pp:5989-5999
Publication Date(Web):2017/01/16
DOI:10.1039/C6RA25863H
Hollow structured CeO2–MnOx hybrid materials with up to three shells were prepared successfully by using carbon spheres as the hard template. It was found that the shells could be well controlled by simply adjusting the calcination rate. Elemental mapping results showed Mn and Ce species exhibited a homogeneous spatial distribution and the existence of Mn could improve the diffusion of CeO2 into the carbon spheres during the construction of the multi-shell structure, suggesting the intensive cooperative interaction between Mn and Ce. When triple-shell CeO2–MnOx hollow spheres were used as a catalyst for selective catalytic reduction of NO with NH3, superior low-temperature catalytic performance was exhibited, compared with traditional CeO2–MnOx nanoparticles, single-shell and double-shell hollow spheres. Combined with XRD, H2-TPR and XPS characterization, it was indicated that the synergistic effects and surface active species enhanced by the special multi-shell CeO2–MnOx hollow structures could account for the excellent performances. The results of the present study shed light on the creation of complex and hybrid hollow structured materials for superior performance in catalysis fields, like NO reduction for environmental protection.
Co-reporter:Kaili Ma;Weixin Zou;Lei Zhang;Lulu Li;Shuohan Yu;Changjin Tang;Fei Gao
RSC Advances (2011-Present) 2017 vol. 7(Issue 10) pp:5989-5999
Publication Date(Web):2017/01/16
DOI:10.1039/C6RA25863H
Hollow structured CeO2–MnOx hybrid materials with up to three shells were prepared successfully by using carbon spheres as the hard template. It was found that the shells could be well controlled by simply adjusting the calcination rate. Elemental mapping results showed Mn and Ce species exhibited a homogeneous spatial distribution and the existence of Mn could improve the diffusion of CeO2 into the carbon spheres during the construction of the multi-shell structure, suggesting the intensive cooperative interaction between Mn and Ce. When triple-shell CeO2–MnOx hollow spheres were used as a catalyst for selective catalytic reduction of NO with NH3, superior low-temperature catalytic performance was exhibited, compared with traditional CeO2–MnOx nanoparticles, single-shell and double-shell hollow spheres. Combined with XRD, H2-TPR and XPS characterization, it was indicated that the synergistic effects and surface active species enhanced by the special multi-shell CeO2–MnOx hollow structures could account for the excellent performances. The results of the present study shed light on the creation of complex and hybrid hollow structured materials for superior performance in catalysis fields, like NO reduction for environmental protection.
Co-reporter:Xiaojiang Yao, Kaili Ma, Weixin Zou, Shenggui He, ... Lin Dong
Chinese Journal of Catalysis 2017 Volume 38, Issue 1(Volume 38, Issue 1) pp:
Publication Date(Web):1 January 2017
DOI:10.1016/S1872-2067(16)62572-X
This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnOx-CeO2 catalysts for selective catalytic reduction of NO by NH3 (NH3-SCR) at low temperature. Five different methods, namely, mechanical mixing, impregnation, hydrothermal treatment, co-precipitation, and a sol-gel technique, were used to synthesize MnOx-CeO2 catalysts. The catalysts were characterized in detail, and an NH3-SCR model reaction was chosen to evaluate the catalytic performance. The results showed that the preparation methods affected the catalytic performance in the order: hydrothermal treatment > sol-gel > co-precipitation > impregnation > mechanical mixing. This order correlated with the surface Ce3+ and Mn4+ content, oxygen vacancies and surface adsorbed oxygen species concentration, and the amount of acidic sites and acidic strength. This trend is related to redox interactions between MnOx and CeO2. The catalyst formed by a hydrothermal treatment exhibited excellent physicochemical properties, optimal catalytic performance, and good H2O resistance in NH3-SCR reaction. This was attributed to incorporation of Mnn+ into the CeO2 lattice to form a uniform ceria-based solid solution (containing Mn-O-Ce structures). Strengthening of the electronic interactions between MnOx and CeO2, driven by the high-temperature and high-pressure conditions during the hydrothermal treatment also improved the catalyst characteristics. Thus, the hydrothermal treatment method is an efficient and environment-friendly route to synthesizing low-temperature denitrification (deNOx) catalysts.Electron interaction between MnOx and CeO2 is influenced by the preparation methods, which can improve the physicochemical properties of MnOx-CeO2 catalysts, and promote the adsorption/activation of reactant molecules to result in excellent catalytic performance.Download high-res image (90KB)Download full-size image
Co-reporter:Lulu Li, Lei Zhang, Kaili Ma, Weixin Zou, Yuan Cao, Yan Xiong, Changjin Tang, Lin Dong
Applied Catalysis B: Environmental 2017 Volume 207(Volume 207) pp:
Publication Date(Web):15 June 2017
DOI:10.1016/j.apcatb.2017.02.041
•TiO2/CeO2 catalysts are modified by ultra-low loading of copper.•The NH3-SCR activity of TiO2/CeO2 are strongly influenced by copper content.•Redox and surface acidic properties are improved by the addition of copper.•The appearance of CuO weakened the adsorption ability of nitrates.A series of ultra-low content copper-modified TiO2/CeO2 catalysts were prepared by wet impregnation method and tested for selective catalytic reduction of NO by NH3. The catalyst with a Cu/Ce molar ratio of 0.005 showed the best low-temperature activity and excellent sulfur-poisoning resistance. It was worth noting that the very small amounts of copper addition can lead to three times the activity at low temperature. The prepared catalysts were characterized by XRD, BET, Raman, XPS, NH3-TPD and the results revealed that the introduction of copper increased the amount of surface adsorbed oxygen and Ce3+ species on the catalyst surface and generated more Brønsted acid sites. The redox and surface acidic properties were also improved by the addition of Cu. All these factors played important roles in enhancing NH3-SCR performance of TiO2-CuO/CeO2 catalysts. Furthermore, in situ DRIFT experiments demonstrated that Cu doping enhanced the adsorption capacity of NH3 while the appearance of CuO weakened the adsorption ability of bridging nitrates, both the two factors synergistically facilitated the NH3-SCR reaction proceed smoothly via the Eley-Rideal pathway.Download high-res image (136KB)Download full-size image
Co-reporter:Yan Xiong;Lulu Li;Lei Zhang;Yuan Cao;Shuohan Yu;Changjin Tang
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 32) pp:21840-21847
Publication Date(Web):2017/08/16
DOI:10.1039/C7CP03735J
A Cu-doped CeO2 solid solution was constructed by co-precipitation and additional acid treatment to investigate the behavior of doped copper under thermal treatment. Acid treatment was used to intentionally remove the surface Cu species. Surface properties and fundamental characteristics of the catalysts were characterized by several techniques, as well as the CO oxidation performance. The results reveal that doped Cu ions could gradually migrate from the matrix to the catalyst surface during calcination. The degree of migration was mostly dependent on the calcination temperature, and also the concentration gradient of Cu between the surface and matrix. Catalytic testing in CO oxidation showed that the migration induced a distinct promotional effect on the activities of catalysts, supposedly closely related to the increased surface active Cu species and improved redox properties generated by the Cu migration. The present study offers renewed understanding of the dynamic behavior of ceria-based solid solution catalysts.
Co-reporter:Lulu Li, Bowen Sun, Jingfang Sun, Shuohan Yu, Chengyan Ge, Changjin Tang, Lin Dong
Catalysis Communications 2017 Volume 100(Volume 100) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.catcom.2017.06.019
•MnOx/CeO2 nanosphere catalyst showed over 80% NO conversion at 75–250 °C.•MnOx/CeO2 nanosphere possessed high amounts of acid sites adsorbed NOx species.•Excellent sulfur-tolerance ability and stability.•Reaction pathway for NH3-SCR over MnOx/CeO2 nanosphere catalyst was illustrated.A novel MnOx-CeO2 nanosphere catalyst with assembled structure from tiny particles was prepared and tested towards low-temperature NH3-SCR. A superior deNOx performance compared to that obtained over the catalyst composed of MnOx supported on CeO2 was obtained. A good resistance to high space velocity and SO2 present in the feed and an excellent stability (no deactivation was observed during 100-h of testing at 150 °C) were obtained. The characterization results suggested that the higher specific surface area, better redox behavior and larger concentration of surface active oxygen species were responsible for the above mentioned excellent performance. The results of the present study suggest that control of catalyst morphology can be an effective strategy to upgrade low-temperature NH3-SCR performance.
Co-reporter:Changjin Tang, Hongliang Zhang and Lin Dong
Catalysis Science & Technology 2016 vol. 6(Issue 5) pp:1248-1264
Publication Date(Web):09 Dec 2015
DOI:10.1039/C5CY01487E
Selective catalytic reduction of NO with NH3 (NH3-SCR) is a powerful technique for the abatement of NOx from stationary sources, and the currently used VOx/TiO2-based catalysts are widely applicable for medium-temperature conditions but not suitable for NH3-SCR operated at low temperatures. Recently, low-temperature NH3-SCR has attracted considerable attention owing to the vast demand in industrial furnaces and its energy-conserving feature. During the past years, a great many studies have demonstrated that ceria-based catalysts are potential candidates as catalysts for low-temperature NH3-SCR. Herein we summarize the recent advances in the application of ceria-based catalysts for low-temperature NH3-SCR. The review begins with a brief introduction of the general guideline for low-temperature NH3-SCR and the interaction between the reactants and CeO2. The different roles of ceria as a pure support/active species, bulk doping component and surface modifier are discussed. As well, the mechanistic investigations (active sites, intermediates, reaction mechanism) and SO2/H2O tolerance are emphasized. Lastly, the perspectives on the opportunities and challenges of ceria-based catalysts for low-temperature NH3-SCR in future research are presented.
Co-reporter:Lei Zhang, Lulu Li, Yuan Cao, Yan Xiong, Shiguo Wu, Jingfang Sun, Changjin Tang, Fei Gao and Lin Dong
Catalysis Science & Technology 2015 vol. 5(Issue 4) pp:2188-2196
Publication Date(Web):07 Jan 2015
DOI:10.1039/C4CY01412J
TixSn1−xO2 was prepared by a co-precipitation method, and a series of CeO2/TixSn1−xO2 samples were prepared to investigate the effect of doping SnO2 into TiO2 for selective catalytic reduction of NO by NH3. The results of catalytic tests suggested that the catalyst with the optimal molar ratio (Ti:Sn = 1:1) exhibited the best catalytic performance. Moreover, the NO removal efficiency of CeO2/Ti0.5Sn0.5O2 was higher than that of CeO2/TiO2. The obtained samples were characterized by BET, XRD, H2-TPR, XPS, NH3-TPD and in situ DRIFT. The results revealed that the introduction of SnO2 resulted in the formation of rutile-type Ti0.5Sn0.5O2 solid solution with larger specific surface area and better thermal stability. The interactions between CeO2 and the Ti0.5Sn0.5O2 support could improve the redox performance of the catalyst, which was beneficial to the enhancement of catalytic activity at low temperature. Furthermore, doping SnO2 enhanced the surface acid sites and weakened the adsorption of nitrates, which played an important role in the catalytic reaction process. Finally, in situ DRIFT demonstrated that the competition adsorption happened between bridging nitrates and NH3 gas and the selective catalytic reduction of NO by NH3 proceeded mainly via the Eley–Rideal mechanism over Ce/TiO2 and Ce/Ti0.5Sn0.5O2.
Co-reporter:Chuanzhi Sun, Yingjie Tang, Fei Gao, Jingfang Sun, Kaili Ma, Changjin Tang and Lin Dong
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 24) pp:15996-16006
Publication Date(Web):15 May 2015
DOI:10.1039/C5CP02158H
Two different precursors, manganese nitrate (MN) and manganese acetate (MA), were employed to prepare two series of catalysts, i.e., xCuyMn(N)/TiO2 and xCuyMn(A)/TiO2, by a co-impregnation method. The catalysts were characterized by XRD, LRS, CO-TPR, XPS and EPR spectroscopy. The results suggest that: (1) both xCuyMn(N)/TiO2 and xCuyMn(A)/TiO2 catalysts exhibit much higher catalytic activities than an unmodified Cu/TiO2 catalyst in the NO + CO reaction. Furthermore, the activities of catalysts modified with the same amount of manganese are closely dependent on manganese precursors. (2) The enhancement of activities for Mn-modified catalysts should be attributed to the formation of the surface synergetic oxygen vacancy (SSOV) Cu+–□–Mny+ in the reaction process. Moreover, since the formation of the SSOV (Cu+–□–Mn3+) in the xCuyMn(N)/TiO2 catalyst is easier than that (Cu+–□–Mn2+) in the xCuyMn(A)/TiO2 catalyst, the activity of the xCuyMn(N)/TiO2 catalyst is higher than that of the xCuyMn(A)/TiO2 catalyst. This conclusion is well supported by the XPS and EPR results.
Co-reporter:Lichen Liu, Chengyan Ge, Weixin Zou, Xianrui Gu, Fei Gao and Lin Dong
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 7) pp:5133-5140
Publication Date(Web):12 Jan 2015
DOI:10.1039/C4CP05449K
Metal–support interactions between Au and TiO2 are studied based on Au/TiO2 catalysts with different TiO2 crystal planes exposed. With ex situ XPS, TEM and in situ DRIFTS, we have investigated the crystal-plane-dependent metal–support interaction effects on the physiochemical properties of Au/TiO2 catalysts. Based on the structural characterization and spectroscopic results, we can observe chemical oscillations (including the electronic structures of Au nanoparticles and the interaction between Au/TiO2 catalysts and CO molecules) during alternate H2 and O2 pre-treatments. Their variation tendencies of oscillations are greatly dependent on the crystal planes of TiO2 and the pre-treatment temperature. Furthermore, their surface and electronic changes after H2 and O2 pre-treatments can be well correlated with their catalytic activities in CO oxidation. Electron-transfer processes across the Au–TiO2 interface are proved to be the origin accounting for their changes after H2 and O2 pre-treatments. The different electronic structures of different TiO2 crystal planes should have relationships with the crystal-plane-dependent metal–support interaction effects in Au/TiO2.
Co-reporter:Weixin Zou, Chengyan Ge, Minyue Lu, Shiguo Wu, Yongzheng Wang, Jingfang Sun, Yu Pu, Changjin Tang, Fei Gao and Lin Dong
RSC Advances 2015 vol. 5(Issue 119) pp:98335-98343
Publication Date(Web):29 Oct 2015
DOI:10.1039/C5RA20466F
In this work, NiO/CeO2 catalysts were synthesized with tunable CeO2 crystal facets ({110}, {111} and {100} facets) to study the crystal-plane effects on the catalytic properties. Kinetic studies of CO oxidation showed that NiO/CeO2 {110} had the lowest activation energy. Furthermore, the obtained samples were characterized by means of TEM, XRD, Raman, N2-physisorption, UV-Vis DRS, XPS, H2-TPR and in situ DRIFTS technologies. The results demonstrated that the geometric and electronic structures of the nickel species were dependent on the NiO/CeO2 interfaces, which had an influence on the synergetic interaction of absorbed CO and active oxygen species, and then the generation of the formate intermediate played an important role in the catalytic performance. The possible interface structures of nickel species on the CeO2 {110}, {111} and {100} surface were proposed through the incorporation model, suggesting that the advantageous NiO/CeO2 {110} interface facilitated CO adsorption/activation and active oxygen species formation, leading to the best catalytic performance.
Co-reporter:Lei Zhang
The Journal of Physical Chemistry C 2015 Volume 119(Issue 2) pp:1155-1163
Publication Date(Web):December 18, 2014
DOI:10.1021/jp511282c
In this work, the influence of sulfated temperature on the selective catalytic reduction of NO by NH3 over the sulfated CeO2 was investigated. The NO conversion of the sulfated CeO2 samples decreased with the increase of sulfated temperature. The fresh CeO2 and the CeO2 sulfated at different temperatures were characterized by X-ray diffraction (XRD), laser Raman spectroscopy (LRS), in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), thermogravimetry and differential thermal analysis (TG-DTA), H2-temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The obtained results indicate that the sulfation process was gradually deepened, and the existence states of sulfate species over CeO2 were changed from surface sulfates to bulk-like sulfates and to bulk sulfates with raising the sulfated temperature. Meanwhile, the formed bulk-like and bulk sulfates were the main reason to result in the decrease of catalytic activity. In addition, the corresponding model was proposed to understand the interaction between sulfate species and CeO2 influenced by sulfated temperature. Finally, bulk sulfates could be eliminated by H2O washing and the NO conversion of CeO2 sulfated at 550 °C was recovered after H2O washing, which supports the proposed model.
Co-reporter:Lihui Dong, Bing Zhang, Changjin Tang, Bin Li, Liya Zhou, Fuzhong Gong, Baozhen Sun, Fei Gao, Lin Dong and Yi Chen
Catalysis Science & Technology 2014 vol. 4(Issue 2) pp:482-493
Publication Date(Web):07 Nov 2013
DOI:10.1039/C3CY00703K
Fe2O3–CeO2–Ti0.5Sn0.5O2 catalysts were prepared by a wet impregnation method and were characterized using XRD, LRS, EPR, H2-TPR, in situ IR, as well as the activity test for the removal of NO by CO. The results showed that the Fe2O3 and CeO2 are highly dispersed on the surface of Ti0.5Sn0.5O2 (the loading of Fe2O3 and CeO2 are 1.2 mmol Fe per 100 m2 and 0.4 mmol Ce per 100 m2, respectively). When the iron oxide loading is increased, the isolated Fe3+ ions change into the polymeric Fe3+ clusters and ceria addition also further promotes the formation of polymeric Fe3+ clusters. Catalysts modified with ceria display better performance in activity, and this would result from the formation of the more polymeric Fe3+ clusters, which are more easily reduced to Fe2+ ions under CO atmosphere. In situ FT-IR results indicated that the Fe2+ ions generated from the reduction of Fe3+ ions are primary active sites for NO + CO reactions. A possible reaction mechanism is tentatively proposed. In the reaction atmosphere, NO adsorbed on the surface of the catalysts forms several types of nitrite species. With the increase of temperature, bridging bidentate nitrate species transform into chelating nitro species, which react with CO gas to produce CO2 + N2O. When temperature reaches beyond 200 °C, NO adsorbed on Fe2+ ions (reduction of Fe3+ ions) reacts with carbonate species adsorbed on the surface of the catalysts, and produces CO2 + N2.
Co-reporter:Yan Xiong, Xiaojiang Yao, Changjin Tang, Lei Zhang, Yuan Cao, Yu Deng, Fei Gao and Lin Dong
Catalysis Science & Technology 2014 vol. 4(Issue 12) pp:4416-4425
Publication Date(Web):31 Jul 2014
DOI:10.1039/C4CY00785A
The influence of CO-pretreatment on the properties of CuO–V2O5/γ-Al2O3 catalysts was investigated in the reduction of NO by CO. Catalytic performance results showed that the pretreated CuO–V2O5/γ-Al2O3 exhibited extremely high activity and selectivity. For example, NO conversion can be remarkably enhanced from 13.8% to 100.0% for the 03Cu01V catalyst. For the catalyst characterization, the XRD results suggested that copper oxide and vanadium oxide were highly dispersed on the surface of γ-Al2O3 and the TPR results gave evidence for the existence of Cu2+–O–V5+ species. The XPS and EPR results demonstrated that Cu2+ and V5+ were reduced to lower valence states (Cu2+ → Cu+, V5+ → V4+) by the CO-pretreatment, which was proved by in situ FT-IR to be beneficial to the adsorption of CO and dissociation of NO. In addition, the interaction between the dispersed copper oxide and vanadium oxide species upon the γ-Al2O3 support before and after CO-pretreatment was tentatively discussed, using the concept of SSOV (surface synergetic oxygen vacancy) which was proposed elsewhere. According to this concept, the dispersed Cu2+–O–V5+ species could be reduced to Cu+–ϒ–V4+ (ϒ represents an oxygen vacancy) by CO-pretreatment and it was considered to be the primary active species for the reaction. Based on the discussion of the experiment results, a possible mechanism was proposed.
Co-reporter:Xiaojiang Yao, Changjin Tang, Fei Gao and Lin Dong
Catalysis Science & Technology 2014 vol. 4(Issue 9) pp:2814-2829
Publication Date(Web):27 May 2014
DOI:10.1039/C4CY00397G
Catalytic elimination is an important technique to reduce the emission of atmospheric molecular contaminants (such as CO, NOx, VOCs, HC, and PM, etc.) efficiently. In this field, the supported metal-oxide catalysts have attracted more and more attention in recent years due to their low cost and excellent catalytic performance. It is well known that catalytic performances are significantly dependent on the supports, surface-dispersed components, and the pretreatment of the catalysts. In this work, we present a brief review and propose some perspectives for supported metal-oxide catalysts according to the above-mentioned three aspects. Meanwhile, this paper covers some interesting results about the preparation of supported metal-oxide catalysts and the improvement of their catalytic performances for the elimination of atmospheric molecular contaminants obtained by our research group. Moreover, we propose the concepts of “green integration preparation (GIP)” and “surface synergetic oxygen vacancy (SSOV)” to understand the relationship between the “composition–structure–activity” of the supported metal-oxide catalysts, and further clarify the nature of the catalytic reactions.
Co-reporter:Xiaojiang YAO, Yan XIONG, Jingfang SUN, Fei GAO, Yu DENG, Changjin TANG, Lin DONG
Journal of Rare Earths 2014 Volume 32(Issue 2) pp:131-138
Publication Date(Web):February 2014
DOI:10.1016/S1002-0721(14)60042-9
In order to investigate the influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 catalyst for NO reduction by CO, two series of catalysts (xCuyMn/Ce and xCu/yMn/Ce) were prepared by co-impregnation and stepwise-impregnation methods, and characterized by means of X-ray diffraction (XRD), Raman spectra, H2-temperature programmed reduction (H2-TPR), in situ diffuse reflectance infrared Fourier transform spectra (in situ DRIFTS) techniques. Furthermore, the catalytic performances of these catalysts were evaluated by NO+CO model reaction. The obtained results indicated that: (1) The catalysts acquired by co-impregnation method exhibited stronger interaction owing to the more sufficient contact among each component of the catalysts compared with the catalysts obtained by stepwise-impregnation method, which was beneficial to the improvement of the reduction behavior; (2) The excellent reduction behavior was conducive to the formation of low valence state copper species (Cu+/Cu0) and more oxygen vacancies (especially the surface synergetic oxygen vacancies (SSOV, Cu+–Mn(4–x)+)) during the reaction process, which were beneficial to the adsorption of CO species and the dissociation of NO species, respectively, and further promoted the enhancement of the catalytic performance. Finally, in order to further understand the difference between the catalytic performances of these catalysts prepared by co-impregnation and stepwise-impregnation methods, a possible reaction mechanism (schematic diagram) was tentatively proposed.Compared with stepwise-impregnation method, co-impregnation method is more beneficial to the sufficient contact among each component of the catalysts, which results in the formation of more Cu2+-O-Mn4+ species and better reduction behavior, and further benefits to the generation of more Cu+ species and oxygen vacancies (especially surface synergetic oxygen vacancies (SSOV, Cu+–Mn(4–x)+)) during the reaction process, consequently promotes the enhancement of catalytic performance remarkably
Co-reporter:Xianrui GU, Hao LI, Lichen LIU, Changjin TANG, Fei GAO, Lin DONG
Journal of Rare Earths 2014 Volume 32(Issue 2) pp:139-145
Publication Date(Web):February 2014
DOI:10.1016/S1002-0721(14)60043-0
The CuO/CeO2 catalysts were investigated by means of X-ray diffraction (XRD), laser Raman spectroscopy (LRS), X-ray photoelectronic spectroscopy (XPS), temperature-programmed reduction (TPR), in situ Fourier transform infrared spectroscopy (FTIR) and NO+CO reaction. The results revealed that the low temperature (<150 °C) catalytic performances were enhanced for CO pretreated samples. During CO pretreatment, the surface Cu+/Cu0 and oxygen vacancies on ceria surface were present. The low valence copper species activated the adsorbed CO and surface oxygen vacancies facilitated the NO dissociation. These effects in turn led to higher activities of CuO/CeO2 for NO reduction. The current study provided helpful understandings of active sites and reaction mechanism in NO+CO reaction.Results of NO conversion (%)
Co-reporter:Hongliang Zhang;Changjin Tang;Yuanyuan Lv;Fei Gao
Journal of Porous Materials 2014 Volume 21( Issue 1) pp:63-70
Publication Date(Web):2014 February
DOI:10.1007/s10934-013-9748-5
A series of Ti-containing SBA-15 samples were firstly prepared in the self-generated acidic condition. The samples were characterized by powder X-ray diffraction, N2-adsorption, transmission electron microscopy, inductively coupled plasma, Fourier-transform infrared spectroscopy, UV–vis diffuse reflectance spectra (UV–vis) and X-ray photoelectron spectroscopy. All the samples possessed well-ordered hexagonal arrays of mesopores and Ti ions could be incorporated into the framework of SBA-15. Catalytic performances of the obtained materials were evaluated in the photodegradation of Rhodamine B (RhB). Catalytic tests indicated that Ti-SBA-15 showed much higher photodegradation ability towards RhB than pure TiO2.
Co-reporter:Lichen Liu;Zhe Liu;Annai Liu;Xianrui Gu;Chengyan Ge;Dr. Fei Gao; Lin Dong
ChemSusChem 2014 Volume 7( Issue 2) pp:618-626
Publication Date(Web):
DOI:10.1002/cssc.201300941
Abstract
In this work, TiO2–graphene nanocomposites are synthesized with tunable TiO2 crystal facets ({100}, {101}, and {001} facets) through an anion-assisted method. These three TiO2–graphene nanocomposites have similar particle sizes and surface areas; the only difference between them is the crystal facet exposed in TiO2 nanocrystals. UV/Vis spectra show that band structures of TiO2 nanocrystals and TiO2–graphene nanocomposites are dependent on the crystal facets. Time-resolved photoluminescence spectra suggest that the charge-transfer rate between {100} facets and graphene is approximately 1.4 times of that between {001} facets and graphene. Photoelectrochemical measurements also confirm that the charge-separation efficiency between TiO2 and graphene is greatly dependent on the crystal facets. X-ray photoelectron spectroscopy reveals that TiC bonds are formed between {100} facets and graphene, while {101} facets and {001} facets are connected with graphene mainly through TiOC bonds. With TiC bonds between TiO2 and graphene, TiO2-100-G shows the fastest charge-transfer rate, leading to higher activity in photocatalytic H2 production from methanol solution. TiO2-101-G with more reductive electrons and medium interfacial charge-transfer rate also shows good H2 evolution rate. As a result of its disadvantageous electronic structure and interfacial connections, TiO2-001-G shows the lowest H2 evolution rate. These results suggest that engineering the structures of the TiO2–graphene interface can be an effective strategy to achieve excellent photocatalytic performances.
Co-reporter:Lichen Liu, Zeyang Ji, Weixin Zou, Xianrui Gu, Yu Deng, Fei Gao, Changjin Tang, and Lin Dong
ACS Catalysis 2013 Volume 3(Issue 9) pp:2052
Publication Date(Web):July 26, 2013
DOI:10.1021/cs4002755
In this work, transition metal oxide clusters (MnOx, FeOx, CoOx, NiOx, and CuOx, denoted as TM-TiO2) are in situ loaded on TiO2 nanosheets through one-pot reaction. Structural and pore structural characterizations prove that metal ions do not dope into the frameworks of TiO2 nanosheets. Through TEM and STEM, we can determine that clusters with ∼2 nm size are finely dispersed on TiO2 nanosheets. PL spectra and photoelectrochemical measurements suggest that these metal oxide clusters can serve as hole traps. Time-resolved PL spectra demonstrate that the charge-transfer process in TM-TiO2 is significantly accelerated, leading to higher charge separation efficiency. Metal oxide clusters show significant promotion effect in photocatalytic water oxidation to O2 compared to RuO2/TiO2 and IrO2/TiO2 nanosheets (denoted as Ru-TiO2(IM) and Ir-TiO2(IM)) prepared through conventional impregnation method. We also prepared RuO2/TiO2 and Ir/TiO2 nanosheets (denoted as Ru-TiO2(HT) and Ir-TiO2(HT)) through the in situ loading method. Ru-TiO2(HT) and Ir-TiO2(HT) show O2 evolution rates much better than those of Ru-TiO2(IM) and Ir-TiO2(IM) due to the smaller sizes of RuO2 and IrO2. However, Mn-TiO2 and Co-TiO2 still display better photoactivities compared to those of Ru-TiO2(HT) and Ir-TiO2(HT). These results indicate that transition metal oxides with small sizes can also work as co-catalysts in photocatalysis to substitute noble metal oxides.Keywords: heterojunctions; interfacial charge transfer; metal oxide clusters; photocatalytic O2 evolution; TiO2 nanosheets
Co-reporter:Lichen Liu, Xianrui Gu, Yuan Cao, Xiaojiang Yao, Lei Zhang, Changjin Tang, Fei Gao, and Lin Dong
ACS Catalysis 2013 Volume 3(Issue 12) pp:2768
Publication Date(Web):October 16, 2013
DOI:10.1021/cs400492w
In this work, Au nanoparticles are loaded on TiO2 nanocrystals with different crystal planes exposed ({100}, {101}, and {001} planes) to investigate the crystal-plane effect on the catalytic properties of Au/TiO2 catalyst. Kinetic studies of CO oxidation show that the catalytic activities of three as-prepared Au/TiO2 samples follow this order: Au/TiO2-{100} > Au/TiO2-{101} > Au/TiO2-{001}. Furthermore, different mechanisms exist at low temperatures (<320 K) and high temperatures (>320 K). With the help of ex-situ XPS and in situ DRIFTS, the interactions between substrate molecules and different Au/TiO2 interfaces are investigated. We find that the activation of O2 and the formation and desorption of carbonates are greatly dependent on the crystal planes of the TiO2 support. Furthermore, we use CO oxidation as a probe reaction to study the relationships between surface structures and catalytic properties in Au/TiO2. The catalytic behaviors of three Au/TiO2 catalysts are well correlated with the spectroscopic results. On the basis of this work, we believe that tuning the crystal plane of TiO2 support will be an effective strategy to control the catalytic properties of Au/TiO2.Keywords: Au/TiO2; CO oxidation; crystal-plane effect; ex-situ XPS; in situ DRIFTS
Co-reporter:Lichen Liu, Qi Fan, Chuanzhi Sun, Xianrui Gu, Hao Li, Fei Gao, Yanfeng Chen, Lin Dong
Journal of Power Sources 2013 Volume 221() pp:141-148
Publication Date(Web):1 January 2013
DOI:10.1016/j.jpowsour.2012.07.105
Novel sandwich-like TiO2@C composite hollow spheres with {001} facets exposed are obtained through hydrothermal carbon-coating treatment for the first time. Based on investigations by transmission electron microscopy (TEM), scanning electron microscopy (FESEM), XRD, laser Raman spectra, and N2 adsorption–desorption isotherms, TiO2 shells are proved to be wrapped in porous carbon layers, which provide conductive support for TiO2, resulting the improvement in electronic conductivity and diffusion of Li+. Moreover, these TiO2 shells expose the reactive {001} facets, which facilitate Li+ insertion/extraction. Through combining the above advantages, TiO2@C composite hollow spheres show more superior rate capability and higher stability than TiO2 nanoparticles (Degussa P25), TiO2 nanosheets with {001} facets exposed, and TiO2 hollow spheres before carbon-coating. This method may be extended to synthesize other sandwich-like composite hollow spheres for energy storage.Graphical abstractHighlights► Sandwich-like TiO2@C hollow spheres with {001} facets exposed are obtained. ► TiO2 shells are wrapped in electron-conductive carbon layers. ► TiO2@C hollow spheres show superior rate capability and stability.
Co-reporter:Chengyan Ge, Lianjun Liu, Xiaojiang Yao, Changjin Tang, Fei Gao and Lin Dong
Catalysis Science & Technology 2013 vol. 3(Issue 6) pp:1547-1557
Publication Date(Web):27 Feb 2013
DOI:10.1039/C3CY20698J
The poor low-temperature (200–300 °C) activity and N2 selectivity of Cu-based catalysts for NO reduction by CO has driven us to further advance this process. The present work offers a simple but very promising strategy to achieve this goal by CO pre-treatment of the binary CuM/γ-Al2O3 (M = V, Mn, Fe, Co, Ni, Zn) catalysts to tailor the surface active sites. The results demonstrate that CO pre-treatment significantly enhanced the low temperature NO conversion and N2 selectivity of CuM/γ-Al2O3, depending on the type of metal oxides. Among these catalysts, CO pre-treated CuNi/γ-Al2O3 exhibited the highest activity/selectivity (i.e., about 90% at 200 °C) and excellent stability. The activity improvement resulted from the following: 1) the obtainment of oxygen vacancies and more Cu+ species with the suitable ratio of dispersed Cu2+/Cu+, 2) the decrease of apparent activation energy for NO conversion and 3) the more favourable activation and dissociation of NO on the reduced surface, as evidenced by X-ray photoelectron spectroscopy (XPS) and in situ Fourier transform infrared (FTIR) spectroscopy results.
Co-reporter:Xiaojiang Yao, Fei Gao, Qiang Yu, Lei Qi, Changjin Tang, Lin Dong and Yi Chen
Catalysis Science & Technology 2013 vol. 3(Issue 5) pp:1355-1366
Publication Date(Web):25 Feb 2013
DOI:10.1039/C3CY20805B
This work is mainly focused on investigating the influence of preparation methods on the physicochemical and catalytic properties of CuO–CeO2 catalysts for NO reduction by CO model reaction. Five different preparation methods have been used to synthesize CuO–CeO2 catalysts: mechanical mixing method (MMM), impregnation method (IM), grinding method (GM), hydrothermal treatment method (HTM) and co-precipitation method (CPM). All of these samples were characterized by a series of techniques such as N2-physisorption, XRD, LRS, H2-TPR, ICP-AES, XPS, in situ FT-IR and NO + CO model reaction. The obtained results show that the catalytic performances of these CuO–CeO2 catalysts can be ranked by CuCe-IM > CuCe-CPM > CuCe-GM > CuCe-HTM > CuCe-MMM, which is in agreement with the orders of the surface oxygen vacancy concentration, reducibility and Cu+ content, suggesting that the synergistic effect between Cu+ species and surface oxygen vacancies of these CuO–CeO2 catalysts plays an important role in this model reaction. In order to further understand the synergistic effect, a possible reaction model is tentatively proposed.
Co-reporter:Xiaojiang Yao, Changjin Tang, Zeyang Ji, Yue Dai, Yuan Cao, Fei Gao, Lin Dong and Yi Chen
Catalysis Science & Technology 2013 vol. 3(Issue 3) pp:688-698
Publication Date(Web):20 Nov 2012
DOI:10.1039/C2CY20610B
NO removal by CO model reaction was investigated over a series of ceria-containing solid solutions, prepared by an inverse co-precipitation method, to explore the relationship between the physicochemical properties and catalytic performances of these catalysts. The synthesized samples were studied in detail by means of XRD, Raman, TEM, UV-Vis spectroscopy, N2-physisorption, H2-TPR, OSC, XPS and in situ FT-IR technologies. These results indicate that the incorporation of Zr4+, Ti4+ and Sn4+ into the lattice of CeO2 leads to a smaller grain size and enhanced reduction behavior. Furthermore, the catalytic performance test shows that the activities and selectivities of these solid solutions are higher than pure CeO2 and that the Sn4+-doped sample shows the best results. The reason may be that: (1) the decrease in grain size results in an enlargement of the BET specific surface area and an increase of surface Ce3+. The former is conducive for sufficient contact between the catalyst and reactant molecules and the latter contributes to the adsorption of COx species; (2) the enhanced reduction behavior is beneficial in generating more surface oxygen vacancies during the reaction process, which can weaken the N–O bond to promote the dissociation of NOx effectively. Finally, in order to further understand the nature of the catalytic performances for these samples, a possible reaction mechanism is tentatively proposed.
Co-reporter:Xiaojiang Yao, Fei Gao, Yuan Cao, Changjin Tang, Yu Deng, Lin Dong and Yi Chen
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 36) pp:14945-14950
Publication Date(Web):18 Jul 2013
DOI:10.1039/C3CP52493K
An in situ technique is employed to tailor the valence states of copper in CuOδ/γ-Al2O3 catalysts with the purpose of inducing superior catalytic performance for simultaneous elimination of NO and CO. The catalyst with zero-valent copper exhibits excellent catalytic performance, which is comparable with the conventional supported noble-metal catalysts.
Co-reporter:Lichen Liu, Xianrui Gu, Zeyang Ji, Weixin Zou, Changjin Tang, Fei Gao, and Lin Dong
The Journal of Physical Chemistry C 2013 Volume 117(Issue 36) pp:18578-18587
Publication Date(Web):August 21, 2013
DOI:10.1021/jp4064774
In this work, we develop a facile and general strategy to control the crystal forms and crystal facets of TiO2 nanocrystals. Ti(OH)4 was used as the precursor and different anions were used as capping agents without any other organic surfactants. These anions can selectively adsorb on the specific crystal facets of anatase, inducing the transformation of conventional {101} facets to unconventional {001} facets and {100} facets or even phase transformation to rutile and brookite. Rutile and brookite TiO2 nanocrystals as well as anatase TiO2 nanocrystals with different facets ({101}, {001}, and {100}) exposed are obtained. Photocatalytic selective reduction of nitrobenzene and selective oxidation of benzyl alcohol are employed as a probe reaction to test the redox properties of the as-prepared TiO2 nanocrystals. The results show that the photocatalytic redox properties of TiO2 NCs are dependent on their crystal forms and crystal facets. Specially the photocatalytic activities of different anatase crystal facets show different orders in reduction and oxidation reactions, respectively. The reduction ability of different anatase crystal facets can be ranked as {101} > {001} > {100}. While the oxidation ability of different facets can be ranked as {101} ≈ {001} ≈ {100}. Surface and electronic structures should be the origin that account for their different activity orders in different reactions. Based on the results in the two model reactions, one important principle should be pointed out. When we discuss the crystal-facet-dependent catalytic activities of TiO2 nanocrystals, we should analyze the results based on specific reactions.
Co-reporter:Lichen Liu, Xianrui Gu, Chuanzhi Sun, Hao Li, Yu Deng, Fei Gao and Lin Dong
Nanoscale 2012 vol. 4(Issue 20) pp:6351-6359
Publication Date(Web):09 Aug 2012
DOI:10.1039/C2NR31859H
In this work, ultra-small Cu2O nanoparticles have been loaded on TiO2 nanosheets with {001} facets exposed through a one-pot hydrothermal reaction. These Cu2O nanoparticles are well-dispersed on TiO2 nanosheets with narrow size distributions and controllable sizes from 1.5 to 3.0 nm. Through XRD, TEM, N2 absorption–desorption isotherms and UV-vis diffuse reflectance spectra, the Cu2O/TiO2 nanosheets show similar phase structures, morphologies, pore structures as compared to pure TiO2 nanosheets. Due to the loading of ultra-small Cu2O nanoparticles, heterojunctions are formed between Cu2O and TiO2, which favors the efficient separation of photo-generated electrons and holes. Caused by the electron transfer from Cu2O to TiO2, Cu2O/TiO2 nanosheets show excellent visible-light activity, about 3 times that of N-doped TiO2 nanosheets with {001} facets exposed. Furthermore, charge transfer rate across the interface of Cu2O and TiO2 shows great dependence on the size of Cu2O particles. The charge transfer across the interface may be more efficient between TiO2 nanosheets and smaller Cu2O nanoparticles. Therefore, the Ti:Cu = 30:1(atomic ratio) sample shows the best activity due to its balance in light harvest and electron transfer rate in the degradation of phenol under visible light.
Co-reporter:Yuanyuan Lv, Hongliang Zhang, Yuan Cao, Lihui Dong, Lingling Zhang, Kaian Yao, Fei Gao, Lin Dong, Yi Chen
Journal of Colloid and Interface Science 2012 Volume 372(Issue 1) pp:63-72
Publication Date(Web):15 April 2012
DOI:10.1016/j.jcis.2012.01.014
The dispersion and physicochemical behaviors of CuO–CoO binary metal oxides supported on γ-Al2O3 were characterized by XRD, LRS, XPS, H2-TPR, and in situ FT-IR techniques. Their activities were evaluated by NO–CO model reaction. The results indicated that (a) for lower loadings, CuO and CoO were able to be highly dispersed on the surface of γ-Al2O3 support; (b) the interaction between dispersed CuO and CoO upon γ-Al2O3 was discussed in the view of incorporation model. According to this model and obtained results, the surface dispersed Cu–O–Co species were considered to exist on the surface of γ-Al2O3; (c) CO or/and NO adsorption FT-IR results evidenced that the surface dispersed copper species could be reduced to lower valence by CO and the NO adsorption species converted with the increase in the temperature; (d) the surface dispersed Cu–O–Co species could be reduced to active Cu-□-Co species by CO among the mixture atmosphere. The formation of the surface synergetic oxygen vacancy (SSOV) was a crucial factor in the process of the NO–CO reaction. And a possible reaction pathway was tentatively proposed to discuss the NO–CO reaction based on all of these results.Graphical abstractHighlights► Both CuO and CoO species were highly dispersed on γ-Al2O3 support at lower loadings. ► Surface dispersed Cu–O–Co species was considered to exist in CuO–CoO/γ-Al2O3 catalysts. ► The reduced Cu–O–Co (Cu-□-Co species) was presumed to be the active species. ► Surface synergetic oxygen vacancy (SSOV) played an important role in NO–CO reaction.
Co-reporter:Hongliang Zhang, Changjin Tang, Chuanzhi Sun, Lei Qi, Fei Gao, Lin Dong, Yi Chen
Microporous and Mesoporous Materials 2012 Volume 151() pp:44-55
Publication Date(Web):15 March 2012
DOI:10.1016/j.micromeso.2011.11.018
A series of bimetallic Fe–Mo-SBA-15 materials were synthesized through direct synthetic strategy and comprehensively characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 sorption, inductively coupled plasma (ICP), thermogravimetry and differential thermal analysis (TG–DTA), Fourier-transform infrared spectroscopy (FT-IR), UV–vis spectroscopy (UV–vis), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), in situ NH3-adsorbed FT-IR (NH3-IR) and temperature-programmed desorption of NH3 (NH3-TPD). The results indicated that: (1) all the samples exhibited typical hexagonal arrangement of mesoporous structure; (2) the incorporation of Fe could efficiently promote the incorporation/dispersion behavior of Mo in SBA-15; (3) the addition of Mo species could enhance the structural ordering of mesoporous materials. Moreover, the prepared materials were evaluated in the selective catalytic reduction (SCR) of NO with NH3. The results showed that the materials containing Fe and Mo exhibited higher catalytic activity than monometallic modified SBA-15 due to the increased intensity and quantity of surface acidity with the addition of Mo species.Graphical abstractThe simultaneous incorporation of Fe and Mo into mesoporous SBA-15 is firstly prepared through the direct synthesis. The addition of Mo species could enhance the structural ordering of mesoporous materials. Fe–Mo-SBA-15 materials exhibit higher SCR activity than monometallic Fe-SBA-15.Highlights► The simultaneous incorporation of Fe and Mo into mesoporous SBA-15 is firstly prepared through the direct synthesis. ► The incorporation of Fe could efficiently promote the incorporation/dispersion behavior of Mo in SBA-15. ► The addition of Mo species could enhance the structural ordering of mesoporous materials. ► Bimetallic Fe–Mo-SBA-15 materials exhibit higher catalytic activity than monometallic Fe-SBA-15.
Co-reporter:Lihui Dong, Lianjun Liu, Yuanyuan Lv, Jie Zhu, Haiqin Wan, Bin Liu, Fei Gao, Xiaoshu Wang, Lin Dong, Yi Chen
Journal of Molecular Catalysis A: Chemical 2012 Volume 365() pp:87-94
Publication Date(Web):December 2012
DOI:10.1016/j.molcata.2012.08.014
CuO/Ti0.5Sn0.5O2 catalysts were prepared and characterized by high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflection spectrum (UV–vis DRS), electron paramagnetic resonance (EPR), laser Raman spectra (LRS), in situ infrared spectroscopy (IR), and activity test for CO oxidation. The results indicated that (1) copper oxide is highly dispersed on Ti0.5Sn0.5O2 support below its dispersion capacity of 0.85 mmol Cu2+/100 m2 Ti0.5Sn0.5O2; (2) three types of copper species are present on Ti0.5Sn0.5O2, which are isolated Cu2+, (CuOCu)2+ species, and crystalline CuO, respectively. Of them, the dispersed (CuOCu)2+ species are the easiest to be reduced by CO; (3) the catalytic activities of CuO/Ti0.5Sn0.5O2 catalysts are related to the state of copper on Ti0.5Sn0.5O2 support, and the dispersed (CuOCu)2+ species are the primary active component. A surface incorporation model was proposed to explain the CuO dispersion of CuO/Ti0.5Sn0.5O2 catalysts.Graphical abstractHighlights► The dispersion capacity of copper oxides on Ti0.5Sn0.5O2 is 0.85 mmol Cu2+/100 m2 Ti0.5Sn0.5O2. ► A surface incorporation model was proposed to explain the CuO dispersion. ► The clustered CuO species shows good catalytic activity due to the ease of reduction by CO. ► The reduction of surface copper oxide by CO plays a significant role for CuO/Ti0.5Sn0.5O2 system.
Co-reporter:Lihui Dong, Lingling Zhang, Chuanzhi Sun, Wujiang Yu, Jie Zhu, Lianjun Liu, Bin Liu, Yuhai Hu, Fei Gao, Lin Dong, and Yi Chen
ACS Catalysis 2011 Volume 1(Issue 5) pp:468
Publication Date(Web):March 21, 2011
DOI:10.1021/cs200045f
CuO/VOx/Ti0.5Sn0.5O2 catalysts were prepared by an impregnation method and were tested on a NO + CO model reaction. Both copper oxide and vanadium oxide can be highly dispersed on Ti0.5Sn0.5O2 (denoted as TS, hereafter) support. The dispersed oxides form V−O−Cu species when coexisting in the catalyst system. The formation of V−O−Cu species renders the dispersed vanadium oxide aggregated and easier to be reduced; in contrast, the reduction temperature of dispersed copper oxide species is evidently higher than that without vanadium oxide (CuO/TS samples). The surface dispersed V−O−Cu species are mainly the active component for the NO + CO reaction. The activities of CuO/VOx/TS catalysts are highly dependent on the operating temperature and the amount of V−O−Cu species. In the reaction atmosphere, NO molecules are adsorbed onto Cu2+ sites, reduced Vx+ (V4+ or V3+) sites, and even TS support, forming −NO and NO3− species. Adsorption of CO molecules proceeds only on Cu+ sites. The active species change with varying reaction temperature; hence, the NO + CO reaction goes through different mechanisms at low and high temperatures over these catalysts.Keywords: copper oxide; in situ FT-IR; NO + CO reaction; Ti0.5Sn0.5O2 mixed oxide; vanadium oxide; V−O−Cu species
Co-reporter:Chuanzhi Sun, Lichen Liu, Lei Qi, Hao Li, Hongliang Zhang, Changshun Li, Fei Gao, Lin Dong
Journal of Colloid and Interface Science 2011 Volume 364(Issue 2) pp:288-297
Publication Date(Web):15 December 2011
DOI:10.1016/j.jcis.2011.07.055
ZrO2-doped TiO2 hollow nanospheres with anatase phase are efficiently fabricated via functionalized negatively charged polystyrene (PS) spheres without any surfactant or polyelectrolyte. The resulting Ti1−xZrxO2 (hereafter denoted as TZ) hollow nanospheres are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF), nitrogen sorption, and UV–vis diffuse reflectance spectroscopy (UV–vis). The Zr4+ incorporation decreases the anatase crystallite size, increases the specific surface area, and changes the pore size distribution. Furthermore, it induces enrichment of electron charge density around Ti4+ ions and blueshift of absorption edges. The TZ hollow nanospheres doped with moderate ZrO2 (molar ratio, Ti:Zr = 10:1) exhibit better photocatalytic activity than the other samples for the degradation of rhodamine B in aqueous solution, which is correlated with the effect of Zr4+ doping on the physicochemical properties in terms of surface structures, phase structures, and the electronic structures.Graphical abstractTi1−xZrxO2 hollow nanosphere exhibits higher photocatalytic activity than that of TiO2 hollow nanosphere, which is ascribed to increased specific surface areas and band gap.Highlights► ZrO2-doped TiO2 hollow nanospheres are efficiently fabricated without any surfactant or polyelectrolyte. ► The addition of Zr4+ obviously results in change in surface structures, phase structures, and pore size distribution. ► The incorporation of Zr4+ induces an enrichment of the electron charge density around Ti4+ ions. ► Ti1−xZrxO2 hollow nanosphere-doped moderate ZrO2 exhibits the highest activity.
Co-reporter:Wujiang Yu, Jie Zhu, Lei Qi, Chuanzhi Sun, Fei Gao, Lin Dong, Yi Chen
Journal of Colloid and Interface Science 2011 Volume 364(Issue 2) pp:435-442
Publication Date(Web):15 December 2011
DOI:10.1016/j.jcis.2011.08.022
XRD, LRS, TPR and in situ NH3 adsorption FT-IR were used to investigate the dispersion state of the copper oxide and molybdena species of MoO3/CeO2 and CuO/MoO3/CeO2 catalysts as well as their surface acidity. The results showed that the molybdena monolayer modification promoted the dispersion of CuO due to the formation of new tetrahedral vacancies. Meanwhile, CuO changed the structure of molybdenum species and then influenced the surface acidity of the samples. A detail discussion about the possible model of the surface structure of the catalyst was presented. In addition, combining with the in situ NH3 adsorption FT-IR, the relationships between the activities for ‘‘NO + NH3 + O2’’ reaction and surface acid properties (Brønsted and Lewis acid sites) of the catalysts were discussed.Graphical abstractThe results showed that the molybdena modification with high Mo loading promoted the dispersion of CuO due to the formation of new tetrahedral vacancies.Highlights► Molybdena monolayer–modified CeO2 increases the dispersion capacity of copper oxide. ► MoO3/CeO2 samples with different MoO3 loadings have different structures. ► After the addition of CuO, the structures of molybdena species change significantly. ► The surface acidity is related to the molybdena species structures tightly. ► The active sites of CuO/MoO3/CeO2 in ‘‘NO + NH3 + O2’’ reaction are proposed.
Co-reporter:Lingling Zhang, Lihui Dong, Wujiang Yu, Lianjun Liu, Yu Deng, Bin Liu, Haiqin Wan, Fei Gao, Keqin Sun, Lin Dong
Journal of Colloid and Interface Science 2011 Volume 355(Issue 2) pp:464-471
Publication Date(Web):15 March 2011
DOI:10.1016/j.jcis.2010.11.076
The present work tentatively investigated the effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the physicochemical properties of CoOx/γ-Al2O3 catalysts calcined in N2. XRD, Raman, XPS, FTIR, and UV–vis DRS results suggested that CoO/γ-Al2O3 was obtained from cobalt acetate precursors and CoO was dispersed on γ-Al2O3 below its dispersion capacity of 1.50 mmol/(100 m2 γ-Al2O3), whereas Co3O4/γ-Al2O3 was obtained from cobalt nitrate precursors and Co3O4 preferred to agglomerate above the dispersion capacity of 0.15 mmol/(100 m2 γ-Al2O3). Compared with Co3O4/γ-Al2O3, CoO/γ-Al2O3 catalysts were difficult to be reduced and easy to desorb oxygen species at low temperatures and presented high activities for CO oxidation as proved by H2-TPR, O2-TPD, and CO oxidation model reaction results. A surface incorporation model was proposed to explain the dispersion and reduction properties of CoO/γ-Al2O3 catalysts.Graphical abstractThe CoO from cobalt acetate is highly dispersed on γ-Al2O3 while the Co3O4 from cobalt nitrate prefers to agglomerate, which leads to their different redox and CO oxidation properties.Research highlights► CoO was obtained from cobalt acetate with its dispersion capacity of 1.50 mmol/(100 m2 γ-Al2O3). ► Co3O4 was obtain from cobalt nitrate with its dispersion capacity of 0.15 mmol/(100 m2 γ-Al2O3). ► CoO/γ-Al2O3 was more difficult to be reduced and easier to desorb oxygen than Co3O4/γ-Al2O3. ► CoO/γ-Al2O3 were more active for CO oxidation than Co3O4/γ-Al2O3. ► A surface model was proposed to explain the dispersion and reduction properties of CoO/γ-Al2O3.
Co-reporter:Qiang Yu, Xiaoxia Wu, Changjin Tang, Lei Qi, Bin Liu, Fei Gao, Keqin Sun, Lin Dong, Yi Chen
Journal of Colloid and Interface Science 2011 Volume 354(Issue 1) pp:341-352
Publication Date(Web):1 February 2011
DOI:10.1016/j.jcis.2010.10.043
The present work focuses on the combination of ceria with another oxide of different ionic valences from period 3 (Mg2+, Al3+, and Si4+) using coprecipitation method, followed by calcination at 450 and 750 °C, respectively. The textural, structural, morphological and redox properties of nanosized ceria–magnesia, ceria–alumina and ceria–silica mixed oxides have been investigated by means of N2 physisorption, XRD, Raman, HRTEM, DRS, FT-IR, and H2-TPR technologies. XRD results of these mixed oxides reveal that only nanocrystalline ceria (ca. 3–6 nm for the 450 °C calcined samples) could be observed. The grain size of ceria increases with the increasing calcination temperature from 450 to 750 °C due to sintering effect. The highest specific surface area is obtained at CeO2–Al2O3 mixed oxides when calcination temperature reaches 750 °C. Raman spectra display the cubic fluorite structure of ceria and the existence of oxygen vacancies, and displacement of oxygen ions from their normal lattice positions in the ceria-based mixed oxides. DRS measurements confirm that the smaller the grain size of the ceria, the higher indirect band gap energy. H2-TPR results suggest that the reductions of surface and bulk oxygen of ceria were predominant at low and high calcination temperature, respectively. Finally, CO oxidation were performed over these ceria-based mixed oxides, and the combination of CeO2–Al2O3 exhibited highest activity irrespective of calcination temperature, which may due to excellent textural/structural properties, good homogeneity, and redox abilities.Graphical abstractThe CeO2–Al2O3 mixed oxides exhibited higher CO oxidation activity than corresponding CeO2–MgO and CeO2–SiO2 mixed oxides due to excellent textural/structural properties, good homogeneity, and redox abilities.Research highlights► The textural characterizations suggested that alumina could be act as a very effective surface stabilizer for ceria-based mixed oxides. ► The structural characterizations showed the presence of CeO2 nanocrystals and amorphous oxides. ► The reducible features exhibited the reductions of surface and bulk oxygen, which was dependent upon calcination temperature. ► CO oxidation results suggested CeO2−Al2O3 exhibited the highest activity due to excellent textural/structural properties and redox properties.
Co-reporter:Dr. Lianjun Liu;Zhijian Yao;Dr. Yu Deng;Dr. Fei Gao;Bin Liu; Lin Dong
ChemCatChem 2011 Volume 3( Issue 6) pp:978-989
Publication Date(Web):
DOI:10.1002/cctc.201000320
Abstract
The present work elucidated the morphology and crystal-plane effects of nanoscale ceria on the activity of CuO/CeO2 catalysts toward NO reduction. CeO2 Nanopolyhedra were enclosed by (111) and (100) planes; the nanorods predominantly exposed (110) and (100) surfaces, and the nanocubes only showed the polar (100) planes. Moreover, the strongest interaction was between CuO and CeO2 rods, followed by CuO/CeO2 polyhedra, and the CuO/CeO2 cubes showed the least interaction. Importantly, Cu2+ ions could be incorporated into the pore and surface lattices by occupying the vacant sites in the nanostructure CeO2 rods. Partial copper oxide species were segregated on the surface of CeO2 cubes with larger particle sizes. As a result, the site geometry and coordination environment of Cu2+ ions were different on the (111), (110), and (100) surfaces of CeO2. This surface structure effect in turn led to a higher surface reducibility, activity and N2 selectivity of CuO/CeO2 nanorods for NO reduction at low temperatures (below 250 °C); the polyhedra and cubes were less active.
Co-reporter:Chuanzhi Sun, Lihui Dong, Wujiang Yu, Lichen Liu, Hao Li, Fei Gao, Lin Dong, Yi Chen
Journal of Molecular Catalysis A: Chemical 2011 Volume 346(1–2) pp:29-38
Publication Date(Web):20 July 2011
DOI:10.1016/j.molcata.2011.06.004
Binary metal oxides V2O5–WO3 supported on Ti0.5Sn0.5O2 (hereafter denoted as TS) catalysts have been characterized by XRD, LRS, TPR, NH3-TPD, in situ FT-IR and the micro-reactor test for the removal of NO by NH3. The results suggest that: (1) both vanadium oxide and tungsten oxide (loadings ≤0.5 mmol/100 m2 TS) are highly dispersed on TS support. (2) The reduction temperature of vanadium species becomes higher due to the formation of the V–O–W bonds. (3) With the loading amounts of WO3 increasing, the amounts of the Brønsted acid sites increase, while the amounts of Lewis acid sites decrease. The strength of Brønsted acid sites is little influenced by the tungsten species which is further proved by the density functional theory (DFT) calculation results. The adsorption of NO is little changed after WO3 addition. Further increase of WO3 (loadings ≥ 1.0 mmol/100 m2 TS) results in the formation of crystalline WO3 and they will cover the vanadium oxide species on the surface of the catalysts. (4) The activity of “NO + NH3 + O2” reaction is tightly related to the amounts of the Brønsted acid sites: the higher SCR activities should be attributed to the larger amounts of Brønsted acid sites when WO3 are highly dispersed. When the crystalline WO3 form, they cover the surface of the catalysts, and lead to the decrease of the activities.Graphical abstractHighlights• The V–O–W bond forms when the vanadium oxide and tungsten oxide are co-impregnated on support. • Brønsted acid sites are the main active sites for “NO + NH3 + O2” reaction. • The acid strength of Brønsted acid and the reducibility of vanadium oxide species are not responsible for the high SCR activities. • The excessive WO3 cover the vanadium oxide species leading to the decrease of the SCR activity. • DFT calculations are employed to elucidate the effect of WO3.
Co-reporter:Dr. Dan Li;Qiang Yu;Shan-Shan Li;Hai-Qin Wan;Lian-Jun Liu;Lei Qi;Bin Liu;Dr. Fei Gao;Dr. Lin Dong; Yi Chen
Chemistry - A European Journal 2011 Volume 17( Issue 20) pp:5668-5679
Publication Date(Web):
DOI:10.1002/chem.201002786
Abstract
NO reduction by CO was investigated over CuO/γ-Al2O3, Mn2O3/γ-Al2O3, and CuOMn2O3/γ-Al2O3 model catalysts before and after CO pretreatment at 300 °C. The CO-pretreated CuOMn2O3/γ-Al2O3 catalyst exhibited higher catalytic activity than did the other catalysts. Based on X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis diffuse reflectance spectroscopy (DRS), Raman, and H2-temperature-programmed reduction (TPR) results, as well as our previous studies, the possible interaction model between dispersed copper and manganese oxide species as well as γ-Al2O3 surface has been proposed. In this model, Cu and Mn ions occupied the octahedral vacant sites of γ-Al2O3, with the capping oxygen on top of the metal ions to keep the charge conservation. For the fresh CuO/γ-Al2O3 and Mn2O3/γ-Al2O3 catalysts, the -Cu-O-Cu- and -Mn-O-Mn- species were formed on the surface of γ-Al2O3, respectively; but for the fresh CuOMn2O3/γ-Al2O3 catalyst, -Cu-O-Mn- species existed on the surface of γ-Al2O3. After CO pretreatment, -Cu-□-Cu- and -Mn-□-Mn- (□ represents surface oxygen vacancy (SOV)) species would be formed in CO-pretreated CuO/γ-Al2O3 and CO-pretreated Mn2O3/γ-Al2O3 catalysts, respectively; whereas -Cu-□-Mn- species existed in CO-pretreated CuOMn2O3/γ-Al2O3. Herein, a new concept, surface synergetic oxygen vacancy (SSOV), which describes the oxygen vacancy formed between the individual Mn and Cu ions, is proposed for CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst. In addition, the role of SSOV has also been approached by NO temperature-programmed desorption (TPD) and in situ FTIR experiments. The FTIR results of competitive adsorption between NO and CO on all the CO-pretreated CuO/γ-Al2O3, Mn2O3/γ-Al2O3, and CuOMn2O3/γ-Al2O3 samples demonstrated that NO molecules mainly were adsorbed on Mn2+ and CO mainly on Cu+ sites. The current study suggests that the properties of the SSOVs in CO-pretreated CuOMn2O3/γ-Al2O3 catalyst were significantly different to SOVs formed in CO-pretreated CuO/γ-Al2O3 and Mn2O3/γ-Al2O3 catalysts, and the SSOVs played an important role in NO reduction by CO.
Co-reporter:Lianjun Liu, Qiang Yu, Jie Zhu, Haiqin Wan, Keqin Sun, Bin Liu, Haiyang Zhu, Fei Gao, Lin Dong, Yi Chen
Journal of Colloid and Interface Science 2010 Volume 349(Issue 1) pp:246-255
Publication Date(Web):1 September 2010
DOI:10.1016/j.jcis.2010.05.044
The present work explored the effect of MnOx modification on the activity and adsorption of CuO/Ce0.67Zr0.33O2 catalyst for NO reduction by CO. XRD, Raman, UV, XPS, H2-TPR, and in situ FT-IR were used to characterize these catalysts. Results suggested that the incorporation of copper and manganese species resulted in the lattice expansion and the decease of microstrain of ceria–zirconia, thus inducing the formation of oxygen vacancies. There was a strong interaction between surface copper, manganese, and the support via charge transfer. The addition of manganese species could promote the reduction of the resultant catalysts and assist copper oxide in changing the valence and the support in supplying oxygen. These reduction behaviors were dependent on the loading amounts of MnOx and the impregnation procedure. In addition, the introduction of MnOx cannot change the adsorption type of NO, but readily helped to activate the adsorbed NO species. As a result, these factors were responsible for the enhancement of activity and selectivity through MnOx modification.The introduction of MnOx onto CuO/Ce0.67Zr0.33O2 assists in a rapid change of the copper valence, and activates the adsorbed NO species, thus promoting the activity for NO reduction.
Co-reporter:Yong Wu, Fei Gao, Bin Liu, Yue Dai, Haiyang Zhu, Binhua Zhou, Yuhai Hu, Lin Dong, Zheng Hu
Journal of Colloid and Interface Science 2010 Volume 343(Issue 2) pp:522-528
Publication Date(Web):15 March 2010
DOI:10.1016/j.jcis.2009.11.050
X-ray diffraction (XRD), Mössbauer spectroscopy, and temperature-programmed reduction (TPR) were employed to investigate the dispersion and reduction behaviors of the Fe2O3/CuO/γ-Al2O3 system. The results indicated that: (1) the crystalline CuO particle in the CuO/γ-Al2O3 samples was redispersed during impregnating CuO/γ-Al2O3 samples with Fe(NO3)3 solutions; (2) two different dispersion states of surface iron species could be observed, i.e., State I corresponding to the iron(III) species located in the D layer on the surface of γ-Al2O3 and State II corresponding to those in the C layer. The dispersed states of surface iron(III) species were closely related to the iron loading amount; (3) the copper species located in the D layer of alumina surface was easily reduced and the copper species located in the C layer were more stable, which could be due to the influence of the iron(III) species in the different layers; (4) in the NO + CO reaction, the catalytic performances were enhanced due to the Cu–Fe synergism and the main active species in this system should be the surface-dispersed copper oxide species.The dispersed copper oxide and ferric oxide locate in the different layers of the preferentially exposed (1 1 0) plane of γ-Al2O3.
Co-reporter:Haiqin Wan, Dan Li, Yue Dai, Yuhai Hu, Bin Liu, Lin Dong
Journal of Molecular Catalysis A: Chemical 2010 Volume 332(1–2) pp:32-44
Publication Date(Web):1 November 2010
DOI:10.1016/j.molcata.2010.08.016
CuO supported on γ-Al2O3 and Mn2O3 modified γ-Al2O3 was prepared and characterized by XRD, UV–vis, XPS, TPR and in situ adsorption IR. NO reduction by CO over these catalysts was also investigated. For the modification of γ-Al2O3 by Mn2O3, manganese oxide was highly dispersed on γ-Al2O3 surface to form a monolayer with a dispersion capacity of about 1.0 mmol Mn3+/100 m2 γ-Al2O3 corresponding to 8.1 wt.% of Mn. For supported copper oxide, CuO dispersion capacity was 0.75 mmol Cu2+/100 m2 γ-Al2O3 on γ-Al2O3, and increased to 1.1 mmol Cu2+/100 m2 γ-Al2O3 on 1.0 MnOx–γ-Al2O3, indicative of an elevated CuO dispersion capacity upon Mn2O3 modification. For NO reduction by CO, the addition of manganese oxide generally enhanced NO conversion and N2 selectivity. Furthermore, the catalyst with the loading amounts of Cu and Mn of 0.6 mmol and 0.3/100 m2 γ-Al2O3 respectively exhibited the most prominent catalytic efficiency among the tested catalysts in terms of NO conversion and N2 selectivity. Additionally, these catalysts showed stable NO conversion and N2 selectivity.Manganese oxide modified γ-Al2O3 could promote the dispersion capacity of CuO on this support because an epitaxil Mn2O3 monolayer formed on the γ-Al2O3 surface which results in the tetrahedral vacant sites of Mn2O3 to be preferentially occupied by Cu2+. The catalytic activities of CuO/γ-Al2O3 for NO reduction by CO were improved by Mn2O3 modification because Cu+ formed in the Cu/Mn–Al catalysts.
Co-reporter:Lianjun Liu, Jinge Cai, Lei Qi, Qiang Yu, Keqin Sun, Bin Liu, Fei Gao, Lin Dong, Yi Chen
Journal of Molecular Catalysis A: Chemical 2010 327(1–2) pp: 1-11
Publication Date(Web):
DOI:10.1016/j.molcata.2010.05.002
Co-reporter:Chunyan Song;Chunling Wang;Haiyang Zhu;Xingcai Wu
Catalysis Letters 2008 Volume 120( Issue 3-4) pp:215-220
Publication Date(Web):2008/01/01
DOI:10.1007/s10562-007-9272-9
Silica hollow spheres were synthesized by sol–gel process using carbon microspheres as templates, and used as supports for CuO/SiO2 catalysts. The samples were characterized by TEM, nitrogen adsorption–desorption, XRD and TPR, and furthermore, the catalytic performance for CO oxidation was approached. The results indicated that the catalytic activity of CuO supported on SiO2 hollow spheres exhibited much higher as compared to that supported on commercial SiO2. Enhancement of the catalytic activity may be attributed to the fact that the unique hollow spherical texture should facilitate the formation of main active species and gas diffusion in catalysts.
Co-reporter:Hai-Yang Zhu, Bin Liu, Ming-Min Shen, Yan Kong, Xi Hong, Yu-Hai Hu, Wei-Ping Ding, Lin Dong, Yi Chen
Materials Letters 2004 Volume 58(Issue 25) pp:3107-3110
Publication Date(Web):October 2004
DOI:10.1016/j.matlet.2004.05.050
A new method was used to prepare the tetragonal zirconia and high temperature X-ray powder diffraction (XRD) and thermo gravimetry and differential scanning calorimetry (TG–DSC) were employed to study the process of the formation and variation of crystal zirconia. The high temperature XRD results showed that [Nature 258 (1975) 703] during the formation of zirconia from zirconium hydroxide, the addition of maltose favored the phase transformation of zirconia from amorphous to tetragonal as the calcination temperature rises (from about 400 to 550 °C), and then monoclinic zirconia gradually formed as the temperature increases (from about 550 to 846 °C), [Appl. Catal. 71 (1991) 363] tetragonal zirconia would partly transform into monoclinic one during the annealing, and which implies that the suitable calcinations temperature for the preparation of tetragonal zirconia should be controlled lower than 550 °C. In addition, it is suggested that the combination of high temperature XRD and TG–DSC is a powerful tool to approach the process of the formation of solid materials.
Co-reporter:Weixin Zou, Lei Zhang, Lichen Liu, Xiaobo Wang, Jingfang Sun, Shiguo Wu, Yu Deng, Changjin Tang, Fei Gao, Lin Dong
Applied Catalysis B: Environmental (February 2016) Volume 181() pp:495-503
Publication Date(Web):February 2016
DOI:10.1016/j.apcatb.2015.08.017
Co-reporter:Qiang Yu, Xiaojiang Yao, Hongliang Zhang, Fei Gao, Lin Dong
Applied Catalysis A: General (7 May 2012) Volumes 423–424() pp:42-51
Publication Date(Web):7 May 2012
DOI:10.1016/j.apcata.2012.02.017
Co-reporter:Qiang Yu, Lianjun Liu, Lihui Dong, Dan Li, Bin Liu, Fei Gao, Keqin Sun, Lin Dong, Yi Chen
Applied Catalysis B: Environmental (7 June 2010) Volume 96(Issues 3–4) pp:
Publication Date(Web):7 June 2010
DOI:10.1016/j.apcatb.2010.02.032
Effects of Ce/Zr ratio on the physicochemical properties of CuO/CexZr1−xO2/γ-Al2O3 catalysts were investigated by BET, XRD, Raman and H2-TPR. The catalytic activity and the interaction between the reactants with these catalysts were compared by NO + CO model reaction and in situ FT-IR. The results suggested that the addition of ceria–zirconia mixed oxides significantly improved NO conversion and N2 yield due to dispersed copper species in proximity to ceria–zirconia. Especially, the ceria-rich catalysts displayed better performance in activity and reducibility than others, which would be resulted from the strong interaction among copper, ceria–zirconia and support. The IR results suggested NO reduction activity was correlated with the presence of Cu+ carbonyl species, and the catalysts with variable Ce/Zr ratios had no distinction at the adsorption type and rate of NO/CO at room temperature. However, on heating treatment would give distinct difference in CO2 intensity and the wavenumber of adsorbed nitrates. Simultaneously, the stability of these N- and C-containing intermediates contacted with alumina was influenced by the modified Ce/Zr ratio.
Co-reporter:Jie Zhu, Lingling Zhang, Yu Deng, Bin Liu, Lihui Dong, Fei Gao, Keqin Sun, Lin Dong, Yi Chen
Applied Catalysis B: Environmental (7 June 2010) Volume 96(Issues 3–4) pp:
Publication Date(Web):7 June 2010
DOI:10.1016/j.apcatb.2010.03.003
Ce0.67Zr0.33O2 solid solutions synthesized by traditional co-precipitation method (hereafter donated as CZ-CP) and hydrothermal method (hereafter donated as CZ-HT) were used as supports for preparing a series of CuO/Ce0.67Zr0.33O2 catalysts. High resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), temperature-programmed reduction (TPR), CO adsorption in situ Fourier transform infrared spectroscopy (CO in situ FT-IR) and the activity of CO oxidation model reaction at low temperature (<200 °C) were used to approach the properties of the catalysts. The results showed that the Ce0.67Zr0.33O2 prepared by hydrothermal method facilitate the formation and stabilization of Cu+ on the surface of support and thus the activity for CO + O2 reaction was improved. A tentative model was suggested that the difference in the preferentially exposed plane of CZ-CP and CZ-HT leads to the great difference in dispersion, reduction and reaction activity of the dispersed copper oxide species on these two supports.
Co-reporter:Yan Xiong, Changjin Tang, Xiaojiang Yao, Lei Zhang, Lulu Li, Xiaobo Wang, Yu Deng, Fei Gao, Lin Dong
Applied Catalysis A: General (5 April 2015) Volume 495() pp:206-216
Publication Date(Web):5 April 2015
DOI:10.1016/j.apcata.2015.01.038
Co-reporter:Haiqin Wan, Dan Li, Yue Dai, Yuhai Hu, Yanhua Zhang, Lianjun Liu, Bin Zhao, Bin Liu, Keqin Sun, Lin Dong, Yi Chen
Applied Catalysis A: General (31 May 2009) Volume 360(Issue 1) pp:26-32
Publication Date(Web):31 May 2009
DOI:10.1016/j.apcata.2009.02.046
Co-reporter:Lianjun Liu, Zhijian Yao, Bin Liu, Lin Dong
Journal of Catalysis (30 September 2010) Volume 275(Issue 1) pp:45-60
Publication Date(Web):30 September 2010
DOI:10.1016/j.jcat.2010.07.024
NO reduction by CO reaction was studied over a series of CuO/CexZr1−xO2 catalysts with different copper loadings and Ce/Zr molar ratios to evaluate the correlation of their structural characteristics with catalytic performance. These catalysts were investigated in detail by means of thermogravimetric analysis (TGA/DSC), X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), electron paramagnetic resonance (EPR), UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and H2-temperature-programmed reduction (H2-TPR) and in situ Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the ceria-rich (pseudocubic t″) phase could disperse and stabilize the copper species more effectively and resulted in stronger interaction with copper than the zirconia-rich (t) phase. Furthermore, compared with the zirconia-rich phase, the synergistic interaction of copper with ceria-rich phase easily promoted the reduction of copper species and support surface oxygen, as well as the activation of adsorbed NO species. Therefore, CuO/Ce0.8Zr0.2O2 catalyst exhibited the higher activity for NO reduction than CuO/Ce0.5Zr0.5O2 and CuO/Ce0.2Zr0.8O2. A surface model was proposed to discuss these catalytic properties. The copper species at the interfacial area did not maintain an epitaxial relationship with CexZr1−xO2, while could penetrate into the CexZr1−xO2 surface lattice by occupying the vacant site on the exposed (1 1 1) plane. The type and coordination environment of copper species were different in ceria-rich and zirconia-rich phases surface, and their stabilities were related to the lattice strains.Copper species could incorporate into the vacant sites on the exposed (1 1 1) plane of ceria–zirconia, and its stronger interaction with ceria-rich phase determined the higher activity than zirconia-rich phase.Download high-res image (160KB)Download full-size image
Co-reporter:Lianjun Liu, Yuan Cao, Wenjing Sun, Zhijian Yao, Bin Liu, Fei Gao, Lin Dong
Catalysis Today (25 October 2011) Volume 175(Issue 1) pp:48-54
Publication Date(Web):25 October 2011
DOI:10.1016/j.cattod.2011.04.018
The present work comparatively explored the morphology and size-dependent reduction and activity of CeO2 nanostructures for NO reduction. CeO2 nanorods were prepared by Ce(NO3)3, while spherical-like nanoparticles with an average size of 4–6 nm were obtained from (NH4)2Ce(NO3)6 and Ce(SO4)2. As compared with CeO2 nanorods, these nanoparticles (4–6 nm) showed the larger lattice strain and higher activity for NO reduction, which was due to the nanosize effect that significantly improved the intrinsic reducibility of surface oxygen and facilitated the formation of oxygen vacancies. In addition, the adsorption type and configuration of NO was similar over these different shaped ceria. However, CeO2 nanoparticles from tetravalent cerium showed the greater capacity to activate the adsorbed NO species than nanorods from the tervalent nitrates.Graphical abstractDownload high-res image (136KB)Download full-size imageHighlights► Compared with CeO2 nanorods prepared from Ce(NO3)3, CeO2 nanoparticles from (NH4)2Ce(NO3)6 show the smaller size (4–6 nm) and higher lattice strain. ► CeO2 nanoparticles from (NH4)2Ce(NO3)6 exhibit the higher activity for NO reduction than nano-CeO2 from Ce(SO4)2, CeO2 and Ce(NO3)3. This is probably due to its nanosize effect that improves its reducibility of surface oxygen and facilitates the formation of surface oxygen vacancy. ► The adsorption type and configuration of NO species is similar over these different shaped ceria. However, CeO2 nanoparticles from tetravalent cerium show the greater capacity to activate the adsorbed NO species than nanorods from the tervalent nitrates.
Co-reporter:Fei Gao, Bin Liu, Wenjing Sun, Yong Wu, Lin Dong
Catalysis Today (25 October 2011) Volume 175(Issue 1) pp:34-39
Publication Date(Web):25 October 2011
DOI:10.1016/j.cattod.2011.06.003
NO reduction by CO reaction was comparatively studied over microwave plasma pretreated CuO/TiO2 catalysts employing transmission electron microscopy (TEM), hydrogen temperature programmed reduction (H2-TPR), and in situ Fourier-transform infrared spectroscopy (in situ FTIR). The catalytic performances indicated that a remarkable improvement in activity and selectivity was achieved after microwave plasma pretreatment, which was dependent on the microwave plasma pretreatment time. The results also suggested that a high active oxygen species (O*) was formed on the surface of plasma pretreated CuO/TiO2 catalysts, which led to the easy oxidation of NO to NO2 at low temperature even without introducing any additional O2 gas into the reaction system. Therefore, these high active oxygen species (O*) should play an important role for the exaltation of the catalytic performances of the catalysts.Graphical abstractDownload high-res image (98KB)Download full-size imageHighlights► The catalytic performances of CuO/TiO2 catalysts for NO reduction will be enhanced by plasma pretreatment. ► New active oxygen species (O*) can be formed on the surface of CuO/TiO2 catalysts after microwave plasma pretreatment. ► These new active oxygen species (O*) should play an important role in SCR pathway.
Co-reporter:Changjin Tang, Jianchao Li, Xiaojiang Yao, Jingfang Sun, Yuan Cao, Lei Zhang, Fei Gao, Yu Deng, Lin Dong
Applied Catalysis A: General (25 March 2015) Volume 494() pp:77-86
Publication Date(Web):25 March 2015
DOI:10.1016/j.apcata.2015.01.037
Co-reporter:Qiang Yu, Xiaoxia Wu, Xiaojiang Yao, Bin Liu, Fei Gao, Jiaming Wang, Lin Dong
Catalysis Communications (15 August 2011) Volume 12(Issue 14) pp:1311-1317
Publication Date(Web):15 August 2011
DOI:10.1016/j.catcom.2011.05.002
A series of transition metal (Mn, Fe, Co, Ni, Cu and Ag) oxides supported on ceria–zirconia–alumina nanocomposite catalysts were prepared through wetness impregnation method. The catalytic performance of these catalysts were evaluated in the catalytic elimination of NO–CO. Activity results revealed supported copper catalyst gave the optimal catalytic activity, which was related to high dispersion of copper species (XRD and Raman), low-temperature reducibility (TPR), and more oxygen vacancies (DRS).Download full-size imageResearch Highlights► Mesoporous ceria–zirconia–alumina nanocomposite was prepared via oxidative co-precipitation method. ► CZA-supported copper catalysts exhibited excellent catalytic performance in the model reaction of NO–CO. ► The higher activity of CuCZA was related to high dispersion of copper species, low-temperature reducibility, and more oxygen vacancies.
Co-reporter:Jie Zhu, Fei Gao, Lihui Dong, Wujiang Yu, Lei Qi, Zhe Wang, Lin Dong, Yi Chen
Applied Catalysis B: Environmental (12 March 2010) Volume 95(Issues 1–2) pp:
Publication Date(Web):12 March 2010
DOI:10.1016/j.apcatb.2009.12.021
MoO3/CeO2 and MxOy/MoO3/CeO2 (M = Fe, Cu, Ni) catalysts had been characterized by XRD, TPR, LRS, NH3-adsorbed in situ FT-IR and activity test for selective catalytic reduction (SCR) of NO by NH3. The results suggested that the addition of NiO, CuO and Fe2O3 to MoO3/CeO2 catalysts had led to the different structures of surface molybdena species, i.e., isolated regular tetrahedral, highly distorted tetrahedral and polymerized octahedral molybdena species, revealing that the intensities of interaction between molybdena species and these metal oxides could be listed as: NiO/MoO3/CeO2 > CuO/MoO3/CeO2 > Fe2O3/MoO3/CeO2. Furthermore, it exhibited the same order for the surface acid intensities of the Lewis acid sites of these samples. The reactivity of “NO + NH3 + O2” reaction is tightly related to acid properties of the catalysts (no matter Brønsted or Lewis acid sites): At low temperature, a weak Lewis acid site (L1) is the main active site for “NO + NH3 + O2” reaction; at middle temperature range, the Brønsted acid site is the primary active site; while at high temperature, another strong Lewis acid site (L2) can also promote the reaction.
Co-reporter:Haiqin Wan, Dan Li, Haiyang Zhu, Yanhua Zhang, Lihui Dong, Yuhai Hu, Bin Liu, Keqin Sun, Lin Dong, Yi Chen
Journal of Colloid and Interface Science (1 October 2008) Volume 326(Issue 1) pp:28-34
Publication Date(Web):1 October 2008
DOI:10.1016/j.jcis.2008.07.036
Dispersion of molybdena on CeO2, ZrO2 (Tet), and a mixture of CeO2 and ZrO2 (Tet), was investigated by using laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and temperature programmed reduction (TPR). The results indicate that molybdena is dispersed on both individual oxide support and mixed oxide support at the adopted molybdena loadings (0.2 and 0.8 mmol Mo6+/100 m2) and the structure of the supported molybdena species is intimate association with its loading amount. Two molybdena species are identified by Raman results, i.e. isolated MoO2−4 species at 0.2 mmol Mo6+/100 m2 and polymolybdate species at 0.8 mmol Mo6+/100 m2. IR spectra of ammonia adsorption prove that isolated MoO2−4 species are Lewis acid sites on the Mo/Ce and/or Zr samples, and the polymolybdate species are Brönsted acid sites on the Mo/Ce and/or Zr samples. Moreover, a combination of the Raman, IR and TPR results confirms that at 0.2 mmol Mo6+/100 m2 Ce + Zr, molybdena is preferentially dispersed on the surface of CeO2 when a mixed oxide support (CeO2 and ZrO2) is present, which was explained in term of the difference of the surface basicity between CeO2 and ZrO2 (Tet). Surface structures of the oxide supports were also taken into consideration.IR spectra of ammonia adsorption indicate that isolated MoO2−4 species are corresponding to Lewis acid sites and polymolybdate species are corresponding to Brönsted acid sites over the Mo/Ce and/or Zr samples.Download full-size image
Co-reporter:Yuan Cao, Lianjun Liu, Fei Gao, Lin Dong, Yi Chen
Applied Surface Science (1 May 2017) Volume 403() pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.apsusc.2017.01.212
•CuO deposited/doped Ce0.7Zr0.3O2 are synthesized and characterized.•CuO on the surface and lattice of Ce0.7Zr0.3O2 have the different neighboring environments.•The decomposition pathways of NO species were determined by the temperature and coordination states of copper species.In this work, CuO modified Ce0.7Zr0.3O2 (CZ) solid solution including CuO-deposited CZ (i.e., Cu/CZ) and −doped CZ (i.e., Cu-CZ) are prepared. The correlation of CuO neighboring structure with the catalytic performance for NO reduction have been proposed by various spectroscopic technologies. Results suggested that the strong synergetic effect between surface deposited copper species and CZ support can easily promote the reducibility of Cu/CZ, which enhances its catalytic performance. In addition, the decomposition of NO occurs through different pathways over Cu/CZ and Cu-CZ, respectively, as suggested by in-situ FTIR results. The distinct chemical state and environment of copper species between Cu/CZ and Cu-CZ can account for these differences. A surface model and the reaction mechanism are proposed to discuss the differences showing in the catalysts.
Co-reporter:Haiqin Wan, Zhe Wang, Jie Zhu, Xiaowei Li, Bin Liu, Fei Gao, Lin Dong, Yi Chen
Applied Catalysis B: Environmental (1 March 2008) Volume 79(Issue 3) pp:254-261
Publication Date(Web):1 March 2008
DOI:10.1016/j.apcatb.2007.10.025
Co-reporter:Changjin Tang, Hongliang Zhang, Chuanzhi Sun, Jianchao Li, Lei Qi, Yangjian Quan, Fei Gao, Lin Dong
Catalysis Communications (1 July 2011) Volume 12(Issue 12) pp:1075-1078
Publication Date(Web):1 July 2011
DOI:10.1016/j.catcom.2011.03.031
A family of metal oxides (Co3O4, NiO and CeO2) confined in SBA-15 with high loadings (≥ 20 wt%) was prepared through a solvent-free method. Characterizations of X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that aggregation-free nanoparticles were obtained and N2 physisorption confirmed they were studded in mesopores. It was proposed that the intermediate molten salt phases ensured successful encapsulation and homogeneous dispersion of metal oxides. Lastly, the importance of the strategy was exemplified by NiO, and the high thermal stability together with superior performance in hydrodechlorination of chlorobenzene suggested great potential of these samples in heterogeneous catalysis.A family of highly loaded, well dispersed and thermally stable metal oxide nanoparticles (Co3O4, NiO, CeO2) confined in SBA-15 is fabricated via a solvent-free strategy. The preliminary catalytic test of NiO in hydrodechlorination of chlorobenzene suggests great potential of the samples in heterogeneous catalysis.Download full-size imageResearch Highlights► Co3O4, NiO and CeO2 are filled into SBA-15 through a solvent-free method. ► The method is facile but efficient. ► The key of the method is based on suppression of distribution of precursors. ► The obtained samples show promising applications in heterogeneous catalysis.
Co-reporter:Xiaojiang Yao, Fei Gao, Qiang Yu, Lei Qi, Changjin Tang, Lin Dong and Yi Chen
Catalysis Science & Technology (2011-Present) 2013 - vol. 3(Issue 5) pp:NaN1366-1366
Publication Date(Web):2013/02/25
DOI:10.1039/C3CY20805B
This work is mainly focused on investigating the influence of preparation methods on the physicochemical and catalytic properties of CuO–CeO2 catalysts for NO reduction by CO model reaction. Five different preparation methods have been used to synthesize CuO–CeO2 catalysts: mechanical mixing method (MMM), impregnation method (IM), grinding method (GM), hydrothermal treatment method (HTM) and co-precipitation method (CPM). All of these samples were characterized by a series of techniques such as N2-physisorption, XRD, LRS, H2-TPR, ICP-AES, XPS, in situ FT-IR and NO + CO model reaction. The obtained results show that the catalytic performances of these CuO–CeO2 catalysts can be ranked by CuCe-IM > CuCe-CPM > CuCe-GM > CuCe-HTM > CuCe-MMM, which is in agreement with the orders of the surface oxygen vacancy concentration, reducibility and Cu+ content, suggesting that the synergistic effect between Cu+ species and surface oxygen vacancies of these CuO–CeO2 catalysts plays an important role in this model reaction. In order to further understand the synergistic effect, a possible reaction model is tentatively proposed.
Co-reporter:Xiaojiang Yao, Fei Gao, Yuan Cao, Changjin Tang, Yu Deng, Lin Dong and Yi Chen
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 36) pp:NaN14950-14950
Publication Date(Web):2013/07/18
DOI:10.1039/C3CP52493K
An in situ technique is employed to tailor the valence states of copper in CuOδ/γ-Al2O3 catalysts with the purpose of inducing superior catalytic performance for simultaneous elimination of NO and CO. The catalyst with zero-valent copper exhibits excellent catalytic performance, which is comparable with the conventional supported noble-metal catalysts.
Co-reporter:Chuanzhi Sun, Yingjie Tang, Fei Gao, Jingfang Sun, Kaili Ma, Changjin Tang and Lin Dong
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 24) pp:NaN16006-16006
Publication Date(Web):2015/05/15
DOI:10.1039/C5CP02158H
Two different precursors, manganese nitrate (MN) and manganese acetate (MA), were employed to prepare two series of catalysts, i.e., xCuyMn(N)/TiO2 and xCuyMn(A)/TiO2, by a co-impregnation method. The catalysts were characterized by XRD, LRS, CO-TPR, XPS and EPR spectroscopy. The results suggest that: (1) both xCuyMn(N)/TiO2 and xCuyMn(A)/TiO2 catalysts exhibit much higher catalytic activities than an unmodified Cu/TiO2 catalyst in the NO + CO reaction. Furthermore, the activities of catalysts modified with the same amount of manganese are closely dependent on manganese precursors. (2) The enhancement of activities for Mn-modified catalysts should be attributed to the formation of the surface synergetic oxygen vacancy (SSOV) Cu+–□–Mny+ in the reaction process. Moreover, since the formation of the SSOV (Cu+–□–Mn3+) in the xCuyMn(N)/TiO2 catalyst is easier than that (Cu+–□–Mn2+) in the xCuyMn(A)/TiO2 catalyst, the activity of the xCuyMn(N)/TiO2 catalyst is higher than that of the xCuyMn(A)/TiO2 catalyst. This conclusion is well supported by the XPS and EPR results.
Co-reporter:Lichen Liu, Chengyan Ge, Weixin Zou, Xianrui Gu, Fei Gao and Lin Dong
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 7) pp:NaN5140-5140
Publication Date(Web):2015/01/12
DOI:10.1039/C4CP05449K
Metal–support interactions between Au and TiO2 are studied based on Au/TiO2 catalysts with different TiO2 crystal planes exposed. With ex situ XPS, TEM and in situ DRIFTS, we have investigated the crystal-plane-dependent metal–support interaction effects on the physiochemical properties of Au/TiO2 catalysts. Based on the structural characterization and spectroscopic results, we can observe chemical oscillations (including the electronic structures of Au nanoparticles and the interaction between Au/TiO2 catalysts and CO molecules) during alternate H2 and O2 pre-treatments. Their variation tendencies of oscillations are greatly dependent on the crystal planes of TiO2 and the pre-treatment temperature. Furthermore, their surface and electronic changes after H2 and O2 pre-treatments can be well correlated with their catalytic activities in CO oxidation. Electron-transfer processes across the Au–TiO2 interface are proved to be the origin accounting for their changes after H2 and O2 pre-treatments. The different electronic structures of different TiO2 crystal planes should have relationships with the crystal-plane-dependent metal–support interaction effects in Au/TiO2.
Co-reporter:Chengyan Ge, Lianjun Liu, Xiaojiang Yao, Changjin Tang, Fei Gao and Lin Dong
Catalysis Science & Technology (2011-Present) 2013 - vol. 3(Issue 6) pp:NaN1557-1557
Publication Date(Web):2013/02/27
DOI:10.1039/C3CY20698J
The poor low-temperature (200–300 °C) activity and N2 selectivity of Cu-based catalysts for NO reduction by CO has driven us to further advance this process. The present work offers a simple but very promising strategy to achieve this goal by CO pre-treatment of the binary CuM/γ-Al2O3 (M = V, Mn, Fe, Co, Ni, Zn) catalysts to tailor the surface active sites. The results demonstrate that CO pre-treatment significantly enhanced the low temperature NO conversion and N2 selectivity of CuM/γ-Al2O3, depending on the type of metal oxides. Among these catalysts, CO pre-treated CuNi/γ-Al2O3 exhibited the highest activity/selectivity (i.e., about 90% at 200 °C) and excellent stability. The activity improvement resulted from the following: 1) the obtainment of oxygen vacancies and more Cu+ species with the suitable ratio of dispersed Cu2+/Cu+, 2) the decrease of apparent activation energy for NO conversion and 3) the more favourable activation and dissociation of NO on the reduced surface, as evidenced by X-ray photoelectron spectroscopy (XPS) and in situ Fourier transform infrared (FTIR) spectroscopy results.
Co-reporter:Xiaojiang Yao, Changjin Tang, Zeyang Ji, Yue Dai, Yuan Cao, Fei Gao, Lin Dong and Yi Chen
Catalysis Science & Technology (2011-Present) 2013 - vol. 3(Issue 3) pp:NaN698-698
Publication Date(Web):2012/11/20
DOI:10.1039/C2CY20610B
NO removal by CO model reaction was investigated over a series of ceria-containing solid solutions, prepared by an inverse co-precipitation method, to explore the relationship between the physicochemical properties and catalytic performances of these catalysts. The synthesized samples were studied in detail by means of XRD, Raman, TEM, UV-Vis spectroscopy, N2-physisorption, H2-TPR, OSC, XPS and in situ FT-IR technologies. These results indicate that the incorporation of Zr4+, Ti4+ and Sn4+ into the lattice of CeO2 leads to a smaller grain size and enhanced reduction behavior. Furthermore, the catalytic performance test shows that the activities and selectivities of these solid solutions are higher than pure CeO2 and that the Sn4+-doped sample shows the best results. The reason may be that: (1) the decrease in grain size results in an enlargement of the BET specific surface area and an increase of surface Ce3+. The former is conducive for sufficient contact between the catalyst and reactant molecules and the latter contributes to the adsorption of COx species; (2) the enhanced reduction behavior is beneficial in generating more surface oxygen vacancies during the reaction process, which can weaken the N–O bond to promote the dissociation of NOx effectively. Finally, in order to further understand the nature of the catalytic performances for these samples, a possible reaction mechanism is tentatively proposed.
Co-reporter:Yan Xiong, Xiaojiang Yao, Changjin Tang, Lei Zhang, Yuan Cao, Yu Deng, Fei Gao and Lin Dong
Catalysis Science & Technology (2011-Present) 2014 - vol. 4(Issue 12) pp:NaN4425-4425
Publication Date(Web):2014/07/31
DOI:10.1039/C4CY00785A
The influence of CO-pretreatment on the properties of CuO–V2O5/γ-Al2O3 catalysts was investigated in the reduction of NO by CO. Catalytic performance results showed that the pretreated CuO–V2O5/γ-Al2O3 exhibited extremely high activity and selectivity. For example, NO conversion can be remarkably enhanced from 13.8% to 100.0% for the 03Cu01V catalyst. For the catalyst characterization, the XRD results suggested that copper oxide and vanadium oxide were highly dispersed on the surface of γ-Al2O3 and the TPR results gave evidence for the existence of Cu2+–O–V5+ species. The XPS and EPR results demonstrated that Cu2+ and V5+ were reduced to lower valence states (Cu2+ → Cu+, V5+ → V4+) by the CO-pretreatment, which was proved by in situ FT-IR to be beneficial to the adsorption of CO and dissociation of NO. In addition, the interaction between the dispersed copper oxide and vanadium oxide species upon the γ-Al2O3 support before and after CO-pretreatment was tentatively discussed, using the concept of SSOV (surface synergetic oxygen vacancy) which was proposed elsewhere. According to this concept, the dispersed Cu2+–O–V5+ species could be reduced to Cu+–ϒ–V4+ (ϒ represents an oxygen vacancy) by CO-pretreatment and it was considered to be the primary active species for the reaction. Based on the discussion of the experiment results, a possible mechanism was proposed.
Co-reporter:Xiaojiang Yao, Changjin Tang, Fei Gao and Lin Dong
Catalysis Science & Technology (2011-Present) 2014 - vol. 4(Issue 9) pp:NaN2829-2829
Publication Date(Web):2014/05/27
DOI:10.1039/C4CY00397G
Catalytic elimination is an important technique to reduce the emission of atmospheric molecular contaminants (such as CO, NOx, VOCs, HC, and PM, etc.) efficiently. In this field, the supported metal-oxide catalysts have attracted more and more attention in recent years due to their low cost and excellent catalytic performance. It is well known that catalytic performances are significantly dependent on the supports, surface-dispersed components, and the pretreatment of the catalysts. In this work, we present a brief review and propose some perspectives for supported metal-oxide catalysts according to the above-mentioned three aspects. Meanwhile, this paper covers some interesting results about the preparation of supported metal-oxide catalysts and the improvement of their catalytic performances for the elimination of atmospheric molecular contaminants obtained by our research group. Moreover, we propose the concepts of “green integration preparation (GIP)” and “surface synergetic oxygen vacancy (SSOV)” to understand the relationship between the “composition–structure–activity” of the supported metal-oxide catalysts, and further clarify the nature of the catalytic reactions.
Co-reporter:Lihui Dong, Bing Zhang, Changjin Tang, Bin Li, Liya Zhou, Fuzhong Gong, Baozhen Sun, Fei Gao, Lin Dong and Yi Chen
Catalysis Science & Technology (2011-Present) 2014 - vol. 4(Issue 2) pp:NaN493-493
Publication Date(Web):2013/11/07
DOI:10.1039/C3CY00703K
Fe2O3–CeO2–Ti0.5Sn0.5O2 catalysts were prepared by a wet impregnation method and were characterized using XRD, LRS, EPR, H2-TPR, in situ IR, as well as the activity test for the removal of NO by CO. The results showed that the Fe2O3 and CeO2 are highly dispersed on the surface of Ti0.5Sn0.5O2 (the loading of Fe2O3 and CeO2 are 1.2 mmol Fe per 100 m2 and 0.4 mmol Ce per 100 m2, respectively). When the iron oxide loading is increased, the isolated Fe3+ ions change into the polymeric Fe3+ clusters and ceria addition also further promotes the formation of polymeric Fe3+ clusters. Catalysts modified with ceria display better performance in activity, and this would result from the formation of the more polymeric Fe3+ clusters, which are more easily reduced to Fe2+ ions under CO atmosphere. In situ FT-IR results indicated that the Fe2+ ions generated from the reduction of Fe3+ ions are primary active sites for NO + CO reactions. A possible reaction mechanism is tentatively proposed. In the reaction atmosphere, NO adsorbed on the surface of the catalysts forms several types of nitrite species. With the increase of temperature, bridging bidentate nitrate species transform into chelating nitro species, which react with CO gas to produce CO2 + N2O. When temperature reaches beyond 200 °C, NO adsorbed on Fe2+ ions (reduction of Fe3+ ions) reacts with carbonate species adsorbed on the surface of the catalysts, and produces CO2 + N2.
Co-reporter:Changjin Tang, Hongliang Zhang and Lin Dong
Catalysis Science & Technology (2011-Present) 2016 - vol. 6(Issue 5) pp:NaN1264-1264
Publication Date(Web):2015/12/09
DOI:10.1039/C5CY01487E
Selective catalytic reduction of NO with NH3 (NH3-SCR) is a powerful technique for the abatement of NOx from stationary sources, and the currently used VOx/TiO2-based catalysts are widely applicable for medium-temperature conditions but not suitable for NH3-SCR operated at low temperatures. Recently, low-temperature NH3-SCR has attracted considerable attention owing to the vast demand in industrial furnaces and its energy-conserving feature. During the past years, a great many studies have demonstrated that ceria-based catalysts are potential candidates as catalysts for low-temperature NH3-SCR. Herein we summarize the recent advances in the application of ceria-based catalysts for low-temperature NH3-SCR. The review begins with a brief introduction of the general guideline for low-temperature NH3-SCR and the interaction between the reactants and CeO2. The different roles of ceria as a pure support/active species, bulk doping component and surface modifier are discussed. As well, the mechanistic investigations (active sites, intermediates, reaction mechanism) and SO2/H2O tolerance are emphasized. Lastly, the perspectives on the opportunities and challenges of ceria-based catalysts for low-temperature NH3-SCR in future research are presented.
Co-reporter:Lei Zhang, Lulu Li, Yuan Cao, Yan Xiong, Shiguo Wu, Jingfang Sun, Changjin Tang, Fei Gao and Lin Dong
Catalysis Science & Technology (2011-Present) 2015 - vol. 5(Issue 4) pp:NaN2196-2196
Publication Date(Web):2015/01/07
DOI:10.1039/C4CY01412J
TixSn1−xO2 was prepared by a co-precipitation method, and a series of CeO2/TixSn1−xO2 samples were prepared to investigate the effect of doping SnO2 into TiO2 for selective catalytic reduction of NO by NH3. The results of catalytic tests suggested that the catalyst with the optimal molar ratio (Ti:Sn = 1:1) exhibited the best catalytic performance. Moreover, the NO removal efficiency of CeO2/Ti0.5Sn0.5O2 was higher than that of CeO2/TiO2. The obtained samples were characterized by BET, XRD, H2-TPR, XPS, NH3-TPD and in situ DRIFT. The results revealed that the introduction of SnO2 resulted in the formation of rutile-type Ti0.5Sn0.5O2 solid solution with larger specific surface area and better thermal stability. The interactions between CeO2 and the Ti0.5Sn0.5O2 support could improve the redox performance of the catalyst, which was beneficial to the enhancement of catalytic activity at low temperature. Furthermore, doping SnO2 enhanced the surface acid sites and weakened the adsorption of nitrates, which played an important role in the catalytic reaction process. Finally, in situ DRIFT demonstrated that the competition adsorption happened between bridging nitrates and NH3 gas and the selective catalytic reduction of NO by NH3 proceeded mainly via the Eley–Rideal mechanism over Ce/TiO2 and Ce/Ti0.5Sn0.5O2.
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![[1,1'-Biphenyl]-ar,ar'-diol](http://img.cochemist.com/ccimg/27000/26983-52-8_b.png)
