Co-reporter:Xuan-Ye Chen, Shi-Long Chen, Ai-Pin Jia, Ji-Qing Lu, Wei-Xin Huang
Applied Surface Science 2017 Volume 393() pp:11-22
Publication Date(Web):30 January 2017
DOI:10.1016/j.apsusc.2016.09.159
Highlights
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Au on a Ti-MCM-41 with hybrid meso/micropores had the highest propylene conversion.
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Kinetic results suggested competitive adsorption of propylene and PO on Ti sites.
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Defective Ti sites and mesopores in the support improved intrinsic activity.
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Mesopores resulted in fast desorption of propylene and oxidation of PO to CO2.
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Micropores stabilized adsorbed propylene and resulted in higher PO selectivity.
Co-reporter:Ju-Fang Yuan, Ce-Qi Luo, Qin Yu, Ai-Ping Jia, Geng-Shen Hu, Ji-Qing Lu and Meng-Fei Luo
Catalysis Science & Technology 2016 vol. 6(Issue 12) pp:4294-4305
Publication Date(Web):25 Jan 2016
DOI:10.1039/C6CY00012F
Catalytic selective hydrogenation of α,β-unsaturated aldehydes to α,β-unsaturated alcohols is very important in the synthesis of various fine chemicals. However, the development of highly efficient catalyst systems is challenging because of the low selectivity and severe deactivation of the currently employed catalysts such as Pt and Au. In this work, a series of CrOx- and FeOx-promoted Ir/SiO2 catalysts were prepared by a sequential impregnation method and tested for gas phase selective hydrogenation of crotonaldehyde. It was found that the addition of promoters could greatly enhance the catalytic performance. The Ir/SiO2 catalyst promoted with combined CrOx–FeOx with a (Cr + Fe)/Ir ratio of 0.05 showed the highest steady state crotyl alcohol yield of 64.5% at a selectivity of 86%, which is 4-fold higher than that of the unpromoted Ir/SiO2 (15.5%) catalyst. Such an enhancement was due to the formation of new active sites generated at the Ir–CrOx and/or Ir–FeOx interfaces. Also, catalysts with low loadings of promoters showed excellent stability due to their appropriate electronic properties, while the catalyst with a high loading of promoters deactivated quickly due to the strong adsorption of products on the surface.
Co-reporter:Jing-Di Liu, Ting-Ting Zhang, Ai-Pin Jia, Meng-Fei Luo, Ji-Qing Lu
Applied Surface Science 2016 Volume 369() pp:58-66
Publication Date(Web):30 April 2016
DOI:10.1016/j.apsusc.2016.02.036
Highlights
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Spinel CoCr2O4 oxides are very active and selective for dichloromethane oxidation.
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High temperature calcination results in replacement of Co by Cr in octahedral sites.
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Surface enriched Cr ions lead to enhanced reducibility/acidity and high performance.
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Quantitative analyses show Cr6+ species had much higher TOF than Cr3+ species.
Co-reporter:Ai-Ping Jia;Yun Deng;Geng-Shen Hu
Reaction Kinetics, Mechanisms and Catalysis 2016 Volume 117( Issue 2) pp:503-520
Publication Date(Web):2016 April
DOI:10.1007/s11144-015-0947-8
Three CuO–MnOx–CeO2 catalysts with different impregnation sequences (i.e. MnOx/CuO/CeO2, CuO/MnOx/CeO2 and CuO–MnOx/CeO2) were prepared and the effects of impregnation sequences on the structures and catalytic behaviors of these catalysts were investigated. It was found that the MnOx/CuO/CeO2 possessed the largest amount of oxygen vacancies but the lowest reducibility; the CuO/MnOx/CeO2 had the largest Cu+ contents but the lowest amount of oxygen vacancies; the CuO–MnOx/CeO2 catalyst had the highest CuO dispersion and the best reducibility, along with moderate amount of oxygen vacancies and Cu+ contents on the surface. The kinetic studies revealed that the apparent activation energies of CO oxidation over the CuO–MnOx/CeO2, MnOx/CuO/CeO2 and CuO/MnOx/CeO2 were 49.5, 51.8 and 73.8 kJ mol−1, in order, and the activities followed an order of CuO–MnOx/CeO2 > MnOx/CuO/CeO2 > CuO/MnOx/CeO2. The highest performance of the CuO–MnOx/CeO2 was ascribed to the highly dispersed CuO species and the mobility of lattice oxygen.
Co-reporter:Qin Yu
The Journal of Physical Chemistry C 2016 Volume 120(Issue 16) pp:8663-8673
Publication Date(Web):April 7, 2016
DOI:10.1021/acs.jpcc.6b00456
A series of FeOx-promoted Ir/SiO2 catalysts were prepared and tested for gas phase selective hydrogenation of crotonaldehyde. It was found that a catalyst containing Ir nanoparticles contacting with highly dispersed FeOx clusters (3Ir/0.1Fe/SiO2) showed excellent activity and stability, with a 5-fold enhanced steady state crotyl alcohol yield (59.6%) compared to that of the bare Ir/SiO2 (12.4%), while a catalyst promoted with high content of Fe (3Ir/3.5Fe/SiO2) had high initial activity but deactivated rapidly. A catalyst with similar highly dispersed FeOx clusters but prepared by an inverse impregnation sequence (0.1Fe/3Ir/SiO2) also suffered severe deactivation. Various characterizations revealed that the observed behaviors were closely related to the Ir–FeOx interactions induced by different morphologies of the catalysts. The active sites generated at Ir–FeOx interface were responsible for the better performance. The catalyst deactivation was attributed to the deposit of heavy compound and strong adsorption of CO on the surface, which was induced by the strong Ir–FeOx interaction due to heavy decoration of FeOx on the Ir surface.
Co-reporter:Shu-Xia Chen, Yu Wang, Ai-Ping Jia, Huan-Huan Liu, Meng-Fei Luo, Ji-Qing Lu
Applied Surface Science 2014 Volume 307() pp:178-188
Publication Date(Web):15 July 2014
DOI:10.1016/j.apsusc.2014.04.012
Highlights
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Al substitution in LaMnO3 structure promoted redox property of the catalyst.
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Al substitution in LaMnO3 structure enhanced surface acidity of the catalyst.
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Activity was determined by synergy of reducibility and surface acidity of catalyst.
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Intrinsic activity was related to the presence of high valent Mn4+ species.
Co-reporter:Ji-Qing Lu, Chong-Xiang Sun, Na Li, Ai-Pin Jia, Meng-Fei Luo
Applied Surface Science 2013 Volume 287() pp:124-134
Publication Date(Web):15 December 2013
DOI:10.1016/j.apsusc.2013.09.091
Highlights
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Kinetic study of CO oxidation was conducted on CuO/MO2 catalysts (M = Si, Ti, Ce).
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Langmuir–Hinshelwood mechanism was proposed for CO oxidation over CuO/SiO2 catalyst.
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Interfacial reaction was proposed over CuO/TiO2 and CuO/CeO2 catalysts.
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Cu atoms located on CuO–support interface of large CuO particles were more active.
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Enhanced activity was due to higher CO chemisorption density on large CuO particles.
Co-reporter:Lian Meng ; Ai-Ping Jia ; Ji-Qing Lu ; Liang-Feng Luo ; Wei-Xin Huang ;Meng-Fei Luo
The Journal of Physical Chemistry C 2011 Volume 115(Issue 40) pp:19789-19796
Publication Date(Web):September 6, 2011
DOI:10.1021/jp2056688
The PdO/Ce1–xPdxO2−δ catalyst prepared by a solution-combustion method contained free surface PdO species and PdO species in Ce1–xPdxO2−δ solid solution, whereas the PdO/CeO2 catalyst prepared by an impregnation method contained only free surface PdO species. The free surface PdO species could be removed by nitric acid. Contributions of the PdO species to catalytic CO oxidation were quantitatively evaluated. The free surface PdO species in the PdO/Ce1–xPdxO2−δ catalyst had the highest activity (969.3 μmolCO gPd–1 s–1), those in the PdO/CeO2 catalyst had medium activity (109.0 μmolCO gPd–1 s–1), and the PdO species in the Ce1–xPdxO2−δ solid solution had the lowest activity (13.2 μmolCO gPd–1 s–1). Synergetic effects of PdO species were responsible for the enhanced reactivity of the PdO/Ce1–xPdxO2−δ catalyst, as the free surface PdO species provided CO chemisorption sites and the Ce1–xPdxO2−δ solid solution generated more oxygen vacancies for oxygen activation.
Co-reporter:Ai-Ping Jia ; Shi-Yu Jiang ; Ji-Qing Lu ;Meng-Fei Luo
The Journal of Physical Chemistry C 2010 Volume 114(Issue 49) pp:21605-21610
Publication Date(Web):November 15, 2010
DOI:10.1021/jp108556u
A series of CuO/CeO2 and inverse CeO2/CuO catalysts were prepared by an incipient wetness impregnation method and tested for CO oxidation. Crystallite sizes of CeO2 and CuO were evaluated by X-ray diffraction and N2O chemisorption, as well as transmission electron microscopy. It was found that a CuO(5)/CeO2-500 catalyst with a CuO crystallite size of 4.1 nm and a CeO2(5)/CuO-500 catalyst with a CeO2 crystallite size of 4.0 nm had identical activities, indicating that the reaction may occur at the interface of CuO−CeO2. According to the turnover frequency based on CuO sites located on the CuO−CeO2 interface, the activity on the larger CuO crystallite was much higher than that on the smaller one, indicating that CuO−CeO2 catalyst for CO oxidation is structure-sensitive. The enhanced activity was ascribed to a higher density of chemisorbed CO on the active sites for the larger CuO crystallite.
Co-reporter:Zhi-Ying Pu, Xue-Song Liu, Ai-Ping Jia, Yun-Long Xie, Ji-Qing Lu and Meng-Fei Luo
The Journal of Physical Chemistry C 2008 Volume 112(Issue 38) pp:15045-15051
Publication Date(Web):August 30, 2008
DOI:10.1021/jp805389k
Ce0.9Pr0.1O2-δ, Ce0.95Cu0.05O2-δ, and Ce0.9Pr0.05Cu0.05O2-δ mixed oxides and pure CeO2 were prepared with a sol−gel method and were characterized by XRD, in situ Raman, and in situ DRIFTS techniques. The XRD results confirmed the formation of Ce−Pr−O solid solution. The Raman results indicated that a higher concentration of oxygen vacancies was obtained on the Pr-doped samples compared to the Ce0.95Cu0.05O2-δ and pure CeO2 samples. Surface chemical states of the Ce0.9Pr0.1O2-δ and Ce0.9Pr0.05Cu0.05O2-δ mixed oxides were determined by in situ Raman spectroscopy, which indicated that the surfaces of the two mixed oxides were both close to oxidation state during the reaction, despite of the presence of reducing reactant CO in the gas mixture. The in situ DRIFTS results evidenced the chemisorption of CO in the Cu-containing samples. The catalysts were tested for CO oxidation, and it was found that the enhanced reactivity was closely related to the higher concentrations of the oxygen vacancies and the chemisorbed CO in the catalysts, due to the fact that the oxygen vacancies provide activation centers for O2 and the Cu+ ions provide chemisorption sites for CO.
Co-reporter:Ai-Ping Jia, Geng-Shen Hu, Lian Meng, Yun-Long Xie, Ji-Qing Lu, Meng-Fei Luo
Journal of Catalysis (May 2012) Volume 289() pp:199-209
Publication Date(Web):1 May 2012
DOI:10.1016/j.jcat.2012.02.010
A series of CuO/Ce1−xCuxO2−δ catalysts were prepared, and corresponding Ce1−xCuxO2−δ catalysts were obtained with nitric acid treatment. X-ray diffraction and Raman spectroscopic results revealed the presence of surface CuO species and CuxCe1−xO2−δ solid solution in the catalysts. CO oxidation testing found that the CO conversion was proportional to the concentrations of chemisorbed CO and oxygen vacancies in the CuO/Ce1−xCuxO2−δ catalysts, suggesting synergetic effects of the surface CuO species and CuxCe1−xO2−δ solid solution on the reactivity, as the former provided sites for CO chemisorption and the latter promoted reducibility of the catalyst for oxygen activation. Kinetic studies showed that the apparent activation energy was 42 kJ mol−1 for CuO/Ce1−xCuxO2−δ and 95 kJ mol−1 for Ce1−xCuxO2−δ. The power-law rate expression was rCO=k1PCO0.74PO20 for CuO/Ce1−xCuxO2−δ and rCO=k2PCO1.04PO20 for the Ce1−xCuxO2−δ catalyst, indicating that the reaction pathway followed a Mars–van Krevelen type mechanism.Synergetic effects of surface CuO species and CuxCe1−xO2−δ solid solution on CO oxidation over CuO/Ce1−xCuxO2−δ catalysts were found, as the former provided sites for CO chemisorption and the latter promoted reducibility of the catalyst for oxygen activation.Download high-res image (67KB)Download full-size image
Co-reporter:Yu Wang, Huan-Huan Liu, Shu-Yuan Wang, Meng-Fei Luo, Ji-Qing Lu
Journal of Catalysis (March 2014) Volume 311() pp:314-324
Publication Date(Web):1 March 2014
DOI:10.1016/j.jcat.2013.12.018
•K-promotion greatly improved activity of CH2Cl2 oxidation over Pt/Al2O3 catalysts.•The enhancement was due to the improved catalyst reducibility after K-promotion.•Surface Pt–O–Kx (x ≈ 2) species accelerated decomposition of formate intermediates.A series of K-promoted Pt/Al2O3 catalysts were prepared by an incipient wetness impregnation method and tested for oxidation of dichloromethane (DCM). It was found that the activity was greatly enhanced by the modification of K, which depended on the K content in the catalyst. The T50 temperature on a 0.42K–2Pt/Al2O3 catalyst was 270 °C, which was much lower than that on a K-free 2Pt/Al2O3 catalyst (400 °C). The remarkable improvement of activity was attributed to the enhanced catalyst reducibility, by the generation of Pt–O–Kx (x ≈ 2) surface species through an intimate interaction between K and Pt. The presence of such Pt–O–Kx species in the catalyst could significantly accelerate the decomposition of formate intermediates formed on Al2O3 surface and thus the overall reaction, as evidenced by the in situ Fourier transform infrared spectroscopic results.Graphical abstractDownload high-res image (130KB)Download full-size image
Co-reporter:Chong-Xiang Sun, Yu Wang, Ai-Ping Jia, Shu-Xia Chen, Meng-Fei Luo, Ji-Qing Lu
Journal of Catalysis (April 2014) Volume 312() pp:139-151
Publication Date(Web):1 April 2014
DOI:10.1016/j.jcat.2014.01.015
•Au/TiO2 catalysts are active for gas-phase epoxidation of 3,3,3-trifluoropropylene.•Addition of Cu promotes activity due to a higher Au content in the catalyst.•Cu+ species in catalyst promoted the selectivity to 3,3,3-trifluoropropylene oxide.Gas-phase epoxidation of 3,3,3-trifluoropropylene (TFP) was conducted on a series of Au/CuTiO2 catalysts with different Cu contents with N2O as the oxidant. These catalysts were effective for this reaction. The best catalytic performance was obtained on a catalyst containing 4.6 wt.% of Au and 0.9 wt.% of Cu (4.6Au/0.9CuTiO2), with a steady-state 3,3,3-trifluoropropylene oxide (TFPO) formation rate of 72.4gTFPOh-1kgcat-1, which was much higher than that on a 2.1Au/TiO2 catalyst (22.1gTFPOh-1kgcat-1). The enhancement was attributed to the higher Au content in the Cu-promoted catalyst and small Au particle size and more importantly to the complicated synergy between the AuCuTiO2 interaction which might be the active sites for epoxidation. Also, high selectivity to TFPO up to 88% was obtained on the Cu-promoted catalyst, due to the proper electronic structure induced by the interaction between Au and low valent Cu species. Catalyst deactivation was due to the significant growth of Au particles and loss of AuCuTiO2 interface because of the segregation of Cu species during the reaction.Graphical abstractDownload high-res image (138KB)Download full-size image
Co-reporter:Tong Liu, Pelin Hacarlioglu, S. Ted Oyama, Meng-Fei Luo, Xiao-Rong Pan, Ji-Qing Lu
Journal of Catalysis (25 October 2009) Volume 267(Issue 2) pp:202-206
Publication Date(Web):25 October 2009
DOI:10.1016/j.jcat.2009.08.002
The epoxidation of propylene with H2–O2 mixtures was studied over a gold catalyst supported on a Ge-modified TS-1 catalyst at 170 °C. Shifts of X-ray diffraction lines to lower angle showed that the Ge was incorporated into the structure of the TS-1. The presence of Ge more than doubled the conversion from 1.6% to 4% while increasing selectivity from 87% to 91%. Density functional theory calculations indicated that the origin of the enhanced activity was a ligand effect of Ge on Ti, which lowered the activation energy for the critical epoxidation step.Gold supported on a Ge-modified TS-1 was active for propylene epoxidation, due to a ligand effect of Ge on Ti, which lowered the activation energy for the critical epoxidation step.Download high-res image (51KB)Download full-size image
Co-reporter:Ju-Fang Yuan, Ce-Qi Luo, Qin Yu, Ai-Ping Jia, Geng-Shen Hu, Ji-Qing Lu and Meng-Fei Luo
Catalysis Science & Technology (2011-Present) 2016 - vol. 6(Issue 12) pp:NaN4305-4305
Publication Date(Web):2016/01/25
DOI:10.1039/C6CY00012F
Catalytic selective hydrogenation of α,β-unsaturated aldehydes to α,β-unsaturated alcohols is very important in the synthesis of various fine chemicals. However, the development of highly efficient catalyst systems is challenging because of the low selectivity and severe deactivation of the currently employed catalysts such as Pt and Au. In this work, a series of CrOx- and FeOx-promoted Ir/SiO2 catalysts were prepared by a sequential impregnation method and tested for gas phase selective hydrogenation of crotonaldehyde. It was found that the addition of promoters could greatly enhance the catalytic performance. The Ir/SiO2 catalyst promoted with combined CrOx–FeOx with a (Cr + Fe)/Ir ratio of 0.05 showed the highest steady state crotyl alcohol yield of 64.5% at a selectivity of 86%, which is 4-fold higher than that of the unpromoted Ir/SiO2 (15.5%) catalyst. Such an enhancement was due to the formation of new active sites generated at the Ir–CrOx and/or Ir–FeOx interfaces. Also, catalysts with low loadings of promoters showed excellent stability due to their appropriate electronic properties, while the catalyst with a high loading of promoters deactivated quickly due to the strong adsorption of products on the surface.
