Co-reporter:Guo-Liang Song, Zhen Hua Li, and Kang-Nian Fan
Journal of Chemical Theory and Computation 2013 Volume 9(Issue 4) pp:1992-1999
Publication Date(Web):March 14, 2013
DOI:10.1021/ct300850q
The divide-and-conquer (DC) scheme, the most popular linear-scaling method, is very important in the quantum mechanics computation of large systems. However, when a chemical system is divided into subsystems, its covalent bonds are often broken and then capped by complementary atoms/groups. In this paper, we show that the charge transfer between subsystems and the complementary atoms/groups causes the nonconservation of the total charge of the whole system, and this is the main source of error for the computed total energy. On the basis of this finding, an extension of the many-body expansion method (energy-based divide-and-conquer, EDC) utilizing charge conservation (E-EDC) is proposed. In the E-EDC method, initially the total energies of the whole system at different many-body correction levels are computed according to the EDC scheme. The total charges of the whole system, that is, the sum of the charges of the subsystems without cap atoms/groups at different many-body correction levels, are also computed. Then the total energy is extrapolated to the value at which the net charge of the whole system equals to the real value. Other properties such as atomic forces can also be extrapolated in a similar way. In the test of 24 and 32 glycine oligomers, this scheme reduces the error of the total energy by about 40–70%, but the computational cost is almost the same as that of the EDC scheme.
Co-reporter:Yu-Jue Du, Zhen Hua Li, Kang-Nian Fan
Journal of Molecular Catalysis A: Chemical 2013 Volume 379() pp:122-138
Publication Date(Web):15 November 2013
DOI:10.1016/j.molcata.2013.08.011
•ODP reaction on four VOx/TiO2 catalysts has been studied by DFT methods.•Key factors affecting activity: support surface, vanadia loading and active sites.•Activity is controlled by the oxidizability and bonding ability of active sites.•The coexistence of OV= and OV–Ti sites enhances the catalytic activity.The oxidative dehydrogenation of propane (ODP) on the anatase supported vanadia catalysts (VOx/TiO2) have been investigated using periodic DFT calculations. Free energy profiles indicate that the first C–H activation step is the rate-determining (RD) step and the transition state (TS) of the propene formation step is the RD–TS. ODP activity can be tuned by vanadia dispersion and support surface via the modification of the electronic structure of the active oxygen sites. For the RD step, on both dimer VOx/TiO2 catalysts terminal sites have higher activity. On monomer VOx/TiO2 (1 0 0) terminal and interface sites exhibit similar activity, while on monomer VOx/TiO2 (0 0 1) interface sites have higher activity. With increasing vanadia loading, the formation of propene changes from propyl radical mechanism to a concerted propoxide one. The results suggest that TiO2 (1 0 0) is a better support surface. Terminal and interface oxygen sites act cooperatively as the first and second C–H bond activation centers, respectively.First principle calculations on the ODP reaction catalyzed by VOx/TiO2 indicate that the catalytic activity is related with support surface, vanadia loading and active sites by affecting the oxidizability and bonding ability of active sites. The coexistence of OV= and OV–Ti sites enhances the catalytic activity.
Co-reporter:Xiaoyu Liu, Pingjun Guo, Songhai Xie, Yan Pei, Minghua Qiao, Kangnian Fan
International Journal of Hydrogen Energy 2012 Volume 37(Issue 8) pp:6381-6388
Publication Date(Web):April 2012
DOI:10.1016/j.ijhydene.2012.01.110
Cu/ZnO catalysts with Cu loadings of 44–5 wt% were prepared by coprecipitation and evaluated in temperature-dependant and shut-down/start-up water–gas shift (WGS) reactions using realistic reformate. These catalysts had similar Cu crystallite sizes, and the metallic Cu surface area and surface Cu content increased with the Cu loading. In temperature-dependent reactions, the CO conversion on the 25wt%Cu/ZnO catalyst slightly exceeded that on 44wt%Cu/ZnO. In shut-down/start-up operation, which is imperative for mobile and residential fuel cell applications, the catalysts with Cu loadings higher than 5 wt% suffered slight activity loss. Among them, the 15wt%Cu/ZnO catalyst deactivated the most reluctantly. As a result, after three shut-down/start-up cycles the CO conversion on 15wt%Cu/ZnO, 25wt%Cu/ZnO, and 44wt%Cu/ZnO became comparable. These results demonstrate the feasibility to lower the Cu loading without degrading the WGS performance of the Cu/ZnO catalyst in shut-down/start-up operation, which will guarantee the operation safety when the catalyst will be operated unattended for domestic small-scale fuel cell applications. Unexpectedly, the CO conversion was doubled on 5wt%Cu/ZnO after one shut-down/start-up cycle, which is interpreted as the redispersion of Cu nanoparticles based on transmission electron microscopy (TEM) and temperature-programmed reduction (TPR).Highlights► The CO conversion on 25wt%Cu/ZnO slightly exceeded that on 44wt%Cu/ZnO in temperature-dependent reactions. ► After three shut-down/start-up cycles, the CO conversions on 15wt%Cu/ZnO and catalysts with higher Cu loadings were comparable. ► The enhanced CO conversion on 5wt%Cu/ZnO after one cycle is attributed to the redispersion of Cu nanoparticles on ZnO.
Co-reporter:Yu-Jue Du, Zhen Hua Li, Kang-Nian Fan
Surface Science 2012 Volume 606(11–12) pp:956-964
Publication Date(Web):June 2012
DOI:10.1016/j.susc.2012.02.016
Periodic density functional theory has been utilized to investigate the structure and stability of monomeric HVOx species on anatase support. The three most stable surfaces of anatase were investigated, namely the (001), (100) and (101) surfaces. Unlike previous theoretical studies it was found that on the (001) surface vanadia species with five-coordinated vanadium atom are more stable than those with tetrahedrally coordinated vanadium atom. On the other hand, on the (100) and (101) surfaces, the vanadium atom in the vanadia species is still tetrahedrally coordinated. The stability of different VOx/TiO2 structures which are not fully dehydrated has been systematically studied and the results show that the vanadia species on the three surfaces follow an order of TiO2 (001) > TiO2 (100) > TiO2 (101). This can be understood from the acidity and basicity of the three anatase surfaces. The results suggest that monomeric VOx species may be better stabilized if the support exposes more (001) surfaces. Our analyses on electronic structure of the most stable VOx/TiO2 structure (D001) suggest that its bridging V–O–Ti oxygen atoms may have higher reactivity than the terminal vanadyl oxygen atoms.Highlights► Adsorption of HVOx species on anatase TiO2 surfaces was modeled by periodic DFT method. ► Five-coordinated vanadia species was found to be more stable on the TiO2(001) surface. ► Monomeric VOx species was found to be stabilized better on the (001) surface. ► Bridging V–O–Ti oxygens may have higher reactivity than terminal vanadyl oxygens.
Co-reporter:Guo-Liang Dai ; Zhen-Hua Li ; Jing Lu ; Wen-Ning Wang ;Kang-Nian Fan
The Journal of Physical Chemistry C 2012 Volume 116(Issue 1) pp:807-817
Publication Date(Web):December 1, 2011
DOI:10.1021/jp208639t
The oxidative dehydrogenation (ODH) of propane to propene over a vanadium-based catalyst suffers from side reactions of further and complete oxidations of propene and other intermediates, which limit the yield of propene. These further oxidation reactions are also referred to as deep oxidation reactions of ODH. In this paper, we present a comprehensive study of the deep oxidation reactions in the ODH of propane over the V2O5(001) surface using the periodic density functional theory method. It is shown that the main source of deep oxidation byproducts originates from the dehydrogenation reaction of the surface intermediate isopropoxide, leading to acetone and the following deep oxidation reactions of acetone and propene. Thorough oxidation of acetone is more difficult than that of propene. Noticeably, formation of acetone and deep oxidation of acetone and propene are only feasible on the terminal oxygen site O(1) of the V2O5(001) surface. The bridging site O(2) has similar reactivity for propene formation but is inert for the side reactions, showing its superiority for selectivity of propane ODH.
Co-reporter:Hao-Cheng Fang, Zhen Hua Li and Kang-Nian Fan
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 29) pp:13358-13369
Publication Date(Web):29 Jun 2011
DOI:10.1039/C1CP21160A
Quantum chemical calculations were carried out on CO oxidation catalyzed by a single gold atom. To investigate the performance of density functional theory (DFT) methods, 42 DFT functionals have been evaluated and compared with high-level wavefunction based methods. It was found that in order to obtain accurate results the functionals used must treat long range interaction well. The double-hybrid mPW2PLYP and B2PLYP functionals are the two functionals with best overall performance. CAM-B3LYP, a long range corrected hybrid GGA functional, also performs well. On the other hand, the popular B3LYP, PW91, and PBE functionals do not show good performance and the performance of the latter two are even at the bottom of the 42 functionals. Our accurate results calculated at the CCSD(T)/aug-cc-pVTZ//mPW2PLYP/aug-cc-pVTZ level of theory indicate that Au atom is a good catalysis for CO oxidation. The reaction follows the following mechanism where CO and O2 adsorb on Au atom forming an Au(OCOO) intermediate and subsequently O2 transfer one oxygen atom to CO to form CO2 and AuO. Then AuO reacts with CO to form another CO2 to complete the catalytic cycle. The overall energy barrier at 0 K for the first CO oxidation step (Au + CO + O2 → AuO + CO2) is just 4.8 kcal mol−1, and that for the second CO oxidation step (AuO + CO → Au + CO2) is just 1.6 kcal mol−1.
Co-reporter:Jie Xu, Miao Chen, Yong-Mei Liu, Yong Cao, He-Yong He, Kang-Nian Fan
Microporous and Mesoporous Materials 2009 Volume 118(1–3) pp:354-360
Publication Date(Web):1 February 2009
DOI:10.1016/j.micromeso.2008.09.007
Mesoporous SBA-15(H2O2) material synthesized via a controlled H2O2-based detemplation at mild conditions has been employed as new type of support to load vanadia. The ordered mesostructure of the SBA-15 host is retained as indicated by XRD and nitrogen adsorption measurements, and the surface areas of the V-SBA-15(H2O2) materials are in the range of 464–667 m2 g−1 comparable to 772 m2 g−1 for the parent SBA-15(H2O2) material. The characterization results also indicate the presence of a high abundance of surface silanol groups inside the silica pores, which can allow controlled vanadia loading up to 4.5 wt% or V coverage up to 1.01 V nm−2. In contrast to conventional calcination-derived SBA-15(C) sample the high population of the surface hydroxyl groups as well as high structural stability of the SBA-15(H2O2) material allowed a very good dispersion of the vanadia on its surface leading to high productivities of propylene during the oxidative dehydrogenation of propane.
Co-reporter:Pingjun Guo, Liangfeng Chen, Qiuyun Yang, Minghua Qiao, Hui Li, Hexing Li, Hualong Xu, Kangnian Fan
International Journal of Hydrogen Energy 2009 Volume 34(Issue 5) pp:2361-2368
Publication Date(Web):March 2009
DOI:10.1016/j.ijhydene.2008.12.081
The Cu/ZnO/Al2O3 catalysts were prepared by the coprecipitation method, and were evaluated in the water–gas shift (WGS) reaction. The effects of the calcination temperature on the BET surface area and crystallite size were characterized. In WGS reaction, the Cu/ZnO/Al2O3 catalysts suffered from continuous deactivation in shut-down/start-up operation – the daily requirement for mobile and residential fuel cell systems. Among them, the Cu/ZnO/Al2O3 catalyst prepared at the calcination temperature of 450 °C showed the best activity and stability, with the decrement of the CO conversion of only 12.8% after three shut-down/start-up cycles. Deactivation of the Cu/ZnO/Al2O3 catalysts is attributed to the blocking or deterioration of the active sites by Zn6Al2(OH)16CO3·4H2O resulting from the degeneration of the oxides under cyclic operations. Removal of the hydroxycarbonate species by calcination in air followed by re-reduction could restore the steady-state WGS activity; however, the regenerated catalyst underwent much severe deactivation in subsequent shut-down/start-up operation.
Co-reporter:Jie Xu;Lun-Cun Wang;Yong-Mei Liu;Yong Cao;He-Yong He
Catalysis Letters 2009 Volume 133( Issue 3-4) pp:
Publication Date(Web):2009 December
DOI:10.1007/s10562-009-0174-x
A new type of mesostructured ceria material was synthesized via template-assisted precipitation method and tested for the oxidative dehydrogenation (ODH) of ethylbenzene to styrene by molecular oxygen. The effect of calcination temperature on the catalytic performances of the ceria catalysts has been investigated. Among the catalysts tested, the CeO2-450 sample derived by calcination at 450 °C exhibited the highest ethylbenzene conversion (34%) and styrene selectivity (87%). Comparing the reaction rates for ODH of ethylbenzene (ca. 6.1 mmol ST gcat−1 h−1 at 450 °C) with the highly active nanostructured carbon-based catalysts in the current literature confirmed the very high activity of these new materials. The superior catalytic performance of the CeO2-450 sample can be attributed to its high specific surface area and enhanced redox properties as revealed by H2-TPR measurements.
Co-reporter:Guo-Liang Song, Zhen Hua Li, Zhi-Pan Liu, Xiao-Ming Cao, Wenning Wang, Kang-Nian Fan, Yaoming Xie and Henry F. Schaefer III
Journal of Chemical Theory and Computation 2008 Volume 4(Issue 12) pp:2049-2056
Publication Date(Web):November 5, 2008
DOI:10.1021/ct800265p
A local hybrid divide-and-conquer method (LHDC) which combines the high accuracy of sophisticated wave function theory (WFT) methods and the low cost of density functional theory (DFT) has been proposed for computational studies of medium and large molecules. In the method, a large system is divided into small subsystems for which the coefficients of the exchange functional in a hybrid functional are first optimized according to the energy calculated by an accurate WFT method. The hybrid coefficients are then used to evaluate the energy of the whole system. The method not only can reproduce the total energies of the chosen WFT method in good accuracy but also provides electronic structure information for the entire system.
Co-reporter:Yan Liu, Zhen Hua Li, Jing Lu and Kang-Nian Fan
The Journal of Physical Chemistry C 2008 Volume 112(Issue 51) pp:20382-20392
Publication Date(Web):2017-2-22
DOI:10.1021/jp807864z
Propane dehydrogenation over perfect Ga2O3(100) was studied in detail by periodic density functional theory (DFT) calculations. It was found that the initial C−H bond activation mainly follows a radical mechanism that the two-coordinated surface oxygen site (O(2)) abstracts a hydrogen atom from propane with the formation of propyl radical and hydroxyl group (O(2)H). Physically adsorbed propyl radical can easily form propoxide or propylgallium intermediate. Subsequently, propene is formed by a second H abstraction from propyl, propoxide, or propylgallium by surface oxygen and Ga sites. H abstraction by O(2) site always has low energy barrier. However, it is difficult for the hydrogen atoms in the hydroxyl groups to leave the surface in the form of either H2 or H2O. In addition, propene formed through H abstraction by oxygen site has high adsorption energy and is prone to further dehydrogenation or oligomerization, leading to fast deactivation of the catalyst. On the other hand, the formation of H2 from GaH and hydroxyl group is much easier, although the formation of GaH has to overcome high energy barrier. Thus, there is a shift of rate-determining step for propane dehydrogenation: at the initial stage of the reaction, the rate-determining step is H abstraction by oxygen sites and then it shifts to H abstraction from various propyl sources by Ga sites to form gallium hydrides after the surface oxygen sites are consumed. Our results also indicate that dehydrogenation of propane mainly follows a direct dehydrogenation mechanism (DDH), whereas oxidative dehydrogenation (ODH) is energetically less feasible but cannot be ruled out in the presence of mild oxidant such as CO2.
Co-reporter:Jianqiang Wang, Youzhen Wang, Minghua Qiao, Songhai Xie, Kangnian Fan
Materials Letters 2007 Volume 61(Issue 28) pp:5074-5077
Publication Date(Web):November 2007
DOI:10.1016/j.matlet.2004.07.068
Attempts have been made to prepare alumina nanofibers by hydrolyzing aluminum nitrate in the presence of hexamethylenetetramine (HMTA) followed by the supercritical fluid drying (SCFD) process. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen physisorption. The results show that δ-Al2O3 nanofibers with diameter of 2 nm, length of 50 nm and with BET surface areas of 412.6 m2 g− 1 were successfully synthesized. The thermal evolution of the fibers and the role of hexamethylenetetramine were also briefly discussed.
Co-reporter:Yan Pei, Jianqiang Wang, Qiang Fu, Pingjun Guo, Minghua Qiao, Shirun Yan and Kangnian Fan
New Journal of Chemistry 2005 vol. 29(Issue 8) pp:992-994
Publication Date(Web):16 Jun 2005
DOI:10.1039/B505701A
A nanosized amorphous Co–Fe–B catalyst exhibited higher selectivity and yield to crotyl alcohol than noble Pt-based catalysts in the hydrogenation of crotonaldehyde and could be prepared by a facile chemical reduction method.
Co-reporter:Xue-Mei Duan, Zhen-Hua Li, Guo-Liang Song, Wen-Ning Wang, Guan-Hua Chen, Kang-Nian Fan
Chemical Physics Letters 2005 Volume 410(1–3) pp:125-130
Publication Date(Web):10 July 2005
DOI:10.1016/j.cplett.2005.05.046
Abstract
A neural-network-based approach was applied to correct the systematic deviations of the calculated heats of formation for 180 organic molecules and led to greatly improved calculation results compared to the first-principles methods [J. Chem. Phys. 119 (2003) 11501]. In this work, this neural network approach has been improved by using new descriptors obtained from natural bond orbital analysis and an enlarged training set including organic, inorganic molecules and radicals. After the neural network correction, the root-mean-square deviations for the enlarged set decreases from 11.2, 15.2, 327.1 to 4.4, 3.5, 9.5 kcal/mol for the B3LYP/6-31G(d), B3LYP/6-311G(2d,d,p) and HF/6-31G(d) methods, respectively.
Co-reporter:Xue-Mei Duan, Zhen-Hua Li, Hai-Rong Hu, Guo-Liang Song, Wen-Ning Wang, Guan-Hua Chen, Kang-Nian Fan
Chemical Physics Letters 2005 Volume 409(4–6) pp:315-321
Publication Date(Web):30 June 2005
DOI:10.1016/j.cplett.2005.04.110
Abstract
The linear regression correction previously developed to reduce quantum chemical calculation errors [X.M. Duan, G.L. Song, Z.H. Li, X.J. Wang, G.H. Chen, K.N. Fan, J. Chem. Phys. 121 (2004) 7086] has been further improved by using new descriptors obtained from natural bond orbital analysis and an enlarged training set of 350 organic, inorganic molecules and radicals. The new scheme is better suited for correcting reaction barriers. Upon linear regression correction, the mean absolute deviation for the new set decreases from 284.1, 8.2, 12.4 kcal/mol to 7.3, 3.3, 2.7 kcal/mol for the HF/6-31G(d), B3LYP/6-31G(d), and B3LYP/6-311G(2d,d,p) methods, respectively, and the mean absolute deviation of 12 barrier heights for six hydrogen transfer reactions is reduced from 5.3 to 2.9 kcal/mol for the B3LYP/6-311G(2d,d,p) method.
Co-reporter:Xiangyu Ye, Zhen-Hua Li, Wenning Wang, Kangnian Fan, Wei Xu, Zhongyi Hua
Chemical Physics Letters 2004 Volume 397(1–3) pp:56-61
Publication Date(Web):11 October 2004
DOI:10.1016/j.cplett.2004.07.115
The parallel π–π stacking of benzene molecules was studied using Density Functional Theory (DFT) and second-order Moller–Plesset perturbation theory (MP2) methods. The DFT methods are proved to be inadequate in prediction of π–π stacking conformation and interaction energy. Cluster model calculations at the MP2/6-311 + G** level predicted an optimized conformation which is very close to the structure of the parallel-displaced benzene dimer. The calculated inter-plane distance of 3.3 Å is in good agreement with the observation in organic molecular crystals. The interaction energy predicted at MP2 level revealed that the pairwise interaction energy increases with the number of the parallel-stacked benzene molecules.
Co-reporter:Jianqiang Wang, Pingjun Guo, Shirun Yan, Minghua Qiao, Hexing Li, Kangnian Fan
Journal of Molecular Catalysis A: Chemical 2004 Volume 222(1–2) pp:229-234
Publication Date(Web):15 November 2004
DOI:10.1016/j.molcata.2004.08.009
A colloidal RuB/Al2O3·xH2O catalyst has been synthesized through a combined coprecipitation–crystallization–reduction strategy and characterized in detail with techniques including ICP-AES, N2 physisorption, XRD, TG/DTA, PSD and TEM. The catalytic behavior in liquid phase selective hydrogenation of benzene to cyclohexene was studied and compared with that of the RuB/γ-Al2O3 catalyst prepared by the incipient-wetness impregnation method. The RuB/Al2O3·xH2O catalyst is found more reactive than the RuB/γ-Al2O3 catalyst, and the maximum yield of cyclohexene is about four times as high as that over the latter. The better activity of the colloidal catalyst is assigned to the higher dispersion of the smaller RuB particles, whereas its superior selectivity is attributed to the improved hydrophilicity due to higher content of structural water and surface hydroxyl groups.A novel colloidal RuB/Al2O3·xH2O catalyst exhibiting superior catalytic performance to the RuB/γ-Al2O3 catalyst in liquid phase selective hydrogenation of benzene was prepared by a combined coprecipitation–crystallization–reduction strategy.
Co-reporter:Bo Liu;Minghua Qiao;Jianqiang Wang;Hexing Li;Songhai Xie
Journal of Chemical Technology and Biotechnology 2003 Volume 78(Issue 5) pp:512-517
Publication Date(Web):1 APR 2003
DOI:10.1002/jctb.817
Microwave heating was utilized in the preparation of amorphous Ni–B/SiO2 catalysts. After wetness impregnation with NiCl2 aqueous solution, the catalyst precursor was dried at 383 K, followed by microwave heating and KBH4 reduction. Liquid phase hydrogenation of acrylonitrile was employed as the probe reaction. While ICP, XRD, XPS and turnover frequency results did not reveal discernable structural and electronic differences between the active components of the catalysts with or without microwave heating, SEM uncovered the formation of smaller Ni–B alloy particles with microwave heating, leading to a higher concentration of active sites and greater thermal stability as verified by H2 chemisorption and DSC. Copyright © 2003 Society of Chemical Industry
Co-reporter:Bo Liu, Minghua Qiao, Jianqiang Wang and Kangnian Fan
Chemical Communications 2002 (Issue 11) pp:1236-1237
Publication Date(Web):07 May 2002
DOI:10.1039/B202499N
A nanosized amorphous Ni-Cr-B catalyst prepared by the chemical reduction method exhibited superior thermal stability and selectivity in hydrogen peroxide synthesis via the anthraquinone route.
Co-reporter:Yonggen He, Minghua Qiao, Huarong Hu, Yan Pei, Hexing Li, Jingfa Deng, Kangnian Fan
Materials Letters 2002 Volume 56(Issue 6) pp:952-957
Publication Date(Web):November 2002
DOI:10.1016/S0167-577X(02)00644-4
Some preparation parameters of amorphous Ni–B alloy were systematically studied. It is found that high-surface-area Ni–B can be readily prepared by adding the Ni2+ solution to the borohydride solution. It is also found that the higher the pH of the Ni2+ solution, the higher the surface area and boron content in the resulting Ni–B alloy. The influences of the precursor salt and the adding rate on the surface area and boron content can be mainly attributed to the effect of pH.
Co-reporter:Yun Wang, Wenning Wang, Kangnian Fan, Jingfa Deng
Surface Science 2001 Volume 487(1–3) pp:77-86
Publication Date(Web):20 July 2001
DOI:10.1016/S0039-6028(01)01072-X
The properties of the I-modified Ag(1 1 1), (1 0 0) and (1 1 0) surfaces are studied via the first-principle local density functional calculation with the ultrasoft pseudopotential and the generalized gradient approximation. The preferred adsorption site, relaxation of the surface structure, adsorption energy, work function change and changes of the properties with the coverage as well as total density of state are investigated. The most energetically favorite adsorption site is hollow site on the (1 0 0) surface in our study. Strong interaction between the iodine atom and the surface and transfer of electronic charges from the silver surface to the iodine atom are observed. The function of the iodine atom in the partial oxidation of the methanol is discussed based on our results.
Co-reporter:Yun Wang, Wenning Wang, Kang-Nian Fan, Jingfa Deng
Surface Science 2001 Volume 490(1–2) pp:125-132
Publication Date(Web):1 September 2001
DOI:10.1016/S0039-6028(01)01320-6
The structural and electronic properties of the three low-index silver surfaces are investigated via the ab initio local density functional calculations with ultrasoft pseudopotential. The Hellmann–Feynman forces are calculated to optimize the surface structure with the conjugate-gradient technique, and the electronic states of surface are also analyzed in detail. We find that the structural and electronic properties of the surface depend on atomic packing significantly. The relation between the surface properties and their performance in catalysis is discussed.
Co-reporter:Xin-Li Yang, Wei-Lin Dai, Ruihua Gao, Kangnian Fan
Journal of Catalysis (25 July 2007) Volume 249(Issue 2) pp:278-288
Publication Date(Web):25 July 2007
DOI:10.1016/j.jcat.2007.05.002
Tungsten-doped ordered SBA-15 prepared by the in situ synthesis method was systematically characterized by UV-Raman, UV–vis DRS, FT-IR, XPS, and H2-TPR. It was found that the dispersion and nature of the tungsten species depend strongly on the tungsten oxide content. The tungsten species are located mainly in isolated tetrahedral or low-condensed oligomeric environments, and there are strong interaction between tungsten species and the silica-based matrix at tungsten oxide content <20 wt%. Higher tungsten oxide content leads to the formation of bulk tungsten species. It was also found that the ordered hexagonal mesoporous structure of SBA-15 is retained, and strong Brønsted and Lewis acid sites are formed on tungsten incorporation. The superior catalytic performance in the selective oxidation of cyclopentene has been attributed to its proper content of tungsten species, high dispersion, and strong surface acidity.
Co-reporter:Yan Pei, Pingjun Guo, Minghua Qiao, Hexing Li, Shiqiang Wei, Heyong He, Kangnian Fan
Journal of Catalysis (10 June 2007) Volume 248(Issue 2) pp:303-310
Publication Date(Web):10 June 2007
DOI:10.1016/j.jcat.2007.03.024
Binary CoB and ternary CoFeB amorphous alloy catalysts with different Fe contents were prepared by the chemical reduction method. In liquid-phase hydrogenation of crotonaldehyde, incorporation of Fe into the CoB catalyst reduced the overall activity while effectively improving the selectivity and yield to crotyl alcohol. On the optimum CoFeB-3 catalyst with a nominal Fe/(Co + Fe) molar ratio of 0.6, the initial selectivity amounted to 71%, and the yield of crotyl alcohol reached 63%. It is found that the selectivity enhancement was due to the lower decrement in the intrinsic formation rate of crotyl alcohol compared with that of butanal, not to the increment in the activation of the CO bond. Based on the characterizations, including X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, and previous findings, the enhanced selectivity from Fe modification was tentatively attributed to an ensemble size effect.
Co-reporter:Ge Luo, Shirun Yan, Minghua Qiao, Kangnian Fan
Applied Catalysis A: General (1 November 2007) Volume 332(Issue 1) pp:79-88
Publication Date(Web):1 November 2007
DOI:10.1016/j.apcata.2007.08.007
Co-reporter:Hao-Cheng Fang, Zhen Hua Li and Kang-Nian Fan
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 29) pp:NaN13369-13369
Publication Date(Web):2011/06/29
DOI:10.1039/C1CP21160A
Quantum chemical calculations were carried out on CO oxidation catalyzed by a single gold atom. To investigate the performance of density functional theory (DFT) methods, 42 DFT functionals have been evaluated and compared with high-level wavefunction based methods. It was found that in order to obtain accurate results the functionals used must treat long range interaction well. The double-hybrid mPW2PLYP and B2PLYP functionals are the two functionals with best overall performance. CAM-B3LYP, a long range corrected hybrid GGA functional, also performs well. On the other hand, the popular B3LYP, PW91, and PBE functionals do not show good performance and the performance of the latter two are even at the bottom of the 42 functionals. Our accurate results calculated at the CCSD(T)/aug-cc-pVTZ//mPW2PLYP/aug-cc-pVTZ level of theory indicate that Au atom is a good catalysis for CO oxidation. The reaction follows the following mechanism where CO and O2 adsorb on Au atom forming an Au(OCOO) intermediate and subsequently O2 transfer one oxygen atom to CO to form CO2 and AuO. Then AuO reacts with CO to form another CO2 to complete the catalytic cycle. The overall energy barrier at 0 K for the first CO oxidation step (Au + CO + O2 → AuO + CO2) is just 4.8 kcal mol−1, and that for the second CO oxidation step (AuO + CO → Au + CO2) is just 1.6 kcal mol−1.
