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Interactions of water and methanol with a mixture of copper and zinc metals: a theoretical <Emphasis Type="Italic">ab initio</Emphasis> study 总被引:1,自引:0,他引:1
Ab initio cluster quantum chemical calculations at the Hartree–Fock and second-order Møller–Plesset perturbation theory levels were carried out to mimic the interactions of water and methanol with a mixture of Cu and Zn metals. It was shown that both molecular and dissociative adsorption of methanol on a mixture of Cu and Zn metal catalyst are preferred over the corresponding adsorptions of water. Estimated transition-state structures for dissociation of methanol into CH·3 and OH· lie about 9.0 and 22.0 kcal/mol higher compared to the dissociated (forward reaction) and molecular adsorption (reverse reaction) complexes, respectively. Based on distinct radicals' bond energies with the active sites of the catalyst considered, it is suggested that hydrogen molecules could be formed through a chain of homogeneous reactions of methyl radicals released into the gas phase with the water and/or methanol molecules. 相似文献
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N. U. Zhanpeisov 《Kinetics and Catalysis》2010,51(6):849-853
The present theoretical DFT study discusses the structure and chemical activity of transition metal and metal oxide catalysts
within the well-known cluster approach. Selective oxidation of carbon monoxide on gold supported on titania (Au/TiO2 (110)) as well as some key points in understanding the effect of non-metal doping on TiO2 with the aim to increase its photocatalytic
functionality have been briefly discussed. It was shown that Au (with formal oxidation state equal to plus one) stabilized
on water-assisted and vacancy containing TiO2 (110) can explain selective oxidation of CO. Here binding of O2 with the vacancy site is energetically preferable than its adsorption on an Au site. Conversely, CO adsorbs on an Au center
of Au/TiO2 (110) which is energetically much more profitable than its interaction with the oxygen vacancy site. Also, carbon and nitrogen
doping on TiO2 (110) leads to two different structures. Energetically most profitable is that carbon occupies an interstitial position in
deep bulk while nitrogen replaces the protruded oxygen atom and forms a surface N-H group. 相似文献
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G. V. Tsintsadze G. M. Zhidomirov M. A. Meladze A. G. Pel'menshchikov E. A. Kvezereli N. U. Zhanpeisov A. P. Narimanidze 《Russian Chemical Bulletin》1988,37(4):810-812
1. | The quantum-chemically calculated proton affinity may be considered a convenient index, characterizing the relative coordinating capacity of the different electron-donor sites of the amides and hydrazides of pyridinecarboxylic acids. |
2. | The calculated change in the electronic structure of the bonds in these molecules upon proton coordination qualitatively corresponds to the nature of the change in their IR spectra upon complexation. |
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Ab initio quantum chemical calculations were performed for four neutral gas phase adenine and four pterin tautomers along with guanine and formycin bases. The water complexes of the lowest energy tautomers of these bases have been studied to mimic their interaction with the ricin toxin A chain (RTA). The water molecules create a full first hydration shell around the bases. Full geometry optimizations without any constraints on the planarity of these hydrated complexes were carried out at the HF/6-31G(d,p) level. Single point calculations were also performed at the correlated MP2/6-31G(d,p)//HF/6-31G(d,p) level of theory. Hydration energies were corrected for the basis set superposition error. Hydration energies of adenine and formycin are predicted to be lower (in magnitude) than those for the pterin and guanine. Due to these properties, two pterin tautomers can be considered as potentially useful inhibitors of RTA. 相似文献
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Nurbosyn U. Zhanpeisov Shinya Higashimoto Masakazu Anpo 《International journal of quantum chemistry》2001,84(6):677-685
Ab initio quantum chemical studies at the HF/Lanl2dz level were carried out to investigate the interaction of ammonia, NO, and a mixture of the two with vanadia/titania. It was found that the replacement of Ti6c by V6c is the only feasible way to form highly dispersed vanadia over the titania. The V?O species thus formed will be in octahedral symmetry with the axial distortions, and no tetrahedrally coordinated V species can be formed. Ammonia fully covers the catalyst surface either through the associative interaction with the Lewis acid site of Ti5c or the dissociative adsorption channels. The dissociation of ammonia on the O site bridging the Ti6c and V6c octahedra and on the V?O group can proceed with the highest gain in energy. The formation of an adsorbed ammonium ion was found to be an energetically highly unfavorable process. The V?O group is no longer expected to play a major role in the stabilization of the surface ammonium ion. NO can be activated on the Ti5c site of the catalyst containing predissociated ammonia on the bridging O site and V?O group. It can be expected that the SCR reaction products are formed through the reactions of both adsorbed NO and NH2 or the desorbed NH2 group with NO in the gas phase. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 相似文献
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N. U. Zhanpeisov W. S. Ju K. Iino M. Matsuoka M. Anpo 《Research on Chemical Intermediates》2003,29(4):407-416
XAFS (both XANES and FT-EXAFS) measurements revealed that the Pb2+ /ZSM-5 catalyst prepared from precursor H-ZSM-5 by a conventional ion-exchange method includes a highly dispersed 3-fold coordinated Pb2+ ion species within the zeolite framework. UV-irradiation of Pb2+ /ZSM-5 led to effective decomposition of NO and N2O producing N2. The photocatalytic decomposition of NO is found to be slightly preferable than that of N2O. The isolated Pb2+ ions play a significant role in the decomposition of pollutant NO
x
. Ab initio and DFT quantum chemical studies at the HF/Lanl2dz and B3PW91/Lanl2dz levels further shed light on local structures of the Pb2+ active site of lead-containing zeolites, as well as on their interactions with pollutant NO and N2O molecules. In agreement with experiments, 3-fold coordination was found to be the most favorable state for the Pb2+ site within the zeolite framework. 相似文献
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In the framework of semiempirical quantum chemical MINDO/3 method the selective oxidation of ethane to acetaldehyde on a specially modified boron — phosphorus mixed oxide catalyst has been considered. On the basis of the results of calculation a possible mechanism for this process is proposed.
MINDO/3 . .相似文献
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Jose R Zhanpeisov NU Fukumura H Baba Y Ishikawa M 《Journal of the American Chemical Society》2006,128(2):629-636
Structures and properties of CdSe quantum dots (clusters) up to a diameter of approximately 2 nm were investigated by combining experimental absorption, photoluminescence (PL), and X-ray diffraction (XRD) spectroscopies as well as ab initio DFT calculations. These CdSe clusters were nucleated and grown from solutions containing respective cadmium and selenium precursors following the hot-injection technique that allows one to obtain size-controlled CdSe clusters having PL efficiency up to 0.5. The DFT calculations were performed at the B3LYP/Lanl2dz level and followed by time-dependent TDDFT calculations to estimate n energy singlet transitions. On the basis of the results of these experimental and theoretical studies, an approach to determine whether the proposed cluster with a mean diameter of approximately 2 nm is more physically reasonable is discussed. It was shown that the minimum nucleus of a CdSe cluster consists of (CdSe)(3) with a six-membered ring and planar structure. No PL is observed for this structure. The formation of the next stable cluster depends on whether hexadecylamine (HDA) was used for the growth of the CdSe clusters. In the absence of HDA, the second cluster was found to be (CdSe)(6) characterized by a broad PL spectrum, while in the presence of HDA, it was found to be (CdSe)(n) (where n > or = 14) with a sharp PL spectrum. 相似文献