標題: A theoretical study of surface reduction mechanisms of CeO2 (111) and (110) by H-2
作者: Chen, Hsin-Tsung
Choi, Yong Man
Liu, Meilin
Lin, M. C.
應用化學系分子科學碩博班
Institute of Molecular science
關鍵字: density functional calculations;reacton mechanisms;reduction;surface chemistry;vibrational spectroscopy
公開日期: 23-Apr-2007
摘要: Reaction mechanisms for the interactions between CeO2(111) and (110) surfaces are investigated using periodic density functional theory (DFT) calculations. Both standard DFT and DFT+U calculations to examine the effect of the localization of Ce4f states on the redox chemistry of H-2-CeO2 interactions are described. For mechanistic studies, molecular and dissociative local minima are initially located by placing an H-2 molecule at various active sites of the CeO2 surfaces. The binding energies of physisorbed species optimized using the DFT and DFT+U methods are very weak. The dissociative adsorption reactions producing hydroxylated surfaces are all exothermic; exothermicities at the DFT level range from 4.1 kcalmol(-1) for the (111) to 26.5 kcalmol(-1) for the (110) surface, while those at the DFT+U level are between 65.0 kcalmol(-1) for the (111) and 81.8kcalmol(-1) for the (110) surface. Predicted vibrational frequencies of adsorbed OH and H2O species on the surfaces are in line with available experimental and theoretical results. Potential energy profiles are constructed by connecting molecularly adsorbed and dissociatively adsorbed intermediates on each CeO2 surface with tight transition states using the nudged elastic band (NEB) method. It is found that the U correction method plays a significant role in energetics, especially for the intermediates of the exit channels and products that are partially reduced. The surface reduction reaction on CeO2(110) is energetically much more favorable. Accordingly, oxygen vacancies are more easily formed on the (110) surface than on the (111) surface.
URI: http://dx.doi.org/10.1002/cphc.200600598
http://hdl.handle.net/11536/10886
ISSN: 1439-4235
DOI: 10.1002/cphc.200600598
期刊: CHEMPHYSCHEM
Volume: 8
Issue: 6
起始頁: 849
結束頁: 855
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