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A Theoretical Study of Surface Reduction Mechanisms of CeO 2 (111) and (110) by H 2
Author(s) -
Chen HsinTsung,
Choi Yong Man,
Liu Meilin,
Lin M. C.
Publication year - 2007
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200600598
Subject(s) - density functional theory , chemistry , adsorption , transition state , binding energy , exothermic reaction , molecule , computational chemistry , potential energy surface , redox , molecular vibration , catalysis , atomic physics , inorganic chemistry , organic chemistry , biochemistry , physics
Reaction mechanisms for the interactions between CeO 2 (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 Ce 4f states on the redox chemistry of H 2 –CeO 2 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 CeO 2 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 kcal mol −1 for the (111) to 26.5 kcal mol −1 for the (110) surface, while those at the DFT+U level are between 65.0 kcal mol −1 for the (111) and 81.8 kcal mol −1 for the (110) surface. Predicted vibrational frequencies of adsorbed OH and H 2 O 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 CeO 2 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 CeO 2 (110) is energetically much more favorable. Accordingly, oxygen vacancies are more easily formed on the (110) surface than on the (111) surface.