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Explicit Roles of Au and TiO 2 in a Bifunctional Au/TiO 2 Catalyst for the Water‐Gas Shift Reaction: A DFT Study
Author(s) -
Hussain Akhtar,
Gracia Jose,
Nieuwenhuys Ben E.,
Niemantsverdriet J. W. Hans
Publication year - 2013
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201300105
Subject(s) - disproportionation , catalysis , chemistry , dissociation (chemistry) , water gas shift reaction , adsorption , anatase , bifunctional , activation energy , molecule , reaction mechanism , surface diffusion , rate determining step , photochemistry , photocatalysis , organic chemistry
The water–gas shift reaction has been investigated by using DFT applied to Au(1 0 0), stepped Au(3 1 0), and TiO 2 anatase (0 0 1) surfaces. The results show that neither Au nor TiO 2 can catalyze the reaction by themselves. Of CO, CO 2 , H 2 O, and H 2 , only CO adsorbs with moderate adsorption energy at low‐coordinated sites, whereas other molecules interact only weakly with Au. The activation of H 2 O is impossible on Au surfaces. However, H 2 O adsorbs dissociatively on the anatase (0 0 1) surface and the diffusion of OH and H is feasible. The energetic data indicate that the rest of the process is possible on the Au surface. Two mechanisms were investigated and compared for the water–gas shift reaction, with H 2 O dissociation on the TiO 2 surface and diffusion of OH and H on Au surfaces in common. The latter is, in principle, the rate‐limiting step. The first mechanism occurs through the disproportionation of two OH groups on Au into H 2 O and an O atom. The latter reacts with CO. In the alternative mechanism, CO combines with OH to give a COOH intermediate, which subsequently reacts with another OH group to form CO 2 and H 2 O. Finally, H atoms recombine on the Au surface to complete the catalytic cycle.