Mechanistic Aspects of the Water–Gas Shift Reaction on Isolated and Clustered Au Atoms on CeO₂(110): A Density Functional Theory Study

Abstract

Density functional theory was employed to study the water−gas shift (WGS) reaction for two structural modelsnamely, a single Au atom and a Au nanorodsupported on the (110) surface of ceria. The carboxyl mechanism involving a COOH intermediate is strongly preferred over the redox mechanism, which would require O− H bond cleavage of ceria-bound hydroxyl groups. Two candidate ratecontrolling elementary reaction steps were identified in the carboxyl mechanism: oxygen vacancy formation and COOH formation from CO and OH adsorbed to Au and the ceria support, respectively. A reaction energy analysis shows that both steps are more favorable on clustered Au atoms than on a single Au atom. CO adsorption on a single Au atom is hindered because of its negative charge. Comparison to literature data shows that the WGS reaction is preferred for a gold cluster on the CeO 2 (110) surface over the CeO 2 (111) one because of the lower binding energy of OH on the former surface. These results are discussed in the light of a large number of experimental and theoretical studies of the Au/CeO 2 catalyzed WGS reaction.

Effect of nanostructured support on the WGSR activity of Pt/CeO2 catalysts

“…Contrary, ceria nanorods with selective exposure of the (110) and (100) crystal planes are shown to provide an optimum platinum-ceria interaction compared to the (111) and (100) crystal planes exposed in the ceria nanoparticles. This observation is in agreement with theoretical calculations of gold clusters supported on ceria catalysts where the WGS reaction is preferred on the CeO 2 (110) surface over the CeO 2 (111) one because of the lower binding energy of OH on the former surface [31]. In addition, the (110) and (100) planes present in the ceria nanorods enhanced the re-oxidation of the ceria with respect to its particles and cubes counterparts, as previously shown in the oxidation reactions in the absence of metal nanoparticles [17,20], playing a key role on the catalytic cycle of the WGSR.…”

Ultrastable single-atom gold catalysts with strong covalent metal-support interaction (CMSI)

“…Mechanistic understanding of supported gold catalysts has attracted significant interest [58,[61][62][63][64][65]. To Nano Res.…”

Gold Clusters and Nanoparticles Stabilized by Nanoshaped Ceria in Catalysis

“…WGS reaction on Au 1 /CeO 2 {110} [81]: As discussed above, a single Au atom prefers to adsorb on the bridge site between two surface O atoms on CeO 2 {110}. One of these surface O atoms prefers to migrate to the bridge site between Ce and Au, generating a highly reactive Au-O s species, which may be easily reduced by CO.…”

“…Such oxygen vacancy between the Au adatom and ceria surface plays an important role in the water activation step [76,80]. Water adsorbs at the interface between Au and the defective ceria surface with an adsorption energy of 61 kJ mol −1 (Figure 19) [81]. Water dissociation proceeds with a low barrier of 45 kJ mol −1 to produce an H atom on the Au atom and an OH group attached to the Ce 3+ site from ceria support.…”

“…As the single Au atom cannot adsorb CO due to its negative charge, we predict that the carboxyl mechanism is also not operative in the low-temperature WGS reaction for this single Au atom model. WGS reaction on Au n /CeO 2 {110} [81]: For the gold cluster model on the CeO 2 {110} surface, CO adsorbs at the interface between the gold cluster and the support surface ( Figure 20). This leads to spontaneous reaction of CO with a ceria surface O atom and desorption as CO 2 , generating one oxygen vacancy at the interface.…”