DFT Study of CO Oxidation Catalyzed by Au/TiO₂: Activity of Small Clusters

Abstract

CO oxidation over a rutile TiO2(110) surface supporting a tetrahedral Au10 cluster has been examined by planewave DFT calculations. O2 adsorbs sideon to the pentacoordinate Ti site of the oxide support with a large energy gain (∼ 2 eV), activated to a peroxide state. O2 adsorption on the cluster is much weaker. The stability and activation state of sideon O2 depends weakly on distance to the cluster. On a Ti site next to the cluster, a sideon O2 reacts with CO adsorbed on the cluster to yield CO2 with a very small energy barrier of 0.13 eV. On a more remote Ti site, a sideon O2 reacts with a gaseous CO to yield CO2 with a barrier of 0.55 eV. Thus, O2 + CO reaction is much faster at the perimeter even for a small cluster such as Au10. Similar results are obtained for a truncated pyramidal Au9, except that a carbonate is formed at the perimeter. The carbonate formation is inhibited if H2O is adsorbed next to O2.

Advances in Gold Catalysis and Understanding the Catalytic Mechanism

“…Concurrently, the occupation of the antibonding orbitals weakens the O–O bond, activating O 2 for CO oxidation. A similar mechanism has been found by the majority of DFT studies,44–46 including ours 47–50. The supported Au clusters thus serve as electron donors to O 2 , as oxygen vacancies do.…”

“…It was found that H 2 O assists O 2 adsorption and activation on Au clusters57 and on Au(111)58 through hydrogen bonding, partial proton sharing, and a surface‐mediated mechanism. We also investigated these effects for two rutile TiO 2 (110)‐supported model clusters: tetrahedral Au 10 and truncated tetrahedral Au 9 48. In the Au 10 model, Ti–O 2 next to the cluster reacted with Au–CO with an activation barrier of 0.13 eV to produce CO 2 and an O adatom.…”

Density Functional Theory Study of Active Oxygen at the Perimeter of Au/TiO2Catalysts

“…Although small clusters can change shape to stabilize Ti-OO-Au, our calculation on Au 10 /TiO 2 (110) still finds that Ti-OO-Au is 0.44 eV less stable than Ti−O 2 . 27 In Ti−O 2 (Figure 2a), the O−O bond is not aligned with the Ti 5c row, but is off by 46.5°. The bond is substantially weakened, with a negative charge on O 2 .…”

“…O vacancy creation is briefly examined (section ). On the other hand, O 2 on Au-only sites are neglected because they are weakly adsorbed. , Ti 5c sites away from the perimeter have been discussed in our previous studies; , they can also activate O 2 , but adsorption is strongest in the immediate vicinity of the perimeter. The effect of water is not considered here and will be addressed in a future work.…”

Au Atom Diffusions on Reduced and Cl-Adsorbed Rutile TiO₂(110) Surfaces: A DFT + <i>U</i> Study

“…The interface between nanosized Au and the TiO 2 surface is the active site of the catalytic CO oxidation of Au/rutile TiO 2 [1,2,[10][11][12][13][14][15]. A high dispersion of Au is therefore necessary for preparing Au/TiO 2 catalysts, and special techniques, such as the deposition-precipitation method [5], gas-phase grafting [16], solid grinding [17], improved impregnation method including the H 2 reduction process [18][19][20], and using an unusual Au precursor [21] are utilized for the preparation.…”