Catalytic Role of Metal Oxides in Gold-Based Catalysts: A First Principles Study of CO Oxidation onTiO2Supported Au

Abstract

CO oxidation on TiO2 supported Au has been studied using density functional theory calculations. Important catalytic roles of the oxide have been identified: (i) CO oxidation occurs at the interface between Au and the oxide with a very small barrier; and (ii) O2 adsorption at the interface is the key step in the reaction. The physical origin of the oxide promotion effect has been further investigated: The oxide enhances electron transfer from the Au to the antibonding states of O2, giving rise to (i) strong ionic bonding between the adsorbed O2, Au, and the Ti cation; and (ii) a significant activation of O2 towards CO oxidation.

Insights into the reactivity of supported Au nanoparticles: combining theory and experiments

“…The results in figure 5 show that the effect of the support on the activation barriers is quite small. Adding the support, however, results in stronger bonding of O 2 , as shown by Hammer et al and Hu et al [57][58][59]98]. It should be noted that the results of Hammer at al.…”

Room-Temperature Reaction of Oxygen with Gold: An In situ Ambient-Pressure X-ray Photoelectron Spectroscopy Investigation

“…[7][8][9][10][11][12][13] One of the most important and controversial issues is the activation mechanism of O 2 on Au. 9,[14][15][16][17][18][19] For instance, based on the experimental observation that a bilayer Au structure, which completely wets the oxide support, exhibits extraordinary catalytic activity, Goodman et al proposed that Au can be directly involved in the activation of O 2 . 9 In contrast, more recently, Behm et al found that the amount of active oxygen species on the Au/TiO 2 surface has a linear relationship with the number of perimeter sites at the interface between the oxide support and the Au NPs, indicating that the support-Au interface plays a dominating role in the oxygen activation.…”

“…14 Using high-intensity in situ X-ray absorption near-edge structure (XANES), van Bokhoven and co-workers observed an increased white line intensity at the Au L 3 edge for Au NPs supported on Al 2 O 3 and TiO 2 substrates during treatment in O 2 , indicating that Au NPs can be oxidized by molecular oxygen. 17,18 However, Liu et al calculated that the dissociation barrier is larger than 2 eV on non-supported Au and even at the Au/TiO 2 interface the dissociation barrier is still 0.52 eV, 15 which means that O 2 has a very weak interaction with Au, and thus spontaneous dissociation of molecular oxygen on the Au surface is not energetically favorable.…”

“…These observations indicate that the proposed gold-only activation mechanism of O 2 is unlikely under these reaction conditions. 8,13,15,16,19 With the help of X-ray irradiation, however, both surfaces can be effectively oxidized under 1 Torr of O 2 . Therefore, our observations demonstrate that X-rays play a critical dual role during in situ measurements and that extreme care must be taken to carry out experiments and interpret spectra, especially when using intense synchrotron radiation.…”

On the Impact of Solvation on a Au/TiO2Nanocatalyst in Contact with Water

“…The size of the gold particles substantially affects the catalytic activity, suggesting the key importance of metal/support interactions on a nanometer scale [4]. Reactions, and in particular CO oxidation, are believed to occur at specific active Au sites at the Au/TiO 2 interface [5][6][7][8]. Although much is known regarding Au/TiO 2 catalytic activity in the presence of a gas phase, the complexity increases steeply when solvent is included.…”