Activation of Oxygen by Metallic Gold in Au/TiO₂ Catalysts

Abstract

Ever since the discovery of heterogeneous gold catalysts for low-temperature oxidation reactions, the mechanism of O2 dissociation on these materials has been controversial. We report Au L3-edge X-ray absorption near-edge structure (XANES) data for an active Au/TiO2 catalyst which indicate that fully reduced metallic gold particles on a reducible support (TiO2) form activated gold-oxygen complexes in the absence of CO. It is possible that these play a role in the mechanism of CO oxidation. These results were obtained with a highly active powder catalyst and the conclusions agree with those derived from model catalysts, for which it was shown that reduced gold is the active component in the oxidation of CO.

Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO2 Catalyst under Oxidative and Reducing Atmospheres

“…In a XANES study on Au/TiO 2 catalyst prepared in the same way but with Au particles with smaller average size than in the present paper, some of us found that the smallest particles are the more "reactive" toward oxygen. 10,23 More precisely, evidence was reported for "activated gold-oxygen complexes" at the surface of 1.7 nm Au NPs. It was suggested that the effect of these complexes could be a "depletion of the Au d-band in otherwise essentially metallic gold clusters.…”

“…2,3 While it is largely accepted that CO adsorbs on the low coordination surface sites of the gold nanoparticles, 4 the important issue of the O 2 activation is still very much controversial. [5][6][7][8][9][10][11][12][13] It has been proposed that oxygen could directly react with gold. 6,12,14 The possible role of the NPssupport interface, or of the sites at the perimeter of the Au NPs, has also been pointed out to explain the oxygen activation.…”

Gold peroxide complexes and the conversion of hydroperoxides into gold hydrides by successive oxygen-transfer reactions

“…The mode of oxygen activation remains unclear, not least as Au-O bonds are thought to be intrinsically weak and in general thermally unstable 5 , and the surfaces of gold catalysts adsorb O 2 only to a very limited extent 6 . It has been proposed that negatively charged gold nanoclusters facilitate O 2 adsorption by electron transfer to give surface superoxo-like species [4][5][6][7][8][9][10][11][12] , whereas Gates and co-workers 13 , and Hutchings et al 14 , showed that high-activity gold catalysts for CO oxidation contain species in higher oxidation states (Au þ , Au 3 þ ). A very recent study postulated that Au 3 þ peroxides and oxides are key intermediates in the electrochemical water splitting on gold electrodes 15 .…”

Layered sphere-shaped TiO 2 capped with gold nanoparticles on structural defects and their catalysis of formaldehyde oxidation

“…Previous results also demonstrated that Au nanoparticles dispersed on a reducible oxide support are better catalysts than those supported on non-reducible supports. This effect is due to the ability of Ti 3+ to efficiently form an active oxygen-rich Au-TiO 2 interface (Weiher et al, 2007). Oxygen vacancy defects reportedly stabilize Au monomers and Au trimers, but larger Au clusters cannot be sufficiently stabilized (Matthey et al, 2007).…”