XAS Study of Au Supported on TiO₂:  Influence of Oxidation State and Particle Size on Catalytic Activity

Abstract

The effect of synthesis and reaction conditions on the structure and activity of Au clusters supported on nanocrystalline and mesoporous TiO2 was investigated. X-ray absorption spectroscopy was applied to correlate the particle size and the oxidation state with several parameters, such as pH of the precursor solution, Au loading, pretreatment, and support structure. The study using mesoporous TiO2 as the support shows that lower Au loadings resulted in bigger Au aggregates with lower reducibility. The high activity state for Au supported in different allotropic forms of TiO2 corresponds to Au in a fully reduced state. Furthermore, once reduced, no reoxidation occurs under reaction conditions, even after flowing air at higher temperatures (150 and 300 °C). Therefore, our results indicate that oxidized Au is not necessary for high activity. The activity decreased with particle growth, and, compared to the other allotropic TiO2, Au on brookite exhibited no significant particle agglomeration and was the most active catalyst after treatment at 300 °C.

Highly stable Pt monolayer on PdAu nanoparticle electrocatalysts for the oxygen reduction reaction

“…2a,b. We note that the XANES of Au from the Pd 9 Au 1 nanoparticles also differs from those observed by others in gold (Au) oxides 12,13 . We attribute these dissimilarities to changes in their electronic states due to the interactions with Pd atoms.…”

Development of novel supported gold catalysts: A materials perspective

“…Third, we have established some correlations between structure and function by means of systematic characterization, although these correlations have not been summarized in detail here. Last but not least, the development of these gold catalysts has provided new opportunities for further fundamental and applied research [130,131,146,186,188,220,[275][276][277][278]. For instance, the development of Au/SiO 2 [75,76] and Au/FePO 4 [86] catalysts makes it possible to study the nature of active sites and reaction mechanisms [130,131,146], and the development of Au/Al 2 O 3 /TiO 2 [71] and SiO 2 /Au/TiO 2 [77,84] catalysts prompted the subsequent DFT studies [186,220].…”

Comparison of the activity of Au/CeO2 and Au/Fe2O3 catalysts for the CO oxidation and the water-gas shift reactions

“…Gold nanoparticles supported on metal oxides can indeed catalyze low-temperature complete oxidation of hydrocarbons and CO, but also epoxidation reactions and hydrogenations, the NO reduction, and several other reactions as has been reviewed in the recent literature [2,3]. Perhaps the most intensively studied reaction to date is the CO oxidation on gold supported on oxides, such as iron oxide and titania [1,[4][5][6][7], and ceria [8][9][10][11], but also on non-reducible oxides, such as alumina [12][13][14][15] and silica [12]. Activity of nanoparticles of gold on non-oxide supports has also been reported [16].…”