Identification of valence shifts in Au during the water-gas shift reaction

In situ X-ray absorption spectroscopy (XAS) has been performed to investigate the active site on Au-based catalysts in the water-gas shift (WGS) reaction. The surface area and hence the WGS activity is higher for AuTiO₂ catalysts supported on carbon nanofibres (CNF) than TiO₂. The WGS reaction rate depends on the Au coordination number with an apparent maximum close to eight which corresponds to a particle size of approximately 2.5–3.0 nm. A likely cause for the changes in the electronic structure of Au is the adsorption of CO on the surface, which also creates a small positive charge in the Au atoms. The catalytic activity significantly improves when titania is present compared to Au deposited directly on CNF.