Au–TiO2 catalysts on carbon nanofibres prepared by deposition-precipitation and from colloid solutions

Au catalysts have been prepared (i) on TiO2, (ii) on carbon nanofibres (CNF) and (iii) on TiO2 deposited onto CNF. Catalysts prepared from deposition-precipitation (DP) and from colloid solutions have been characterised using XRD, TEM, TGA and XAS and tested in the water–gas shift (WGS) reaction. DP yields large Au particles (>50 nm) on CNF-containing supports. High Au dispersion on carbon nanofibres requires preparation via other methods such as colloid formation. Au particle growth is more pronounced during the synthesis steps than during thermal treatments. This increase is not observed for the Au particles on TiO2 but only when CNF is present, indicating that the surface properties of TiO2 are altered by the CNF. TiO2 XANES analyses show that distortions in the lattice symmetry of TiO2 are introduced when the oxide is deposited on CNF. The distortion of the TiO2 structure by the CNF may also introduce changes that promote the turnover frequencies. The WGS activity significantly improves when titania is present. This shows that coexistence of Au and TiO2 is needed to obtain high catalytic activity in the WGS reaction, indicating that the active sites are either on the Au–TiO2 interface or that the reaction follows a bifunctional mechanism.