Effect of Gold Electronic State on the Catalytic Performance of Nano Gold Catalysts in n-Octanol Oxidation

This study aims to identify the role of the various electronic states of gold in the catalytic behavior of Au/M(x)O(y)/TiO(2) (where M(x)O(y) are Fe(2)O(3) or MgO) for the liquid phase oxidation of n-octanol, under mild conditions. For this purpose, Au/M(x)O(y)/TiO(2) catalysts were prepared by deposition-precipitation with urea, varying the gold content (0.5 or 4 wt.%) and pretreatment conditions (H(2) or O(2)), and characterized by low temperature nitrogen adsorption-desorption, X-ray powder diffraction (XRD), energy dispersive spectroscopy (EDX), scanning transmission electron microscopy-high angle annular dark field (STEM HAADF), diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy of CO adsorption, temperature-programmable desorption (TPD) of ammonia and carbon dioxide, and X-ray photoelectron spectroscopy (XPS). Three states of gold were identified on the surface of the catalysts, Au(0), Au(1+) and Au(3+), and their ratio determined the catalysts performance. Based on a comparison of catalytic and spectroscopic results, it may be concluded that Au(+) was the active site state, while Au(0) had negative effect, due to a partial blocking of Au(0) by solvent. Au(3+) also inhibited the oxidation process, due to the strong adsorption of the solvent and/or water formed during the reaction. Density functional theory (DFT) simulations confirmed these suggestions. The dependence of selectivity on the ratio of Brønsted acid centers to Brønsted basic centers was revealed.