Probing properties of the interfacial perimeter sites in TiOx/Au/SiO2 with 2-propanol decomposition

Article abstract of DOI:10.1016/j.apcata.2017.06.027

The decomposition of 2-propanol was studied over SiO₂, SiO₂ with an overlayer of TiO₂ (Ti/SiO₂), Au/SiO₂, and Au/SiO₂ with an overlayer of TiO₂ (Ti/[Au/SiO₂]) at 170–190 °C. There was no reaction on SiO₂. Propene was the only product on Ti/SiO₂, and its rate of formation increased proportionally with the Ti content. Acetone was the major product (selectivity 65–99%) on all Au-containing catalysts. Its rate of formation also increased with Ti loading. In addition, small amounts of propene were also formed on Ti/[Au/SiO₂] the rate of which increased with Ti loading. Characterization of the catalysts with N₂ adsorption, STEM, DR-UV-vis spectroscopy, XPS, XANES and EXAFS suggested that the Ti formed an amorphous TiO₂ overlayer on the catalyst. At high Ti loadings (4–5 wt.%), there were patches of thick porous TiO₂ layer, and some microdomains of crystalline TiO₂ could be detected. Au was present as 1–3 nm nanoparticles on all catalysts, before and after used in reaction. Only Lewis acid sites were detected based on results from pyridine adsorption, and their quantities increased with Ti loading. Based on the comparison of reaction rates, the dependence of the kinetics on 2-propanol partial pressure, the apparent activation energies, and the effect of co-feeding O₂ among different catalysts, it was concluded that propene was formed on the TiO₂ overlayer, acetone was formed primarily at the Au-TiO₂ interfacial perimeter sites, and α-C-H bond breaking preceding acetone formation was more facile on Au at the interfacial site than other surface Au atoms. Implication of these results to the selective acetone formation in the oxidation of propane in the presence of a O₂/H₂ mixture was discussed.