(750a) 2-Propanol Decomposition on TiOx/Au/SiO2: Probing Properties of the Interfacial Perimeter Sites.

Interfacial perimeter sites of Au and TiO₂ has been shown to be essential in a number of oxidation reactions. One of them is the selective formation of acetone in the oxidation of propane, where the interfacial perimeter site between the metal and (Ti,Si)O₂ was shown to be necessary for acetone formation over a Au/SiO₂ catalyst. Since 2-propoxide is a likely intermediate in this reaction and it can be generated in the decomposition of 2-propanol, this reaction was studied as a probe for the properties of the interfacial perimeter sites.

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 ºC. The SiO₂ support was inactive. Without Au in the Ti/SiO₂ catalysts, propene was the only product and its rate of formation increased proportionally with the Ti content. Acetone was the major product (selectivity >65%) on all Au-containing catalysts, and its rate of formation also increased with Ti loading. The presence of Ti in the Ti/[Au/SiO₂] catalysts also resulted in the formation of small amounts of propene and 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 a porous, amorphous TiO₂ overlayer on the catalyst. Au was present as 1-2 nm nanoparticles which did not change after reaction. Only Lewis acid sites were detected based on results from pyridine adsorption, and the quantities increased with Ti loading. From the characterization and kinetic data, especially the reaction rates and the apparent activation energies, it was concluded that the propene formation was on the TiO₂ overlayer, whereas acetone was formed at the Au-TiO₂ interfacial perimeter sites. Breaking of the α-C-H bond in 2-propoxide preceding acetone formation occurred on Au at the interfacial site.