Confinement of Lewis Acid-Base Sites by Microporous Silica Layers on Titania for Enhanced Alkanol Dehydration Reactivity

Alkanol dehydration offers a pathway to upgrade biomass-derived short-chain oxygenates into alkenes, essential chemical building blocks widely used in industrial applications. Transition metal oxides with Lewis acid-base site pairs are attractive catalysts due to their high reactivity and cost-effectiveness. This work demonstrates a synthetic pathway to manipulate local environments around active Lewis acid-base pairs in anatase TiO2 to enhance their reactivity in alkanol dehydration. Microporous SiO2 layers with an average pore diameter of ~0.6 nm and a controlled thickness of 0.8-33 nm are deposited on anatase TiO2 powders by using a molecular templated SiO2 deposition method. The Lewis acid-base strength of accessible Ti-O pairs remains unchanged, as shown by temperature-programmed surface reactions of surface-bound formic acid-derived species and temperature-programmed desorption of pyridine. However, measured alkanol dehydration rates on confined Ti-O pairs are much higher (by up to 7-fold) than those on TiO2. The extent of rate enhancements depends on the reactant size and functional group positioning, suggesting that the rate enhancements reflect the interactions between the guest molecules (reactants and transition states) and the surrounding SiO2 micropore environments. By providing a detailed synthetic procedure to tailor the local environments around active sites in bulk oxides, this approach offers an additional avenue for enhancing catalytic performance.. Authors: Vyas, Manasi [Colorado School of Mines]; Ithisuphalap, Kemakorn [Colorado School of Mines]; Patterson, Lynsey [Colorado School of Mines]; Rasmussen, Mathew [National Laboratory of the Rockies, Golden, CO (United States)]; Bian, Yingxue [Colorado School of Mines]. DOE Contract: AC36-08GO28308. Subjects: 09 BIOMASS FUELS; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; alkanol dehydration; confinement effects; heterogeneous catalysis; molecular templating method; titania