Investigation of Lewis Acidity in Silica-Alumina and Its Importance to Rhenium-based Metathesis Catalysts

Introduction We employ a combined computational-experimental approach to probe the Lewis acidity of silica-alumina, and extend this study to the effect of Lewis acidity on the activation and activity of a supported methyltrioxorhenium (MTO) metathesis catalyst. Despite the widespread use of amorphous silica-alumina as a catalyst and a catalyst support, the structures of its Lewis acid sites remain elusive. Previous experimental studies have used probes such as acetonitrile and pyridine to quantify the number and strength of these sites, but unlike the extensive work on Brønsted acidity in zeolites, there have been few attempts to pair experimental probe studies with theory to assess the types of aluminum geometries required to generate the Lewis sites.