(616b) Spectroscopic Characterization of Inverse Catalysts

Platinum-tungsten oxides are among the most studied metal-metal oxide pair catalysts for C-O hydrogenolysis reactions. The Brønsted acid density and synergy between Pt and WO_x, especially in the inverse structure, are critical to reactivity and selectivity. However, a clear molecular-level understanding of the formation and dynamics of Brønsted acid sites (BAS) is lacking. Here, using in-situ spectroscopic characterizations (Raman and FTIR), chemical probing (CO chemisorption and pyridine titration), density-functional theory (DFT) calculations, and a model reaction (tert-butanol dehydration), we demonstrate the structural evolution of WO_x species and associated BAS dynamics in various environments. In-situ Raman and DFT calculations show that below monolayer coverage, the WO_x species stay as isolated monomers on the SiO₂ support and W₃O_x trimers on Pt. The W₃O_x trimers on Pt are more active toward dehydration than those on the SiO₂ support. H₂ plays a complex role: at low temperatures, it creates more BAS by reversible hydrogen spillover, and at higher temperatures it partially reduces the W₃O_x. This study provides a strategy for tuning Brønsted acid density and regenerating sites by pretreatment and catalyst composition.