Dynamic Formation of Brønsted Acid Sites over Supported WO_x/Pt on SiO₂ Inverse Catalysts─Spectroscopy, Probe Chemistry, and Calculations

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 dynamic and 10× more active toward dehydration than the WO_x species on the SiO₂ support. H₂ plays a complex role: at low temperatures (<473 K), it creates more BAS in the form of W₃O₇H on Pt by reversible hydrogen spillover, and at higher temperatures (>573 K), it partially reduces the W₃O_x. We further show that the inverse configuration allows changes in the BAS density via catalyst pretreatments. This study provides a strategy for tuning Brønsted acid density and regenerating sites by pretreatment and catalyst composition.