Dynamic Brønsted acid centers on silica-supported platinum tungsten oxide inverse catalyst

Abstract

Platinum-tungsten oxides are among the most studied metal-metal oxide (M-MO) paired catalysts in C-O hydrogenolysis reactions. The Brønsted acid density and synergy between Pt and WOx in the inverse metal oxide/metal structure, affected the reaction reactivity and selectivity significantly. However, a clear molecular-level understanding requires systematic implementation of in-situ characterization techniques, currently missing in the literature. This work integrates multiple in-situ spectroscopic characterizations (Raman, FT-IR, and UV-vis) techniques, chemical probing (CO chemisorption and pyridine titration), and model reaction (tert-butanol dehydration) to elucidate the Brønsted acid sites in different environments, including annealing, reduction, and H2-cofeeding. Dynamic changes of W=O and W-OH upon H2 exposure were observed by in-situ Raman and FT-IR, respectively. H2 plays a complex role, where reversible hydroxylation by H2 spillover creates more Brønsted acid sites but also induces reduction. The study provides a strategy for tuning Brønsted acid density, and regenerating sites by varying pretreatment conditions and catalyst composition.