Dynamic Formation of Brønsted Acid Sites over Supported WO<i><sub>x</sub></i>/Pt on SiO<sub>2</sub> Inverse Catalysts─Spectroscopy, Probe Chemistry, and Calculations
Yurong Wu, Sagar Sourav, Alfred Worrad, Jiahua Zhou, Stavros Caratzoulas, George Tsilomelekis, Weiqing Zheng, Dionisios G. Vlachos
Abstract
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 SiO 2 support and W 3 O x trimers on Pt. The W 3 O x trimers on Pt are dynamic and 10× more active toward dehydration than the WO x species on the SiO 2 support. H 2 plays a complex role: at low temperatures (<473 K), it creates more BAS in the form of W 3 O 7 H on Pt by reversible hydrogen spillover, and at higher temperatures (>573 K), it partially reduces the W 3 O 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.