Synergistic Effect between Oxygen Vacancy and Bro̷nsted Acid Sites Boosting Efficient Hydrogenolysis of Esters to Alkanes

Fundamental knowledge of the active site requirements for the activation of C−O bonds on heterogeneous catalysts is essential for the design of efficient hydrodeoxygenation catalysts. Pt−WO_x (x < 3) catalysts have shown activity and selectivity for the C−O bond breaking of various biomass-derived oxygenates. Yet, the nature of the active sites and the structure−performance relationship have not been well understood because of the intimate coupling of multiple sites. Here, we construct a hybrid catalyst with integrated defective tungsten oxide (e.g., WO_2.72) and Pt/C to investigate the role of multiple sites (e.g., metal sites, Bro̷nsted acid, and oxygen vacancy) that are active toward the hydrogenolysis of esters to alkanes in Pt−WO_x catalysts. Experimental and theoretical results suggest that oxygen vacancies derived from the defective tungsten oxide (WO_x) supply coordinatively unsaturated sites to adsorb and activate the oxygen atom of the carbonyl group of esters, while Pt metal provides an active hydrogen atom for this process. More importantly, it is found that the hydroxyl derived from W−OH in WO_x, as a typical Bro̷nsted acid site, can contribute to the adsorption and activation of the C−O bond of esters. The synergistic effect of oxygen vacancies and Bro̷nsted acid sites results in a remarkably efficient acyl C−O bond cleavage of esters, which boosts the hydrodeoxygenation of esters under mild conditions (T ≤ 200 °C). These insights into the structure−performance relationships offer rational methods for designing efficient catalysts for low-temperature hydrodeoxygenation of biomass-derived esters.