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Free keywords:
heterogeneous catalysis; bimetallic; biomass; platinum; rhenium; Brønsted acidity; X-ray photoelectron spectroscopy
Abstract:
Rhenium substantially promotes the rate of Pt-catalyzed glycerol hydrogenolysis to propanediols and shifts the product selectivity from 1,2-propanediol to a mixture of 1,2 and 1,3-propanediols. This work presents experimental evidence for a tandem dehydration-hydrogenation mechanism that occurs over a bifunctional Pt-Re catalyst. Infrared spectroscopy of adsorbed pyridine and the rate of aqueous-phase hydrolysis of propyl acetate were used to identify and quantify Brønsted acid sites associated with the Re component. Near ambient pressure XPS revealed a range of Re oxidation states on the Pt-Re catalysts after reduction in H2 at 393 and 493 K, which accounts for the presence of Brønsted acidity. A mechanism involving acid-catalyzed dehydration followed by Pt-catalyzed hydrogenation was consistent with the negative influence of added base, a primary kinetic isotope effect with deuterated glycerol, an inverse isotope effect with dideuterium gas, and the observed orders of reaction.
