Evidence for the Bifunctional Nature of Pt–Re Catalysts for Selective Glycerol Hydrogenolysis

• Published in: ACS catalysis 2015-10, Vol.5 (10), p.5679-5695
• Main Authors: Falcone, Derek D, Hack, John H, Klyushin, Alexander Yu, Knop-Gericke, Axel, Schlögl, Robert, Davis, Robert J
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.5b01371

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.