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

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

Selective Hydrodeoxygenation of Vegetable Oils and Waste Cooking Oils to Green Diesel Using a Silica-Supported Ir-ReO x Bimetallic Catalyst

“…The Ir 4f spectrum shows the binding energies (BE) for 4f 7/2 and 4f 5/2 peaks at approximately 60.8 and 63.8 eV, respectively,i ndicating Ir exists in the metallics tate. [66] The analysiss uggestsa significant portion of Re is partially reducedt oR e 2 + ,R e 4 + ,a nd Re 6 + (27 %, 17 %, and 4%,r espectively), which is consistent with our prior report of the Ir-ReO x /SiO 2 -catalyzed HDO of high-carbon furylmethanes. [66] The analysiss uggestsa significant portion of Re is partially reducedt oR e 2 + ,R e 4 + ,a nd Re 6 + (27 %, 17 %, and 4%,r espectively), which is consistent with our prior report of the Ir-ReO x /SiO 2 -catalyzed HDO of high-carbon furylmethanes.…”

Nanostructured Metal Catalysts for Selective Hydrogenation and Oxidation of Cellulosic Biomass to Chemicals

“…Although recent work has shown that surface carboxylic intermediates adsorbed on metal surface might influence the position where C−O cleavage rupture occurs, it is still generally accepted that catalyst structures are crucial for both activity and selectivity towards 1,3‐PDO formation during glycerol hydrogenolysis. To date, there are two types of bimetallic nanocatalysts which display promising performances for 1,3‐PDO formation (Scheme ) . Re promoted Rh and Ir bimetallic catalysts show good selectivity towards 1,3‐PDO under very mild conditions .…”

Understanding the Growth, Chemical Activity, and Cluster–Support Interactions for Pt–Re Bimetallic Clusters on TiO2(110)

“…24,28 Alternatively, it has also been suggested that CO is removed via the enhanced WGS activity at ReO x sites on the Pt−Re/TiO 2 catalysts. 12,13,16 Superior properties for the Pt−Re catalysts have been observed in reactions associated with biomass reforming, such as glycerol hydrogenolysis to propanediols 23,29 and selective hydrogenation of carboxylic acids 30,31 and aldehydes 32 to alcohols. In addition, a number of studies report unusual and desirable chemical activity for the bimetallic Pt−Re surfaces.…”