Influence of the Support of Bimetallic Platinum Tungstate Catalysts on 1,3-Propanediol Formation from Glycerol

Three aluminium oxide materials and a HZSM-5 zeolite were used as supports of bimetallic Pt-WOx catalysts to establish structure-activity relationships in the glycerol hydrogenolysis reaction. The surface W density and the intimate contact between Pt and WOx were key parameters. Surface W density controls the formation of polytungstates, the only species able to produce the weak Bronsted acidity that is required to produce 1,3-propanediol selectively. The comparison between the HZSM-5 and the Al2O3 supports demonstrated that an increment of the medium Bronsted acidity is detrimental for the selective 1,3-propanediol formation as it promotes reactions that yield 1-propanol and propane. An increase of the dispersion of Pt on the Pt/WOx/Al2O3 catalysts led to higher glycerol conversions but also promoted the hydrogenolysis routes that lead to 1,2-and 1,3-propanediol similarly. On the contrary, an increase of the Pt metal content favoured the hydrogenolysis route that leads to 1,3-propanediol significantly. A more intimate contact between Pt and WOx promoted the hydrogenation of the intermediate carbocation, formed and stabilised on a polytungstate active site, into 1,3-propanediol.