Selective Hydrogenolysis of Glycerol to 1,3-Propanediol over Supported Platinum-Tungsten Oxide Catalysts

Glycerol is a versatile platform compound that is formed in considerable amounts as a by-product of biodiesel production. The catalytic selective hydrogenolysis of glycerol to 1, 3-propanediol (1, 3-PDO) provides a sustainable route for the synthesis of this important diol. In this study, a series of platinum-tungsten oxide (Pt-WOx) catalysts with different WOx surface densities dispersed on titanium(IV) oxide, zirconium(IV) oxide, and aluminum oxide supports were prepared and evaluated for the glycerol hydrogenolysis to 1, 3-PDO. The highest reaction activity and 1, 3-PDO selectivity were achieved at a WOx density of approximately 1.5-2.0 W.nm(-2), with all three support materials. Such a strong dependence on the surface density of WOx revealed the critical role of the dispersed WOx domains in the hydrogenolysis of glycerol to 1, 3-PDO. The infrared spectra for carbon monoxide adsorption confirmed the electron transfer and strong interaction between the Pt particles and WOx domains. These phenomena were hypothesized to contribute to the superior selectivity to 1, 3-PDO over 1, 2-PDO of the supported Pt-WOx catalysts when compared with the corresponding supported Pt catalysts. The realized superior 1, 3-PDO selectivity was consistent with its higher stability on the Pt-WOx catalysts, as reflected by the lower reaction rate constant of 1, 3-PDO than those of 1, 2-PDO and glycerol obtained in their hydrogenolysis reactions. There existed a volcano-type dependence of the glycerol reaction activity on the hydrogen partial pressure. Such a dependence, together with the measured ratio (1 : 2) of the secondary to the primary C-H bonds in 1, 3-PDO in the presence of deuterium and deuterium oxide (replacing hydrogen and water, respectively), indicated that the glycerol hydrogenolysis proceeds by the kinetically relevant dehydrogenation of glycerol to the glyceraldehyde intermediate, followed by the dehydration and hydrogenation of glyceraldehyde to 1, 3-PDO over the Pt-WOx catalysts.