The role of tungsten oxide in the selective hydrogenolysis of glycerol to 1,3-propanediol over Pt/WO x /Al 2 O 3

Abstract

Bi-functional heterogeneous catalysts combining a noble metal with an oxophilic metal (mainly W or Re) were reported to be selective for the CO hydrogenolysis of glycerol to the high added-value 1,3-propanediol. Despite intensive research work carried out, there is a great deal of controversy about the role of the oxophilic metal. In this work, the hydrogenolysis of glycerol over Pt/WOx/Al2O3 catalysts was studied in real time by in-situ attenuated total reflection infrared (ATR-IR) spectroscopy. Moreover, ex-situ ATR-IR spectroscopic studies were also used to study the interactions between glycerol and the different catalytic surfaces. The results obtained indicate a stronger adsorption of glycerol through the primary hydroxy group/s when tungsten oxides are grafted onto the γ-Al2O3 support. The competitive adsorption between the reactant and the main reaction products for the same active sites, and the effect of the hydrogen availability were also studied. The evidences found in this work point out a triple role of tungsten oxide in the reaction, acting as: (i) a strong anchoring site for the primary hydroxy group/s of glycerol, (ii) a supplier of protons, and (iii) a stabilizer of the secondary carbocation. Under the best conditions, a remarkable high yield of 1,3-propanediol of 38.5% was obtained after only 4 h of reaction time.