Nanoparticulate Pt on mesoporous SBA-15 doped with extremely low amount of W as a highly selective catalyst for glycerol hydrogenolysis to 1,3-propanediol
It has been documented that W-modified Pt catalysts with relatively high tungsten contents are effective for the catalytic transformation of biodiesel-derived glycerol to 1,3-propanediol (1,3-PDO). Herein, we report a new finding that Pt/W–SBA-15 catalysts with extremely low W/Si atomic ratios (≤1/80) exhibit excellent catalytic performance in the hydrogenolysis of glycerol to 1,3-PDO. In particular, a Pt/W–SBA-15 catalyst with the W/Si ratio of as low as 1/640 (Pt/W–SBA-15(1/640)) gave rise to the highest 1,3-PDO selectivity of 70.8% at a high glycerol conversion of 86.8% and thus afforded the highest yield of 1,3-PDO of 61.5%. A combination of characterization techniques evidenced that tungsten was homogeneously incorporated into SBA-15 in the form of isolated tetragonal WO4 and only displayed Lewis acidity. The particle size of Pt evolved in a reverse volcanic curve with the W/Si ratio, with the smallest size being observed for Pt/W–SBA-15(1/640). Control experiments indicated strong synergy between Pt nanoparticles (NPs) and WO4 in the hydrogenolysis of glycerol. A probe reaction suggested that Brønsted acid sites were generated in situ on the Pt/W–SBA-15 catalysts in a H2 atmosphere by the reaction between WO4 and spillover H atoms from the Pt NPs. It is plausible that the hydrided WO4 functioned as a highly selective active centre in the hydrogenolysis of glycerol to 1,3-PDO, whereas the Pt NPs played the role of a reservoir of spillover H atoms. Thus, a good match between the isolated WO4 and the small Pt NPs was responsible for the superior catalytic performance of Pt/W–SBA-15(1/640).