Sustainable utilization of waste glycerol for 1,3-propanediol production over Pt/WOx/Al2O3 catalysts: Effects of catalyst pore sizes and optimization of synthesis conditions.

Abstract

Recycling of waste glycerol derived from biodiesel production to high value-added chemicals is essential for sustainable development of Bio-Circular-Green Economy. This work studied the conversion of glycerol to 1,3-propanediol over Pt/WOx/Al2O3 catalysts, pointing out the impacts of catalyst pore sizes and operating conditions for maximizing the yield of 1,3-propanediol. The results suggested that both pore confinement effect and number of available reactive metals as well as operating conditions determined the glycerol conversion and 1,3-propanediol selectivity. The small-pore 5Pt/WOx/S-Al2O3 catalyst (6.1nm) gave a higher Pt dispersion (32.0%), a smaller Pt crystallite size (3.5nm) and a higher number of acidity (0.47mmol NH3 g-1) compared to those of the large-pore 5Pt/WOx/L-Al2O3 catalyst (40.3nm). However, glycerol conversion and 1,3-propanediol yield over the small-pore 5Pt/WOx/S-Al2O3 catalyst were significantly lower than those of the large-pore Pt/WOx/L-Al2O3 catalyst, suggesting that the diffusional restriction within the small-pore catalyst suppressed transportation of molecules to expose catalytic active sites, favoring the excessive hydrogenolysis of 1,3-propanediol, giving rise to undesirable products. The best 1,3-propanediol yield of 32.8% at 78% glycerol conversion were achieved over the 5Pt/WOx/L-Al2O3 under optimal reaction condition of 220°C, 6MPa, 5h reaction time and amount of catalyst to glycerol ratio of 0.25gmL-1. However, the 1,3-propanediol yield and glycerol conversion decreased to 19.6% and 51% after the 4th reaction-regeneration which were attributed to the carbonaceous deposition and the agglomeration of Pt particles.