Environmental Pollution ( IF 6.792 ) Pub Date : 2020-11-20 , DOI: 10.1016/j.envpol.2020.116029 Thanapha Numpilai; Chin Kui Cheng; Anusorn Seubsai; Kajornsak Faungnawakij; Jumras Limtrakul; Thongthai Witoon
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 (6.1 nm) gave a higher Pt dispersion (32.0%), a smaller Pt crystallite size (3.5 nm) and a higher number of acidity (0.47 mmol NH3 g-1) compared to those of the large-pore 5Pt/WOx/L-Al2O3 catalyst (40.3 nm). 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 oC, 6 MPa, 5 h reaction time and amount of catalyst to glycerol ratio of 0.25 g mL-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.