Study On Catalysts For Hydrogenolysis Of Glycerol Into Diols And Steam Reforming Of Glycerol To Prepare Hydrogen

Hydrogenolysis of glycerol into diols and steam reforming of glycerol to preparehydrogen are effective for using glycerol. In the present work, the hydrogenolysis ofglycerol on Ni₂P/SiO₂and Ni/SiO₂was first investigated, and the factors influencingthe conversion of glycerol and the selectivities to different products were discussed.Afterwards, the effect of rare earth metal oxide promoters (including CeO₂, La₂O₃,Y₂O₃and Pr₆O₁₁) on the structure and reactivity of Ni/γ-Al₂O₃for the steamreforming of glycerol was studied.Ni₂P/SiO₂, Ni/SiO₂and modified Ni/γ-Al₂O₃catalysts were prepared byimpregnation method followed by temperature-programmed reduction. Theirstructural properties were characterized by N2absorption-desorption, H₂-TPR, XRD,XRF, CO and H₂chemisorption, TGA, H₂-TPD and NH₃-TPD. The performaces ofthe catalysts were tested on a fixed-bed reactor.In the hydrogenolysis of glycerol, Ni₂P/SiO₂was more active than Ni/SiO₂. Thisis attributed to the synergism between acid and metal sites on Ni₂P/SiO₂. Glycerolwas mainly converted to1,2-propanediol on Ni₂P/SiO₂, while it was mostly convertedto not only1,2-propanediol but also ethylene glycol and ethanol on Ni/SiO₂. Theincreased temperature and H₂pressure did not promote the formation of ethyleneglycol and ethanol on Ni₂P/SiO₂, while they mainly promoted the furtherhydrogenolysis of1,2-propanediol to form1-propanol. Thus, compared with Ni/SiO₂,Ni₂P/SiO₂was more active for the cleavage of C–O bond and less active for thecleavage of C–C bond. In addition, with the increases of the glycerol concentrationand H₂/glycerol molar ratio and with the decrease of the weight hourly space velocity,the selectivity to1,2-propanediol on Ni₂P/SiO₂decreased, while the selectivity to1-propanol increased. This is due to the further hydrogenolysis of1,2-propanediol toform1-propanol. We suggest that, for Ni₂P/SiO₂, the higher activity for the cleavageof C–O bond can be ascribed to its acidity, while the lower activity for the cleavage ofC–C bond may mainly be related to its electronic and geometrical properties.In the stream reforming of glycerol, compared with Ni/γ-Al₂O₃, the Ni/γ-Al₂O₃catalysts modified with rare earth metal oxide promoters not only gave higherglycerol conversion and H₂output, but also restrained carbon deposition leading to abetter stability. This is attributed to their more surface Ni sites and less acid sites. In addition, compared with La₂O₃and Y₂O₃, Pr₆O₁₁and CeO₂were more effective forimproving the reactivity of Ni/γ-Al₂O₃, which is due to their redox properties.