The Influence of Incorporating Alkaline Metals on Alumina for Xylitol Hydrogenolysis over Ni Catalysts.

Bifunctional nickel catalysts, Ni/MO-Al2O3 (M = Ba, Ca, Mg, and La) were prepared by the coprecipitation method for the support, followed by wet impregnation of Ni, and used for the hydrogenolysis of xylitol to glycols. According to the XRD data, the crystal structure of the support was maintained after the loading of Ni. All the prepared catalysts were mesoporous, according to N2 physisorption isotherms. XPS revealed Ni 2p peaks, which were assigned to NiO on the surfaces of the catalysts. The bifunctional catalysts showed good xylitol conversions and glycol selectivity over a period of 24 h. The surface structure suggests that Ni/BaO-Al2O3 (Ni/BA) promotes dehydrogenation and the retro-aldol reaction, which favors C2-C3 bond cleavage. The incorporation of alkaline metals reduced the formation of cracked products, such as methane and carbon dioxide, while increasing glycol yields. A combined yield of 80% of propylene glycol (PG) and ethylene glycol (EG) was thus obtained over Ni/BA at 200 °C and 40 bar H2 pressure.