Reaction Route Selection for Cellulose Hydrogenolysis into C(2)/C(3) Glycols by ZnO-Modified Ni-W/β-zeolite Catalysts

A β-zeolite-supported nickel and tungsten catalyst (Ni-W/β) was employed to generate C(2)/C(3) glycols (ethylene and propylene glycols) in a satisfactory yield from cellulose. After optimizing the acidity of the support, the Ni-W synergy and the co-catalyst, the yield of C(2)/C(3) glycols reached 70.1% (C %), with propylene glycol accounting for 51.1% of the product. This performance was attributed to the effective control of the major reaction steps, namely, hydrolysis, isomerization, retro-aldol condensation and hydrogenation, by the tailored Ni-W-ZnO/β catalyst. The characterization and reaction results indicated that the cellulose hydrolysis step was promoted by the appropriate acidic sites of the β-zeolite, and the reaction routes to C(2)/C(3) glycols were influenced by the mass loading of Ni-W through the synergy of nickel and tungsten oxide, in which Ni is effective in the hydrogenation while W facilitates bond cleavage via a retro-aldol condensation (C(6) to C(2)/C(3)). Moreover, with the leaching of metal during four cycles of reuse, the catalytic performance was also influenced by the synergy of Ni and W. In addition, the isomerization of glucose to fructose was promoted by ZnO and afforded a high yield of propylene glycol.