Hydrogenolysis of Xylitol to Propanediols Over Nickel Catalysts Supported on Sulfated Zirconia: Controlling Intrinsic Activity via Metal Support Synergy.

Nickel catalysts supported on zirconia (Ni/ZrO2) and sulfated zirconia (Ni/SZx) were synthesized via wet impregnation and used for xylitol hydrogenolysis to propanediols. Overall, catalysts were reduced at low temperatures and exhibited low metallic Ni dispersion, attributed to the low support surface area. Both Brønsted and Lewis acid sites were detected in all the catalysts. Sulfate introduction into zirconia had a positive impact on xylitol conversion and diol selectivity. Ni/SZx catalysts showed an improved propanediol selectivity than the Ni/ZrO2 catalyst. Ni/SZ-400 and Ni/SZ-700 were selective to 2-propanol (21.7% and 41.6%, respectively). Ni/SZ-500 showed better selectivity to propanediols with 81.5% xylitol conversion during the 8 h reaction. This performance was attributed to favorable metal-support-interactions, overall acidity and better intrinsic activity of the catalytic site for hydrogenation. Moreover, Ni/SZ-500 remains effective for about three reaction runs, after which its catalytic performance declines sharply. Prolonged reaction times were beneficial for the formation of 1,3-propanediol and 1,3-butanediol; however, they also led to increased formation of gaseous and lower alcohols.