NiCo/Al2O3 nanocatalysts for the synthesis of 5-amino-1-pentanol and 1,5-pentanediol from biomass-derived 2-hydroxytetrahydropyran

Al₂O₃-supported monometallic Ni, Co, and bimetallic Ni–Co nanocatalysts originated from layered double hydroxide precursors were synthesized by co-precipitation method, and used for the synthesis of useful 5-amino-1-pentanol (5-AP) and 1,5-pentanediol (1,5-PD) by reductive amination (RA) or direct hydrogenation of biofurfural-derived 2-hydroxytetrahydropyran (2-HTHP), respectively. In both reactions, the yield of the target products decreased monotonously with the increasing amounts of Co in the NiCo/Al₂O₃ catalysts, owing probably to the replacement of highly reactive Ni by Co component with inferior hydrogenation activity at the low reaction temperature of 60 °C. However, the incorporation of Co could improve the reducibility of the NiCo/Al₂O₃ bimetallic catalysts and promote the reaction stability of the catalysts, especially for Ni₂Co₁/Al₂O₃, in both reactions with over 180 h time-on-stream. Characterization of the catalysts before and after the reaction showed that the incorporating Co could inhibit the sintering of metal particles and hinder the surface oxidation of the more reactive Ni⁰ species, thanks to the formation of Ni–Co alloy in the bimetallic catalysts. DFT-based modeling of the reaction mechanisms is also performed, supporting the reaction pathway proposed previously and also the much higher activity of Ni in the RA of 2-HTHP as compared with Co.