Double-Volcano Catalytic Response in Furfural Reductive Amination Over Inverse Ni─Al Catalysts.

Reductive amination of aldehydes and ketones to primary amines is an important route for biomass valorization, yet achieving efficient synergy between substrate and hydrogen activation in cascade reactions remains challenging. Herein, we construct a compositionally tunable Ni─Al catalyst system whose architecture evolves from conventional Ni/Al2O3 to inverse Al2O3/Ni. This structural evolution gives rise to an unusual double-volcano catalytic behavior in furfural reductive amination. Two activity maxima are identified over 30Ni/Al2O3 and inverse Al2O3/90Ni, respectively, with the optimal Al2O3/90Ni catalyst delivering 98.5% furfurylamine yield and a space-time yield of 65 mmol gcat -1 h-1 under mild conditions. Adsorption studies, initial-rate kinetic isotope effect and reaction-order measurements, apparent activation-energy analysis, and in situ infrared spectroscopy indicate that the double-volcano behavior reflects the coupled evolution of catalyst composition and architecture and a composition-dependent balance between Lewis-acid-assisted intermediate formation and hydrogen-dependent intermediate conversion. Hydrogen-dependent steps exert a stronger kinetic influence over 30Ni/Al2O3 than over Al2O3/90Ni, while the inverse catalyst exhibits enhanced H2 adsorption and activation and more rapid Schiff base conversion. These results indicate a shift in the dominant kinetic limitation between the two catalysts and provide a framework for designing efficient non-noble-metal catalysts for multifunctional cascade reactions involving coupled substrate and hydrogen activation.