Ni/SiO₂ catalysts derived from carbothermal reduction of nickel phyllosilicate in the hydrogenation of levulinic acid to γ-valerolactone: The efficacy of nitrogen decoration

Ni catalysts derived from the carbothermal reduction of nickel phyllosilicate were investigated and their application in the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was revealed. The most effective catalyst (S₃M_1.5@NiPS-600) was prepared by using a sucrose-melamine mixture (molar ratio = 2:1) as the reducing agent with a proper thermal treatment (maintained at 600 °C for 2 h). By using S₃M_1.5@NiPS-600, a high GVL productivity (1387 mmol GVL/g surface Ni/h), good recyclability (4.9% loss of initial activity in five cycles), and a negligible deactivation rate were observed. The promising outcome was attributed to grafted carbon and nitrogen species on the carbothermally reduced Ni/SiO₂ catalyst. Grafted carbon species improve catalyst stability whereas immobilized nitrogen species induce Ni^δ+ (δ>2) with a strong Lewis acidity. Paired Ni^δ+ and Ni⁰ sites are active in the reduction of the ketone group of LA, thereby enhancing the production of GVL.