Selective hydrodeoxygenation of furfural to 2-methylfuran over Ni-Co/SiO2 bimetallic catalysts: Synergistic effect of metal and acid sites

Abstract

The development of Ni-based bimetallic catalysts with optimized surface composition and optimized structural properties is crucial for the selective hydrodeoxygenation (HDO) of furfural (FF) into 2-methylfuran (2-MF) which can be used as a fuel additive. In this study, a series of Ni-Co nanoparticles with various Ni/Co molar ratios, supported on SiO₂ were synthesized via the deposition-precipitation method and applied to this HDO reaction. The Ni-Co nanoparticles were uniformly dispersed on silica and displayed a core-shell structure with a gradient of Ni concentration, transitioning from a Ni-enriched core to a Co-enriched outer shell. Optimizing the Ni/Co ratio in these nanoparticles and leveraging the acidic sites generated by CoO_x species led to complete FF conversion and a 2-MF yield of up to 90 % at 170 °C, 2 MPa, after 180 min of reaction. The surface composition in Ni and Co was correlated to the catalytic performance. It was found that Co addition not only altered FF adsorption on nanoparticles from a parallel to a tilted configuration, but also transferred electrons from Co to Ni, resulting in electron-rich Ni⁰ sites. This electron transfers enhanced H₂ dissociation into H⁺ and H^-, which then migrated to oxygen vacancies (O_V) near Co^δ+ species, effectively hydrogenating the CO bond adsorbed on Co^δ+ species and promoting the high production of 2-MF. Kinetic studies revealed that the HDO of FF follows a first-order reaction. The Ni-Co/SiO₂ catalyst also demonstrated excellent reusability, maintaining high activity over three cycles.