WOx boosted hollow Ni nanoreactors for the hydrodeoxygenation of lignin derivatives

Abstract

Reasonable design of non-noble metal catalysts with hollow open structure for hydrodeoxygenation (HDO) of lignin derivatives to value-added chemicals is of great significance but challenging. Herein, a novel MOF-derived multilayer hollow sphere coated nickel‑tungsten bimetallic catalyst (Ni₂-WO_x@CN-700) was fabricated via by confined pyrolysis strategy using bimetallic MOFs as a self-sacrificial template, which exhibits robust activity for the typical model HDO of vanillin to 2-methoxy-4-methylphenol (Yield of 100 % at 140 °C for no less than 10 cycles). The characterizations revealed that WO_x facilitated the dispersion of Ni nanoparticles and adjusted the acidic capacity of the catalyst through the formed Ni-WO_x heterojunction. Density functional theory (DFT) calculations confirms that WO_x species enhanced the electron-rich nature of the active sites, while the adsorption energies of H₂ and vanillin on Ni-WO_x decreased from -0.572 eV and - 0.622 eV on Ni to -3.969 eV and - 4.922 eV, respectively. These results further indicated that the high activity of Ni₂-WO_x@CN-700 was attributed to the Ni-WO_x heterojunction. Based on the characterizations and the thermodynamic calculations, the reaction mechanism was proposed. In addition, the catalyst shows good substrate universality, which enables its good commercial application prospect.

Keywords: Hydrodeoxygenation; Lignin derivatives; Ni-WO(x) heterojunction; Vanillin.