Robust MOF-derived carbon-supported bimetallic Ni–Co catalysts for aqueous phase hydrodeoxygenation of vanillin

Abstract

Currently, rapidly increasing consumption of fossil resources has propelled the upgrading of biomass as an alternative and sustainable technology to produce important chemicals and bio-oils. In this regard, the rational design of low-cost and robust supported metal-based catalysts that exhibit excellent catalytic hydrodeoxygenation (HDO) performance for the conversion of biomass is quite necessary. Herein, we developed hierarchical flower-like nitrogen-doped carbon layer-coated bimetallic Ni–Co nanoparticles, which were distributed over the carbonaceous matrix (Ni_xCo@NC@C), via a metal–organic framework (MOF) ZIF-67 precursor approach, assisted by the etching of Ni²⁺ ions, hydrothermal treatment together with glucose, and following carbonization processes. The as-fabricated Ni₃Co@NC@C catalyst bearing a 3 : 1 Ni/Co molar ratio showed a superior catalytic HDO activity towards aqueous phase HDO of vanillin to other bimetallic NiCo catalysts with different Ni/Co molar ratios under mild reaction conditions, along with a 100% selectivity to 2-methoxy-4-methylphenol at a full vanillin conversion, despite its smaller number of exposed metallic sites. It was revealed that over the Ni₃Co@NC@C catalyst, the surface abundant defective oxygen vacancies and electron-rich Co⁰ species were conducive to the adsorption and activation of vanillin and the reaction intermediate, thereby giving rise to the outstanding catalytic activity. Moreover, for Ni₃Co@NC@C, the adequate protection effect of surface carbon layers, as well as the unique hierarchical flower-like microstructure, could significantly inhibit the leaching of active metal species in the reaction medium, thereby leading to high structural stability. The present findings afford a promising strategy for constructing low-cost and robust carbon-supported bimetallic catalysts for the HDO of lignin-derived derivatives.