Simultaneous Pd Nanoparticle Deposition and Enhancement in the Surface Oxygen Vacancy of Bi2MoO6 Nanoflakes for Room Temperature Vanillin Hydrodeoxygenation

Abstract

A promising method for transforming lignin derivatives into high-value chemicals and biofuels is hydrodeoxygenation (HDO), which is anticipated to be a viable and feasible protocol for the biorefinery. Nonetheless, the requirements of high temperature and high H2 pressure are two main hurdles in the HDO process. Herein, we developed highly active Pd-decorated Bi2MoO6 nanoflakes for complete and selective vanillin (a typical lignin-derived platform molecule) conversion at room temperature and mild H2 pressure. The acquired results reveal that the selection of solvents in vanillin HDO has a detrimental effect, specifically on the product selectivity. When the reaction was performed in dichloromethane solvent, 2-methoxy-4-methylphenol (MMP) was obtained after a 4 h reaction with >99% vanillin conversion and >99% MMP selectivity. Conversely, if water is the reaction medium, it suppresses the formation of MMP, resulting in the selective formation of vanillin’s hydrogenation product vanillyl alcohol (VOL) with 88% vanillin conversion and 91% VOL selectivity. X-ray photoelectron spectroscopy (XPS), Raman, Fourier transform infrared (FT-IR), and ultraviolet (UV)-visible adsorption experimental studies revealed that the superior catalytic performance of the presented catalyst was due to the efficient adsorption of the reactant preferentially through the aldehyde moiety over the catalyst surface and enhancement in surface oxygen vacancies (SOVs) of bismuth molybdate nanoflakes as a result of the treatment with NaBH4 used for Pd nanoparticle deposition. No significant loss in the catalytic activity after multiple cycles proves the stability and good recyclability of the proposed catalyst. This study improves the catalysis strategy of HDO of lignin derivatives and paves the path toward the development of advanced and highly efficient metal-based catalysts for valuable fuels and chemical production from biomass under mild conditions.