Catalytic Hydrodeoxygenation of Vanillin, a Bio-Oil Model Compound over Renewable Ni/Biochar Catalyst

Abstract

This study aims to examine the hydrodeoxygenation (HDO) of vanillin, an oxygenated phenolic compound present in bio-oil, into creosol. Biochar residue generated when wood is slowly pyrolyzed is utilized as a catalyst support. To improve biochar’s physicochemical properties, H2SO4 (sulfuric acid) and KOH (potassium hydroxide) are used as chemical activators. By means of a wet impregnation method with nickel salt, an Ni/biochar catalyst was prepared and utilized in the HDO of vanillin using a 100 mL Parr reactor, catalyst loading 0.4–0.8 g, temperature 100 °C to 150 °C, hydrogen (H2) pressures of 30 to 50 bar, and a stirring rate of 1000 rpm. The prepared catalysts were characterized with the nitrogen-sorption isotherm technique, carbon dioxide temperature-programmed desorption (CO2-TPD), scanning electron microscopy (SEM) coupled with energy dispersed X-ray analysis (EDX), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Based on chemical treatment, Ni/biochar (KOH) pore sizes were found to be dominated by mesopores, with a surface area increase of 64.7% and a volume increase of 65.3%, while Ni/biochar (H2SO4) was mostly microporous and mesoporous, with an area increase of 372.3% and a volume increase of 256.8% in comparison to Ni/biochar (74.84 m2g−1 and 0.095 cm3g−1). Vanillin conversion of up to 97% with 91.17% selectivity to p-creosol was obtained over Ni/biochar catalyst; in addition to being highly selective and active for p-creosol, a plausible fuel, the catalyst was stable after four cycles. Chemical treatments of the biochar support resulted in improved physicochemical properties, leading to improved catalytic performance in terms of vanillin conversion and p-creosol yield in the order Ni/biochar (H2SO4) > Ni/biochar (KOH) > Ni/biochar.