Catalytic hydrodeoxygenation of vanillin, a bio-oil model compound over renewable Ni/biochar catalyst

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 pyro-lyzed 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 tem-perature-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 van-illin conversion and p-creosol yield in the order Ni/biochar (H₂SO₄) > Ni/biochar (KOH) > Ni/biochar.