Catalytic hydrodeoxygenation of biomass model compounds using Ni, Co and Fe over HZSM-5

• Gas-phase hydrodeoxygenation (HDO) of vanillin and guaiacol was performed at 300 °C and atmospheric pressure over metal/HZSM-5 catalysts. • 10%Ni/HZSM-5 achieved optimal performance with 65.64% conversion and 96.35% selectivity toward guaiacol from vanillin. • Guaiacol HDO over 10%Ni/HZSM-5 produced phenol as the dominant product (57.5% selectivity). Hydrodeoxygenation (HDO) is an essential step in the upgrading of biomass into biofuels, which serve as sustainable and clean alternatives to fossil fuels. Several challenges are encountered in this catalytic process, primarily related to catalyst deactivation. In the current work, new catalysts were explored for the HDO of biomass model compounds, namely vanillin and guaiacol, into partially deoxygenated biofuel precursors. The pathway investigation starts with carrying out an HDO reaction on vanillin to produce guaiacol, followed by another HDO reaction on guaiacol to produce phenol. Nickel (Ni), cobalt (Co), iron (Fe) and the noble metal rhodium (Rh) were used over HZSM-5 zeolite support. Seven HDO reactions were carried out on vanillin with H 2 flow rate of 100 mL/min at 300℃ and atmospheric pressure. Ni/HZSM-5 catalyst showed the best performance among the transition metals with the peak performance being at the 10% loading with a 96.35% selectivity towards guaiacol. Loading the same catalyst with 0.5% of the noble metal rhodium (i.e. 0.5%Rh-10%Ni/HZSM-5) boosted the conversion to 72.86% while maintaining almost the same selectivity towards guaiacol. Several products were obtained from the guaiacol HDO at the same conditions over 10%Ni/HZSM-5 including phenol, m -cresol and o -cresol, with phenol dominating at 57.5% selectivity. This study has industrial implications, as it establishes a viable HDO pathway for an oxygenated biomass model compound under the investigated conditions.