SBA-15 and carbon supported nickel, heteropoly acid catalysts for the hydrodeoxygenation of lignin derived trans-Anethole to sustainable aviation fuel

Abstract Catalytic hydrodeoxygenation (HDO) of lignin derivatives is the important means of producing alkyl aromatics and cycloalkanes, key components of 100% sustainable aviation fuels (SAF). Mono and bi-functional catalysts of nickel (Ni) and heterophosphotungstic acid (HPW) supported on SBA-15 and carbons were prepared, characterized and evaluated for the HDO of lignin derived trans-anethole. The SBA-15 structure was intact but its surface area and pore volume decreased with the incorporation of Ni and HPW. UV-Visible DRS and XPS confirmed the presence of Nio and Ni2+ in the bi-functional catalysts. FTIR spectra of pyridine adsorbed Ni(10)-HPW(10)/SBA-15 catalyst has shown the presence of both Brønsted and Lewis acid (Ni2+) sites and hence its acidity was higher than mono functional HPW/SBA-15 catalyst as indicated by the ammonia TPD studies. The synergy between them might be the possible reason for the higher and stable conversion over bi-functional catalysts besides higher HDO selectivity, and more importantly selectivity for propyl benzene and propyl cyclohexane, the desired components of 100% SAF, compared to mono functional catalysts. Among the bi-functional catalysts, best catalytic performance was observed over Ni(10)-HPW(10)/SBA-15 due to its mean Ni particle size of 31.02 nm which is large enough for co-adsorption of hydrogen and benzene ring of propyl benzene may possibly be the reason for its highest selectivity to propyl cyclohexane by following the hydrogenation mechanical pathway. Optimum temperature for maximum conversion and, HDO selectivity was found to be 400oC for the bi-functional catalysts. Carbon supported Ni-HPW catalysts have shown lower selectivity for HDO, thus mesoporous SBA-15 was found to be advantageous.