Phosphonic acid promotion of supported Pd catalysts for low temperature vanillin hydrodeoxygenation in ethanol

[Display omitted] •Phosphonic acids were used to modify Pd/Al2O3 for application in low-temperature liquid-phase vanillin hydrodeoxygenation.•Modification of the catalyst with chloromethylphosphonic acid improved creosol yield from 2.5% to 87% at 50 °C.•The yield improvement was attributed to a bifunctional mechanism in which the phosphonic acid modifier introduced acid sites. Bifunctional catalysts with activity for both hydrogenation and dehydration have been frequently investigated for hydrodeoxygenation (HDO). Here, we report the application of organophosphonic acids (PAs) to Pd/Al2O3 catalysts for low-temperature vanillin HDO. Reaction studies indicated that PA-modification significantly improved the liquid-phase HDO activity; the yield to the desirable product, p-creosol (CR), increased from 2.5% to 87% at 50 °C. This improvement was attributed to the creation of metal/acid bifunctional sites upon PA modification. In addition, HDO activity positively correlated with the Brønsted acidity of the PA modifier, which could be tuned by adjusting the PA tail functionality.