Enhancement of phenol hydrodeoxygenation over Pd catalysts supported on mixed HY zeolite and Al2O3. An approach to O-removal from bio-oils

This contribution describes the effect of the support (zeolite ultrastable HY, alumina (Al) and mixed HY–Al carriers) on the catalytic activity of Pd catalysts in the phenol hydrodeoxygenation (HDO) reaction carried out in a flow fixed-bed reactor at T = 523–573–623 K, P = 15 bar and WHSV = 0.5 h−1. Phenol dissolved in n-octane was used as model compound of bio-oil species derived from fast pyrolysis of lignocellulosic biomass. The catalysts were characterized by N2 physisorption, XRD, TPR, TPD-NH3, DRIFT spectroscopy of adsorbed CO, HRTEM, X-ray photoelectron spectroscopy (XPS) and TPO/TGA techniques. The largest phenol conversion (63%) achieved at 523 K over the reduced Pd/20%HY–Al catalyst was similar to that obtained on a commercial NiMo/Al2O3–zeolite hydrocracking sample (HCK) activated by sulfidation. Regardless of the reaction temperature, the only products detected in the HDO of phenol over all catalysts studied were four O-free compounds: benzene, cyclohexene, cyclohexane, and methylcylopentene. Both reduced Pd/20%HY–Al and sulfided commercial HCK catalysts produced similar yields of O-free products. From the catalyst activity-structure correlation, it can be concluded that the HDO of phenol is favoured on the bifunctional Pd/20%HY–Al catalyst which possesses moderate acidity and improved Pd dispersion on the support surface. The contributions of the acid sites to the catalyst activity and deactivation by coke are discussed.