Synergistic effect of oxygen vacancies and highly dispersed Pd nanoparticles over Pd-loaded TiO2 prepared by a single-step sol–gel process for deoxygenation of triglycerides

Renewable diesel has gained attention in recent years due to its superior fuel properties compared to the conventional biodiesel. The uses of Pd supported TiO2 (Pd/TiO2) and Pd supported activated carbon (Pd/C) catalysts for the deoxygenation of triglycerides to renewable diesel were investigated. Two different types of titania supports, i.e. mesoporous titania synthesized by a surfactant-assisted templating sol–gel method (SG-TiO2) and commercial P25-TiO2 (P25-TiO2), were used to investigate the effect of TiO2 crystal structure on the catalytic activity. The prepared catalysts were characterized by N2 adsorption-desorption isotherms, X-ray diffraction (XRD), H2 chemisorption, H2 temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The liquid products obtained from the deoxygenation of triglycerides in beef fat over the prepared catalysts at 325 °C, 500 psig, and H2/triglyceride molar ratio of 30 were in the diesel fuel specification range (C15-18). The main liquid products were n-heptadecane (n-C17) and n-pentadecane (n-C15), resulting from the decarboxylation or decarbonylation pathways. It was found that the Pd/P25-TiO2 catalyst exhibited a higher catalytic performance compared to the Pd/C catalyst. The formation of defects (oxygen vacancies and Ti3+) on TiO2, Pd dispersion and inducement of SMSI effect play an important role in the catalytic activity and the diesel yield on Pd/SG-TiO2 catalysts. Furthermore, the Pd incorporation methods, i.e. incipient wetness impregnation (IWI), photochemical deposition (PCD) and single-step sol–gel (SSSG), were also investigated. The Pd/TiO2 prepared by SSSG method exhibited the highest conversion of beef fat and selectivity to the diesel fuel (C15-18) which could be due to its well-dispersed Pd nanoparticles with relatively small size, high defects on TiO2 support and strong SMSI behavior.