Highly selective bifunctional Ni zeo-type catalysts for hydroprocessing of methyl palmitate to green diesel

Highly selective bifunctional micro-mesoporous Ni-Beta catalysts, with different accessibility of both redox and acidic sites, for the production of green diesel from algal oil, were synthesized by modifying the zeolite features by desilication or desilication/dealumination treatments and by introducing the Ni nanoparticles (NPs) inside the pore system or on the external surface. The textural and acidic properties of these catalysts, as well as the size and dispersion of the Ni NPs were analysed by different techniques (porosimetry, NH3-TPD, pyridine FT-IR, CO chemisorption, XPS), and correlated to the results of the catalytic testing in the hydroconversion reaction of methyl palmitate, selected as a model molecule of microalgal oil. The best performances were obtained by depositing Ni NPs through sol-immobilization method on a desilicated/dealuminated Beta zeolite, due to the highest accessibility not only of the redox sites localized on the external surface but also of the acidic sites conferred by dealumination. The increased accessibility of the active sites, associated to the targeted localization of Ni NPs, affects the proximity between the acidic and the hydrogenation functions, leading to a highly selective catalytic system to C15 and C16 diesel range products.