Insights into the roles of Niδ+ species on the selective hydrogenation of oleic acid to jet fuel

Abstract

Revealing the exact catalytic sites and reaction mechanism is crucial for the production of bio-jet fuel from biomass-derived oleic acid. The activation of C–O bonds and C–C bonds of oleic acid were the keys in waste oil upgrading, yet the active sites and mechanism still remain inconclusive on Ni-based catalysts. Herein, we studied the activation characteristics of C-O bonds and C–C bonds of Ni species to clearly distinguish the role of Ni^δ+ of Ni-based catalysts in selective hydrogenation reaction. The ultrafine Ni species of Ni/ZS-NP (Ni/ZSM-22-SBA-15) promoted the generation of more Ni^δ+ species, which could greatly facilitate the adsorption of reactants. Then the adsorbed carboxyl groups on Ni^δ+ was further hydrogenated by H, which was activated by the adjacent metal sites. Meanwhile, the activation of C-O and C–C bonds adsorbed on Ni^δ+ species occurred in the subsequently selective hydrogenation process, and the higher jet fuel yield implied that the activation of C–C bonds by Ni^δ+ species in the isomerization and hydrocracking reactions was particularly significant. Ni/ZS-NP exhibited the higher jet fuel yield of 62.3 % and the higher iso/n alkane ratio of 3.33 at 320 °C, which were superior to the catalysts reported in the previous literature. These findings distinguish different roles of Ni species in Ni-based catalysts, providing different insights into the fundamental understanding of the selective hydrogenation process of oleic acid hydrogenation to jet fuel.