Biohydrogenated Diesel from Palm Oil Deoxygenation over Unsupported and γ-Al2O3 Supported Ni–Mo Catalysts

This research work aimed to investigate the performance of unsupported and γ-Al2O3 supported nickel–molybdenum (Ni–Mo) catalysts for palm oil deoxygenation to biohydrogenated diesel. Three preparation methods of supported catalyst (one-step hydrothermal, physical mixing, and incipient wetness impregnation) were studied. In all experiments, the main products were n-alkanes (n-C14, n-C15, n-C16, n-C17, and n-C18). For palm oil deoxygenation over an unsupported NiMoS2 catalyst, increasing the palm oil concentration enhanced the decarbonylation (DCO) and decarboxylation (DCO2) pathways, while prolonging the reaction time led to an increased relative rate of hydrodeoxygenation (HDO) rather than DCO and DCO2 reactions. The unsupported 0.2-NiMoS2 catalyst (at a Ni/[Ni + Mo] molar ratio of 2) prepared by a hydrothermal method was the efficient catalyst, while the appropriate reaction conditions were 300 °C for 3 h at an initial hydrogen pressure of 40 bar, with a catalyst/palm oil ratio of 0.1, to give the highest C14–18 alkane yield of 67.0 wt %. The selectivities for n-C15, n-C16, n-C17, and n-C18 alkanes were 19.6%, 20.2%, 26.8%, and 33.0%, respectively. A new supported NiMoS2 catalyst prepared by a one-step hydrothermal method was proposed. This technique merges the advantages of both an alumina (Al2O3) support and our previous hydrothermal method. The H-NiMoS2/γ-Al2O3 supported catalyst with a 20 wt % Al2O3 loading (H-NiMoS2/γ-Al2O3-0.2) prepared by the hydrothermal method presented a higher dispersion of Ni–Mo–S species than the unsupported catalyst, which results from the Al2O3 support. Without needing further presulfidation, the H-NiMoS2/γ-Al2O3-0.2 catalyst showed good HDO activity under appropriate conditions, which gave a high C14–18 yield of 55.4 wt % and a selectivities for n-C15, n-C16, n-C17, and n-C18 of 14.1%, 25.3%, 19.7%, and 36.3%, respectively. The 0.2-NiMoS2 and H-NiMoS2/γ-Al2O3-0.2 catalysts could be reused for at least three cycles of deoxygenation while maintaining a good performance.