Deoxygenation of oleic acid under an inert atmosphere using molybdenum oxide-based catalysts

In this study, the deoxygenation of oleic acid under a N-2 atmosphere over metal oxide catalysts is investigated for the production of green diesel hydrocarbons. The molybdenum oxide catalysts with promoters (Ni, Co, and Cu) and varying catalyst loadings (19-34 wt%) on gamma-Al2O3 support are prepared by an incipient wetness impregnation method and characterized by XRD, FE-SEM/EDX, TEM, XPS, and N-2 sorption. The catalytic testing is carried out in a batch reactor with various reaction times (3-9 h) and temperatures (300-350 degrees C) under N2 pressure (10 and 40 bar). The NiMo oxide/gamma-Al2O3 exhibits the highest performance with over 80% conversion and good selectivity toward C17 hydrocarbon products. The catalytic performance of the NiMo oxide/gamma-Al2O3 remains stable during 4 reaction cycles. Decarboxylation (DCO2) and decarbonylation (DCO) are observed to be the reaction pathways of the deoxygenation and these reactions are enhanced by increasing reaction temperature and time. Stearic acid and other hydrogenated compounds were produced via the in situ hydrogenation which was proposed as a competitive reaction in the deoxygenation of oleic acid under the N-2 pressure. The DFT calculations confirm that the dehydrogenation and hydrogenation reactions could occur on the MoO3 surface. These processes are responsible for the in situ formation of hydrogen species, leading to the formation of hydrogenated products. Hydroxyl groups on the terminal oxygen sites created by dehydrogenation could contribute to the surface vacancy and further promote the DCO2 or DCO pathway. The molybdenum oxide-based catalysts show a great potential for green diesel production without the use of H-2 feed.