Green diesel production by solvent-free deoxygenation of oleic acid over nickel phosphide bifunctional catalysts: Effect of the support

Abstract

An alternative to non-renewable fuels is the production of green diesel from deoxygenation of vegetable oils. In this study, the effect of the supports on nickel phosphide catalysts for deoxygenation of oleic acid to produce hydrocarbons was investigated. Nickel phosphide catalysts supported on USY, H-ZSM-5 and Al-SBA-15 were synthetized by temperature programmed reduction (TPR) of metal phosphate precursors and the prepared catalysts were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), small angle X-ray scattering (SAXS), temperature programmed reduction of hydrogen (TPR), nitrogen physisorption, temperature programmed desorption of ammonia (TPD), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). The catalytic tests were performed in an autoclave batch reactor at 260 °C, 280 °C and 300 °C and 50 bar of hydrogen. The production of hydrocarbons (C10-C18) at 300 °C followed the order: Ni2P/Al-SBA-15 > Ni2P/H-ZSM-5 > Ni2P/USY. The Ni2P/Al-SBA-15 exhibited a remarkable deoxygenation activity, compared to noble metals. All the catalysts achieved more C17 than C18 hydrocarbons, therefore, decarbonylation/decarboxylation reactions prevail. With regard the temperature effect, the amount of hydrocarbons increased from 260 °C to 280 °C but it decreased from 280 °C to 300 °C for all catalysts, which can be ascribed to catalyst deactivation.