Efficient and stable Ni-Cu catalysts for ex situ catalytic pyrolysis vapor upgrading of oleic acid into hydrocarbon: Effect of catalyst support, process parameters and Ni-to-Cu mixed ratio

To eliminate the problematic need for liquid phase, high temperature, and high pressure, as well as the excessive consumption of hydrogen and production of aromatic hydrocarbons, associated with traditional aviation oil preparation processes, Ni–Cu bimetallic catalysts were synthesized and evaluated for ex situ catalytic pyrolysis vapor upgrading of oleic acid under a N2 atmosphere. The effects of catalyst support (AC, Al2O3, ZrO2, HZSM-5, HUSY, Hβ and MCM-41), pyrolysis process parameters (pyrolysis temperature, catalytic temperature and amount of oleic acid injected), and the mixing ratio of modified metals (Ni:Cu = 0:1,2,1:1,1:2,1:0) on the catalytic conversion of oleic acid to high-quality chemicals were studied. The catalysts were characterized by XRD, BET and NH3-TPD. Modified bimetallic catalysts show great potential for green diesel production without the use of H2 feed. The abundance of Brønsted acid sites favors HDO routes (such as HZSM-5, HUSY, Hβ and MCM-41), while Lewis acid sites (such as ZrO2 and Al2O3) favor hydrogenation and decarbonylation reactions. The addition of Cu enhances the reducibility of Ni and inhibits the cracking reaction and deactivation caused by coke. The addition of Ni effectively promotes the conversion of oleic acid, accelerates the fracture of C–C and effectively improves the production of hydrocarbons. The highest conversion was 100% with 85.68% selectivity towards hydrocarbons under pyrolysis at 450 °C, a catalytic temperature of 500 °C, and a feed quantity of oleic acid of 0.25 ml/min using Ni–2Cu/MCM-41 catalysts, and the oxygen removal efficiency and selectivity of C17 hydrocarbon were the highest (85.68% and 26.77%, respectively). The main products were olefins. In addition, the regenerated catalyst had good stability and could be used for at least 3 reaction cycles without observation of significant deactivation.