Bimetallic Rex-Ru/C catalyst for fatty acid esters to diesel-range alkanes under low temperature

Abstract

ABSTRACT The hydrogenation of bio-based oil into biodiesel is a key strategy in reducing reliance on fossil fuels. However, efficient catalysts are needed to enable low-temperature hydrogenation reactions due to the current high-temperature requirement for bio-based oil hydrogenation. Here, bimetallic catalysts Rex-Ru/C for low-temperature hydrogenation of bio-based oils were prepared. The presence of Re oxides (ReOx) in the catalyst enhances the abundance of weak and medium acid sites, thereby facilitating the adsorption of H2. The DFT calculation shows the introduction of Re also improved the adsorption capacity of the catalyst for fatty acid methyl ester and H2. The Re0.25-Ru/C catalyst exhibits superior conversion, selectivity, and recyclability at low temperatures compared to the previously reported catalysts, achieving 100% conversion of methyl stearate with 100% selectivity toward n-heptadecane (C17) and n-octadecane (C18) (reaction conditions: 150°C, 4 h, 2.5 MPa H2). Moreover, the catalyst also shows excellent hydrogenation activity toward various fatty acids or esters, including methyl palmitate, stearic acid, and palmitate at low temperatures. The Re0.25-Ru/C catalyst showed consistent recycling performance over 9 cycles. The decline in catalytic performance of the catalyst was primarily caused by a reduction in ReOx content, resulting in a decrease in acid site concentration. Consequently, there was reduced adsorption of H2 and oil on the catalyst.