Hydrodeoxygenation of vegetable oils over biochar supported bimetallic carbides for producing renewable diesel under mild conditions

Bimetallic Mo-W carbides supported on biochar were synthesized and used in the catalytic hydrotreatment of canola oil at 250 °C to produce diesel-range hydrocarbons. The effects of carburization temperature and metal content on the nature of active sites were investigated by using X-ray diffraction (XRD), N 2 physisorption, X-ray photoelectron spectroscopy (XPS), and CO and H 2 chemisorption. Varying temperature over the range of 550-700 °C did not have any effect on the formation of the Mo 2 C phase in the bimetallic carbide. As for the tungsten component in the mixed carbide, formation of the WC phase at a high temperature of 700 °C was dominant and increased the density of hydrogen activating sites, whereas at lower temperatures (≤600 °C), W 2 C and metallic W phases were formed and showed more CO adsorption sites. Increasing metal loading enhanced the particle size resulting in a lower density of catalytically active sites. The addition of W into the molybdenum carbide system strongly increased the catalytic performance with >95% conversion and >76% hydrocarbon yield over all mixed metal carbides at a mild temperature of 250 °C. These values were both higher than those obtained using Mo 2 C/C and Ru/Al 2 O 3 (48 and 35% hydrocarbon yield, respectively) under identical conditions. All carbide catalysts favor hydrodeoxygenation (HDO) products over decarboxylation/decarbonylation (DCO) products; however, W addition into mixed metal carbides increases the DCO selectivity in comparison with Mo 2 C/C due to higher ratios of H 2 /CO adsorption sites. The bimetallic carbides still retained a high catalyst activity after regeneration. Conversion and product selectivity of canola oil HDO over various metal carbides under mild condition, T = 250 °C, p = 450 psig, WHSV = 5 h −1 , TOS = 2-3 h.