Selective, bifunctional Cu–WOx/Al2O3 catalyst for hydrodeoxygenation of fatty acids

Abstract

Selective hydrodeoxygenation of oleic acid (OA; in a batch reactor, at 300 °C, 30 bar H₂ pressure, reaction time of 1 h and reactant-to-catalyst weight ratio of 2 g OA/0.2 g) forming n-octadecane in yields as high as 93% over a non-noble metal, sulfur-free, bimetallic Cu–WO_x/Al₂O₃ catalyst is reported for the first time. Several Cu–WO_x/Al₂O₃ compositions were prepared by a sequential wet-impregnation method and evaluated. A catalyst with 10 wt% Cu and 4 wt% W enabled the highest activity and selectivity. Upon adding WO_x, the amount of moderate and strong acid sites increased and more Cu in the catalyst was in reduced electron-rich metallic (Cu⁰) state. The crystallite size and dispersion of Cu were little affected. WO_x promoted the fatty acid hydrodeoxygenation activity of Cu. While a monometallic Cu catalyst (10Cu/Al₂O₃) yielded n-octadecane and n-heptadecane along with high amounts of intermediate octadecanol and octadecanal products, the bimetallic catalyst (10Cu–4WO_x/Al₂O₃) gave mainly n-octadecane. Acidity and the high amount of reduced Cu⁰ species are responsible for the high catalytic hydrodeoxygenation performance of this bimetallic catalyst.