Promoting Effect of Ce and La on Ni-Mo/δ-Al₂O₃ Catalysts in the Hydrodeoxygenation of Vanillin

A crucial aspect of adding an economical and environmental dimension to the upgrading of bio-oils is to develop catalysts with enhanced and prolonged activity. In the present study, the effect of doping δ-alumina (Al₂O₃) with oxides of cerium (Ce) and lanthanum (La) before thermal treatment was investigated. The performance of such an Al₂O₃-supported nickel-molybdenum (Ni-Mo) catalyst was evaluated by studying the selectivity for the direct hydrodeoxygenation (HDO) of vanillin to cresol under continuous-flow conditions. In addition, the effect of adding H₂S during catalyst activation and/or performance tests was also evaluated. Overall, enhanced performance of the doped NiMo catalyst in the HDO process has been demonstrated and an increased selectivity for cresol via direct HDO observed. The advantage of adding La and Ce is supported by the characterization results, where less sintering and enhanced pore diameter of the doped Al₂O₃ were observed after thermally inducing the transformation from the δ to θ phases. The improved characteristics and prolonged activity of the doped Al₂O₃ were also deduced by the lower acidity of the catalyst, which resulted in reduced coke formation during the HDO process.