Anisole Hydrodeoxygenation over Nickel-Based Catalysts: Influences of Solvent and Support Properties

The realization of biofuels and chemicals requires the development of highly active and selective catalysts, which are resistant to deactivation. A conventional ZSM-5 (SiO₂/Al₂O₃ = 30) was modified with 0.2 M NaOH to generate a mesoporous zeolite support. The parent zeolite, mic-ZSM-5, the modified zeolite, hie-ZSM-5, and a mesoporous silica support, SiO₂, were impregnated with 5% nickel and characterized using X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis of nitrogen sorption, scanning electron microscopy with energy dispersive X-ray (SEM-EDX), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H₂-TPR), ammonium hydrogen temperature-programmed desorption (NH₃-TPD), and thermogravimetric analysis (TGA). The influences of the support properties and solvent during the hydrodeoxygenation of anisole were investigated by measuring concentration profiles and rates in a high-pressure batch reactor. NaOH treatment significantly improved the pore structure, acidity of the support, and metal dispersion as well as the interaction of nonframework Ni species with zeolite and, hence, the catalytic activity and selectivity. The highest anisole conversion of 100% was obtained in 120 min over the hie-Ni/ZSM-5 catalyst with cyclohexane selectivity of 88.1%. In addition, the Ni/SiO₂ catalyst was 84.5% selective to toluene at 48.9% anisole conversion in 120 min; as such, it was proposed that the transformation of anisole proceeds via either a direct deoxygenation–hydrogenation or isomerization–direct deoxygenation pathway. However, no substantial differences in anisole conversion or product selectivity were observed when decalin and n-decane were compared as solvents. A catalyst reusability test showed hie-Ni/ZSM-5 as the most stable of the three catalysts in terms of anisole transformation, even though the catalyst recorded the biggest weight loss of 9.2% suggesting high resistance to carbon deactivation. Therefore, with this very good catalytic activity, good selectivity to liquid product, and stability, the mesoporous Ni/ZSM-5 catalyst is a potential candidate for economically beneficial future industrial applications.