Influence of metallic promoters on the performance of Ni/SiO₂ catalyst in the hydrodeoxygenation of anisole

Ni/SiO₂ and Ni-based bimetallic Ni₃₀M/SiO₂ catalysts (with a Ni/M atomic ratio of 30; M=Fe, Co, Cu, Zn and Ga) were prepared by the impregnation method and characterized by the means of H₂-TPR, XRD, H₂ chemisorption, NH₃-TPD and N₂ sorption; the effect of M promoters on the structure and performance Ni-based catalysts in the hydrodeoxygenation of anisole was investigated. The results indicated that the metallic promoters have a significant influence on the reducibility of nickel species, due to the interaction between M and Ni species, although the sizes of Ni-M bimetallic crystallites in Ni₃₀M/SiO₂ are similar to that of Ni crystallite in Ni/SiO₂. Because of the interaction between Ni and M and the enrichment of certain M promoters on the surface of Ni-M bimetallic particles, the adsorption quantity of H₂ on Ni₃₀M/SiO₂ is lower than that on Ni/SiO₂. In addition, the Ni₃₀M/SiO₂ catalysts also have more acid sites (especially the weak ones) than Ni/SiO₂. For the hydrodeoxygenation of anisole under 300℃, 0.1 MPa, weight hourly space velocity (WHSV) of anisole of 1.0 h^-1 and H₂/anisole molar ratio of 25, the Ni₃₀M/SiO₂ catalysts exhibit lower anisole conversion than Ni/SiO₂, probably due to the lower H₂ uptakes on the bimetallic catalysts. However, Ni₃₀Ga/SiO₂ and Ni₃₀Zn/SiO₂ give much higher selectivities to BTX (benzene, toluene and xylene) (81.7% and 76.8%, respectively) than Ni/SiO₂ (71.5%). Meanwhile, Ni₃₀Zn/SiO₂ exhibits higher activity in methyl transfer and lower activity in C-C bond hydrogenolysis than other catalysts; owing to the high oxophilicity of Zn, from the aspects of increasing carbon yield and reducing H₂ consumption, Ni₃₀Zn/SiO₂ is probably an appropriate catalyst in hydrodeoxygenation.