The promotion effects of MoOx species in the highly effective NiMo/MgAl2O4 catalysts for the hydrodeoxygenation of methyl palmitate

The hydrodeoxygenation of methyl palmitate into long-chain hydrocarbon is one of the most effective technologies for the production of alternative bio-diesel. But the development of non-sulphided Ni based catalysts with high hexadecane yield and excellent catalytic stability is still a challenge. In this work, a series of Ni/MgAl2O4, Mo/MgAl2O4 and NiMo/MgAl2O4 catalysts are prepared by the wetness impregnated method. The physical-chemical property and catalytic performance for the hydrodeoxygenation of methyl palmitate of all catalysts are investigated. The characteristic results indicate that Ni-MoOx composites with metallic Ni covered by the MoOx species are formed for NiMo/MgAl2O4 catalysts. The introduction of MoOx reduces the size of bimetallic particles and the electron transfer from Ni to MoOx improves the H-spillover effect. Furthermore, more oxygen vacancies and acid sites of NiMo/MgAl2O4 catalysts effectively promote the production of hexadecane via the hydrodeoxygenation pathway. Owing to these modifications, NiMo/MgAl2O4 reveal significantly improved catalytic performance and the Ni1Mo1/MgAl2O4 catalyst with Ni/Mo mass ratio of 1:1 demonstrates the highest pentadecane and hexadecane total yield of 92.0%. Additionally, the C15/C16 molar ratio over the Ni1Mo1/MgAl2O4 catalyst is only 1.63, suggesting enhanced hydrodeoxygenation pathway and less carbon emission. Moreover, the long-term test of 60 h indicates that the Ni1Mo1/MgAl2O4 catalyst reveals excellent catalytic stability due to the less carbon deposition and more stable support structure. Therefore, this work has provided an effective method for the design of Ni based catalysts for the production of the green diesel.