Preparation of Ni–Mo–S catalysts by hydrothermal method and their hydrodeoxygenation properties

Abstract Unsupported Ni–Mo–S catalysts with different Ni/(Ni + Mo) molar ratio were prepared by hydrothermal method using ammonium heptamolybdate and thiocarbamide as materials. The resultant catalysts were characterized by X-ray diffraction, nitrogen physisorption and transmission electron microscopy, and their activities were measured using the hydrodeoxygenation (HDO) of p -cresol as a probe reaction. The addition of Ni promoter caused a reduction in the surface area. The peaks attributed to NiS 2 on catalyst surface became noticeable as the Ni content increased in the catalyst. The catalyst with an optimal Ni/(Ni + Mo) molar ratio (0.3) exhibited the highest activity (99.8% deoxgenation degree at 300 °C and 4.0 MPa hydrogen pressure for 6 h). The HDO of p -cresol on these prepared Ni–Mo–S catalysts proceeded with two parallel routes: hydrogenation-dehydration (HYD) and direct deoxygenation (DDO), and HYD/DDO closely related to the Ni/(Ni + Mo) molar ratio in the catalyst, the HDO reaction temperature and H 2 pressure. The comparison of Ni–Mo–S with MoS 2 –NiS 2 (prepared by two hydrothermal method) and MoS 2  + NiS 2 (prepared by physically mixing separately MoS 2 and NiS 2 ) indicated that the high HDO activity of Ni promoted MoS 2 catalyst was attributed to the synergistic effect of MoS 2 and NiS 2 rather than the formation of Ni–Mo–S phase, which could be well explained by the remote control model.