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 NiS2 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 4.0MPa hydrogen pressure for 6h). 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 H2 pressure. The comparison of Ni–Mo–S with MoS2–NiS2 (prepared by two hydrothermal method) and MoS2+NiS2 (prepared by physically mixing separately MoS2 and NiS2) indicated that the high HDO activity of Ni promoted MoS2 catalyst was attributed to the synergistic effect of MoS2 and NiS2 rather than the formation of Ni–Mo–S phase, which could be well explained by the remote control model.