Correlation Between Catalytic Activities and Surface Properties of Ni-Mo Sulfide Catalyst (II)

Support Effect

Abstract

Two series of Ni-Mo catalysts were prepared using Al₂O₃ and TiO₂ supports. Ni/ (Ni+Mo) ratio of the catalysts was varied, while a total metal loading of Ni and Mo was kept constant. Sulfiding conditions were optimized to give superior catalytic activities. After sulfiding, model test reactions were carried out to evaluate hydrogenation (HY), hydrocracking (HC) and hydrodesulfurization (HDS) activities of the sulfide catalysts.
The highest HY activities of Al₂O₃ and TiO₂ supported catalysts were obtained when the Ni/ (Ni+Mo) ratios were 0.25 and 0.12, respectively, showing different interaction between support and active metals. XPS measurements revealed that the atomic ratio of active metal sulfide {NiS/ (NiS+MoS₂)}, which gave the highest HY activities, was 0.2 on both supports. This indicates that sulfided active metals such as NiS or MoS₂ play an important role for the formation of HY active sites.
Both catalysts supported on Al₂O₃ and TiO₂ showed the highest HDS activities when the NiS/ (NiS+MoS₂) ratio was 0.4. This ratio is different from that obtained in HY measurements. While HC activities of the two series of sulfide catalysts decreased with increasing of Ni loading.
These results clealy show that HY, HC and HDS active sites of Ni-Mo sulfide catalysts are different each other and that proper selection of each active metal loading is required for preparing highly selective catalysts.