Fig. 1 DBT HDS efficiencies of serial NiMo catalysts under different weight time and reaction temperatures.
The HDS performances of serial NiMo catalysts over DBT reactant at different weight time and reaction temperatures are displayed in Fig. 1. It shows that the HDS performance follows the order of NiMo/SBA-16 < NiMo/AT-10 < NiMo/AT-0 < NiMo/AT-5 < NiMo/AT-2.5 < NiMo/AT-7.5. This result can verify that Al and Ti cooperative modification can significantly improve the HDS performance, which should be ascribed to the fact that the incorporation of Al and Ti atoms into SBA-16 silica can improve the acidity of catalyst and the properties of active metals including dispersion degree and distribution. Although the total amount of acidity of NiMo/AT-10 is the highest, NiMo/AT-0 catalyst presents a better HDS performance than that of NiMo/AT-10 catalyst, which should be due to its higher proportion of MoS2 and NiMoS phases (XPS results) and better dispersion for MoS2 phases (HRTEM results). The NiMo/AT-7.5 catalyst shows the highest HDS efficiency of 97.8% under the reaction conditions of T=340 °C, P=4.0 MPa and WHSV=20 h-1. The HDS efficiency can be correlated to the factors of physico-chemical properties of supports, acidities of catalysts, dispersion and distributions of active metals. The reasons for the highest HDS performance for NiMo/AT-7.5 catalyst should be ascribed to the following factors. The pore volume and pore size of AT-7.5 support are relatively high, and the acidity of corresponding NiMo/AT-7.5 catalyst is appropriate. The XPS results disclose that the proportion of active MoS2 phase in sulfide NiMo/AT-7.5 catalyst is the highest of 0.56, and the proportion of active NiMoS phase is 0.41, which is only lower than that of sulfide NiMo/AT-2.5 catalyst. Finally, from HRTEM results, the slab length of MoS2 is short and the dispersion degree of MoS2 (fMo) is high. Above all, the synergistic effect of the incorporation by Al and Ti species can enhance the HDS efficiency. In addition, NiMo/AT-2.5 catalyst also exhibit high HDS performance, which may be due to its highest pore size, shortest slab length of 4.0 nm and the highest fMo value of 0.22. However, the HDS efficiency of NiMo/AT-2.5 catalyst is lower than that of NiMo/AT-7.5 catalyst due to its poor acidic properties.