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.