Fig. 3 (A) the product distributions of DBT HDS reaction; (B) the
HYD/DDS ratios for various catalysts; (C) the correlation between
S-edge/Mo-edge ratio and HYD/DDS ratio.
DBT HDS reaction includes HYD and DDS routes, whose corresponding
products are tetrahydrodibenzothiophene (THDBT), biphenyl (BP) and
cyclohexylbenzene (CHB). The distributions of DBT HDS reaction routes
for serial NiMo catalysts are displayed in Fig. 3A. It can be seen that
DDS route should the primary path in DBT HDS reaction due to the HYD and
DDS ratios are lower than 1.0. From Fig. 3B, the HYD and DDS ratios
follows the order of NiMo/AT-10 < NiMo/AT-7.5 <
NiMo/AT-5 < NiMo/SBA-16 < NiMo/AT-2.5 <
NiMo/AT-0. The distribution of HDS route can be related with the acidity
of catalyst. Compared with NiMo/SBA-16 catalyst, the selectivity of DDS
routes for NiMo catalysts containing Al species are enhanced, which
should be due to the fact that B acid site can promote the formation of
coordinatively unsaturated sites (CUS) by accepting an electron from
MoS2 active phase.[9] NiMo/AT-10
catalyst presents the lowest HYD and DDS ratio of 0.25. In addition, the
HYD and DDS ratio for NiMo/AT-0 catalyst is the highest of 0.45,
verifying that the incorporation of Ti atoms into SBA-16 structure can
improve the selectivity of HYD route. The improvement of HYD selectivity
after Ti modification should be assigned to the special structure and
electronic properties of active phases formed on surface of
catalyst.[57] Meanwhile, CO-IR results can also
disclose the correlation between HDS route and types of active
metals.[6] It is recognized that vacant (CUS)
sites are responsible for S removal through DDS route, whereas the HYD
pathway should be enhanced by a fully sulfide MoS2phase.[58] Caused the Mo-edge and S-edge sites
play different roles in HDS reaction route, the improvement of DDS route
must be at the expanse of HYD route. Therefore, the concentration ratio
of S-edge and Mo-edge may be applied to correlate with the HDS
selectivity. The relationship between S-edge/Mo-edge ratio and HYD/DDS
ratio is shown in Fig. 3C. It shows that the HYD/DDS ratio decreases
with the increasing S-edge/Mo-edge ratio. Therefore, the HYD/DDS ratios
can be well linked with the S-edge/Mo-edge ratios.
Table 7 the pseudo-first-order constants (10-4 mol
g-1 h-1) and TOF
(h-1) of DBT HDS reaction routes for serial NiMo
catalysts, which are obtained at the HDS conversions lower than 30%.