CO-IR spectra were applied to investigate the concentration of active
metals over serial sulfide NiMo catalysts, which were shown in Fig. S17.
It is well investigated that MoS2 slabs possess two
types of edges including the sulfur-terminated edge (S-edge) and
Mo-terminated edge (Mo-edge).[53] Because the
sample are detected without H2 treatment, the
symmetrical band at about 2105 cm-1 assigned to CO
adsorption on the Mo-edge sites with a high sulfur coordination number
can be observed, which is also considered as fully sulfide
species.[54] Three bands at 2065
cm-1, 2045 cm-1 and 2020
cm-1 signify the existence of CO adsorbed on the
S-edge with different sulfur coverage.[7,56] The
band at about 2130 cm-1 should be assigned to partial
sulfided MoOxSy phase or NiMoS phase.[55,56] The
band appears at 2156 cm-1 is due to CO adsorbed on
surface OH group.[55] The decomposition data of
CO-IR spectra were concluded in Table 5. As the addictive amounts of
metals are same, a higher total concentration of Mo-edge and S-edge will
indicate a better dispersion of active metals. It shows that the total
concentrations of Mo-edge and S-edge increase after Al and Ti
modification, which follows the sequence of NiMo/SBA-16 <
NiMo/AT-10 < NiMo/AT-0 < NiMo/AT-7.5 <
NiMo/AT-5 < NiMo/AT-2.5, demonstrating that the incorporation
of Al and Ti species into SBA-16 material can enhance the dispersion
degree of metals. The total concentration of Mo-edge and S-edge for
NiMo/AT-10 catalyst is lower than NiMo/AT-0 catalyst, verifying that Ti
modification can improve higher dispersion degree of active metal than
that of Al modification. However, as the mass percentage of
TiO2 in support reaches 10%, the total concentration
for NiMo/AT-0 catalyst is lower than other catalysts containing both Al
and Ti species. It should be noteworthy that the concentration of S-edge
exhibits an increasing trend with the Al contents in supports, peaking
at 9.70 μmol/g for NiMo/AT-7.5 catalyst. Hence, incorporation of Al
species into SBA-16 silica can promote the formation of S-edge. In order
to acknowledge the influence of acidity on the formation of S-edge
sites, the plots of amount of B acid sites and the concentration of
S-edge are shown in Fig. S18. It shows that the S-edge concentration
presents an increasing tendency with the amounts of B acid, indicating
that the B acid sites can facilitate the formation of S-edge sites.
However, the lower concentration of S-edge for NiMo/AT-10 catalyst than
NiMo/AT-7.5 catalyst should be assigned to its lower dispersion degree
fMo of MoS2, which can be recognized
from HRTEM results. Moreover, the concentration of fully sulfide Mo-edge
sites over sulfide NiMo catalysts exhibit an increasing trend with the
contents of Ti species. As the TiO2 content reaches 10%
in support, the concentration of Mo-edge site becomes lower than other
catalysts containing Ti species, which may be also related to its
relatively low dispersion degree of active metals. In addition, the
ratios of S-edge and Mo-edge are also calculated and exhibit an
increasing trend with the contents of Al species.
HRTEM measurement was applied for obtaining the dispersion information
of active phase MoS2. The representative images of
different sulfide catalysts are displayed in Fig. S19. The
stacking-number distributions of MoS2 crystallines for
serial sulfide catalysts are exhibited in Fig. S20. It is obvious that
the proportion of MoS2 phases with lower stacking
layers, especially the 2 layers, show an increasing tendency with the Al
and Ti compositions in the catalysts. It can be verified from
H2-TPR result that the interaction strength between
active Mo (Oh) phase and support become stronger after Al and Ti
modification, which will lead to the decrement of stacking layers of
MoS2. Fig. S21 exhibits that the frequency of
MoS2 phases with short slab length ranging from 0-2 nm
and 2-4 nm increases after Al and Ti modification. Whereas, the
frequency of MoS2 with higher slab length present the
reverse trend. Moreover, the average length and number of slabs and
dispersion degree (fMo) for MoS2 slabs
are displayed in Table S1. As compared with NiMo/SBA-16 catalyst, the
average length and stacking layers of various NiMo/Al-Ti-SBA-16
catalysts are relatively lower. The dispersion degree of
MoS2 phase over sulfide NiMo/Al-Ti-SBA-16 is improved
after the incorporation of Al and Ti species into SBA-16 materials,
which follows the order of NiMo/SBA-16 (0.14) < NiMo/AT-10
(0.16) < NiMo/AT-0 (0.18) < NiMo/AT-7.5 (0.20)
< NiMo/AT-5 (0.21) < NiMo/AT-2.5 (0.23). Above all,
sulfide NiMo/SBA-16 catalyst presents the highest slab numbers, longest
slab length and lowest dispersion degree, which are adverse for HDS
reaction. Al and Ti modification can make an improvement of properties
for active metals and further enhance the HDS efficiency for the
corresponding catalysts. However, the NiMo/AT-0 catalyst exhibits
relatively lower dispersion degree of MoS2, which may be
caused by the fact that the pore size of AT-0 support is the lowest from
the above BET result.