FT-IR pyridine spectroscopy has been applied to obtain the surface acid
amount of various catalysts. The FT-IR pyridine spectra recorded at two
adsorption temperatures of 200 °C and 350 °C are displayed in Fig. S14.
As reported, the peak appearing at 1540 cm-1 can be
ascribed to the Brönsted acid sites (B). The peak at about 1490
cm-1 is resulted from both Brönsted and Lewis acid
sites. Two characteristic peaks at 1450 cm-1 and 1610
cm-1 can be ascribed to Lewis acid sites
(L).[47] In addition, a shoulder at about 1620
cm-1 appeared in the patterns of the NiMo catalysts
containing Al species can be assigned to Lewis acid
sites,[48] which may be caused by exposed
Al3+ ions. It should be noteworthy that the intensity
of peaks belonging to B and L acid sites increase after Al and Ti
modification. Therefore, it can deduce that the incorporation of Al and
Ti atoms into SBA-16 material can increase the amount of B acid sites
and L acid sites. The amounts
of
Brönsted, Lewis, total acid sites and the B/L ratios determined from
Fig. S14 are concluded in Table 2. The adsorption intensity of pyridine
molecules degassed at 200 °C and 350 °C on the surface of NiMo catalysts
should be ascribed to the amount of total acid sites and the amounts of
medium and strong acid sites, respectively.[14]From Table 2, the amounts of B acid sites, L acid sites and B+L acid
sites for other catalysts increase after Al and Ti modification. The
total amounts and the amounts of medium and strong acid sites follow the
order of NiMo/SBA-16 < NiMo/AT-0 < NiMo/AT-2.5
< NiMo/AT-5 <NiMo/AT-7.5 <NiMo/AT-10.
Therefore, incorporation of Al species into SBA-16 materials can
generate more acid sites than those of Ti species. Moreover, the B/L
ratio for NiMo/SBA-16 catalyst is higher than those of NiMo/Al-Ti-SBA-16
catalysts, indicating that Al and Ti modification can generate more L
acid sites than B acid sites. For NiMo/SBA-16 and NiMo/AT-0 catalysts,
the amount of medium and strong acid sites of B type are 0
µmol·g-1, confirming that the incorporation of Ti
atoms into SBA-16 material can mainly generate L type acid sites by Ti
species appending to the support through surface silanol
groups.[49]
Table 3 the proportion of Mo species over different sulfide catalysts,
as determined by XPS spectra.