To study the proportions of active metals over the surface of different
NiMo sulfide catalysts, XPS spectroscopy were detected. The XPS patterns
of Mo3d in the ranges of 220-242 eV is displayed in Fig. S15. As
reported, the binding energies for sulfide Mo 3d5/2 species, including
Mo6+(MoO3),
Mo5+(oxysulfide),
Mo4+(MoS2), are 232.3±0.3 eV,
228.6±0.3 eV, 230.7±0.3 eV, respectively. Moreover, the peak at 226.0 ±
0.3 eV can be corresponding to S2s. [21] The
positions of peaks assigned to Mo 3d3/2 species are fixed at adding 3.1
eV on the basis of those of Mo 3d5/2 species. The area ratios of Mo
3d5/2 and the Mo 3d3/2 species are fixed at 1.5. The half peak widths
for all sulfide catalysts are same. Meanwhile, the corresponding data of
the fitted peaks for Mo species are shown in Table 3. The
Mo4+(MoS2) species are generally
treated as active phase for HDS reaction. The proportions of
Mo4+ species over various catalysts follow in the
sequence of NiMo/SBA-16 (0.30) < NiMo/AT-10 (0.45) <
NiMo/AT-7.5 (0.56) < NiMo/AT-5 (0.52) < NiMo/AT-2.5
(0.54) < NiMo/AT-0 (0.53). Therefore, Al and Ti modification
can significantly increase the proportion of MoS2species. As the Al and Ti compositions are 7.5% and 2.5%, the
NiMo/AT-7.5 exhibit the highest proportion of
Mo4+(MoS2). Hence, the incorporation
of Ti species can also facilitate the formation of MoS2active phases, which is in accordance with the
literature.[50] Moreover, Ni/Si and Mo/Si ratios
on the surface of serial NiMo/AT-SBA-16 catalysts, which can reflect the
dispersion degree of Ni and Mo active metals, were higher than those of
NiMo/SBA-16. Therefore, Al and Ti modification can improve the
dispersion degree of active metals, which may allow a high HDS
efficiency.
Table 4 The distributions of the Ni species for different sulfide
catalysts, as derived from XPS analysis.