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.