In situobservation of Ni–Mo–S phase formed on NiMo/Al₂O₃catalyst sulfided at high pressure by means of Ni and MoK-edge EXAFS spectroscopy

Abstract

To obtain direct evidence of the formation of the Ni-Mo-S phase on NiMo/Al(2)O(3) catalysts under high-pressure hydrodesulfurization conditions, a high-pressure EXAFS chamber has been constructed and used to investigate the coordination structure of Ni and Mo species on the catalysts sulfided at high pressure. The high-pressure chamber was designed to have a low dead volume and was equipped with polybenzimidazole X-ray windows. Ni K-edge k(3)chi(k) spectra with high signal-to-noise ratio were obtained using this high-pressure chamber for the NiMo/Al(2)O(3) catalyst sulfided at 613 K and 1.1 MPa over a wide k range (39.5-146 nm(-1)). The formation of Ni-Mo and Mo-Ni coordination shells was successfully proved by Ni and Mo K-edge EXAFS measurement using this chamber. Interatomic distances of these coordination shells were almost identical to those calculated from Ni K-edge EXAFS of NiMo/C catalysts sulfided at atmospheric pressure. These results support the hypothesis that the Ni-Mo-S phase is formed on the Al(2)O(3)-supported NiMo catalyst sulfided under high-pressure hydrodesulfurization conditions.

Understanding Ni Promotion of MoS2/γ‐Al2O3 and its Implications for the Hydrogenation of Phenanthrene

“…The reference NiAl 2 O 4 spinel displayed a quite sharp feature at the edge, which was observed to some extent also in NiS x /γ‐Al 2 O 3 and in the Ni( x )MoS 2 materials with a lower intensity. This implied that a small fraction of Ni was always present as NiAl 2 O 4 spinel, in line with the UV/Vis spectra (see the Supporting Information) . The absorption edge energy and the local environment around Ni for the sulfide catalysts were similar to the Ni 3 S 2 reference, in agreement with the XRD results of the sample with the highest Ni loading.…”

“…The presence of Ni incorporated into the MoS 2 edge was further confirmed by the presence of Ni−Mo contributions in EXAFS. The distance and coordination number of this contribution was in good agreement with a model of direct substitution of Ni for Mo in the whole edge structure …”

“…During the adsorption of CO, the intensity of the 2084 cm −1 band (carbonyls on NiS x ) strongly increased with the addition of Ni above 3 wt %. On the other hand, the rather low Ni−S and Ni−Ni coordination numbers in EXAFS analysis compared with reference Ni 3 S 2 pointed to an important contribution of very small Ni 3 S 2 particles . The coordination number N Ni−Ni decreased for high Ni concentrations.…”

γ‐Al2O3‐Supported and Unsupported (Ni)MoS2for the Hydrodenitrogenation of Quinoline in the Presence of Dibenzothiophene

“…The MoÀNi contribution indicates the formation of a NiÀ MoÀS phase, which dominates the performance (vide infra). The MoÀNi coordination number of 0.2 is smaller than that generally reported for NiÀMoÀS, [19,44] however, the NiÀS and NiÀMo distances match very well with the millerite-type structure proposed for this phase. [45] The difference in MoÀS coordination numbers for promoted and unpromoted catalysts (6.6 and 5.7, respectively) is also in line with the features expected for the NiMoS and MoS 2 phases.…”

Quasiin situNiK-edge EXAFS investigation of the spent NiMo catalyst from ultra-deep hydrodesulfurization of gas oil in a commercial plant

“…Furthermore, the surface structure of the spent catalyst should be compared with that of the fresh catalyst sulfided at high pressure to clarify the deactivation mechanism, because the catalyst is exposed to a high-pressure sulfiding atmosphere under ultra-deep HDS conditions. In our previous work (Koizumi et al, 2010), a high-pressure EXAFS chamber equipped with Cu-free polybenzimidazol (PBI) windows was newly constructed. In situ Ni and Mo K-edge EXAFS measurements with this high-pressure chamber successfully probed the Ni-Mo and Mo-Ni coordination shells related to the Ni-Mo-S phase in NiMo/Al 2 O 3 catalysts sulfided at high pressure (613 K, 1.1 MPa).…”