In situ observation of Ni–Mo–S phase formed on NiMo/Al₂O₃ catalyst sulfided at high pressure by means of Ni and Mo K-edge EXAFS spectroscopy

To obtain direct evidence of the formation of the Ni–Mo–S phase on NiMo/Al₂O₃ 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 k³χ(k) spectra with high signal-to-noise ratio were obtained using this high-pressure chamber for the NiMo/Al₂O₃ 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 Al₂O₃-supported NiMo catalyst sulfided under high-pressure hydrodesulfurization conditions.