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 k(3)chi(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. (C) 2010 International Union of Crystallography Printed in Singapore - all rights reserved