X-ray absorption near edge structure and X-ray photo electron spectroscopy analyses of NiMo/Al2O3 catalysts containing boron and phosphorus

In this work, three catalysts namely NiMo/Al2O3, NiMoB/Al2O3, NiMoP/Al2O3 were prepared and surface structure studied using X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES) and X-ray photo electron spectroscopy (XPS). In the boron and phosphorus containing catalysts, boron and phosphorus concentrations were maintained at 1.7 and 2.7 wt.%, respectively. The surface structure of the catalysts at different stages of reactions (after 1 and 2 days of sulfidation, after 1 and 5 days of precoking and after 30 days of run time) was studied. Results from EXAFS analysis indicated the presence of similar P-O bond distance in all phosphorus containing samples. XPS and S K-edge spectra obtained from XANES showed the presence of two oxidation states of sulfur such as -2 and +6. Boron and phosphorus significantly increased the sulfidity of the catalyst, confirmed from XPS analysis. These catalysts showed less carbon deposition during hydrotreating process. Ni and Mo dispersion also increased significantly with the incorporation of boron in NiMo/Al2O3 catalyst, thus increasing the extent of hydrotreating reactions. (c) 2005 Elsevier B.V All rights reserved.