The effect of NO adsorption on the chemical state of promoted hydrotreating catalysts

The chemical state of the active phase (Ni-Mo-S and Ni-W-S) of sulfided NiM o and NiW catalysts during the interaction with NO is investigated by exten ded X-ray absorption fine structure (EXAFS). The results show that approxim ately 30 % of the Ni atoms in the active phase are oxidized already at room temperature (RT) upon NO exposure. On the average, the chemical state of t he W atoms in sulfided NiW/Al2O3 is hardly changed. Essentially all the Ni atoms in the active Ni-Mo-S phase are oxidized above 150 degreesC. Although the present results indicate that significant structural and chemical chan ges occur when NO is used as a probe molecule in activated hydrotreating ca talysts, NO temperature-programmed desorption (TPD) and NO chemisorption ca n, nevertheless, provide important insight into the nature of the active ph ase. (C) 2000 Elsevier Science B.V. All rights reserved.