Applied catalysis. A: General vol:239 issue:1-2 pages:221-228
Two commercial sulfided oxide catalysts for the hydrotreatment of hydrocarbons were investigated: NiO-MoO3 and CoO-MoO3 on alumina.. Fresh and cokes-contaminated pellets were first explored by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The samples were then studied with low energy ion scattering (LEIS). The spectra show a clear distinction between fresh, partly contaminated and heavily contaminated pellets. For both catalysts the comparison of the peak signals suggests that C is preferentially deposited on the Mo- and Al-atoms. This confirms the role that is attributed to Mo in Ni-Mo(Al2O3) catalysts by other authors who found that the introduction of small amounts of Mo into Ni(Al2O3) catalysts greatly improves their resistance to coking. Next the contaminated pellets were regenerated by heat-treatment at 450degreesC in a furnace. The LEIS-spectra give evidence that this treatment has no influence on the fresh catalysts, but completely restores the contaminated pellets to their original state. The results clearly demonstrate that, by its monolayer surface sensitivity, LEIS can give clear-cut information even on very rough surfaces of commercial sulfided oxide catalysts. (C) 2002 Elsevier Science B.V. All rights reserved.