Performance of molybdenum oxide in spent hydrodesulfurization catalysts applied on the oxidative desulfurization process of dibenzothiophene compounds

In order to understand the role of Mo in spent hydrodesulfurization catalysts, which could be used as catalysts for oxidative desulfurization (ODS) process, the preparation method of Mo based catalysts was modified to change the stability of Mo species anchored to support. Mo-supported catalysts were prepared by the impregnation of ammonium heptamolybdate solutions at acidic and near neutral pH on alumina and pseudoboehmite, and were tested in the batch ODS process, using different oxidants such as tert-butyl hydroperoxide, H2O2 or cumene hydroperoxide (CHP). The activity of the catalysts and their performance is discussed in terms of the Mo species evaluated by temperature-programmed reduction. The results show that H2O2 was the best oxidant in the two-phase system (L-S) and three-phase system (L-L-S), whereas CHP presents evident oxidation in the homogeneous phase without a solid catalyst. The best oxidant was selected to study the catalytic stability in a continuous fixed-bed ODS reactor. Two activity contributions of the Mo species were determined: supported Mo-tetrahedral species are the main participant in the oxidation-heterogeneous reactions, and Mo-octahedral species are partially leached into the extraction-solvent and contribute to the homogeneous catalytic reaction.