Influence of the preparation method on the hydrotreating activity of MoS2/Al2O3 extrudates: A Raman microspectroscopy study on the genesis of the active phase

Raman microspectroscopy was used to study the preparation of industrial MoS2/Al2O3 extrudates. Using this technique, the influence of the impregnation solution composition on the nature and macrodistribution of Mo complexes inside these catalyst bodies was evaluated during their preparation process (impregnation, drying, and calcination). It was found that poor dispersion of the MoOx phase in the calcined samples can be brought about by the formation of bulk (NH4)3[Al(OH)6Mo6O18] during impregnation or redistribution of Mo complexes during drying. The formation of crystalline MoO3 and Al2(MoO4)3 in the oxidic precursors leads to a poorly dispersed MoS2 phase in the final catalyst and significantly lower hydrodesulfurization activity. The spatially resolved information that can be obtained, and its inherent sensitivity for the detection of crystalline phases make Raman microspectroscopy a powerful characterization technique for studying the preparation of industrial supported metal oxide catalysts.