Study of oxidic and sulfided selective hydrodesulfurization catalysts for gasoline using Raman spectroscopy

A series of CoMo/Al₂O₃ catalysts for selective hydrodesulfurization (HDS) of gasoline were studied with Raman spectroscopy, a powerful method that creates specific signals for the states and the distributions of oxidic precursors and sulfided active phases. The higher the Mo and Co, the lower the tetrahedrally coordinated molybdate, and the higher the polymolybdate. But the amount of polymolybdate decreased when CoMoO₄ appeared. Cobalt-promoted polymolybdate was the precursor, and its relative content correlated well with the HDS selectivity. For sulfided catalysts, adding the cobalt-promoter led to local distortion-disorder of the MoS₂ structure and the formation of a CoMoS phase. This method can provide important information for designing new industrial selective-HDS catalysts.