The effect of phosphate and glycol on the sulfidation mechanism of CoMo/Al2O3 hydrotreating catalysts: an in situ QEXAFS study

The sulfidation of CoMo/γ-Al2O3 catalysts prepared in the presence of phosphate and triethylene glycol (TEG) was studied by in situ Mo and Co K-edge QEXAFS. In a classic CoMo catalyst, prepared without phosphate and TEG, MoS2 is formed through intermediate MoS3-like species. In the presence of phosphate, alone or with TEG, this intermediate species is not observed and the molybdenum is directly sulfided to MoS2. The additives increased the sulfidation degree of molybdenum with respect to the standard catalyst, leading to a better sulfur saturation of the MoS2 slabs and to a higher static order. Co K-edged QEXAFS showed that the sulfidation rate of Co increases in the presence of phosphate and TEG.