INVESTIGATION OF THE SULFIDATION OF MO/TIO2-AL2O3 CATALYSTS BY TPS AND LRS

A series of Mo/Al2O3 and Mo/TiO2-Al2O3 catalysts were investigated by temperature programmed sulfiding (TPS) and laser Raman spectroscopy (LRS). The effect of TiO2 on the sulfidability of molybdena was studied in detail. It is found that Mo/Al2O3 catalysts can be partially sulfided by O-S exchange at low temperature, forming molybdenum oxysulfide. The Mo-S bond subsequently ruptures in the presence of H-2 to produce H2S. At 530-550 K deep sulfiding of molybdenum oxysulfide occurs forming crystalline MoS2. When the surface of Al2O3 was covered by a monolayer of TiO2, the sulfiding rate of molybdena at low temperature was not only greatly increased, but H2S produced in the reduction of Mo-S species caused deep sulfiding of the catalyst which resulted in a decrease of the TPS peak temperature by 80-100 K. The results indicate that this promotion of the sulfiding of molybdena is enhanced with TiO2 loading. The function of TiO2 is explained by the weakened interaction between MoO3 and Al2O3 due to the coverage of the Al2O3 surface by TiO2.