Effect of Thermal Treatment under Nitrogen on the Ammonium Thiosulfate-Presulfidized Mo/Al2O3 Catalyst

A series of Mo/Al2O3 catalysts were presulfidized with (NH4)2S2O3 aqueous solution, dried at ambient temperature, and thermally treated in N2 flow. The catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry-mass spectrometry, and sulfur analysis. Thermal pretreatment in N2 had a significant effect on the catalytic performance of the (NH4)2S2O3-presulfidized Mo/Al2O3 for the hydrodesulfurization (HDS) of thiophene. The sample pretreated at 80 °C in N2 flow and activated at 200 °C in H2 gave the highest thiophene conversion. This is due to that the modification of the Al2O3 support by sulfate ions weakened the interaction of Mo species with the support, which increased its sulfidization to form a highly active multilayer Type II MoS2 structure. In contrast, N2 thermal treatment obove 200 °C led to the decomposition of (NH4)2S2O3 and decreased the sulfiding degree, which resulted in the formation of a less active single layer Type I MoS2 structure with a low activity for thiophene HDS.