Effects of temperature and time on the facile low-temperature pre-sulfurization of tube-like unsupported Co-Mo catalysts for hydrodesulfurization

A Co-Mo sulfide catalyst with tube-like structure was prepared through a low-temperature pre-sulfurization process using rod-like CoMoO 4 as the precursor. The pre-sulfurization temperature greatly affected the total pore volume, the concentration of CoMoS species, the microstructure of (Co)MoS 2 slabs and the catalytic desulfurization activity. The increased temperature can promote the formation of hollow structure and the sulfurization degree of the precursor. It was found that the excessive temperature induced the Co atoms to form more isolated Co 9 S 8 species, hindering the formation of highly active CoMoS species. Therefore, appropriate temperature is more favorable to form the (Co)MoS 2 slabs with shorter length and higher stacking number, leading to more coordinatively unsaturated sites, especially the corner sites. According to the results of hydrodesulfurization reaction, the reaction rate of dibenzothiophene and the yields of liquid products are highly depended on the number of surface-active sites, which are mainly originated from the Type II CoMoS species. Moreover, the extended pre-sulfurization time can further improve the catalytic desulfurization activity of the catalyst at an appropriate pre-sulfurization temperature.