Catalysis performance of nonpromoted and co-promoted MoS2 catalysts on a hydrodesulfurization reaction: A DFT study

To elucidate the function of the metal Co in the hydrodesulfurization (HDS) process, a closed cycle mechanism, including generation/regeneration of sulfur vacancy, adsorption of thiophene and complete HDS reaction of thiophene (hydrogenation (HYD) and direct desulfurization (DDS) pathways), was investigated via density functional theory (DFT-D) calculations on pure MoS2 and Co-MoS2 catalysts. All possible products were taken into consideration; for example, both HYD and DDS pathways could produce four kinds of products (butadiene, 1-butene, 2-butene, and butane), while the HYD pathway on the S edge of 100% Co-MoS2 catalyst produced three of the same products without butane. From the functional analysis of Co, the Co promoter has changed the original reaction mechanism and related product distribution. The sulfur vacancy on the 50% Co-promoted S edge exhibited the most commendable HDS activity, and 2-butene is obviously improved. Whereas 50% of the Co-promoted Mo edge inhibits the HDS process, Co-doping in the Mo edge could limit its catalysis performance. The generation/regeneration of sulfur vacancies could be the rate-limiting step on the S edge of nonpromoted and Co-promoted MoS2 catalysts; however, it will not be the rate-limiting step on the Mo edge.