Influence of sulfur vacancy on thiophene hydrodesulfurization mechanism at different MoS2 edges: A DFT study

The detailed hydrogenation (HYD) and direct desulfurization (DDS) pathways of thiophene over the sulfur vacancy of different MoS2 edge structures were investigated by density functional theory (DFT) calculations. The interaction energies were evaluated by dispersion corrected methods (DFT + D). Innovatively, a detailed thiophene hydrodesulfurization (HDS) reaction network over the sulfur vacancy was proposed, involving most of products which could be detected in the experiments. Taking the influence of sulfur vacancy into consideration, it could be found that the sulfur vacancy at Mo-edge was more beneficial for the formation of intermediates and products contained in DDS pathway by comparing the reaction barriers of DDS and HYD pathways. The HYD reaction pathway, which involved hydrogenation to 2-hydrothiophene followed by hydrogenation to 2,3-dihydrothiophene and 2,5-dihydrothiophene, could proceed with a mild reaction barrier at the S-edge with the creation of sulfur vacancy. The results also showed that butane could be formed at both S and Mo edges with relatively high reaction barriers of 52.60 kcal/mol (Mo-edge, DDS), 53.99 kcal/mol (S-edge, DDS) and 58.07 kcal/mol (Mo-edge, HYD), however, the formations of 1-butene and 2-butene were much more favored with energy barriers of 33.45 kcal/mol (S-edge HYD) and 35.20 kcal/mol (Mo-edge DDS), respectively. These results demonstrated that the sulfur vacancy at the different edges of MoS2 catalysts had a great impact on the overall HDS reaction routes. Based on the systematic calculations, the contribution of sulfur vacancy to the formation of certain intermediates and products was clearly orientated, which provided theoretical guidance for designing highly active catalysts for HDS technology. (C) 2017 Elsevier Ltd. All rights reserved.