The effect of microwave electric field on sulfur vacancies formation over the edge sites of Co/Ni-promoted and unpromoted MoS2 catalysts through DFT investigations

The elementary reactions for the formations of sulfur vacancies over various edges of Mo-based active phases were systematically investigated and compared under the action with/without microwave electric field via DFT calculations. The results reveal that the H-2 dissociation is extremely difficult over the M-edge of pure MoS2 clusters. The partial doping of Co/Ni can significantly reduce the difficulty, while the difficulty over the S-edge is obviously lower than that of the M-edge. Compared with CoMoS-I, H-2 dissociation becomes more favorable over the S-edge of NiMoS. The atomic H migration is unlikely to occur over the edge of MoS2, however, it becomes spontaneous after being dopped by Co/Ni along specific paths. The effect of electric field direction differs on each step of the vacancy formation over various edges. Either EX+ (the field applied along the direction of the x-axis) or E-X-field would highly benefit H-2 dissociation, H migration and H2S desorption on both M-edge and sulfur edge, thus it presents great significance that microwave, the existence of variable electromagnetic field is conducive to the formation of sulfur vacancies. The findings would shed more light on understanding the promotion mechanism of Co/Ni doping and microwaves on the HDS process.

Automated summary

The formations of sulfur vacancies over various edges of Mo-based active phases were investigated using DFT calculations. Co/Ni doping was found to reduce the difficulty, and the S-edge had lower difficulty than the M-edge. The effect of electric field direction differed for each step of vacancy formation.