Few-layer MoS₂ dispersion induced by sulfur atom sharing to promote CO₂ hydrogenation to methanol

Abstract

With the ongoing interest in developing more stable and versatile catalysts for CO₂ hydrogenation to methanol, molybdenum sulfide (MoS₂) has been recently proposed as an alternative material. However, in its bulk state, CO₂ hydrogenation over MoS₂ typically favors methane formation. In this work, a wet impregnation method is applied for the production of ZnS-supported MoS₂, as confirmed by characterization via X-ray Diffraction, Raman and X-ray Photoelectron Spectroscopy. In contrast with the negligible methanol production shown by the pure MoS₂ reference, 2% MoS₂/ZnS presents a methanol selectivity of 78% at a CO₂ conversion of 2.3% under the mild reaction conditions of 200 °C and 20 bar. Density Functional Theory and Transmission Electron Microscopy suggest that the improved catalytic activity arises from an even dispersion of few-layer MoS₂ with exposed basal plane sites at the ZnS surface, an arrangement possibly enabled by the structural similarity and the shared S atoms between 2H-MoS₂ and W–ZnS phases. This hypothesis is strengthened by the comparison with the reference sample consisting of ZrO₂-supported MoS₂ sample, in which more agglomerated MoS₂ particles resulted in a lower and less selective methanol production. Moreover, in situ X-ray absorption spectroscopy and H₂ temperature-programmed reduction suggest further evidence of a MoS₂/ZnS interaction during the H₂ pretreatment, which may promote not only the expected formation of S-vacancies but also a partial reconstruction of MoS₂ given the close contact and sharing of S atoms with the ZnS support.