Mn-promoted MoS2 catalysts for CO2 hydrogenation: enhanced methanol selectivity due to MoS2/MnOx interfaces

Abstract

Considering the alarming scenario of climate change, CO₂ hydrogenation to methanol is considered a key process for phasing out fossil fuels by means of CO₂ utilization. In this context, MoS₂ catalysts have recently shown to be promising catalysts for this reaction, especially in the presence of abundant basal-plane sulfur vacancies and due to synergistic mechanisms with other phases. In this work, Mn-promoted MoS₂ prepared by a hydrothermal method presents considerable selectivity for CO₂ hydrogenation to methanol in comparison with pure MoS₂ and other promoters such as K and Co. Interestingly, if CO is used as a carbon source for the reaction, methanol production is remarkably lower, which suggests the absence of a CO intermediate during CO₂ hydrogenation to methanol. After optimization of synthesis parameters, a methanol selectivity of 64% is achieved at a CO₂ conversion of 2.8% under 180 °C. According to material characterization by X-ray Diffraction and X-ray Absorption, the Mn promoter is present mainly in the form of MnO and MnCO₃ phases, with the latter undergoing convertion to MnO upon H₂ pretreatment. However, following exposure to reaction conditions, X-ray photoelectron spectroscopy suggests that higher oxidation states of Mn may be present at the surface, suggesting that the improved catalytic activity for CO₂ hydrogenation to methanol arises from a synergy between MoS₂ and MnO_x at the catalyst surface.