Mn-promoted MoS catalysts for CO hydrogenation: enhanced methanol selectivity due to MoS/MnO interfaces.

Considering the alarming scenario of climate change, CO hydrogenation to methanol is considered a key process for phasing out fossil fuels by means of CO utilization. In this context, MoS 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 MoS prepared by a hydrothermal method presents considerable selectivity for CO hydrogenation to methanol in comparison with pure MoS 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 CO hydrogenation to methanol. After optimization of synthesis parameters, a methanol selectivity of 64% is achieved at a CO 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 MnCO phases, with the latter undergoing convertion to MnO upon H 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 CO hydrogenation to methanol arises from a synergy between MoS and MnO at the catalyst surface.