Bridge sulfur vacancies in MoS_2 catalyst for reverse water gas shift: A first-principles study

摘要

Vacancies, typically exist in various types and morphologies on the surfaces of transition metal compound catalysts, have been shown to play an important role in many catalytic reactions. However, identifying the optimal type and morphology of vacancy and the key factors that control its performance remains a significant challenge. By density functional theory calculations and microkinetic modeling, we show that compared to various threefold S vacancy morphologies on the basal plane, the lower coordination number at the bridge S vacancy of Mo edge on MoS2 tunes the relative adsorption strength of key intermediates (such as O relative to OH). This not only increases CO2 hydrogenation rate by 7-11 orders of magnitude, but also leads to clearly distinct mechanism (associative & redox). The large destabilization of O and low H coverage on the Mo edge also hinder C-O scission and hydrogenation (give CH4 and CH3OH) relative to CO desorption, leading to almost 100% CO selectivity. The inexpensive MoS2 catalyst provides an alternative to the traditional noble metal catalysts for reverse water gas shift, and the coordination number of vacancy modulated catalytic performance illustrates a promising way to design transition metal compound catalysts for other important reactions of technological interest.