Synergistic effect and coordination environment tuned water-gas shift reaction on MoS2 catalyst

Abstract

Molybdenum disulphide (MoS₂) has received increased interest as a potential S-tolerant catalyst for the water-gas shift (WGS) reaction, which is widely used in hydrogen production from fossil fuels. Edges and S vacancies or the transition metal modified (001) basal plane of MoS₂ catalysts have been identified as the active sites for various reactions. Differentiating unbiasedly among the intrinsic reactivity of various edge sites and modified in-plane sites is crucial to identify the active sites for WGS on MoS₂. Using density functional theory calculations and microkinetic modeling, we show that compared to S vacancy modified MoS₂(001) (MoS_2−v(001)), weakened O binding and enhanced WGS activities are obtained on Cu-doped MoS_2−v(001) (Cu/MoS_2−v(001)) and MoS₂ edges. The CO conversion rate follows the order S edge > Mo edge > Cu/MoS_2−v(001) > MoS_2−v(001) at 450–630 K, 1 bar and H₂O/CO ratio of 1, suggesting that S edges are the likely active sites. Only CO₂ is formed on Cu/MoS_2−v(001) and Mo edges, while small amounts of CH₄ are also formed on S edges. The WGS reaction proceeds predominantly through a redox mechanism on Cu/MoS_2−v(001), in which the rate-limiting step (RLS) is CO oxidation. However, both associative and redox mechanisms prevail on Mo edges, and the RLS shifts from COOH formation to CO oxidation with increasing temperatures. On the S edge, the associative mechanism is dominant, with the RLSs of CO* and COOH* reaction with OH*. This work highlights synergistic interactions and coordination effects on MoS₂ catalysts, and the insights can be used to enrich the design principles for WGS and other reactions of technological interest.