Shale and other natural gas sources can be acidic, containing varying amounts of CO
2 and H
2S. The removal of these acidic components requires expensive chemical treatment though the problem of CO
2 disposal remains. Alternatively, a catalytic process based on a sulfur tolerant catalyst, like MoS
2,
1 can be capable of hydrogenating CO
2 in the presence of H
2S. The work
1 suggests the heterogeneity of edge sites as established via a Boltzmann distribution, thereby indicating that active sites evolve as a function of reaction condition, i.e. it could either be coordinative unsaturated sites (CUS), a Mo-O pair, brim sites and/or the undercoordinated Mo-S pair under different regimes of H
2, H
2S and H
2O partial pressures. With the help of electronic structure calculations, we elucidate the mechanism of reverse water gas shift chemistry on the plausible active sites. Specifically, the two catalytically active regions
on MoS
2, the Mo-edge and S-edge are considered in this study. Our results suggest the importance of coordinative unsaturation (CUS) on Mo-edge and Mo-S pair on S-edge, which supports the redox over the associative mechanism, consistent with transient kinetic experiments,
1 for reverse water gas shift chemistry in the absence of H
2S. Furthermore, in presence of H
2S, our results suggest a H
2S mediated mechanism through which we explore the feasibility of CO production versus the production of COS, which supports the experimental evidence suggesting that H
2S can either behave like a co-catalyst or co-reactant under the presence of H
2S (>60 ppm).
1
The details of our calculations and models, the likely reaction mechanism, and supporting experimental evidence will be presented and discussed.
References
[1] âInhibitor, co-catalyst, or co-reactant? Probing the different roles of H2S during CO2 hydrogenation on MoS2 catalystâ, Lohit Sharma, Ronak Upadhyay, Srinivas Rangarajan, Jonas Baltrusaitis*, submitted.
