(560bo) DFT Investigation of the Mechanism and Site Requirements for Reverse Water Gas Shift on Transition Metal Sulfides
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Poster Session: Catalysis and Reaction Engineering (CRE) Division
Wednesday, November 13, 2019 - 3:30pm to 5:00pm
Shale and other natural gas sources can be acidic, containing varying amounts of CO2 and H2S. The removal of these acidic components requires expensive chemical treatment though the problem of CO2 disposal remains. Alternatively, a catalytic process based on a sulfur tolerant catalyst, like MoS2,1 can be capable of hydrogenating CO2 in the presence of H2S. The work1 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 H2, H2S and H2O 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 regionson MoS2, 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 H2S. Furthermore, in presence of H2S, our results suggest a H2S mediated mechanism through which we explore the feasibility of CO production versus the production of COS, which supports the experimental evidence suggesting that H2S can either behave like a co-catalyst or co-reactant under the presence of H2S (>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.