Inhibitor, Co-Catalyst, or Co-Reactant? Probing the Different Roles of H2S during CO2 Hydrogenation on the MoS2 Catalyst

Highly stable Fe/CeO2 catalyst for the reverse water gas shift reaction in the presence of H2S

This study focused on evaluating the catalytic properties for the reverse water gas shift reaction (RWGS: CO₂ + H₂ → CO + H₂O ΔH ⁰ = 42.1 kJ mol^-1) in the presence of hydrogen sulfide (H₂S) over a Fe/CeO₂ catalyst, commercial Cu-Zn catalyst for the WGS reaction (MDC-7), and Co-Mo catalyst for hydrocarbon desulfurization. The Fe/CeO₂ catalyst exhibited a relatively high catalytic activity to RWGS, compared to the commercial MDC-7 and Co-Mo catalysts. In addition, the Fe/CeO₂ catalyst showed stable performance in the RWGS environment that contained high concentrations of H₂S. The role of co-feeding H₂S was investigated over the Fe/CeO₂ catalyst by the temperature programmed reaction (TPR) of CO₂ and H₂ in the presence of H₂S. The result of TPR indicated that the co-feeding H₂S might enhance RWGS performance due to H₂S acting as the hydrogen source to reduce CO₂.

Hydrogenation of CO2 Promoted by Silicon-Activated H2S: Origin and Implications

Unlike the usual method of CO_x (x = 1, 2) hydrogenation using H₂ directly, H₂S and HSiSH (silicon-activated H₂S) were selected as alternative hydrogen sources in this study for the CO_x hydrogenation reactions. Our results suggest that it is kinetically infeasible for hydrogen in the form of H₂S to transfer to CO_x at low temperatures. However, when HSiSH is employed instead, the title reaction can be achieved. For this approach, the activation of CO₂ is initiated by its interaction with the HSiSH molecule, a reactive species with both a hydridic H^δ− and protonic H^δ+. These active hydrogens are responsible for the successive C-end and O-end activations of CO₂ and hence the final product (HCOOH). This finding represents a good example of an indirect hydrogen source used in CO₂ hydrogenation through reactivity tuned by silicon incorporation, and thus the underlying mechanism will be valuable for the design of similar reactions.

Site-dependent reactivity of MoS2 nanoparticles in hydrodesulfurization of thiophene

The catalytically active site for the removal of S from organosulfur compounds in catalytic hydrodesulfurization has been attributed to a generic site at an S-vacancy on the edge of MoS2 particles. However, steric constraints in adsorption and variations in S-coordination means that not all S-vacancy sites should be considered equally active. Here, we use a combination of atom-resolved scanning probe microscopy and density functional theory to reveal how the generation of S-vacancies within MoS2 nanoparticles and the subsequent adsorption of thiophene (C4H4S) depends strongly on the location on the edge of MoS2. Thiophene adsorbs directly at open corner vacancy sites, however, we find that its adsorption at S-vacancy sites away from the MoS2 particle corners leads to an activated and concerted displacement of neighboring edge S. This mechanism allows the reactant to self-generate a double CUS site that reduces steric effects in more constrained sites along the edge.