Abstract:

In-depth understanding of the mechanisms of hydrogen sulfide (H₂S) adsorption on catalysts during desulfurization from industrial waste gas streams is important for developing effective catalysts to be used in the decomposition of H₂S. In this work, the dissociation behavior of H₂S adsorbed on a single-atom catalyst (Ti or V-decorated Ti₂CO₂ surface) was investigated by performing density functional theory (DFT) calculations. The corresponding diffusion behavior revealed that Ti or V atoms could be dispersed on the Ti₂CO₂ monolayer, without aggregation in the form of single atoms. In addition, analyses of the partial density of states (PDOS), Hirshfeld charges, and electron density difference indicated that the decorated Ti or V atoms led to charge redistribution on the Ti₂CO₂ surface and significantly improved the interaction between the H₂S gas molecules and Ti₂CO₂, thereby enhancing the catalytic activity of V/Ti₂CO₂. In order to gain a deeper understanding of the mechanism of H₂S decomposition (H₂S → HS* + H* → H₂ + S*), a comparative analysis of the results for the decomposition of H₂S on the Ti/Ti₂CO₂ and V/Ti₂CO₂ surfaces was carried out. The catalytic dissociation behavior of H₂S is explained as follows: once H₂S is adsorbed on the V/Ti₂CO₂ or Ti/Ti₂CO₂ surface, it spontaneously dissociates into HS*/H* without any energy barrier on the catalyst surface. Subsequently, the V atoms would not only promote the cleavage of the H-S bond, but also play a major role in the formation of S atoms. Moreover, the rate-limiting step for the entire process proceeded on the Ti/Ti₂CO₂ surface with an energy barrier of 0.86 eV, while that for V/Ti₂CO₂ was 0.28 eV, indicating that the H₂S molecules easily dissociated into S and H₂ on the V/Ti₂CO₂ surface at room temperature. The reaction time for H₂S decomposition on the V/Ti₂CO₂ surface at 500 K was 65.79 ns, which was almost two orders of magnitude higher than that at room temperature. Thus, the decomposition of H₂S on the V-doped Ti₂CO₂ surface is associated very fast kinetics. Furthermore, the S atoms can form elemental sulfur with aggregation on the V/Ti₂CO₂ surface to promote recycling reactions. Compared with previously reported catalytic systems, the single-atom catalyst (SAC) V/Ti₂CO₂ catalyst has greater application prospects in terms of sustainable economy or removal efficiency for H₂S treatment. Our results suggest that V-doped Ti₂CO₂ is an excellent candidate for a highly effective non-noble metal catalyst applicable to H₂S decomposition.

Key words: MXene, SACs, H₂S dissocoation, Ti₂CO₂, DFT