DFT Study of the Decomposition Mechanism of H2S on V-Decorated Ti2CO2 Single-Atom Catalyst

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* -> H-2 + 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 H-2 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.