基于密度泛函理论下H_(2)S在单原子催化剂V/Ti_(2)CO_(2)上的分解机理研究

DFT Study of the Decomposition Mechanism of H_(2)S on V-Decorated Ti_(2)CO_(2) Single-Atom Catalyst

解析工业脱硫气中硫化氢与催化剂的相互作用机制及其分解机理对于开发处理H_(2)S气体的催化剂具有重要意义。本研究采用密度泛函理论计算方法研究了H_(2)S分子在单原子催化剂(SACs,Ti和V原子负载的单层MXene-Ti_(2)CO_(2))表面上的吸附和催化解离行为。分波态密度(PDOS)、电荷分析以及差分电荷密度的结果表明:单原子Ti和V的负载导致了Ti_(2)CO_(2)表面上的电荷进行重新分配,并且显著改善了H_(2)S分子与Ti_(2)CO_(2)之间的相互作用,从而提高SACs的催化活性。为了深入理解硫化氢分子的催化处理过程及其分解机理(H_(2)S→HS^(*)+H^(*)→H2+S^(*)),本研究对硫化氢分子在Ti/Ti_(2)CO_(2)和V/Ti_(2)CO_(2)表面上的分解反应路径进行了对比分析。结果表明:硫化氢分子在被Ti和V负载的Ti_(2)CO_(2)表面上都能够自动解离形成-HS基团和一个质子(HS^(*)/H^(*)),而且在V负载的Ti_(2)CO_(2)的SACs上,整条路径的速率限制步骤所要跨越的能垒低至0.28 eV,该结果表明H_(2)S分子可在室温下能容易地被单原子催化剂V/Ti_(2)CO_(2)解离成H2分子和S原子,而且S原子能够在该催化剂表面团聚形成稳定的单质硫,从而完成催化循环。此外,使用该SACs催化剂分解H_(2)S,相比于已经报道过的其它体系的催化剂,无论是在可持续经济角度还是处理能力方面都有较好的应用前景。综上所述,我们发现V负载的Ti_(2)CO_(2)催化剂能够高效催化分解硫化氢气体。

In-depth understanding of the mechanisms of hydrogen sulfide(H_(2)S)adsorption on catalysts during desulfurization from industrial waste gas streams is important for developing effective catalysts to be used in the decomposition of H_(2)S.In this work,the dissociation behavior of H_(2)S adsorbed on a single-atom catalyst(Ti or V-decorated Ti_(2)CO_(2) 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 Ti_(2)CO_(2) 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 Ti_(2)CO_(2) surface and significantly improved the interaction between the H_(2)S gas molecules and Ti_(2)CO_(2),thereby enhancing the catalytic activity of V/Ti_(2)CO_(2).In order to gain a deeper understanding of the mechanism of H_(2)S decomposition(H_(2)S→HS^(*)+H^(*)→H2+S^(*)),a comparative analysis of the results for the decomposition of H_(2)S on the Ti/Ti_(2)CO_(2) and V/Ti_(2)CO_(2) surfaces was carried out.The catalytic dissociation behavior of H_(2)S is explained as follows:once H_(2)S is adsorbed on the V/Ti_(2)CO_(2) or Ti/Ti_(2)CO_(2) 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/Ti_(2)CO_(2) surface with an energy barrier of 0.86 eV,while that for V/Ti_(2)CO_(2) was 0.28 eV,indicating that the H_(2)S molecules easily dissociated into S and H2 on the V/Ti_(2)CO_(2) surface at room temperature.The reaction time for H_(2)S decomposition on the V/Ti_(2)CO_(2) 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 H_(2)S on the V-doped Ti_(2)CO_(2) surface is associated very fast kinetics.Furthermore,the S atoms can form elemental sulfur with aggregation on the V/Ti_(2)CO_(2) surface to promote recycling reactions.Compared with previously reported catalytic systems,the single-atom catalyst(SAC)V/Ti_(2)CO_(2) catalyst has greater application prospects in terms of sustainable economy or removal efficiency for H_(2)S treatment.Our results suggest that V-doped Ti_(2)CO_(2) is an excellent candidate for a highly effective non-noble metal catalyst applicable to H_(2)S decomposition.