First-Principles Study Of H₂S Adsorption And Dissociation On Rhodium And Nickel Surfaces

First-principles based on density functional theory(DFT)have been employed to extensively study the mechanism of adsorption and dissociation of small molecules on transition metal surfaces,owing to a key part of the heterogeneous catalysis.The rhodium and Rh-based catalysts as well as nickel and Ni-based catalysts play an important role in numerous fields,i.e.hydrogenation,hydrodesulfurization and hydrodenitrogenation of hydrocarbons,hydrogen evolution reaction,Fischer-Tropsch synthesis,petroleum refinery and water gas shift etc.However,these catalysts are highly susceptible to corrosion and deactivated rapidly by hydrogen sulfide and sulfur dioxide.Therefore,it is very significant to investigate the effect of small molecules such as H2S,HS,S and H on Rh and Ni surfaces which shows immense research interest and applications.The adsorption and dissociation of H2S on Rh(100),Rh(110),perfect Ni(110)and sulfur covered Ni(110)have been investigated by using self-consistent periodic density functional theory.In this study,we have calculated and analyzed all the significant values and parameters such as adsorption energy,structural parameters,and vibrational frequencies of adsorbed H2S.Furthermore,we also elucidated and mapped out all the possible dehydrogenation pathways and barrier energies of the adsorbed H2S and SH monomers over these surfaces.Primarily,we investigated the adsorption and dissociation of H2S on Rh(100)surface by first-principles method.It is found that H2S is weakly adsorbed on bridge,top and hollow sites with their adsorption energies of-0.98,-0.86 and-0.82 eV,respectively.In contrast to H2S,HS is strongly chemisorbed on Rh(100)surface at hollow site with the adsorption energies of-4.33 eV,whereas S and H prefered to be absorbed at hollow site.By using CI-NEB method,we found the four most feasible paths for H2S dissociation on Rh(100),with energy barrirers of 0.19 eV,0.25 eV,44 meV and 98 meV,respectively.The energy barrier to break the S-H bond of HS with H co-adsorption or without H co-adsorption was almost the same low.This study reveals that H2S decomposition on Rh(100)surface is a facile process both kinetically and thermodynamically.Secondly,we systematically studied the adsorption and dissociation of H2S over Rh(110)surface via first-principles based on DFT method.For adsorption mechanisms,we probe the sites preference and is determined that H2S vigorously adsorbed over high symmetry adsorption sites with preferred long-bridge(LB)site having adsorption energy-1.00 eV.Also we found that HS chemisorption is higher as compared to H2S on Rh(110)surface having-3.76 eV adsorption energy,where atomic S and H binding at hollow and short-bridge site is more stronger.The energy barriers to split the bond of S-H in first and second H2S dehydrogenation are 0.18-0.36 and 0.30 eV.To further investigate,electronic density of state are employed to illustrate the interaction of adsorbed H2S with the surface of Rh(110).Hence,our calculated results confirm that H2S dissociation over Rh(110)surface is exothermic as well as an easy process.Finally,we investigated the H2S adsorption and its dissociation on perfect and sulfur covered Ni(110)surface.On both surfaces,we probe the site preference for H2S,HS,H and S adsorption,and found that H2S is energetically adsorbed on their high symmetry adsorption sites with the preferred short-bridge(SB)site on both surfaces.Furthermore,we found that chemisorption of HS is more stronger in contrast to H2S at favourable short-bridge(SB)with binding energy of-3.59 eV on perfect Ni(110)surface,and on S-covered Ni(110)surface at favourable hollow site having binding energy of-3.57 eV.In first H2S dehydrogenation,energy barriers for S-H bond breaking over clean surface are 0.08-0.46 eV and little bit higher on S-covered surface are 0.1-0.78 eV,while in second dehydrogenation the energy barriers on clean surface is 0.19 eV.For further detail,electronic density of state are used to characterize the interaction of adsorbed H2S with both surfaces.Hence,our results show that decomposition of H2S over perfect and sulfur covered Ni(110)surfaces is exothermic and also an easy process,however kinetically and thermodynamically the subsistence of surface sulfure avoid the H-S bond breaking process.