Density Functional Theory Study On Reaction Activity Of The Late Transition Bimetallic(Ni?Pd?Pt)surfaces

The studies of the interaction of small molecules with the transition bimetallic catalyst surfaces are important topics in the domain of many sciences,such as in catalyze,corrosion,environmental protection,chemical defense and electrochemistry areas,etc.Since there are the ensemble,ligand and strain effects in the bimetallic catalysts,it leads that the activity,selectivity and the stability.of the bimetallic catalysts are improved to some extent.Theoretically,it is helpful for us to study the adsorption and dissociation properties of small molecules on the bimetallic catalysts surfaces,which can help us to understand the bonding mechanism,electronic structure and reaction path.In this paper,we have studied the adsorption and dissociation properties of H2S,HCN and CH₄ molecules on the late transition bimetallic surfaces?Ni?Pd and Pt?by density functional method.The calculation results show that:1.The calculated adsorption energies of H2S on Ni/Pd?111?single and bimetallic surfaces follow an order of Ni-Pd-Ni?111?>Pd-Ni?111?>Ni?111?>Pd?111?>Pd-Ni-Pd?111?>Ni-Pd?111?.The introducing Pd atoms on Ni?111?can enhance the binding strength between H2S and the surface,while a reverse effect is achieved when the Ni monolayer is formed on Pd?111?surface.Two elementary steps are found for all Ni/Pd?111?metal surfaces,and the breaking of H2S into HS and H is the rate-determining step.Our calculated results indicate that such breaking of H-S bond only needs to overcome a small energy barriers?<0.4 eV?.Additionally,it is worth noting that the Ni-Pd?111?surface is a special case,in which the energy barrier of TS1?0.31 eV?is larger than the corresponding binding energy of H2S molecule?0.21 eV?.This result suggests that on the Ni-Pd?111?surface,H2S tends to be desorbed before decomposing reaction is happened.Therefore,the Ni-Pd?111?bimetallic surface will exhibit the best resistance to sulfur.2.HCN is preferentially tilted with the CN bond parallel to the Ni/Pt?111?single and bimetallic surfaces.The adsorption energy of the most stable HCN adsorption geometry decreased in the order:4Ni@Pt?111?>3Ni@Pt?111?>Ni?111??2Ni@Pt?111?>1Ni@Pt?111?>Pt?111?,indicating that the introduction of Ni to the Pt catalyst could increase the activity of the bimetallic catalyst.After the adsorption of HCN molecule on each metal surafce,the linear structure changes into bent structure.The C and N atoms are transformed into SP2 hybrids by the SP hybridization in gas phase molecules.The charge transfer from metal surfaces to the 2?*antibonding orbital,resulting in the C-N and C-H bond length are increased to some extent compared to gas phase molecule,and the vibrational frequencies red shifted.3.CH₄ molecules on the single metal Ni?111?and Rh?111?are more inclined to adsorb on the top position,while prefer to adsorb on the three-fold hcp site on the 4Rh@Ni?111?bimetallic surface.For CH₄ molecules,the CH cleavage reaction is the rate-determining step in the whole decomposition reactions,and the corresponding energy barrier on 4Rh@Ni?111?bimetallic surface is the highest,its value is 1.57eV.It indicated that CH₄ molecules on 4Rh/Ni?111?bimetallic surface is more difficult to crack into C atoms and interacted with surface metal atoms,4Rh@Ni?111?bimetallic surface performs the strongest ability to resist carbon poisoning compared with Ni?111?and Rh?111?surfaces.