A DFT Investigation Of Adsorption And Decomposition Of H₂O And CO₂ On Pt Alloy Cluster Model

In this paper,the adsorption and dissociation of H₂O,CO₂ on the surface of Pt and Pt alloys have been investigated by DFT method.Simultaneously,the comparison study of CO oxidation on different slab model surfaces has been performed.After comprehensively calculating the adsorption structure,the stable adsorption position,the adsorption energy,the TS structure and the reaction activation energy of the adsorbed species,the following conclusions were obtained:1.By comparing the adsorption energy of adsorbed species on the Pt and Pt alloys cluster,we found that the displacement position and the number of atoms in the model are the main factors that affect the stability of the model and the adsorption intensity.The alloy cluster with a replacement atom at subsurface is the most stable,and the size of the cluster and the number of atoms are still consistent with this rule.The different replacement of Pt-X?X=Cu,Fe,Co,Ni?alloy cluster have obvious influence to adsorption of H,O,CO,OH.When the mixed atom X at subsurface in alloy model,the adsorption of OH and CO on the alloy cluster model is the strongest,and the adsorption on the alloy clusters is the weakest for the adsorption of O and H.2.The decomposition energies of CO₂ and H₂O on the different clusters of Pt and their alloys were studied.By comparing activation energy of molecule on different cluster,the different replacement site have obvious influence to activation energy of react.The activation energy on the alloy cluster model with a replacement atom at subsurface is bigger than that of Pt cluster.3.By comparing the adsorption energy of adsorption species on the slab and cluster model,the adsorption on the surface of the cluster model is more strong than the surface of the slab model.We studied CO oxidation on the Pt-Ni bimetallic catalysts(including Pt?111?,Pt/Ni/Pt?111?,Ni/Pt?111?,NiO_1-x/Pt?111?and Ni O_1-x/Pt/Ni/Pt?111?)by using the density functional theory calculations in this work.We have found that at the lower oxygen coverage,CO oxidation reaction would process with a higher reaction barrier due to its reaction channel via the Langmuir-Hinshelwood mechanism;when at higher oxygen coverage?at metallic catalysis?or in the presence of molecular oxygen(on NiO_1-x-x systems),CO oxidation reaction would take place with a lower barrier via the Eley-Rideal mechanism.The calculation results show that the reactivity of CO oxidation follows the order:Pt?111?<Pt/Ni/Pt?111?<Ni/Pt?111??1MLoxygen?<NiO_1-x/Pt?111?<Ni O_1-x/Pt/Ni/Pt?111?,which is in general agreement with the experimental observations.