The Dissociation Process Of Ethane On Pt(111):A Density Functional Theory Study

As one of the important catalysts in the chemical industry,platinum-based catalysts have been the focus of researchers at home and abroad.The dissociation process of ethane in an anaerobic environment is often used as a probe reaction to explore the catalytic performance of the catalyst.According to the literature,Pt（111）surface is one of the main active surfaces of platinum catalyst,which may be the catalytic active center of platinum catalyst.Therefore,based on the DFT theory,the paper studies the dissociation process of ethane on Pt（111）by using GGA-PW91 functional,slab periodic model and microscopic surface dynamics.Firstly,based on the optimized Pt（111）model,this paper focuses on the adsorption properties of 15 intermediates involved in the dissociation of ethane in Pt（111）surface,adsorption configuration and geometry of intermediates.The results showed that:the bond length of the C-Pt bond in the molecular adsorption configuration adsorbed at the top site is longer than the bond of the C-Pt bond in the molecular adsorption configuration adsorbed at the bri and fcc sites.The adsorption configuration of C,CH,and CH₃C on Pt（111）is relatively stable,and the physical adsorption of Pt（111）on CH₃CH₃ and CH₄ molecules is relatively easy to desorption reaction.During the adsorption process,the C-C bond of most C₂ species will be elongated,and other intermediate molecules or atoms themselves and catalyst substrates will not change much before and after adsorption.Secondly,this paper conducts a detailed theoretical study on 29 elementary reactions.A comparative discussion is made in combination with thermodynamic and kinetic properties.The main conclusions are:in the 29 elementary reactions involved in the dissociation of ethane on the surface of Pt（111）,CH₂CH₂*+*→2CH₂*,CHCH*→CHCH+*,CH₃C*+*→CH₃*+C*and CH₂C*+*→CH₂*+C*reactions are basically not thermodynamically.For CH₃CH₃,the Pt（111）surface is more prone to C-H bond cleavage,not C-C bond cleavage.For three parallel reactions with the intermediate CH₂CH₃ as the reactant,CH₂CH₃ is preferentially selected to form CH₂CH₂.The intermediate CH₃CH also has two decomposition modes on the surface of Pt（111）:the cleavage of C-H bond and the cleavage of C-C bond.In terms of kinetics,CH₃CH preferentially selects C-C bond cleavage.Ethylene continues to decompose on the surface of Pt（111）,and it is more prone to form intermediate CH₂CH than C-C bond cleavage.Similarly,in the kinetics,the intermediate CH₂CH preferentially generates CH₂C;the intermediate CH₃C preferentially generates CH₂C.For CHCH,the probability of C-C bond cleavage on Pt（111）is greater than that of C-H bond cleavage.Intermediate CH₂C is more prone to CHC on Pt（111）surface.Thermodynamically,there is no acetylene in the dissociation product of ethane on Pt（111）,only ethylene and methane.Finally,this paper quantitatively analyzes and discusses the dissociation of ethane on Pt（111）by microscopic surface dynamics.The results show that ethylene reacts on Pt（111）to form ethylene:the dehydrogenation of ethane produces ethyl（CH₃CH₂）,and the ethyl group continues to catalytically dehydrogenate until CH₂C is formed,followed by CH₂C to form CH₂CH₂.The reaction mechanism of ethane cracking on Pt（111）to form methane is that after dehydrogenation of ethane to CH₃CH,intermediate CH₃CH is cleaved to form C₁species,and then C₁ species is combined to form methane.More importantly,in the reaction environment of H₂,the product formed by the surface catalysis of Pt（111）is mainly methane,and the second is ethylene.Under the reaction conditions,CHCH can hardly be formed.