Density Functional Theory And Experiment Study Of The Dehydrogenation Of Methane On Ni₃Fe（111）surface And O Pre-adsorption’s Influence On Carbon Deposition

In order to clarify the dehydrogenation mechanism,as well as to understand the microscopic mechanism of how the doped Fe prevent carbon deposition on the catalyst surfaces,by using density functional theory and periodic boundary model,the single adsorption,co-adsorption of CH₄ and its dissociative species on Ni₃Fe catalyst were investigated.Based on the transition states of the elementary reaction in methane sequence dissociation process,the reaction energy barrier and rate constant were obtained,which preliminarily revealed the mechanism of the dehydrogenation of methane on Ni₃Fe catalyst and the effect of doped Fe on the catalytic activity of the Ni-based catalyst.In addition,the effect of doped Fe on the carbon deposition resistance of Ni catalyst was also investigated by the pre-adsorption model of O and dry reforming reaction experiment of methane.The most stable single adsorption and co-adsorption configurations of methane and its dissociated species on Ni（111）,Fe（111）and Ni₃Fe（111）surfaces were obtained by comparing the adsorption energies.Dynamic simulation results indicated that on the above three surfaces,CH dissociation of C and H is the rate determined step,and the order of CH dissociation energy barrier is Ni（111）>Ni₃Fe（111）>Fe（111）.Based on the analysis of thermodynamics,the exothermic reaction in methane dissociation process on Ni（111）and Ni₃Fe（111）is the dissociation of CH₂,but the dissociation of CH₂ on Ni₃Fe（111）is more exothermic than that on Ni（111）.Based on the kinetic and thermodynamic calculations,the Ni₃Fe（111）surface is more beneficial to methane dissociation reaction.The effect of O species on CH and C on metal surface was explored by building O pre-adsorption surface model.Compared with O-Ni（111）,CH on O-Ni₃Fe（111）is more inclined to combine with O to transform into CHO rather than directly to dissociate into C and H.And then CHO dissociates into CO and H.Additionally,C is more likely to combine with O to form CO on the O-Ni₃Fe（111）surface.Therefore,the formation and accumulation of C species are both reduced on Ni₃Fe（111）.What’s more,the dry reforming reaction experiment of methane on Ni₃Fe catalyst shows that the conversion rate of methane is improved and the carbon deposition of the catalyst is reduced.The theoretical calculation and experimental results indicate that doped Fe can not only improve the catalytic activity of Ni catalyst for methane dissociation reaction,but also improve the resistance to carbon deposition of Ni catalyst in dry reforming reaction.