DFT-based KMC Modeling:NO-CO Reaction On Rh Catalyst

The reaction between NO and CO over Rh catalyst is of high current interest for both applied and fundamental chemistry.On the one hand,it is one of the key reactions taking place in the automobile-exhaust aftertreatment.A thorough knowledge of its kinetics may be helpful in op-timizing the design of existing automotive catalytic converters and producing more efficient but economical next-generation catalysts.On the other hand,this reaction system contains a control-lable number of elementary steps.It can be treated as a prototypical heterogeneous catalytic reaction to develop kinetic-modeling approaches.Meanwhile,in the field of microkinetic modeling for heterogeneous catalysis,the density-functional-theory(DFT)-based kinetic Monte Carlo(kMC)method has formed a quite fast-growing area of research in recent years.DFT calculations are employed at the atomic level to determine the reaction mechanism and obtain the corresponding energy evolution.Combined with transition-state theory,the kinetic parameters such as rate constants for the elementary steps can be predicted with reasonable accuracy.Subsequent kMC simulations integrate these static information to evaluate the kinetic evolution of the reaction system,providing more insights into it from a statistical point of view.Up to now,this method has been successfully applied to relatively simple heterogeneous catalytic reaction systems,but there are still many problems to be overcome when considering the extension to more sophisticated ones.Considering the aforementioned backgrounds,the DFT-based kMC modeling for the NO-CO reaction system on Rh(100)and Rh(111)surfaces was carried out in this thesis.First,we systemati-cally studied the detailed mechanism of the reaction system through DFT calculations.The specific elementary pathways for a variety of reaction processes were revealed.These processes include the surface diffusion of N,O,NO,and CO,the dissociation of NO,the formation of N2,the formation of CO2,the formation,transformation,desorption,and dissociation of N2O,the formation of O2,the formation of NO2,and the direct reaction between NO and CO.Second,we proposed an augmented pairwise additive interaction model to determine the lateral interaction energy of any adsorbate con-figuration efficiently and accurately.The parameters used in the particular model developed for the targeted reaction system were then collected based on DFT calculations.Third,in order to quantify the dependence of activation energy upon the variation of lateral interaction energy,the extended Bronsted-Evans-Polanyi relation was fitted for each reaction step in the reaction system based on DFT calculations and the constructed lateral-interaction-calculation model.Finally,on the basis of the information obtained above,we accomplished the kMC modeling for the targeted reaction sys-tem.In consideration of the characteristics of this reaction system,the kMC model was separated into two parts:one for the complicated reaction processes involving N2O,the other for the whole catalytic cycle of the NO-CO reaction system.Through the simulations based on the constructed kMC model,we tentatively investigated the steady-state kinetic properties of the NO-CO reaction system on Rh(100)and Rh(111)surfaces under a diversity of physical environments.These properties include average coverages of all kinds of adsorbates,characteristic adsorbate configurations,turnover frequencies of all kinds of products,the selectivity for N-contained products,and the selectivity for N2-formation pathways.Through the comparison analysis,some enlightening insights were acquired for the kinetic performance of the reaction system.Prospectively,the kMC model constructed here may be used to detailedly investigate the ki-netic properties of the NO-CO reaction system on Rh(100)and Rh(111)surfaces,which may further assist the design and optimization of practical catalytic converters.Meanwhile,some treatments we applied here in the DFT-based kMC-model-construction procedure may also be instructive to the kMC modeling for other heterogeneous catalytic reaction systems.