Research On Single-atom Catalytic Mechanisms In C-B-N Low-dimensional Materials

In the thesis,based on density functional theory（DFT）calculations with Nudged Elastic Band Method（NEB）,we investigate the catalytic ability and mechanism of B-doped,N-doped,and B-N co-doped fullerenes at different doping concentration from first-principles perspective.The first part of this thesis is about mono-atomic catalysis,where we focus on the adsorption of small molecules and CO oxidization process of single B or N doped fullerenes.The undoped fullerene shows weak physical adsorption of O₂ molecules,with a high barrier heitght of 1.53 eV,indicating it is in an inert state.After doping with single B or N atom,the adsorption of O₂ molecule is strengthened.Our calculations show that both C₅₉B and C₅₉N can assist the oxidization of CO.In the case of C₅₉B,a more stable oxide catalysis C₅₉BO₃can be formed via the CO oxidization or O₂ decomposition processes in the early stages of catalytic reactions.The highest energy barrier for C₅₉BO₃ is estimated to be 0.59 eV,showing good catalytic property.Similar to that of C₅₉B,C₅₉N can be oxidized to form C₅₉NO too.However,the CO protect C₅₉N against oxidization.Thus,under a CO-rich condition,C₅₉N can finish the whole catalytic cycle,with a rate-determining barrier of 0.44 eV.If the CO suppy is insufficient,C₅₉N will be oxidized to form C₅₉NO,where the highest barrier for CO oxidization is increased to 0.80 eV.These oxides formed during the reaction can serve as durable,highly efficient catalysts for CO oxidization cycles,which will be investigated in future works.In the second part,we investigate the catalytic behaviors of B,N doped fullerenes with different concentrations,e.g.,2 and 12 B or N atoms are doped into fullerenes respectively..Our calculations show that the doping atoms tend to disperse in the fullerene.For example,in the most stable configuration for 2-B（N）-atom-doped C_60,the 2 doping atoms occupy the opposite positions in a C₆ ring.After checking the catalytic properties of C₅₈B₂,C₅₈N₂,C₄₈B₁₂,C₄₈N₁₂,we find that their catalytic abilities are comparable to that of single-atom-doped C₆₀.Moreover,after a few initial reaction cycles,the above doped fullerences would be oxidized to form corresponding oxides,which dominates the following CO oxidization process.The calculated rate-determining barrier is close to that of single-atom-doped C₆₀.No obvious synergetic effects were found in multi B（N）doped C₆₀.In the third part of the thesis,we study the B-N co-doped C60.Three kinds of doping strategies,namely B-N equal concentration,B-rich,N-rich dopings are applied.Four different structures,C₅₆B₃N,C₅₆BN₃,C₅₈BN,C₅₄B₃N₃ are chosen to investigate the effects of different doping concentration and configuration on catalytic properties.Our calculations show that B and N tend to cluster when co-doped into C₆₀.Both B-rich C₅₆B₃N and N-rich C₅₆BN₃ show good catalytic abilities.In the catalytic progress for CO oxidization,C₅₆B₃N can be oxidized at the initial stage.Interestingly,the produced fullerence oxidization will serve as new catalyst for CO oxidization,with a rate-determining barrier of 0.42 eV.In C₅₆BN₃,however,the central B atom is protected by the surrounding N atoms from being oxidized.This stability against oxidization makes this system a durable,recyclable catalyst,with a rate-determining barrier of 0.63 eV.In the investigation of equal concentration doping,two systems,C₅₈BN and C₅₄B₃N₃ are involved.Both C₅₈BN and C₅₄B₃N₃ can chemically adsorb O₂ and CO molecules and can be further oxidized to form new catalysts,with rate-determining barrier of0.42 and 0.44 eV,respectively.However,the oxidization energy barrier is 1.60 eV for C₅₄B₃N₃,indicating that C₅₄B₃N₃ itself is a good catalyst for CO oxidization.In this case,the rate-determining barrier is 0.84 eV.