Catalytic Performance Of Low Dimensional Boron Nitride Materials:A Density Functional Theory Study

In recent years,low dimensional nanomaterials represented by low-dimensional boron nitride have received extensive attention from researchers due to their unique physical and chemical properties.However,the application of boron nitride in the field of catalysis has been challenged due to its chemical inertness.Therefore,it is very important to functionalize low dimensional boron nitride materials to improve their chemical activity.In this thesis,we used the strategy of doping impurity atom or loading single metal atom to functionalize low dimensional boron nitride materials,and the catalytic performance in multiple catalytic reactions was studied through density functional theory calculations.The main research results are as follows:(1)A novel mercury-free catalyst,carbon-doped boron nitride nanotubes(BNNTs),was constructed for acetylene hydrochlorination reaction.The effect of two types of carbon doped BNNTs with different diameters(boron substituted and nitride substituted with carbon)on catalytic performance were studied in detail.Results show the adsorption of C₂H₂ on carbon doped BNNTs is dominant in the adsorption process due to the stronger interaction of C₂H₂ with carbon-doped BNNTs.During the adsorption process,HCl can be dissociated on carbon-doped BNNTs with small diameter.The C₂H₂ is chemically adsorbed on the doped impurity C atom and is activated to continue the addition reaction with the gaseous HCl molecule.The rate-limiting step is the splitting of HCl molecule and the attack of H and Cl atoms on C=C bond of the activated C₂H₂.The reaction energy barrier on carbon-doped BNNTs is only 28.47 kcal/mol,indicating the reaction is easy to proceed.The doping site and curvature have a slight impact on the catalytic performance in the reaction based on the comparison of energy barrier.The study reveals that the doped impurity C atom can largely improve the activity of BNNTs,and carbon-doped BNNTs can be an effective non-metal catalyst in the acetylene hydrochlorination reaction.(2)Single atom catalysts(SACS)supported on defective boron nitride nanotube(BNNT)were constructed for the catalytic reaction of N₂O+CO.The adsorption strength of reactant and product on catalyst show that Cr single atom can avoid catalyst poisoning among five low-price transition metal atoms(Ti,Cr,Mn,Fe,and Co).The stepwise mechanism was considered which reveals the reaction path involves N₂O decomposition,CO oxidation and CO₂ desorption.The rate-limiting step is CO₂desorption with the desorption barrier of 0.42 e V.Along the reaction path,optimized structures and electronic property analyses indicate Cr atom acts as bridge to transfer electron because its 3d orbital is not full,which plays an important role in activation of N₂O and CO molecules.Meanwhile,chemical inert BNNT support acts as electron reservoir,withdrawing or donating electron,to facilitate the whole reaction.Therefore,Cr/BNNT is proposed to be a promising and highly efficient catalyst for eliminating environmentally unfriendly N₂O and CO gas simultaneously.(3)An efficient bifunctional single atom electrocatalyst was designed to electrocatalyze the overall water splitting.The catalytic activity of single transition metal(TM)atom suppported on defective boron nitride nanoribbon(TMN₄-BNNR,TM=Cr,Mn,Fe,Co,Mo,Ru and Rh)were systematically investigated for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).Our computation demonstrated that all TM atoms can bind strongly with uncoordinated four N atoms on N-doped defective BNNR.Furthermore,Fe N₄-BNNR and Rh N₄-BNNR are screened as the highest catalytic activity catalysts for both HER and OER from these TMN₄-BNNRs,with the low HER/OER overpotential being 0.07/0.52 V and 0.18/0.27 V.The activity of TMN₄-BNNR is constrained by the binding strength toward intermediates and depends on the electron-donating ability and d band center of catalyst.This work proposes a cost-effective and high-performance single atom catalyst for water electrochemical splitting.