First-principles Study Of The Hydrogenation Mechanism Of Small Molecules

The conversion of small molecules into energy substances is a hot topic.It plays an irreplaceable role in many fields such as energy,chemical industry,agriculture and material synthesis.Finding a heterogeneous catalyst with high activity and selectivity is the direction of many researchers.Through the combination of experiment and theory,the feasibility of designing high-efficiency heterogeneous catalysts is very high,and the first problem is to understand the reaction mechanism involved in the catalysis process.In the experiment,limited to the experimental conditions,it is difficult to accurately detect the multiple intermediates involved in the experiment process,so the reaction mechanism is vague.Therefore,we need to use theoretical calculation to build cata-lyst models on the atomic and molecular scales,and through comparative analysis of their possible complex reaction paths,to provide theoretical support for understanding the reaction mechanism and accurately designing high-efficiency catalysts.This thesis mainly contains four chapters.First introduce the density functional theory(DFT)and the hydrogenation of small molecule,secondly introduce the work of electrochemical reduction of N2 to ammonia,and then briefly introduce the hydrogenation of CO2 to formic acid and methanol.The last chapter is a brief summary of the work have been done and the prospects.The first chapter gives a brief introduction to density functional theory(DFT).Subsequently,we introduced several exchange correlation functionals,including local spin density approximation(LSDA),generalized gradient approximation(GGA)and hybrid functionals.Then,I briefly introduced several software packages and transition state calculation methods.Finally,I introduced the reaction mechanism and research status of the hydrogenation of small molecules N2 and CO2.The second chapter introduces the theoretical research on the nitrogen reduction reaction(NRR).There are three parts here:The first part introduces the preparation and electronic structure of graphene,the preparation of N-doped graphene,and the influence of N-doped graphene on NRR.The second part is about the theoretical study of pyridine-N doped graphene supported Mo1(Cr1)as high-efficiency NRR electrocatalysts.Af-ter screening from several aspects,it is finally determined that Mo1(Cr1)/pyridine-N3-G is a high-efficiency nitrogen fixation electrocatalyst.It is finally determined that Mo1(Cr1)/pyridine-N3-G are the high-efficiency nitrogen fixation electrocatalysts.The third part is to explore the influence of the coordination environment of doped transition metal atoms on the nitrogen fixation.We replaced the pyridine-N with pyrrolic-N,and the machine learning methods are used to confirm the essential factors affecting activity and selectivity.The third chapter introduces the production of formic acid and methanol by carbon dioxide reduction reaction(CO2RR).We first introduces a work on the electrocatalytic reduction of CO2 to formic acid that cooperated with the experimental group of Zeng Jie et al.By chemically coupling indium oxide with graphene oxide,so as to achieve the purpose of synergistic catalysis of CO2 reduction to formic acid.Then we introduce a single-atom catalyst Pt1@MIL,and explores the mechanism of the hydrogenation of CO2 to methanol.We found that*HCOO is the key intermediate in the entire reaction process through DFT calculations,and its activation barrier is only 0.71 eV,which is 0.80 eV lower than the energy barrier for the formation of another intermediate*COOH,ensuring high selectivity for methanol production on Pt1@MIL.Finally,we introduce a work that we are doing,using N-doped Co nanosheets to catalyze the hydrogenation of CO2 to methanol.And through DFT,the synergistic effect of the intermediate*NHx on CO2 was explained,and the mechanism of its high activity for methanol production was revealed.The fourth chapter is a summary and prospect.We are mainly engaged in first-principles research on hydrogenation of small molecules,starting with NRR and CO2RR,designing materials with high stability,high activity and high selectivity,and revealing the hidden reaction mechanism to prepare for the subsequent precise design of high-efficiency catalysts.In the future,we plan to design new high-efficiency catalysts through several modification methods to reduce CO 2 molecules to high value-added C2 products,such as ethanol and ethylene,to solve the energy crisis.