Studies On The Catalytic Processes Of Sub-nano Metal Systems For Several Hydrogenation Reactions

Various chemical products are produced by different production technologies and different chemical reactions in the chemical industry.Among those chemical reactions,hydrogenation reaction is one of the most important reactions.Hydrogenation reaction is a key reaction step in important chemical processes such as Fischer-Tropsch process,ammonia fixation,ethylene purification(removal of acetylene impurities),etc.,and has a crucial impact on human production and life.Regarding the hydrogenation reaction,although many previous studies have made many breakthroughs in the preparation of catalysts,the revelation of the catalytic mechanism,and the design of catalytic reactors,there are still some improvements in the process technologies of some hydrogenation reactions.For example,the conditions for preparing ammonia by the Haber-Bosch process are relatively harsh,and the whole process consumes a lot of energy.Therefore,it is possible to try to make the ammonia synthesis reaction under milder conditions.The removal of acetylene impurities in ethylene by hydrogenation is prone to over-hydrogenation,so special attention should be paid to the improvement of catalytic selectivity.Further reducing the catalyst cost of nitrobenzene hydrogenation reaction and benzaldehyde hydrogenation reaction is also the problem to be solved.Therefore,how to improve the above catalytic hydrogenation reaction process is the focus of this thesis.In addition,sub-nano systems have unique physical and chemical properties,such as the advantages of high catalytic activity and the high selectivity.So this work attempts to select different sub-nano metal systems to catalyze different catalytic hydrogenation reactions.Therefore,the catalytic process of metal sub-nano systems in different hydrogenation reactions is the focus of this work.This thesis contains five chapters.The first chapter mainly introduces the industrial background and importance of nitrogen reduction reaction,selective hydrogenation of acetylene to ethylene,nitrobenzene hydrogenation and benzaldehyde hydrogenation reaction.Among these reactions,a brief overview of the technologies in industry is introduced.Finally,the main research content of this thesis is introduced.The second chapter of this thesis mainly studies the catalytic process of the iron-based catalysts in electrochemical nitrogen reduction reaction.In this chapter,the mechanism of electrochemical nitrogen reduction reaction is introduced.The experimentally synthesized Fe2/g-C3N4 catalyst has good catalytic performance and high selectivity in electrocatalytic ammonia synthesis.It is found that appropriate tensile stress or doping positively sodium atom in the Fe2/g-C3N4 catalyst can further enhance the catalytic performance and significantly improve the selectivity.Among them,the application of tensile stress breaks the linear correlation between the adsorption energy of nitrogen-containing species.In addition,based on this work,the black phosphorus nanosheets,iron cluster and the g-C3N4 monolayer are further combined.The sub-nano metal composite g-C3N4/Fe19/BP has excellent catalytic performance and high selectivity in the electrochemical nitrogen reduction reaction.The intrinsic mechanism why the catalytic performance improves is derived from two factors caused by black phosphorus.Black phosphorus and g-C3N4 monolayer form a confined space and black phosphorus affects the Fe-N bonding situation.These two factors affect the adsorption energies of the adsorbed species in distinct directions.The third chapter mainly focuses on the palladium-based catalysts in the semi-hydrogenation of acetylene to ethylene.In this chapter,the following studies are carried out to realize the improvement of the selectivity of acetylene hydrogenation reaction in the industry.We impose the comfinement space on granphene monolayer and Pd(111)surface,and this work improves the selectivity and activity of acetylene hydrogenation in industry.Besides,we find the new Pd1@Cu-SiW catalyst has excellent catalytic performance and good selectivity in the semi-hydrogenation of acetylene reaction.The catalyst immobilizes an isolated single Pd atom in a polyoxometalate based metal organic framework(POMOF).Based on this,our work further explores the reason for the high reaction selectivity.It can be found that the structure of the Pd1@Cu-SiW catalyst caused the difference in adsorption energies between acetylene and ethylene,which lead to the preferential release of ethylene,thereby inhibiting the formation of ethane.Moreover,a spatial microenvironment is formed between the catalyst and reactant molecules,which facilitates the entry and exit of reactants and products.The fourth chapter of this thesis mainly explores the catalytic process of platinum diatomic catalyst in the hydrogenation of nitrobenzene and benzaldehyde reactions.In this chapter,by first-principles,it is found that Pt2/mpg-C3N4 has outstanding selectivity and catalytic performance in the hydrogenation of nitrobenzene to aniline and the hydrogenation of benzaldehyde.Moreover,the catalytic performance of Pt2/mpg-C3N4 in the hydrogenation of nitrobenzene is far better than the Pt single atom catalysts and Pt nanoparticles.Then,this chapter reveals the fundamental reasons for the distinctive catalytic performance of Pt2/mpg-C3N4,finding that platinum diatoms interact with the π antibonding orbitals in the nitro group to promote N-O bond cleavage,and the bonded unsaturated N and O atoms further facilitate H2 dissociation through polarization.The fifth chapter summarizes the work of the second chapter to the fourth chapeter in thesis and looks forward to the possible directions of follow-up research work.The catalytic hydrogenation reactions have a close relationship with the national economy and people’s livelihood.The author hopes that the research in this thesis can help to further improve the process technologies of the catalytic hydrogenation reactions,and hope to provide several new ideas for the design of catalytic hydrogenation reaction system.