Regulating Hydrogenation Selectivity Of Pd,Pt Catalysts And Insight Into Mechanisms

Supported noble metal catalysts play a very important role in the catalytic reaction process,but their structures are complex and their catalytic selectivity is often poor.However,improving the selectivity and minimizing waste generation in the catalytic hydrogenation process is one of the core tasks of sustainable social development,so it is very important to adopt effective strategies to regulate the selectivity,and revealing the selectivity-enhancing mechanism will facilitate the design of more efficient catalyst.In Chapter 1,we give an overview of heterogeneous catalysts,emphasize the importance of hydrogenation selectivity and summarize strategies for modulating the selectivity of supported noble metal catalysts.The relevant mechanisms for regulating the selectivity are introduced from three aspects of inorganic modifier,organic modifier and support,as well as the basis and research content of this thesis are further determined.In Chapter 2,we construct defective Al2O3 rich in penta-coordinated Al3+ions and F-centers,and employ a in-situ reduction and anchoring method to load ultra-small Pd NPs on Al2O3 surface,rich metal-support interfaces and metal surfaces play a key role in the selective hydrogenation of phenol.The metal-support interface is responsible for substrate activation,and the metal surface is responsible for substrate hydrogenation.In Chapter 3,we construct a simple decoupled catalytic system by the reducible support(In2O3)and the organic ligand(ethylenediamine).The special organic ligandmetal interface,metal-support interface and support surface enable the hydrogenation activation and hydrogenation reactions to occur at different sites,achieving high activity and selectivity for the hydrogenation of nitrocyclohexane.In Chapter 4,We extended the catalyst system of nitro decoupling hydrogenation to an inexpensive SnO2 support,and systematically studied the reaction kinetics of the Pt/SnO2 catalyst in the hydrogenation of nitroaromatics under the action of ethylenediamine surface coordination and hydroxylamine disproportionation assistant,and finally achieved highly selective 2e stepwise hydrogenation of nitroaromatics to obtain nitroso,hydroxylamine and amine products,respectively.In Chapter 5,well-defined single-atom catalysts are employed for studying the specific role of metal-support interfaces,which exhibit high performance in the selective hydrogenation of benzaldehyde.In protic solvents,the hydrogenation process involves an extremely large tunnelling H-transfer contribution and is a multiple concerted hydrogen tunneling.Tunneling probability was controlled by changing the protic solvent.In Chapter 6,atomically precise metal nanoclusters are used to study the local structure of single-atom catalysts and catalytic performance of active sites.The open steric structure endows the performance of single-atom Pd catalytic hydrogenation of alkenes,the terminal alkenes with small steric hindrance are easily hydrogenated,while the alkenes with large steric hindrance are not hydrogenated,thus showing good regioselectivity.In Chapter 7,we summarize the research works of this paper,and propose further research ideas and prospects.