Synthesis And Selective Hydrogenation Catalysis Of Intermetallic Palladium-Based Nanomaterials

Selective catalytic hydrogenation is of great importance in the production of fine chemicals.For example,the selective catalytic hydrogenation of acetylene to produce ethylene is widely used in the removal of trace acetylene from ethylene in the feed stream of an ethylene polymerization unit.Since any acetylene hydrogenated with acetylene causes loss of feed gas,this selective catalytic hydrogenation requires a highly optimized catalyst which gives it excellent selectivity.Silver(Ag)-modified palladium(Pd)-based catalysts are generally widely used in the reaction system.Despite these modifications to the catalysts,the alkane and high hydrocarbons produced by the excessive hydrogenation and oligomerization of acetylene are still factors limiting the practical application of the reaction.Therefore,the modification of palladium-based materials is still one of the important strategies for the development of highly selective catalytic hydrogenation catalysts.Intermetallic compounds(IMCs),due to their specific crystal structure and highly ordered nature of surface atomic arrangements,can provide spatial separation of active sites to enhance strong interactions between metals,charge transfer and orbit rehybridization,ultimately optimization of catalytic performance.In addition,the IMCs generally exhibit outstanding structural stability in catalytic reactions due to the high mixing enthalpy.Nevertheless,effective structural control of IMCs remains a huge challenge,not to mention systematic structural regulation.To this end,achieving system control of intermetallic catalysts is greatly challenging,especially for optimization of catalytic performance.In this thesis,by controlling the morphology and surface geometry and electronic structure of intermetallic Pd-based nanomaterials,Pd2Sn nanoparticles(NPs)and intermetallic Pd3Pb nanocubes(NCs)with different concave degrees were synthesized and their structures were synthesized.And the structure-effect relationship has been studied in depth.The main contents are summarized as follows:Chapter 1.The first chapter briefly summarizes the research progress of intermetallic Pd-based nanomaterials and performance and mechanism of selective hydrogenation reaction,further clarifies the basis and research content of this paper.Chapter 2:The preparation of hollow intermetallic Pd2Sn NPs with enhanced direct synthesis of H2O2(DSHP)was successfully prepared.The key to the successful preparation of the hollow nanostructure is the Kirkendall effect(different diffusion rates for different atoms).The larger specific surface area,hollow structure and the number of linear adsorbed Pd active sites contribute to improvement of DSHP catalytic activity,selectivity and stability.Chapter 3.Based on the synthesis experience in Chapter 2,further exploration was carried out,and the intermetallic Pd2Sn NPs with different particle sizes were successfully synthesized.Meanwhile,TiO2 nanosheets(NSs)were prepared according to the literature.Subsequently,TiO2 NSs were calcined in different atmospheres to obtain TiO2 with different oxygen defects.The above intermetallic Pd2Sn NPs were loaded on TiO2 for DSHP performance test.The support defects and Pd2+active sites in the Pd2Sn/TiO2 can enhanee the adsorption and activation of H2/O2 to further boost the DSHP performance.Chapter 4.Intermetallic Pd3Pb NCs with different concave degrees were successfiolly synthesized.Among them,the factors of successful synthesis are largely attributed to the regulation of small molecules on morphology.The Pd3Pb concave NCs with the stepped surface increases the active site of Pd,promote the formation of styrene on selective hydrogenation of phenyl acetylene and inhibit the subsequent excessive hydrogenation reaction.The Pd,Pb concave NCs exhibit the optimal phenyl acetylene conversion and styrene selectivity and stability.