Design And Construction Of Au, Ag, Pd, Cu And Ni Nanocatalysts And Study Of Catalytic Redox

Research and development of transition metal nanocatalysts has been as present the most important topic in catalysis field. Transition metal nanocatalysts can be divided into two groups:noble metal nanocatalysts and non-noble metal nanocatalysts, which show rather high catalytic activity and product selectivity in catalytic reaction, having good potential application in the fields of petrochemical catalysis, photocatalysis, electrochemistry, novel energy and green redox process etc.Sustainable development is the development strategy of the world economy. The research of alternative and green selective catalytic redox process has become one of the most important subjects in organic synthesis field. The design and development of transition metal nanoparticles provides novel ways for the green chemical synthesis. In this graduation thesis, novel catalysts with special properties were designed and constructed by sol-immobilization and chemical reduction method on the base of the catalytic properties of noble and non-noble metal nanocatalsyts. The relationship between the preparation conditions and structure, shape and particle size of the catalysts were investigated. O2 was used as the clean oxide agent, and H2 and NaBH4 were used as the clean hydrogen agent. The structure-activity relationship between the structure, particle size and support of transition metal nanocatalysts and their catalytic activity were evaluated in the oxidation of 1,2-propanediol, hydrogenation of maleic anhydride and reduction of nitroaromatics, in order to reveal the selective catalytic redox mechanism and reaction kinetics. The main results are as follows:1. Selective catalytic oxidation of 1,2-propanediol over Au, Pd and Ag monometallic or bimetallic nanoparticles catalystsHydroxylapatite nanorods and Mg(OH)2 nanoslices were prepared by hydrothermal method and precipitation method and used as supports. Au and Pd monometallic and bimetallic nanoparticles sols were then prepared by chemical reduction method. The metallic sols were immobilized on the supports by sol-immobilization to form supported Au-Pd/HAP and Au-Pd/Mg(OH)2 nanoparticle catalysts. It was found that the Au and Pd monometallic nanopartilces and Au-Pd bimetallic nanoparticles of the catalysts had polycrystalline structures and were well dispersed on the surfaces of HAP nanorods and Mg(OH)2nanoslices. There was strong interaction between the Au and Pd nanoparticles and the supports. Base sites were found on the surface of the catalysts. Electron transfer was found between Au and Pd atoms of the bimetallic catalysts. The particle size of metallic Pd nanocubes was controlled by change of the amount of organic modifier PVP and KBr. Metallic Ag nanoparticles were also prepared by chemical reduction method. It was found that there was different interaction between the Ag+ ion and the organic modifiers with different functional groups, which significantly affected the structure and particle size of the Ag nanoparticles. The as-prepared Ag nanoparticles had polycrystalline structures.The oxidation of 1,2-propanediol was carried out in aqueous phase with O2 as the oxide agent and using supported Au and Pd monometallic and bimetallic nanoparticles, supported Pd momometallic nanocubes, and Ag nanoparticles as the catalysts, respectively. When the Au-Pd/HAP were used as catalysts, the 1,2-propanediol conversion and lactic acid selectivity were 96.6% and 97.1%, respectively under 0.1 MPa O2, showing that the Au-Pd/HAP catalysts showed high catalytic activity in selective oxidation of 1,2-propanediol to lactic acid. The high specific surface areas of HAP favoring high dispersion of Au and Pd nanoparitlces and the basicity of HAP enhanced the catalytic activity over the Au-Pd/HAP catalysts. The catalytic activity and lactic acid selectivity over bimetallic catalysts was much higher than that over the monometallic due to the synergistic effect between Au and Pd nanoparticles. When Au-Pd/Mg(OH)2 were used as catalysts, higher catalytic activity and lactic acid selectivity were found on the Au-Pd/Mg(OH)2 catalyst with Mg(OH)2 nanoslices as support than the Au-Pd/Mg(OH)2 catalyst with Mg(OH)2 microslices as support.The 1,2-propanediol conversion and lactic acid selectivity were 97.5% and 88%, respectively when Auo.75Pdo.25/Mg(OH)2 were used as catalyst under 1 MPa O2. Meanwhile, it was found that the catalytic activity over HAP supported Pd nanocubes was high than that over HAP supported Pd nanospheres. There was close relationship between the catalytic oxidation activity and the surface structure of the Pd nanoparticle catalysts in the catalytic oxidation of 1,2-propanediol.When the selective oxidation of 1,2-propanediol was catalyzed by Ag nanoparicles at 120℃,1.0 MPa O2 for 4 h, it was found that polyhedral AgTween nanoparticles with particle size of 25.3 nm favored the conversion of 1,2-propanediol to lactic acid, with the 1,2-propanediol conversion of 65.6% and the lactic acid selectivity of 62%, while the spherical AgcA nanoparticles favored the conversion of 1,2-propanediol to formic and acetic acids with the 1,2-propanediol conversion of 100% and the selectivities of formic and acetic acids of 30.5% and 63.2%, respectively under the same reaction conditions. There was close relationship between the catalytic oxidation activity and the surface structure of Ag nanoparticles in the catalytic oxidation of 1,2-propanediol catalyzed by Ag nanoparticle catalysts.In the oxidation of 1,2-propanediol catalyzed by Au, Pd and Ag monometallic and bimetallic nanoparticle catalysts, it was founthat there was storng interaction between the Au, Pd and Ag monometallic and bimetallic nanoparticles and the terminal hydroxyl of 1,2-propanediol, which favored the dehydrogenation of 1,2-propanediol to form the intermediate, futher being oxidized to lactic acid.2. Selective hydrogenation of maleic anhydride over metallic Ni nanopariclesMetallic Ni nanoparticles were also prepared by chemical reduction method in ethanol solution. It was found that the as-prepared Ni nanoparticles had polycrystalline structures. There was different interaction between the Ni2+ ion and the organic modifiers with different functional groups, which significantly affected the structure and particle size of the Ni nanoparticles.In the catalytic hydrogenation of maleic anhydride over metallic Ni nanoparticles, the maleic anhydride conversion and succine anhydride selectivity were 99.8% and 100%, respectively when using NicA with citrate acid as organic modifier to catalyze the hydrogenation of maleic anhydride at 80℃,2 MPa H2 for 150 min, which was 6 times higher than that when using Raney Ni to catalyze the hydrogenation of maleic anhydride. Small sized Ni nanoparticles with polycrystalline structure favored the hydrogenation of C=C bond of maleic anhydride rather than the C=O bonds.3. Selective hydrogenation of maleic anhydride over metallic Ni nanopariclesMetallic Cu nanoparticles were also prepared by chemical reduction method in ethanol solution. It was found that type of organic modifiers and alkaline condition played important role in the reduction of Cu2+ ion to metallic Cu. The particle sizes of Cu nanoparticles were changed by changing the type of organic modifier. The particle size of Cu significantly increased without the organic modifier. The as-prepared Cu naoparticles had polycrystalline structures.In the selective reduction of 3-nitro-4-methoxyacetanilide (NMA) to 3-Amino-4-methoxyacetanilide (AMA) over metallic Cu nanoparticles, under the same reaction conditions, smaller sized metallic Cu nanoparticles showed higher catalytic activity, and favored the complete conversion of NMA to AMA at room temperature when, using NaBH4 as the hydrogen agent. In the reaction, Gu nanoparticles played the role as the active sites for hydrogen transfer, resulting in hydrogenation of the nitro group of NMA to amino group.