Metal Nanowires: Synthesis And Application In Catalysis

Catalysis is the driving force behind the development of our chemical industry. Itensures us use our natural resources more efficient, it helps us prevent waster and airpollution, and it makes our chemical industry safer and more efficient. In the pastcentury, catalysis has been the basis of large-scale processes in bulk chemistry andpetro-chemistry, however, some problems still need solving. With the development ofthe nanotechnology, catalysis faces new challenges and opportunities. Nanoparticles canbe used as the heterogeneous catalysts for developing energy, manufacturing medicinesand protecting our environment as they always have smaller diameters and largersurface areas. However, nanoparticles always have higher surface energy as their largersurface areas. This factor can lead to aggregation and will make the catalysts deactive.Some other problems still exist (e.g. loss the active components and recycle thecatalysts) when these nanoparticles were used as the catalysts in reactions.Nanomaterials will show their advantages as catalysts if we can solve these problems.In order to avoid the aggregation and make the nanoparticles catalysts recyclable,reserchers used some stable supporters to fix these nanoparticles. However, the loadprocess will generate new problems such as insufficient reduction of metal ions and adecrease in catalytic activity.Nanowires as one of one-dimension nanomaterials have attracted many researchersattention as their highly ordered crystal structures since1990and developed rapidly inthe next twenty years. Compared with nanoparticles, nanowires still have highercatalytic activity as they keep small size effect (the diameter is nano scale). Nanowirescan be separated from reactions easily as their macro-characteristics like bulk materials(the length is micro scale). When nanowirs were used as the catalysts, no supporter wasneeded and we can make good use of the active sites of the catalysts. How to synthesizethese1-D nanowires materials successfully is another challenge for nano-researcherswhen nanowires were used as catalysts. Now, some metal nanowires have beensynthesized successfully, but the application of these nanowires was less reported. Inthis thesis, we synthesized several metal nanowires (Au, FePt, Pt, Pd et. al.) and used them as the catalysts for organic reactions.This thesis mainly includes three parts:(1) synthesize novel nanowires;(2) conductreactions using these nanowires as catalysts;(3) illustrate the reaction mechanism. Wedesign and synthesize novel nanowires and select the suitable reaction conditions to geta high activity and selectivity catalytic system. This will be a supplementary for thetraditional catalytic systems and will help prevent environment pollution in organicreactions. Using this kind of nanomaterials may make a breakthrough in the fields ofsynthetic chemistry and industrial application. The research program is focused on thedesign, synthesis, characterization of novel nanomaterials (Au, FePt, Pt and Pd) andtheir applications in catalysis. The mechanisms of corresponding reactions are proposedand proved by density functional theory (DFT) calculation. The main contents are asfollows:(1) Synthesize nanomaterials: design and synthesize of ultra-thin nanowires (Au,FePt, Pt and Pd) with controllable structures, morphologies and components;characterize the relevant parameters for catalytic activity like structures, morphologies,components, distribution and valence of the surface atoms by transmission electronmicroscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD),inductively coupled plasma (ICP) and so on.(2) Study on catalytic performance: Au nanowires can be used as the catalysts foralkenes and alkylbenzenes oxidation with high catalytic activity under mild reactionconditions. Pt nanowires were obtained by acid ecthing of FePt nanowires and thisultrathin nanowires show high catalytic activity in hydrogenation of unsaturatedcompounds like nitroaromatics, alkene, alkynes, aromatic rings and nitrogenheterocyclic compounds. These reactions can be conducted under mild reactionconditions and they are environment friendly. Pt nanowires can be used as effectivecatalysts for azocompounds synthesis from the hydrogenation of nitroaromatics withbase as the additive. Pd nanowires can also be used as effective catalysts forazocompounds synthesis using nitroaromatics as the substrates. N-Alkylamines can besynthesized using Pt nanowires as the catalyst, nitroaromatics and aldehydes(acetophenone) as the substrates. The reaction goes through a different mechanism thantraditional "reductive amination". N-Alkylamines were directly obtained byintermolecular dehydration over Pt nanowires under a hydrogen atmosphere, instead ofintramolecular water elimination and imines hydrogenation. These nanowires are stable and can be recycled easily, especially Pt nanowires. They show outstanding stability inweak base, neutral and acidic conditions and the catalytic activities almost keepunchanged after recycled several times.(3) Put forward and clarify he reaction mechanism: Density functional theory(DFT) calculations were performed based on the models we constructed from ournanowires catalysts. The morphologies and crystal forms of the different nanomaterialswere compared to study the influence factors of the catalytic activity and selectivity.The reaction mechanism of the reaction was illustrated by the absorbance of thereactants on the surface of catalysts and the change of activation energy of the reaction.Our nanowires as catalysts for organic reactions showed higher catalytic activityand selectivity than that of traditional catalysts. Most importantly, Pt nanowires arestable and can be recycled many times. Therefore, Pt nanowires can be used in a widespread reactions and have very good outlook in industrial application.