Controllable Synthesis And Application Of Pt-based Nanocatalysts

Nanocatalysis is among the pioneer applications of nanoscience,which is vital to our living and development.Compared with bulk catalysts,nanomaterials,because of their unique sizes and structures,have special nature including the surface effect,volume effect,small size effect,macroscopic quantum tunnel effect and so on.It meets the requirements of sustainable development and long-term plan of human beings that developing suitable nanocatalysts to boost greener and more efficient organic transformation,and to obtain cleaner energy resources or technologies.Among all the nanocatalysts,Pt-based nanomaterials are one of the most studied and applied cases.They show striking rapid development in the past few decades.Pt-based nanocatalyts are widely used in organic catalytic reaction,such as hydrogenation or coupling,electrocatalytic reaction and thus derived new energy devices,such as fuel cells.They are indispensable in both academic researches and industrial productions.Through optimization different synthesis conditions,the composition,size and morphology can be well controlled to meet different requirements in various types of catalysis.Nowadays,the researchers mainly focus on two aspects.One is to enhance the utilization of Pt atoms.Structures with high surface area are designed and prepared to expose the active atoms as much as possible.For another,the inherent activity of Pt-based nanocatalysts are expected to be enhanced through synergistic effect with other composites or the introduction of tensile stain.Thus,the electron state of the Pt on the surface could be changed.There are quite specific differences among zero dimensional nanoparticles,one dimensional nanowires,two dimensional nanoplates and three dimensional porous structures.So developing new strategies to design and synthesize these Pt-based nanocatalysts is of great significance to further promot the applications of nanocatalysts.In this paper,the main research is about the controllable synthesis of novel Pt-based nanocatalysts.We developed several new strategies to obtain zero dimensional,one dimensional,two dimensional and three dimensional Pt-based nanomaterials,during which covalent organic frameworks?COF?are used as a novel template,or alloy/de-alloy methods are applied,or small gas molecules?H₂/NH₃?are used as shape-directing regents.The synthetic conditions are carefully optimized and the formation mechanisms are systematically investigated.Through the characterization,it is confirmed that we obtain several novel Pt-based nanocatalysts of high quality.Then they are used in both organic catalytic reaction?mainly in the selective synthesis of amine?and electrocatalytic reaction?mainly in the methanol oxidation and oxygen reduction reaction?.The main contents are as follows:?1?Synthesis of nanomaterials:zero dimensional,one dimensional,two dimensional and three dimensional Pt-based nanomaterials?COF-ultrafine nanoparticles,ultrathin Pt nanowires,wormlike PtMo nanowires,dendritic PtIr tripods,Pt nanodendrites,PtRu nanodendrites?.And the morphology,composition,surface atomic distribution,valence state and stability of the as-prepared materials are characterized by the scanning electron microscope?SEM?,transmission electron microscope?TEM?,X-ray photoelectron spectroscopy?XPS?,X-ray diffraction?XRD?and so on.?2?Study on organic catalytic performance:the COF templated ultrafine Pt and Pd nanoparticles are used in the reduction of 4-nitrophenol and Suzuki-Miyaura coupling reactionrespectively.Both of them show excellent activity and stability.Ultrathin Pt nanowires obtained through de-alloy strategy are used in the selective synthesis of tertiary amines from the reductive coupling of nitriles with piperidines and selective synthesis of N-alkyl dibenzylamines from the coupling of nitromethane or methylamine.All the processes above are green,efficient and possess high practical value in real production.?3?Study on electrocatalytic performance:the small molecule H₂ gas is used as shape-directing regent.Three dimensional PtRu nanodendrites with high surface area are obtained.They can provide numerous catalytic sites.One dimensional wormlike PtMo nanowires are prepared and they also have enhanced surface area.Their unique structure is not susceptice to aggregation.Both of the PtRu nanodendrites and PtMo nanowires show excellent activity and stability in electrocatalytic methanol oxidation.The small molecule NH₃ gas is used as shape-directing regent.Different Pt nanodendrites are obtained via changing the types of halides used.Dendritic PtIr nanotripods are also synthesized using H₂ gas and each arm of these nanotripods are rough and dendritic.Both the Pt nanodendrites and dendritic PtIr nanotripods show excellent activity and stability in electrocatalytic oxygen reduction.