Controlled Synthesis Of Amorphous Noble Metal Nanosheets And Their Catalytic Applications

Noble metal nanomaterials have been widely employed towards industrial catalysis,energy storage and conversion fields,owing to their superior catalytic activity and stability.In recent years,in an effort to design more efficient noble metal catalysts,how the surface atomic arrangement of noble metal nanostructures influence their catalytic performance have been extensively investigated.Accordingly,various noble metal nanomaterials with different surface atomic arrangement have been precisely manipulated,such as alloying,crystal plane,crystal phase and amorphous structure.Since the adsorption/desorption kinetics of intermediate species have affinity with the surface structure,manipulating atomic arrangement of noble metal on the atomic level can effectively improve the number of surface active sites and simultaneously increase intrinsic activity,and thus greatly optimizing the catalytic activity and selectivity of noble metal catalysts while reducing the loading of noble metal.Among the precise control of the atomic arrangement,the amorphous nanostructures featuring with the disordered atomic arrangement endow the surface of noble metal catalysts with large amount of unsaturated coordination sites and special atomic coordination states.Thus,the construction of noble metal catalysts with amorphous nanostructure shows great potential for enhancing catalytic performance.In this dissertation,we have been absorbed in the precisely controlled synthesis approach for amorphous noble metal nanomaterials at the atomic level.By precisely designing the amorphous structure of noble metal catalysts at the atomic level,the intrinsic activity and the number of active sites of noble metal catalysts were effectively increased.Moreover,we have well investigated the growth mechanism,catalytic application and structure-activity relationship of amorphous noble metal catalysts,which can provide a new pathway for designing highly efficient noble metal catalysts.The main contents are listed as follows:1.We briefly summarize the recent research progress about the precise control of atomic structure for noble metal catalysts.2.By using alkali salts as the templates,a simple and general synthesis approach for synthesizing amorphous noble metal nanosheets has been developed.Besides amorphous monometal nanosheets(such as amorphous Ir nanosheets,amorphous Rh nanosheets and amorphous Ru nanosheets),dozens of different amorphous bimetallic nanosheets(such as amorphous RhFe nanosheets,amorphous IrRu nanosheets,etc.)and amorphous trimetallic nanosheets(such as amorphous IrRhRu nanosheets)can be conveniently and successfully accessed.Through analysis of the radial distribution function and extended X-ray absorption fine structure spectrum,amorphous Ir nanosheets have the special atomic coordination configuration,in which the average bond length of the Ir-Ir metal bond is slightly larger than that of crystalline Ir nanosheets.Due to the unique atomic structure and coordination configuration,amorphous Ir nanosheets exhibit excellent catalytic performance in oxygen evolution reaction under acidic media.In addition,in-situ X-ray absorpotion fine structure spectra indicate the valence state of Ir in the amorphous Ir nanosheets increased to less than+4 during the oxygen evolution reaction process.After the reaction,the atomic structure of the amorphous Ir nanosheets recover to its initial state,which reveal the stability of amorphous atomic structure.3.Through a simple pyrolysis reaction,we have obtained atomically dispersed Fe sites modified partially oxidized amorphous Ru nanosheets.X-ray absorption fine structure spectrum and aberration-corrected high-resolution transmission electron microscopy have confirmed that Fe species were atomically dispersed on partially oxidized amorphous Ru nanosheets.Due to amorphous atomic structure and decoration of atomically dispersed Fe sites,the amorphous RuFe nansheets could remarkably facilitate the formation of superoxide radicals and thus leading to significantly enhancing activities towards the oxidative dehydrogenation of indoline.