Controlled Synthesis Of Noble Metal At The Atomic-Level And Their Catalytic Applications

Noble metal nanocrystals have been researched intensively for decades due to their excellent properties in catalytic applications.The properties of noble metal nanomaterials are determined by their sizes,shapes,structures and compositions.Accordingly,various noble metal nanocrystals have been successfully prepared with different morphologies and sizes.However,the global shortage of noble metal resources as well as environmental pollution have received increasing attention.An efficient strategy to solve this problem is to improve the atomic efficiency of noble metal nanocatalysts.To this end,extensive efforts have been devotes to synthesize noble metal nanocatalysts at the atomic-level to further improve their intrinsic activities and broaden applications.In this dissertation,we focused on the precisely controlled preparation of noble metal nanocatalysts at the atomic-level by wet-chemical methods,especially for palladium-based and ruthenium-based nanocatalysts.Moreover,we investigated the growth mechanism at the atomic-level and proved the key factors which effected the intrinsic activities of noble metal nanocatalysts offer a guideline for developing economic and efficient noble metal catalytic systems.The main contents are listed below:1.We briefly reviewed the recent research progress in the synthetic approaches to the design of noble metal nanocrystals at atomic-level to improve their catalytic performance and catalytic applications.This is followed by introducing the research significance and Ph.D.projects.2.Monolayer Ru atoms covered highly ordered porous Pd octahedra have been synthesized via the underpotential deposition and thermodynamic control.Shape evolution from concave nanocube to octahedron with six hollow cavities was observed.Using aberration-corrected high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy,we provided quantitative evidence to prove that only a monolayer of Ru atoms was deposited on the surface of porous Pd octahedra.The as-prepared monolayer Ru atoms covered Pd nanostructures exhibited excellent catalytic property in terms of semihydrogenation of alkynes.3.We report a one-pot synthesis of atomically dispersed Ru on ultrathin Pd nanoribbons.By using synchrotron radiation photoemission spectroscopy(SRPES),extended X-ray absorption fine structure(EXAFS)measurements in combination with aberration corrected high-resolution transmission electron microscopy(HRTEM),we show that atomically dispersed Ru with content up to 5.9 wt%was on the surface of the ultrathin nanoribbon.Furthermore,the ultrathin Pd/Ru nanoribbons could remarkably prohibit the hydrogenolysis in chemoselective hydrogenation of C=C bonds,leading to an excellent catalytic selectivity compared with the commercial Pd/C and Ru/C.4.An ordered mesh of palladium with a thickness of about 3 nm was synthesized by a solution-based oxidative etching.The ultrathin palladium nanomeshes have an interconnected two-dimensional network of densely arrayed,ultrathin quasi－nanoribbons that form ordered open holes.The unique mesoporous structure and high specific surface area make these ultrathin Pd nanomeshes display superior catalytic performance for ethanol electrooxidation(mass activity of 5.40 A mg-1 and specific activity of 7.09 mA cm-2 at 0.8 V vs.RHE).Furthermore,the regular mesh structure can be applied to support other noble metals,such as platinum,which exhibits extremely high hydrogen evolution reaction activity and durability.