Surface And Interface Engineering Of Pd And Ru Based Nanomaterials And Their Applications In Catalysis

Noble metal nanomaterials have a wide range of applications in energy,environmental protection and many other fields.Their property can be not only modulated by the size,morphology and component,but also quite sensitive to the surface and interface structure.Therefore,the surface and interface engineering of noble metal nanomaterials are critical to the design,construction,optimization and application in various fields.In this thesis,three projects are going to be studied and discussed in detail:1)surface restructuring of Pd–Ag alloy nanotubes by electrochemical etching and its impact on the formic acid and methanol electro-oxidation reaction.2)the modulation of localized surface plasmon resonance（LSPR）and its mechanism on methanol electro-oxidation reaction of Pd–Ag system.3)The interfacial bonding mode,location of nitrene ligands and free Ru sites on the surface of nitrene-functionalized ruthenium nanoparticles,and the ligand effect on catalytic hydrogenation of styrene.The thesis includes the following three aspects:Firstly,noble metal nanomaterials with diverse surface and interface structures exhibit various physical and chemical properties.In order to study the influence of the surface and interface structure on the catalytic performance,Ag nanowires were used as the precursor to prepare a well-defined hollow Pd–Ag alloy nanotubes by Galvanic displacement method,which not only reduce the use of precious metal Pd,but also modulate the electronic structure of palladium.The results revealed that,the activity and stability for electro-oxidation of formic acid（FAOR）and methanol（MOR）of Pd–Ag alloy nanowires was significantly improved by electrochemical etching,due to the dissolution of Ag atoms and formation of an ultra-thin Pd shell on the surface of the alloy nanotubes,as demonstrated by CV,XPS and STEM–EDX measurements（Pd–Ag@Pd）.Compared with the as-prepared Pd–Ag alloy nanotube,the catalytic performance of Pd–Ag@Pd towards FAOR and MOR were greatly enhanced,due to the rougher surface,enhanced electrochemical surface area and the unique electronic structure of Pd–Ag@Pd.Secondly,Considering the strong localized surface plasmon resonance（LSPR）of Ag nanowires,we further studied the impact of the LSPR on the MOR performance of Pd–Ag alloy nanotubes in this chapter.It is observed that the mass activity of MOR is enhanced linearly with light intensity,then a superlinear dependence on the light intensity when the light intensity is further increased.UV-vis spectroscopy indicated that Ag nanowires and Pd–Ag alloy nanotubes exhibited strong LSPR absorption.Further studies revealed a consistent positive shift of the oxidation potential of Pd–Ag and the open circuit voltage of the electrochemical cell with the light intensity,which is are attributed to the high energetic holes from LSPR.The dissolution of Ag atoms and formation of a Pd-skin on the surface of Pd–Ag nanotubes over the catalytic process is favorable for MOR.To be noted that the photo-enhancement is reversible but it is not instantaneous,the minutes-scale response to LSPR excitation may be reflective of a gradual approach of the photoinduced surface temperature and/or surface photopotential to a steady-state value,and the gradual formation of Pd–Ag@Pd_skin,which is facilitated to the catalytic process.The synergy between the LSPR and intrinsic electrocatalytic catalysis is of great significance in improving catalytic activity,reducing the load of precious metals,and in the cost of fuel cell catalysts.Thirdly,Surface functionalization of nanoparticles with small organic ligands has proven to be powerful in regulation of physical and chemical properties of metal nanomaterials.We successfully prepared nitrene-functionalized ruthenium nanoparticles（Ru=N）.The Ru=Nπbond was demonstrated by experimental and DFT-calculated FTIR of Ru=N nanoparticles with ¹⁵N-labeled nitrene ligands.In addition,the impact of the nitrene ligands on the catalytic performance of Ru nanoparticles were further explored by DFT calculation over the nitrene-preferred adsorption site on Ru,electrochemical CO stripping and solid ¹³C–NMR of CO poisoned Ru=N nanoparticles.This work highlights the importance of coordination chemistry of nitrenes on metal nanoparticles and,and is of great significance for the rational design of high-performance metal catalysts by surface/interface engineering of metal nanoparticles.