Ag-Capping Agents & Ag-Ce Interaction And Structure-Activity

Size and shape play critical roles in the catalytic properties of catalyticcolloids. Capping ligands are often employed to control the size and shape of colloids by modifying the kinetics of nucleation and growth. Therefore, it is of great importanceto understand the interaction between capping ligands and colloids. In this thesis, we prepared Ag colloids with various structures employing different capping ligands and then systemically studied the Ag-capping ligands interaction; we further utilized various Ag colloids to prepare Ag@Ce(OH)x and Ag@CeOx composites and studied the interfacial interaction and structure-activity relation in CO oxidation. The main results are:1)Ag cubes, plates, and irregular particles were acquired by the reduction of AgNO3 respectively in poly-(vinylpyrrolidone) (PVP) and ethylene glycol, PVP and dimethylformamide (DMF), and DMF. PVP adsorbs on Ag cubes via its N and O atoms with charge transferring from PVP to Ag. DMF adsorbs on irregular Ag particles in two configurations with charge transferring from Ag to DMF. One adsorbs on fineAg particlesvia the N atom, and the other adsorbs on large Ag particlesvia the N and O atoms.PVP adsorbs on Ag plates viathe N atoms with charge transferring from PVP to Ag, whereas DMF adsorbs on Ag plates via the N and O atoms with charge transferring from Ag to DMF, but the PVP-to-Ag chargetransfer is more profound than the Ag-to-DMF charge transfer.These results reveal rich capping ligand-Ag colloid interactions that will strongly affect the surface chemistry and surface-mediated properties of Ag colloids.2)Ag cubes and plates were used as the templates to prepare Ag@Ce(OH)x and Ag@CeOx compositesin the ethanol-water solution at room temperature. The Ag-Ce interfacial interactions were found to stabilize low-valent Ce species and such a stabilization effect depended on the thickness of Ce(OH)x and CeOx.Ag@CeOx with a low valent Ce is significantly less active in catalyzing CO oxidation than Ag@CeO2. These results have strong implcations in fundamentally understanding the metal-CeO2 interfacial interaction and structure-activity relation in CO oxidation of metal-CeO2composite catalysts.