Catalytic CO Oxidation on Nanocatalysts

Abstract

CO oxidation, as one of the simplest catalytic reactions, has been widely studied in heterogeneous catalysis. Since CO can be easily adsorbed on active metals like Au, Pt, Pd, Rh, and Ru, many researchers have attempted to observe surface phenomena, including adsorption, surface restructuring, and oxidation kinetics on diverse metal surfaces ranging from single crystals to nanoparticles (NPs). The rapid advances in nanochemistry have further stimulated studies of catalytic reactions, and in-depth understanding of CO oxidation is possible based on analyses of how the size, shape, and composition affect the activity and determine the most effective active site of metal NPs. Recent research has demonstrated that the CO oxidation activity varies with the size of metallic NPs. The oxidation state of the NPs varies as a function of the size, and the surface oxide layers formed on NPs have been found to be important in enhancing or suppressing CO oxidation. Surface segregation of bimetallic NPs also influences the CO oxidation rate. The NP surfaces undergo significant adsorbate-induced structural changes, as confirmed by various in situ characterization techniques under catalytically relevant CO oxidation conditions. Based on the knowledge of support-induced catalytic properties, various metal-support interactions have been investigated for enhancing CO oxidation. By changing the reaction environments to either CO- or O-rich atmospheres, the synergetic effect at the interfaces of NPs and support oxides have been largely clarified. Versatile nanostructures with confined shells of small metal NPs have also been designed as core@shell-type catalysts. Using in situ characterization techniques combined with well-defined NPs, it is possible to study CO oxidation on the molecular level in order to gain vital mechanistic insights under catalytic working conditions.