Abstract
SiO2 spheres were modified with Ag nanoparticles (NPs) via a silver-mirror reaction and then examined by scanning electron microscopy (SEM), UV–vis absorption, X-ray diffraction (XRD), Raman, FT-IR, depth-profiling X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction experiments. Ag 3d, Si 2p, and O 1s XPS peaks were found at much higher binding energies (BEs) due to localized surface charging in the Ag/SiO2 sphere. The charging effect was significantly diminished after thermal annealing due to the formation of good interfacial contact. CO oxidation reactions were demonstrated using temperature programmed mass spectrometry. Kinetic parameters were obtained from the CO conversion (%) profiles and the Arrhenius plots versus reaction temperatures. In the first CO oxidation test run, no significant difference was observed in response to differences in Ag particle size and thermal pretreatment in air. However, in the second run the sample pretreated at 450°C in air was completely deactivated. In the second test run, the oxidation activities were all degraded due to aggregation of Ag NPs. Better oxidation performance was observed for SiO2 modified with smaller Ag NPs.
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