SiO2 nanospheres modified by Ag nanoparticles: Surface charging and CO oxidation activity

• SiO2 nanospheres were surface-modified with Ag nanoparticles.
• Fundamental natures and CO oxidation activity were examined.
• Charges were highly localized in Ag/SiO2 spheres evidenced by depth-profiling X-ray photoelectron spectroscopy.
• Particle size, thermal treatment and perimeter play significant roles in the occurrence of catalytic activity.
• Ag particle size and thermal pretreatment determine the CO oxidation performance after 2nd test runs, but not in the 1st test run.

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.

Figure optionsDownload high-quality image (150 K)Download as PowerPoint slide