Supported Pt catalysts were prepared by ion exchange of Pt(II) tetraamine hydroxide [Pt(NH3)4(OH)2] onto SiO 2, Al2O3, and TiO2 and by adsorption of Pt bis-acetylacetonate [Pt(acac)2] onto MgO. All the catalysts except Pt/TiO2 were characterized by in situ X-ray absorption fine structure (XAFS) spectroscopy after reduction at 300°C in flowing H2, and the Pt/SiO2 and Pt/MgO catalysts were examined after subsequent exposure to 1% NO/He at 25-300°C. NO decomposition pathways were investigated by temperature-programmed reaction spectroscopy (TPRS) using a 1% NO/He feed, and steady-state conversions for direct NO decomposition were measured at 600°C. NO decomposition at low temperatures (200-400°C) produces N2O and N2, and in situ XAFS spectroscopy indicates that the supported Pt particles are partially oxidized under these conditions. Over each catalyst, O2 production begins at ∼350°C; N2O production declines above 400°C; and N2 and O2 are the only detectable NO decomposition products at 600°C. Nanometer-sized Pt clusters on SiO2 sinter during heating in 1% NO/He at 300°C, whereas larger Pt particles supported on SiO2 and MgO are resistant to sintering under these conditions. The turnover frequency for direct NO decomposition over Pt/SiO2 catalysts is insensitive to Pt particle size. Pt/SiO2, Pt/Al 2O3, and Pt/TiO2 catalysts have equivalent NO decomposition activities suggesting the absence of support effects for these metal oxides. In contrast, the NO decomposition activity of Pt supported on strongly basic MgO is significantly lower.
All Science Journal Classification (ASJC) codes
- EXAFS spectroscopy
- NO decomposition
- Particle size effects
- Support effects
- Temperature-programmed reaction spectroscopy
- XANES spectroscopy