Stabilization of active Rh 2O 3 species for catalytic decomposition of N 2O on La-, Pr-doped CeO 2

Abstract

CeO 2 and La- or Pr-doped CeO 2 were prepared at calcination temperatures of 600, 800, and 1000 °C. The samples were characterized by Raman, XRD, and N 2 adsorption and tested as Rh 2O 3 support for the catalytic decomposition of N 2O at low temperature (starting at 200 °C). Catalyst characterization was done by XPS analysis of fresh and in situ treated catalysts, TPR, and TEM. As deduced by XPS analysis and catalytic tests, Rh 2O 3 is more active than Rh 0 for N 2O decomposition. Pure CeO 2 calcined at low temperature (600 °C) and La or Pr-doped CeO 2 calcined at 600, 800 or 1000 °C can keep Rh 2O 3 stable under reaction conditions. In contrast, Rh 2O 3 supported on pure CeO 2 calcined at high temperature (800 or 1000 °C) is reduced to Rh 0 under reaction conditions. The redox properties of the support are decisive for Rh 2O 3 stabilization and catalytic performance; the larger the reducible surface CeO 2 (determined by TPR), the better the catalytic activity. In addition, structural and textural features of the support (crystallinity, BET surface area, and particle size) affect Rh 2O 3 dispersion, the smaller the support particle size (the higher the surface area), the better the dispersion and the catalytic activity. The redox properties and particle size of supports depend on calcination temperature. Doping improves thermal stability with regard to pure CeO 2. La and Pr form solid solutions with CeO 2, preventing sintering and maintaining a high percentage of reducible CeO 2 at high calcination temperatures (800 and 1000 °C).