Improved three-way catalytic activity of bimetallic Ir-Rh catalysts supported on CeO2-ZrO2

摘要

The addition of a small amount of Ir caused a significant increase in not only CO and C3H6 oxidation activity but also NO reduction activity of Rh/CeO2-ZrO2 with a Ce/Zr molar ratio of 1/4 for NO-CO-C3H6-H-2-O-2 reaction under stoichiometric conditions. The optimum Ir/Rh atomic ratio was 1/9. The Ir additive was found to suppress the preferential oxidation of CO and C3H6 by O-2, leading to an improvement in the efficiency of CO and C3H6 utilization for NO reduction. Catalyst characterization such as H-2-TPR and X-ray absorption spectroscopy (XANES and EXAFS) revealed that the Rh species in the Ir-Rh/CeO2-ZrO2 samples is mainly present as Rh2O3 nanoparticles and that the addition of a small amount of Ir (Ir/Rh = 1/9) can improve the reducibility of Rh2O3 nanoparticles. On the basis of surface analysis by XPS and FT-IR spectroscopy following CO adsorption and STEM observation, the formation of Ir-Rh nanoparticles composed of finely-divided Ir species on the surface of Rh particles with a size of 1 nm was considered to be responsible for the high catalytic activity of Ir-Rh/CeO2-ZrO2 for NO-CO-C3H6-H-2-O-2 reaction. Ir-Rh/CeO2-ZrO2 with Ir-Rh loading of 0.3 wt% still showed high catalytic performance, which is comparable with that of 0.5 wt% Rh/CeO2-ZrO2, minimizing Rh usage.