| AVS 57th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | T. Fujitani, National Institute of Advanced Industrial Science and Technology (AIST), Japan |
| Authors: | T. Fujitani, National Institute of Advanced Industrial Science and Technology (AIST), Japan A. Takahashi, National Institute of Advanced Industrial Science and Technology (AIST), Japan I. Nakamura, National Institute of Advanced Industrial Science and Technology (AIST), Japan |
| Correspondent: | Click to Email |
The reaction of NO and CO has been studied over various transition- and noble-metal catalysts because of its importance for three-way catalytic converters. Recently, Ir-based catalysts were found to be effective for the selective reduction of NO with CO in the presence of O2. However, the reaction mechanism, kinetics, and adsorption behavior for the NO + CO reaction on Ir-based catalyst surfaces are not fully understood.
In this study, we investigated the adsorption and thermal reactivity of NO and CO over Ir single crystals to clarify the influence of the Ir surface structure. Furthermore, we examined the kinetics and mechanism of the NO + CO reaction over Ir single crystals at high-pressure and compared the results with results for a conventional Ir/SiO2 powder catalyst.
The kinetics of the NO reduction with CO over the Ir single crystal and the powder Ir/SiO2 catalyst were investigated under real reaction conditions. N2 and CO2 were formed by the reaction of NO + CO. The Ir(111) plane showed low activity for N2 and CO2 production compared with the Ir(100) and Ir(211) planes. The TOFs for N2 and CO2 formation for the Ir planes decreased in the order (100) > (211) >> (111). The apparent activation energies for N2 and CO2 formation were estimated to be 107–115 kJ/mol and 110–120 kJ/mol, respectively; and these values were almost the same, regardless of the changes of the Ir surface structure. Furthermore, the order of the pre-exponential factors for the various surface structures was in good agreement with the order of the planes with respect to NO dissociation activity, indicating that the catalytic activity for NO reduction over Ir surfaces was strongly dependent on the NO dissociation activity.
The activation energies for N2 and CO2 formation over an Ir/SiO2 catalyst were estimated to be 117.2 kJ/mol and 123.1 kJ/mol, respectively, and these values were similar to those of the Ir single crystal. The TOFs for N2 and CO2 formation over Ir/SiO2 were almost same for those for Ir(211), which indicates that the Ir surface structure of Ir/SiO2 was close to that of Ir(211). That is, the Ir(211) surface can be regarded as an appropriate model catalyst for the NO + CO reaction over an Ir/SiO2 catalyst because the apparent activation energies and the TOFs for N2 and CO2 formation over Ir(211) were in good agreement with those over the Ir/SiO2 catalyst.