Dynamics of Rh nanoparticle surface structure during NO reduction revealed by operando transmission electron microscopy

Abstract Elucidating the NOx purification mechanism of exhaust gas catalysts such as Rh nanoparticles is essential for the development of air purification technology required for environmentally conscious automobiles. In this study, operando observations of Rh nanoparticles in NO gas were performed to understand the Rh surface structure and dynamics. A system comprising a high-voltage electron microscope (HVEM) connected to a high-sensitivity quadrupole mass spectrometer (QMS) (HVEM-QMS system), which was newly developed by Nagoya University and JEOL, was used for gas analysis. While confirming the onset of the NO reduction reaction using the QMS, structural changes in the Rh nanoparticles in the presence of NO gas with increasing temperature were investigated. The repeated appearance and disappearance of a surface oxide film was observed for the first time, suggesting that the metastable surface oxidation state contributes to the uptake and release of oxygen during NO decomposition.