NOx removal by rhodium catalysts supported on carbon nanotubes: Evidence for the stoichiometric reduction of NO2 and NO by the carbon support

The catalytic removal of NO and NO2 over rhodium particles supported on carbon nanotubes (Rh/CNT) was studied in the absence and presence of oxygen. It was found that the stoichiometric oxidation of the carbon support by adsorbed oxygen deriving from the rhodium-catalyzed scission of NO is crucial to achieve steady-state conversion of NOx. The proposed reaction pathway is verified by complete nitrogen and oxygen balances. In the absence of excess oxygen, Rh/CNT catalysts exhibit high activities in the catalytic reduction of NO and NO2 with the carbon support acting as the reducing agent. Oxidative pretreatment of the CNT support enhances the catalytic activity. The lifetime of the catalysts is limited by the stoichiometric oxidation of the support material. The structural degradation during the time on stream is evidenced by transmission electron microscopy.