Ethylene and propylene adsorption and the formation of hydrocarbon complexes with NO2 upon interaction of adsorbed olefins with an NO + O2 mixture over HZSM-5 and CuZSM-5 zeolites studied by TPD and ESR

Adsorption of C2H4 and C3H6 on copper in oxidized samples of CuZSM-5 is found to increase with the copper concentration; simultaneously, olefin adsorption on the Brönsted acid sites decreases. The Cu2+ cations in the square-planar coordination exhibit higher reactivity in olefin adsorption than copper cations in the square-pyramidal coordination. Thermal treatment of CuZSM-5 with hydrogen results in regeneration of the Brönsted acid sites for olefin adsorption and the disappearance of Cu2+ cations, the active sites of adsorption, due to the reduction of Cu2+ to Cu+ and Cu0. Desorption peaks appear in the TPD spectra upon the interaction between the adsorbed hydrocarbons and NO2. These peaks are not observed upon separate adsorption of the reactants, and they are likely due to decomposition of NO2-hydrocarbon complexes over both the Brönsted and copper-containing sites of the zeolite