NO decomposition over La-doped Cu-ZSM5 monolith under adsorption-reaction conditions

The decomposition of nitrogen oxide has been studied under non steady state reaction conditions over a La-stabilised Cu-ZSM5 structured catalyst after adsorbing NO on the zeolite. The three main steps of the experiments are the following: (i) NO adsorption at 50 C until zeolite saturation, (ii) reactor isolation and heating up to the reaction temperature (480 or 520 C), (iii) cooling down back to 50 C re-opening the reactor once the adsorption temperature has been reached. No NOx are emitted during all steps. TPD tests have been performed after one or more cycles (i)-(iii) to check the mass balance. A very high NO conversion, much higher than those obtained under flowing (steady state) reaction conditions, is reached in all cycles. The unreacted NO is re-adsorbed on the zeolite in the step (iii). After two/three cycles (steps i-iii) the experiments are repeatable. The effect of O2 (2.5 vol.%) co-feeding during adsorption step has been also studied; the adsorption capacity during the first cycle is higher than that obtained under O2-free reaction conditions, while NO conversion decreased. After few cycles, adsorption capacity and NO conversion appeared unaffected by O 2 feed