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

Abstract

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 (2.5vol.%) 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 O2 feed.