Nitrates and nitrous oxide formation during the interaction of nitrogen oxides with Cu-ZSM-5 at low temperature

The interaction of NO with Cu-ZSM-5 has been investigated in a temperature range (25-225°C) in which no steady-state reactions occur. The study has been conducted by performing NO adsorption tests at variable exposure times and analysing the occurring phenomena by continuous monitoring the gaseous effluents as well as by performing a subsequent TPD. The effect of temperature, catalyst pre-treatment and composition of the adsorbing mixture (NO/He, NO/O2/He, N2O/He and N2/He) has been evaluated. In situ FTIR experiments have also be carried out under similar conditions. The main observed phenomena are: i) reduced Cu+ sites are quickly re-oxidised by NO producing large amounts of N2O ii) adsorbed NO slowly reacts with gaseous NO to give surface nitrates and N2O in the gas phase regardless the copper oxidation state. A mechanism of copper re-oxidation and of nitrates formation under the different conditions explored has been proposed on the basis of these finding