Effect of pre-treatment and modification conditions of natural zeolites on the decomposition and reduction of N2O
The decomposition of N2O and reduction of N2O with NH3 on natural and modified zeolites were studied by a steady state reaction. Two different natural zeolites having different phase compositions were modified by ion exchange (0.5 M NH4NO3) and acid leaching (1 M HCl) and treated under low temperature, high temperature and steam conditions. It was observed that the surface modification of natural zeolites depends strongly on their structure and composition. The modification of zeolites by ion exchange and acid leaching increases the decomposition activity of N2O because of the formation of isolated iron and Fe-O-Al species. However, these modifications insignificantly affect the reduction of N2O with NH3. High temperature and steam treatments lead to dealumination, loss of crystallinity, sintering of phases and the formation of amorphous material in zeolites, resulting in a significant decrease in the decomposition and reduction activity of N2O. The kinetic evaluation for N2O decomposition predicts that the rate-limiting step is the recombinative desorption of molecular oxygen.