The catalytic performance of Cu-containing zeolites in N 2O decomposition and the influence of O 2, NO and H 2O on recombination of oxygen

Abstract

The catalytic decomposition of N 2O was studied over Cu-containing zeolites with different Cu loadings and framework topologies (MFI, MOR, FER, BEA, and FAU). The influence of NO, O 2, and H 2O on the rate of N 2O decomposition was investigated in detail. A kinetic model was developed based on the relevant elementary reaction steps in the mechanism of N 2O decomposition. The recombination of oxygen atoms into molecular oxygen is recognized as the rate-limiting step in N 2O decomposition. The rate of oxygen desorption depends strongly on the Cu loading. At low Cu loadings, migration of oxygen atoms is required for recombinative desorption. NO accelerates oxygen recombination, because it provides an alternative route for oxygen migration via gas-phase NO 2. The effect of water differs for Cu-containing zeolites with high and low Cu loadings. At high Cu loading, the rate is suppressed by competitive adsorption of water on the active sites, resulting in an increase in apparent activation energy. The rate of N 2O decomposition is increased substantially for catalysts with a low Cu loading. This is tentatively attributed to water-induced mobility of Cu ions, which facilitates oxygen migration. The effect of water addition is fully reversible.