NH3 Storage on a Zeolite SCR Catalyst Measured Using a Microwave-based Method: Reduced Sensitivity for More Strongly Held NH3

Abstract

One method for reduction of nitrogen oxides from the exhaust of modern diesel vehicles is the selective catalytic reduction (SCR) of NOx by NH3 injected onto a zeolite SCR catalyst. Knowledge of the amount of NH3 stored on these catalysts is useful for optimal conversion. Here, measurements of the NH3 storage on a Cu-chabazite zeolite SCR catalyst were done using the microwave-frequency resonator cavity method. Shown are results for NH3 loading on a previously empty catalyst and for the subsequent desorption of the more weakly held NH3. Temperature was held constant at 250°C. We demonstrate that a comparison of the frequency changes of the resonant modes can help determine variations in the spatial profile of the NH3 storage along the SCR axis. Analysis of desorption data shows that the sensitivity of the resonant frequency change per mass of NH3 stored on the catalyst is lower for that more strongly held.