NH_3 storage on a zeolite SCR catalyst measured using a microwave-based method: Reduced sensitivity for more strongly held NH_3

摘要

One method for reduction of nitrogen oxides from the exhaust of modern diesel vehicles is the selective catalytic reduction (SCR) of NO_x by NH_3 injected onto a zeolite SCR catalyst. Knowledge of the amount of NH_3 stored on these catalysts is useful for optimal conversion. Here, measurements of the NH_3 storage on a Cu-chabazite zeolite SCR catalyst were done using the microwave-frequency resonator cavity method. Shown are results for NH_3 loading on a previously empty catalyst and for the subsequent desorption of the more weakly held NH_3. 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 NH_3 storage along the SCR axis. Analysis of desorption data shows that the sensitivity of the resonant frequency change per mass of NH_3 stored on the catalyst is lower for that more strongly held.