Correlation of Ammonia Storage and Dielectric Properties of SCR Catalyst Materials by Microwave Cavity Perturbation

摘要

The ammonia-based selective catalytic reduction (SCR) has become the major NO_x control strategy for light and heavy diesel engines. Before reducing NO_x, storage of ammonia on the active sites of the catalyst is crucial. A better understanding of the ammonia storage behavior is needed for improvements in efficiency and control of the exhaust gas aftertreatment systems. Therefore, the aim of.this article is the correlation of the dielectric properties of the SCR material with the amount of stored ammonia. Recently, a laboratory setup using the microwave cavity perturbation method had been developed especially for this purpose and has been significantly improved. This article describes the improvement process and first experimental data. Zeolite-based SCR active material in its H-form was investigated. The powder catalyst sample was monitored by the microwave cavity perturbation method under reaction conditions while storing and depleting ammonia with and without admixed NO_x at different temperatures. It could be shown that both values of the complex dielectric permittivity are strongly correlated to the stored mass of ammonia. The influence of the temperature on the ammonia storage behavior was described. It could be shown by experiment that the response of the real part and the imaginary part of the complex permittivity to ammonia storage have different temperature dependencies.