Analysis of microstructural changes in lean nox trap materials isolates parameters responsible for activity deterioration

The rapid loss of performance of lean NO_x traps is well-known and has been attributed to precious metal sintering, based on the analysis of catalysts aged on bench-top reactors, on dynamometers, and on vehicles. This precious metal sintering leads to reduction in surface area contact between the precious metals and NO_x adsorbers. As a result, the catalyst sites available for NO_x oxidation and the adsorber sites available for NO₂ adsorption are drastically reduced. The use of bench-top reactors, dynos and vehicles to provide aged catalyst samples for analysis is tedious and time consuming. In order to rapidly screen catalysts for microstructural changes, we have designed an ex-situ reactor that allows us to expose catalyst samples on a TEM grid to operating conditions using a simulated exhaust. Thus, we can analyze by TEM several selected areas of a catalyst sample for microstructural changes, starting from fresh samples and progressing through samples exposed to various operating conditions. Here, we present our results on the TEM study of a model lean NO_x trap catalyst exposed to lean, rich, lean-rich cycling, and accelerated aging conditions, using our ex-situ reactor.