Diagnostics of Field-Aged Three-Way Catalyst (TWC) on Stoichiometric Natural Gas Engines 2019-01-0998

Three-way catalysts have been used in a variety of stoichiometric natural gas engines for emission control. During real-world operation, these catalysts have experienced a large number of temporary and permanent deactivations including thermal aging and chemical contamination. Thermal aging is typically induced either by high engine-out exhaust temperatures or the reaction exotherm generated on the catalysts. Chemical contamination originates from various inorganic species such as Phosphorous (P) and Sulfur (S) that contain in engine fluids, which can poison and/or mask the catalyst active components. Such deactivations are quite difficult to simulate under laboratory conditions, due to the fact that multiple deactivation modes may occur at the same time in the real-world operations.

In this work, a set of field-aged TWCs has been analyzed through detailed laboratory research in order to identify and quantify the real-world aging mechanisms. Based on the measured NOx conversion efficiency, we identified that thermal aging was the major aging mechanism for all the field-aged TWCs investigated. Additionally, chemical contaminants such as Phosphorous (P) and Sulfur (S) containing species were also detected at the front portion of the catalyst location that is closer to the engine outlet, leading to decreased NOx and CH₄ conversions at this location. However, the NOx and CH₄ conversions at the rest of the catalyst locations were mildly impacted due to the sharp axial gradient of these chemical contaminants deposition.