Reactivity Retention of Modern Converters for Stringent Emission Control

The push for environmental protection and sustainability has led to strict emission regulations for automotive manufacturers as evident in EURO VII and 2026 EPA requirements. The challenge lies in maintaining fuel efficiency and simultaneously reducing the carbon footprint while meeting future emission regulations. Modern internal combustion engines typically employ various in-cylinder emission reduction techniques along with a multi-stage exhaust after-treatment system to comply with emission standards. Three-way catalyst has been the primary workhorse for the automotive industry for exhaust after-treatment in stoichiometric burn engines, owing to its exceptional conversion efficiency and single-stage simultaneous reductive and oxidative emission mitigation. However, fuel and lubricant-borne sulfur and phosphorus compounds have been shown to have a significant long-term effect on the activity of three-way catalysts, particularly during the lean-rich transitions and oxygen storage processes. In the present study, the impact of sulfur contamination on the conversion efficiency and oxygen storage capacity of the three-way catalyst has been investigated on a production engine as well as a heated flow reactor bench platforms. The influence of sulfur accumulation on the water-gas shift reaction and activity of ceria has been studied. Additionally, the process of sulfur removal at high temperature (~700-750C) has also been explored. Relevant engine-out exhaust conditions from the SI engine platform, including flow, temperature, and exhaust species, were replicated on a heated aftertreatment flow bench during contamination and regeneration cycles. A comprehensive analysis of species before and after the catalyst sections was performed using Fourier-transformed infrared (FTIR) and mass spectrometers to study and quantify the conversion and formation of species, including ammonia, nitrogen oxides (particularly N2O), and hydrogen, under different catalyst conditions. The conversion selectivity of different species is also investigated.