Impact of Chemical Contaminants on Stoichiometric Natural Gas Engine Three-Way Catalysts with High Mileage History

Stoichiometric natural gas engines with three-way catalysts emit less NOx and CH₄ due to their higher efficiency compared to lean-burn natural gas engines. Although hydrothermal aging of three-way catalysts has been extensively studied, a deeper understanding beyond hydrothermal aging is needed to explain real-world performance, especially for natural gas engines with near-zero NOx emissions. In this investigation, field-aged three-way catalysts were characterized to identify the contribution of chemical aging to their overall performance. It was found that the sulfur species on the field-aged TWCs were entirely distributed along the catalyst length, showing a decreasing trend, whereas phosphorous contamination was mainly observed at the inlet section of the three-way catalysts, and the phosphorous concentration declined sharply along the axial length. The amount of sulfur on the catalyst surface was quantified by temperature-programmed desorption and inductively coupled plasma spectroscopy. The performance was assessed before and after removal of sulfur from the three-way catalysts to isolate the contribution of degradation due to hydrothermal aging + P and S. By applying the above method to the cores taken at different axial locations, the dominant aging mechanisms operating at different axial locations in the given field-aged three-way catalyst after-treatment systems were identified. Comparison of the field-aged and reactor standard bench cycle aged catalysts was also undertaken to identify potential gaps in the aging contributions.