Effect of hydrothermal aging on CO and C3H6 oxidation over a Pt-Pd-based wiremesh catalyst as a motorcycle aftertreatment device

Abstract

Motorcycles are major contributors to air pollutants, i.e. CO, VOCs, and PM, emissions to the atmosphere in some regions around the world. Hydrothermal aging of the Pd-Pt-based wiremesh catalyst, as an emission control device for 4-stroke carburetor motorcycles, was studied under laboratory-simulated aging conditions. Aging temperature and reaction atmosphere were selected as independent variables affecting aging. Catalyst properties were characterized by ICP, XPS, BET, EDS, and FE-SEM analysis. Increasing aging temperature and oxidizing atmosphere led to a more pronounced particle size growth and sintering after aging. Regardless of the aging temperature, surface inhibition effects gradually disappeared by shifting the light-off curves to higher temperatures, whether the reason for this shift is oxygen deficiency in the reaction mixture or hydrothermal aging of the catalyst. The surface concentration of the most active phase of platinum, Pt0, decreased in the following order: fresh sample > reducing-aged at 750 °C ≈ reducing-aged at 900 °C > oxidizing-aged at 750 °C > oxidizing-aged at 900 °C. The overall trend of activity for different samples is as follows: fresh sample > reducing-aged at 750 °C > oxidizing-aged at 750 °C > reducing-aged at 900 °C > oxidizing-aged at 900 °C. The less extent of deactivation under reducing atmosphere was attributed to the preservation of metallic Pt content and limited particle size growth under such aging conditions. Analysis of the effect of the air-fuel ratio on the light-off profiles indicated that under all aging conditions, the rich atmosphere resulted in the highest degree of deactivation compared to stoichiometric and lean conditions.