Commercial automotive catalysts: Chemical, structural and catalytic evaluation, before and after aging

This paper presents the effect of aging on a series of commercial three way catalysts, of the same supplier, by analyzing their chemical, textural, structural and catalytic properties. The catalysts were aged in a motor bench test, involving runs of 150 or 300 h and using gasoline with two sulfur levels: 400 and 700 ppm. The catalysts were characterized by X-ray diffraction (XRD) and fluorescence (XRF), surface area, pore volume and pore diameter. The catalytic activities were determined based on CO and propane conversions. After aging, a decrease in surface area and pore volume was observed, as well as an increase in mean pore diameter. Evidence of the presence of α-Al2O3, δ-Al2O3 and PdO phases was found according to XRD data, which can be attributed to a severe thermal deactivation of the catalysts. Some crystalline compounds containing fuel contaminants like cerium phosphate were also identified. The activity for CO and C3H8 oxidation presented a slight correlation with the surface area of the aged catalysts.