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1557225 
Journal Article 
Thermal and chemical aging of model three-way catalyst Pd/Al2O3 and its impact on the conversion of CNG vehicle exhaust 
Matam, SK; Otal, EH; Aguirre, MH; Winkler, A; Ulrich, A; Rentsch, D; Weidenkaff, A; Ferri, D 
2012 
Yes 
Catalysis Today
ISSN: 0920-5861 
184 
1 
237-244 
WOS:000303108100026 
Thermal and chemical aging induced physical and chemical
modifications in the model three-way catalyst Pd/Al2O3 for compressed natural gas vehicles
exhaust were studied. The fresh catalyst Pd/Al/F (calcined at 500 degrees C for 4 h) was
subjected to either thermal (Pd/Al/700) or chemical (poisoned with phosphorous (P), XP/Pd/Al; X =
1.8 or 7.5 wt%) aging under air flow at 700 degrees C for 5 h. The catalysts were analyzed by N-
2-physisorption, CO-chemisorption, high angular annular dark-field scanning transmission electron
microscopic (HAADF-STEM), X-ray diffraction (XRD), solid state P-31 MAS NMR, H-2-temperature
programmed reduction (H-2-TPR) and in situ X-ray absorption near edge structure spectroscopy
(XANES) during H-2-TPR. Characterization results reveal that thermal aging leads to merely
physical modifications such as decreased surface area of the support and palladium (Pd)
dispersion in Pd/Al/700. Whereas, chemical aging causes both severe physical and chemical
modifications in XP/Pd/Al: (i) physical modifications are clogging of support pores and fouling
of Pd nanoparticles with P as evident from N-2-physisorption, CO-chemisorption and HAADF-STEM and
(ii) chemical alterations are the conversion of support aluminum oxide into aluminum phosphate as
evident from solid state P-31 MAS NMR, and decreased reducibility of PdOx species as evident from
H-2-TPR and in situ XANES. Consequently, chemical aging is more detrimental than thermal aging
for three-way catalytic (TWC) performance as evident from the activity data. Undoubtedly, P
(chemical aging) profoundly decreases the TWC efficiency. On the other hand, mere thermal aging
considerably decreases CO and CH4 oxidation efficiency, but interestingly improves the NO
reduction efficiency. (C) 2011 Elsevier B.V. All rights reserved. 
Three-way catalyst; Pd/Al2O3; Thermal aging; Chemical aging; Phosphorous; Aluminum phosphate; PdOx species; Reducibility; CNG