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A series of ceria and ceria-zirconia supported Pd model automotive catalysts were prepared and aged under air or redox conditions at 1050°C for 12 h. The supports were manufactured by different methods and represent a range of compositions. The samples were characterized before and after aging by BET, X-ray diffraction, mercury porosimetry, XPS, H2 temperature-programmed reduction, and oxygen storage capacity measurements. Oxygen storage measurements revealed that the behavior of the catalysts varied according to aging conditions and temperature of measurement. Pd/ceria-zirconia catalysts showed higher oxygen storage characteristics after 1050°C aging than Pd/ceria catalysts, and the phase purity of the ceria-zirconia was shown to positively affect the amount of oxygen storage. The initial rates of oxygen release from the model catalysts at 350°C were shown to depend on the preparation conditions of the supports.

Desulfation characteristics of several model and fully-formulated monolithic lean NOx trap materials were studied in a laboratory flow reactor employing a chemical ionization mass spectrometer. For all samples, desulfation at elevated temperatures under reducing conditions resulted in appearance of sulfur dioxide (SO2) followed by carbonyl sulfide (COS) and hydrogen sulfide (H2S). The data appear consistent with a desulfation mechanism involving elimination of SO2 from stored sulfates under reducing conditions, followed by reaction of the SO2 with CO and H2 to produce COS and H2S, respectively. Based on these observations, several cyclic and multistage desulfation strategies were devised which greatly decreased H2S emissions while achieving relatively rapid and complete sulfur removal.