Three way catalytic activity of thermally degenerated Pt/Al2O3 and Pt/CeO2–ZrO2 modified Al2O3 model catalysts

• Three way catalytic activities were improved by OSC of CeO2 or Ce0.8Zr0.2O2 modified Al2O3.
• Direct observation of NO and CO transient behavior in rich to stoichiometric phase.
• Total buffering to A/F fluctuation was discussed with OSC and redox of Pt.

The effect of ceria and ceria–zirconia modification to alumina on the three-way catalytic (TWC) performance of alumina supported Pt catalyst was investigated. Sintering of Pt was induced by thermal treatment at 1000 °C and suggested the inhibition effect of sintering by doping Ce on Al2O3 support. TWC activity for three catalysts follows the sequence of Pt/Ce0.8Zr0.2O2/Al2O3 > Pt/CeO2/Al2O3 ≫ Pt/Al2O3. Low temperature CO conversion increased clearly upon the addition of CeO2 and CeO2–ZrO2 into Pt/alumina, indicating that the OSC promotes CO oxidation activity and NO is reduced by C3H6 in light-off process. TWC performance with 0.5 Hz dynamic condition at 620 °C indicated better conversions with the same sequence corresponding to OSC of each catalyst. In model transient experiment, CO conversion in rich phase with the sequence of Pt/Ce0.8Zr0.2O2/Al2O3 > Pt/CeO2/Al2O3 ≫ Pt/Al2O3 indicated that the OSC of CeO2 and Ce0.8Zr0.2O2 solid solution on alumina was a major cause for improvement of CO conversion in total dynamic operation even after thermally aged Pt catalysts. Regarding NOx conversion in model transient experiment, the NOx (NO + NO2) low concentration versus time is delayed (with more NOx removal activity) in the cyclic rich to stoichiometric condition for catalysts with OSC component of CeO2 and Ce0.8Zr0.2O2. The oxidized and recovered state of Pt on ceria zirconia should be related to NO removal reaction. Under rich-lean cycle condition, total oxidation and reduction of catalyst affect both transient CO and NO conversions over Pt, so that oxygen storage/release functions of OSC catalyst are effective to total buffering to A/F fluctuation.

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