In Situ Time-Resolved Redox Dynamics of Pd Catalysts Under Oscillating A/F Conditions
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The redox dynamics of Pd catalysts under lean/rich perturbation conditions was analyzed by in situ time-resolved reflectance spectroscopy. The real-time redox of Pd/Al2O3 was monitored using the reflectance at 650 nm at every second under simulated exhausts (CO–C3H6–NO–O2), which were switched between air-to-fuel ratio of 14.1 (rich) and 15.0 (lean). Compared to the fast oxidation of metallic Pd (Pd0) upon rich-to-lean switching, the reduction of Pd oxide (Pd2+) upon reverse (lean-to-rich) switch started after a long induction period and proceeded slowly. Because the similar result was also observed for a Pd metal foil, the unequal redox rates under the lean/rich perturbation condition is characteristic of Pd. The temperature dependence of the redox rate demonstrated that the activation energy for the reduction of Pd oxide is greater than that of the Pd oxidation. The faster oxidation rate of Pd surface is considered as the primary reason for steep decrease of NO reduction efficiency in a slightly lean A/F region.
KeywordsThree-way catalysts Redox dynamics Palladium In situ reflectance spectroscopy
Part of this work was supported by the MEXT program, “Elements Strategy Initiative to Form Core Research Center” (since 2012), which is run by MEXT (Ministry of Education Culture, Sports, Science and Technology), Japan.
- 1.Heck RM, Farrauto RJ, Gulati ST (1995) Catalytic air pollution control: commercial technology. Wiley, HobokenGoogle Scholar
- 14.Nur ASM, Funada E, Kiritoshi S, Matsumoto A, Kakei R, Hinokuma S, Yoshida H, Machida M (2018) Phase-dependent formation of coherent interface structure between PtO2 and TiO2 and its impact on thermal decomposition behavior. J Phys Chem C 122(1):662–669. https://doi.org/10.1021/acs.jpcc.7b10858 CrossRefGoogle Scholar
- 15.Crozier PA, Datye AK (2000) Direct observation of reduction of PdO to Pd metal by in situ electron microscopy. In: Corma A, Melo FV, Mendioroz S, Fierro JLG (eds) Studies in surface science and catalysis. Elsevier, Amsterdam pp 3119–3124. https://doi.org/10.1016/S0167-2991(00)80501-7 CrossRefGoogle Scholar
- 19.Wittanadecha W, Laosiripojana N, Ketcong A, Ningnuek N, Praserthdam P, Monnier JR, Assabumrungrat S (2014) Preparation of Au/C catalysts using microwave-assisted and ultrasonic-assisted methods for acetylene hydrochlorination. Appl Catal A 475:292–296. https://doi.org/10.1016/j.apcata.2014.01.043 CrossRefGoogle Scholar
- 20.Tanaka H, Hirotoshi F, Takahashi I (1995) Excellent oxygen storage capacity of perovskite-Pd three-way catalysts. SAE Paper:950256Google Scholar
- 23.Szekely J, Evans JW, Sohn HW (1976) Gas–solid reactions. Academic Press, Inc., New York, p 10Google Scholar