Kinetics of Oxygen Exchange over CeO2-ZrO2 Fluorite-Based Catalysts
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- 作者：Ekaterina M. Sadovskaya ; Yulia A. Ivanova ; Larisa G. Pinaeva ; Giacomo Grasso ; Tatiana G. Kuznetsova ; Andre van Veen ; Vladislav A. Sadykov ; Claude Mirodatos
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：May 24, 2007
- 年：2007
- 卷：111
- 期：20
- 页码：4498 - 4505
- 全文大小：133K
- 年卷期：v.111,no.20(May 24, 2007)
- ISSN：1520-5215
文摘
The kinetics of 18O/16O isotopic exchange over CeO2-ZrO2-La2O3 and Pt/CeO2-ZrO2 catalysts have beeninvestigated under the conditions of dynamic adsorption-desorption equilibrium at atmospheric pressure anda temperature range of 650-850 
C. The rates of oxygen adsorption-desorption on Pt sites, support surface,oxygen transfer (spillover) from Pt to the support as well as the amount of oxygen accumulated in the oxidebulk, and oxygen diffusion coefficient were estimated. The nanocrystalline structure of lanthana-doped ceria-zirconia prepared via the Pechini route with a developed network of domain boundaries and specific defectsguarantees a high oxygen mobility in the oxide bulk (D = (1.5 
2.0)·10-18 m2 s-1 at 650 C) and allowsaccumulation of over-stoichiometric/excess oxygen. For Pt/CeO2-ZrO2, oxygen transfer from Pt to support(characteristic time < 10-2 s) was shown to be responsible for the fast exchange between the gas-phaseoxygen and oxygen adsorbed on the mixed oxide surface. The rate of direct exchange between the gas phaseand surface oxygen is increased as well due to the increased concentration (up to 2 monolayers) of surface/near subsurface oxygen species accumulated on the oxygen vacancies (originated from the incorporation ofhighly dispersed Pt atoms). The characteristic time of diffusion of the oxygen localized in the subsurfacelayers is about 1 s. The overall quantity of over-stoichiometric oxygen and/or hydroxyl groups accumulatedin the bulk can reach the equivalent of 10 monolayers, and characteristic time of oxygen diffusion within thebulk is about 20 s. All these kinetic data are required for the further step of modeling partial oxidation ofhydrocarbons under steady- and unsteady-state conditions.
C. The rates of oxygen adsorption-desorption on Pt sites, support surface,oxygen transfer (spillover) from Pt to the support as well as the amount of oxygen accumulated in the oxidebulk, and oxygen diffusion coefficient were estimated. The nanocrystalline structure of lanthana-doped ceria-zirconia prepared via the Pechini route with a developed network of domain boundaries and specific defectsguarantees a high oxygen mobility in the oxide bulk (D = (1.5 2.0)·10-18 m2 s-1 at 650 C) and allowsaccumulation of over-stoichiometric/excess oxygen. For Pt/CeO2-ZrO2, oxygen transfer from Pt to support(characteristic time < 10-2 s) was shown to be responsible for the fast exchange between the gas-phaseoxygen and oxygen adsorbed on the mixed oxide surface. The rate of direct exchange between the gas phaseand surface oxygen is increased as well due to the increased concentration (up to 2 monolayers) of surface/near subsurface oxygen species accumulated on the oxygen vacancies (originated from the incorporation ofhighly dispersed Pt atoms). The characteristic time of diffusion of the oxygen localized in the subsurfacelayers is about 1 s. The overall quantity of over-stoichiometric oxygen and/or hydroxyl groups accumulatedin the bulk can reach the equivalent of 10 monolayers, and characteristic time of oxygen diffusion within thebulk is about 20 s. All these kinetic data are required for the further step of modeling partial oxidation ofhydrocarbons under steady- and unsteady-state conditions.