Issue 8, 2015

Surface controlled reduction kinetics of nominally undoped polycrystalline CeO2

Abstract

Ceria is an interesting material for high temperature redox applications like solar-thermal splitting of CO2 and H2O. Technical implementation and reactor design for solar-thermal redox-based fuel generation requires reliable data for the chemical surface exchange coefficient and the chemical diffusivity of oxygen. The results of thermogravimetric relaxation experiments and equilibrium oxygen isotope exchange experiments with subsequent depth profiling analysis suggest that the reduction reaction of even dense samples of pure ceria (1 mm thickness, 93% of theoretical density) with a grain size of about 20 μm is surface reaction controlled. The chemical surface exchange coefficient exhibits a negative apparent activation energy (−64 kJ mol−1). This finding is corroborated by similar data from literature for the tracer surface exchange coefficient. The structure of the derived expression for the apparent activation energy further suggests that the chemical surface exchange coefficient should show only a very weak dependence on temperature for ceria doped with lower valence cations.

Graphical abstract: Surface controlled reduction kinetics of nominally undoped polycrystalline CeO2

Article information

Article type
Paper
Submitted
09 Dec 2014
Accepted
17 Jan 2015
First published
20 Jan 2015
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2015,17, 5849-5860

Author version available

Surface controlled reduction kinetics of nominally undoped polycrystalline CeO2

N. Knoblauch, L. Dörrer, P. Fielitz, M. Schmücker and G. Borchardt, Phys. Chem. Chem. Phys., 2015, 17, 5849 DOI: 10.1039/C4CP05742B

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