title: Kinetics of CO2Reduction over Nonstoichiometric Ceria.
abstract: The kinetics of CO2reduction over nonstoichimetric ceria, CeO2-δ, a material of high potential for thermochemical conversion of sunlight to fuel, has been investigated for a wide range of nonstoichiometries (0.02 ≤ δ ≤ 0.25), temperatures (693 ≤T≤ 1273 K), and CO2concentrations (0.005 ≤pCO2≤ 0.4 atm). Samples were reduced thermally at 1773 K to probe low nonstoichiometries (δ < 0.05) and chemically at lower temperatures in a H2atmosphere to prevent particle sintering and probe the effect of higher nonstoichiometries (δ < 0.25). For extents greater than δ = 0.2, oxidation rates at a given nonstoichiometry are hindered for the duration of the reaction, presumably because of near-order changes, such as lattice compression, as confirmed via Raman Spectroscopy. Importantly, this behavior is reversible and oxidation rates are not affected at lower δ. Following thermal reduction at very low δ, however, oxidation rates are an order of magnitude slower than those of chemically reduced samples, and rates monotonically increase with the initial nonstoichiometry (up to δ = 0.05). This dependence may be attributed to the formation of stable defect complexes formed between oxygen vacancies and polarons. When the same experiments are performed with 10 mol % Gd3+doped ceria, in which defect complexes are less prevalent than in pure ceria, this dependence is not observed.
authors.affiliation: Department of Mechanical and Process Engineering, ETH Zürich , Sonneggstrasse 3, 8092 Zürich, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Ackermann
authors.affiliation: Department of Mechanical and Process Engineering, ETH Zürich , Sonneggstrasse 3, 8092 Zürich, Switzerland.
authors.forename: Laurent
authors.initials: L
authors.lastname: Sauvin
authors.affiliation: Department of Mechanical and Process Engineering, ETH Zürich , Sonneggstrasse 3, 8092 Zürich, Switzerland.
authors.forename: Roberto
authors.initials: R
authors.lastname: Castiglioni
authors.affiliation: Department of Materials, ETH Zürich , Hönggerbergring 64, 8093 Zürich, Switzerland.
authors.forename: Jennifer L M
authors.initials: JL
authors.lastname: Rupp
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of Florida , Gainesville, Florida 32611 , United States.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Scheffe
authors.affiliation: Department of Mechanical and Process Engineering, ETH Zürich , Sonneggstrasse 3, 8092 Zürich, Switzerland.
authors.forename: Aldo
authors.initials: A
authors.lastname: Steinfeld