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    Enhanced Intermediate-Temperature CO2 Splitting Using Nonstoichiometric Ceria and Ceria-Zirconia

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    Type
    Article
    Authors
    Zhao, Zhenlong cc
    Uddi, Mruthunjaya
    Tsvetkov, Nikolai
    Yildiz, Bilge
    Ghoniem, Ahmed F.
    Date
    2017
    Permanent link to this record
    http://hdl.handle.net/10754/625793
    
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    Abstract
    CO2 splitting via thermo-chemical or reactive redox has emerged as a novel and promising carbon-neutral energy solution. Its performance depends critically on the properties of the oxygen carriers (OC). Ceria is recognized as one of the most promising OC candidates, because of its fast chemistry, high ionic diffusivity, and large oxygen storage capacity. The fundamental surface ion-incorporation pathways, along with the role of surface defects and the adsorbates remains largely unknown. This study presents a detailed kinetics study of CO2 splitting using CeO2 and Ce0.5Zr0.5O2 (CZO) in the temperature range 600-900℃. Given our interest in fuel-assisted reduction, we limit our study to relatively lower temperatures to avoid excessive sintering and the need for high temperature heat. Compared to what has been reported previously, we observe higher splitting kinetics, resulting from the utilization of fine particles and well-controlled experiments which ensure a surface-limited-process. The peak rates with CZO are 85.9 μmole g–1s–1 at 900℃ and 61.2 μmole g–1s–1 at 700℃, and those of CeO2 are 70.6 μmole g–1s–1 and 28.9 μmole g–1s–1. Kinetics models are developed to describe the ion incorporation dynamics, with consideration of CO2 activation and the charge transfer reactions. CO2 activation energy is found to be – 120 kJ mole-1 for CZO, half of that for CeO2, while CO desorption energetics is analogous among the two samples with the value of ~160 kJ mole-1. The charge-transfer process is found to be the rate-limiting step for CO2 splitting. The evolution of CO32- with surface Ce3+ is examined based on the modeled kinetics. We show that the concentration of CO32- varies with Ce3+ in a linear-flattened-decay pattern, resulting from a mismatch between the kinetics of the two reactions. Our study provides new insights into the significant role of the surface defects and adsorbates in determining the splitting kinetics.
    Citation
    Zhao Z, Uddi M, Tsvetkov N, Yildiz B, Ghoniem AF (2017) Enhanced intermediate-temperature CO2 splitting using nonstoichiometric ceria and ceria–zirconia. Phys Chem Chem Phys 19: 25774–25785. Available: http://dx.doi.org/10.1039/c7cp04789d.
    Sponsors
    This study is financially supported by a grant from the British Petroleum (BP) and the King Abdullah University of Science and Technology (KAUST) Investigator Award.
    Publisher
    Royal Society of Chemistry (RSC)
    Journal
    Phys. Chem. Chem. Phys.
    DOI
    10.1039/c7cp04789d
    ae974a485f413a2113503eed53cd6c53
    10.1039/c7cp04789d
    Scopus Count
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