Inhibiting the interaction between FeO and Al2O3 during chemical looping production of hydrogen
Fennel, Paul S
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Liu, W., Ismail, M., Dunstan, M., Hu, W., Zhang, Z., Fennel, P. S., Scott, S., & et al. (2014). Inhibiting the interaction between FeO and Al2O3 during chemical looping production of hydrogen. RSC Advances, 1759-1771. https://doi.org/10.1039/c4ra11891j
Hydrogen of high purity can be produced by chemical looping using iron oxide as an oxygen carrier and making use of the reaction between steam and either iron or FeO. However, this process is viable only if the iron oxide can be cycled between the fully-oxidised and fully-reduced states many times. This can be achieved if the iron oxide is supported on refractory oxides such as alumina. Unfortunately, the interaction between alumina and oxides of iron to form FeAl2O4 hinders the kinetics of the reactions essential to the production of hydrogen, viz. the reduction of Fe(II) to metallic iron by a mixture of CO and CO2 prior to the oxidation by steam. Here, oxygen carriers containing Fe2O3 and Al2O3 were doped with Na2O and, or, MgO, in order to inhibit the formation of FeAl2O4 by forming NaAlO2 or MgAl2O4, respectively. The performance of the modified oxygen carriers for producing hydrogen, i.e. cyclic transitions between Fe2O3 (or Fe3O4) and metallic Fe at 1123 K were investigated. It was found that the interaction between FeO and Al2O3 was successfully mitigated in an oxygen carrier containing Mg, with an Al: Mg ratio of 2, resulting in consistently stable and high capacity for producing hydrogen by chemical looping, whether or not the material was oxidised fully in air in each cycle. However, the oxygen carrier without Mg only remained active when a step to oxidise the sample in air was included in each cycle. Otherwise it progressively deactivated with cycling, showing substantial interaction between Al2O3 and oxides of Fe.
The authors would like to thank Mr S.J. Griggs from the Department of Materials Sciences and Metallurgy, University of Cambridge for access to SEM; Prof C.P. Grey from the Department of Chemistry, University of Cambridge for access to XRD; the EPSRC funded National Chemical Database Service hosted by the Royal Society of Chemistry for crystallographic data. Financial support from the Engineering and Physical Sciences Research Council (Grant number: EP/G063265/1) is acknowledged. This work is also funded by the National Research Foundation (NRF), Prime Minister's Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme.
External DOI: https://doi.org/10.1039/c4ra11891j
This record's URL: https://www.repository.cam.ac.uk/handle/1810/246906
Attribution 2.0 UK: England & Wales
Licence URL: http://creativecommons.org/licenses/by/2.0/uk/
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