The structure, oxygen stoichiometry, and chemical and thermal expansion of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) between 873 and 1173 K and oxygen partial pressures of 1 × 10 -3 to 1 atm were determined by in situ neutron diffraction. BSCF has a cubic perovskite structure, space group Pm3 hm, across the whole T-pO 2 region investigated. The material is highly oxygen deficient with a maximum oxygen stoichiometry (3δ) of 2.339(12) at 873 K and a pO 2 of 1 atm and a minimum of 2.192(15) at 1173 K and a pO 2 of 10 -3 atm. Good agreement is obtained between oxygen stoichiometry data determined by neutron diffraction and thermogravimetry. In the range covered by the experiments, the thermal and chemical expansion coefficients are 19.0(5)-20.8(6) × 10 -6 K -1 and 0.016(2)-0.026(4), respectively.

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CO(2)-free hydrogen can be produced from coal gasification power plants by pre-combustion decarbonisation and carbon dioxide capture. Potassium carbonate promoted hydrotalcite-based and alumina-based materials are cheap and excellent materials for high-temperature (300-500 degrees C) adsorption of CO(2), and particularly promising in the sorption-enhanced water gas shift (SEWGS) reaction. Alkaline promotion significantly improves CO(2) reversible sorption capacity at 300-500 degrees C for both materials. Hydrotalcites and promoted hydrotalcites, promoted magnesium oxide and promoted gamma-alumina were investigated by in situ analytical methods (IR spectroscopy, sorption experiments, X-ray diffraction) to identify structural and surface rearrangements. All experimental results show that potassium ions actually strongly interact with aluminium oxide centres in the aluminium-containing materials. This study unambiguously shows that potassium promotion of aluminium oxide centres in hydrotalcite generates basic sites which reversibly adsorb CO(2) at 400 degrees C.

The present paper discusses the oxygen transport properties, oxygen stoichiometry, phase stability, and chemical and mechanical stability of the perovskites Ba 0:5 Sr 0:5 Co 0:8 Fe 0:2 O 3Àδ (BSCF) and SrCo 0:8 Fe 0:2 O 3Àδ (SCF) for air separation applications. The low oxygen conductive brownmillerite phase in SCF is characterized using in-situ neutron diffraction, thermographic analysis and temperature programmed desorption but this phase is not present for BSCF under the conditions studied. Although both materials show oxygen fluxes well above 10 ml/ cm 2 •min at T=1,273 K and pO 2 =1 bar for self-supporting, 200 μm-thick membranes, BSCF is preferred as a membrane material due to its phase stability. However, BSCF's longterm stable performance remains to be confirmed. The deviation from ideal oxygen stoichiometry for both materials is high: δ>0.6. The thermal expansion coefficients of BSCF and SCF are 24×10 −6 and 30×10 −6 K −1 , respectively, as determined from neutron diffraction data. The phenomenon of kinetic demixing has been observed at pO 2 <10 −5 bar, resulting in roughening of the surface and enrichment with alkaline earth metals. Stress-strain curves were determined and indicated creep behavior that induces undesired ductility at T=1,073 K for SCF. Remedies for mechanical and chemical instabilities are discussed.