Nickel and iron modified perovskites for partial oxidation of methane in chemical looping Matthew Guy 1 , Ian Metcalfe 1 , Wenting Hu 1 , Kelly Kousi 2 , Dragos Neagu 3 1 Newcastle University, UK, 2 University of Surrey, UK, 3 University of Strathclyde, UK Fuel cells have been developed as an attractive low emission energy conversion device using, in some cases, methane as fuel 1 . These fuel cells produce electricity, plus carbon dioxide and water at the anode and reduced/ depleted oxygen at the cathode 2 . However, if the methane were partially oxidised, it would enable syngas (hydrogen and carbon monoxide in a 2:1 ratio) production at the anode. This can be used for blue hydrogen production involving carbon capture. Similarly, chemical looping (CL) allows a chemical process to be broken into two separate sub-reactions in this case, connected by an oxygen carrier material (OCM). This produces two outputs where the reactants remain separated 3 . In CL partial oxidation of methene (POM) the methane is partially oxidised by the OCM in the first sub-reaction. Sub-reaction 1: CH 4 +MO → 2H 2 +CO+MO 1-δ . Re-oxidation of the OCM in the second sub-reaction, is performed in air or other oxidising gas. The re-oxidised OCM can be used for the partial oxidation of methane, completing the loop. Sub-reaction 2: Air+MO 1-δ → Air -δ +MO. The OCM for POM should have resistance to degradation through sintering or carbon deposition, long term stability, high oxygen capacity, high oxygen transport rates and selectivity to syngas. Lanthanum Strontium Ferrite (La 0.6 Sr 0.4 FeO 3 /LSF641) is a perovskite which inherently has many of these properties 4 . LSF641 can however degrade through coking, has relatively low oxygen capacity, requires high operating temperatures and is not selective to syngas. The perovskite structure can be tailored using many modifying elements. This work describes the modification of LSF641 using nickel to promote higher reactivity of methane to syngas and lower reaction temperatures, as the nickel activates the C-H bond in methane 5 . The incorporation of iron oxide into the bulk of the perovskite increases oxygen capacity acting as an oxygen reservoir. Iron oxide has high oxygen capacity, however in isolation loses surface area, and thus activity, rapidly on cycling 6 . The oxygen capacity of LSF641 can be more than doubled by the addition of 5wt% iron into the perovskite. The impregnation of nickel on the surface of the OCM reduces the activation temperature of methane on LSF641 by 200 o C. Exsolution, another method of incorporating nickel into the surface of the OCM to activate methane, is considered. Combining these improvements on the base LSF641 is key to the development of a tailored OCM for CL POM and the principles used can be applied to other CL reactions. References 1. Murray E.P. et al. (1999) Volume 400 , pages 649-651. 2. Tu B. et al. (2020) International Journal of Hydrogen Energy, Volume 45 , pages 27587-27596. 3. Leeuwe C. et al. (2021) Chemical Engineering Journal. Volume 423 , page 130174. 4. Murugan A. et al. (2011) Energy Environ. Sci. Volume 4 , pages 4639-4649. 5. Choudhary T.V. and Goodman D.W. (2000) Journal of Molecular Catalysis A: Chemical. Volume 163 , Issues 1-2, pages 9-18. 6. Gemmi M. et al. (2005) Appl. Crystallogr . Volume 38 , pages 353−360.
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