In-situ metal doping to boost the reactivity of layered double hydroxide derived Mg-Fe-Al-O oxygen carriers for chemical looping CH4 reforming with CO2 reduction

Abstract

Employing layered double hydroxide (LDH) as a self-template to synthesize iron-based oxygen carrier is a powerful pathway to achieve efficient chemical looping CH4 reforming with CO2 reduction. However, the inevitable formation of inactive component causes a harmful effect on the reactivity. This work proposes an in-situ metal doping strategy to solve this issue. Mg-Fe-Al-O oxygen carriers with varying metal dopants (Ni, Cu, Mn, Ca) and substitution ratios (0–0.5) are examined to investigate its influence on cyclic reactivity and redox mechanism. Ni and Cu dopants enhance the reactivity whilst Mn and Ca make a worse impact. Doping Ni with a ratio of 0.5 (Mg1Ni0.5Fe0.75Al0.25) exhibits a superior reactivity: syngas space time yield (10 mmolCO·kgOC-1·s-1 and 18 mmolH2·kgOC-1·s-1) and CO space time yield (60 mmolCO·kgOC-1·s-1). This originates from: (i) Ni is segregated from solid solution to promote methane activation, and (ii) the re-oxidation of more generated iron and carbon produces more CO.