Investigation of novel mixed metal ferrites for pure H2 and CO2 production using chemical looping

Abstract

The mixed metal oxides NiFe2O4 and CoFe2O4 are candidate materials for the Chemical Looping Hydrogen (CLH) process, which produces pure and separate streams of H2 and CO2 without the use of complicated and expensive separations equipment. In the CLH process, syngas reduces a metal oxide, oxidizing the H2 and CO in the syngas to H2O and CO2, and “stores” the chemical energy of the syngas in the reduced metal oxide. The reduced metal oxide is then oxidized in steam to regenerate the original metal oxide and produce H2. In this study, we report thermodynamic modeling and experimental results regarding the syngas reduction and H2O oxidation of NiFe2O4 and CoFe2O4 to determine the feasibility of their use in the CLH process. Modeling predicts the oxidation of nearly all the CO and H2 in syngas to H2O and CO2 during the reduction step for both materials, and regeneration of the mixed metal spinel phase during oxidation with excess H2O. Laboratory tests in a packed bed reactor confirmed over 99% conversion of H2 and CO to H2O and CO2 during reduction of NiFe2O4 and CoFe2O4. Powder XRD analysis of the reduced materials showed, in accordance with thermodynamic predictions, the presence of a spinel phase and a metallic phase. High reactivity of the reduced NiFe2O4 and CoFe2O4 with H2O was observed, and XRD analysis confirmed re-oxidation to NiFe2O4 and CoFe2O4 under the conditions tested. When compared with a conventional Fe-based CLH material, the mixed metal spinels showed a higher extent of reduction under the same conditions, and produced four times the H2 per mass of active material than the Fe-based material. Analysis of the H2 and CO consumed in the reduction and the H2 produced during the oxidation showed over 90% conversion of the H2 and CO in syngas back to H2 during oxidation.