Catalyst-assisted chemical looping for CO2 conversion to CO

A bifunctional 5% Ni/CeO2-Fe2O3 (1:1) sample was prepared for the transformation of CO2 to CO by catalyst-assisted chemical looping. Generation of CO from CO2 through CH4 + CO2/CO2 redox cycles was investigated between 873 K and 973 K. In the reduction step, CH4 + CO2 is converted over Ni into syngas, which then reduces the CeO2-Fe2O3 oxygen storage material, yielding CO2 and H2O. CO is produced upon re-oxidation of the oxygen storage material by CO2. The addition of Ni to CeO2-Fe2O3 has a beneficial effect upon the activity of the material during periodic cycling. The crystallographic structure of the sample was examined using time-resolved in situ X-ray diffraction under H-2 reduction and CO2 oxidation. H-2-TPR reduced the Fe2O3 phase to Fe3O4, FeO and Fe. From 600 K onwards NiO reduction is initiated. Interaction between Ni and Fe leads to Ni3Fe alloy formation from 850 K onwards. This alloy remains stable up to 873 K during CO2 re-oxidation but is completely decomposed into Ni and Fe3O4 at 973 K. This re-oxidation of iron follows a one-step pathway to Fe3O4 between 773 K and 873 K, but a two-step pathway above 873 K. The methane reforming on the Ni-based catalyst is accompanied with formation and accumulation of surface carbon. This carbon is removed by oxidation with lattice oxygen from CeO2-Fe3O4 during or after re-oxidation with CO2. (C) 2014 Elsevier B.V. All rights reserved.