CO2 splitting by thermo-chemical looping based on ZrxCe1−xO2 oxygen carriers for synthetic fuel generation

Abstract

The thermochemical CO2 splitting via cerium-based mixed oxides is considered. This process targets the recycling and upgrading of CO2 emissions for the production of solar fuels. The CO2 reduction is achieved by thermochemical looping using ceria–zirconia solid solutions as oxygen carriers: (1) the mixed oxide is first reduced by thermal activation for releasing some oxygen from its lattice, (2) the reduced oxide is then oxidized with CO2 for producing carbon monoxide and the initial metal oxide that is recycled to the first step. Reactive cerium-based mixed oxides were first synthesized as nanopowders by different soft chemical routes. Their reactivity was then investigated experimentally by thermogravimetry analysis to demonstrate that the produced nanoparticles react efficiently with CO2. The two-step process consisting of thermal activation and CO2-splitting reaction was able to produce CO repeatedly. The influence of the synthesis method, the Zr content in ZrxCe1−xO2, and the temperature of the CO2 reduction reaction was investigated. The material was reduced at 1400°C in flowing Ar and the CO2 reduction was performed below this temperature (typically in the range of 700–1200°C). Both the CO production and the material cyclability were improved when decreasing the Zr content, although the reduction extent was lessened. The Ce0.75Zr0.25O2 and Ce0.9Zr0.1O2 redox catalysts withstood repeated cycles without any noticeable sintering and reactivity losses. The most reactive material was the powder synthesized via the Pechini method (242μmol CO/g at 1000°C).