Perovskite Nanocomposites for Methane Partial Oxidation and CO2 Splitting in a Cyclic Redox Scheme

The current study explores a methane partial oxidation (POx) and CO₂ splitting scheme assisted by industrial waste heat or solar-thermal energy. Specifically, we report mixed oxide nanocomposites as highly effective redox catalysts to facilitate the abovementioned redox scheme. Close to 100% CO₂ to CO conversion was consistently achieved over 30 redox cycles. In this process, methane is introduced as an oxygen “sink” to promote the reduction of the redox catalyst followed with re-oxidation via CO₂ splitting. Separate streams of Fischer-Tropsch/methanol ready syngas and near pure CO were produced from methane and CO₂.

A number of mixed metal oxides with varying structures (Perovskite, Ruddlesden-Popper, and Fluorite) and compositions were studied. It was determined that single phase perovskite and Ruddlesden-Popper (R –P) materials exhibited excellent initial performance but deactivated over multiple redox cycles. Nanocomposites of inert ceramic support and perovskite/R-P materials, however, exhibit excellent recyclability, activity, and selectivity. The effect of support was subsequently determined by detailed characterization of nanocomposites both during and after the redox reactions. Up to 96% syngas selectivity in the methane partial oxidation step was achieved, in addition to close to complete conversion of CO₂ to CO. The corresponding CO productivity and production rate were about 7 times higher than those in state-of-the-art solar-thermal CO₂ splitting processes, which are carried out at significantly higher temperature. In addition to optimizing the bulk structure and compositions of these mixed oxides, surface promotions were attempted to enhance the activity of the redox catalysts for methane activation. The resulting redox catalysts exhibited satisfactory activity/selectivity for methane POx and CO₂-splitting at temperatures lower than 600 °C. Integration of solar-thermal or waste heat and the ability to produce methanol ready syngas and concentrated CO can potentially simply the production of chemicals derived from methanol carbonylation (e.g. acetic acid and ethylene glycol), resulting in reduced energy consumptions and CO₂ emissions.