Experimental investigation of La(0,6)Sr(0,4)Mn(0,6)Cr(0,4)O3 perovskite oxidation kinetics for thermochemical carbon dioxide splitting redox cycles

An ever so intense effort aimed at a green transition to mitigate the effects of anthropic climate change is undergoing worldwide. The path is long though, and presents complex issues, one of them being the strong dependency on fossil fuels of various key sectors of the current society such as electricity and heat production, transport and industries. In this context, the production of renewable fuels, and more specifically solar fuels, is considered extremely promising by the scientific community. The most exploited way to obtain solar fuels as of now is to employ electrolysers to split H2O and CO2 molecules, reducing them to a mixture of H2 and CO, which is called a syngas and can be exploited both as fuel and as platform for the synthesis of more complex hydrocarbons. Such process has strong efficiency limitations though and it is worth it to explore different options, amongst which a promising one is represented by thermochemical redox cycles. In thermochemical cycles an oxygen carrier is reduced at high temperature, losing part of its oxygen content by generating some vacancies or rearranging its structure. The material then undergoes an oxidation step in which H2O and/or CO2 are supplied. In this step the oxygen carrier claims back the oxygen atoms that are missing in its lattice and therefore reduces the H2O and CO2 molecules to a syngas. The two described steps can then be repeated in a loop. The utilization of carbon dioxide as a valuable feedstock and the possibility to supply the high temperature heat through renewable technologies like solar concentrators make this process extremely interesting from the environmental point of view, while also presenting much higher potential efficiency with respect to electrolysis, since the transformation of solar energy in electrical energy is not required in this case. However, in order to make redox thermochemical cycles technologically and economically viable, suitable oxygen carriers as well as reactor layouts must be investigated. This work studies an innovative perovskite with chemical composition La0.6Sr0.4Mn0.6Cr0.4O3 in properly designed thermochemical cycles as oxygen carrier for carbon dioxide splitting. The tests are conducted in a machine for thermogravimetric analysis, in experimental conditions that have been optimized one by one. The perovskite’s performances in terms of CO yield are assessed, with particular attention to the reaction kinetics of the oxidation step. Such an approach was chosen since there are not known kinetics studies on this specific material, which is relevant since knowing more about oxidation kinetics means to better understand the reaction mechanisms, as well as to be capable of more precisely tuning the features of a reactor in potential future developments.