La1−xSrxFeO3−δ perovskites as redox materials for application in a membrane reactor for simultaneous production of pure hydrogen and synthesis gas

This work reports on the preparation and characterization of perovskitic materials with the general formula La1−xSrxFeO3 (x = 0, 0.3, 0.7, 1) for application in a dense mixed conducting membrane reactor process for simultaneous production of synthesis gas and pure hydrogen. Thermogravimetric experiments indicated that the materials are able to loose and uptake reversibly oxygen from their lattice up to 0.2 oxygen atoms per “mole” for SrFeO3 with x = 1 at 1000 °C. The capability of the prepared powders to convert CH4 during the reduction step, in order to produce synthesis gas, as well as their capability to dissociate water during the oxidation step, in order to produce hydrogen were evaluated by pulse reaction experiments in a fixed bed pulse reactor. The high sintering temperatures (1100–1300 °C) required for the densification of the membrane materials result in decreased methane conversion and H2 yields during the reduction step compared to the corresponding values obtained with the perovskite powders calcined at 1000 °C. Addition of small quantities of NiO, by simple mechanical mixing, to the perovskites after their sintering at high temperatures, increases substantially both their methane decomposition reactivity, their selectivity towards CO and H2 and their water splitting activity. Maximum H2 yield during the reduction step is achieved with the La0.7Sr0.3FeO3 sample mixed with 5% NiO and is 80% of the theoretically expected H2, based on complete methane decomposition. In the oxidation – water splitting step, 912 μmol H2 per gr solid are produced with the La0.3Sr0.7FeO3 sample mixed with 5% NiO. The experimental results of this work can be equally well applied for the “chemical-looping reforming” process since they concern using the lattice oxygen of the perovskite oxides for methane partial oxidation to syngas, in the absence of molecular oxygen, and subsequent oxidation of the solid.