La 1−xSr xFeO 3−δ perovskites as redox materials for application in a membrane reactor for simultaneous production of pure hydrogen and synthesis gas

Abstract

This work reports on the preparation and characterization of perovskitic materials with the general formula La 1− x Sr x FeO 3 ( 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 SrFeO 3 with x = 1 at 1000 °C. The capability of the prepared powders to convert CH 4 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 H 2 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 H 2 and their water splitting activity. Maximum H 2 yield during the reduction step is achieved with the La 0.7Sr 0.3FeO 3 sample mixed with 5% NiO and is 80% of the theoretically expected H 2, based on complete methane decomposition. In the oxidation – water splitting step, 912 μmol H 2 per gr solid are produced with the La 0.3Sr 0.7FeO 3 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.