Characterization of mixed-conducting La 2Ni 0.9Co 0.1O 4+ δ membranes for dry methane oxidation

Abstract

The oxygen permeation through dense La 2Ni 0.9Co 0.1O 4+ δ membranes, prepared by the standard ceramic synthesis technique and via glycine-nitrate process (GNP), is determined by the kinetics of interfacial processes, either surface oxygen exchange at high p(O 2) or oxidation reactions under air/H 2 and air/CH 4 gradients. Despite moderate differences in the ceramic microstructures, the GNP-synthesized membranes possess higher oxygen permeability. In combination with surface-limited oxygen transport, the stability of La 2Ni 0.9Co 0.1O 4+ δ , evaluated by the measurements of total conductivity and Seebeck coefficient as functions of the oxygen partial pressure, is sufficient for the oxidation of dry CH 4 in mixed-conducting membrane reactors operating at temperatures up to 1173 K. Tests of a model reactor, comprising disk-shaped nickelate membrane with porous Pt/La 2Ni 0.9Co 0.1O 4+ δ layer applied onto permeate-side surface, showed high CO 2 selectivity decreasing when temperature increases. At 1173 K, the methane conversion and CO selectivity achieved 20 and 17%, respectively. The observed behavior suggests significant role of the complete methane oxidation on the interface between mixed-conducting membrane and gas phase, thus making it necessary to incorporate reforming catalysts in the reactors.