Characterization of mixed-conducting La2Ni0.9Co0.1O4+δ membranes for dry methane oxidation

The oxygen permeation through dense La(2)N(0.9)Co(0.1)O(4+)delta 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/CH4 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 La2N0.9Co0.1O4+delta, evaluated by the measurements of total conductivity and Seebeck coefficient as functions of the oxygen partial pressure, is sufficient for the oxidation of dry CH4 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/La2N0.9Co0.1O4+delta layer applied onto permeate-side surface, showed high CO2 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. (C) 2003 Elsevier B.V. All rights reserved.