Initiation of oxygen permeation and POM reaction in different mixed conducting ceramic membrane reactors

Abstract

The initiation of oxygen permeation and POM were studied in mixed conducting ceramic membrane reactors. Membrane material composition, and catalyst-loading mode were proven to have an important effect on the initiation of oxygen permeation and POM reaction. The initiation time for compositions of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCFO) and BaCo 0.4Fe 0.4Zr 0.2O 3− δ (BCFZO) are 20 and 2 h, respectively. When the catalyst was loaded directly on the membrane surface the oxygen permeation flux increased 8–10-fold of that under air/He gradient. The good POM performance of the methane conversion, higher than 96% and the CO selectivity, higher than 95%, was achieved successfully. However, when the catalyst was loaded on a place away from the membrane surface or the catalyst was not loaded, the lower oxygen permeation flux (1–2-fold) and the poor POM performance (the methane conversion is lower than 30% and the CO selectivity is lower than 20%) were obtained. The characterization of XRD and SEM-EDS indicated that the initial process might be finished through initiating the catalyst and adjusting the membrane structure (the formation of a thin CoO containing porous layer with a thickness of about 10 μm). The great increase of oxygen permeation flux can be ascribed to the great decrease of the oxygen partial pressure and the adjustment of the surface structure.