Titanium-based perovskite-type mixed conducting ceramic membranes for oxygen permeation Jianhua Tong, Weishen Yang * , Rui Cai, Baichun Zhu, Liwu Lin State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, P.O. Box 110, 457 Zhongshan Road, Dalian 116023, PR China Received 21 November 2001 Abstract A titanium-based perovskite-type oxide was synthesized by an improved method of combining EDTA acid and citric acid complexes. High structural stability, good sintering ability, and relatively high oxygen permeation flux were obtained simultaneously for disks synthesized from this ceramic oxide. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Perovskite-type; Mixed conducting ceramic (Fe, Sr, Co, Fe, O) 1. Introduction Mixed conducting ceramic oxides with high oxygen ionic and electronic conductivities could form the basis for dense ceramic membranes that separated oxygen from other oxygen-containing gases by completely selective diffusion. Such membranes were of interest not only for simple gas separation, but also for their potential use in membrane reactors that could produce syngas (CO+H 2 ) by direct conversion of hydrocarbons such as methane [1–3]. For this application, materials were required to have good structural stability in reducing atmosphere as well as high oxygen perme- ability. Attracted by the unusual high permeability, the properties of SrCo 0.8 Fe 0.2 O 3Àd (SCFO), such as the surface exchange kinetics, the conductivity, the non- stoichiometry, the phase structure and stability, and the oxygen permeation behavior, etc., were exam- ined or re-examined [4–7] by investigators. Un- fortunately, it was found that this oxide had very limited chemical and structural stability in reducing atmosphere [5–7]. Its perovskite structure was thermo-dynamically stable only at higher oxygen pressures (>0.1 atm) and at higher temperatures (>1063 K). A perovskite and brownmillerite two- phase region existed at lower oxygen partial pres- sure(<0.1 atm) and at lower temperature (<1063 K) [6]. The proper substitution of metal ions in SCFO might lead to the improvement of phase stability or oxygen permeability of this material. The substitution of Fe with other metal ions such as Cr, Co, and Cu resulted in the shift of the order–disorder temperature to higher temperature [7]. And the substitution of strontium ions in SCFO with higher valence state metal ions such as lanthanum led to the increase of 0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0167-577X(02)00646-8 * Corresponding author. Tel.: +86-411-4671991-704; fax: +86- 411-469-4447. E-mail address: yangws@dicp.ac.cn (W. Yang). www.elsevier.com/locate/matlet November 2002 Materials Letters 56 (2002) 958 – 962