Ceramic membranes for catalytic membrane reactors with high ionic conductivities and low expansion properties

A method for preparing a gas-impermeable membrane having an expansion coefficient less than 15.times.10.sup.-6 /.degree.C. and which exhibits a total syngas production rate of at least about 10 ml/min.multidot.cm.sup.2 and which comprises an ionic- and electronic-conducting material which method comprises the steps of:

• a. admixing precursors of the metals Sr, Ca, Ln and M where Ln is selected from the fblock lanthanides and yttrium or mixtures thereof, B is Ga, Al or In or mixtures thereof;
• and M is selected from the d block transition metals or mixtures thereof in relative molar amounts according to the mixed metal oxide formula:
• Ln.sub.x Sr.sub.2-x-y Ca.sub.y B.sub.z M.sub.2-z O.sub.5+.delta.
• where 0.01.ltoreq.x.ltoreq.1.0;
• 0.01.ltoreq.y.ltoreq.0.7;
• and 0.01.ltoreq.z.ltoreq.1.0;
• b. milling the mixture to obtain a homogeneous powder;
• c. calcining the milled powder at temperatures ranging from about 1175-1250.degree. C. until the reaction is complete;
• d. optionally mixing the calcined powder with a binder and pressing the powders isostatically to form a desired membrane shape;
• e. sintering the shaped membrane in air at temperatures ranging from about 1175-1350.degree. C. to form a dense membrane which is gas-impermeable.