THE PREPARATION AND PROPERTIES OF HIGHLY CONDUCTIVE NONSTOICHIOMETRIC OXIDE CATALYSTS

Inter-oxide compounds of rare earth and transition metal oxides can be made highly nonstoichiometric by the partial substitution of divalent ions, such as strontium, for the rare earth element. These compounds become highly conductive when suitably treated in oxygen at high temperatures, and have been found to function as efficient oxidation catalysts at low temperatures between 100-300-degrees-C. The thermodynamics, transport properties and catalytic behavior for CO and CH4 oxidation of some systems having the perovskite or the K2NiF4 structure are discussed, e.g. La1-xSrxMO3-delta (M = Cr,Mn,Fe,Co,Y) and La2-xSrxCuO4-delta. The catalytic behavior is similar for the Cr,Mn,Fe and Co perovskites, but the solid electrolyte La0.8Sr0.2YO2.9 has no effect in CO oxidation but the greatest activity for CH4 oxidation.