Perovskite oxide catalysts and electrocatalysts

Two perovskite oxide systems with the compositions {dollar}rm LaCrsb{lcub}1-x{rcub}Nisb{lcub}x{rcub}Osb3 (0le xle1){dollar} and BaBi{dollar}rmsb{lcub}x{rcub}Osb{lcub}y{rcub} (2.6le xle3){dollar} were investigated. The {dollar}rm LaCrsb{lcub}1-x{rcub}Nisb{lcub}x{rcub}Osb3{dollar} materials were investigated for their possible use as electrocatalysts for the combustion of methane in solid oxide fuel cells. The BaBi{dollar}rmsb{lcub}x{rcub}Osb{lcub}y{rcub}{dollar} materials were investigated for their possible mixed ionic and electronic conductivity and use as electrocatalysts.; The {dollar}rm LaCrsb{lcub}x{rcub}Nisb{lcub}1-x{rcub}Osb3{dollar} series was synthesized by a modification of the Pechini method. The {dollar}rm LaCrsb{lcub}x{rcub}Nisb{lcub}1-x{rcub}Osb3{dollar} compositions have the orthorhombic GdFeO{dollar}sb3{dollar} structure (x = {dollar}sim{dollar}0.6) and the rhombohedral LaAlO{dollar}sb3{dollar} structure (x {dollar}>{dollar} 0.6). The surface and bulk compositions were equivalent by elemental analysis. Compositions with x {dollar}le{dollar} 0.5 were found to be stable in H{dollar}rmsb2/Hsb2O{dollar} with respect to reduction to nickel metal at temperatures below 900{dollar}spcirc{dollar}C.; The {dollar}rm LaCrsb{lcub}1-x{rcub}Nisb{lcub}x{rcub}Osb3{dollar} oxides showed moderate surface areas (2-9 {dollar}rm msp2gsp{lcub}-1{rcub}).{dollar} The substitution of Cr by Ni in {dollar}rm LaCrOsb3{dollar} produced higher catalytic activities for methane combustion. The non separable (composition, temperature) kinetics behavior is well correlated by an oxidation reduction mechanism for all catalysts. Based on the observed nonlinear increase in catalytic activity with nickel content, Ni-O-Ni ensembles were proposed as the key surface reagent.; The electrical conductivities of the stoichiometric and reduced {dollar}rm LaCrsb{lcub}1-x{rcub}Nisb{lcub}x{rcub}Osb3{dollar} oxides {dollar}rm(0le xle0.6){dollar} were measured in O{dollar}sb2{dollar} and {dollar}rm Hsb2/Hsb2O.{dollar} The conductivity in oxygen (49 to 73% dense samples) increased with x. The conductivity in hydrogen showed a decrease, in general, with x. The conductivity was significantly lower under reducing conditions.; The compositions {dollar}rm BaBisb{lcub}x{rcub}Osb{lcub}y{rcub}{dollar} (x = 2.6, 2.75, 2.9, 3.0) were synthesized by the coprecipitation method. The materials undergo slow (2-3 days) and reversible phase transitions with temperature. The perovskite related structure changes from cubic at 630{dollar}spcirc{dollar}C to orthorhombic at 700{dollar}rmspcirc C{lcub}-{rcub}730spcirc{dollar}C then to cubic at 730{dollar}rmspcirc C{lcub}-{rcub}770spcirc{dollar}C. The BaBi{dollar}rmsb{lcub}x{rcub}Osb{lcub}y{rcub}{dollar} system over the studied compositions was found to be a very good ionic conductor, one order of magnitude higher than yttria stabilized zirconia. The conductivity did not vary significantly with x.