A-site deficient lanthanum-calcium chromite-titanates doped with 3d transition metals: synthesis, oxygen nonstoichiometry, electrical conductivity, and catalytic activity

Abstract

Six ${\text{La}}_{{0.4}} {\text{Ca}}_{{0.5}} {\text{Ti}}_{{0.5}} {\text{Cr}}_{{0.4}} {\text{M}}_{{0.1}} {\text{O}}_{{3 - \delta }}$ (M = Cr, Mn, Fe, Co, Ni, Cu) and two ${\text{La}}_{{0.4}} {\text{Ca}}_{{0.4}} {\text{Ti}}_{{0.4}} {\text{Cr}}_{{0.4}} {\text{M}}_{{0.2}} {\text{O}}_{{3 - \delta }}$ (M = Ni, Cu) single-phase compositions were prepared by conventional solid-state reactions. Oxygen nonstoichiometry, electrical conductivity, phase transformations under reduction-reoxidation at high temperatures and catalytic activity for hydrocarbons oxidation of these compositions were investigated in a wide temperature and oxygen partial pressure range. The Cu-, Ni-, Co-, and Fe-containing compositions are decomposed in reducing Ar/H₂O/H₂ atmosphere with pH₂O / pH₂ = 0.3 at 1,000 °C, while the Cr- and Mn-containing ceramics remain stable at the same conditions. The metallic particles of the added 3d elements formed after decomposition were registered by X-ray diffraction method in case of Cu- and Ni-containing compositions. These formed composites can be completely reoxidized with formation of initial compositions by treatment in air at 1,000 °C. The electrical conductivity of the ceramics investigated in air and Ar/H₂O/H₂ gas flow increases with rising M content. The highest catalytic activity for oxidation of CH₄ and C₃H₆, which was comparable with the activity of the ${\text{La}}_{{0.4}} {\text{Ca}}_{{0.5}} {\text{Ti}}_{{0.5}} {\text{Cr}}_{{0.5}} {\text{O}}_{{3 - \delta }} + 5\% {\text{NiO}}$ composite, shows the Cu-containing powders.