Aluminium substituted lanthanum based perovskite type oxides, non-stoichiometry and performance in methane partial oxidation by framework oxygen

• Rh-promoted samples of La0.75Sr0.25(Fe0.80Co0.20)(1-x)AlxO3-δ (x = 0.10, 0.25, 0.40, 0.60) and La0.8Sr0.2Fe0.8Co0.2O3-δ were synthesized as single phase materials.
• Structural characterization by means of X-Ray and neutron powder diffraction revealed rhombohedral symmetry for all samples (space group R-3c). A decrease in unit cell size occurs on increasing Al-content.
• The Al-substitution alters the redox properties, as shown by flowing titrations.
• A correlation between the redox properties of the perovskite type oxide and the product evolution during reaction of the Rh-promoted oxides with CH4 was observed.
• The possibility of tuning the product evolution through the redox properties of the oxides (Al-substitution) was successfully demonstrated.

A series of Rh-promoted La0.75Sr0.25(Fe0.80Co0.20)(1-x)AlxO3-δ (x = 0, 0.10, 0.25, 0.40, 0.60) samples were investigated as oxygen reservoirs for the conversion of CH4 to syngas at 873 K and 1 atm. Neutron powder diffraction studies revealed a decreasing rhombohedral distortion on increasing Al-content. XPS and TEM were employed to investigate surface chemistry and morphology of the Al = 0.25 sample. The influence of Al-substitution on the redox properties was studied by flowing titration whereas catalytic properties were studied by means of transient pulses of CH4 and O2, as well of 13CH4 and CO. The products (CO, H2, CO2 and H2O) of the reaction between CH4 and the studied oxides were successfully tuned by tailoring the redox properties of the reducible oxides through the Al-substitution.

CO selectivity as a function of non stoichiometry (δ) for Rh/La0.75Sr0.25(Fe0.80Co0.20)(1-x)AlxO3-δ samples during methane pulsing at 873 K.Figure optionsDownload high-quality image (115 K)Download as PowerPoint slide