Key words: mixed La—Al-oxides, lanthanum aluminate, lanthanum oxide, structure, water fluid, catalysts, stability, oxidative coupling of methane
The catalytic properties in the oxidative coupling of methane (OCM) and the structural features of a series of mixed lanthanum-aluminum oxides with a constant atomic ratio La : Al = 1 : 1 were studied. The samples were prepared from precursors containing La and Al nitrates and organic component — filter paper or starch. After drying and burning the organic component, the samples were subjected to additional heat treatment and exposure to water fluid (WF) with a density of 0.2 g cm-3 at 415 °C. After calcination at 900°C, all the samples contain a phase of lanthanum aluminate LaAlO3 with a cubic perovskite structure. Varying the type of organic component, as well as the sequence of procedures and processing conditions leads to the production of samples with different morphologies and catalytic properties. The minimum activity, selectivity for OCM products and stability over time is demonstrated by the sample obtained under conditions conducive to the formation of the most ordered structure — successively calcined at 900 °C, treated in a WF medium and re-calcined at 900 °C. The most efficient and stable turned out to be the sample whose crystal structure was formed mainly in the WF medium. It was noted that there is no correlation between the morphology of particles and the specific surface area of the samples, on the one hand, and their catalytic properties, on the other. It was assumed that the catalytic properties are determined by the type and number of point defects in the crystal structure — primarily cation vacancies and, as a consequence, hole centers of the [O–] type in the anion sublattice.
doi:10.34984/SCFTP.2023.18.3.005