Key words: mixed oxides, synthesis, lanthanum aluminate, lanthanum oxide, structure, water fluid, catalysts, methane oxidation
The synthesis of mixed La—Al-oxide systems with the atomic ratio La : Al 1 : 1 was studied. At the first stage, the dried mass containing La and Al nitrates and starch was burned. Heat treatment of the resulting amorphous product at a temperature of 700°C leads to the formation of LaAlO3 aluminate with a cubic perovskite structure. The composition and morphology of the product formed during subsequent processing in a water fluid (WF, density 0.2 g/cm3, 415°C) medium depends on the degree of ordering of the precursor. Crystalline LaAlO3 (cubic) in a WF medium undergoes additional ordering with a decrease in the specific surface area (Ssp.) while maintaining the crystalline structure; further calcination at 900°C does not lead to a change in the value of Ssp. and structure. When processing an amorphous precursor in a WF medium, the value of Ssp. increases and a mixture of LaAlO3 aluminates of cubic and orthorhombic structure and La and Al hydroxides is formed. Further calcination at 900°C leads to the formation of a mixture of LaAlO3 (cub.), La2O3 (hex.) and, possibly, X-ray amorphous Al2O3. The synthesized systems were studied as catalysts for methane oxidation. There was no correlation between activity and selectivity for oxidative coupling products (ethane ethylene) with the value of Ssp., but their dependence on the phase composition of the mixed La—Al-oxide was established. The systems that underwent intermediate treatment in a WF environment and contained the LaAlO3 (cub.) and La2O3 (hex.) phases turned out to be the most efficient. The results obtained indicate the high structural sensitivity of the catalytic process parameters.
doi:10.34984/SCFTP.2023.18.2.006