Formation of Compounds and Phases in La–M–Al (M = Ca, Mg, Sr, Ba) Oxide Systems Subjected to Treatment in a Water Fluid Medium and Their Catalytic Properties in the Oxidative Coupling of Methane

The formation of mixed oxides in La₂O₃/MO–Al₂O₃ systems (M is a group IIA element: Mg, Ca, Sr, Ba) subjected to a high-temperature treatment and treatment in a water fluid (WF) medium is studied. It is shown that the high-temperature treatment of a group IIA element aluminate with supported lanthanum nitrate leads to the formation of LaAlO₃ only in the case of an Mg-containing system. In other cases, original aluminates do not undergo transformations, and lanthanum oxide is formed. The treatment of La/M–Al ternary systems in a WF medium leads to the formation of LaAlO₃ in all cases; in addition, in all samples, except for the Ba-containing system, phases of free oxides of group IIA metals appear. The increase in the activity and selectivity of La/M–Al ternary oxide systems in the oxidative coupling of methane compared to the respective parameters of M–Al binary systems is attributed to the presence of an individual La₂O₃ oxide phase.