Catalytic fuel combustion, reactions and catalysts. XIV: Thermal stability of the La2O3-Al2O3 system

The x-ray diffraction technique was used to study the thermal stability of the La/Al 2 O 3 system at temperatures in the range from 873 to 1573 K and at lanthanum concentrations from 0 to 13 wt %. It was shown that the stabilization of transient forms of alumina occurs in the presence of lanthanum ions. The stability of the La 2 O 3 -Al 2 O 3 system is governed by the nature of the initial low-temperature aluminum oxide, the way lanthanum is introduced, and the La 3+ concentration. The role played by the resultant alumina-based oxide compounds of lanthanum in the phase transformation of Al 2 O 3 is discussed. A hypothesis was put forward that the formation of the x-ray-amorphous solid solution of La 3+ in γ-Al 2 O 3 at low temperatures (≤873 K) became possible. The La 3+ ions present in the γ-Al 2 O 3 support restrict the diffusion of aluminum ions and prevent the appropriate rearrangement of the structure to produce the high-temperature alumina modifications. The above solid solution is a precursor of a La 2 O 3 .11Al 2 O 3 phase. It is also shown that both LaAl 3 and La 2 O 3 could not be considered as the stabilizers for the transient alumina forms.