Structural Aspect of a Thermal Activation Effect in the MnOx/γ-Al2O3 System

Solid-phase reactions in the aluminum–manganese oxide system, including the structural mechanism of the thermal activation of catalysts, were studied at temperatures up to 1100°C. It was found that the solid-phase reaction at 900–1000°C occurred via two pathways because of the diffusion of manganese ions to aluminum oxide and aluminum ions to manganese oxide. Nanoheterogeneous state of the active component, which was observed in the range 25–600°C, is the product of incomplete decomposition of the high-temperature aluminum–manganese phase Mn2.1 – xAl0.9 + xO4 (0 ≤ x ≤ 0.6) with a cubic spinel structure; this phase was equilibrium at the synthesis temperature but metastable below 650°C.