THERMAL-ACTIVATION OF A POSTCOMBUSTION MANGANESE-ALUMINA CATALYST STUDIED BY IR, UV SPECTROSCOPY, AND EXAFS

The phase compositions of alpha- and gamma-alumina-supported manganese oxide catalysts (including X-ray amorphous phases) are found to depen d on the calcination temperature. In all cases, highly defective phase s are formed, whose structures are not completely identical to those o f corresponding bulk oxides. It is shown that the reasons for the form ation of such phases are Al3+ dissolution in manganese oxides, nonstoi chiometry of the oxide composition, and the effect of stabilization of the interaction of manganese oxides with the support. The gamma-Al2O3 to alpha-Al2O3 transition in the presence of supported manganese is p roven to occur at lower temperatures than in the bulk systems. The hig hly defective beta-Mn3O4 and beta-Mn2O3 phases modified with Al3+ ions , which are formed in the course of thermal activation, are assumed to be active in catalytic complete oxidation.