Thermal decomposition of manganese carbonate supported on active alumina

The effect of aluminium oxide support on the thermal behaviour of manganese carbonate was investigated using TG, DTA, dDTA and XRD techniques. The concentrations of MnCO3 were 0.025, 0.05 and 0.125 mol/mol Al2O3. The results obtained showed that the employed support material retards the thermal decomposition of manganese carbonate due to the formation of a manganese/aluminium adduct which decomposes readily at 350 degrees C instead of 250 degrees C in the absence of Al2O3, to give gamma-MnO2. This compound decomposed at 500 degrees C into Mn2O3 (partridgeite). The produced Mn2O3 decomposed at 940 degrees C yielding Mn3O4 which interacted with atmospheric oxygen during the cooling processes to give Mn2O3. However, Mn3O4 formed in the case of unloaded Mn2O3 did not interact easily with O-2 and remained stable. The results might indicate the role of Al2O3 in increasing the degree of dispersion of the produced manganese oxides thus increasing their reactivity towards reoxidation by O-2. The produced manganese oxide (Mn2O3) enhanced markedly the crystallization of aluminium oxide at 800 degrees C into theta-Al2O3. Solid-solid interaction between Mn2O3 and Al2O3 occurred at 800 degrees C giving MnAl2O4 which decomposed at 1000 degrees C yielding Mn2O3 and alpha-Al2O3 (corundum).