A series of Mn-oxides in the range MnO2-MnO were subjected to thermogravimetry on heating up to 1100 degrees C in the reactive gas atmosphere of O-2, CO and CO+O-2. Some selected solid residues were analyzed for the MnOx composition by infrared spectroscopy, and for carbon deposits by CHNS-analyzer. The CO+O-2 gas stream was chromatographically analyzed, following heating the gas/solid interface to some selected temperatures. The results indicate that Mn-oxides in the range MnO2-Mn-1.3 exhibit catalytic properties towards the CO oxidation in the gas phase. The higher thermal stability (up to similar to 1000 degrees C) of compositions in the range MnO1.5-1.3 i.e. in the Mn2O3-Mn3O4 system, may render them particularly interesting in the field of applied catalysis. The experimental approach adopted in the present investigation may help accounting for the interfacial chemistry of solid-state reactions involving the surrounding gas atmosphere.