The effect of varying amounts of carbon support on the decomposition of mixed Mn and Co nitrates and the formation of spinel MnCo2O4 is studied in this work. The molar ratios of the studied samples were n(Mn):n(Co):n(NO3-):n(C) = 1:2:6: Y and Y was varied from 0 to 25. IR and XRD measurements of the samples heated at various temperatures revealed spinel formation from the pure nitrates at 240degreesC but from the supported nitrates (Y= 15) already at 160degreesC. The spinel prepared from pure nitrates at temperatures less than or equal to400degreesC was clearly non-stoichiometric. The supported nitrates produced a less non-stoichiometric spinel with smaller crystallite size. TG measurements revealed that compared with the pure nitrates, the decomposition of the supported nitrates initiated and was completed at lower temperatures. When carbon content was increased from Y= 0 to 20, the onset of the nitrate decomposition was shifted to lower temperatures. The increase of carbon amount beyond Y= 20 did not result in any considerable change. The decomposition of the supported nitrates was completed at temperatures 50-70degreesC lower than the pure nitrates. Both the decomposition of nitrates and the presence of spine] oxide enhanced the oxidation of carbon. (C) 2004 Elsevier B.V. All rights reserved.