Catalytic characteristics Of MOV0.3Te0.23Nb0.12, catalysts in propane ammoxidation depend strongly on the quantity of oxalic acid present during slurry preparation and on the redox conditions during thermal treatment of the catalyst. Two stage thermal treatment (320 degrees C in air, 600 degrees C in He) and oxalate anion to niobium ratio in the slurry C2O4 (2-)/Nb = 3-5 have been shown to result in the catalysts with the best catalytic properties. Optimal catalysts have been found to contain M I and M2 crystalline phases in the ratio of 3:1 or more. When the molar ratio C2O4 (2 -)/Nb exceeds 3.5, tellurium is lost during calcination in He and other phases beside Ml and M2 are formed. (c) 2007 Elsevier B.V. All rights reserved.