Manganese and cobalt oxide catalysts supported on gamma-Al2O3 have been found to be effective in catalyzing air oxidation of the sulfur impurities in diesel to corresponding sulfones at a temperature range of 130-200 degrees C and atmospheric pressure. The sulfones were removed by extraction with polar solvent to reduce the sulfur level in diesel to as low as 40-60 ppm. Oxidation of model compounds showed that the most refractory sulfur compounds in hydrodesulfarization of diesel were more reactive in oxidation. The oxidative reactivity of model impurities in diesel follows the order: trialkyl-substituted dibenzothiophene > dialkyl-substituted dibenzothiophene > monoalkyl-substituted dibenzothiophene > dibenzothiophene. (c) 2005 Elsevier B.V. All rights reserved.