Hydrolysis reaction products of 1- and 2-nitropropane and 2-methyl-2-nitropropane were compared on a platinum-alumina catalyst, in the conditions of NO lean reduction by propene (gas phase,low concentrations and in the presence of water and oxygen). N2O formed during the reaction decreased in the order 1-nitropropane > 2-nitropropane >> 2-methyl-2-nitropropane, i.e. following the degree of substitution of the carbon atom in the alpha position of the nitro group. The Nef(19) reaction mechanism is proposed to explain this observation.