Two MoO3/gamma-Al2O3 catalysts containing 11% (w/w) MoO3 prepared by equilibrium-deposition-filtration at two different pairs of pH and Mo concentration values (pH = 3.9, C-Mo = 1.1 x 10(-3) mol L-1 and pH = 6.3, C-Mo = 2.7 x 10(-2) mol L-1) were studied for the ethane oxidative dehydrogenation. The two catalysts demonstrated similar ethane conversions in a temperature range 450-600degreesC. Selectivity to ethene was 15% higher for the catalyst prepared at relatively low pH than for the sample prepared at a higher pH. The observed difference in ethylene selectivity was related to the different structural characteristics of the molybdena phase in the two catalysts. (C) 2004 Elsevier B.V. All rights reserved.