A series of molybdenum-based catalysts have been prepared and studied in regard to their performance in the oxidative dehydrogenation (ODH) of ethane. The effect of alkali (K and Li) and halide (Cl-) modifiers on catalyst performance has been evaluated by doping at a low level (dopant/Mo molar ratio = 0.1). The changes in reaction performance are related to the nature of the supported MoOx surface species that are significantly affected by the introduction of chlorine. While the addition of halide modifiers is known to positively affect the gas-phase mechanisms of ethane ODH at higher temperatures (>650degreesC), current work indicates that the effect for surface redox mechanisms over MoOx-based c atalysts may be somewhat less-pronounced, but still beneficial, at lower temperatures of operation. (C) 2003 Elsevier B.V. All rights reserved.