Molybdenum oxide supported on SiC is shown to be an active and stable catalyst for the dehydrogenation of n-butane. The activity of the catalyst was studied in a fixed bed microreactor, and the reaction product was analysed by an on-line FTIR technique that enabled study of the activity of the catalyst during the first minutes on stream. At 560 degrees C under atmospheric pressure, the conversion of n-butane and the selectivity for C-4 alkenes were stable at 20% and 70%, respectively. The n-butane feed was diluted with hydrogen and water, which were required for the formation of the active phase and for stable operation. The active phase in dehydrogenation was composed of molybdenum oxide modified with carbon and limited to the uppermost layer of the catalyst.