A series of vanadia/theta-alurnina catalysts have been prepared, characterised and tested for n-butane dehydrogenation. We examined two catalysts having vanadium loadings of 1 and 3.5% V in more detail. The extent of carbon laydown is extremely sensitive to the nature of vanadia surface species. Studies show that the isolated VOx species are much more effective at catalysing carbon deposition during dehydrogenation than the polyvanadate species. It is also clear that polyvanadate species are more effective at dehydrogenation compared to the isolated vanadia species. (c) 2006 Elsevier B.V. All rights reserved.