In the context of fuel upgrading by selective ring opening of naphthenes, we have investigated the catalytic conversion of cyclopentane in large hydrogen excess over iridium and platinum single-crystal surfaces. Both (111) and (112) orientations have been considered. The catalytic tests have been performed at 1 kPa and 25-600 degrees C using a recently developed surface reactor equipped with laser heating and online gas chromatography. Only cyclopentene and C-1-C-4 cracking products are formed on iridium, while platinum additionally catalyzes the formation of pentane around 200 degrees C, which dehydrogenates to pentene at 250 degrees C. Noticeably, on both metals, the surface steps prevent hydrocarbon cracking (up to 400 degrees C) at the benefit of dehydrogenation. In all cases, a carbon overlayer is formed on the surfaces in the course of the reaction. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.