The ageing processes of a model Ir/CeO2 catalyst during ethanol steam reforming was investigated. Various causes of deactivation were identified, depending on reaction temperature and time on stream. The initial, fast and but rather limited deactivation process was ascribed essentially to a loss of ceria surface (smoothing by loss of microporosity and/or roughness in the presence of steam), coinciding with an active phase build-up formed by a monolayer of carbonaceous reacting intermediates. In addition, a progressive and long-term deactivation was found to superimpose, originating from structural changes at the ceria/Ir interface linked to the It particles sintering and the ceria restructuring. The continuous build-up of an encapsulating layer of carbon at moderate temperature, coming from C-2 intermediate polymerization, was found not to contribute significantly to the catalyst deactivation, at least under the operating conditions investigated in this study. (C) 2012 Elsevier B.V. All rights reserved.