Exposure of freshly activated Fe-, Mn-promoted sulfated zirconia (SFMZ) to carbon monoxide at temperatures up to 50 degrees C induced permanent loss of activity, while the addition of CO after the beginning of the reaction had a reversible effect, regardless of whether the butane flow has been interrupted or not. Similar experiments using dissociated hydrogen instead of CO led to irreversible poisoning in all cases. These finding were interpreted based on (i) the occurrence of initiation sites that are consumed stoichiometrically and very rapidly upon exposure to butane, (ii) such initiation sites which are also consumed by CO or dissociated hydrogen, (iii) CO which competes effectively for adsorption sites without affecting accumulated reaction intermediates, and (iv) such intermediates that are removed in the presence of dissociated hydrogen.