Deactivation of ferrierite during the skeletal isomerization of 1-butene at atmospheric pressure and 0.15 atm 1-butene partial pressure was studied. At 300 degreesC, the carbon content shows a sharp increase during the first 30 min-on-stream, with a slower growth thereafter. Temperature-programmed oxidation profiles corresponding to different times-on-stream are similar, showing two well-defined combustion peaks centered at about 325 and 640 degreesC, respectively. When starting the 1-butene feed with the catalytic bed at 100 or 200 degreesC and then increasing the temperature up to 300 degreesC, no significant difference is observed, neither in carbon content nor in oxidation profiles. Important differences in the profiles are observed by comparing at the same time at each temperature. The lower the temperature, the higher the reactivity toward oxidation at low temperature. The carbonaceous deposit formed at 100 degreesC shows the main combustion peak at the lowest temperature (135 degreesC) and a more olefinic character; it could be related to a strong adsorption of reactant molecules. At 200 degreesC, the proportion of saturated species associated to oligomers increases; while at 300 degreesC, coke shows both aromatic and olefinic species.