The progressive deactivation of various iron oxide-iron phosphate catalysts in the isopropanol dehydration reaction was studied at atmospheric pressure and 220-280°C. The deactivation of the catalysts is mainly due to coke, rather than the water present. The decay of activity with time on-stream is satisfactorily expressed by a very simple exponential equation, the parameters of which depend on the amount of acid and on temperature. Coke can be easily burnt off, restoring the behaviour of the fresh catalyst. Coke formation follows the Voohries equation.