The activity of solid catalysts is often reduced by the formation of coke. Thus, regeneration by coke burn-off is needed from time to time. A new method to monitor in situ the coke load during coking and decoking by electrical sensors is presented, which could be used as a controlling instrument of high value. Single particles of an Al2O3 catalyst were electrically contacted and characterised by impedance spectroscopy. A clear relationship between coke load and the impedance is observed. The sensor was tested by regeneration experiments both with single particles and in a coked fixed bed reactor. The results show that the coke burn-off within a single coked catalyst particle can be monitored and that it is possible to distinguish how strong the decoking of a single particle is influenced by pore diffusion. For a fixed bed, the axial coke profile can be monitored by means of axially distributed sensors, and the velocity of the reaction front and the length of the reaction zone are directly deduced by the local change of the coke profile with time. (c) 2010 Elsevier B.V. All rights reserved.