For a couple of years, unsteady state processing has been discussed to be possibly advantageous for chemical process engineering. Specifically periodic changes of reaction parameters are expected to enhance the rates of certain reactions [Chem. Eng. Commun. (1973) 111]. For different reaction systems, concentration cycling has been performed [P.L. Silveston, Composition Modulation of Catalytic Reactors, Gordon and Breach, Amsterdam, 1998]. In contrast, a fast periodic modulation of the reactor temperature, even though potentially beneficial, has long been considered to be beyond reach because of the large thermal masses and the poor surface-to-volume ratio which restrict the heat exchange between conventional reactor systems (e.g. fixed bed reactors) and heating/cooling systems. Recently, microstructure devices for fast temperature cycling have been described [J.J. Brandner, G. Emig, M. Fichtner, M.A. Liauw, K. Schubert, A new microstructure device for fast temperature cycling for chemical reactions, in: M. Matlosz, W. Ehrfeld, J.P. Baselt (Eds.), Proceedings of the Fifth International Conference on Microreaction Technology, IMRET 5, Springer, Berlin, 2001, pp. 164-174; Chem. Eng. Sci. 56 (2001) 1419; Gen. Eng. News 22 (11), 42]. The devices make it possible to obtain a periodic temperature change by 100 K in the second to subsecond range. A method for catalyst integration into microstructure devices will be described briefly. First results on the stability of catalyst carrier layers with respect to fast temperature changes are very promising. The oxidation of carbon monoxide was chosen as model reaction. Under fast temperature cycling conditions, a considerably higher yield compared to the steady state could be observed. (C) 2003 Elsevier B.V. All rights reserved.