The average reactivity of a catalytic surface was appreciably enhanced through spatio-temporally variable operation. Computer steering of a focused laser beam allowed the realization of controlled temperature profiles and their interaction with intrinsic system (reaction/transport) time and space scales. Real-time monitoring of the product concentration then enabled the exploration/implementation of strategies towards optimizing the overall reaction rate, The ability to dictate reaction conditions in space and time, whether in open or in closed loop [1-3] [Science 292 (2001) 1357; Nature 361 (1993) 240; Science 294 (2001) 134], opens new directions for reaction control (e.g., of activity and selectivity in more complex reaction networks) through the combination of chemistry and systems theory. (C) 2002 Elsevier Science B.V. All rights reserved.