Microstructured reactors were fabricated on silicon by deep reactive ion etching and were used to study the catalytic oxidative dehydrogenation of methanol to formaldehyde on silver catalyst at temperature up to 823 K. The reaction was carried out with higher oxygen concentration than that typically used in conventional lab-scale or larger reactors. Even when the reaction was performed with undiluted oxygen, conversion of methanol 60-75% with selectivity similar to 90% was obtained. The reaction was carried out safely at conditions within the flammability limits. Effect of temperature, methanol concentration and residence time was also studied. The results show that the reaction was ca. 0.5 order with respect to methanol. Conversion increased with temperature almost linearly within the temperature range studied, with a slight decrease in selectivity to formaldehyde. The benefits of using microreactors for studying highly exothermic reactions were demonstrated, by comparing the silicon microreactor performance with that of a small quartz tube reactor. (c) 2005 Elsevier B.V. All rights reserved.