In situ X-ray absorption spectroscopic studies have been performed at the silver K-edge, of a silver catalyst deposited in a microstructured reactor cell at operating conditions. Oxidative dehydrogenation of methanol to formaldehyde was performed at atmospheric pressure and 773 K with a feed containing 9.7% CH3OH, 18-8% O-2 (N-2 as balance) at residence time of similar to 10 ms. The as-prepared catalyst shows that only metallic silver phase is present. Analysis of the EXAFS data recorded during calcination at 773 K in air, indicates that some of the silver metal catalyst is oxidised. Upon introduction of methanol/air mixture, part of the oxygen coordination is removed suggesting that an oxidation/reduction cycle takes place during the reaction. This work demonstrates that such microfabricated reactors can be readily used for in situ X-ray absorption spectroscopy. (c) 2007 Elsevier B.V. All rights reserved.