This paper describes the development of a structured aluminum-anodized alumina microreactor that exhibits high catalytic activity for the decomposition of anhydrous ammonia to nitrogen and hydrogen at moderate temperatures. Modifications such as adjustments to the geometry of the microreactor features, surface area enhancement of the anodized catalyst support, choice of Ru precursor, and application of a catalyst promoter are each shown to affect the reactor performance to varying degrees. The reactor converts 99% of ammonia at 600 degreesC into the equivalent of 60 W of hydrogen. These numbers are sufficient for to merit serious consideration for use in practical applications, particularly in mobile devices fueled by hydrogen where monolithic structures are advantageous. (C) 2004 Elsevier B.V. All rights reserved.