This paper focuses on a CFD approach to optimize the design parameters for a high throughput microreactor prior to reactor micromachining and assembling. A molybdenum-based microreactor has been designed for the screening of catalytic coatings in the 100-800 degreesC temperature range in gas phase reactions involving large heat effects (DeltaH(298) = +/-500 kJ/mol). The microreactor consists of eight microstructured compartments, each with a cross section of 2.28 mm x 10.18 mm and 40 mm in length. Eight 100 mum thick molybdenum plates with a deposited catalytic layer with a thickness up to 10 mum are to be inserted in each compartment at distances of 130 mum from each other. Using the CFD code Fluent(R)6.0, it is demonstrated that a low-pressure drop flow diffuser, positioned upstream of the microreactor, distributes reactants evenly in a flow range of 50-1000 cm(3)/min (STP) throughout all compartments. The gas sampling section allows to analyse the reaction products from a selected compartment with no interference from adjacent compartments. The quench section provides a fast quench of the effluent gases within milliseconds to avoid consecutive reactions. The corrosion resistance of the reactor can be improved by atomic layer deposition of a 200 nm alpha alumina layer. (C) 2003 Elsevier B.V. All rights reserved.