Loughborough University researchers have designed, constructed and evaluated a compact CO preferential oxidation (PROX) reactor for PEM fuel cell applications. The reactor design is based on catalyst coating of high-surface-area heat transfer technology. A mixed transition metal oxide promoted PtRu formulation is suitable for this reactor application, i.e. acceptable CO oxidation activity and selectivity at 130-200°C. The reactor design has been sized for 20 kWe PEMFC applications, and is based on 2x2 1 catalyst washcoated compact fin heat exchangers. The PROX reactor has being integrated and commissioned with a methanol steam reformer, demonstrating reductions in fuel CO concentrations from 2.7% to