A fundamental chemical engineering analysis of a novel annular catalytic reactor is presented, wherein the oxidation of CO is used as model reaction. External mass transfer was measured and modeled, through the analysis of experiments over a Pt-containing catalyst. The study of the reactor behavior under chemical and mixed chemical-diffusional regimes was performed by investigating CO combustion over a hexa-aluminate catalyst. The information gained suggest that the present reactor design is especially suited for studying catalytic processes which involve very short contact times and/or high operating temperatures.