The catalytic partial oxidation of C2H6 over Pt and Rh coated monolithic supports (4.7 wt% M/alpha-Al2O3 45 PPI) was investigated with a capillary sampling technique for a range of C2H6/air ratios at constant inlet flow (similar to 8 ms contact time), with and without H-2 addition. Effluent data clearly indicate the differences in product distribution between catalysts and equilibrium. Rh effectively converts the reactant mixtures to syngas with similar to 80% selectivity, whereas Pt produces C2H4 with similar to 55% C-atom selectivity, while neither produces thermodynamically favored C. Spatially resolved measurements provide direct evidence of the multi-zone nature of the reactors. With Rh, complete conversion of O-2 occurs to produce mostly CO, H-2 and H2O within the first 3 mm of catalyst, followed by a reforming zone to produce additional syngas. Pt consumes O-2 more slowly, which results in a steady increase in temperature along the reactor. Ethylene formation correlates to reactor temperatures > 750 degrees C, regardless of C/O, in line with the onset of homogeneous reactions. Hydrogen addition tests (C2H6/O-2/H-2 = 2/1/2) clearly exhibit preferential oxidation of H-2 and O-2 over Pt, which shifts the maximum in temperature upstream while preserving a portion of the C2H6 for C2H4 production. H-2 addition modifies the concentration and temperatures profiles minimally on Rh. The main differences between catalysts are the high reforming and O-2 consumption activity with Rh compared to Pt, which are likely responsible for differences in C2H4 yields. (C) 2010 Elsevier Ltd. All rights reserved.