Catalytic partial oxidation of ethane to ethylene and syngas over Rh and Pt coated monoliths: Spatial profiles of temperature and composition

The catalytic partial oxidation of C2H6 over Pt and Rh coated monolithic supports (4.7 wt% M/α-Al2O3 45 PPI) was investigated with a capillary sampling technique for a range of C2H6/air ratios at constant inlet flow (∼8 ms contact time), with and without H2 addition. Effluent data clearly indicate the differences in product distribution between catalysts and equilibrium. Rh effectively converts the reactant mixtures to syngas with ∼80% selectivity, whereas Pt produces C2H4 with ∼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 O2 occurs to produce mostly CO, H2 and H2O within the first 3 mm of catalyst, followed by a reforming zone to produce additional syngas. Pt consumes O2 more slowly, which results in a steady increase in temperature along the reactor. Ethylene formation correlates to reactor temperatures >750 °C, regardless of C/O, in line with the onset of homogeneous reactions. Hydrogen addition tests (C2H6/O2/H2=2/1/2) clearly exhibit preferential oxidation of H2 with O2 over Pt, which shifts the maximum in temperature upstream while preserving a portion of the C2H6 for C2H4 production. H2 addition modifies the concentration and temperature profiles minimally on Rh. The main differences between catalysts are the high reforming and O2 consumption activity with Rh compared to Pt, which are likely responsible for differences in C2H4 yields.