Catalytic partial oxidation of ethanol over Rh/Al2O3: Spatially resolved temperature and concentration profiles

• High hydrogen yields in partial oxidation of ethanol to hydrogen on Rh/Al2O3.
• Axial concentration and temperature profiles inside monolithic channels measured.
• Total/partial oxidation zone at catalyst entrance followed by reforming zone.
• Homogeneous gas-phase reactions in front of the catalyst produce acetaldehyde.
• Not all channels behave alike due to temperature gradient across the monolith.

The catalytic partial oxidation (CPOX) of ethanol was studied over rhodium/alumina-coated monoliths. An in situ sampling technique was used for ethanol CPOX, yielding spatially resolved temperature and concentration profiles. Molar C/O ratios from 0.65 to 0.85 were studied. Catalytic and blank experiments were both performed. The investigations clearly showed two zones inside the catalytic channel, an oxy-reforming zone as long as oxygen is present, with total oxidation and steam reforming as prevalent reactions, and a reforming zone, with steam reforming as the dominating reaction. Moreover, homogeneous gas-phase reactions, leading mainly to acetaldehyde and water, were observed in front of the catalyst. This was confirmed by blank experiments, which showed that homogeneous conversion of ethanol by oxidative dehydrogenation may occur in absence of a catalyst at temperatures higher than 640 K. Additionally, axial profiles were collected at a fixed C/O ratio in three catalytic channels, which were differently located across the monolith. A radial heat loss from the center to the outer channels of the monolith was observed, which led to variations in the axial concentration profiles across the honeycomb.

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