Preferential CO oxidation over a platinum ceria alumina catalyst in a microchannel reactor

Abstract

We have demonstrated the application of a Pt/Al 2O 3/CeO 2 catalyst into a microreactor to reduce the CO content by preferential oxidation in a H 2 rich model gas mixture. At temperatures between 120 °C and 260 °C and CO:O 2 ratios smaller than 0.7 CO conversion of up to 98% for CO 2-selectivities of 20%–35% were reached. The maximum space time yield was about 0.35 mmol g −1 min −1. To increase the CO conversion and CO 2-selectivity the concept of adding air or an air + N 2 mixture through microholes to the CO + H 2 mixture has been investigated with the design of an SSMR (staged supply microreactor). It was found that the CO 2 selectivity is higher compared to the case of feeding of all gases in one passage, but only for lower CO conversion rates. The best results for the preferential oxidation reaction were obtained at low reactant partial pressures. We found that the highest CO conversion rates are reached at reactant partial pressures in the range between 1 and 5 mbar. These values can be locally reached for total flows with 1–2 vol.-% CO and O 2 by feeding N 2 into the coated microchannels and the reactant gases into the uncoated microchannels. In this case, CO and H 2 are equally lowered and the CO oxidation may be favoured over the H 2 oxidation steps. A strong argument supporting this assumption is our measurements with varying the H 2 inlet stream.