Preferential CO Oxidation in the Presence of H2, H2O and CO2 at Short Contact-times

Abstract

High selectivities and conversions in the preferential oxidation of CO in the presence of large quantities of H2, H2O and CO2 are demonstrated on noble metal catalysts at millisecond contact times (~10–15 ms) for temperatures between 150 and 500 °C. With a simulated water-gas shift product stream containing 0.5% CO and varying amounts of H2, H2O and CO2, we are able to achieve ~90% CO conversions on a Ru catalyst at temperatures of ~300 °C using a stoichiometric amount of O2 (0.25%). Experiments with and without O2 and with varying H2O reveal that significant water-gas shift occurs on Pt and Pt-ceria catalysts at temperatures between 250 and 400 °C, while significant CH4 is formed on Ru and Rh catalysts at temperatures greater than 250 and 350 °C, respectively. The presence of H2O blocks H2 adsorption and allows preferential CO oxidation at higher temperatures where rates are high. We propose that a multistage preferential oxidation reactor using these catalysts can be used to bring down CO content from 5000 ppm at the reactor entrance to less than 100 ppm at very short contact-times.