Catalytic Oxygen Reduction for Deep O ₂ Removal from CO ₂ Streams

Streams of CO2 from various capture processes may contain several impurities of which O2 is often overlooked as a problematic impurity. Because of its reactivity, the National Energy Technology Laboratory has recommended a stringent limit, less than 10 ppm, for the O2 level in treated CO2 products for safe transport, storage, and utilization. In this study, a variety of catalytic oxygen reduction approaches using commercial automotive exhaust emission catalysts are evaluated for O2 removal from CO2 streams using different reducing agents, including H2, CO, CH3OH, and CH4. When the amount of reductant added into the feed is carefully controlled, H2, CO, or CH3OH can effectively remove O2 from 1.5% to below 10 ppm with a single-reactor design (>99.93% removal efficiency), while simultaneously meeting the impurity limits for other species. With CH4 as a reductant, it is challenging to simultaneously meet the the O2 and CO specifications in a single-reactor design because CH4 also reacts with CO2 to produce high levels of CO in the stream (at several hundred ppm). A dual-reactor design is developed to enable the use of CH4, a readily available and low-cost reductant, for the purification of CO2 streams to meet the specifications for O2 and other impurities.