Cyclic water gas shift reactor (CWGS) for carbon monoxide removal from hydrogen feed gas for PEM fuel cells

Reduction of the carbon monoxide content in a hydrogen-rich reformate feed gas for fuel cell applications down to a level of 10–50 ppm normally involves high and low temperature water gas shift reactors followed by selective oxidation of residual carbon monoxide. In this contribution it is shown that the carbon monoxide content can be reduced in one single reactor, namely by a cyclic water gas shift reaction process (CWGS) which is based on an iron redox cycle. During the reduction phase of the cycle, the raw gas mixture of H2 and CO reduces a Cr2 O3–Fe3O4–CeO2–ZrO2 sample, while during the oxidation phase steam re-oxidizes the iron and simultaneously hydrogen is being produced. The activity of Cr2O3–Fe3O4–CeO2–ZrO2 was investigated during the reduction by H2 and CO, and the re-oxidation by H2O and CO2. The Cr2O3–Fe3O4–CeO2–ZrO2 showed high activity and stability during 100 repeated reduction/oxidation cycles. Some carbon monoxide in the hydrogen product stream was observed during the re-oxidation phase which was formed by steam gasification of carbon deposited on the iron surface. The carbon formation can be suppressed by controlled oxygen conversion in the Cr2O3–Fe3O4–CeO2–ZrO2. The investigated cyclic process generated hydrogen with a CO content less than 10 ppm.