Chemical Engineering Journal 134 (2007) 168–174 Cyclic water gas shift reactor (CWGS) for carbon monoxide removal from hydrogen feed gas for PEM fuel cells Vladimir Galvita a,∗ , Kai Sundmacher a,b a Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstraße 1, 39106 Magdeburg, Germany b Otto von Guericke University, Process Systems Engineering, Universit¨ atsplatz 2, 39106 Magdeburg, Germany Abstract 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 H 2 and CO reduces a Cr 2 O 3 –Fe 3 O 4 –CeO 2 –ZrO 2 sample, while during the oxidation phase steam re-oxidizes the iron and simultaneously hydrogen is being pro- duced. The activity of Cr 2 O 3 –Fe 3 O 4 –CeO 2 –ZrO 2 was investigated during the reduction by H 2 and CO, and the re-oxidation by H 2 O and CO 2 . The Cr 2 O 3 –Fe 3 O 4 –CeO 2 –ZrO 2 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 Cr 2 O 3 –Fe 3 O 4 –CeO 2 –ZrO 2 . The investigated cyclic process generated hydrogen with a CO content less than 10 ppm. © 2007 Elsevier B.V. All rights reserved. Keywords: Water gas shift reaction; Iron oxide; Hydrogen production; Carbon monoxide reduction; PEM fuel cell 1. Introduction Fuel cell technology allows the highly efficient conversion of chemical energy into electrical energy without emissions of environmental pollutants, thereby making fuel cells one of the most promising sources for future power generation. High-purity hydrogen is required for the operation of the low temperature polymer electrolyte membrane fuel cell (PEMFC). Hydrogen can be produced from hydrocarbon fuels or alco- hols by reforming processes. The product streams of reforming processes typically contain mixtures of hydrogen, carbon monoxide, carbon dioxide and steam. The carbon monoxide level in the gas has to be reduced to a level below 20 ppm in order to avoid poisoning of the catalyst at the fuel cell electrodes [1–3]. Conventionally, this is accomplished by a multi-step purifica- tion train including high and low temperature water gas shift (WGS) reactors and a preferential oxidation reactor (PROX) or a methanation unit for CO removal [1,2]. ∗ Corresponding author. E-mail address: galvita@mpi-magdeburg.mpg.de (V. Galvita). The homogeneous WGS reaction, i.e. CO + H 2 O = CO 2 +H 2 , has been employed for 40 years in industrial processes for H 2 production [4,5]. The role of the WGS reaction is to increase the H 2 yield and to decrease the CO concentration [5–7]. The WGS reaction is traditionally carried out in two fixed bed adiabatic reactors, connected in series with a cooler between them [5]. The first reactor operates at temperatures ranging from 300 to 500 ◦ C and employs a Fe/Cr catalyst. The second reactor with a Cu/Zn/Al catalyst operates at lower temperatures (180–300 ◦ C) in order to increase the possible equilibrium conversion of CO, since the WGS reaction is exothermic. A final reactor for CO preferential oxidation (CO-PROX: CO + 0.5O 2 → CO 2 ) is capable to completely remove the CO down to a limit of 20 ppm [2]. During the PROX process the desired CO oxidation reaction is accompanied by undesired H 2 oxidation which – by consuming hydrogen – leads to a loss of fuel efficiency. As an alternative to the described conventional technology, hydrogen purification from CO can be achieved by a novel cyclic water gas shift reactor which is based on the iron redox cycle [8–12]. This process can be carried out in one single reactor with- out any additional post-processing steps for the gas. The process is based on repeated reduction/re-oxidation cycles of iron oxides. 1385-8947/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2007.03.046