Activity and Stability of Cu−CeO₂ Catalysts in High-Temperature Water−Gas Shift for Fuel-Cell Applications

Abstract

Copper-containing cerium oxide materials are shown in this work to be suitable for the hightemperature water-gas shift (WGS) reaction integrated with hydrogen separation in a membrane reactor to generate pure hydrogen. Copper-ceria is a stable high-temperature shift catalyst, unlike iron-chrome catalysts that deactivate severely in CO 2 -rich gases. Such gas mixtures will prevail if a catalytic membrane reactor is used to remove hydrogen. We also found that iron oxide-ceria catalysts have much lower activities than copper-ceria catalysts. Ceria participates in the WGS reaction; its surface properties are crucial for high activity and are sensitive to the presence of dopants. The kinetics of the WGS reaction over 10 atom % Cu-Ce-(30 atom % La)O x were measured in the temperature range 300-450 °C. A strong dependence on CO and a weak dependence on H 2 O were found at 450 °C, whereas inhibition by the reaction products was weak. The apparent activation energy over the catalyst stabilized in the reaction gas mixture at 450 °C is 70 kJ/mol. The catalyst lost some activity in the initial time on stream but was stabilized thereafter. A loss of catalyst surface area (∼20%) and copper enrichment of the ceria surface during the WGS reaction at 450 °C can explain the observed activity loss.

Synthesis and Structural Characterization of a Series of Carboxylic Acid Modified Cerium(III) Alkoxides

“…[1,2] Recently, we have become interested in thin films of cerium oxide (CeO x ) as an anticorrosion material. In addition, CeO x has demonstrated a wide variety of other applications, such as barrier layers, [3][4][5] counter electrodes for electrochromic glasses, [6] catalysts, [7][8][9][10][11] electrolytes for solid oxide fuel cells, [12][13][14] polishing agents for soft and hard optical glasses, [15,16] and numerous other applications. Due to the widespread use of CeO x , it is surprising that only a few structurally characterized cerium alkoxides [Ce(OR) 3 ] have been reported in the literature, [17][18][19][20][21][22][23][24][25][26][27][28][29] and no systematic studies were possible from this eclectic mix of potential precursors.…”

The water‐gas shift reaction: from conventional catalytic systems to Pd‐based membrane reactors—a review

“…Experimental evidence showed that the Cu-promoted Fe-Cr HT shift catalyst is less resistant to rate inhibition by high levels of CO 2 than the Cu-ceria one. On the other hand, Qi and FlytzaniStephanopoulos [81] identified Cu-Ce(La-doped)O x catalyst as the best composition for MR applications in the temperature range 300-600 • C using simulated coal gas. The WGS reaction was also conducted with artificially high CO 2 concentrations at 450 • C, showing stability during 10 h of operation.…”

Water gas shift reaction over Cu catalyst supported by mixed oxide materials for fuel cell application

“…CeO2 retains its defective fluorite-type crystal structure during the oxygen storage and release processes, and thus is an active oxide component of various oxidation catalysts used in diverse redox catalytic reactions [4,5]. Ceria-based catalysts are very good WGS catalysts [6][7][8][9], and the Cu-CeO2 system was first reported by Li et al as a promising lowtemperature shift catalyst [6]. The choice of Cu-CeO2 for high-temperature WGS applications was also rationalized [9], because this copper-based system is more stable than the commercial Cu/ZnO.…”

“…Ceria-based catalysts are very good WGS catalysts [6][7][8][9], and the Cu-CeO2 system was first reported by Li et al as a promising lowtemperature shift catalyst [6]. The choice of Cu-CeO2 for high-temperature WGS applications was also rationalized [9], because this copper-based system is more stable than the commercial Cu/ZnO. For a practical fuel cell system, operating under frequent shutdown and restart cycles, ceria needs to be modified by addition of zirconia [10] or another dopant to avoid formation of Ce(III) hydroxycarbonate during shutdown to RT in the watercontaining reaction gas.…”

“…Another approach is to regenerate the catalyst frequently by oxidation at 400-450 o C [10,11] or to run the reaction in oxygen-assisted mode [11]. Despite this issue, ceria and doped ceria remains the support of choice when a highly dispersed metal preparation is desired, which must remain stable over a wide temperature range [9]; and when surface oxygen availability to the metal is required, as in the case of the water-gas shift reaction [8].…”