Activity and stability of Cu-CeO2 catalysts in high-temperature water-gas shift for fuel-cell applications

Copper-containing cerium oxide materials are shown in this work to be suitable for the high-temperature 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 CO2-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 degreesC. A strong dependence on CO and a weak dependence on H2O were found at 450 degreesC, whereas inhibition by the reaction products was weak. The apparent activation energy over the catalyst stabilized in the reaction gas mixture at 450 degreesC 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 (similar to20%) and copper enrichment of the ceria surface during the WGS reaction at 450 degreesC can explain the observed activity loss.