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 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)Ox were measured in the temperature range 300−450 °C. A strong dependence on CO and a weak dependence on H2O 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.