The stability and deactivation of Pd–Cu–Clx/Al2O3catalyst for low temperature CO oxidation: an effect of moisture

Abstract

The catalytic stability of a Pd–Cu–Cl_x/Al₂O₃ catalyst for low temperature CO oxidation was investigated in different conditions. Under ∼0.1% moisture, the CO conversion over the Pd–Cu–Cl_x/Al₂O₃ catalyst can be maintained at 100% for 30 h even at 0 °C, but it deactivated reversibly at 25 °C with ∼0.6% moisture and irreversibly deactivated at 25 °C with ∼3.1% moisture or 0 °C with ∼0.6% moisture. The reversible deactivation is resulted from physical capillary condensation in the small pores of the catalysts. The irreversible deactivation is due to a breakage of the close-knit structure of Pd–Cu–Cl leading to an aggregation or transformation of the active copper phase, and the formation of a carbonate species on the catalyst surface, meaning that the inactive Pd⁰ species over the surface of the Pd–Cu–Cl_x/Al₂O₃ catalyst is hard to re-oxidize back to the active Pd⁺ sites by copper species in the high moisture reaction conditions.