On the Role of Residual Ag in Nanoporous Au Catalysts for CO Oxidation: A Combined Microreactor and TAP Reactor Study

The influence of residual Ag on the formation of stable adsorbed active oxygen species (oxygen storage capacity, OSC) and its correlation with the activity and stability in the CO oxidation reaction on nanoporous gold (NPG) was investigated by a combination of kinetic and temporal analyses of products (TAP) reactor measurements, comparing four different NPG samples with different Ag contents. The data demonstrated that oxygen can be activated and stored on the NPG catalysts at room temperature. Clearly the surface Ag content influenced both the OSC and activity, with a more qualitative correlation for the fresh catalysts and an approximately linear relationship for the stable catalysts after 1000 min on stream. A strictly linear correlation between catalytic activity and OSC, both before and after the reaction, indicated that the active oxygen detected by the TAP reactor measurements also represents the active oxygen species for the reaction at atmospheric pressure. Consequences for the mechanistic understanding of the CO oxidation reaction on NPG catalysts are discussed.