Alumina-Supported Silver Catalyst for O3-Assisted Catalytic Abatement of CO: Effect of Ag Loading

A series of Ag/Al2O3 catalysts with different Ag loading in a range of 0.5–10 wt% was synthesized by incipient wetness impregnation. The obtained catalysts were characterized by XRD, SEM-EDX, TEM and UV-Visible spectroscopy. It was shown that at low Ag loading (0.5 and 1 wt% Ag) an isolated Ag+ species predominate on the alumina surface. The formation of Agn clusters begins as Ag content was increased to 3 wt% Ag. Higher Ag loading (10 wt%) causes an agglomeration of Agn clusters and formation of relatively large Ag nanoparticles (AgNPs). The catalytic performance of the Ag/Al2O3 catalysts was studied in the conventional (with O2) and O3-assisted catalytic CO oxidation (with O3) and O3 decomposition reactions within the temperature range of 25–350 °C. Analysis of the data obtained allows concluding that conventional CO oxidation proceeds mainly over Agn clusters, while for O3-assited CO oxidation Ag+ species are also necessary. The Ag+ species promote the ozone decomposition and, as a consequence, the formation of highly reactive atomic oxygen species, which are favorable for low-temperature CO activation. The contribution of large metal species (large Agn clusters and AgNPs) to the overall catalytic performance appears to be less pronounced.