Influence of pretreatment on the properties of Ag/α-Al2O3 catalysts containing large (± 1 µm) pure and Cs-promoted silver particles. Part 2.—CO oxidation measurements

Abstract

The catalytic activity for the oxidation of CO with molecular oxygen of silver catalysts containing large silver particles (ca. 1 µm) has been studied. Both pure and caesium-promoted silver catalyst were investigated. The various pretreatments to which the catalysts were subjected, i.e. reduction or oxidation at different temperatures, influenced their activity. The promoted catalyst proved to be somewhat less susceptible to the various pretreatments.

Arrhenius plots of the catalysts often exhibited a sharp break, giving rise to two sets of kinetic parameters. An apparent activation energy of 40 kJ mol^–1 was found at low temperatures, whereas an activation energy of 60 kJ mol^–1 was observed at high temperatures. It is argued that the activation energy of 40 kJ mol^–1 can be ascribed to the reaction of CO with oxygen atoms in the neighbourhood of defects and the activation energy of 60 kJ mol^– to the reaction of CO with oxygen penetrated into the bulk at the same sites. The variation in activity could be attributed to changes in the pre-exponential factor.

A separate discussion is devoted to a comparison of the present results with the findings on silver catalysts with a smaller mean particle size we reported on previously.