Laws of selective CO oxidation over a Ru/Al2O3 catalyst in the surface ignition regime: II. Transition states

Abstract

The kinetics of selective CO oxidation (or individual CO or H2 oxidation) over ruthenium catalysts are considerably as affected by the heat released by the reaction and specifics of the interaction of ruthenium with feed oxygen. In a reactor with reduced heat removal (a quartz reactor) under loads of ∼701 gCat−1 h−1 and reagent percentages of ∼1 vol % CO, ∼1 vol % O2, ∼60 vol % H2, and N2 to the balance, the reaction can be carried out in the catalyst surface ignition regime. When catalyst temperatures are below ∼200°C, feed oxygen deactivates metallic ruthenium, the degree of deactivation being a function of temperature and treatment time. Accordingly, depending on the parameters of the experiment and the properties of the ruthenium catalyst, various scenarios of the behavior of the catalyst in selective CO oxidation are realized, including both steady and transition states: in a non-isothermal regime, a slow deactivation of the catalyst accompanied by a travel of the reaction zone through the catalyst bed along the reagent flow; activation of the catalyst; or the oscillation regime. The results of this study demonstrate that, for a strongly exothermic reaction (selective CO oxidation, or CO, or H2 oxidation) occurring inside the catalyst bed, the specifics of the entrance of the reaction into the surface ignition regime and the effects of feed components on the catalyst activity should be taken into account.