Kinetics and mechanism of CO oxidation over Cu mordenite

Abstract

Cu mordenite (CuM) has proved to be highly active for the oxidation of CO with oxygen. The effect of pretreatment, the kinetics, and the mechanism of the CO + O 2 reaction have been studied using a continuous-stirred tank reactor (CSTR), Bennett-type unit, and standard BET system. Redox cycles performed using CO O 2 showed that the sample was stable and could be reversibly reduced and oxidized many times at temperatures up to 500 °C. The extent of reduction was 0.8 e/Cu. Pretreatment in CO at 750 °C did not affect the reversibility of the redox cycles but produced a larger valence change, 1.8 e/Cu, even at reduction temperatures as low as 300 °C. XRD patterns show the appearance of finely dispersed CuO on the partially destroyed mordenite lattice. This solid, CuM ∗, shows different catalytic behavior compared to CuM. The kinetic studies on the latter were performed in the range 200–340 °C. Between 200 and 250 °C the rate function was zero order in CO and close to first order in O 2. In the upper temperature range this pressure dependency became first order in CO and zero order in O 2. The Arrhenius plot shows a break at 250 °C. At temperatures higher than 250 °C the oxidation reaction on CuM is severely limited by mass transport. On CuM ∗ the reaction rate was first order in CO and zero order in O 2 over the entire temperature range, 200–325 °C. The reduction and catalytic behavior of CuO SiO 2 and CuO γ-Al 2O 3 were also studied to confirm the important role played by copper oxide produced by the CO pretreatment on CuM ∗. The results obtained are analyzed in terms of the reaction mechanisms, and the predominance of individual steps, due to either different pretreatments and/or operating conditions, is assessed.