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.
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