¹⁸O tracer studies of CO oxidation with O₂on MoO₃. Part 2.—Active sites for CO oxidation with O₂and for oxygen isotope exchange between CO₂and MoO₃

Abstract

Oxygen isotope exchange between C 1802 and MOO, has been examined in connection with the catalytic oxidation of C l60 with "02 on MOO,. Oxide ions at mobile and immobile sites on MOO,, which oxidize CO in the catalytic oxidation, were found to work also as active sites in the oxygen isotope exchange between C 1802 and Mo "03. The observed time dependences of the yields of C 1802, C '*O ' 6O and C ' 602 in the exchange agreed satisfactorily with those calculated from the mobile and immobile site model. In the calculation, the number of immobile sites was estimated to be 1.8% of the total surface lattice oxide ions. The exchange rate at immobile sites was 13% of the total exchange rate.

Kinetic Study of Heterogeneous Oxygen-Exchange Reactions and Bulk Self-Diffusion of Oxygen

“…The surface-oxygen concentration was treated as a constant as long as the slope remained constant. The above assumption of a pseudo-firstorder reaction is similar to the one proposed by Lizuka et al 22 and was shown to be efficient in the interpretation of the oxygenisotope exchange between CO 2 and MoO 3 . The rate constant was evaluated by solving the material balance, treating the reactor as an integral reactor where F is the molecular flow, C tot the total concentration, C Os the surface-oxygen concentration, W the amount of catalyst, and y the molar ratios of the respective species tested.…”

“…The surface-oxygen concentration was treated as a constant as long as the slope remained constant. The above assumption of a pseudo-first-order reaction is similar to the one proposed by Lizuka et al …”