18O tracer studies of CO oxidation with O2 on MoO3. Part 2.—Active sites for CO oxidation with O2 and for oxygen isotope exchange between CO2 and MoO3

Abstract

Oxygen isotope exchange between C ¹⁸O₂ and MoO₃ has been examined in connection with the catalytic oxidation of C ¹⁶O with ¹⁸O₂ on MoO₃. Oxide ions at mobile and immobile sites on MoO₃, which oxidize CO in the catalytic oxidation, were found to work also as active sites in the oxygen isotope exchange between C ¹⁸O₂ and Mo ¹⁶O₃. The observed time dependences of the yields of C ¹⁸O₂, C ¹⁸O ¹⁶O and C ¹⁶O₂ 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.