Carbon-13 Kinetic Isotope Effects in the Catalytic Oxidation of CO over Ag

Abstract

The 13C kinetic isotope effects in the catalytic oxidation of carbon monoxide over silver wool were found in the temperature range 343−453 K with the following temperature dependence: 100 ln(k12/k13) = (3.398−630/T) ± 0.083. A reaction CO/O2 gas mixture of 1:2 ratio was used in a static system with initial pressures ranging from 20 to 40 kPa. Under these conditions the reaction obeys the rate law dPCO/dt = −k1PCO and has an apparent activation energy of 59.3 ± 1.7 kJ mol-1. In our theoretical interpretation, based on Bigeleisen's formalism, various geometries of (CO2)⧧ were applied as transition states of the rate determining step, and only a (CO2)⧧ with an interbond angle of 110° and stretching force constants of 1700 and 1000−1400 N m-1 could explain the experimental results.