Carbon-13 Kinetic Isotope Effects in CO Oxidation by Ag

Abstract

In the catalytic oxidation of carbon monoxide over silver wool the 13C kinetic isotope effects in the 343−453 K temperature range were experimentally determined and the following temperature dependence was found: 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 is of order 1 with respect to CO and order 0 with respect to O2 and CO2 pressure. The apparent activation energy is 59.3 ± 1.7 kJ mol-1. In our theoretical interpretation of the experimental data various geometries of (CO2)⧧ and (CO3)⧧ transition states were applied, and only a (CO2)⧧ with an interbond angle of 110° and CO stretching force constants of 1700 and 1000−1400 N m-1, respectively, with an asymmetric reaction coordinate was found to be acceptable.