13C and 14C kinetic isotope effects in the catalytic oxidation of CO over NiO catalyst

For the reaction CO + 1/2O2 → CO2 over NiO catalyst, 13C and 14C kinetic isotope effects were determined in the temperature range from 250 to 5000C. The method used was the isotopic analysis of CO2 formed during the reaction up to a known conversion. It was found that the kinetic isotope effects for both were temperature independent over the whole temperature range studied and were equal to 1.0255 +- 0.0014 for 13C and 1.0493 +- 0.0013 for 14C, respectively. Preliminary calculations show that these effects can be theoretically interpreted only when the CO2 structure, not the CO3 structure, is considered as the activated complex of the rate-determining and carbon isotope fractionation-governing step of the reaction mechanism