Transient rate tracer studies in heterogeneous catalysis: Oxidation of carbon monoxide

Establishment of the mechanism of a catalytic reaction is important from the viewpoints of both catalyst development and construction of suitable rate equations for design purposes. The use of transient tracing employing isotopes is a useful tool for this purpose. In this paper, a new method is described in which the transfer of isotopic species is superposed on a heterogeneous catalytic reaction conducted under steady-state conditions. An efficient method of modeling the system of first-order differential equations describing tracer transfer is presented. The method is applied to the oxidation of carbon monoxide over hopcalite catalyst. A relatively simple model with one type of site for adsorbed carbon oxide species correlates the data well for both 13CO2 and 13CO marking. The final step, CO2 adsorption and desorption, is fast and reversible.