Integral Characteristic of Complex Catalytic Reaction Accompanied by Deactivation

Abstract

New theoretical relationships for a complex catalytic reaction accompanied by deactivation are obtained, using as an example the two-step catalytic mechanism (Temkin–Boudart mechanism) with irreversible reactions and irreversible deactivation. In the domain of small concentrations, Alim=NSk1CAkd, where Alim is the limit of the integral consumption of the gas substance, NS is the number of active sites per unit of catalyst surface; k1 and kd, are kinetic coefficients which relate to two reactions which compete for the free active site Z. CA is the gas concentration. One reaction belongs to the catalytic cycle. The other reaction with kinetic coefficient kd is irreversible deactivation. The catalyst lifetime, τcat=1CZ′1kd, where CZ′ is the dimensionless steady-state concentration of free active sites. The main conclusion was formulated as follows: the catalyst lifetime can be enhanced by decreasing the steady-state (quasi-steady-state) concentration of free active sites. In some domains of parameters, it can also be achieved by increasing the steady-state (quasi-steady-state) reaction rate of the fresh catalyst. We can express this conclusion as follows: under some conditions, an elevated fresh catalyst activity protects the catalyst from deactivation. These theoretical results are illustrated with the use of computer simulations.