The Multiplicity of Steady States in a Two-Step Catalytic Reaction Linear with Respect to the Intermediates

Abstract

The multiplicity of steady states (MSS) in a chemical reaction is a critical phenomenon at which the steady-state kinetic curve of the reaction demonstrates ambiguity (hysteresis effect) under the same reaction conditions (concentrations of reactant, etc.). It is known that mathematical models of catalytic reactions proceeding in an open gradientless reactor according to the ideal kinetic law of mass action (LMA) can describe MSSs of the kinetic (nonthermal) nature only due to the steps involving nonlinear interactions of different reactants (the necessary condition for multiplicity). Therefore, it is generally assumed that, if MSS is experimentally established for a reaction proceeding in an open isothermal system, its mechanism contains elementary steps of interaction of two or more different reactants. In this case, as a rule, it is obviously assumed that the kinetic law is invariably ideal. Real chemical processes exhibit deviations from the LMA. Violation of the ideal LMA kinetic law may significantly affect the steady-state pattern of the reaction proceeding even in an isothermal open system. However, by now only an open system, whose nonideality is accounted for by linear corrections, was investigated for the possibility of MSS occurrence, whereby it was shown that, under these assumptions, MSS can occur even without steps of interaction of different reactants, but only with the availability of trimolecular steps (no lower than third-order nonlinearity). In the present study, the possibility of the occurrence of MSS in simpler reactions was investigated, and it was demonstrated that kinetic hysteresis of the rate can be observed for the simplest two-step catalytic Temkin reaction that is linear with respect to the intermediates and proceeds in accordance with nonideal Marcelin-de Donder kinetic law in an open isothermal system.