Carbonic acid gas synthesis in carbon mono-oxide oxidation reaction is considered. The system of differential equations for modelling of the processes based on Langmuir-Hinshelwood mechanism is written down, and the results for a reduced system with neglected diffusion and constant reaction rates are presented. The temperature T of the system equals 520^oC, partial pressures of incoming components are P_CO=2.13*10^-3Pa and P_O=2.66*10^-2Pa for carbon mono-oxide and oxygen, respectively. Peculiar to the presented model is an attempt to take into consideration near-surface interactions through near-surface concentrations of CO and O₂. Catalyst surface layer is considered to consist of free active sites and adsorbed carbon mono-oxide and oxygen, near-surface layer consists of CO, O₂ and the product (CO₂). Results were as it would be expected: optimal incoming concentration ratio of CO to O₂ is 2:1. Deviation from the optimal conditions leads to poisoning by CO or O particles (a typical feature is the adsorption of all species on the catalyst surface). The reaction product occupies space in near-surface area instead of CO. Time of formation of the steady state is not more than 2s for the optimal initial conditions. We also suggest using the dependence between the adsorbed CO and O coverage as a qualitative index for finding the optimal initial conditions. The optimal conditions are achieved when the curve transforms to a closed loop. The critical minimal value for the closed loop formation is the 24% surface coverage by the adsorbed oxygen. Our suggestion to receive the optimal results by varying initial conditions is to increase the oxygen concentration until the optimal values are reached.

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1. "CO oxidation on thin Pt crystals : stoichiometric and mathematical models."