The effect of inactive adsorbed impurities on kinetics of catalytic synthesis of carbon dioxide is investigated in the framework of the lattice-gas model. Namely, two cases of equilibrium impurities with fast, compared with the reaction's rate, and slow self dynamics are analyzed. It is revealed that the adsorbed impurities shift the phase diagram to the region of lower temperatures and higher pressures pCO. In the case of slow impurities the bistable region is narrowed far more than in the case when their dynamics is fast and their distribution on the surface can be assumed to be equilibrium. The critical concentration of impurities at which the bistable region disappears, is found. From analysis of the kinetic equations the condition of the existence of the bifurcation region is analytically obtained. Poisoning phenomenon has played a great role in the development of the theory of catalysis. Considering heterogeneous catalytic reactions one often speaks about poisons which reduce the activity of catalysts. These impurities can exist in raw materials which are used for preparation of catalysts or can be entered together with the reactants. It is usually assumed that they are chemosorbed at active sites of the surface, block up interactions between reagent and the surface and are inhibitors for the reaction. Mexted (1) mentioned that metals are the most sensitive to poisoning. Oxides and suldes used as catalysts are more persistent. Metallic catalysts can be poisoned by: 1) molecules which consist of elements of groups VB and VIB if their active atoms are not completely saturated; 2) compounds or ions of some metals; 3) molecules or ions with multiple bonds. Typical catalytic poisons are sulphur compounds (H2S, CS2, mercaptan), hydrocyanic acid (HCN), carbon monoxide (CO), free halides (J2, Cl2, Br2), mercury and mercury salts (HgCl2, Hg(CN)2), compounds of phosphorus, arsenic, lead. Since sorption of impurities can be reversible and irreversible, one can distinguish reversible and irreversible poisoning. For example, Pt catalyst is poisoned in the presence of CO and CS2 but its activity can be quickly restored in pure initial mixture of gases. At H2S and PH3 poisoning Pt deactivates irreversibly and completely. To prevent catalysts from poisoning, special demands are set to the equipment and to the cleaning of initial reactants. However, it is practically impossible to remove all the impurities in a real crystal sample. Considering catalytic reactions theoretically we take into account the presence of impurity atoms or molecules which do not take part in the reaction course but decrease the number of active sites on the catalyst's surface and lower its activity (2{4). It is experimentally known (5{7) that active reaction-diusion media can be constructed containing poisons and that the scale and nature of these poisons can drastically aect spontaneous pattern formation on the modied substrate. Increments of the density of impurities lead to a smaller regions of existence of oscillations (2). Eventually a critical concentration of inert sites is reached at which the region vanishes and oscillations are no longer possible, due to inability of the lattice to reach the minimum local concentration of adsorbate required to trigger the surface reconstruction mechanism. An attempt to investigate the eect of impurity atoms on one of the catalytic reactions, namely the reaction of catalytic CO oxidation on Pt surface (8{14), is made in the paper. Specically , our