Kinetics of heterogeneous catalytic reactions on nanoclusters is considered. The size of organic molecules used in various catalytic transformations is often ca. 0.5-1 nm, whereas nanoparticles in the range 2-4 nm are used in supported heterogeneous catalysts. Proposed quantitative treatment of a heterogeneous catalytic mechanism with two kinetically significant steps assumes that a finite number of molecules per a single metal cluster can be adsorbed. A general equation with polynomial terms in the numerator and the denominator is derived for nonideal (nonuniform) surfaces when all kinetic and adsorption constants depend on the spatial arrangements of reacting molecules. A simplified case of a two-step catalytic cycle is discussed, with the first step being adsorption on nanoclusters and the second one being further transformation of absorbed species. The corresponding kinetic equations are derived and numerically analyzed for the case of ideal (uniform) surfaces as well as the presence of induced nonuniformity, when contrary to the ideal case there are lateral interactions between adsorbed species. The form of kinetic equations allows not only saturation, typical for Eley-Rideal kinetics, but also positive cooperativity, i.e., S-shaped behavior of the reaction rate as a function of substrate concentration. Comparison with experimental data on hydrodechlorination of dichlorobenzenes is given.