Isothermal multiplicity in catalytic surface reactions was considered for the case of polyatomic species on nonuniform surfaces. The surface electronic gas model was chosen for the description of surface inhomogeneity. When the interaction between adsorbed species is of attractive nature a hysteresis appears in the adsorption isotherm, however it disappears when polyatomic molecules with multi-centered character of adsorption react with the surface. The same trend follows from the consideration of a two-step sequence reaction mechanism. Thus loops for one-centered species in the plane:reaction rate - reaction parameter vanish in the instance of multi-centered adsorption.