Two models of bimolecular surface reactions [GRAPHICS] occurring on irregular substrates (probabilistic supports and Sierpinski carpets) are investigated by means of Monte Carlo Simulations. Steady-state regimes controlled by the reaction exhibit fractal kinetics features which are compared to those observed when these reactions are simulated on a regular lattice. Noninteger rate orders and modifications of the phase diagram (case n=2) are presented as a function of the concentration of the inactive sites of the surface. These fractal kinetics properties are tentatively interpreted in terms of structural specifics that characterize the ramification of both the substrate and the reactive adsorbate.