The reversible monomer-monomer model occurring without diffusion on irregular substrates (probabilistic supports and Sierpinski carpets) is investigated by means of Monte Carlo simulations. The strong influence of the catalyst surface structure on the kinetics of the reaction and its fractal like features such as noninteger reaction rate orders is investigated for steady-state regimes controlled by the reaction. We succeed in separating the dependence of the reaction rate orders on adsorbate cluster parameters from that on bare surface geometry specifics. The inactivity ratio rho appears to be the relevant parameter to characterize the bare surface structure effects on the Langmuir-Hinshelwood reaction kinetics.