Pore fractal objects are expected to be optimal catalysts, since material is supplied to the narrower pores, which are also shorter through the larger pores where diffusion resistance is smaller. To demonstrate this, diffusion and reaction were simulated on Sierpinski-gasket-type fractal objects and on the corresponding nonfractal uniform-pore structures of the same size, porosity and reactive area. Positive order reactions limited by Knudsen diffusion were shown to exhibit larger rates in fractal than in uniform-pore objects. Fractal catalysts also exhibited a new intermediate domain in which the rate depends only weakly on the kinetics parameters. In nonmonotonic kinetics the branching point (bifurcation point) was extremely sensitive to the pore structure.