Macropores act as broad highways for molecules to move in and out of a nanoporous catalyst. The macropore "distributor" network in such a hierarchically structured porous, catalyst, containing both nanopores and macropores, is optimized with the aim to find the optimal effectiveness factor, eta(opt), of a single reaction with general kinetics in the catalyst. Molecular diffusion is assumed to dominate transport in macropores. It is found that the eta(opt)-Phi(0) relation qualitatively recovers the universal eta-Phi relation when the generalized distributor Thiele modulus, Phi(0), is defined in a way analogous to the generalized Thiele modulus, Phi, but using the molecular diffusivity in the macropores rather than the effective diffusivity in the nanopores. This is because the concentration gradient inside the optimal hierarchically structured, porous catalyst exists only in one principle direction (e.g., the radial direction in a spherical catalyst particle), and molecular diffusion in the macropores dominates the transport process in this principle direction. The universal eta(opt)-Phi(0) relation is used to design a catalyst for power plant NOx emission control. Overall catalytic activity in a mesoporous catalyst with a median pore size of 32.5 nm could be increased by a factor of 1.8-2.8 simply by introducing macropores (occupying 20-40% of the total volume of the catalyst) with a width of 2-22 mu m into the mesoporous catalytic material, so that the remaining mesoporous macropore walls are 5-33 mu m thick. In practice, this would correspond to a deNO(x) catalyst consisting of mesoporous particles with a diameter of 5-33 mu m and macropores in between them with a size of around 2-22 mu m. Information like this is readily applicable to practical catalyst synthesis.