During the last ten years design of catalyst particles and porous structures has made considerable progress. Because of the complicated interaction of diffusion and reaction in catalysts there is a demand for more detailed models of porous structures. We have taken a three-dimensional network of interconnected cylindrical pores as pore model. Other pore structures, e.g. slit pores, could also be taken. The network has a predefined pore radii distribution, connectivity and porosity. Mass transport in the single pores of the network is described by the dusty-gas model. Unlike in previous publications, the present network model can be applied to any reaction kinetics. To solve the mass balances of the whole network, the mass balances of the single pores of the network have to be salved simultaneously, because these single mass balances are coupled by the boundary conditions in the nodes of the network. At each node of the network a condition similar to Kirchhoff＇s Law has to hold. At the outer nodes of the network boundary conditions either of the Dirichlet type or the Neumann type can be formulated. The resulting system of differential equations has been solved by the finite-difference method. This leads to a large system of non-linear equations. To solve this non-linear system a damped Newton method has been applied.