Computer simulations of the dissociation-recombination reaction of diatomic molecules have been carried out in the pore networks of the zeolites silicalite and ZK4. This kind of processes can provide interesting insights into the effect of the confinement on the reaction dynamics. The diffusion of the species involved in the recombination processes has been separately investigated through equilibrium simulations. Considerable differences between silicalite and ZK4, both in the recombination probability and in the relaxation rate of excited molecules, as well as in the diffusive properties, are discussed and interpreted on the basis of the different properties of the two environments.