Chemical reactions are often carried out in nanoporous materials, which can influence chemical reactions through several different effects. The factors that affect reactions in confinement can be classified into three main groups: (1) the effective reduced dimensionality of the pore space due to overlap interactions with the confining material, (2) attractive interactions with the pore walls through either dispersion or electrostatic forces and (3) the formation of chemical bonds with the surface that may give rise to alternative reaction mechanisms. In this work we present results of ab initio calculations illustrating all three effects and their relative importance. These results can serve as guidelines for a systematic design of improved catalytic materials.