The transport in composite media obtained by dispersing a porous active catalyst inside an inert porous medium has been considered here. Since such systems show a wide variety of advantages, it is necessary to obtain the correct transport equations. Very dilute systems are considered (volume fraction of catalysts ≪ 1/3), a condition that any one dispersed catalyst microsphere cannot feel the influence of others arises. An averaged conservation equation at steady state is obtained under the above condition as well as the condition that any one microsphere can be randomly placed in the medium. Similarly, an effective diffusion coefficient has been obtained.

The results differ from the ones previously in use. The enhancement in the reaction rate on diluting a catalyst is seen to be much less than the values previously suggested although a qualitative similarity exists.