A survey is given of the potentials of a new kind of catalytic membran
es consisting of a catalyst that is immobilised in a dense polymer mat
rix. When homogeneous, catalytically active complexes are occluded, th
ese membranes constitute a new way of heterogenation. In the case of s
olid state catalysts, these composite membranes can improve the activi
ty of the catalyst by changing sorption or by allowing experimental se
t-ups in which solvents become redundant.