Phase-transfer catalysis. IV. Localization of reaction sites in supported catalysts

Abstract

Assuming that there is no basic difference between the two-phase (PTC) and three-phase (TC L-S-L) catalysis, as in both cases the active anion must be transferred from the aqueous phase into the organic phase and the displaced anion must be transferred back into the aqueous phase, possible routes of the transfer are demonstrated. It was found that the activities of catalysts immobilized on a polymer or inorganic carrier did not differ much from each other. The dependence of reaction rate on particle size and its independence of pore size are used to demonstrate that the reaction may proceed predominantly in the surface zone of the catalyst. Experimental data seem to prove that the cause of the surface reaction does not consist of a considerably higher reaction rate compared with the diffusion of the substrates to reaction sites. An analysis of the results of controlled sorption of the Cu(II) ion and of the reaction between the polymer and an agent soluble only in the organic phase, the course of which can be followed by observing the cross-section of the particle, seems to favour a view that pores of the catalyst are filled with one phase only (usually, the continuous aqueous phase), which effectively prevents diffusion of the other phase into the particles.