Oxidation and photooxidation of sulfur-containing compounds in the presence of immobilized phthalocyanine complexes

Abstract

Immobilized cobalt(II) and zinc(II) phthalocyanine and SALEN complexes have been studied as catalysts or photocatalysts for oxidation of 2-mercaptoethanol and sodium thiosulfate. The complexes have been anchored on silica or intercalated in the galleries and cavities of layered double hydroxides (HT) and NaX zeolite. Both the degree of monomerization of phthalocyanine complexes and their activity as catalysts or photocatalysts, after intercalation within supports with well defined intracrystalline cavities, are higher than those observed for the complexes supported on SiO 2. The coadsorption of water in the galleries and cavities of hydrotalcite and the zeolite retards the diffusion of dioxygen and sulfur-containing compounds towards the active catalytic sites. For this reason the activity of the immobilized catalyst samples for the oxidation and photooxidation is lower than that of the complexes in homogeneous phase. After hydrophobic modification of hydrotalcite and NaX zeolite by dodecylsulfate or tetrabutylammonium ions the catalysts sample activity is increased 2–8 ×, because of the improved diffusion of the reactants towards the phthalocyanine molecules intercalated within the bulk of the supports. The degree of photodestruction of the zinc phthalocyanine complexes in the volume of the hydrotalcite or the faujasite is lower in comparison to that in homogeneous phase owing to the retarded diffusion of dioxygen towards the photoactive molecules. After hydrophobic modification of the catalysts samples the diffusion of dioxygen and quantum yield of the generated 1O 2∗ ( 1 Δ g) are promoted and the degree of photodestruction of the immobilized phthalocyanine complexes is increased. The stability of zinc phthalocyanine complexes intercalated within the bulk of hydrotalcite or NaX zeolite is quite higher than that in the homogeneous phase due to deactivation of the singlet dioxygen on the walls of the supports.