Comparative study of Cu(II) catalytic sites immobilized onto different polymeric supports

Abstract

AbstractThe catalysts with copper(II) ions stabilized onto different polymeric matrixes are prepared on either bulk (Cu/chitosan, Cu/polyethyleneimine‐polyacrylic acid (PPA), and Cu‐diiminate‐impregnated polystyrene, polyarylate, or polymethylmethacrylate) or composite supports (egg‐shell type Cu/chitosan/SiO2 and Cu/PPA/SiO2). The morphology of the samples and peculiarities of Cu(II) cationic sites are studied by SEM and ESR methods, and the catalyst activities are compared in oxidation of o‐ and p‐dihydroxybenzenes by air in water. The catalytic activity of Cu(II) centers is governed by the coordination of isolated copper ions: for the most active catalysts, i.e., Cu/chitosan and Cu/PPA, the symmetry of isolated Cu2+‐sites approximates a coordinatively unsaturated square‐planar structure. At the same time, accessibility of active sites to water differs for different polymers, so the contribution of hydrophilicity to the reaction pattern cannot be excluded. Redox transformations of the active sites in the course of catalytic tests do not cause copper leaching from the polymer matrix. The binary composite systems with a film of low‐loaded hydrofilic Cu‐polymer supported on macroporous SiO2 demonstrate substantially higher activity in oxidation of hydroquinone and 3,4‐dihydroxyphenylalanine, as compared with the bulk Cu/polymer samples. In turn, the specific activity of Cu/chitosan/SiO2 exceeds significantly that of Cu/PPA/SiO2 due to stabilization of a thinner and more uniform film of chitosan at the surface of silica.