Mechanistic explanation for differences between catalytic activities of dissolved and aerogel immobilized Cu(II) cyclen

The copper(II) complex of 1,4,7,10-tetraazacyclododecane [Cu(II)-cyclen] was covalently immobilized in mesoporous silica aerogel. This immobilization significantly alters the catalytic activity Cu(II)-cyclen when referenced to dissolved oxidation phenol by H2O2 aqueous solution. In order understand this phenomenon, functionalized aerogel characterized scanning electron microscopy (SEM), N2 porosimetry, small angle neutron scattering (SANS), infrared spectroscopy (IR) and paramagnetic resonance (EPR). Aerogel morphology is typical aerogels, coordination mode Cu(II) well-related but not identical solution phase Cu(II)-cyclen. mechanisms reactions involving were explored fine kinetic experiments using capillary electrophoresis (CE) on-line UV–vis spectrophotometry. Hydroquinone, pyrocatechol related benzoquinones identified as main intermediates both reaction systems. A detailed model postulated based on global data fitting, which clearly highlights mechanistic differences two Interestingly, activation catalyst more effective case aerogel, total conversion slower due hindered mass transport compared