The grounds for the activity of TPAP in oxidation catalysis in supercritical carbon dioxide when confined in hybrid fluorinated silica matrices

Abstract

Fluorinated organo-silica gels doped with tetra-n-propylammonium perruthenate (TPAP) are excellent catalysts for the aerobic oxidative dehydrogenation of alcohols in supercritical CO₂ (scCO₂). Their activity and stability are subtly dictated by structure, depending on the degree of fluorination and on the length of the fluoroalkyl chain linked to the silica network. Such dependence reflects the hydrophilic–hydrophobic balance (HHB) of the matrix, as evaluated by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The remarkable correlation between the materials’ HHB and reactivity provides a finding of general validity for reaction-controlled mechanisms, which opens the route to the synthesis of second generation sol–gel entrapped catalysts for the production of fine chemicals in scCO₂.