Enhanced catalytic activity of TAPO-5 in the oxidation of cyclohexene with hydrogen peroxide under anhydrous conditions

This work studies the influence of the amount of water accompanying and stabilizing the conventional oxidant agent H2O2 on the activity of different TAPO-5 materials in cyclohexene oxidation, in comparison to that of the par excellence large-pore Al-free Ti-beta zeolite. It was proved that the catalytic activity of a TAPO-5 markedly and systematically increases as the amount of the oxidant H2O2 (30 wt.% in aqueous solution) decreases, suggesting the strong inhibitor role of water in the catalytic activity of TAPOs. Following this noteworthy result, we have developed a method for removing water from the mixture solvent (acetonitrile)/H2O2 30 wt.% (aqueous solution) based on a Soxhlet extraction. Water content was quantified by FTIR, which certified the reproducible reaching of a nearly anhydrous system (5 mg H2O/g CH3CN). Under these conditions, TAPO-5 catalysts were able to convert cyclohexene in an extension higher that half of that given by Ti-beta. The product selectivity given by TAPOs and Ti-beta is completely different, as the former favors the cyclohexene reaction through radicalary mechanism and Ti-beta almost exclusively gives epoxidation products. The catalytic features of the conventional Ti(IV)APO-5 is improved by the new so-called Ti(III)APO-5 catalyst, synthesized from gels containing Ti(III).