Direct hydroxylation of aromatics with a mixture of H2 and O2 gases over Fe- and Pd-incorporated zeolites

The hydroxylation of benzene and phenol with in-situ-generated oxidant was performed under mild reaction conditions over the bicatalytic system which has dual abilities of direct H₂O₂ generation and the hydroxylation activity by combining Pd-zeolite with redox zeolites such as TS-1, Ti-MCM-41, V-MCM-41 and Fe-zeolite. The amount of H₂O₂ formed directly from H₂ and O₂ increases with increasing Pd loading over zeolite up to 0.6% and subsequently decreases slightly as the Pd loading increases. The optimum amount of H₂O₂ produced is 6.4 mmol. Over Pd/HBEA + Fe/Y, when H₂ : O₂ = 40 : 40 ml/min is supplied, phenol conversion increases from 4.6% at 2 h to 13.6% at 8 h with high catechol selectivity in the range of 65–79%. The hydroxylation activities over redox catalyst with H₂O₂ are compared. Hydroxylation activity is improved by encapsulating FePc onto Y zeolite. In terms of TON, FePc/Y exhibits 3.5 times higher capacity than Fe/Y.