Mesoporous ZSM-5 zeolites via alkali treatment for the direct hydroxylation of benzene to phenol with N2O

An alkali treatment of a commercial ZSM-5 zeolite induces substantial intra crystalline mesoporosity through desilication process. The resulting mesoporous H-ZSM-5 zeolite has been tested for the hydroxylation of benzene and it was found to increase the lifetime of the catalyst by suppressing the catalyst deactivation and enhancing the phenol yield and selectivity with time on stream. The EPR investigations showed that the state of Fe was not altered upon alkali treatment. It is suggested that the improvements in the catalytic performances are due to the presence of mesopores in the crystals, which likely reduce the lengths of remaining micropores and improve the transport of the phenol molecule out of the zeolite crystal.