Enhancing the selectivity of Pare-dihydroxybenzene in hollow titanium silicalite zeolite catalyzed phenol hydroxylation by introducing acid–base sites

• MgO–Al2O3 mixed oxide has been introduced to the micropores of HTS zeolite by precipitation.
• MgO–Al2O3-HTS zeolites are of high p-dihydroxybenzene selectivity in phenol hydroxylation.
• Steric hindrance effect plays a role in enhancing the selectivity of para-dihydroxybeneze.
• Synergistic effect between base–acid and tetrahedral Ti sites favors the formation of para-isomer.

A facile and effective method for enhancing the selectivity of Pare-dihydroxybenzene in phenol hydroxylation has been developed by introducing acid–base sites (MgO–Al2O3 binary oxide) to the micropores of hollow titanium silicalite (HTS, Ti/Si = 25) zeolite. For MgO–Al2O3 modified HTS zeolites, the biggest ratio of para- to ortho-dihydroxybenzene is over 2, while that is close to 1 for conventional HTS zeolite. The high pare-dihydroxybenzene selectivity is ascribed to the steric hindrance and the synergistic effect between acid–base sites of mixed oxide and tetrahedral framework Ti species in HTS zeolite.

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