Effect Of Crystallization-mediating Agent On The Catalytic Activity Of TS-1Zeolite And TS-1Membrane

Titanium silicalite-1(TS-1) zeolite was first synthesized by Taramasso et al. in1983, which has attracted increasing attention in the catalytic field owing to itsexcellent catalytic activity in oxidation of organic compounds under mild conditions,especially where aqueous H2O2is used as oxidant.TS-1has become one of the most studied catalysts in heterogeneous catalysis inthe last decades, but there are still two conundrums preventing its application in thefield of industrial catalysis. On the one hand, the titanium atoms incorporated into thezeolite framework serve as catalytic sites, while the extra-framework anatase TiO2lowers the catalytic activity by decomposing H2O2into H2O. Fortunately, somescientists found that the additions (such as ammonium carbonate) in the crystallizationsolution could mediate the crystallization mechanism to increasing the framework Ticontents, and improvemrnt the catalytic activity of TS-1zeolites. On the other hand,the high cost hindered TS-1zeolite particles used in industrial catalysis and the TS-1zeolite with small particle size lead to recycle difficulties from the catalytic reactionsolution. In order to resolve the recycle and reusing problem of tiny TS-1zeoliteparticles in reaction solution, the TS-1zeolite membranes on porous substrates wereprepared. The TS-1membranes on porous substrate were easy to recycle and reusing,and could applied to membrane reactors to integrate the reaction and separationprocesses.In this work, TS-1zeolites were synthesized with or without ammoniumcarbonate ((NH4)2CO3) as crystallization-mediating agent via hydrothermal method.The catalytic performances of TS-1zeolites were evaluated in the hydroxylation ofphenol. The results showed that the crystallization-mediating agent could improve thecatalytic activity of TS-1zeolites. But the excessive crystallization-mediating agentwill lead to emerge of anatase in zeolites, which could hasten the oxidant decomposesand decrease the phenol conversion.Titanium silicalite-1membrane was synthesized on α-Al2O3substrates bysecondary growth method using ammonium carbonate as crystallization-mediatingagent. For the purpose of comparison, the traditional TS-1membrane was also prepared via seeding methods. The probe reaction of direct hydroxylation of benzeneto phenol was used for testing the catalytic activities of TS-1membranes, the resultsrevealed that TS-1membrane with ammonium carbonate as crystallization-mediatingagent was possessed of remarkable catalytic performance.