Abstract
Despite the development of several synthetic strategies employing various templates as (pore) structure directing agents, the preparation of high-quality aluminum-rich hierarchical zeolites (designated as ZH) with Si/Al < 5 from its molecular precursors is still a challenge to the scientific community. For the first time, we report here, a successful synthesis methodology for the preparation of hierarchical zeolites, having FAU and LTA topologies with uniform micropores and mesopores by a rationally designed method. Here, a stable supramolecular self-assembly was achieved under the challenging synthesis conditions by tailoring the zeolitization process, viz., by a homogeneous nucleation and a multi-step crystallization. This has resulted in regular mesoporosity in FAU-type zeolites and a unique mesoporosity in LTA-type zeolites, hitherto not reported so far.
Highlights
The successful development of zeolites and their innovative application in refineries and separation processes has renewed the industrial catalysis to a greater extent[1,2,3,4,5]
The concept of supramolecular templating has been adopted for the preparation of hierarchical zeolites[25,26,27] wherein the existence of two or more types of pores of different sizes, i.e., micropores and mesopores, can possibly overcome the diffusion problems in small pores. Engineering such pore structures through this approach is tricky owing to challenging synthesis conditions
Tailoring the crystallization process in order to achieve the desired pore-architecture in zeolites is still a major challenge. We have overcome this incongruity for the synthesis of hierarchical FAU (ZH-X, ZH-Y) and LTA-type (ZH-A) structures by a controlled zeolitization process
Summary
Vapour phase tertiary-butylation of phenol was carried out in a fixed-bed down flow reactor using 0.5 g of zeolite sample. The reactor set-up was pre-heated to 350 °C in the flow of air for 2 h followed by cooling to desired reaction temperature using N2. The ratio of reactants, weight hour space velocity and Si/Al ratio of the catalysts has been varied in order to study the activity of the catalyst. Nitrogen was used as carrier gas and liquid injection (Miclins) pump was used to feed the mixture of reactants. The transformed gaseous products are condensed in an ice bath and the resulted liquids were collected every hour. The products, viz., ortho- tertiary-butyl phenol (2-t-BP), para-tertiary-butyl phenol (4-t-BP) and 2,4-di-tertiary-butyl phenol (2,4-di-t-BP), were analysed using Perkin-Elmer gas chromatograph with a ZB-1 capillary column
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