Interzeolite transformation
has been used to produce a novel family
of hierarchical catalysts featuring excellent textural properties,
strong acidity, and superior catalytic performance for the Friedel–Crafts
alkylation of indole with benzhydrol, the Claisen–Schmidt condensation
of benzaldehyde and hydroxyacetophenone, and the cracking of
polystyrene. Intermediate solids of the FAU interzeolite transformation
into BEA display both increased accessibility—due to the development
of mesoporosity—and strong acidity—caused by the presence
of ultrasmall crystals or zeolitic fragments in their structure. The
use of surfactants allows for the development of the hierarchical
catalysts with very narrow pore size distribution. The properties
of interzeolite transformation intermediates (ITIs) can be fine-tuned
simply by stopping the interconversion at different times.
Surfactant‐templating is a versatile method to introduce tailored intracrystalline mesoporosity in zeolites. This method has been proven to be extremely effective to finely control both the amount of mesoporosity and the size of their mesopores, while maintaining the main features of the original zeolite, such as crystallinity, acidity, and hydrothermal stability. By building on the knowledge generated during the last 30 years in the field of amorphous mesoporous materials, the surfactant‐templating method has been successfully applied to develop intracrystalline mesoporosity into a variety of zeolite structures including FAU, BEA, MOR, LTL, and MFI. The improvement in both the textural and diffusional properties of the zeolite results in excellent catalytic performances in different industrially relevant processes, ranging from fluid catalytic cracking to the synthesis of active pharmaceutical ingredients. As a result of the excellent catalytic performances shown by the surfactant‐templated mesoporous Y zeolite, this is currently being used in several refineries, being the first industrial and large‐scale application of hierarchical zeolites. In this progress report, the literature regarding the surfactant‐templating method in zeolites is critically reviewed.
Micelle formation
inside faujasite (FAU) zeolite, a critical step
in the introduction of mesoporosity in zeolites by surfactant templating,
has been confirmed by both
13
C NMR and Raman spectroscopy.
Here we provide unambiguous evidence of the incorporation of surfactant
molecules inside zeolites during the first step of the surfactant-templating
process followed by their self-assembly into micelles after hydrothermal
treatment. The homogeneous presence of these micelles throughout zeolite
crystals has been directly observed by Raman microspectroscopy, confirming
the uniform incorporation of mesoporosity in zeolites by surfactant
templating.
Zeolite interconversion is a widely used strategy due to its unique advantages in the synthesis of some zeolites. By using a long-chain quaternary amine as both a structure-directing agent and porogen, we have produced superior catalysts, which we named Hybrid Zeolites, as their structures are made of building units of different zeolite types. The properties of these materials can be conveniently tuned, and their catalytic performance can be optimized simply by stopping the interconversion at different times. For cracking the 1,3,5-triisopropylbenzene, Hybrid Zeolites made of FAU and MFI units show a 5-fold increase in selectivity towards the desired product, that is, 1,3-diisopropylbenzene, compared to the commercial FAU, and a 7-fold increase in conversion at constant selectivity compared to MFI zeolite.
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