A novel method has been developed of making zeolites with a tailored porosity in a timely and energy efficient way that also improves its performance in catalysis
Zeolites, derived from the Greek words zeo (to boil) and lithos (stone), are aluminosilicate minerals that seemed to froth or boil when heated in a blowpipe in flame.
Zeolites are used in many industries due to internal pore structure.
Zeolites are a class of microporous (< 2nm) materials (mainly microporous silica-alumina frameworks), which has been discovered for more than 250 years with wide practical applications in refining and (petro)chemical industries, heterogeneous catalysis, organic synthesis, adsorption, separation, purification, etc.
However, the microporous nature of zeolites also impose accessibility issues for their practical applications, for example, the reduced accessibility of the reactants to the active sites within the framework (low reaction rate) and the diffusion limitation of the products from the framework to the bulk media (fast deactivation of zeolites due to coking).
In general, there are two strategies that can be explored to address the issue above, i.e. the development of nanozeolites (nanosized zeolite crystals) and the development of mesoporous zeolites (zeolite with hierarchical pore networks, microporous phase connected with mesoporous channels (2-50 nm)).
The mesoporous structures can be created by (i) controlling the synthesis of zeolites (e.g. using sacrificial mesoscale templates) and (ii) post-synthetic modification (e.g. steaming and acid/alkaline leaching). The latter is more attractive, practical and economical because it can employ commercial zeolites. But the post-synthetic methods are in general lengthy and energy intensive (e.g. hours of reaction time and the requirement of steam generation).
Our new approach is a microwave assisted (MWAC) post-synthetic modification method that allows for minute(s) timescale and produces exceptional hierarchical mesoporous features. Exemplified by FAU zeolite Y, the MWAC method produces exceptional hierarchical mesoporous features – specific external surface area (Sext.) >300 m2/g and mesopores volume (Vmeso) >0.46 cm3/g.
The obtained zeolites also show enhanced catalytic activities and stabilities in laboratory-scale catalytic cracking and hydrocatalytic decomposition.
The direct application of mesoporous Y zeolite is in (petroleum refining processes) Fluid Catalytic Cracking (FCC) process which converts higher fractions of petroleum into more valuable lower fraction products (olefinic gases, gasoline, etc.)
Also, the method to produce mesopores is generic and thus applies to other zeolite structures (MFI, BEA, etc.) that have applications in adsorbents and ion-exchange.
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