The conventional method of BEA zeolite synthesis involves hydrothermal crystallization of alkaline silico-alumina reaction mixtures with high concentration of organic structure-directing agent (OSDA) (OSDA/SiO 2 = 0.4–0.6) at elevated temperatures (130–150 ☌) and autogenous pressure. 11,13,14 However, there is a lack of information on the means to control these morphological features and on their effect on the catalytic performance of BEA catalysts.

9 It is well known that BEA zeolite can be obtained in the form of individual crystals (including nanocrystals), 10,11 polycrystals with intergrown nanocrystallites 12 and hierarchical aggregates of nanocrystals with high content of intercrystallite mesopores. 8 In addition, it shows high potential for the transformation and valorisation of bio-sourced substrates. Due to these properties BEA zeolite is an excellent catalyst and sorbent for a broad range of industrial processes 1 including alkylation and hydroalkylation of aromatics, 2,3 alkanes alkylation, 4 transalkylation of alkylaromatics, 5 Friedel–Crafts acylation, 6 catalytic cracking 7 and depollution/decontamination processes (SCR of NO x, VOC adsorption). It exhibits a three-dimensional pore system formed by 12-membered ring channels with a diameter of 0.76 × 0.64 and 0.55 × 0.55 nm, which ensures good accessibility of acid sites, high thermal stability and high acidity. Introduction BEA zeolite is among the most widely used zeolites. The decrease of particle size and formation of intercrystalline mesoporosity in hierarchical aggregates improves the accessibility of acidic sites and facilitates the diffusion of reaction products, which leads to the significant improvement of catalytic activity and reduces the deactivation resulting in higher stability with time on stream in cumene synthesis from benzene and propylene. In contrast, Si-rich seeds (SiO 2/Al 2O 3 = 250) dissolve into tiny fragments, which serve as individual nuclei leading to formation of tiny isolated nanocrystallites aggregated into small hierarchical aggregates with high intercrystalline mesoporosity. Al-rich seeds (SiO 2/Al 2O 3 = 25) do not dissolve during gel preparation and initiate dense oriented crystal growth on their surface resulting in the formation of large polycrystals (1–2 μm) with ordered densely intergrown nanocrystallites. The results show that variation of the SiO 2/Al 2O 3 ratio from 25 to 250 in BEA seeds changes the mechanism of seeding from “core–shell” to a “dissolution” mechanism, which can serve as a tool for engineering the morphological, textural and catalytic properties of BEA zeolites. The catalysts are characterized by X-ray diffraction, scanning and transmission electron microscopy, nitrogen adsorption–desorption, Hg-porosimetry, X-ray fluorescence and TPD of ammonia, and evaluated in benzene alkylation with propene. The mechanism of seeding of zeolite BEA via steam assisted conversion has been studied using BEA seeds with different composition.

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