The course of hydrothermal crystallisation of aluminosilicates (zeolites) as well as their particulate properties can be affected by many factors, which influence processes at molecular level, especially nucleation events. Using kinetic data (rate of crystallisation, rate of crystal growth) and crystal size distributions of zeolite A at the end of crystallisation, the kinetics of nucleation and distribution of nuclei within the gel matrix were determined. Zeolite A was obtained by hydrothermal treatment (at 80 °C) of aluminosilicate hydrogels (3.05 Na₂O × Al₂O₃ × 1.91 SiO₂ × 238.1 H₂O) aged at 25 °C for various times, t_a = 0 to 209 h. We have found that the distribution of nuclei in gel matrix considerably changes with the time of hydrogel ageing. The nuclei formed during the precipitation of hydrogel are non-homogeneously distributed within the gel matrix and concentrated closer to the centres of the gel's particles, while the new nuclei are formed at the surface and sub-surface regions of gel's particles. The appearance of large number of nuclei, at the moment when gel is almost completely dissolved, was observed for the first time. The influence of gel ageing on crystallisation course as well as the observed effects of crystals particulate properties are discussed. On the grounds of obtained data, the definition of the term “autocatalytic nucleation” was extended.

A twofold (black, red) interpenetrated network of a Zn(Gly-l-Phe)₂coordination polymer, with hydrogen bonds (green) between neighboring layers.

Various factors affect the process of zeolite formation and thus the characteristics of the ultimate material. The present study is devoted to the influence of the density of the starting aluminosilicate hydrogels, i.e. the amount of the solid phase in the system, on the characteristics of the final product. Different density (viscosity) of the five alumosiliate gels was obtained by changing the ratio SiO₂/H₂O, while the ratios Na₂O/H₂O and SiO₂/Al₂O₃ remained constant. The freshly prepared hydrogels were hydrothermally treated at 80 °C under static conditions. The reaction course was followed by a set of complementary analyses including XRD, chemical analysis, microscopy and thermogravimetry. The linear rate of crystal growth was calculated according to Zhdanov and Samulevich's method. The crystal size distribution curves of the end products were measured and the corresponding curves of nuclei distribution within gel matrix and specific number of crystals were calculated. The observed effect of “local ordered structure” (potential nuclei) formation was commented on from the viewpoint of the autocatalytic nucleation theory.

Displacement of TPA ⁺ ions from the nanoparticle shell exposes the terminal silanol groups, which enables the aggregation of the collided nanoparticles.

The number and the strength of acid sites in catalysts have paramount importance on their efficiency. In zeolites chemistry, increased content of framework Al in zeolites gives a higher number of strong acid sites. Their strength can be a disadvantage in catalytic reactions (e.g., methanol to olefins conversion) due to undesired secondary reactions of coke formation. Here, the Faujasite type of zeolite with higher content of Al has been used for investigating the role of defects in structure and inserted (wet impregnation and thermal treatment) metal cations (Mg, Co, Ni, Zn) on the strength of OH acid sites. Desorption of deuterated acetonitrile, as a probe molecule, was used for OH groups acid strength measurements at different temperatures (150, 200, and 300 °C).

Two different synthesis methods to obtain hierarchical Beta zeolite are investigated: direct synthesis using cetyltrimethylammonium bromide (CTAB) as a mesoporous template and post-synthesis desilication by etching with NaOH and TPAOH. The main focus of this study is to show the possibility of fine tuning of the acid site (OH) strength (Brønsted and Lewis acid sites) through wet impregnation of these hierarchical Beta zeolites with divalent metal cations (Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺), which are important for various applications. Fourier transform infrared spectroscopy (FTIR) and deuterated acetonitrile as the probe molecule were used as a powerful technique to analyze the quantity and number of Brønsted/Lewis acid sites in the modified zeolite Beta structure. Investigating the influence of different divalent metal cations with a comparable ionic radius on the acidity of the hierarchical Beta zeolites, the present research aims to shed light on the structure–activity relationship that determines their catalytic behavior, for the development of efficient and environmentally friendly catalysts for various industrial applications.