Oleksiy V. Shvets

A family of zeolites with controlled pore size prepared using a top-down method

The properties of zeolites, and thus their suitability for different applications, are intimately connected with their structures. Synthesizing specific architectures is therefore important, but has remained challenging. Here we report a top-down strategy that involves the disassembly of a parent zeolite, UTL, and its reassembly into two zeolites with targeted topologies, IPC-2 and IPC-4. The three zeolites are closely related as they adopt the same layered structure, and they differ only in how the layers are connected. Choosing different linkers gives rise to different pore sizes, enabling the synthesis of materials with predetermined pore architectures. The structures of the resulting zeolites were characterized by interpreting the X-ray powder-diffraction patterns through models using computational methods; IPC-2 exhibits orthogonal 12- and ten-ring channels, and IPC-4 is a more complex zeolite that comprises orthogonal ten- and eight-ring channels. We describe how this method enables the preparation of functional materials and discuss its potential for targeting other new zeolites.

Postsynthesis transformation of three-dimensional framework into a lamellar zeolite with modifiable architecture.

Mild treatment of zeolite UTL results in degradation of its structure with preservation of the initially present dense layers connected by D4R bridges. The lamellar product obtained through this 3D to 2D zeolite conversion has been structurally modified similar to methodologies applied to layered zeolite precursors, which show the opposite 2D to 3D zeolite transformation.

Synthesis of isomorphously substituted extra-large pore UTL zeolites

The influence of various synthesis parameters (e.g. gel composition, pH of the reaction mixture, duration of crystallization) on the phase selectivity of zeolite formation in germanosilicate reaction medium in the presence of different three-valent heteroatoms (B, Al, Ga, Fe or In) was systematically studied and compared with a controlled crystallization from pure germanosilicate media. The boundary conditions of the formation of the pure phase of isomorphously substituted extra-large pore zeolite UTL were established. In the presence of 1 mol% of the respective heteroelement in the initial gel the pH borders of UTL formation are found to be 7.5–11.9 for Fe-, 7.8–12.0 for B-, 8.2–11.0 for Ga-, 11.0–12.0 for In-, and 11.3–12.0 for Al-containing reaction mixtures. The maximum concentration of heteroelements in the reaction mixture for the successful synthesis of UTL is 1.5 mol% for Al and Ga, 6 mol% for In, and 13 mol% for B. The size of UTL crystals decreases in the order Al- > In- > Ga- > Fe- ≈ B-UTL. The nature of isomorphous substituent influences the textural properties (pore size distribution) of the respective UTL zeolites.

Extra‐Large‐Pore Zeolites with UTL Topology: Control of the Catalytic Activity by Variation in the Nature of the Active Sites

The catalytic behavior of isomorphously substituted B‐, Al‐, Ga‐, and Fe‐containing extra‐large‐pore UTL zeolites was investigated in the acylation of p‐xylene with benzoyl chloride and Beckmann rearrangement of 1‐indanone oxime. The clear synergism between the Brønsted acidity (i.e., the concentration and the strength of protonic acid sites) of UTL catalysts and their activity in benzoylation was established. (Ga)UTL zeolite containing the Brønsted acid sites of medium strength is characterized by the optimum activity and selectivity in the benzoylation of p‐xylene. Because of a higher accessibility of active centers, (Al)UTL zeolite appears to be a more active and selective catalyst than (Al)BEA in the benzoylation of p‐xylene. In contrast to (B), (Ga), and (Al)UTL, the leaching of active sites occurs in the benzoylation over (Fe)UTL. All UTL zeolites showed 100u2009% selectivity in the Beckmann rearrangement of 1‐indanone oxime, which provides the target 3,4‐dihydroquinolin‐2(1H)‐one. (B) and (Fe)UTL zeolites containing the weakest acid centers were found to be more active in the Beckmann rearrangement of 1‐indanone oxime than (Ga) and (Al)UTL: 100u2009% yield of the target amide was achieved in 240u2005min of the reaction time over (B) and (Fe)UTL.

Catalytic performance of Metal-Organic-Frameworks vs. extra-large pore zeolite UTL in condensation reactions

Catalytic behavior of isomorphously substituted B-, Al-, Ga-, and Fe-containing extra-large pore UTL zeolites was investigated in Knoevenagel condensation involving aldehydes, Pechmann condensation of 1-naphthol with ethylacetoacetate, and Prins reaction of β-pinene with formaldehyde and compared with large-pore aluminosilicate zeolite beta and representative Metal-Organic-Frameworks Cu3(BTC)2 and Fe(BTC). The yield of the target product over the investigated catalysts in Knoevenagel condensation increases in the following sequence: (Al)beta < (Al)UTL < (Ga)UTL < (Fe)UTL < Fe(BTC) < (B)UTL < Cu3(BTC)2 being mainly related to the improving selectivity with decreasing strength of active sites of the individual catalysts. The catalytic performance of Fe(BTC), containing the highest concentration of Lewis acid sites of the appropriate strength is superior over large-pore zeolite (Al)beta and B-, Al-, Ga-, Fe-substituted extra-large pore zeolites UTL in Prins reaction of β-pinene with formaldehyde and Pechmann condensation of 1-naphthol with ethylacetoacetate.

Selective Isomorphism of Silicon, Aluminium and Titanium in the Extra-large Pore Zeolite-like Germanate IPC-3

Zeolite IPC-3 — which is isostructural with the extra-large pore germanate zeolite ASU-16 — and its Si, Al and Ti forms were synthesized using 1,6-diaminohexane as the template. It was established that the Si atoms occupy the tetrahedral positions in the IPC-3 framework, the Al atoms occupy the octahedral or tetrahedral positions and the Ti atoms the octahedral positions. The germanate zeolite IPC-3 and Si-, Al- and Ti-IPC-3 are stable up to 200–300°C. Despite the presence of the template, which stabilizes the framework of IPC-3, the adsorption capacities of samples previously degassed at 200°C were up to 0.13 cm3/g.

Search of conditions for the synthesis of extra-large porous zeolites

The search of templates from the number of nitrogen-containing organic compounds, mono-and polynuclear complexes of 3d metal was performed; several bulky templates with quaternary nitrogen atoms, promising for preparation of new types of extra-large porous zeolites, were synthesized. The conditions of their preparation were studied and factors, which have the influence on formation of zeolites with large micropore volume, were established. Two new zeolite phases were synthesized, XRD spectra of which contained low angle reflexes in range 4.2–5.7New silica/germanium oxide and alumina/germanium dioxide analogues of ASU-16 zeolite were prepared.

Effect of Template Structure and Synthesis Conditions on the Adsorption and Acid Properties of Hierarchical Titanosilicate MTW Zeolites

The type and morphology of titanosilicate hierarchical zeolites are a function of the structure of polyammonium surfactants used as structure-directing agents (SDA) and the composition of the reaction mixture. Depending on the SDA structure, nanoneedles or nanoparticles of these MTW zeolites aggregate to give nanosponges with external surface up to 200 m2/g and mesopore volume up to 0.4 cm3/g. All these titanosilicate materials have two types of Lewis moderate-strength acid sites with total concentration up to 30 μmol/g.

Effect of the Acidity of Ca,H-Bea Zeolites on Their Catalytic Characteristics in the Dimethyl Ether Production from Methanol

It was shown that Ca,H-BEA zeolites are active and highly selective catalysts for the dehydration of methanol. It was established that the catalytic activity of the zeolites in the synthesis of diethyl ether is determined by the ratio of the concentrations of weak and medium acid sites. The highest productivity is given by zeolites with a ratio of weak and medium acid sites close to 1.5.

Catalytic Properties of Hierarchical Zeolites ZrAl-BEA in the Synthesis of 4-Methoxybenzyl sec-Butyl Ether from Anisaldehyde

It was shown that increase of the size and charge of the hydrophilic part of the structure-directing agents leads to increase of the concentration of acid sites in aluminum–zirconium–silicate zeolites possessing hierarchical porosity. This improves their catalytic activity in the production of 4-methoxybenzyl sec-butyl ether from anisaldehyde and 2-butanol by the Meerwein–Ponndorf–Verley reaction.