Том 59, № 8 (2019)

The review discusses aspects of the synthesis and application of new composite materials with molecular sieve properties, formed on the basis of metal–organic framework (MOF) structures and ionic liquids (ILs). Ways of creation, physicochemical characteristics, and problems of practical application of IL/MOF systems to selective adsorption and gas separation are considered.

The review presents the data of the research in the field of zeolites and zeolite-like materials which have been performed at various laboratories of the Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences for the last 15 years. The first part of the review is devoted to the investigation of the properties of FeZSM-5 zeolites in the activation of methane upon its oxidation by nitrous oxide and influence of the reaction conditions on the yield of methanol. The second part of the review shows the possibility for isomorphic replacement of aluminum ions by iron ions in ZSM-5 zeolites to obtain hierarchical FeZSM-5 zeolites using polystyrene beads as the template. The third part is devoted to the application of NMR spectroscopy for the determination of the acidity of zeolites and mechanism of joint aromatization reaction of methane and light alkanes. The fourth part presents the data on the investigation of the influence of the synthesis conditions of the corresponding SAPO-31 silicoaluminophosphate on the catalytic properties of Pt(Pd)/SAPO-31 materials.

Synthetic zeolites differing in composition, framework parameters, and exchange cations that balance charges of aluminum–oxygen framework tetrahedra and natural finely divided clinoptilolite-containing tuffs have been used for heterogenization of metal complex catalysts. In the reaction of incomplete hydrolysis of alkylaluminum compounds with water contained on the surface and in the intracrystalline cavities of synthetic zeolites, bonded alkylalumoxanes have been synthesized and further used to create immobilized zirconocene olefin polymerization catalysts, close in activity to similar homogeneous Zr-cene systems, and heterogenized vanadium catalysts. Based on finely divided natural zeolites and ultrahigh-molecular-weight polyethylene, the following materials have been fabricated using the polymerization filling method: a composite that combines high wear-resistant properties with a low friction coefficient, has good strain–stress characteristics, and can be used for manufacturing friction units under load; an organomineral sorbent suitable for solving environmental problems associated with the treatment of natural water for the removal of cesium and strontium radionuclides, heavy metals, and ammonium.

Transformations of granules based on kaolin and phosphoric acid under conditions of vapor-phase crystallization in a mixture of water vapor and a structure-directing agent have been studied. It has been shown that silicoaluminophosphate granules obtained in the presence of dipropylamine, triethylamine, or tetramethylammonium hydroxide as a structure-directing agent consist of a shell formed by dense nonporous cristobalite, tridymite, and berlinite phases and the core made mainly of microporous crystalline silicoaluminophosphates. The formation of the shell, which ensures the strength of the silicoaluminophosphate granules, is due to the interaction of steam with the material of the granules at the initial stages of vapor-phase crystallization. It has been established that the selectivity of the structure-directing action of the amines under vapor-phase crystallization conditions basically corresponds to the template hydrothermal synthesis. It has been assumed that the specific features of the structure-directing action of dimethylamine during vapor-phase transport synthesis are due to its low boiling point, which ensures the primary contact of the granules with template, rather than water molecules. As a result, the products of the transformation of granules in the presence of a mixture of dimethylamine and water do not contain dense nonporous phases and are cocrystallized silicoaluminophosphate and calcium aluminosilicate with the gismondine structure.

The process of dealumination of mordenites differing in morphology and crystal size obtained under identical conditions from reaction mixtures of similar composition has been studied. Parameters that have been chosen to change the morphology and crystal size are the dry matter concentration in the reaction mixture, the pH of the reaction mixture, the crystallization time, the presence of crystalline seeds, and agitation during the synthesis. Dealumination has been performed by heat treatment at 700°C followed by acid treatment. It has been shown that the stability of the mordenite crystal framework to dealumination depends on the thickness of the primary needle crystal, which forms the basis of large zeolite crystals, not on the size of the zeolite crystal as a whole. With a decrease in the average needle crystal thickness from 250 to 90 nm, the Si/Al molar ratio in the crystal lattice, determined from ²⁹Si NMR data, increases from 6.8 to 9.5. The dealumination is accompanied by a change in the texture of large mordenite crystals associated with a decrease in the packing density of the primary needles.

A method for obtaining a new magnetic nanocomposite Fe₃O₄@SiO₂@Mg/AlFe-LDH with the core/shell structure is described. The procedure for the synthesis of the nanocomposite includes three steps: preparing magnetite nanoparticles, coating the surface of the obtained magnetic nanoparticles with silica, and in situ growing Mg/AlFe-LDH on the Fe₃O₄@SiO₂ surface. Samples obtained at each synthesis step have been characterized using X-ray diffraction analysis and transmission electron microscopy. It has been proved that the layered double hydroxide (LDH) particles “grow” on aggregates of magnetic Fe₃O₄@SiO₂ core/shell nanoparticles and have the so-called “flower-like” morphology.

A mathematical model of the adsorption process in the adsorption stage of the system is proposed. The mathematical model has been tested on a binary mixture of nitrogen and oxygen used as an example. The data obtained by numerical simulation agree within the limits of error with experimental data obtained earlier. A scheme of a hybrid membrane–adsorption system for creating an artificial breathing atmosphere in a closed room, consisting of an adsorption unit in the first stage and a membrane unit in the second stage of separation, has been proposed. In the hybrid system, the feed stream drawn into the compressor comprises air from the external environment and air coming from the ventilated room and the adsorbent is regenerated by the reject stream of the membrane unit.

Both freshly prepared and steamed MFI zeolite catalysts have been tested for service life. It has been shown that the zeolite cycle length is increased from 7 to 60 days by steaming. In contrast, comparative testing under mild conditions at 300°С has demonstrated low on-stream stability of the catalyst after steaming. Thermogravimetric analysis data indicate different mechanisms of coke formation on samples at 300°С: polyaromatic coke is produced on the fresh sample and predominantly polyaliphatic coke forms on the steamed sample. It has been found that correct comparison of oligomerization catalysts differing in acidity requires a temperature no less than 380°С, which ensures the formation of polyaromatic coke on both catalysts. As a result of the study, a rapid procedure for accelerated deactivation testing has been developed that makes it possible to obtain data comparable with those of long-term service life tests.

The physicochemical properties of catalysts synthesized from zeolites of the BEA and MWW framework types using pseudoboehmite as a binder and their catalytic activity in benzene alkylation with propylene in the gas-phase and liquid-phase modes have been studied. It has been found that the MWW-based catalyst is characterized by stronger acidity in terms of both amount and strength of acid sites; however, the catalytic activity of this sample is inferior to that of zeolite BEA. The observed effect is attributed to the higher accessibility of acid sites in the three-dimensional system of zeolite BEA. With respect to some parameters, such as cumene selectivity and on-stream stability, zeolite MWW is superior to zeolite BEA; the difference is attributed to the structural features of these zeolites.

Kinetic analysis of isobutylene synthesis from ethanol in the presence of a ZnO/ZrO₂ catalyst synthesized by incipient wetness impregnation of zirconium hydroxide with zinc nitrate has been conducted. Analysis data have been used to determine primary, secondary, stable, and unstable products. The selectivity for the reaction products and the order of their formation have been determined. A general scheme of the reaction routes for ethanol conversion to isobutylene has been proposed.