E. E. Knyazeva

Design of composite micro/mesoporous molecular sieve catalysts*

Two series of composite micro/mesoporous materials with different contributions of micro- and mesoporosity were prepared by dealumination and recrystallization of mordenite zeolite. The materials were characterized by X-ray diffraction, infrared spectroscopy, 27Al magic angle spinning (MAS) NMR, nitrogen adsorption–desorption, and temperature-programmed desorption of ammonia (TPD NH3). Catalytic properties were studied in transalkylation of biphenyl with diisopropylbenzene. Both types of composite materials showed remarkably high activity, stability, and selectivity toward formation of di-isopropylbiphenyls with respect to both pure microporous and mesoporous materials. The effect is due to high zeolitic acidity combined with improved accessibility of active sites and transport of bulky molecules provided by mesopores.

An approach to heterometallic alkoxide-β-diketonate complexes with a M4O4 cubane-like core and new prospects of their application in preparation of solid catalysts. X-ray single crystal study of (Co,Ni)4(acac)4(μ3-OMe)4(MeOH)4, Co2Ni2(acac)4(μ3-OMe)4(OAc)2 and Mg4(acac)4(μ3-OMe)4(MeOH)4

Abstract The interaction of the individual M4(acac)4(μ3-OMe)4(MeOH)4 complexes, M=Co, Ni in toluene/methanol media provided crystals of (Co,Ni)4(acac)4(μ3-OMe)4(MeOH)4 (I) — the product of co-crystallization of isomorphous products. The oxidation of a MeOH solution of I in air in the presence of NaOAc and aminoalcohols as catalysts gave Co2Ni2(acac)4(μ3-OMe)4(OAc)2 (II), an individual heterometallic derivative. The interaction of Mg(OCH(CH3)CH2NMe2)2 with Cu(acac)2 in toluene/methanol media produced Mg4(acac)4(μ3-OMe)4(MeOH)4 (III) as the only isolatable product. The starting Co and Ni homometallic complexes as well as the heterometallic CoNi complex II were used to prepare the zeolite-supported oxide catalysts which exhibited extremely high activity towards methanol oxidation.

Micro/mesoporous catalysts obtained by recrystallization of mordenite

Micro/mesoporous composite materials with different contribution of micro- and mesoporosity were prepared by recrystallization of mordenite. The materials were characterized by XRD, IR spectroscopy, nitrogen adsorption — desorption and TPD NH3. Catalytic properties were studied in transalkylation of biphenyl (BP) with para-diisopropylbenzene (p-DIPB) and cracking of 1,3,5-triisopropylbenzene (TIPB). Composite materials showed remarkably high activity, stability and selectivity with respect to both pure microporous and pure mesoporous materials. The effect is due to high zeolitic acidity combined with improved accessibility of active sites and transport of bulky molecules provided by mesopores.

Zeolite membranes: Synthesis, properties, and application

The review represents a brief analysis of the known methods for the preparation of zeolite membranes with a continuous selective layer and zeolite crystals embedded in their matrix. The principles of separation on zeolite membranes and the fields of application of these materials are discussed. Some examples of the separation of substances and membrane catalysis on zeolite membranes are given to confirm their high efficiency. Along with the discussion of published data, the authors present their own results.

The physicochemical properties of micro/mesoporous materials prepared by the recrystallization of zeolite BEA

Micro-mesoporous materials with various ratios between micro- and mesopores were prepared by the recrystallization of zeolite BEA in an alkaline medium in the presence of cetyltrimethylammonium bromide. The materials were characterized by X-ray diffraction, low-temperature nitrogen adsorption, and IR spectroscopy. Recrystallization under mild conditions did not cause substantial changes in the number of acid centers but increased the accessibility of acid centers to large-sized molecules because of the creation of mesopores. An increase in the degree of recrystallization caused first partial and then complete zeolite transformation into MSM-41 mesoporous aluminosilicate, which was accompanied by a decrease in the number of acid centers. The IR spectra were used to determine the diffusion coefficients of cumene in the initial and recrystallized samples. Recrystallization increased the diffusion coefficient by 3–4 times.

Microporous crystalline silicoaluminophosphates: Effect of synthesis conditions on the physicochemical and catalytic properties in the reaction of methanol to C2-C4 olefins conversion

Effect of the synthesis parameters (reaction mixture composition, crystallization temperature and duration) on the physicochemical and catalytic properties of microporous crystalline silicoaluminophosphates (SAPOs) has been studied. Methods for the directional control of phase composition, degree of crystallinity, morphology and size of SAPO crystals crystallized from colloidal silicoaluminophosphate sols stabilized in tetraethylammoniun hydroxide solution as a template have been developed. It has been determined that the use of more severe synthesis conditions (increase in temperature and duration of crystallization) leads to the formation of larger crystals and a growth in the concentration of medium strength sites in the samples, which causes a rapid deactivation of the samples in the reaction of methanol conversion to C2-C4 olefins. Crystallization under milder conditions (a decrease in pH and temperature) promotes the acid formation of CHA/AEI intergrowth crystals exhibited a high and steady performance in the methanol conversion for more than 8 h at a total yield of olefins of 95 wt %.

Modification of MCM-41 and SBA-15 mesoporous silicas by imidazolium ionic liquids

MCM-41 and SBA-15 mesoporous molecular sieves are modified with imidazolium ionic liquid (IL) via both physical adsorption and covalent grafting. The considerable effect of IL grafting on the porous structure and the particle morphology of mesoporous supports is shown. The pore size of these supports is found to be a key parameter determining the possibility of loading IL into such support materials.

Adsorption properties of hemoglobin

The isotherms of hemoglobin adsorption on adsorbents of different nature and porous structure are obtained at different adsorption times. The maximum adsorption values are determined, and the adsorption’s relationship with the adsorbent pore size is established. The possibility of using hemoglobin as a test protein to determine the adsorbent surface area available for protein monolayer formation is demonstrated.

Benzene alkylation with dodecene-1 over micro-mesoporous molecular sieves

The alkylation of benzene with dodecene-1 has been studied over catalysts with a combined micro-mesoporous structure with different amounts of mesopores obtained by the hydrothermal recrystallization of Beta and mordenite zeolites. The main features of the reaction of benzene alkylation with dodecene-1 over the micro-mesoporous catalysts have been established. The formation of transport pores and an increase in the accessibility of acid sites as a result of recrystallization under mild conditions facilitate an increase in the activity, with a high selectivity for linear phenyldodecanes being retained; a higher degree of recrystallization to MCM-41 leads to a decrease in the conversion and selectivity; the mordenite-based catalysts are more active than zeolite Beta.

Design of micro/mesoporous zeolite-based catalysts for petrochemical and organic syntheses

This review systematizes and analyzes the physicochemical and catalytic properties of micro/mesoporous materials prepared by two-step recrystallization. The materials are divided into three groups according to the degree of recrystallization: (1) mesostructured zeolites (RZEO-1), (2) micro/mesoporous nanocomposites (RZEO-2), and (3) mesoporous materials with zeolite fragments (RZEO-3). Particular attention is focused on the catalytic properties of the recrystallized materials in petrochemical and organic syntheses. Main advantages of the micro/mesoporous molecular sieves over zeolites and mesoporous materials are demonstrated, and ways of obtaining new catalytic systems based on these molecular sieves are suggested.