Understanding the dynamic nature of catalyst surfaces under operational conditions remains a major challenge in heterogeneous catalysis. This study employs in situ IR and solid-state NMR spectroscopy to demonstrate that trace water in the activation environment critically controls the formation of active sites in MoO3/Al2O3 propylene metathesis catalysts. Usage of the TRAPDOR technique allowed to conclude that all active Br & oslash;nsted acid sites (BAS) are associated with aluminum, and the presence of terminal Mo-OH groups on the partially hydrated MoO3/Al2O3 surface is unlikely.

The conventional method of ion-exchange in zeolites is usually multistep, time-consuming, labour-intensive and producing wastes. Herein we report on the fast, efficient, waste-free, and technologically viable method of ion-exchange under vapor-phase conditions. The technique involves the incipient wetness impregnation of powdered or granulated zeolite samples with aqueous solution of corresponding salt followed by heating the sample at elevated temperatures in the range of 200-300 degrees C. The method can be performed in the autoclave under static conditions or in a fixed bed flow reactor under dynamic conditions. The advantages of the method are shown with an example of Na+ to Cs+ ion-exchange in zeolite Y. It is shown that the novel technique allows to reach the degrees of ion-exchange of up to 77 % in one step and up to 88 % in 3 steps, whereas the conventional ion-exchange technique in solution gives only 27 % in one step and 68 % in 5 steps. The method is shown to be amenable to various zeolite materials with different chemical composition and the size of crystals. The degree of ion-exchange depends on the number of exchange cycles, the Si/Al ratio and the size of the crystals.

A series of MOR-type zeolites with a Si/Al ratio of 5 were synthesized via seed-assisted hydrothermal crystallization. Their physicochemical properties were characterized by low-temperature nitrogen adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence spectrometry (XRF), and infrared spectroscopy of adsorbed pyridine (FTIR-Py). Their catalytic performance was tested in gas-phase toluene disproportionation. At a seed content of 10 wt

A novel approach for steam-assisted synthesis of zeolite MFI based on the crystallisation of silica grains impregnated with the aqueous solution containing structure directing template, alkali and a source of aluminum has been developed. Both powdered MFI samples and binder-free MFI catalysts have been prepared using this method. It provides significant advantages over conventional hydrothermal crystallisation allowing for 3-5-fold reduction in water and template consumption, while increasing the zeolite yield and autoclave productivity by a factor of 2-3. Furthermore, the synthesis procedure is virtually waste-free making it more environmentally friendly. The physicochemical properties of the materials obtained have been investigated utilising X-ray diffraction, X-ray fluorescence, scanning electron microscopy, low-temperature nitrogen adsorption, and temperature-programmed ammonia desorption, while their catalytic performance has been evaluated in toluene disproportionation. The data demonstrate that MFI zeolites produced by steam-assisted crystallisation of impregnated silica are comparable in physicochemical and catalytic properties to zeolites obtained by the traditional hydrothermal method, and that binder-free granulated MFI zeolite is a promising catalyst for toluene disproportionation.

This study investigates how hydrothermal synthesis parameters affect the physicochemical properties and catalytic performance of ZSM-23 zeolites. The synthesized zeolites were characterized by low-temperature nitrogen adsorption, XRD, SEM, XRF, NH3-TPD, and IR spectroscopy of adsorbed pyridine. Their catalytic performance was tested in a model n-hexadecane hydroisomerization reaction. Both the length and diameter of ZSM-23 crystals can be adjusted by varying the seed crystal content and the crystallization conditions. This control provides a means to tune catalytic activity and selectivity during n-hexadecane hydroisomerization.

A series of model catalysts has been synthesized by hydrothermal crystallization in a fluoride medium by varying H2O/SiO2 from 3.6 to 9.6 in the reaction gel. The zeolites obtained show similar structure, morphology and textural characteristics, but they are characterized by different distribution of Al atoms over T-sites and acidic properties: the higher the H2O/SiO2 ratio, the more is the number of strong acid sites according to NH3-TPD data. In the 27Al MAS NMR spectra of the synthesized samples, 4 signals of nonequivalent Al atoms with delta iso = 54.3, 55.7, 58.6 and 59.8 ppm have been distinguished, which are assigned to T5 + T8 + T9, T1 + T2, T6 + T7 and T3 + T4 sites, respectively. In the series of model zeolites, intensity of the signals at 58.6 and 59.8 ppm increases with the H2O/SiO2 ratio in the gel. Beta-7.6 and Beta-9.6 samples show higher catalytic activity in the toluene disproportionation reaction compared to Beta-3.6 and Beta-5.6, which coincides with the NH3-TPD data. A correlation between the initial rate of xylenes' formation and the number of Al atoms corresponding to the signals at 58.6 ppm (T6 + T7 sites) and 59.8 ppm (T3 + T4 sites) in the 27Al MAS NMR spectra has been established. In the course of crystallization T6 and T7 positions in zeolite framework tend to be the mostly occupied with an increase of the induction period by changing Si/Al or H2O/SiO2 ratio in the reaction gel.

A detailed investigation of the MFI zeolite crystallisation mechanism in an alkaline synthetic gel system has been carried out using XRD, SEM, nitrogen adsorption, ammonia TPD, elemental analysis, NMR and FTIR spectroscopy. During the first stage of the synthesis, a highly crystalline zeolite is formed via solid hydrogel transformation mechanism, while for a prolonged synthesis, a second stage of crystallisation is clearly distinguished. The zeolite yield and its Si/Al ratio increase during the second stage, whereas the number of defect sites and the mesopore volume decrease. The second stage leads to increased diffusion limitations owing to the blockage of the transport mesopores and to shortened catalyst lifetime in the MTH and butenes oligomerisation processes as well as to a lower activity in toluene alkylation with methanol. Identification of the second stage of crystallisation potentially allows for fine tuning of the zeolite catalytic properties by varying the crystallisation time.

Interzeolite transformation is a rapidly developing method of zeolite synthesis, which allows a precise design of the active site structure. We report on the application of MOR to MFI interzeolite transformation (IZT) for the preparation of MFI zeolite with variable content of paired sites and the elucidation of their role in the MTH reaction. IZT procedure involved hydrothermal treatment of the reaction mixture containing mordenite zeolite as a source of silica and alumina, alkali, TPAOH, TPABr and water. Tuning of paired sites was achieved by variation of the content of water and alkali in the reaction mixture and the application of seeding. The results demonstrate that IZT procedure allows to tune paired sites content within 10-65 % without affecting other characteristics of MFI products, such as Si/Al ratio, crystal size, texture, acid sites type, content and strength, as well as the amount of EFAL species and the distribution of aluminum between channels and intersections of the MFI structure. The evaluation of MOR-to-MFI zeolites with different paired sites content in the MTH reaction pointed to significant effect of paired sites on the stability of catalytic activity with time on stream and on the propylene/ethylene selectivity.

The review is devoted to an analysis of the metathesis of lower olefins on molybdenum-containing heterogeneous catalysts. Individual aspects of the cross-metathesis reaction are analyzed: the main industrial processes based on metathesis are described, the kinetic and thermodynamic issues of the reaction are considered, and the mechanisms of individual stages are discussed. The relationship between the structure of catalysts and their catalytic activity is demonstrated. Particular attention in this review is given to methods for improving catalytic systems based on molybdenum oxide.

Novel and conventional strategies for the synthesis of zeolite-encapsulated subnanometric metal clusters are reviewed. Further perspectives for the rational design of zeolite-encapsulated subnanometric metal clusters are analyzed.

The paper describes the physicochemical characterization and catalytic testing of MFI zeolites with different SiO2/Al2O3 ratios synthesized by steam-assisted crystallization (SAC) and modified with phosphorus (4 wt

One important way to increase the production of higher-margin products from less valuable unsaturated hydrocarbons is the widely used process of catalytic metathesis. Progress in the development of more advanced metathesis catalysts is hampered by obvious gaps in scientific knowledge about this process. This work is aimed at establishing the influence of physicochemical properties of Mo-containing lower olefins metathesis catalysts and developing methods for increasing their activity through promotion. A classic support for Mo-oxide metathesis catalyst was promoted with NH4HF2, (NH4)2SiF6, H3BO3 additives. The synthesized systems were analyzed by a large set of methods. The catalytic properties of obtained systems were determined in the propylene metathesis reaction. It was shown that the proposed promotion leads to an increase in activity of the catalyst up to 8.5 times. It was shown that strong Brønsted acid sites play a decisive role in increasing activity. In addition, it has been experimentally proven that the formation of active centers occurs when the substrate interacts with Brønsted, but not Lewis acid sites on the surface of the catalyst. The discoveries obtained in this work can serve as the basis for the creation of a new generation highly active lower olefins metathesis catalysts.

Two series of zeolites, vis., the MEL and MFI types, with different Si/Al molar ratios were synthesized by a steam-assisted crystallization method, specifically dry gel conversion (DGC). Their physicochemical properties were characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray fluorescence analysis. The acidic properties were examined by IR spectroscopy of adsorbed pyridine and 2,6-di-tert-butylpyridine as well as by ammonia temperature-programmed desorption. The DGC-synthesized zeolites were distinguished by high crystallinity, small crystal size, and well-developed surface. All the samples exhibited high activity and deactivation resistance in the oligomerization of a butane–butylene fraction. A comparative assessment of the catalytic performance the MEL and MFI samples demonstrated that the structural difference between the MEL and MFI types barely affects their deactivation resistance. Therefore, MEL zeolite is a valid alternative to the MFI type in the development of oligomerization catalysts.

The physicochemical properties of BEA zeolites with SiO2/Al2O3 ratios of about 40–50 and 200–250 synthesized in fluoride and alkaline media have been characterized, and their catalytic activity have been tested in liquid-phase disproportionation of toluene. It has been found that samples with a close SiO2/Al2O3 ratio obtained by fluoride synthesis have a smaller number of acid sites. The samples with lower SiO2/Al2O3 ratios exhibite a higher activity in toluene disproportionation than the samples with lower Al content, regardless of the synthesis method. The BEA zeolites that have Al atoms in the T6 positions of the framework which are more active. Synthesis in an alkaline medium promotes the localization of aluminum at the T6 position.

Based on quantum-chemical computation, a solution with periodic boundary conditions (PBC) was employed within density functional theory (DFT) simulations in order to assign the chemical shifts in the 27Al MAS NMR spectra of Al-BEA (HBEA) zeolite (Si/Al = 31) to the individual crystallographic T-sites calculated for polymorph B of an identical zeolite. The results were compared both to relevant published reports (Si/Al = 71 and 75) and to the experimental data previously obtained by the authors for a mixture of polymorphs (Si/Al = 25). Deconvolution of the 27Al MAS NMR spectrum into Al signals at different T-sites of polymorph B was compared to a similar deconvolution for polymorph A.

A series of tandem catalysts based on a ZnGa2O4 spinel and on MFI-type acidic components with varying SiO2/Al2O3 ratios were prepared by mechanical mixing at a spinel to MFI weight ratio of 2 : 1. These catalysts were tested in the conversion of carbon dioxide to olefins at 380°C and 27 bar. The hydrogenating component (ZnGa2O4) was prepared by co-precipitation of the corresponding hydroxides followed by heat treatment. The zeolites were synthesized by steam-assisted crystallization. A reference catalyst was prepared from ZnGa2O4 and a hydrothermally synthesized commercial zeolite CBV28014. The physicochemical properties of the catalysts and their components were characterized by low-temperature nitrogen adsorption–desorption, chemical analysis, NH3-TPD, H2-TPR, XRD, and SEM. The sample with the highest SiO2/Al2O3 ratio (250) achieved the highest CO2 conversion; this parameter dropped as the aluminum content in the samples increased. The highest selectivity towards light olefins was observed for the catalyst with SiO2/Al2O3 = 172 in the acidic component, likely because this zeolite had an optimum acidity for the production of light olefins.

A series of BEA-type zeolites with SiO2/Al2O3 ratios of about 50 were synthesized by steam-assisted (SAC) and hydrothermal crystallization (HTC) in fluoride and alkaline media. Their physicochemical properties were characterized by low-temperature nitrogen adsorption, XRD, SEM, XRF, and NH3-TPD. The catalytic performance was investigated in liquid-phase toluene disproportionation. The SAC-synthesized samples were distinguished by a higher concentration of acid sites. The BEAs prepared by SAC in alkaline media exhibited a higher activity in toluene disproportionation. The samples synthesized in fluoride media, both by steam-assisted and hydrothermal crystallization, proved to be comparable in activity.

This review presents the current understanding of the effects of the physicochemical properties of molecular sieve catalysts on their deactivation in methanol-to-hydrocarbons conversion. The catalysts are classified on the basis of the composition of the so-called hydrocarbon pool and the catalyst deactivation rate during methanol conversion. For each group of catalysts, the correlations of their physicochemical properties with their catalytic performance, coke formation, and deactivation behaviors are discussed.

Benzene hydroalkylation with acetone has been studied over tandem catalytic systems containing copper and zeolite components. The kinetic study in the wide range of acetone conversions allowed to determine the main reaction pathways leading to the target hydroalkylation products, cumene and diisopropylbenzenes, and to the by-products of acetone condensation. To prevent the side reaction pathways and to achieve high selectively towards target products, three strategies for assembling metal and zeolite components in the catalytic system were used: i) metal encapsulation in zeolite pores; ii) mortar mixing of copper supported on silica with zeolite component; iii) dual-bed layered arrangement of Cu/SiO2 and zeolite components. The best catalytic performance was achieved over dual-bed layered catalytic system, containing Cu/SiO2 in the upper layer and zeolite BEA in the bottom layer, which showed the highest yield of hydroalkylation products (93wt%) and stable catalyst operation.