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

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.

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.

The paper describes the physicochemical characterization and catalytic testing of MFI zeolites with crystal sizes ranging from 0.15 to 6 μm supplied by different manufacturers. The physicochemical properties were examined by atomic absorption spectrometry, X-ray fluorescence analysis, scanning electron microscopy, low-temperature nitrogen adsorption, and ammonia temperature-programmed desorption. The MFI zeolites were then added to a cracking catalyst and subjected to catalytic testing in the conversion of cyclohexane and hydrotreated vacuum gas oil (HTVGO). It was found that the conversion of the model cyclohexane feedstock was significantly enhanced when the crystal size of the MFI zeolite added to the cracking catalyst was reduced from the micro- to submicro-scale; on the other hand, an equal downsizing had almost no effect on the conversion of the real HTVGO feed. However, the use of submicrosized MFI crystals in HTVGO cracking decreased the contribution of hydrogen transfer reactions, thus reducing coke deposits.

The paper is devoted to characterization of BEA and MFI zeolite samples synthesized in alkaline and fluoride media. Using a number of synthesized and commercial samples, enzyme adsorption isotherms were recorded, specifically for Aspergillus oryzae β-galactosidase. The highest adsorption capacity (32–33 mg/g) was achieved on fine-crystalline (0.2–0.6 μm) MFI samples. The fine-crystalline BEA samples (0.3–1 and ˂0.1 μm) exhibited maximal adsorption capacities of 18 and 26 mg/g, respectively. The coarse-crystalline BEA and MFI zeolites prepared by fluoride synthesis reached a markedly lower enzyme adsorption capacity, not exceeding 6 mg/g. The NMR spectroscopy data indicate that the low adsorption capacity of the zeolites synthesized in fluoride media was not only owing to their crystal size but also to the low content of hydroxyl groups on their surface.

MFI and MEL zeolites with different crystal sizes and close Si/Al ratios were synthesized by hydrothermal crystallization. The crystal size was controlled by tuning the template content in the reaction mixture. The resultant zeolites were coated with Pt (1 wt %) by incipient wetness impregnation. The catalytic performance of the catalysts prepared was evaluated in n-hexadecane dewaxing. Zeolites Pt-MEL and Pt-MFI with larger crystals exhibit lower catalytic activity due to diffusion limitations. The crystal size, as well as the structure of the zeolite (MEL or MFI), do not significantly affect the product distribution in the n-hexadecane dewaxing reaction.

The effect of the chemical composition of nanocrystalline zeolites BEA on their physicochemical and catalytic properties in benzene alkylation with propylene is studied. It is shown that a decrease in the Al2O3 content in the reaction mixture during the synthesis of nanocrystalline zeolites leads to a decrease in the size of both the primary nanocrystals and their aggregates. The acidic properties of nanocrystalline zeolites BEA correlate with the aluminum concentration in the samples. The high concentration of acid sites of about 1400 μmol/g and the developed surface of zeolites BEA represented by nanocrystal aggregates provide a high activity of the samples and a high selectivity for the target product—cumene—owing to a decrease in the contribution of side reactions, namely, the secondary alkylation and oligomerization of propylene.