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.

Composite films containing poly(vinyl alcohol) filled with different amounts of graphene oxide (2 and 4 wt

The effect of annealing on the porous structure formed upon deformation of poly(ethylene terephthalate) (PET) in a physically active liquid medium has been studied by means of small-angle X-ray scattering. Isometric annealing of the crazed polymer at temperatures below T g has been ccompanied by decrease in specific surface area of the fibrils connecting the walls of the crazes, the bulk porosity remaining unchanged. During PET annealing at temperatures exceeding T g , reduction in the dispersion of the fibrillated material of crazes has been accompanied by decrease in the volume of microvoids, more pronounced at higher treatment temperature. The obtained results have been analyzed from the point of view of changes in the structure of crazes during annealing.

Approaches to the development of submicron and nanocrystalline silicate materials of MFI structure in a fluorinated surfactant medium were studied with perfluorononanoic acid as an example. In fluorinated surfactants, the crystal structure of the zeolite framework is formed more slowly than in the case of silicalite-1 because of the presence of aluminum atoms. The fractions of the formed Brønsted and Lewis acid sites in zeolites are independent of the amount of aluminum introduced into the reaction mixture. In oligomerization of light alkenes, the activity and operation stability of the synthesized zeolite with lower concentration of Brønsted acid sites and smaller crystal size are similar to those of the commercially available catalyst.

This study investigates the effects of the degree of ion exchange of sodium cations for cesium cations in FAU(Y) on its physicochemical properties. Using aqueous and solid-state ion exchange, a number of NaY samples with an exchange degree of sodium cations for cesium cations varying from 29 to 89% were prepared. The samples were examined by SEM, X-ray fluorescence, low-temperature nitrogen adsorption, XRD, NH3-TPD, IR spectroscopy of adsorbed chloroform, and 27Al MAS NMR. It was demonstrated that samples with exchange degrees up to 87% can be synthesized with their crystalline structure intact. The test of the catalytic properties of the synthesized samples in aniline alkylation with methanol showed a growth in the selectivity for N-alkylated products as the number and strength of basic sites were progressively increased. Impregnating the Cs-containing zeolites with CsOH was found to significantly enhance the operating stability of the samples and the yield of N-alkylated products, compared to CsNaY. The CsOH-modified catalysts with a Na+/Cs+ exchange degree of 54–77% proved to be the most active and stable in aniline alkylation with methanol: they provided aniline conversion of 81–88% and selectivity for N-alkylation products as high as 99.6–99.7 mol %.

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.

This study investigated the effects of reaction conditions in a one-step gas-phase synthesis of butadiene from formaldehyde and propylene over a SiO2-supported silicotungstic heteropoly acid catalyst. The physicochemical properties of the catalyst were examined by X-ray fluorescence spectroscopy, low-temperature nitrogen adsorption, XRD, SEM, and NH3–TPD. It was found that, with increase in reaction temperature, the yield of butadiene passes through its maximum. Increasing the WHSV of the reactant feed lowers the formaldehyde conversion and enhances the butadiene selectivity. Raising the propylene to formaldehyde molar ratio increases the formaldehyde conversion, with the butadiene selectivity passing through its maximum. Finally, diluting the reactants with an inert gas barely affects the process performance.

A series of samples of zeolite MFI with the same morphology, but different concentrations of Brønsted acid sites, have been obtained by means of ion exchange. Methods of temperature-programmed desorption of ammonia (TPD NH3) and IR spectroscopy of absorbed 2,6-di-tert-butylpyridine have demonstrated that the samples differ in the ratio of acid sites in the bulk of zeolite and on the external surface. Stability of the samples against deactivation has been determined in the oligomerization reaction of butylenes using the accelerated deactivation test under severe conditions. It has been shown that the main contribution to deactivation is made by acid sites located on the external surface of zeolite crystals.

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.