The surface of 316L stainless steel flat substrates has been modified by annealing in an air stream, anodizing in an acid solution, and sequential anodizing first in an acid solution and then in an ...alkali solution. A zeolite of the MFI structure with a Si/Al ratio = 20, 80, or ∞ has been crystallized onto the initial and modified substrates under hydrothermal conditions. The morphology and chemical and phase compositions of the initial and modified substrates and the synthesized zeolite layer have been studied using XRD, SEM, EDS, and XPS methods. On the substrates anodized in the acid solution, a uniform continuous coating with zeolite crystals with a Si/Al ratios of 80 and ∞ is observed as early as after 3 h of crystallization, and further crystallization only leads to an increase in the thickness of the zeolite layer, whereas a continuous layer of the zeolite phase in the case of Si/Al = 20 is observed as late as after 20 h of crystallization. On the unmodified substrates annealed in an air stream and anodized in an alkali solution, a continuous zeolite coating is not formed after 20 h of crystallization.
The Silicon Tracking System (STS) of the BM@N experiment will be based on modules with Double-Sided microstrip Silicon Detectors (DSSD) which have been initially developed for the CBM experiment at ...FAIR. Each module consists of a DSSD, two front-end boards with 8 ASICs each, and a set of low-mass aluminum microcables. During the module assembly the microcables are tab-bonded to the sensor and readout ASICs. The module has 1024 channels on each side of the sensor. For the quality assurance of the ultrasonic bonding process a dedicated procedure based on the noise per channel measurements with a Pogo Pin test device was developed.
The study investigates adsorption of chicken egg lysozyme and bovine serum albumin over BEA zeolites synthesized in alkaline and fluoride media. The protein adsorption value achieved on the samples ...synthesized in the alkaline medium was higher. An evaluation of the surface areas occupied by protein molecules showed that only a portion of the external surface was involved in the adsorption. The protein adsorption reduced the concentration of acid sites in the zeolite samples.
Na-LTA membranes have been synthesized on porous nickel supports by in situ crystallization from a true solution. K-LTA and Ca-LTA membranes have been prepared from Na-LTA membranes by ion exchange ...in 1 M KCl and CaCl
2
solutions, respectively. The formation of the LTA structure, its preservation during ion exchange, and achievement of nearly 100% replacement in the near-surface layer of the zeolite membranes have been proven by means of XPD and SEM-EDX. All the zeolite membranes synthesized have been tested in pervaporation of isopropanol–water, ethanol–water, and methanol–water mixtures containing 10 wt % water. It has been found that the mass flux of alcohol does not depend on the nature of alcohol or zeolite cation if the kinetic diameter of alcohol molecule is greater the effective diameter of zeolite pores. A new method for evaluating of the mass flux through nonzeolite pores based on pervaporation data has been proposed. The estimated mass flux through nonzeolite pores for all the zeolite membranes tested is 15 ± 3 g m
−2
h
−1
which is 1.6 to 7.6% of the total transmembrane mass flux depending on the alcohol chosen.
We address the effect of exposure to sc CO
2
on the properties of Nafion membranes. A simple model is proposed to describe the pressure-induced reorganization of the phase-separated matrix. The model ...predicts that the cylindrical ionic pores in Nafion restructure under pressure applied: wider pores shrink in diameter to a larger degree than narrower ones. As a result, the pores ensemble becomes more monodisperse and narrower as a whole, which should determine detectable changes in the transport properties. The consistency of the model predictions with the main experimental observations was checked. In particular, the membranes were exposed to sc CO
2
at 45 °C and pressures ranging from 20 to 750 bar. The modified samples demonstrate the lower water uptake, the higher the pressure during the treatment. This observation correlates well with the cylindrical channels becoming more monodisperse and narrower. Moreover, both proton conductivity and relative crystallinity increase with increasing pressure from 96 to 105 mS/cm and from 20 to 22%, respectively. Methanol permeability decreases from 16 × 10
–7
cm
2
/s for pure Nafion to 10 × 10
–7
cm
2
/s for the treated membrane. DSC measurements reveal larger fraction of bound water for the modified films. Apparently, the bound water is sufficient to ensure high proton conductivity. The improved selectivity is explained by the narrower channels.
Mixed aluminum-containing metal-organic frameworks (MOF) modified with Fe, V, and Ti are synthesized in two steps. At the first step, the amorphous precursors of metal-organic frameworks containing ...various amounts of transition metals are obtained by the electrochemical method. At the second step, the precursors are crystallized under solvothermal conditions. Study of the effect of synthesis conditions shows that Fe-containing metal-organic frameworks crystallize in the presence of dimethylformamide; V- and Ti-containing counterparts crystallize in the presence of water. The time and temperature of crystallization are varied in the range from 150 to 200°С and 24 to 72 h depending on the concentration of the transition metals. The resulting samples are investigated by low-temperature nitrogen adsorption, scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and thermogravimetric and differential thermal analysis (TGA-DTA). Research into the influence of catalyst composition on its activity in 1-octene epoxidation by
tert-
butyl hydroperoxide suggests that that the titanium-containing samples are catalytically inactive, while the vanadium-containing samples are more active than the iron-containing ones. Testing of the vanadium-containing samples in propylene epoxidation demonstrates that their activity is comparable with the activity of a commercial titanium silicate catalyst.
Dealumination of Nanosized Zeolites Y Yakimov, A. V.; Zasukhin, D. S.; Vorobkalo, V. A. ...
Petroleum chemistry,
05/2019, Letnik:
59, Številka:
5
Journal Article
Recenzirano
The dealumination of nanosized zeolites is an important scientific problem, which should be solved to improve the activity of catalysts based on this zeolite in a broad range of heterogeneous ...catalytic reactions, particularly in commercial processes. However, the smaller the required size of the synthesized crystals, the lower the Si/Al ratio and the lower the degree of dealumination of this material can be achieved. In this study, the dealumination of zeolites Y with a crystal size of 50–1100 nm by treatment with ammonium hexafluorosilicate and steam heat treatment is discussed. It is shown that the dealumination with ammonium hexafluorosilicate is a “gentler” method in terms of structure preservation, whereas the dealumination by steam heat treatment provides a higher Si/Al ratio in the products; however, this method is inapplicable for crystals smaller than 500 nm, because it leads to the complete degradation of the structure. However, nanosized crystals can be dealuminated by treating with ammonium hexafluorosilicate. In this case, the degree of dealumination is close to 40%. A significant disadvantage of this method is the formation of a SiO
2
film on the crystal surface; this feature substantially restricts the use of the ammonium hexafluorosilicate treatment in the synthesis of cracking catalysts.
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.
Synthesis of isobutylene from ethanol in the presence of ZnO/ZrO
2
catalysts has been studied. The samples have been synthesized by incipient wetness impregnation of zirconium hydroxide derived from ...zirconyl chloride with zinc nitrate and subsequent calcination at 550°C. The synthesized samples have been studied by low-temperature nitrogen adsorption, SEM, XRD, IR spectroscopy of adsorbed CO, and TGA–DTA. Studies of the effect of the catalyst composition and the test conditions have revealed that, during the synthesis of isobutylene from ethanol, an optimum Zr : Zn molar ratio providing the production of isobutylene with a selectivity of 45–50% is 8–20 and optimum conditions for ethanol conversion to isobutylene are 500°C, a feed space velocity of 3 g/(g h), and a feedstock in the form of a 50% ethanol solution in water. According to thermogravimetric analysis, an increase in the zinc content in the samples leads to a decrease in the amount of coke deposits.
Solid solution samples of yttrium orthophosphate–yttrium orthovanadate of general formula Y(VO4)1-x(PO4)x (x = 0.25; 0.50; 0.75) were obtained using solid state synthesis. The samples crystallize in ...zircon structure (I41/amd sp. gr.) as the pure end-members of the system do. Unit cell parameters calculated using XRD data were found to be in good agreement with those calculated from the Vegard law. SEM-EDS spectra of samples are given. Heat capacities of the samples (x = 0.50; 0.75) were measured by means of adiabatic calorimetry at low temperatures (6–344 K). Thermodynamic functions in the studied temperature range were calculated and compared to those of pure yttrium orthophosphate and orthovanadate. According to the data obtained solid solution Y(VO4)1-x(PO4)x can be considered as ideal, thus making it possible to calculate thermodynamic functions for any other substitution x by summation of obtained values for closest compounds with corresponding coefficients or pure substances.
