The LTA and SOD zeolites were synthesized from the mechanically activated solid mixtures of metakaolin, NaOH and gamma -Al sub(2)O sub(3). The process of synthesis is controlled by X-ray diffraction, ...IR-spectroscopy, and scanning electron microscopy. The stages of both thermal treatment and hydrothermal crystallization were investigated and optimized. The size of LTA particle was directly measured by scanning electron microscopy as well as calculated using the X-ray diffraction spectroscopy data. It was shown that the maximum content of LTA can be achieved with an gamma -Al sub(2)O sub(3) excess over the stoichiometry of the synthesis reaction in an amount of 30-50 mol%. The absence of aluminum oxide in the reaction mixture leads to the formation of SOD. It was found that the optimal temperature of the thermal treatment is 600 degree C. An increase of the temperature leads to a decrease in the amount of the zeolite crystalline phase as well as in the formation of nepheline. The optimum concentration of the NaOH solution at the hydrothermal crystallization stage was defined to form both LTA and SOD. They are 2-4 mol/l for the LTA and more than 8 mol/l for the SOD. Under these conditions, the amount of the zeolites is more than 90 wt.%.
The effect of ultrasonic treatment on the thermal behavior of the mixtures from metakaolin, sodium hydroxide and alumina designed for LTA zeolites synthesis was studied. X-ray diffraction analysis, ...infrared spectroscopy, scanning electron microscopy and synchronous thermal analysis have been used. It was shown that after evaporation of the suspension, LTA zeolite (24 mass%) is contained in the samples. It was established that the new phase (sodium aluminum silicate) is formed at a calcination temperature of about 600 °C. It was demonstrated that at a calcination temperature over 800 °C, nepheline is synthesized. The reaction of nepheline formation has been described by the topochemical equation of four-dimensional nucleation/nucleus growth according to Avrami/Erofeev. Using the Ozawa–Flynn–Wall analysis for non-isothermal data, the values of the activation energy and the pre-exponential factor have been calculated. It is shown that after the ultrasonic treatment the activation energy of the nepheline synthesis reaction has smaller values than in the sample without pretreatment. These phenomena have been explained by differences between the structural parameters of the particles (dimension of the coherent scattering region, the value of microdeformations).
Synthesis of a molded adsorbent (MA) based on zinc oxide doped with oxides of transition metals (cobalt, copper, magnesium, titanium) was considered. The influence of these dopants on the physical ...properties and performance of the MA was shown. The role of the amount of the dopant in the specific surface area and porosity of the MA was evaluated, and the effect of transition metal oxide dopants on its surface morphology and strength was demonstrated. The chemisorption capacity of the oxide systems synthesized toward carbon disulfide was experimentally determined. The influence of carbon disulfide chemisorption on the surface morphology, as well as on the strength properties of the MA, was investigated. Using thiophene as a model hydrogen acceptor, the activity of the MA in the destructive reduction of organosulfur compounds was examined. The selectivity of thiophene hydrogenation to 2,3-dihydrothiophene in the temperature range from 350 to 410°C was shown. The optimal temperature of thiophene reduction was found to be 390°C, irrespective of the dopant amount. Using gas chromatography, the chemical composition of the hydrogenate was determined, and the complex dependence of its composition on the nature of the doped oxide was shown. It was demonstrated that doping with small amounts (up to 1.5 wt %) of cobalt and copper oxides provides for significant catalytic ability of the MA in the thiophene reduction reaction and that doping with 0.5 wt % titanium and magnesium oxides affords improvement of the strength properties of the MA. Use of aqueous ammonia solutions of various concentrations for the charge preparation did not noticeably affect the strength characteristics of the MA. The increments in the strength of the MA after the desulfurization process were estimated. It was shown that the MA operation has little effect on its morphology and crystallinity.
Granular LTA and SOD zeolites have been synthesized, characterized, and further used to study the kinetics of water adsorption and desorption. It has been shown that LTA zeolite in a static mode ...provides adsorption of water vapor at the level of ~30 wt % for LTA and ~20 wt % for SOD. It has been found that during water adsorption from the gas phase on the LTA or SOD zeolite in a flow-through unit, the dew point reaches –50 or –9°С, respectively. The kinetics of adsorption of water vapor on zeolite granules has been studied; the values of apparent activation energy of the adsorption process have been calculated, which amount to about 50 kJ mol
–1
; and the rate order of the process has been determined (0.2 for LTA and 0.9 for SOD). The apparent activation energies for water desorption from the zeolites have been calculated by isoconversional analysis in terms of the Friedman, Ozawa–Flynn–Wall, and Kissinger–Akahira–Sunose models. It has been shown that all three models give similar results. It has been found that at given degree of conversion, the activation energies are not higher than 60 kJ mol
–1
, a value that corresponds to desorption of physically bound water. The increase in activation energy to 110 kJ mol
–1
(for SOD) or 80 kJ mol
–1
(for LTA) is associated with the removal of water from the α- and β-cages of zeolites.
The behavior of the mixtures 6Al
2
Si
2
O
7
: 12NaOH and 6Al
2
Si
2
O
7
: 12NaOH : 2Al
2
O
3
during heat-treatment was studied by means of x-ray diffraction and simultaneous thermal analysis. It was ...shown that hydrated zeolite LTA forms after ultrasonic treatment and evaporation of a suspension, granulation of paste, and drying. It was determined that sodium aluminum silicate Na6Al
4
Si
4
O
17
is synthesized at temperatures up to 700°C. Sodium aluminum silicate Na
8
Al
4
Si
4
O
18
, mullite, and nepheline were found in the systems after heat-treatment at temperatures above 800°C. It is shown that the calculations performed by Friedman’s isoconversion method (differential) and the Kissinger–Akahir–Sunose (integral) method, for which the temperature interval 500 – 800°C is of interest, give close values of
E
. The growth of the apparent energy of activation with increasing degree of transformation attests a change in the reaction mechanism.
Two methods of synthesizing composite precursors for obtaining catalysts of the process of liquid-phase hydrogenation based on nickel and silica gel are considered. A comparative analysis is made of ...methods of synthesis as a function of methods of preparation is presented, and the influence of mechanoactivation on the textural properties of catalysts is also investigated. Bulk density, particle porosity, specific surface area, total pore volume, and the radial distribution of the pores were chosen as the main textural properties. X-ray phase analysis, scanning electron microscopy, and low-temperature adsorption of nitrogen were used for these purposes.
In this work, the process of decomposition of 2,4-dichlorophenol (2,4-DCP) vapor under the influence of atmospheric pressure DBD in oxygen was studied. The studies were carried out in two modes: with ...a catalyst (natural vermiculite doped with zirconium) and without it. A number of basic characteristics of the catalyst were assessed. The rates and effective rate constants of sorption processes, as well as decomposition processes in plasma and plasma-catalytic systems, were determined. Based on these data, the energy efficiency of the decomposition process was calculated. The data obtained suggested that the initial stage of decomposition is the reaction of interaction of electrons with pollutant molecules. The catalyst has been shown to speed up the decomposition process, increase energy efficiency and the conversion of 2,4-DCP to CO
2
molecules, and prevent the formation of condensed products on the reactor walls. The work estimates the carbon and chlorine balances before and after treatment, which reach a maximum of 99 and 60%, respectively. It was also shown that the catalyst retains its activity for at least 7 h of continuous operation.
Zeolite membranes were synthesized using metakaolin, sodium hydroxide, and alumina with 6Al
2
Si
2
O
7
: 12NaOH : 2Al
2
O
3
molar ratio as raw ingredients. For this purpose, a combined approach was ...employed which involved ultrasonic processing of the initial suspension and microwave crystallization. The synthesis was followed by a comparative assessment of the separation capacity of the samples prepared by physicochemical treatment versus the samples obtained by conventional methods, such as crystallization under convective heating. The highest content of LTA crystalline phase was achieved by a combination of ultrasonic processing and microwave crystallization. Moreover, this approach produced defect-free membranes which did not contain non-zeolite pores and ensured a high degree of ethanol/water pervaporation at 60°C.
It is shown that, with the help of adsorption–catalytic deformation, it is possible to significantly change the composition of the skeletal nickel hydrogenation catalyst by changing the steric factor ...directly under the conditions of the chemical reaction. Various substances were tested as model compounds undergoing reduction: hydrogen peroxide, sodium maleate, and propen-2-ol-1. It is shown that, during the hydrogenation reaction, as a result of strong local overheating, the catalyst grain is deformed and the aluminum atoms that were previously in the bulk of this grain appear on the surface, after which aluminum becomes available for further leaching, while yielding additional hydrogen.
The zeolite A was synthesized from the mechanically activated solid mixtures of metakaolin, sodium hydroxide and aluminum oxide. The stages of both thermal treatment and hydrothermal crystallization ...were investigated and optimized. The size of zeolite A particle was directly measured by scanning electron microscopy as well as calculated using the X-ray diffraction spectroscopy data. The thermal stability of the zeolite A was studied by the differential thermal analysis. It was shown that the optimum thermal treatment temperature providing the zeolite A yield of about 65 wt% and the particle size in the range of 0.2–0.3 μm is 600 °C. The furthermore increase in the thermal treatment temperature results in decreasing amount of zeolite A crystalline phase as well as in the formation of nepheline. It was also found that the optimum NaOH concentration providing the zeolite A yield of about 90 wt % and the particle size more than 0.7 μm after the hydrothermal crystallization stage is 2–4 mol/l. The higher alkali concentrations result decreasing amount of the zeolite A phase and cause the recrystallization into the sodalite. The use of KOH in the hydrothermal crystallization stage allows one to obtain the potassium-containing zeolite A by direct synthesis.
