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11OBTAINING OF FERRIC-CONTAINING CATALYST ON THE BASE OF ZEOLITIC
MATRIX
Akhalbedashvili L.
Kvatashidze R.
Todradze Loria N.
Janashvili N.
Jalaghania S.
Gagniashvili N.
Ivane Javakhishvili Tbilisi State University, Caucasian Institute of Mineral Resources, Tbilisi, Georgia
ABSTRACT
The paper presents the research findings related to study the changes of structure and locations of ferric ions in modified zeolite clinoptilolite (CL) from Georgian deposit Dzegvi, prepared by different methods.
The redox-oxidative behaviour of Fe3+, located in zeolite structure, in cationic forms and in the form of occluding hydroxy-oxidic compounds is investigated by means of ESR spectroscopy. While the structural Fe3+ ions are very resistant to reduction, the Fe3+ ions in cationic sites are very easily reduced. Dehydrated and dehydrox-ylated zeolites with Fe3+ valence state can be prepared only by heat treatment in oxygen atmosphere.
Keywords: natural zeolite, modify, iron-contained forms, EPR.
Introduction
The dependence of chemical activity on size of reacting participles due to the fact that the properties of the individual atoms of the elements and formed the clusters from these atoms and nanoparticles are different from the properties of the compact, volumetric substance. In the first approximation for understanding and analyzing the chemical size-dependent properties can be compared reactivity of compact substances, nano-particles, and atomic and molecular clusters [1].
The boundaries between these dimensional modes are changed for each element and must be studied specifically. Most catalytic systems are nanosystems [2, 3]. In heterogeneous catalysis, the active substances deposite on the carrier as nanoparticles and increase their surface area. For example, it is established that increasing the specific activity of platinum nanocrystalls in regard to oxidation of carbon monoxide at increasing d from 10 to 60 nm depend on that small nanocrystsalls on surface of catalyst are more than "costal" structural elements which form transition sites between faces (100) and (111). The CO molecules on transition sites are in linear form, nonmobile and have the deficit of electron density to compare with molecules on faces [3, 4]. In recent years, metal/zeolites, crystalline alumino-silicates with properties and characteristics of mi-croporous molecular sieves, have received more attention, as the possibility of their use as catalysts in environmental control processes and particularly in the nitrogen oxides (NOx) reduction to N2 in exhaust gases.
Natural and synthetic zeolites because of the unique structure are reported in literature as effective and widely used materials in industrial processes, particularly related to environmental control and catalysis [5, 6].
In the catalysis field, the incorporation of an active species into the zeolite framework, by high cation exchange capacity and selectivity, is particularly useful in the design and development of new catalytic materials to apply in many organic and inorganic reactions [6]. Activated zeolite can be formed in many ways such as
acid, base or salt treatments and high-temperature calcinations. The hybrid method can make the activation of zeolite more efficient than others [7, 8]. According to [7 ] the first aim of acid treatment is to remove the impurities and substances from the cavities and pores of natural zeolite especially Fe2O3 since iron always attends as in industrial, so in laboratory samples. But till now there is no undivided opinion of what locations of Fe(III) corresponds to the observed EPR-signals - lattice or nonlattice [9-12].
The second purpose is to make more effective space, so that the large radius of cations such as Ca2+, Mg2+ and Na+, can be displaced by H+, and this is called proton exchange. But there is also a disadvantage in the dealumination and reduction of thermal stability by acid treatment.
In this paper, with purpose to obtain catalysts, active in oxidative-redox reactions iron in oxide and cati-onic forms were put on the surface of the predecation-ized natural zeolite clinoptilolite (CL) from Georgian deposit Dzegvi by different methods, and to study the changes of structure and locations of ferric ions in modified zeolite.
Experimental part
Fe-zeolite systems were prepared by ion exchange in aqueous medium using a 0.05 mol/l solution of chloride of iron (III) (sample FeDecCL-I) and in the solid state using the same FeCl3 (sample FeDecCL-II) and fresh precipitated Fe(OH)3 (sample FeDecCL-III) in a repeated impregnation of natural zeolite clinoptilolite (deposit Dzegvi, Georgia). This CL had a Si/Al ratio of 5.6 in initial state and 23 in decationated form (DecCL). Decationation was carrying out by multiple treatments with 1N solution of HCl at ~ 900C during 4 hours. All newly made Fe-contained material has a red-brown color.
After the ion exchange, the samples were filtered, washed with distillated water and dried at 110 °C. Further, the samples were thermally treated at 450 °C under air flow during 1 h.
The full chemical analysis of initial and prepared samples was carried out using AAS, electrophotocolor-imetric, titration and gravimetric analysis.
The content of heavy metals was determined with AA-spectrophotometer AAnalyst 200 ("Perkin Elmer"). The XRD patterns were obtained on a Dron-2 Diffractometer using a monochromatic CuKa radiation. The ESR experiments were carried out on ESR-spectrophotometers THOMSON-CSF TSN-254 and
The chemical content
РЭ- 1307 with computer system of accumulation of a signal at 250C. As the standard the powder of DPPH, Ho of a field 3400G were used, the scanning amplitude varies from 3000 up to 500G, modulation amplitude is 5G.
The chemical analysis, expressed in table, showed that exchange degree of Fe3+ in obtained samples varied from 1.45% for FeDecCL-I to 2.42% for FeDecCL-II and 3.06% for FeDecCL-III.
Table.
of studied samples
No Sample SiO2 Al2O3 Fe2O3 TiO2 SO3 MgO CaO K2O Na2O H2O MnO P2O5
1 CL 59.64 12.29 1.00 0.50 0.02 0.95 2.17 1.46 9.93 13.55 0.04 0.50
2 DecCL 74.92 6.46 0.05 0.01 0.03 0.67 1,05 0.78 5.24 9.87 0.09 1.10
3 Fe/DecCL-I 74.92 6.46 2.07 0.01 0.03 0.52 1.05 0.78 2.27 9.87 0.09 1.10
4 FeDecCL-II 74.84 6.48 3.45 0.01 0.03 0.52 1.05 0.78 2.32 9.84 0.09 1.10
5 Fe/DecCL-III 74.84 6.48 5.80 0.01 0.03 0.54 1.05 0.78 1.22 9.86 0.09 1.10
Results and discussion
The safety of structure and crystallinity of the CL in natural, decationated forms and after the treatment with ferric salts and freshly made ferric hydroxide, verified by X-ray (fig. 1, 2). The ESR analysis was used to identify the location of Fe3+ ions in FeDecCL-I and FeDecCL-II systems. The X-ray diffraction patterns of calcined ferrizeolite showed that the symmetry of the calcined Fe-contained zeolite is orthorhombic. In the calcined crystals with a monoclinic symmetry, the splitting of reflections in the XRD pattern is usually observed at 26= 24.4o and 29.3o. Therefore, the persistence of the orthorhombic symmetry even in the calcined state provides supplementary evidence for the lattice positions of iron in the ferri-zeolites [3, 4, 13]. However, it was observed that the peak intensities decrease with the increase of Fe content. This decrease is attributed to the higher X-ray absorption coefficient of Fe compounds than Na, K and Ca compounds, enclosed in CL.
The major sites of Fe in structure of Fe/DecCL-III have no bonds to framework oxygen. It is known that 45% of Fe in CL is found in the center of the ten-mem-bered A channel forming a disordered square planar Fe2p-tetraammine complex with two additional H2O molecules complex [13]. In the eight-membered B channel 43% of the total Fe forms an approximately square planar H2O complex.
Usually, the interpretation of the ESR spectrum of Fe(III) in zeolite materials is difficult because of overlap of different signals. It is known that x-band ESR spectrum of iron-doped [14] zeolites are composed of two groups of signals: one at low resonance field, i.e. at g-4.3; the other group at geff -2.0 and geff -2.3, where the two signals are largely superimposed.
According to interpretations of [6] the g-4.3 signal is assigned to Bronsted acid iron sites; charge un-compensated, tetra-coordinated Fe (III) is responsible for the gejf -2.0. Lewis acid, tri-coordinated Fe (III) yields signals from gef-2.0 to gef-4.0. The gef-2.0 has been assigned to both framework and extra-framework highly symmetric sites.
According to obtained data the ESR spectrum of the samples shows the presence of Fe3+, irrespective of the method used in the preparation of zeolite. But the intensity of signal of Fe3+ in Fe/DecCL-III with g= 4.23 is less than intensity of Fe/DecCL-I sample. Possibly in our case iron can precipitate as a-FeOOH [13, 15]. In ion exchange in the solid-state, the precipitation of a -FeOOH on the solid surface can generate solids with Fe/Al > 1/3. During the activation, the precipitated a-FeOOH is dehydrated to form hematite [13]. The Fe/DecCL samples showed a g value of 4.29 for the activated samples and a g value of 4.23 for the sample non-activated. So, the difference in the lines of the spectra and therefore in g values is attributed to the different chemical environments of the Fe atoms.
Conclusion
Thus, the redox-oxidative behaviour of Fe3+, located in zeolite structure, in cationic forms and in the form of occluding hydroxy-oxidic compounds is investigated by means of ESR spectroscopy. While the structural Fe3+ ions are very resistant to reduction, the Fe3+ in cationic sites are very easily reduced. Dehydrated and dehydroxylated zeolites with Fe3+ valence state can be prepared only by heat treatment in oxygen atmosphere. This must be taken into account when evaluating the effect of Fe3+ ions on the properties, especially the catalytic activity of zeolites.
Fig. 1 The difractogram of initial CL (Dzegvi, Georgian). The content of CL phase in rock 93%
Fig.2. The difractogram of DecCL (after treated with HCl)
Fig.3. The ESR spectra of Fe/DecCL-III after ion exchange (a); after activation at 5200 C Fe/DecCL-II (b);
obtained by impregnation Fe/DecCL-III (c).
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ИССЛЕДОВАНИЕ ВЛИЯНИЯ РАЗЛИЧНЫХ ФАКТОРОВ НА КАЧЕСТВО ПЛЕНОК SbiTes
Гаджиева К.И.
Кандидат химических наук, старший научный сотрудник Института Катализа и Неорганической Химии имена академика М.Нагиева НАНА
Ализаде И.Э.
Диссертант Института Катализа и Неорганической Химии имена академика М.Нагиева НАНА
Халилова М.И.
Кандидат химических наук, старший научный сотрудник Института Катализа и Неорганической Химии имена академика М.Нагиева НАНА,
Аббасова Н.И.
Кандидат химических наук, старший научный сотрудник Института Катализа и Неорганической Химии имена академика М.Нагиева НАНА,
Гамидов Р.Г.
Кандидат химических наук, ведущий научный сотрудник Института Катализа и Неорганической Химии имена академика М.Нагиева НАНА,
Мирзоева А.М.
Бакинский Государственный Университет, канд.хим. наук,
INVESTIGATION OF THE INFLUENCE OF VARIOUS FACTORS ON QUALITY OF
Sb2Te3 FILMS
Gadziyeva K.I.
Candidate of Chemical Sciences, senior researcher of Institute of Catalysis and Inorganic Chemistry named after of academician M.Nagiyev of ANAS
Alizade I.E.
Postgraduate students of Institute of Catalysis and Inorganic Chemistry named after
of academician M.Nagiyev of ANAS Khalilova M.I.
Candidate of Chemical Sciences, senior researcher of Institute of Catalysis and Inorganic Chemistry named after of academician M.Nagiyev of ANAS
Abbasova N.I.
Candidate of Chemical Sciences, senior researcher of Institute of Catalysis and Inorganic Chemistry named after of academician M.Nagiyev of ANAS
Hamidov R.H.
Candidate of Chemical Sciences, leading researcher of Institute of Catalysis and Inorganic Chemistry named after of academician M.Nagiyev of ANAS
Mirzoeva A.M. Baku State University, PhD
АННОТАЦИЯ
Проведено совместное электроосаждение теллура и сурьмы из солянокислого электролита. Изучено влияние HCl, NH4Cl температуры, перемешивания на состав и качество сплава сурьма-теллур. На качество осадков заметное влияние оказывали перемешивание электролита и повышение температуры электролита. При перемешивании и температурах 20-500С на катоде получаются блестящие, хорошо сцепленные с поверхностью катода тонкие слои сплава сурьма-теллур. Качество катодных осадков сильно зависит от времени электролиза. При длительном электролизе, особенно при высоких плотностях тока, качество катодных осадков ухудшается, они становятся черными и порошкообразными. Предложен оптимальный состав электролита и режим электролиза для получения качественных тонких полупроводниковых пленок сплавов Sb-Te.
ABSTRACT
The combined electrodeposition of tellurium and antimony from the hydrochloric acid electrolyte was carried out. The influence of HCl, NH4Q temperature, mixing on the composition and quality of the antimony-tellurium alloy was studied. The quality of the sediments was significantly affected by the mixing of the electrolyte and the increase in the temperature of the electrolyte. With mixing and temperatures of 20-500C, the cathode produces
