2. V. Z. SASCA a, Orsina VERDES a, Livia AVRAM a, A. POPA a A. ERDÕHELYI b and A. OSZKO b a Institute of Chemistry Timisoara-Romanian Academy b Institute of Physical Chemistry and Material Science-University of Szeged ETHANOL CONVERSION ON Cs x H 3-x PW 12 O 40 CATALYSTS AND THEIR MICROSTRUCTURE The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

3. INTRODUCTION The heteropoly compounds-HPCs offer good opportunities for catalysts design as result of: - the control of acidic and redox properties in a large scale of values by choosing the constituent elements of anion and countercations, - the pseudo-liquid behaviour, - the structure defined at molecular level and unique complex formation with various organic and organometallic compounds. Among HPCs, heteropoly acids (HPA) with Keggin anion structures have received considerable attention due to their simple preparation and strong acidity (Misono 1987; Kozhevnikov 1995). Specifically, 12- tungstophosphoric acid (H 3 PW 12 O 40 ), denoted as H 3 PW hereinafter, is among the most extensively studied (Misono and Nojiri 1990; Corma 1995; Okuhara et al. 1996) since it possesses the highest Brönsted acidity (Misono et al. 1982). This type of HPCs are effective catalysts in important catalytic reactions that use the renewable raw material as the bioethanol. The microstructure for acidic salts of the H 3 PW, especially with Cs, are controversial in the literature: - some authors propose a model of catalysts particles with a core of Cs 3 PW 12 O 40 coated of the H 3 PW layers; - the others sustain a homogeneous structure of the acid salts. The goal of this study was to unravel the Cs x H 3-x PW microstructure by corroboration of structure, texture and surface catalysts composition data with catalytic properties for ethanol conversion and selectivity to products reactions taking into account the type of reactions, in bulk or surface The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March,, 2011, SZEGED

4. EXPERIMENTAL ● The tungstophosphoric acid H 3 [PW 12 O 40 ]  xH 2 O (H 3 PW) was synthesized according to the methods described of J. C. Bailar(Inorg. Synth., 1, 1939, 132- 133) and M. Misono et. al. (Bul. Chem. Soc. Jpn., 55, 1982, 400-406). Na 2 HPO 4 H 2 O and Na 2 WO 4 2H 2 O were dissolved in hot distilled water, under stirring and the solution was kept at 80 o C, 2 hours. After, HCl 37% was added by dropwise. When the solution has cooled, ether was added until, after shaking, three layers remain. The lower layer was separated and it was washed with water a several times. After separation from water, the ether was evaporated by air bubbling and a precipitate was formed. When precipitate no longer smell of ether, it was dissolved in a small quantity of water. After slow water evaporation the H 3 PW crystals are obtained. 12WO 4 2- + HPO 4 2- + 23H + [PW 12 O 40 ] 3- + 12H 2 O ● The salts of H 3 PW were prepared by precipitation from an aqueous solution of the parent acid adding the required stoichiometric quantity of counter-ion salts as cesium nitrate under stirring. The pH was under 1.5 during the all syntheses. The precipitates were dried at 50 o C under stirring until a paste was obtained. After, the Cs x H 3-x PW samples were heated at 250 o C in air for nitrate anion total decomposition. The water content of all prepared heteropoly compounds was determined after their keeping in air at room temperature until constant weight was observed. The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED SYNTHESIS

5. EXPERIMENTAL ● The thermal analyses were carried out on thermoanalyzer system Mettler TGA/SDTA 851/LF/1100. The measurements were conducted in dynamic atmosphere of synthetic air (50ml/min), using the alumina plates crucibles of 150 μl. Heating rates were 2.5-10  C min-1 and the mass samples were about 30 mg. ● The IR absorption spectra were recorded with a Jasco 430 spectrometer (spectral range 4000-400 cm -1 range, 256 scans, and resolution 2 cm -1 ) using KBr pellets. ●Powder X-ray diffraction data were obtained with a XR Fischer diffractometer using the Cu Kα radiation in the range 2θ = 5÷60 . ● Specific surface and porosity measurement by BET method were calculated from the nitrogen adsorption-desorption isotherms, date using a Nova 1200 Quantachrome equipment. The sample was previously degassed to 10 -5 Pa at 250 0 C for 2 h. ● The Bronsted acidity of catalysts were measured by temperature programmed desorption-TPD of n-butylamine (adsorption at 373 K and desorption by increasing the temperature from 373 K to 873 K). ● The surface morphology for synthesized compounds was observed by SEM method with a Jeol JSM 6460 LV instrument equipped with an EDS analyser. The samples were heated at 523 K, 1h and then were covered with a film of Au before the measurements.. Catalyst characterization and catalytic activity PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

6. EXPERIMENTAL Catalytic activity for conversion of ethanol was studied by pulse reactant technique-PRT. Two micro reactors, with fixed bed of about 100 mg catalyst, connected directly to a GC with thermal conductivity detector-TCD for CO and CO 2 detection, Ar carrier gas flow of 30 cm 3 ·min -1, respectively, a GC with flame ionisation detector-FID, N 2 carrier gas flow of 30 cm 3 ·min -1, for detection of ethanol, ethylene, diethyl ether and other hydrocarbon fractions (C3-C6) were used. The reaction products were separated on the Porapak QS 80- 100 mesh packed columns, 3 m length, at 453 K for TCD-GC and with a temperature programme from 323 K to 473 K for FID-GC. The standard experimental protocol consisted of “in situ” catalysts drying, at 523 K for 1 h under flow of carrier gas, followed of six successive pulses of 3 μl liquid ethanol at 523, 573 and 623 K in the catalyst bed. For each temperature a fresh sample of catalysts was used. Catalyst characterization and catalytic activity Fig. 1. The instalation scheme for catalytic activity measurement by PRT: 1. Six port valve ; 2. Gas sample loop; 3. Liquid sample evaporator; 4. Microreactor heated by electric furnace; 5. Gas-cromatograf; 6. – Integrator. The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

7. EXPERIMENTAL The powder samples were pressed into tablets with about 1 cm diameter and a few tenth of mm thickness and placed into the load lock of the spectrometer. Sample treatments were carried out in a high pressure cell (catalysis chamber) directly attached to the main chamber and isolated from that with a gate valve. The samples were transferred from the analysis chamber into the high pressure cell in high vacuum, without the reach of air. The samples were pre-treated in the same way as described above. After the pre- treatment the samples were cooled to room temperature. Afterwards the high pressure cell was evacuated and the sample was taken back to the analysis chamber. XP spectra were taken with a SPECS instrument equipped with aPHOIBOS 150 MCD 9 hemispherical electron energy analyzer operated in the FAT mode. The excitation source was the K alfa radiation of a magnesium anode (h = 1253.6 eV). The X-ray gun was operated at 180 W power (12 kV, 15 mA). The pass energy was set to 20 eV, the step size was 25 meV. To compensate for possible charging effects the binding energies were normalized with respect to the position of C (1s), this value being assumed constant at 285.1 eV. Typically five scans were added to get a single spectrum. For data acquisition and evaluation both manufacturers' (SpecsLab2) and commercial (CasaXPS) software were used. Fig.2.SPECS instrument equipped with a PHOIBOS 150 MCD 9 hemispherical electron energy analyzer XPS analysis The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

8. Keggin primary and secondary structure Figure 4. Keggin units and water molecules arrangement in H 3 PW 12 O 40 · 6H 2 O RESULTS AND DISCUSSION Figure 3. Keggin unit structure represented by triads of edge-linked MoO 6 octahedra and central thetraedra PO 4 and its hexahydrate (down). The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

9. The complete elimination of the crystallization water after isothermal heating for 1 h at the temperatures of 523-623 K without the loss of constitutional water was observed, see Figure 5. RESULTS AND DISCUSSION Thermal stability, water content and Brőnsted acidity The constitutional water content (the water formed from the protons and the oxygen of the [PW 12 O 40 ] 3-, denoted as Keggin unit-KU hereinafter) of the acid and all acidic salts was measured of the TG curves (segment 1-2). Close values to theoretical ones were found for all compounds. Fig.5. The TG, DTA curves and the temperature heating program-T curve for H 3 PW. The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

10. RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED The H 3 PW and Cs x H 3-x PW thermal decomposition scheme

11. RESULTS AND DISCUSSION TPD for Brőnsted acidity measurements Fig. 6. The TG and DTG curves for TPD of NBA in the temperature range of 100-600 o C on (1) H 3 PW, (2) CsH 2 PW, (3) Cs 2 HPW, (4) Cs 2.25 H 0.75 PW, (5) Cs 2.5 H 0.5 PW and (6) Cs 3 PW The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March,, 2011, SZEGED

12. RESULTS AND DISCUSSION TPD for Brőnsted acidity measurements Sasca, L. Avram, O. Verdes, A. Popa, Appl. Surf. Sci., 256(2010) 5533-5538 The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March,, 2011, SZEGED The method is based on the alkylammonium ions formation when alkyl amines are protonated by Brønsted sites and their decomposition to ammonia and olefins in a well-defined temperature: HRNH 2 + ZOH HRNH 3 + ··· ZO - R + NH 3 + ZOH (1)

13. Water content and Brőnsted acidity Table 1. The physical adsorbed and crystallization water molecules per KU and proton content per KU for the synthesized compounds. RESULTS AND DISCUSSION Catalysts Physical adsorbed water, mol Crystallization water, mol H + /KU H 3 PW 1.0-1.5 5.5-6.02.85-2.90 Cs 1 H 2 PW 1.0-2.0 3.5-4.01.90-1,96 Cs 2 H 1 PW 2.0.-3.0 2.0-2.31.00-1,05 Cs 2.25 H 0.75 PW 4.0-5.0 1.3-1.50.72-0,75 Cs 2.5 H 0.5 PW 5.0-7.0 0.9-1.00.48-0,51 Cs 3 PW 8.0-9.0 -0.00 The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

14. Catalysts primary structure. RESULTS AND DISCUSSION The 3200-3400 cm-1 band is assigned to crystallization water-hydrogen bonded and to hydrogen-bond vibrations (hydrogen-bonds formed between neighbouring KUs). The 1715 cm-1 band is ascribed to hydroxonium ions, H 3 O + or H 5 O 2+, δ vibrations and the 1615 cm-1 band is assigned to δ vibrations of nonprotonated water molecules. The specific absorbtion bands of the Keggin Unit - [PW 12 O 40 ] 4- are: ν as P-O i -W; 1060-1080; ν as W- O t, 960-1000; ν as W-O c -W, 840- 910; ν as W-O e -W, 780-820 cm -1. The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED Fig. 8. The FTIR spectra: (1)H 3 PW6-7H 2 O (2) CsH 2 PW6-7H 2 O, (3) Cs 2 HPW5- 6H 2 O, (4) Cs 2.25 H 0.75 PW4-5H 2 O, (5) Cs 2.5 H 0.5 PW6-8H 2 O şi (6) Cs 3 PW8-9H 2 O

15. Catalysts primary structure. RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED Fig. 9. The FTIR spectra: (1)H 3 PWx 1 H 2 O (2) CsH 2 PWx 2, (3) Cs 2 HPWx 3 H 2 O, (4) Cs 2.25 H 0.75 PWx 3 H 2 O, (5) Cs 2.5 H 0.5 PWx 4 H 2 O and (6) Cs 3 PWx 5 H 2 O after heating at 300 o C, 1 hour

16. Catalysts primary structure. RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED Fig. 10. The FTIR spectra: (1)H 3 PWx 1 H 2 O (2) CsH 2 PWx 2, (3) Cs 2 HPWx 3 H 2 O, (4) Cs 2.25 H 0.75 PWx 3 H 2 O, (5) Cs 2.5 H 0.5 PWx 4 H 2 O and (6) Cs 3 PWx 5 H 2 O after heating at 600 o C, 1 hour.

17. Catalysts secondary structure The all synthesized compounds, H 3 PW6-7H 2 O and Cs x H 3-x PW5-8H 2 O, have a cubic structure and they show the XR-diffraction pattern in agreement with the literature data, as can be seen in Figure 11.. RESULTS AND DISCUSSION Fig. 11. The X-ray diffraction spectra for H 3 PW and its Cs x H 3-x PW salts The increase of width for the diffraction maxima with the Cs /KU ratio increasing was observed, which can be an effect of the crystallites size changes function of the chemical composition. The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR,, 24-25 March 2011, SZEGED

18. Catalysts secondary structure. RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR,, 24-25 March 2011, SZEGED Fig. 12. The X-ray diffraction spectra for H 3 PW heated at 600 o C

19. Catalysts secondary structure. RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR,, 24-25 March 2011, SZEGED Fig. 13. The XRD spectra : (1)H 3 PWx 1 H 2 O (2)CsH 2 PWx 2, (3)Cs 2 HPWx 3 H 2 O, (4)Cs 2.25 H 0.75 PWx 3 H 2 O, (5)Cs 2.5 H 0.5 PWx 4 H 2 O and (6)Cs 3 PWx 5 H 2 O after heating at 600 o C, 1 hour.

20. Catalysts texture λ– X-ray wavelength(CuKα) in angstroms (1.54Å) θ – diffraction angle β – line width (radians) Β 0 - instrumental line width (radians). Table 2. Surface area, pores volume and estimated crystallites size of the Cs x H 3- x PW catalysts with Scherrer equation CatalystSurface area, m 2 /g Pores volume, cc/g Size of crystallites(D), Ǻ H 3 PW 3.10.0025575 CsH 2 PW 1.80.0067175 Cs 2 HPW 6.60.022145 Cs 2,25 H 0.75 PW 54.20.0489145 Cs 2,5 H 0.5 PW 130.30.119117 Cs 3 PW 137.80.118117 RESULTS AND DISCUSSION Scherrer equation for crystallites size estimation based on XRD spectra:, (1) The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

21. Figure 15. HRSEM micrographs of bulk Cs 2.5 H 0.5 PW 12 O 40 salt taken at x150 000 magnification. Microp.Mes.Mater. 80 (2005) 43-55 Catalysts texture RESULTS AND DISCUSSION Figure 14. SEM micrographs of bulk Cs 2.5 H 0.5 PW 12 O 40 salt taken at x50 000 magnification. The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

22. Correlation of catalytic activity with Bronsted acidity The dehydration of ethanol in the presence of strong Brönsted acid sites could involve a complex series of reactions, including oligomerization, aromatization, cracking and hydrogenation. The reaction products detected by the pulse reactant technique on Cs x H 3-x PW catalysts were: methane, C2 fraction (ethylene, ethane), C3 (propene, propane), C4 (butane, butene), C5 (pentane, pentene), C6 (hexane, hexene) and diethyl ether. The aromatic compounds, as benzene, toluene and xylene, could be also present but in undetectable quantities. In plus, very small quantities of H 2 and CO were detected with GC-TCD. For the hydrocarbons formation, the selectivity to C4 fraction has the higher values and its variation function of the number of pulses show the same trends for the all hydrocarbons fractions, so, from the point of view of the our research goal the conversion of ethanol and selectivity to ethylene as main reaction product, respectively the selectivity to C4 hydrocarbon fraction will be analyzed. All the results were an average of the pulses 4-6, as the quantity of reaction products for the pulses 1-3 varies significantly and for the next pulses only the small changes were observed from one to the other. The average of values for three pulses has reduced the error of liquid sample introduction also. Typical examples of conversion and selectivities variation function of pulse number can be seen in Figure 10a,b,c. RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

23. Correlation of catalytic activity with Bronsted acidity Fig. 16a,b,c. Ethanol conversion (a), selectivity to ethylene (b) and selectivity to C4 hydrocarbons fraction (c) at 573 K on Cs 2.25 H 0.75 PW 12 O 40. RESULTS AND DISCUSSION a) c) b) The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

24. Correlation of catalytic activity with Bronsted acidity RESULTS AND DISCUSSION Figure 17a, b, c. The ethanol conversion and selectivity on the Cs x H 3-x PW catalysts function of Brőnsted acidity: 0-Cs 3 PW, 0.5-Cs 2.5 H 0.5 PW, 0.75- Cs 2.25 H 0.75 PW, 1-Cs 2 H 1 PW, 2- Cs 1 H 2 PW 12, 3-H 3 PW: a)523 K; b) 573 K; c) 623 K The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

25. In purpose to explain the catalytic behaviour, a model of catalysts particles as cubes or spheres of Cs 3 PW 12 O 40 coated of the H 3 PW 12 O 40 layers was built on the basis of: -The highest catalytic selectivity for C4 hydrocarbon fraction on Cs 2.25 H 0.75 PW, respectively on Cs 2.5 H 0.5 PW, a surface reaction type; -The equivalence of strenth for all Bronsted acidic sites; -Higher specific surfaces for content of Cs>2 and pores volume values increase for higher content of Cs; -The size of microcrystallites calculated with the Scherrer relation of X-ray diffraction spectra and the size of aggregates estimated from SEM data. Model of catalysts particles RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

26. 550 Ǻ 19.16 Ǻ Figure 19. The Keggin units and water molecules arrangement in H 3 PW 12 O 40 · 6 H 2 O Model of catalysts particles Figure 18. The cubic model of Cs 3 PW conglomerate coated of H 3 PW nanocrystals RESULTS AND DISCUSSION G.M. Brown, M.-R. Noe-Spirlet, W.A. Busing and H.A. Levy, Acta cryst. B33 (1977) 1038 The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

27. Model of catalysts particles Table 3. The molar ratio of H 3 PW/Cs 3 PW from acidic Cs salts and Acid layers on the Cs 3 PWaggregates RESULTS AND DISCUSSION The Caesium acidic salts of H 3 PW The acidic salts written down as mixture of H 3 PW and Cs 3 PW Molar ratio of H 3 PW/ Cs 3 PW from Cs x H 3-x PW as mixture The number of H 3 PW layers on the Cs 3 PW aggregates Molar ratio of H 3 PW of outer layers/ Cs 3 PW of inner aggregates Cs 2.5 H 0.5 PW 1H 3 PW+5Cs 3 PW= 6Cs 2.5 H 0.5 PW 1/511/5.1 Cs 2.25 H 0.75 PW 1H 3 PW+3Cs 3 PW= 4( Cs 2.25 H 0.75 PW ) 1/31,51/3.3 Cs 2 H 1 PW 1H 3 PW+2Cs 3 PW= 3( Cs 2 H 1 PW ) 1/22,31/2 Cs 1.29 H 1.71 PW * 4H 3 PW+3Cs 3 PW= 7( Cs 1.29 H 1.71 PW ) 4/354/3.1 Cs 1 H 2 PW 2H 3 PW+1Cs 3 PW= 3( Cs 1 H 2 PW ) 2/17 The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

28. Concentration of constituent elements on the catalyts surface by XPS RESULTS AND DISSCUTION Fig. 20. Caesium,Oxygen, Phosphorus and Wolfram spectra on the catalysts surface for: a) W 12 O, b)H 3 PW, c)Cs 2 H 1 PW, d)Cs 2.5 H 0.5 PW, e)Cs 3 PW. PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

29. Concentration of constituent elements on the catalyts surface by XPS Fig. 21. Oxygen and Wolfram concentration on the catalysts surface function of Cesium ions/KU: 0 (H 3 PW) ; 2 (Cs 2 H 1 PW); 2.5 (Cs 2.5 H 0.5 PW); 3 (Cs 3 PW). RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

30. Concentration of constituent elements on the catalyts surface by XPS Fig. 16. Phosphor and Cesium concentration on the catalysts surface function of Cesium ions/KU : 0.H 3 PW ; 2. Cs 2 PW; 2.5. Cs 2.5 PW; 3.Cs 3 PW. RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

31. Concentration of constituent elements on surface layers Fig. 17. Phosphor and Cesium concentration on the catalysts surface for: 0.H 3 PW ; 2. Cs 2 PW; 2.5. Cs 2.5 PW; 3.Cs 3 PW. RESULTS AND DISCUSSION The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

32. CONCLUSIONS ►The higher ethanol conversion, over 95%, was observed on the Cs x H 3-x PW catalysts where x = 0; 2.0; 2.25 and 2.5. The selectivity to ethylene decreases with increasing of the selectivity to C4 hydrocarbons fraction on the catalysts with Cs content of 2-2.5, especially on the Cs 2.5 H 0.5 PW catalyst ► A model of catalysts particles as cubes or spheres consist of Cs 3 PW coated of the H 3 PW layers is proposed on the basis of: - catalytic activity; -Bronsted acidity; -specific surfaces and pores volume values; - the size of microcrystallites calculated with the Scherrer relation of X-ray diffraction spectra and SEM data of literature. ► The model explains the abrupt increase of specific surface area for content of Cs>2 and the highest catalytic selectivity at ethanol conversion for C3 and C4 hydrocarbons fractions on Cs 2.25 H 0.75 PW, respectively on Cs 2.5 H 0.5 PW. ►The XPS measurements of Cs, W, P and O concentration in the surface layers for the H 3 PW, Cs 2 H 1 PW, Cs 2.5 H 0.5 PW and Cs 3 PW has confirmed the model, the Cs concentration for acid salts Cs 1 H 2 PW, Cs 2 H 1 PW being lower than theoretical, for surface layers. The higher concentrations of W and P as the theoretical ones could be explain as a result of the lower concentration of O in the surface layers The PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED

33. Thank you for attention! PROJECT “CATBIOETAMETCON”, HURO 901/090/2.2.2, SEMINAR, 24-25 March 2011, SZEGED