Molecular Sieves - Science and Technology - Vol. 6 - Characterization II / 01-Chemical Analysis of Aluminosilicates, Aluminophosphates and Related Molecular Sieves

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Procedure

Stir ca. 100 mg of sample with 50 mL of 0.05 M solution of HCl or HNO3 for 1 h at 50 ◦C. Centrifuge and make to volume.

This treatment allows removal of non-framework titanium without affecting framework titanium of Ti-silicalite [65].

7.2.2

X-ray Photoelectron Spectroscopy (XPS)

XPS is one of the spectroscopic methods that are limited to the analysis and characterization of the surface region of a solid (compare also Volume 4, Chapter 6 of the present series). In principle, XPS works as follows:

A solid sample is irradiated by an X-ray source, which causes low-lying electrons to leave the surface. The energy spectrum of these electrons can be measured and used for the determination of the binding energies of electrons. The binding energies are characteristic of the elements and are influenced by the surrounding of atoms from which the electrons are released. The latter allows, in some cases, the differentiation between framework and nonframework atoms. As the depth of penetration of the X-rays comprises only few atom layers, XPS can give information about the qualitative and quantitative composition of these layers only. A depth profile, however, can be obtained by sputtering the surface with an appropriate gas.

Relevant characteristic data are [89]

•detected elements: Z > 3

•analyzed surface (beam area): µm2 to mm2

•analyzed thickness (depth): 0.5 to 3 nm.

The application of XPS requires evacuation of the gas phase down to about 10–8 Pa. It is evident that this high-vacuum treatment may simultaneously have an influence on some properties of the sample under investigation, i.e., on valency or rearrangement of the surface layer of the sample due to possible partial desorption. This has to be taken into account, especially when binding energies should be measured, but is less important when only the chemical composition of the surface region is investigated.

One of the most serious problems that have to be taken into account for zeolites is the charging of the insulating sample due to the escape of electrons from the surface effected by X-rays (XPS) or ultraviolet radiation (UPS). This leads to a loss of any sample-independent reference level. However, this problem can be overcome (or at least minimized) by using the C(1s) binding energy of carbon impurities [90] always present in the samples or by various pretreatments (gold layer, ion irradiation, specimen bias, pulsed primary beam etc.). The right choice will depend on the aim of the measurement.

Because the detection of electrons from the sample surface is not limited to a special geometric shape of the surface, XPS, UPS and Auger spectroscopy

62	H. Kosslick · R. Fricke

(AES) can also be applied for the investigation of zeolite powders [90]. Usually, however, these methods are applied for the determination of the binding energies of elements forming the zeolite lattice. The reason for their good suitability for qualitative analysis is the high sensitivity of these methods.

Concerning the quantitative determination of the chemical composition of the surface layers with or without sputtering, XPS can only be regarded as a method which is able to give a rough estimation of the composition [91]. Of course, it is possible to calibrate the spectrometer by signal processing (background corrections, signal deconvolution etc.) as is also possible with other spectroscopic methods. Nevertheless, two points have to be taken into consideration which limit the use of these methods,

a)the absolute concentration of the elements to be analyzed quantitatively should not be lower than 3–5%,

b)the relative error of the determination of the concentration of elements is

estimated to be not better than 10%.

XPS spectra were used to differentiate between framework and nonframework titanium in Ti silicalite [65]. The presence of non-framework titanium is evidenced by the signal at 458 eV in the Ti 2p spectra (Fig. 25). After leaching, this signal disappears, revealing removal of non-framework titanium. Because the bulk chemical composition determined by ICP-AES does

Fig. 25 Ti 2p photoelectron spectra of calcined (r23, r50) and acid-leached (r50a) Tisilicates [65]

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not change after leaching, evidence is given for a location of non-framework Ti species near the crystal surface. On the other hand, framework Ti (signal at 460.3 eV) is not affected by leaching. After leaching, the Si/Ti surface ratio has increased, and correlates now with the unit cell volume (Table 9).

Gross et al. [92] have used XPS measurements for the investigation of the surface composition of dealuminated Y zeolites. A series of NH4NaY zeolites of varying ammonium content have been used as starting material for thermochemical treatment and extraction with EDTA which resulted in different degrees of dealumination. The Al/Si and Na/Si ratios were obtained from Al2p/Si2p and NaKL2,3/ Si2p peak area ratios. The error was estimated to be lower than 20%. Non-framework aluminum is enriched at the external crystal surface leading to a Si/Al ratio< 1. After thermal treatment at 815 ◦C the Si/Al an framework ratio is increased from 0.41 to 1.36.

Mohamed et al. [93] have shown by a combined XPS and catalytic investigation of barium-loaded MFI zeolites that the Ba/Si ratio determined by XPS as a function of the total barium loading shows a maximum at about 4. At greater loadings, the surface Ba/Si ratio is lower than the bulk Ba/Si ratio. They were able to correlate the olefin selectivity in the conversion of methanol with the surface Ba/Si ratio.

In a combined XPS and ISS (ion-scattering spectroscopy) investigation of different zeolite structures published by Grünert et al. [94], the authors derive detailed conclusions on the differences between the surface and bulk composition of the H and Na forms of the zeolites and on the dealumination processes within the crystal lattice.

The surface composition of various types of zeolites (NaA, HY, NH4- erionite, Na-mordenite) was also studied by Kaushik et al. [95]. The composition of the bulk and surface (expressed as Si/Al ratio) of most of the zeolites was nearly equal to what did not meet the results of 29Si MAS NMR.

Applying XPS spectroscopy, the dispersion and formation of bimetallic Pt – Pd particles on PtPd/H-beta zeolites has been studied by Fiermans et al. [96]. By careful analysis of the intensity changes of the Pd 3d and Pt 4d photolines, the authors come to the conclusion that segregation of Pd particles occurred towards the surface of zeolite beta.

Table 9 Si/Ti surface atomic ratios before and after acid leaching and unit cell volume of silicalites with different amounts of lattice titanium [65]

Sample	˚3	Si/Ti surface atomic ratio
	Unit cell volume/A
		leached	unleached
silicalite	5322	–	–
r100a	5337	167	91
r50a	5363	143	91
r63a	5400	100	56

64	H. Kosslick · R. Fricke

The dispersion of Ga on H-ZSM-5 and H-MOR has been investigated by Garcia-Sanchez et al. by applying XPS in combination with ICP, NMR and FTIR spectroscopy [97]. On the zeolite samples modified by CVD of trimethylgallium, the dispersion depends on the kind of treatment and on pore blocking effects.

Also in the case of K-L zeolites, XPS has been successfully applied to study the dispersion of Pt species. In their investigation, Zheng et al. could demonstrate that Fe has a stabilizing effect on the dispersion of Pt in Pt – Fe/KL zeolites [98].

References

1.Heinrichs H (1989) Laborpraxis Dezember 1140

2.Heinrichs H (1990) Laborpraxis Januar/Februar 20

3.Dolezal J, Powondra P, Sulcek Z (1968) Decomposition techniques in inorganic analysis. Elsevier, New York

4.Tschöpel P, Kotz L, Schulz W, Veber M, Tölg G (1980) Fresenius Z Anal Chem 302:1

5.Hannaker Oh, Hou Qing-Lie (1984) Talanta 31:1153

6.Guignard J, Hazebrouk GJ (1966) Chem Phys 63:1351

7.Mullen JP, Riley JP (1955) Anal Chim Acta 12:162

8.Schwarzenbach G (1956) Die komplexometrische Titration. Ferdinand Enke Verlag, Stuttgart

9.Jerschkewitz H-G (1961) Analytische Chemie, Teil I: Theoretische Grundlagen und qualitative Halbmikroanalyse. Teubner, Leipzig

10.Petzold W (1955) Die Cerimetrie E. Merck AG (ed) Verlag Chemie, Weinheim

11.Schnick W, Lücke J (1992) Angew Chem 104:208

12.Buresch O, von Schnering HG (1984) Fresenius Z Anal Chem 319:418

13.Krom MD (1980) Analyst 105:305

14.Fraser AR, Russell JD (1969) Clay Miner 8:229

15.Kudeyorov V (1970) Khim Sel’sk Khoz 8:708

16.Searle PhL (1984) Analyst 109:549

17.Welz B (1983) Atomabsorptionsspektrometrie. Verlag Chemie, Weinheim

18.Haswell SJ (ed) (1991) Atomic absorption spectrometry. Elsevier, Amsterdam

19.Encyclopedia of analytical science (1995) Academic Press, Harcourt Brace & Comp Publ, London, vol 1 p 195 (Fig. p 202)

20.Slickers K (1992) Die automatische Atom-Emmissions-Spektralanalyse. Buchvertrieb K.A. Slickers, Gießen

21.Thompson M, Walsh JN (1989) Handbook of inductively coupled plasma spectrometry, 2nd edn. Blackie, Glasgow

22.Montaser A, Golightly DW (1992) Inductively coupled plasmas in analytical spectroscopy, 2nd edn. VCH, New York

23.Welz B (ed) (1986) Fortschritte in der atomspektrometrischen Spurenanalytik. Verlag Chemie, Weinheim

24.Erzinger J, Heinschild HJ, Stroh A (1986) In: Welz B (ed) Fortschritte in der atomspektrometrischen Spurenanalytik, vol 1. Verlag Chemie, Weinheim, p 211; Erzinger J, Heinschild HJ, ibid., vol 2, p 333

25.Godelitsas A, Charistos D, Tsipis A, Tsipis C, Fillipidis A, Triantafyllidis C, Manos G, Siapkas D (2001) Chem-A Eur J 7:3705

Chemical Analysis of Molecular Sieves

65

26.Bertin EP (1978) Introduction to x-ray spectrometric analysis. Plenum Press, New York

27.Jenkins R (1988) X-ray fluorescence spectrometry. Wiley, New York

28.Van Grieken RE, Markowicz AA (eds) (1992) Handbook of x-ray spectrometry. Marcel Dekker, New York

29.Scholz O (1972) Atomphysik kurz und bündig. Vogel-Verlag, Würzburg, p 93

30.Knippenberg WF (1974/75) Philipps Techn Rdsch 34:298

31.Weiss J (1985) Handbuch der Ionenchromatographie. Wiley-VCH, Weinheim

32.Bogenschütz G, Loyall U, Schäfer J (1990) LaborPraxis, March, p 120

33.Franklin KR, Lowe BM (1988) Thermochim Acta 127:319

34.Minchev Chr, Valtchev V, Mintova S (1995) Thermochim Acta 264:59

35.Bedard RL, Bowes CL, Coombs N, Holmes AJ, Jiang T, Kirkby SJ, Macdonald PM, Malek AM, Ozin GA, Petrov S, Plavac N, Ramik RA, Steele MR, Young D (1993) J Am Chem Soc 115:2300

36.Kosslick H, Tuan VA, Fricke R, Jedamzik J, Lanh HD (1991) J Therm Anal 37:2631

37.McClennen WH, Buchanan RM, Arnold NS, Dworzanski JP, Meuzelaar LC (1993) Anal Chem 65:2819

38.Kürschner U, Jerschkewitz H-G, Schreier E, Völter J (1990) Appl Catal 57:167

39.Lischke G, Eckelt R, Jerschkewitz H-G, Parlitz B, Schreier E, Storek W, Zibrowius B (1991) J Catal 132:229

40.Kosslick H, Richter M, Tuan VA, Fricke R, Storek W (1992) J Chem Soc Faraday Trans 88:2421

41.Bhatia S, Beltrami DD (1990) Catal Today 3:309

42.Lohse U, Parlitz B, Patzelova V (1989) J Phys Chem 93:3677

43.Karge HG, Dondur V, Weitkamp J (1991) J Phys Chem 95:283

44.Szynkowska MI, Lesniewska E, Paryjczak T (2003) Pol J Chem 77:657

45.Berndt H, Kosslick H, Martin A, Lücke B (1994) Microporous Mater 2:197

46.Miessner H, Kosslick H, Lohse U, Parlitz B, Tuan VA (1993) J Phys Chem 97:9741

47.Kosslick H, Berndt H, Hoang DL, Martin A, Miessner H, Tuan VA, Jänchen J (1994) J Chem Soc Faraday Trans 90:2837

48.Baranski A, Dal T, Galuszka J (1979) Bull Acad Polon Sci, Ser Sci Chim 27:363

49.Lok BM, Marcus BK, Angell CL (1986) Zeolites 6:185

50.Hunger B, Heuchel M, Clark LA, Snurr RQ (2002) J Phys Chem B 106:3882

51.Li G, Kan QB, Wu TH et al. (2003) Stud Surf Sci Catal 146:149

52.Wallau M, Melo RAA, Urquieta-Gonzales EA (2003) Stud Surf Sci Catal 146:745

53.Kofke TJG, Kokotailo GT, Gorte RJ, Farneth WE (1989) J Catal 115:265

54.Kofke TJG, Kokotailo GT, Gorte RJ (1989) J Catal 116:252

55.Kofke TJG, Gorte RJ, Kokotailo GT (1989) Appl Catal 54:177

56.Kosslick H, Tuan VA, Fricke R, Peuker Ch, Pilz W, Storek W (1993) J Phys Chem 97:5678

57.Depmeier W (1984) Acta Crystallogr B40:185

58.Flanigen EM, Khatami H, Szymanski HA (1971) Adv Chem Ser 10:201

59.Flanigen EM (1976) In: Rabo JA (ed) Zeolite Chemistry and Catalysis. ACS Monograph 171, Washington, DC, p 80

60.Fichtner-Schmittler H, Lohse U, Miessner H, Manek HE (1990) Z Phys Chem, Leipzig, 271:69

61.Sohn JR, De Canio SJ, Lunsford JH, O’Donnell DJ (1986) Zeolites 6:225

62.Breck DW, Flanigen EM (1968) Molecular sieves. Soc Chem Ind London, p 47

63.Breck DW (1974) Zeolite molecular sieves. Wiley, New York, p 104

64.Millini R, Massara EP, Perego G, Bellussi G (1992) J Catal 137:497

66	H. Kosslick · R. Fricke

65.Grohmann I, Pilz W, Walther G, Kosslick H, Tuan VA (1994) Surf Interface Anal 22:403

66.Kosslick H, Tuan VA, Fricke R, Peuker Ch (1992) Ber Bunsenges Phys Chem 96:1761

67.Morell H, Angermund K, Lewis AR, Brouwer DH, Fyfe CA, Gies H (2002) Chem Mater 14:2192

68.Engelhardt G, Michel D (1987) High-resolution solid-state NMR of silicates and zeolites. Wiley, Chichester

69.Lippmaa E, Mägi M, Samoson A, Tarmak M, Engelhardt G (1981) J Am Chem Soc 103:4992

70.Engelhardt G, Radeglia R (1984) Chem Phys Lett 108:271

71.Klinowski J (1991) Chem Rev 91:1459

72.Griffiths JM, Griffin RG (1993) Analysis Chimica Acta 283:1081

73.Simon A, Gougeon RD, Paillaud J-L, Valtchev V, Kessler H (2001) Phys Chem Chem Phys 3:867

74.Newsam JM, Jacobson AJ, Vaughan DEW (1986) J Phys Chem 90:6858

75.Thomas JM, Klinowski J, Fyfe CA, Anderson MW (1983) ACS Symp Ser, Washington, DC, 218:159

76.Kosslick H, Tuan VA, Parlitz B, Fricke R, Peuker Ch, Storek W (1993) J Chem Soc Faraday Trans 89:1131

77.Bradley SM, Howe RF, Kydd RA (1993) Magn Reson Chem 31:883

78.Gabelica Z, Mayanez C, Monque R, Galiasso R, Giannetto G (1992) Synthesis of microporous materials. In: Occelli ML, Robson HE (eds) Molecular sieves, vol 1. Van Nostrand Reinhold, New York, p 190

79.Kosslick H, Tuan VA, Walther G, Miessner H, Fricke R, Storek W (1996) In: Occelli ML, Kessler H (eds) Synthesis of microporous materials: zeolites, clays, and nanostructures, Chap. 17. Marcel Dekker, New York

80.Behrens P, Kosslick H, Tuan VA, Fröba M, Neissendorfer F (1995) Micropor Mater 3:433

81.Wang YX, Song JQ, Gies H (2003) Solid State Sci 5:1421

82.Vidal-Moya JA, Blasco T, Rey F, Corma A, Puche M (2003) Chem Mater 15:3961

83.Oumi Y, Mizuno R, Azuma K et al. (2001) Micropor Mesopor Mat 49:103

84.Muller M, Harvey G, Prins R (2000) Micropor Mesopor Mat 34:135

85.Grobet PE, Martens JA, Balakrishnan I, Mertens M, Jacobs PA (1989) Appl Catal 56:L21

86.Müller D, Jahn E, Ladwig G, Haubenreisser U (1984) Chem Phys Lett 109:332

87.Prasad S, Haw JF (1996) Chem Mater 8:861

88.Monque R, Parisi A, Gonzalez S, Gianetto G (1992) Zeolites 12:806

89.Darque-Ceretti E, Aucouturier M (1995) Analysis 23:49

90.Moretti G (1994) Zeolites 14:469

91.Hercules DM (1996) Fresenius J Anal Chem 355:209

92.Gross Th, Lohse U, Engelhardt G, Richter KH, Patzelová V (1984) Zeolites 4:25

93.Mohamed MH, Abdillah MM, Abbas NM, Siddiqui AB (1995) Appl Surf Sci 90:409

94.Grünert W, Muhler M, Schröder KP, Sauer J, Schlögl R (1994) J Phys Chem 98:10920

95.Kaushik VK, Bhat SGT, Corbin DR (1993) Zeolites 13:671

96.Fiermans L, De Gryse R, De Doncker G et al. (2000) J Catal 193:108

97.Garcia-Sanchez M, Magusin PCMM, Hensen EJM et al. (2003) J Catal 219:352

98.Zheng J, Schmauke T, Roduner E et al. (2001) J Mol Catal A-Chem 171:181