Proceedings of The Sixth International

ZEOLITE Conference

CONTENTS

DON BRECK MEMORIAL SYMPOSIUM

1. The Word and Work of Don Breck. 3 Ε. M. Flanigen

2. Z e o l i t e Synthesis: Some Chemical Aspects. 17 R. M. Barrer.

3. A d s o r p t i o n i n A, X and Y Z e o l i t e s : T h i r t y Years o f Science and 31 Technology. D. M. Ruthven.

4. Speculations on Molecular Sieve and I o n i z a t i o n E f f e c t s i n Y 41 Zeol i t e . J. A. Rabo.

5. Considerations on Some E f f e c t s of Cation Location i n t h e 49 Faujasite-Type Z e o l i t e s . J. B. Uytterhoeven.

6. New V i s t a s i n Cry s t a l S t r u c t u r e s of Molecular Sieves and Some 56 Personal Reminiscences of Donald W. Breck. J. V. Smith.

7. Z e o l i t e E x p l o r a t i o n : The E a r l y Days. 68 F. A. Mumpton.

8. Z e o l i t e Chemistry V - S u b s t i t u t i o n f o r Aluminum i n Z e o l i t e s v i a 87 Reaction w i t h Aqueous Ammonium F l u o r o s i 1 i c a t e . G. W. Skeels and D. W. Breck.

9. Synthesis o f A1P0* Molecular Sieves. 97 S. T. Wilson, Β. M. Lok, C. A. Messina and Ε. M. Flani g e n .

10. Studies on t h e P r e d i c t i o n o f Multicomponent Ion-Exchange 110 E q u i l i b r i a I n v o l v i n g Natural and Sy n t h e t i c Z e o l i t e s . R. P. Townsend, P. F l e t c h e r and M. L o i z i d o u .

11. D i f f u s i o n a l T r a n s i t i o n i n Z e o l i t e NaX: 122 1. Single C r y s t a l Gas Permeation Studies. D. L. Wernick and E. J. Osterhuber.

12. The Cation D i s t r i b u t i o n i n F a u j a s i t e s . 131 M. J. Sanders and C. R. A. Catlow.

13. S t a t i s t i c a l and To p o l o g i c a l Approaches t o Mo d e l l i n g Z e o l i t e 141 A c i d i t y , A c t i v i t y and S t a b i l i t y . W. A. Wächter.

14. Agglomeration Mechanism During t h e Preparation o f N i ( 0 ) 151 and Fe(0) Z e o l i t e s . F. Schmidt, Th. Bein, IJ. O h l e r i c h and P. A. Jacobs.

Discussion 161

i

ADSORPTION - DIFFUSION

1. Experimental and T h e o r e t i c a l Analysis of th e Adsorption 172 o f Methane i n A Z e o l i t e s : I n f r a r e d and Neutron Spectroscopy Studies. E. Cohen De Lara and R. Kahn.

2. NMR D i f f u s i o n Studies i n Z e o l i t e s . 184 J. Karger, Η. P f e i f e r and W. Heink.

3. I n v e s t i g a t i o n s o f Motion, I n t e r a c t i o n and Ox i d a t i o n o f 201 Carbon Monoxide i n A l k a l i and A l k a l i n e Earth Ιοη-Exchanged..Zeolite A. H. Bose, H. F o r s t e r , W. Frede and M. Schumann.

4. Gas Chromatographic S o r p t i o n Studies o f Hydrocarbons i n 210 P e n t a s i l s w i t h D i f f e r e n t Si/AI R a t i o s . H. Lechert and W. Schweitzer.

5. D i r e c t Measurement of D i f f u s i v i t y f o r Butane Across 217 a Single Large S i l i c a l i t e C r y s t a l . A. Paravar and D. T. Hayhurst.

6. Experimental and T h e o r e t i c a l I n v e s t i g a t i o n s o f t h e 225 Adsorption of n - P a r a f f i n s , η-Olefins and Aromatics on Si 1 i c a l i t e . H. Stach, Η. Thamm, J. Janchem, K. F i e d l e r and W. Schirmer.

7. D i f f u s i o n a l T r a n s i t i o n i n Z e o l i t e NaX: 2. P o l y c r y s t a l l i n e 232 G r a v i m e t r i c S o r p t i o n S t u d i e s . 0. H. Tezel, D. M. Ruthven and D. L. Wernick.

8. D i f f u s i o n o f Benzene i n NaX Z e o l i t e . 242 M. Bulow, W. Mietk, P. Struve, W. Schirmer and M. K o c i r i k and J. Karger

9 The E f f e c t o f Cation on Ads o r p t i o n and D i f f u s i o n i n ZSM-5. 251 P. Wu and Υ. H. Ma.

10. Temperature Programmed Water Desorption o f Z e o l i t e s . 2. 261 A l k a l i Metal and A l k a l i n e Earth C a t i o n i c Forms o f Z e o l i t e X. W. A. McCann and L. V. C. Rees.

11. Adsorption o f Co Aromatics on NaY Z e o l i t e . 268 M. Goddard and D. M. Ruthven.

12. Z e o l i t e RHO. Part I I I . S o r p t i o n o f I n o r g a n i c Gases and 276 Hydrocarbons. R. M. B a r r e r and M. A. Rosemblat.

13. The Use o f I s o p i e s t i c Vapour Pressure Measurements 288 t o Study S a l t I m b i b i t i o n by Z e o l i t e s . S. G. Fegan and Β. M. Lowe.

Discus s i o n 298

ii

GENERAL ACID CATALYSIS

1. Dehydration of Cyclohexanol as a Test Reaction f o r 308 Z e o l i t e A c i d i t y . .. H. G. Karge, Η. Kosters, and Y. Wada.

2. R e l a t i o n Between Acidi c P r o p e r t i e s and C a t a l y t i c 316 Performance For Gasoline Synthesis from Methanol Over ZSM-5 Class Z e o l i t e s . T. I n u i , H. Matsuda, and Y. Takegami.

3. Factors I n f l u e n c i n g the S e l e c t i v i t y i n t h e E t h y l a t i o n 325 of Toluene Over ZSM-5 Z e o l i t e s . Κ. H. Chandavar, S. G. Hegde S. B. K u l k a r n i , P. Ratnassamy, G. C h i t l a n g i a , A. Singh and Α. V. Deo.

4. I s o m e r i z a t i o n - D i s p r o p o r t i o n a t i o n of M-Xylene Over Dealuminated 331 Mordenites. N. Giordano, P. V i t a r e l l i , S. Ca v a l l a r o , R. Ottana and R. Lembo.

5. Modified Mordenites f o r C a t a l y t i c Conversion o f Methanol. 337 J. Bandiera, C. Hamon, and C. Naccache.

Discussion 345

METAL CATALYSIS

1. Physical and C a t a l y t i c P r o p e r t i e s of Noble Metals i n Z e o l i t e s . 352 P. G a l l e z o t .

2. S t r u c t u r a l and C a t a l y t i c P r o p e r t i e s of Ze o l i t e - S u p p o r t e d Cu-Pt, 368 Cu-Ir, Cu-Rh, and Cu-Ru B i m e t a l l i c C l u s t e r s . I . Tebassi, A. M. Satarum, A. Ghorbel, M. Dufaux, Y. Ben T a a r i t .

3. Nickel S u l f i d e s i n X-Type Z e o l i t e . 377 D. Cornet, A. Ezzamarty, and J. F. Hemidy.

4. Mechanisms of Reduction and Metal P a r t i c l e Growth i n N i 2 + , P d 2 + , 387 and P t ^ + Exchanged F a u j a s i t e s . D. Exner, Ν. I . Jaeger, R. Nowak, G. S c h u l z - E k l o f f and P. Ryder.

5. C h a r a c t e r i z a t i o n and R e a c t i v i t y o f Nickel Loaded Mordenite 396 Towards the C0+N0 Reaction. E. Garbowski, M. Primet and Μ. V. Mathieu.

6. P r e p a r a t i o n and C h a r a c t e r i z a t i o n o f Molybdenum Z e o l i t e s . 405 Mark B. Ward and J. H. Lunsford.

7. I n t r i n s i c a l l y Corrected XP Spectra o f Z e o l i t e s at 417 Elevated Temperatures: XPS Study of Ni Containing A, X, Y, and ZSM-5 Z e o l i t e s . F. Steinbach, J. Schutte, R. K r a l l , Chr. Minchev, V. Kanazirev, and V. Penchev

8. n-Alkane Transformation, A c t i v i t y and S t a b i l i t y o f 427 Platinum-Zeol i t e s . G. Perot, P. H i l a i r e a u and M. Guisnet.

iii

9. S y n t h e s i s , C h a r a c t e r i z a t i o n and C a t a l y t i c P r o p e r t i e s 435 of Rhodium Carbonyl Cluster Compounds W i t h i n Y Z e o l i t e Cages. F. L e f e b v r e , P. G e l i n , C. Naccache and Y. Ben T a a r i t .

10. H y d r o s u l f u r i z a t i o n of the C=C Bond on Me 2 + - Z e o l i t e s . 444 D. K a l l o , G. Onyestyak and J. Papp, J r .

Discussion 454

PENTASIL CATALYSIS

1. Acid C a t a l y s i s With Medium Pore Z e o l i t e s . 466 W. 0. Haag.

2. C o r r e l a t i o n Between t h e S o r p t i v e and C a t a l y t i c P r o p e r t i e s 479 of a Series o f P e n t a s i l Z e o l i t e s . I . D. H a r r i s o n , H. F. Leach and D. A. Whan.

3. The Reaction Mechanism o f th e F i r s t C-C Bond Formation 489 i n t h e Methanol t o Gasoline Process. J. H. C. van Hooff, J. P. van den Berg, J. P. Wolthuizen and A. Volmer.

4. Shape S e l e c t i v i t y and A c i d i t y o f ZSM-5 and ZSM-11 497 Type Z e o l i t e s . J. C. Vedrine, A. Auroux, G. Coudurier, P. Engelhard, J. P. Gallez and G. Szabo.

5. Shape S e l e c t i v i t y o f Pentasi1-Type Z e o l i t e s i n t h e 508 B i f u n c t i o n a l Conversion of Ethyl benzene and Propyl benzene. R. C. Sosa, M. N i t t a , Η. K. Beyer and P. A. Jacobs.

6. D i f f u s i o n and C a t a l y t i c Reaction o f 2, 2-Dimethylbutane i n 517 ZSM-5 Z e o l i t e . M.F.M. Post, J. Van Anstel and H.W. Kouwenhoven

7. Sorption and C a t a l y t i c Reaction i n D i f f e r e n t Preparations 528 of Z e o l i t e HZSM-5. J. H e r r i n g and L. Ri e k e r t and L. Marosi

8. Ammoxidation o f Toluene and Related Aromatics over Z e o l i t e 536 ZSM-5. A New A p p l i c a t i o n of Z e o l i t e ZSM-5. J. C. Oudejans, F. J. van der Gaag and H. van Bekkum

9. A I u m i n o s i 1 i c a t e and B o r o s i l i c a t e Z e o l i t e s and The i r Use 545 i n t h e Conversion o f Methanol t o O l e f i n s . W. H o l d e r i c h , H. Eichorn R. Lehnert L. Marosi, W. Mross, R. Reinke, W. Ruppel and H. Schlimper

Discussion 556

iv

GEOLOGY AND MINERALOGY

1.. Mineralogy of Natural Z e o l i t e s : Present Status. 570 R. R i n a l d i .

2.. Z e o l i t e Occurrences i n T r i a s s i c - J u r a s s i c Sedimentary Rocks, 584 Baja C a l i f o r n i a Sur, Mexico. D. A. Barnes, J. R. Boles and J. Hickey.

3J. Diagenetic Z e o l i t e Zone Modified by Recent High Heat Flow 595 i n Miti-Kuromatsunai Hole, Southwest Hokkaido, Japan. A. I i j i m a , K. Aoyagi and T. Kazama.

4.. Zonal D i s t r i b u t i o n of Z e o l i t e s and Au t h i g e n i c P l a g i o c l a s e . 604 M. Utada and J. D. Vine.

5J . Thermodynamic Studies of Z e o l i t e s . Analcime S o l i d S o l u t i o n s . 616 W. S. Wise.

Discussion 623

ION EXCHANGE

Π . Binary and Ternary Cation Exchange i n Z e o l i t e A. 626 L. V. C. Rees.

22. Thermodynamic S t a b i l i t y o f the Si 1 v e r - P y r i d i n e Complex i n 641 Z e o l i t e Y. E. Rasquin, A. Maes and A. Cremers.

33. Pore Size Engineering by Modifying t h e Z e o l i t i c Pore 651 system o f Mordenite. G. Peeters, A. Thys, E. F. Vansant and P. DeBievre.

44. Evaluation of Z e o l i t e Mixtures f o r Decontamination of 660 H i g h - A c t i v i t y - L e v e l Water i n t h e Submerged Demineral i z e r System (SDS) Flowsheet at the Three M i l e I s l a n d Nuclear Power S t a t i o n , U n i t 2. L. J. King, D. 0. Campbell, E. D. C o l l i n s , J. B. Knauer and R. M. Wallace.

Discussion 669

NEW TECHNIQUES

11. Surface P r o p e r t i e s of O f f r e t i t e and ZSM-34 Z e o l i t e s . 674 M. L. O c c e l l i , R. A. Innes, Τ. M. Apple and B. C. G e r s t e i n .

22. Study of Cation E f f e c t s i n LiNaA Z e o l i t e s by S i l i c o n - 2 9 684 and Lithium-7 NMR. Μ. Τ. Melchior, D. Ε. W. Vaughan, A. J. Jacobson and C. F. P i c t r o s k i .

ν

3. A High R e s o l u t i o n S o l i d S t a t e 1 3C NMR I n v e s t i g a t i o n 694 of Occluded Templates i n Pentasi1-Type Z e o l i t e s ; Some 2 9 S i S o l i d S t a t e NMR C h a r a c t e r i s t i c s of ZSM-5 G. Boxhoron, R. A. van Santen, W. A. van Erp, G. R. Hays, N. C. M. Alma, R. Huis and A. D. H. Clague.

4. The A p p l i c a t i o n of Fast Atom Bombardment Mass Spectrometry 704 (FABMS) t o t h e Study o f Z e o l i t e s . A. G. Ashton, J. Dwyer, I . S. E l l i o t t , F. R. F i t c h , G. Qin, M. Greenwood and J. Speakman.

5. A Non-Empirical Molecular O r b i t a l Study of the S i t i n g and 717 P a i r i n g of Aluminum i n Mördern"te.

E. G. Derouane and J. G. F r i p i a t .

D i s cussion 727

STRUCTURE 1. S t r u c t u r a l Chemistry of Z e o l i t e s : t h e I n t e r f a c e Between 734

S t r u c t u r e and A c t i v i t y . W. J. M o r t i e r .

2. Recent Results i n S t r u c t u r a l Studies o f Z e o l i t e s 747 and Z e o l i t e - L i k e M a t e r i a l s . S. M e r l i n o .

3. Z e o l i t e s : The Future. 760 G. T. K o k o t a i l o .

4. I n f l u e n c e o f Th a l l i u m Ion on Cupric Ion Locations i n 774 Cu-TlX Z e o l i t e Studied by El e c t r o n Spin Resonance and E l e c t r o n Spin Echo Modulation Spectrometry. M. Narayana and L. Kevan.

5. Study of the Dealuraination and Realumination o f ZSM-5 783 Type Z e o l i t e s by Si and Al High Resolution Magic Angle Spinning NMR Spectroscopy. P. A. Jacobs, M. T i e l e n , J. B. Nagy, G. Debras, E. G. Derouane, and Z. Gabelica.

6. High R e s o l u t i o n E l e c t r o n Microscopic and O p t i c a l 793 D i f f r a c t o m e t r i c Studies of Z e o l i t e s . G. R. M i l l w a r d , J. M. Thomas, S. Ramdas and Μ. T. Barlow.

7. Three Dimensional Mapping of the Zoned Aluminum D i s t r i b u t i o n 803 i n ZSM-5. R. von Ballmoos, R. Gubser and W. M. Meier.

8. The E f f e c t of Dehydration upon the Crystal S t r u c t u r e 812 of Z e o l i t e RHO. L. B. McCusker and C. Baerlocher.

9. The P o s s i b i l i t i e s and L i m i t a t i o n s of the Powder 823 Method i n Z e o l i t e S t r u c t u r e A n a l y s i s . The Refinement o f ZSM-5. C. Baerlocher.

vi

10. Topological Changes i n Dehydrated Z e o l i t e s : Breaking of 834 T-O-T Bridges. A. A l b e r t i and G. V e z z a l i n i .

1 1 . Neutron and X-ray Refinements o f S c o l e c i t e . 842 J. V. Smith, J. J. P l u t h , G. A r t i o l i and F. K. Ross.

12. Framework Topology and Systematic D e r i v a t i o n of 851 Z e o l i t e S t r u c t u r e s .

M. Sato.

Discussion 858

SYNTHESIS 1. Isomorphous Replacements i n Z e o l i t e s and Other T e c t o s i 1 i c a t e s . 870

R. M. Barrer.

2. Determination o f Boundary Conditions of C r y s t a l l i z a t i o n of 887 ZSM-5 - ZSM-11 i n One "Al-Free" System. L. Y. Hou and L. B. Sand.

3. The Synthesis and C h a r a c t e r i z a t i o n of Z e o l i t e EU-1. 894 J. L. Casciand, Τ. V. Whittam and Β. M. Lowe.

4. C r y s t a l l i z a t i o n of Z e o l i t e Y from S o l u t i o n Phase. 905 S. Ueda, N. Kageyama and M. Koizumi.

5. On the Use of M u l t i n u c l e a r High R e s o l u t i o n S o l i d State NMR 914 Spectroscopy t o Characterize I n t e r m e d i a t e Phases Formed During ZSM-5 Z e o l i t e Synthesis. Z. Gabelica, J. B. Nagy, G. Debras and E. G. Derouane.

6. d / A l and 6 : 7 S i NMR Studies of Aluminosi 1 i c a t e Species i n S o l u t i o n . 925 L. S. Dent Glasser and G. Harvey.

Discussion 934

ZEOLITE TECHNOLOGY

1. The Use of Sodium Type A Z e o l i t e i n Laundry Detergents. 940 R. A. Llenado.

2. Self-Bonded P h i l l i p s i t e P e l l e t s From T r a c h y t i c Products. 957 R. A i e l l o , C. C o l e l l a , A. Nastro, and R. Sersale.

3. E f f e c t s of S u r f a c t a n t S t r u c t u r e on Detergency Performance 966 of Laundry Powders Formulated w i t h Z e o l i t e 4A as B u i l d e r . L. Kravetz.

4. Use of Z e o l i t e NaA f o r Removal o f Trace Heavy Metals from 975 Metal P l a t i n g Wastewater. E. P. Hertzenberg.

Discussion 984

vii

GEOLOGY AND MINERALOGY AD HOC MEETING 985

POSTER PAPERS 986

DEPOSITORY OF SUPPLEMENTARY MATERIAL 990

AUTHOR INDEX 991

SUBJECT INDEX 995

viii

AGGLOMERATION MECHANISM DURING THE PREPARATION OF Ni(O) AND Fe(O) ZEOLITES

F. .Schmidt, Th. Bein, U. O h l e r i c h and P. A. Jacobs*

I n s t i t u t f u r P h y s i k a l i s c h e Chemie der Universität Hamburg, Laufgraben 24, 0-2000 Hamburg 13 (F.R.G.)

* Centrum voor Oppervlaktescheikünde en Col 1 o i d a l e Scheikunde, K a t h o l i e k e U n i v e r s i t e i t Leuven, De Croylaan 42, B-3030 Heverlee (Belgium)

M a g n e t i z a t i o n measurements have been used t o study the reduc­t i o n process of N i - z e o l i t e s and the thermal decomposition of i r o n pentacarbonyl adsorbed on NaY z e o l i t e s . The Ni(0 ) p a r t i ­c l e s i z e d i s t r i b u t i o n i n H2»reduced NiNaA, Ni NaX, Ni NaY and NiNaM i s b i d i s p e r s e . The amount and the volume of p a r t i c l e s exceeding the cage dimensions increases i n the sequence Μ,Υ,Χ,Α z e o l i t e s . P a r t i c l e f u s i o n i s found t o be the r a t e d etermining s t e p . With decomposition of Fe(C0) 5/NaY adducts, up t o 97 wt.% of the i r o n p a r t i c l e s produced are smaller than 1.3 nm. F l u i d -ized sample bed, i n e r t gas atmosphere and f a s t h e ating up t o 440 Κ are e s s e n t i a l t o reach mononodal d i s p e r s i o n .

INTRODUCTION

T r a n s i t i o n metal c o n t a i n i n g z e o l i t e s are very promising c a t a l y s t s f o r petrochemical r e a c t i o n s ( 1 ) . The metal phase i n t r o d u c e d i n t o the z e o l i t e pore system (2) i s s u b j e c t t o p a r t i c l e growth or ' s i n t e r i n g ' . Since t o t a l a c t i v e metal s u r f a c e area i s i n f l u e n c e d c o n s i d e r a b l y by t h i s e f f e c t , knowledge i s d e s i r a b l e about agglomeration mechanisms of metal species supported on z e o l i t e s .

In g e n e r a l , the fo r m a t i o n of an i n i t i a l metal d i s p e r s i o n d u r i n g p r e p a r a t i o n must be d i s t i n g u i s h e d from the p a r t i c l e growth under c a t a l y t i c c o n d i t i o n s . Because of the complexity of the l a t t e r process, the present study i s concerned w i t h t h e r m a l l y a c t i v a t e d agglomeration phenomena i n the absence of r e a c t a n t s .

The i n f l u e n c e of the p r e p a r a t i o n method w i l l be t r e a t e d by means of two completely d i f f e r e n t ways of i n t r o d u c i n g the metal:

- n i c k e l ( 0 ) z e o l i t e i s prepared by ion exchange, dehydration and subsequent r e d u c t i o n by molecular hydrogen,

- i r o n ( 0 ) z e o l i t e i s obtained by abso r p t i o n and thermal decomposition of i r o n p e n t a c a r b o n y l .

The l a t t e r p r e p a r a t i o n method has been chosen i n order t o avoid p o s s i b l e contamination w i t h t h e s t r o n g reducing agents r e q u i r e d t o reduce i r o n ( I I ) z e o l i t e s , e.g. a l k a l i metal vapour (3) or atomic hydrogen.

EXPERIMENTAL

1. M a t e r i a l s

The s t a r t i n g m a t e r i a l s f o r the Ni samples were: Linde A z e o l i t e ( S i / A l = 1) and NaY ( S i / A l = 2 . 4 6 ) , NaX (Si/Al=1.18) and Na-mordenite (Si/Al=5.41) from Norton, which i s r e f e r r e d t o as NaM. The s t o i c h t o m e t r i c a l l y N i ( I I ) exchanged samples were dehydrated i n a stream of argon (9.5 cm 3 min ) by he a t i n g up t o 823 Κ ( h e a t i n g

151

T a b l e I Decomposition c o n d i t i o n s f o r the i r o n z e o l i t e s

Sample a

P r e s s u r e / mbar

Heating r a t e / K-min" 1

max. temp./ Κ

O u t g a s s i n g / hours

FeYOSB 1 0 - 4 0.2 373 14 FeY480FB He, 480 15 445 5 FeY17FB He, 17 15 420 5 FeYOFB ΙΟ" 2 15 410 5

a: SB: f i x e d s h a l l o w bed; FB: f l u i d i z e d bed c o n d i t i o n s -4

b: performed a t a temperature of 373 Κ and a p r e s s u r e of 10 mbar

Table I I Approximate PSD o f N i (0) i n v a r i o u s z e o l i t e s as

a f u n c t i o n o f t h e t e m p e r a t u r e o f r e d u c t i o n ( T R )

Sample

NiNaM 573 723 773 823

wt % o f p a r t i c l e s i n d i f f e r e n t s i z e f r a c t i o n s (V ' /nm ) :

<0.5

1

72.6 71 .7 74.9 71 .7

0.5

5.8 5.5 1 .8 3.7

1 .0

Ο 1 .0 1 .4 2.9

2.0 - 8.0

21 .6 21 .8 21 .9 21 .7

NiNaY 623 673 723 773

35.1 37. 3 37.0 39.8

17.0 13.7 1 4.0 14.3

22. 5 23.7 18.0 16.7

25.4 25.3 31 .0 29.2

NiNaX 623 673 723 773

823

57.6 34.7 36.8 21 .9

3.2

0 0 0

4.5

26.4

32.2 28.7 22 .0 25.9

O. 3

10.2 36.6 41 .2 47.7

70.1

152

r a t e : 11 K/min), m a i n t a i n i n g the samples at t h a t temperature f o r 4 hours and then c o o l i n g down t o room temperature d u r i n g 90 minutes. A l l samples were reduced i n f l o w i n g hydrogen (10 cm m i n " 1 ) f o r two hours at elevated temperatures between 573 and 823 K. The f i n a l Ni weight content was: NiNaA = 7.8 wt % Ni; NiNaX = 7.3 wt % N i ; NiNaY = 5.5 wt % Ni and NiNaM = 5.9 wt % N i .

For the p r e p a r a t i o n of i r o n z e o l i t e s , s y n t h e t i c NaY from Strem Chemicals ( S i / A l = 2 . 4 6 ) was used. A l l treatments were performed i n a greaseless r e a c t i o n system w j t h a heatable quartz bulb of 5mm diameter, connected t o a b u f f e r volume o f 1 dm"3, a Fe(C0) 5 r e s e r v o i r and a high vacuum l i n e . The samples completely dehydrated were loaded at 293 Κ w i t h p r e d i s t i l l e d dry Fe(CO)^ (Ventron) at a p a r t i a l pressure of 8 mbar f o r 5 hours i n the dark. Decopposition of the sorbed ca r b o n y l was performed a f t e r evacuation f o r 2 hours at 10 mbar i n s t a t i c s h a l l o w bed (SB) or i n f l u i d i z e d bed c o n d i t i o n s (FB). The f l u i d i z e d bed was generated by h o r i z o n t a l v i b r a t i o n at 50 Hz w i t h an amplitude of 2 mm. Conditions o f decomposition are l i s t e d i n Table I .

2. Methods

A Faraday balance was used i n the temperature range from 6 - 300 Κ and f i e l d s up t o 1 T. Some samples have been measured using a Foner magnetometer i n t h e temperature range from 2.2 Κ t o 200 Κ and f i e l d s up t o 8 T. A f t e r p r e p a r a t i o n , a l l sample bulbs were sealed o f f under high vacuum. These bulbs were d i r e c t l y used f o r measurements of the magn e t i z a t i o n . E l e c t r o n microscopy was performed w i t h an a n a l y t i c a l TEM-SCAN 100S from J e o l . The Ni-samples were embedded i n Spurr ( a i r f r e e ) and cut w i t h an u l t r a m i c r o t o m e . Deep frozen Fe-samples were c a r e f u l l y contacted w i t h a i r , suspended i n EtOH, placed on a g r i d and d r i e d .

RESULTS AND DISCUSSION

1. E v a l u a t i o n of the Magnetic Measurements

The m e t a l l i c p a r t i c l e s i z e d i s t r i b u t i o n , PSD, was determined by an a l y z i n g t h e mag n e t i z a t i o n isotherms. In metal z e o l i t e systems, t h e measured magnetization can be approximated by

Μ v. Β Μ v 9B Mv.B

I - "ι L < — k ¥ > + > · · · · + i i L <-TT->

w i t h L ( x) = coth (x - 1/x) and χ = M sv^B/(kT). σ i s the s p e c i f i c m a g n e t i z a t i o n at the f i e l d Β and the temperature Τ,σ^ i s the s p e c i f i c s a t u r a t i o n m a g n e t i z a t i o n a t the temperature T, v^ i s the volume of the p a r t i c l e i , M S(T) i s the spontaneous magnetization at the temperature T.

In cases of a b i d i s p e r s e or m u l t i d i s p e r s e PSD, t h e s u p e r p o s i t i o n o f the s i n g l e Langevin isotherms cannot be ob t a i n e d . This i s the normal s i t u a t i o n i n metal z e o l i t e systems. Here, the a n a l y s i s of the low temperature/high f i e l d isotherm i s more s e n s i t i v e t o the smal l e s t p a r t i c l e s and the high temperature/low f i e l d isotherm i s s e n s i t i v e t o the l a r g e r p a r t i c l e s ( 4 ) . U s u a l l y , the low f i e l d volume v L p and the high f i e l d volume v H p are taken from the m a g n e t i z a t i o n i s o t h e r m at one temperature ( 5 ) . The exact expression w i l l be low argument volume V j _ ^ and high argument volume V u ß depending on whether χ = (m $vB)/kT i s much smaller than u n i t y or much l a r g e r tnan 4 (magnetic s a t u r a t i o n ) . I f a l l p a r t i c l e f r a c t i o n s -even the smallest ones - are m a g n e t i c a l l y s a t u r a t e d (x^ > 4 ) , the c a l c u l a t e d mean p a r t i c l e volume V ^ A i s independent of the form of the ac t u a l PSD - f u n c t i o n . Depending on the PSD present, s u i t a b l e temperatures must be choosen f o r t h e

153

a n a l y s i s of the magnetization isotherms i n order t o i n c l u d e al 1 p a r t i c l e s . In summary, the a n a l y s i s of the magnetization isotherm at low temperatures gives the PSD and hence v H A and at high temperatures the PSD and v L A .

At temperatures as low as 6 Κ and f i e l d s s maller than 1 Τ the m a g n e t i z a t i o n isotherm σ(Β) i s l i n e a r f o r i o n s , charged c l u s t e r s , and p a r t i c l e s s m a l l e r than about 0.5 nm as w e l l . As a consequence, these t h r e e species cannot be d i s t i n g u i s h e d . This i s important f o r i n c o m p l e t e l y reduced samples or f o r e l e c t r o n d e f i c i e n t c l u s t e r s . Therefore i n such samples these t h r e e f r a c t i o n s are regarded as one s i n g l e f r a c t i o n , r e f e r r e d t o as PS (paramagnetic s p e c i e s ) .

2. Formation of Ni P a r t i c l e s During Reduction w i t h H?

The PSD of Ni (0) i n A, X, Y, and Μ z e o l i t e s obtained upon r e d u c t i o n at v a r i o u s temperatures are given i n Table I I . For a l l samples a l a r g e amount of paramagnetic species i s found (column 1 ) , i n c r e a s i n g from A z e o l i t e t o mordenite.

The f r a c t i o n of Ni p a r t i c l e s s maller than the dimensions of the z e o l i t e cages ranges from 60% t o 90% w i t h the exception of NiNaA. The amount of the l a r g e r p a r t i c l e s at high temperatures of r e d u c t i o n increases i n the sequence Μ < Υ < X < A (see column 4 ) .

Metal p a r t i c l e growth can occur d u r i n g thermal treatment by two d i s t i n c t mechanisms. The model developed by Pulvermacher and Ruckenstein (5,6) describes the s i n t e r i n g process by the m i g r a t i o n of metal c r y s t a l l i t e s over the support surface f o l l o w e d by coalescence w i t h other metal c r y s t a l l i t e s upon c o l l o s i o n ( c r y s t a l l i t e m i g r a t i o n - CM model).

Mass t r a n s f e r i s proposed t o proceed by two d i f f e r e n t mechanisms: Large p a r t i c l e s migrate by a momentary accumulation of metal atoms on one side r e s u l t i n g i n a movement i n the corresponding d i r e c t i o n ( 7 ) . In c o n t r a s t , very small c l u s t e r s can m i g r a t e as an unperturbed u n i t .

According t o the atomic m i g r a t i o n model (AM model) proposed by Flynn and Wanke ( 8 ) , s i n g l e metal atoms are t r a n s f e r r e d i n d i v i d u a l l y from one p a r t i c l e and are deposited on the growing p a r t i c l e . I n t h i s case gas phase d i f f u s i o n and surface d i f f u s i o n can be regarded as w e l l .

Since the bonding energies of Fe or Ni metal atoms t o the metal c r y s t a l l i t e s are much l a r g e r than the bonding energies of the metal atoms t o the z e o l i t e support, the AM model i s u n l i k e l y except f o r very high temperatures and/or charged c l u s t e r s (see below).

A l l samples e x h i b i t a b i d i s p e r s e PSD. Since t h e r e may be d i f f e r e n t mechanisms of s i n t e r i n g , depending on the s i z e of the p a r t i c l e s , the nodes w i l l be discussed s e p a r a t e l y w i t h respect t o the s i n t e r i n g models mentioned above.

The f r a c t i o n o f paramagnetic species (PS) can be formed as f o l l o w s :

a. Incomplete r e d u c t i o n of N i ( I I ) ions which remain then i n hidden s i t e s or i n s i t e s , where they can merge w i t h reduced N i ( 0 ) atoms, i n t h i s way forming charged c l u s t e r s . The l a t t e r are expected t o show strong p a r t i c l e support i n t e r a c t i o n due t o the e l e c t r o s t a t i c f o r c e s .

b. Reaction of N i ( 0 ) w i t h hydroxyl groups of the z e o l i t e ( 9 ) , or w i t h the acid centers formed d u r i n g H 2 r e d u c t i o n . At higher temperatures these centers also can be dehydroxylated. The water thus formed can o x i d i z e the m e t a l . The metal surface f i n a l l y can be passivated by a surface l a y e r of oxide/hydroxide.

154

The second way of s i n t e r i n g should lead t o an increase of the PS at the expense of the m e t a l l i c p a r t i c l e s . On the other hand, f u r t h e r r e d u c t i o n can i n c r e a s e the PS t o o . Hence, evidence f o r t h i s mechanism can only be obtained i f t h e amount of l a r g e p a r t i c l e s decreases upon s i n t e r i n g . This i s not found i n NiNaM and i n Ni NaX. Only i n Ni NaY t h i s may be a p o s s i b l e mechanism. The high number of PS and the small changes i n t h e i r amount i n NiNaM and NiNaY i n d i c a t e a r e s i s t a n c e towards s i n t e r i n g due t o a strong i n t e r a c t i o n of the z e o l i t e w i t h the charged c l u s t e r s (way 1 ) . In t h i s case, s i n t e r i n g can only proceed according t o t h e AM model. The f r a c t i o n of p a r t i c l e s w i t h v 1 ' 3 g r e a t e r than 0.5 nm can migrate a c c o r d i n g t o the AM model or CM model as w e l l . None of these models, however, can e x p l a i n the enormous increase of the number of l a r g e p a r t i c l e s i n NiNaX as compared t o NiNaY.

3. A Model f o r P a r t i c l e Growth i n M a t r i x D i s l o c a t i o n s

E l e c t r o n micrographs of a l a r g e number of reduced n i c k e l z e o l i t e s always show f o c a l d i s t o r t i o n s o f t h e m a t r i x , though t he samples seem t o be completely " c r y s t a l l i n e " as evidenced by x-ray d i f f r a c t i o n . F i g . 1 gives an example of NiNaY z e o l i t e , reduced at 673 K. Along the one-dimensional d e f e c t , the p a r t i c l e s can m i g r a t e e a s i l y . Assuming t h a t the formation o f d e f e c t s i n the m a t r i x i s the main i n f l u e n c e on the r a t e of s i n t e r i n g , one would expect t h a t p a r t i c l e growth should i n c r e a s e i n the sequence M<Y<X<A z e o l i t e , as a r e s u l t of the decreased thermal s t a b i l i t y of the p r o t o n i c forms of these z e o l i t e s which are generated upon r e d u c t i o n . The r e s u l t s given i n Table I I c o n f i r m t h i s assumption. The AM model cannot e x p l a i n the d i f f e r e n c e s i n PSD between Α-, X-, Y- and M-zeolites and can be r e j e c t e d f o r the d i f f u s i o n through channels (see above) or along a defect path. The s i n t e r i n g can occur by c r y s t a l m i g r a t i o n along the de f e c t path i n case of l a r g e p a r t i c l e s and through the channels i n case of small p a r t i c l e s .

I t remains t o be answered whether the p a r t i c l e growth w i l l be s i n t e r i n g c o n t r o l l e d ( f u s i o n c o n t r o l l e d ) or d i f f u s i o n c o n t r o l l e d . For high temperatures d i f f u s i o n w i l l be r a p i d and the aggregation i s expected t o be the r a t e d e termining s t e p . This i s a reasonable assumption i f the m a t r i x has t o be destroyed by the growing p a r t i c l e . According t o Ruckenstein and Pulvermacher ( 6 ) , magnetic measurements can be used t o decide between s i n t e r i n g c o n t r o l and d i f f u s i o n c o n t r o l . High values of the r a t i o v H ^ / v L A i n d i c a t e s i n t e r i n g c o n t r o l . Excluding t h e paramagnetic species the mean p a r t i c l e s i z e d e f i n e d as

„ V i VHA = f T~qT

was found t o be 3.2 nm i n NiNaY, reduced at 723 Κ and measured at 6 K. The corresponding low argument mean p a r t i c l e volume

2 „ V i

\A = [TV 7 measured at 295 Κ was found t o be 8.1 nm3*

The r a t i o v L A / v H A > 2 i n d i c a t e s t h a t t h e s i n t e r i n g process i s f u s i o n c o n t r o l l e d .

4. Thermal Decomposition of Fe(C0)p;/NaY Adducts under S t a t i c Conditions

NaY z e o l i t e s a t u r a t e d w i t h Fe(C0)g shows an i v o r y - l i k e c o l o u r . I f the sample i s heated up slowly under vacuum i n the shallow bed mode (sample FeYOSB, Table I ) , the colour t u r n s t o dark grey. A f t e r outgassing, t he gene r a t i o n of i r o n p a r t i c l e s

155

Figure 1 E l e c t r o n Micrograph o f NiNay: T R = 773 K. The Arrown I n d i c a t e s a L a t t i c e Defect

w i t h diameter g r e a t e r than approximately 10 nm i s found by e v a l u a t i n g the m-agnetization isotherms ( 1 0 ) . This p i c t u r e i s confirmed by i n s p e c t i o n of i s o l a t e d i r o n z e o l i t e c r y s t a l s by TEM/EDS. The c r y s t a l s show i r o n / s i l i c o n r a t i o s ranging from n e a r l y zero up t o two and are covered by p o l y c r y s t a l 1 i ne Fe (s u r f a c e o x i d i z e d ) p a r t i c l e s w i t h diameters between 20 and 50 nm, r e s p e c t i v e l y .

5. Highly Dispersed I r o n P a r t i c l e s by Decomposition of Fe(C0)g/NaY Adducts i n a F l u i d i z e d Bed

I f Fe(C0)r/NaY adducts are heated r a p i d l y under f l u i d i z e d bed c o n d i t i o n s (FeY480FB, FeY17FB, FeYOFB, see Table I ) , at a c e r t a i n temperature the i v o r y l i k e c o l o u r suddenly changes t o dark grey w i t h i n a few seconds. The s t a r t i n g t emperature f o r t h i s f a s t r e a c t i o n ranges from 410 Κ t o 440 Κ going from the FeYOFB t o the FeY480FB samples. A f t e r outgassing the i r o n weight content amounts t o 10 wt %. I r o n p a r t i c l e s i z e d i s t r i b u t i o n s i n these samples obtained from m a g n e t i z a t i o n measurements are given i n Table I I I ( a ) .

Great d i f f e r e n c e s are found f o r the f r a c t i o n of p a r t i c l e s exceeding 1.27 nm, which approximately i s the diameter of the f a u j a s i t e supercage:

- As a r e s u l t of vacuum decomposition (Table I I I , FeYOFB), 25% of the i r o n phase c o n s i s t s o f p a r t i c l e s l a r g e r than 1.27 nm and up t o 10 nm.

- A smaller amount of these l a r g e p a r t i c l e s i s formed under 17 mbar of helium (FeY17FB): only 19% of the i r o n phase e x h i b i t s diameters between 1.6 and 10 nm, r e s p e c t i v e l y .

- A d i s t i n c t l y p o s i t i v e e f f e c t of i n e r t gas atmosphere on the i r o n d i s p e r s i o n shows up when decomposition occurs under 480 mbar of helium (FeY480FB): the i r o n phase n e a r l y completely c o n s i s t s of p a r t i c l e s s maller than the size of the supercage. Only 2.7% of the i r o n i s found t o have dimensions g r e a t e r than 1.6 nm.

For a l l samples decomposed under f l u i d i z e d bed c o n d i t i o n s , the i r o n f r a c t i o n encaged i n s i d e t h e z e o l i t e m a t r i x shows a s i z e d i s t r i b u t i o n down t o the t h e o r e t i c a l l i m i t of a three-dimensional c l u s t e r .

I f the i r o n z e o l i t e s formed d u r i n g f l u i d i z e d bed decomposition are subjeced t o prolonged heating at 550 Κ i n the sealed ampoule, the o r i g i n a l p a r t i c l e s i z e d i s t r i b u t i o n remains almost c o n s t a n t . A f t e r 6 hours h e a t i n g at t h i s temperature, even the h i g h l y dispersed sample proves t o be s t a b l e a g a i n s t s i n t e r i n g (Table I I I ) ( b ) ) .

6. A Model f o r the Thermal Decomposition Process of Fe(C0^/NaY Adducts

The supercages of the NaY z e o l i t e were found t o be f i l l e d completely w i t h t h r e e Fe(C0) 5 molecules upon s a t u r a t i o n ( 1 1 ) . A r e l a t i v e l y s t r o n g complex-matrix i n t e r a c t i o n leads t o increased thermal s t a b i l i t y of the adduct compared t o the f r e e complex (12,13,14). This i n t e r a c t i o n i s not s u f f i c i e n t l y s t r o n g , however, t o prevent the carbonyl from p a r t i a l d e s o r p t i o n upon h e a t i n g under vacuum (12,14,15).

Two slow processes of decomposition at low and high temperatures, separated by a f a s t endothermic r e a c t i o n , have been d i s t i n g u i s h e d by thermogravimetry ( 1 4 ) . The f a s t r e a c t i o n s t a r t s at a CO/Fe r a t i o equal t o 3 ± 0.5 and leaves r e l a t i v e l y thermostable species w i t h CO/Fe equal t o 0.4 ± 0.2, which s t r o n g l y i n t e r a c t w i t h the m a t r i x . From i . r . r e s u l t s , these two i n t e r m e d i a t e phases are assigned t o species bearing bridged CO and t o h i g h l y unsaturated F e x ( C 0 ) y

c l u s t e r s , r e s p e c t i v e l y . The slow departure of the f i r s t CO li g a n d s upon h e a t i n t j i s i n l i n e w i t h high d i s s o c i a t i o n energies determined f o r the f i r s t bond s c i s s i o n (16,17).

157

Table I I I Approximate PSD o f Fe(0) i n Y z e o l i t e a f t e r d e c o m p o s i t i o n o f the Fe(CO)^/NaY adduct i n a f l u i d i z e d bed under d i f f e r e n t atmospheres (a) and a f t e r s i n t e r i n g a t 55 3 Κ f o r 6 hours (b)

Amount o f p a r t i c l e s i n each

/nm FeYOFB

(a) (b)

45. 6.5

19.

4.4

34. 14. 21 .

7.8

10.1

3.6 9.5 2.2

6.0

3.9 7.6 5.8

s i z e f r a c t i o n /wt %

FeY17FB

(a) (b)

26. 23. 32.

26. 22. 29.

4.1

10.3 8.7

8.1 9.2

0.6 1.6

FeY480FB

(a)

1 .0

(b)

57. 55. 14.6 16. 2.8 4.0

20. 20. 2.8 3.0 0.5 0.5 0.3 0.4 0.9 1 .0

0.1

p r e p a r a t i o n c o n d i t i o n s a re g i v e n i n Table I

dashed l i n e : approximated supercage dimensions

158

A l t e r n a t i v e l y , an a u t o c a t a l y t i c step may be in v o l v e d i n thermal decomposition o f Fe(C0)c ( 1 8 ) , since the complex was observed t o decompose at i r o n s u r f a c e s a l r e a d y a t 333 Κ ( 1 9 ) . A model i s proposed f o r the thermal decomposition o f Fe(C0)^/NaY adduct, t a k i n g i n t o account the r e s u l t s discussed.

- Under vacuum ( F i g . 2 a ) , a great amount of Fe(CO)^ adsorbed moves along the channels and passes l a t t i c e d e f e c t s or the c r y s t a l surface upon h e a t i n g . Due t o the a u t o c a t a l y t i c e f f e c t of i r o n , i n i t i a l l y generated i r o n n u c l e i act as agglomeration centres f o r the carbonyl molecules. The formation o f l a r g e i r o n p a r t i c l e s as w e l l as c o n s i d e r b l e loss of i r o n are the r e s u l t of t h i s e f f e c t .

- A s u f f i c i e n t l y high i n e r t gas pressure leads t o a l i m i t e d mean f r e e path of the carbonyl molecules ( F i g . 2 b ) . Due t o the r e s t r i c t e d m o b i l i t y , o n l y a small f r a c t i o n reaches places where agglomeration can occur; most molecules are thus decomposed t o h i g h l y unsaturated i n t e r m e d i a t e s (CO/Fe = 0.4) i n s i d e the z e o l i t e l a t t i c e . These 'anchored' species h a r d l y undergo f u r t h e r f u s i o n u n t i l they are completely decomposed t o m e t a l l i c i r o n . The use o f f a s t h e a t i n g r a t e s and homogeneous bed temperatures as we l l as f a s t gas exchange by a p p l i c a t i o n of f l u i d i z e d bed c o n d i t i o n s improve the d i s p e r s i o n .

These h i g h l y dispersed i r o n systems are s u r p r i s i n g l y s t a b l e against s i n t e r i n g even at 550 K. Since much g r e a t e r , g r a p h i t e supported i r o n p a r t i c l e s were r e p o r t e d t o s i n t e r already above 450 Κ ( 2 0 ) , the present r e s u l t s c l e a r l y s t r e s s t h e unique s t a b i l i z i n g f u n c t i o n of an i n t a c t z e o l i t e m a t r i x .

CONCLUSIONS

Magnetic isotherms have been used t o c h a r a c t e r i z e h i g h l y dispersed N i - and Fe-phases on z e o l i t e s i n the nm range. N i ( I I ) exchanged NaA, NaX, NaY and NaM z e o l i t e s reduced by hydrogen between 573 and 823 Κ e x h i b i t a b i d i s p e r s e Ni phase. The amount and the volume of p a r t i c l e s exceeding the cage dimensions increases i n the sequence of the z e o l i t e s : Μ < Υ < X < A. The growth o f the p a r t i c l e s i s mainly c o n t r o l l e d by the c o n c e n t r a t i o n of l a t t i c e d e f e c t s i n t h e m a t r i x . P a r t i c l e f u s i o n i s found t o be the r a t e d e t e r m i n i n g step. The f r a c t i o n o f the small p a r t i c l e s remains n e a r l y constant as a r e s u l t of c o m p e t i t i o n between f u r t h e r r e d u c t i o n and s i n t e r i n g .

Y z e o l i t e s s a t u r a t e d w i t h i r o n pentacarbonyl v i a the gas phase proved t o be s u i t a b l e precursors f o r h i g h l y dispersed i r o n systems. A p a r t i c u l a r p r e p a r a t i o n method, i n c l u d i n g f a s t thermal decomposition of the adducts i n a f l u i d i z e d bed under i n e r t atmosphere, provides the best d i s p e r s i o n . About 97 wt% of t h e i r o n phase i s accommodated i n the supercages of the z e o l i t e . The i r o n systems are s t a b l e against s i n t e r i n g at t y p i c a l CO hydrogenation r e a c t i o n temperatures due t o the z e o l i t e pore s t r u c t u r e . Work i s i n progress t o determine the i n f l u e n c e o f d i f f e r e n t z e o l i t e pore dimensions on p a r t i c l e s i z e , s t a b i l i t y , and c a t a l y t i c behaviour of i r o n model c a t a l y s t s .

ACKNOWLEDGMENTS

The authors are g r a t e f u l t o Prof. Gunsser f o r his i n t e r e s t . Τ. B. i s indebted t o Prof. J. W. Geus f o r very f r u i t f u l d i s c u s s i o n s . He acknowledges a research g r a n t from the ' A l f r i e d Krupp von Bohlen and H a l b a c h - S t i f t u n g ' .

P. A. J. acknowledges a research p o s i t i o n as 'Senior Research Associate' from NFWO-FNRS (Be l g i u m ) .

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The help of Dr. L. Rodrique (UCL Belgium) i n the microprobe a n a l y s i s i s a p p r e c i a t e d . We thank cand. ehem. M. Bauer f o r the performance of several magnetic measurements.

REFERENCES

1 . H. Heinemann, C a t a l . Rev., Sc. Ä Eng., 23_ (1981), 315.

2. P. A. Jacobs i n "Metal M i c r o s t r u c t u r e s i n Z e o l i t e s " , Ed.: P. A. Jacobs et a l . E l s e v i e r (1982), 71.

3. F. Schmidt, W. Gunsser, J. Adolph, ACS Symposium S e r i e s , _40 (1977), 291.

4. F. Schmidt i n "Metal M i c r o s t r u c t u r e s i n Z e o l i t e s " , P. A. Jacobs et a l . , eds, E l s e v i e r , (1982) 191.

5. B. Pulvermacher and E. Ruckenstein, J. C a t a l . , _35_ (1974) 115.

6. B. Pulvermacher and E. Ruckenstein, J. C a t a l . , 29_ (1973) 224.

7. J. R. Anderson, " S t r u c t u r e of M e t a l l i c C a t a l y s t s " , Academic Press, (1975) 280.

8. P. C. Flynn and S. E. Wanke, J. C a t a l . , _34 (1974) 390, P. C. Flynn and S. E. Wanke, J. C a t a l . , 34_ (1974) 400.

9. E. Garbowski, C. Mirodatos and M. Primet, i n "Metal M i c r o s t r u c t u r e s i n Z e o l i t e s " , P. A. Jacobs et a l . , eds., E l s e v i e r , (1982) 235.

10. F. Schmidt, W. Gunsser and A. Knappwost, Z. Nat. f o r s c h . , 30a (1975) 1627.

11. Th. Bein, P. A. Jacobs and F. Schmidt,^ i n "Metal M i c r o s t r u c t u r e s i n Z e o l i t e s " , P. A. Jacobs et a l . , eds. E l s e v i e r , (1982) 111.

12. J. B. Nagy, M. Van Eenoo, E. G. Derouane, J. C a t a l . , bS_ (1979), 230.

13. Th. Bein and P. A. Jacobs, J. Chem. S o c , Faraday Trans., J^, (1983), i n press.

14. Th. Bein and P. A. Jacobs, submitted t o J. Chem. S o c , Faraday Trans., _L,

15. D. B a l l i v e t - T k a t c h e n k o and G. Coudurier, I n o r g . Chem., J8_ (1979) 558.

16. G. P. Smith and R. M. Laine, J. Phys. Chem., _85 (1981) 1620.

17. P. C. Engelking and W. C. Lineberger, J. Am. Chem. S o c , _101_ (19) (1979) 5570.

18. A. Brenner and D. A. Hucul, I n o r g . Chem., _18 (10) (1979) 2836.

19. A. M i t t a s c h , Z. ang. Ch., 41_ (1928) 831.

20. J. P h i l l i p s , B. Clausen, J. A. Dumesic, J. Phys. Chem., 84 (1980), 1814.

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