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    Clays and Clay Minerals

    197 3 Vol. 21 pp. 379-389. Pergamon Press. Printed in Grea t Britain

    P R O P E R T I E S O F T H E Z E O L I T E F A U J A S I T E

    S U B S T I T U T I O N A L S E R I E S :

    A R E V I E W W I T H N E W D A T A

    DENNIS N. STAMIRES

    Internat ional A pplied Science, Inc. , 4630 Campus Dr ive, New por t Beach, C alifornia 92660, U.S.A.

    Received 26 S e p te mb e r 1972)

    A bs t r ac t - - N ew inf or mat ion i s p r esen ted r e la t ing to the hydr o the r mal s tab i l ity , l a t t i ce pa r amete rs , and

    adsor p t ive , e lec tr ica l, and ca ta ly t ic p r oper t ie s o f syn the t ic and na tur a l f au jas i te . P r esen t concepts con-

    ce r n ing the na tur e and r e la tionsh ip of synthe t ic and na tur a l f au jas ite a r e r es ta ted to be cons i s ten t w i th

    the exper imen ta l ev idence and the d eve loped phys ica l mode l. T he major s t r uc tur a l and phys icochemi-

    cal prope r t ies ref lect the c lose s imilar i t ies and smoo th gradations expec ted of su bst i tut ional mem bers

    of a con tinuous ser ies . The exis t ing divis ion of the range 2-6) of SiO2/A1203 mole rat ios S/A) at 3 into

    two comp osit ional subranges is shown to be unjust if iable and rathe r mis leading. Ind ividual com posi-

    t ions f rom these tw o sub ranges do n ot represe nt dis t inct ly dif ferent zeoli te species ; ins tead, i t is

    demon s t r a ted tha t they a r e mem ber s of a cont inuous se r ies w i th smooth ly changing p r oper t ie s over

    the stud ied rang e of SiO2/AI~O3.Some of the pr oper t ie s o f the na tur a l minera l f au jas i te a re f ound to be

    very s imilar to th ose of the synthet ic analogs with the same SiO2/A1203 mole rat io.

    Final ly , a plea is made fo r a uniform nom enclature which wil l serve to identify specif ic s ingle)

    com posit ions ins tead of ranges of com posit ions) ; ref lect the con tinuity, c lose s imilar it ies an d inter -

    relat ionships in their main s tructural and physicoc hem ical prope r t ies ; and also identify the cha racter is-

    t ics of the faujas i te group.

    INTRODUCTION

    H IS TO R IC A LL Y , e x p e r i m e n t a l w o r k o n c r y s t a l l i n e

    a l u m i n o s i l ic a t e s o f t h e f a u j a s i t e t y p e s t a r t e d w h e n

    D a m o u r 1 84 8) p u b l i s h e d a c h e m i c a l a n a l y s i s o f

    f a u j a s i t e . S y n t h e t i c z e o l i t e s d e s i g n a t e d a s X a n d Y

    w e r e p r o d u c e d b y M i l t o n 1 95 9) a n d B r e c k 1 96 4).

    T h e X - r a y w o r k o f B a u r 1 96 4), B e r g e r h o f f

    et al.

    1 95 6) a n d B r o u s s a r d a n d S h o e m a k e r 1 96 0) a n d t h e

    a d s o r p t i o n s t u d i e s o f B a r r e r e t a l . 1957) es tab-

    l i s h e d t h e s t r u c t u r a l i d e n t i t i e s o f t h e s e s y n t h e t i c

    z e o l i t e s a n d t h e n a t u r a l m i n e r a l . H o w e v e r , t h e l o c a -

    t i o n o f c e r t a i n c a t i o n s i n t h e a l u m i n o s i l i c a t e

    f r a m e w o r k a n d t h e r e l a t i v e d e g r e e o f S i , A 1) o r d e r -

    i n g in t h e l a t t i c e s ti l l r e m a i n u n c e r t a i n a n d m a y b e

    d i f f e r e n t i n t h e s y n t h e t i c a n d n a t u r a l s p e c i e s .

    I t i s p o s s ib l e t o s y n t h e s i z e h y d r o t h e r m a l l y a c o n -

    t i n u o u s s e r i e s o f f a u j a s i t e z e o l i t e s w i t h u n i f o r m

    c o m p o s i t i o n a l w a r i at i o n . B r e c k 1 96 4) h a s d i v i d e d

    t h i s s e r i e s in t o t w o c o m p o s i t i o n a l r a n g e s , o n e a

    h i g h a l u m i n a s p e c i e s d e s i g n a t e d a s t y p e X , t h e

    o t h e r a h i g h s i l i c a s p e c i e s d e s i g n a t e d a s t y p e Y .

    O v e r t h e e n t i r e s i l i c a - a l u m i n a r a n g e f r o m 2 --6 , t h e

    u n i t c e l l d i m e n s i o n s f o r z e o l i t e s in b o t h r a n g e s w e r e

    f o u n d B r e c k a r id F l a n i g e n , 1 96 8) t o v a r y l i n e a r l y

    w i t h t h e d e g r e e o f r e p l a c e m e n t o f S i b y A 1 i n th e

    c r y s t a l f r a m e w o r k . A S IO 2 /A 1 20 3 m o l e r a t i o h e r e -

    a f t e r r e f e r r e d t o a s S / A ) o f t h r e e w a s c h o s e n

    B r e c k , 1 9 6 4 ) a s t h e b o u n d a r y b e t w e e n t y p e X a n d

    t y p e Y . I t h a s a l s o b e e n s t a t e d B r e c k , 1 96 4) t h a t

    Z e o l i t e X i s d i s t i n c t l y d i f f e r e n t f r o m Z e o l i t e Y a n d

    t h a t b o t h a r e d i f f e r e n t f r o m n a t u r a l f a u j a s i t e . T h u s ,

    a c c o r d i n g t o t h i s s c h e m e , t h e r e o c c u r s w i t h i n t h e

    s u b s t i t u t i o n a l s e r i e s t h r e e d i s t i n c t l y d i ff e r e n t z e o -

    l i te s p e c i e s ; n a m e l y , X , Y a n d n a t u r a l f a u j a s i t e . T o

    j u s t i f y t h is d i s t i n c t i o n B r e c k 1 96 4) s t a t e d t h a t X -

    r a y d a t a s t r u c t u r a l p r o p e r t i e s ) h a d t o b e c o n s i -

    d e r e d t o g e t h e r w i t h o t h e r p r o p e r t i e s , s u c h a s c h e m -

    i c a l c o m p o s i t i o n , h y d r o t h e r m a l s t a b i l i t y , a d s o r p -

    t i o n , a n d i o n e x c h a n g e .

    T h i s p a p e r r e v i e w s t h e e a r l ie r w o r k a n d p r e s e n t s

    n e w i n f o r m a t i o n w h i c h e s t a b l i s h e s t h e c l o s e s i m i -

    l a r i t y i n t h e h y d r o t h e r m a l s t a b i l i t y , a d s o r p t i o n a n d

    o t h e r p r o p e r t i e s o f b o t h s y n t h e t i c a n d n a t u r a l f a u -

    j a s i t e . It i s a l s o s h o w n t h a t t h e r e i s n o j u s t if i c a t i o n

    w i t h i n t h e s e p r o p e r t i e s o f t h e s u b s t i t u t i o n a l s e r i e s

    t o w a r r a n t a d i v i s i o n a t a S / A o f t h r e e , o r a t a n y

    o t h e r p o i n t .

    T h e m a i n c r i te r i a u s e d b y B r e c k 1 96 4) f o r t h e

    379

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    380 DENNIS N STAMmES

    distinction between X, Y and natural faujasites

    were hydrothermal stability, ionic conductivity,

    and sorption properties. In this paper, these same

    properties and additional structural data support

    the lack of any such distinction and demonstrate

    the similarities in the properties o f the substitu-

    tional members of the faujasite series. Further,

    these new data should help resolve the conflicts in

    the conclusions of Breck 1964); Dempsey, KiJhl

    and Olson 1969); Wright, Rupert and Granquist

    1968, 1969); recently summarized by Smith 1971).

    MATERIALS AND METHODS

    The zeolites were synthesized from pure chemi-

    cals by the procedures of Barrer 1959); Milton

    1959) and Breck 1964). Samples were analyzed by

    X-ray diffraction and fluorescence, chemical

    analysis, and by the electron microprobe. Repeat

    preparations were made at each desired composi-

    tion, and those samples with the highest crystallin-

    ity and most uniform crystals were selected for the

    detailed study. Special care was taken to eliminate

    occlusion of free sodium silicate in the zeolite

    crystals. The Na20/A1203 mole ratio was kept close

    to unity by ion exchange with NaCI. The selected

    zeolites contained less than 20 ppm Fe and less than

    80 ppm Ca and Mg. The S A was determined both

    by wet chemical analysis and by X-ray fluores-

    cence.

    The samples usually were activated by room

    temperature desorption under vacuum for several

    hours followed by a slow temperature increase

    about 2~ to the 400--450~ range where the

    samples were kept at approximately 10 7 orr for

    periods of 8-16 hr until the dehydration was com-

    plete. A McBain balance and a mass spectrometer

    were used routinely to establish complete dehydra-

    tion of the samples and to avoid unnecessarily pro-

    longed heating. The samples with higher AI con-

    tents required longer heating under vacuum to re-

    lease the last traces of water.

    The X-ray measurements were done with CuKa

    radiation at scanning rates of 2~ and 0.25 ~ 20/min.

    An average value of the unit cell parameter a was

    obtained from several diffraction peaks for each

    sample. The 9 values were corrected by the known

    reflections of either NaC1 or metal oxides, which

    were mixed together with a portion of zeolite

    sample.

    Ion exchange was usually done by percolation;

    i.e. a concentrated solution of the salt of the ex-

    changing ion was allowed to flow through the zeo-

    lite sample.

    EXPERIMENTAL RESULTS AND DISCUSSION

    Hydrothermal stabil i ty

    The hydrothermal stability of each sample, over

    a wide range of S/A, was determined and compared

    with results available in the literature. In order to

    make the comparison valid, the same experimental

    conditions Breck, 1964) were used: steaming the

    samples at 410~ and atmospheric pressure for 3 hr.

    The steamed samples were activated by heating at

    460~ and 10 7 torr by the monitoring procedure al-

    ready described. Oxygen sorption capacity at

    -183~ and 100 torr was measured on each sample

    before and after steaming.

    Four samples of the same S/A were studied to

    establish the reproducibility of the method. The

    first few experiments indicated that a steaming

    period of 3 hr was not sufficient and that up to 5 hr

    was required to obtain equilibrium. Oxygen sorp-

    tion capacities and X-ray intensities of the steamed

    samples were used to establish this equilibrium.

    Non-reproducible results were obtained with com-

    mercial synthet ic faujasite with Fe- content in the

    range of 0.05-0.1 per cent and with samples con-

    taining appreciable occluded sodium silicate; i.e.

    non-reproducibility correlated with impurity con-

    tent. Preliminary results indicate that both iron

    which on heating forms the ferromagnetic species

    Fe304, Singer and Stamires, 1965) and occluded

    sodium silicate enhance the hydrothermal decom-

    position of the crystalline zeolite. Thus, the pres-

    ence of these impurities causes a considerable vari-

    ation in the stability data.

    A sample of natural faujasite Kaiserstuhl oc-

    currence) was included for comparison with the

    series of synthetic samples. The sample was con-

    verted to the sodium form remaining Ca and Mg

    was less than 0.03 weight per cent) by repeated ion

    exchange, and ground to a fine powder before use.

    The results are presented in Fig. 1, where the per-

    cent crystallinity retained after steaming is plotted

    as a function of S/A. For comparison, the data of

    Breck 0964) are also shown. All data were corre-

    lated using third degree polynomials to determine

    the r.m.s, deviation, and the most probable values.

    These results also appear in Fig. 1.

    Although it is questionable if statistical treatment

    of the Breck 1964) data is justifiable because of the

    large spread, it is interesting to note that the smooth

    curve obtained from the correlated data closely re-

    sembles that of the new equilibrium results. Thus, it

    can be concluded that a smooth continuous curve is

    indeed the best representation for the data. The plot

    of the new equilibrium results, without the large

    spread of data, lies generally below the Breck

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    Zeolite, faujasite, substitutional series: a review with new data 381

    curve, as would be expected from the increased

    severity of the steaming process. The plots con-

    verge at ratios near 5. The position of the natural

    faujasite in the plot is in accord with its composi-

    tion. Thus, the stability data demonstrate the exis-

    tence of a continuous substitutional series with

    natural faujasite as a member.

    The crystallinity remaining in these samples after

    steaming was also measured by X-ray diffraction

    techniques and was found to vary with the S/A in

    much the same way as the retained crystallinity

    shown in Fig. 1.

    Mechanism of structural degradation by steaming

    The drastic changes induced by steaming can be

    viewed as similar to the changes occurring during

    the heating of NH4*-exchanged faujasite. The hy-

    drolysis of the A104/2)-Na+ site results in the for-

    mation of a hydroxyl group associated with the

    AIO412)- etrahedron. The distribution of the charge

    density in the hydroxyl group varies according to

    its location and crystal environment. In the high

    alumina members of the series where there are a

    large number of Na cations on type iii) sites

    Breck and Flanigen, 1968), the hydrolysis results in

    the production of a substantial number of protons

    in the supercage. These protons are probably as-

    m

    z

    o

    DO I 1

    /

    o EXPERIMENTAL ALUESOF R.F. J

    9 CALCULATEO ALUESRASEDON RMS

    DEVIATIONSOF D.E. DATA

    ~, PRESENT XPER{MENTAL ATA

    ~ATURALFAUJASITE

    1 O 1.5

    E.15 310 t

    .15 4.10 4.15 5.0 5.15

    Fig. 1. Variation of hydrothermal stability with varying

    SiOdA120~ mole ratio. Experimental values of Breck

    1964), these data after statistical analysis and correlation,

    and new equilibrium results.

    sociated with the oxygen 4-membered rings which

    constitute very weak cation sites. This association

    in turn makes these protons very reactive, to the

    extent that they can hydrolyze part of the

    alumino-silicate framework. At the same time,

    some of the Na probably migrates into the sodalite

    cages, or disperses in the remaining portion of the

    crystals.

    The mechanism by which these chemical changes

    proceed has been ascertained earlier Szymanski,

    Stamires and Lynch, 1960; Rabo et al. 1960) and

    further substantiated by Uytterhoeven, Christner

    and Hall 1965).

    In addition, Stamires 1965) has studied the e.s.r.

    spectra of stabilized atomic hydrogen produced by

    -/-irradiation of synthet ic zeolites and the interac-

    tion of such hydrogen with the crystal lattice at

    liquid helium or nitrogen temperatures. In the pres-

    ent work, the e.s.r, spectra of samples, exposed to

    steam only for short periods followed by vacuum

    activation at 460~ and -/-irradiation, showed a

    large amount of hydrogen atoms present. This hy-

    drogen is introduced by the replacement in the

    structure of some Na + by protons resulting from

    the steam hydrolysis. Then, the protons react with

    the lattice oxygens to form hydroxyl groups which

    further by radiolysis produce hydrogen atoms and

    lattice-oxygen radicals. In high-A1 samples, the

    hyperfine splitting constant of the spectrum of ad-

    sorbed atomic hydrogen is smaller approximately

    498 G) than the value of approximately 508 G for

    the free hydrogen atom. No changes were observed

    in the G-values; however, the line width increased

    with decreasing silica content. The brodening is at-

    tributed to unresolved hyperfine lines resulting

    from a distribution of various trapping sites Sta-

    mires and Turkevich, 1964; Stamires, 1968) within

    the unit cell. As the overall effect observed in the

    e.s.r, spectra includes both short and long term in-

    teractions, Stamires and Turkevich, 1963) it ap-

    pears that the distribution of the strengths of the

    individual hydroxyl groups probably varies from

    one cell to the other. However, the largest differ-

    ences are observed among the extreme members in

    the silica-alumina range investigated.

    The decrease in the hyperfine splitting constant is

    attributed to the strong electric field in the super-

    cage produced primarily by the high density of sur-

    rounding protons and sodium ions. The close prox-

    imity of the A104jE)- sites with which the hyd-

    rogens are associated and the high reactivity of

    those hydrogens are responsible for the structural

    changes in the crystal. The strong electric field in

    the supercage tends to expand the electronic wave

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    382

    DENNIS N ST MIRES

    f u n c t i o n o f t h e u n p a i r e d e l e c t r o n i n t h e h y d r o g e n

    a t o m s o a s t o d e c r e a s e t h e c h a r g e d e n s i t y a t t h e

    n u c l e u s , a n d h e n c e t o d e c r e a s e t h e h y p e r t i n e c o n -

    s t a n t . H o w e v e r , w h e n h y d r o g e n a t o m s a r e p r o -

    d u c e d o n s t e a m e d s a m p l e s w i t h v e r y l o w a l u m i n a

    c o n t e n t s , t h e c o n c e n t r a t i o n o f a t o m i c h y d r o g e n i s

    c o n s i d e r a b l y s m a l le r a n d t h e h y p e r f i n e c o n s t a n t i s

    c l o s e r t o t h a t o f f r e e a t o m i c h y d r o g e n ( a p p r o x -

    i m a t e l y 5 0 4 G ) . F r o m e l e c t r o s t a t i c c o n s i d e r a t i o n s ,

    i t a p p e a r s t h a t t h e c e n t e r o f t h e s o d a l i te u n i t w o u l d

    b e a s u i t a b le t r a p p i n g s i t e f o r s u c h t y p e s o f h y d -

    r o g e n .

    I n s o m e f a u j a s it e s a m p l e s w i t h i n te r m e d i a t e S / A ,

    t h e e . s . r , s p e c t r a s h o w e d a d o u b l e t w i t h h y p e r f i n e

    l i n e s c o r r e s p o n d i n g t o t h e t w o e x t r e m e c a s e s d i s -

    c u s s e d a b o v e ; i . e . h y d r o g e n a t o m s t r a p p e d i n t h e

    s u p e r c a g e a n d i n t h e s o d a l i t e u n i t. A l t h o u g h t h e a p -

    p e a r a n c e o f t h i s d o u b l e t a l l o w s a g r o s s d i s t i n c t i o n

    t o b e m a d e b e t w e e n h y d r o g e n s l o c a t ed i n t h es e t w o

    d i f f e r e n t s i t e s ( t h e s e t w o s i t e s c o u l d b e i d e n t i f i e d

    w i t h t h o s e f o u n d i n t h e i . r . w o r k c o r r e s p o n d i n g t o

    t h e 3 5 5 0 a n d 3 6 5 0 c m -1 a b s o r p t i o n f r e q u e n c i e s ) , t h e

    u n r e s o l v e d h y p e r f i n e s t r u c tu r e o f t h e i n d i v id u a l

    l i ne s o f t he do ub le t i nd i ca t e s t ha t t he re i s s ti ll

    a n o t h e r d i s t r i b u t i o n o f s i t e s w i t h i n t h e i n d i v i d u a l

    s o d a l i t e a n d s u p e r c a g e u n i t s . T h i s c o n c l u s i o n i s i n

    c o n t r a s t t o t h e i n f o r m a t i o n o b t a i n e d f r o m i .r . ( U y t -

    t e r h o e v e n , C h r i s t n e r a n d H a l l , 1 9 65 ) a n d X - r a y d i ff -

    r a c t i o n ( O l s o n a n d D e m p s e y , 1 96 9) , w h e r e o n l y t w o

    t y p e s o f h y d r o g e n h a v e b e e n i d e n t i f i e d ( t h o s e a s -

    s o c i a t e d w i t h t h e 0 3 a n d O l l a t t i c e o x y g e n s ) .

    T h e r e s o l u t i o n o f i .r . is l im i t e d w h e n a p p l i e d t o

    p o l y c r y s t a l l i n e s o l i d s , p a r t i c u l a r l y i n c a s e s w h e r e

    t h e p e r tu r b a t i o n o n s o m e o f t h e h y d r o g e n s , p r o -

    d u c e d b y t h e e l e c t r i c fi el d o f t h e e n v i r o n m e n t , i s

    r e l a t i v e l y s m a l l . I n t h a t c a s e s m a l l s h i f t s , d u e t o

    s e c o n d o r d e r e f f e ct s i n th e h y d r o x y l b a n d s , w i ll n o t

    b e s e e n i n th e i .r . s p e c t r a . F u r t h e r , X - r a y a n a l y s i s i n

    i t s e lf i s n o t s e n s i t i v e e n o u g h t o l o c a t e a n d d i f f e r e n -

    t ia t e t h e s t r u c t u r a l p o s i t i o n s o f t h e h y d r o g e n a t o m s .

    E a r l i e r c o n c l u s i o n s r e g a r d i n g t h e p o s i t i o n s o f t h e

    h y d r o g e n s w e r e b a s e d o n i n d i r e c t i n f o r m a t i o n i n

    X - r a y s t u d i e s .

    T h e e x c h a n g e o f s o d i u m f o r h y d r o g e n i o n s i n -

    d u c e d b y s t e a m i n g a p p e a r s t o p r o d u c e t h e s a m e

    t y p e o f p r o d u c t a s t h e t h e r m a l a c t i v a t i o n o f t h e c o r -

    r e s p o n d i n g N H 4 f o r m . B a s e d o n s i m i la r it i es i n t h e

    e . s . r , s p e c t r a , a s i m i l a r m e c h a n i s m f o r t h e f o r m a -

    t i o n o f h y d r o g e n a n d i t s s t a b i l i z a t i o n i n t h e z e o l i t e

    s t r u c t u re a p p e a r s t o o p e r a t e a l s o i n th e c a s e o f t h e

    N H 4 f a u j a s i t e s d u r i n g t h e i r t h e r m a l a c t i v a t i o n .

    H o w e v e r , b o t h t h e w i d t h o f th e e . s .r , l i ne s a n d

    h y p e r f in e s p l it ti n g c o n s t a n t s w e r e f o u n d t o b e

    s t r o n g l y d e p e n d e n t o n t h e a c t i v a t i o n t e m p e r a t u r e

    a n d p u r i t y o f t h e z e o l i t e c r y s t a l s . A d e t a i l e d d i s c u s -

    s i o n o f t h e e . s . r , s p e c t r a o f a t o m i c h y d r o g e n i n

    s y n t h e t i c f a u j a s i t e s w i l l b e p r e s e n t e d e l s e w h e r e

    ( S t am i r e s , i n p r e ss ) . H o w e v e r , i t i s w o r t h m e n t i o n -

    i n g h e r e t h a t h y d r o g e n i n t h e h i g h s i l ic a s a m p l e s i s

    s t ab i l i z ed i n t he sm a l l e r c av i t i e s ( soda l i t e un i t s ) .

    D u e t o t h e r e l a t i v e l y w e a k e l e c t r i c f i e l d a n d l a r g e

    s e p a r a t i o n b e t w e e n t h e A 1 0 4 /., )- u n i t s , t h e h y d r o g e n

    i n th i s e n v i r o n m e n t i s c o n s i d e r a b l y l e s s c h e m i c a l ly

    r e a c t i v e . I n c o n t r a s t , h y d r o g e n t r a p p e d i n t h e

    s u p e r c a g e s o f th e h i g h - a lu m i n a m e m b e r s o f t h e

    s e r i e s i s m o r e r e a c t i v e a n d i s r e s p o n s i b l e f o r t h e

    d e s t r u c t i o n o f t h e c r y s t a l . I n s a m p l e s w i t h i n t e r -

    m e d i a t e o r l o w A 1 c o n t e n t , s o m e o f t h e N a a n d

    p r o b a b l y t h e p r o t o n s c a n b e s t a b i l i z e d i n t h e s m a l l

    c a v i t i e s ; t h u s , s o m e o f t h e c r y s t a l l i n i t y is r e t a in e d .

    I n o t h e r c a s e s , w h e n t h e h y d r o l y z e d z e o l i te i s in

    p h y s i c a l c o n t a c t w i t h a n o t h e r a l u m i n o - s i l i c a t e

    p h a s e , s u c h a s k a o l i n i t e o r h a l l o y s i t e , b o t h t h e e x -

    c e s s s o d i u m a n d h y d r o g e n p r o b a b l y d i f f us e a n d b e -

    c o m e s t a b i l i z e d i n t h e n o n - z e o l i t e p h a s e . T h e s e

    e f f e c t s , w h i c h p r o b a b l y i n v o l v e i o n e x c h a n g e , d i f fu -

    s i o n a n d h y d r o l y s i s i n t h e s o l i d s t a t e , a r e e n h a n c e d

    b y t h e h y d r o t h e r m a l c o n d i t i o n s . T h i s c h a n g e i n

    r e a c t i v i t y i s i l l u s t r a t e d b y t h e v a r i a t i o n w i t h A I -

    c o n t e n t o f th e s t e a m s t a b i li t y c u r v e . T h e s u b s t i t u -

    t i o n o f S i f o r A 1 i n t h e s t r u c t u r e r e s u l t s i n a g r a d u a l

    i n c r e a s e o f s t e a m s t a b i li t y o f t h e z e o l i t e s a m p l e s , a s

    s h o w n i n F i g . 1 . S i m i l a r b e h a v i o r i s t o b e e x p e c t e d

    i n t h e v a r i a t i o n w i t h A l - c o n t e n t o f t h e t h e r m a l s t a -

    b i l i t y o f t h e N H 4 * - e x c h a n g e d f a u j a s i t e s e r i e s .

    onic conduction

    S t a m i r e s ( 1 9 6 0 , 1 9 6 2 ) ; F r e e m a n a n d S t a m i r e s

    (1 96 1 ) ; S c h o o n h e y d t a n d U y t t e r h o e v e n (1 96 9) h a v e

    s h o w n t h a t t h e c u r r e n t - c a r r y i n g s p e c i e s i n s y n t h e t ic

    z e o l i t e s a r e c a t i o n s m i g r a t i n g i n t h e s t r u c t u r e b y a

    j u m p m e c h a n i s m . F u r t h e r , t h e a c t i v at i o n e n e r g y

    f o r c o n d u c t i o n i s d u e t o th e e l e c t r o s t a t i c i n t e r a c t i o n

    of t he ca t i on wi th i t s s i t e i n t he a lum ino- - s i l i c a t e

    f r a m e w o r k . T h i s s i t u a t i o n i s p a r t i c u l a r l y a p p l i c a b l e

    i n c a s e s w h e r e a r e l a t i v e l y s m a l l i o n ( f o r e x a m p l e ,

    N a ) , i s l o c a t e d i n a n o p e n f r a m e w o r k w h i c h h a s a

    v e r y m i n o r s t e r i c e f f e c t o n t h e m i g r a t i o n o f t h e c a -

    t i o n in t h a t s t r u c t u r e . S i n c e t h e n e g a t i v e c h a r g e o f a

    c a t i o n s i t e m u s t b e d i s t r i b u t e d o v e r t h e o x y g e n s

    b o u n d t o a g i v e n a l u m i n u m , t h e g e o m e t r i c a l c o n -

    f i g u r a t i o n o f t h e c a t i o n / c a t i o n - s i t e p a i r d e t e r m i n e s

    t h e m a g n i t u d e o f t h e c o u l o m b i c i n t e r a c t i o n . I n t h i s

    c a s e , t h e c o n f i g u r a t i o n s h o u l d b e a n i s o t r o p i c w i t h

    r e s p e c t t o t h e u n i t c e l l d i a g o n a l .

    F r o m X - r a y i n v e s ti g a t io n s ( B r o u s s a r d a n d

    S h o e m a k e r , 1 96 0 ; B r e c k , 1 96 4 ) i t h a s b e e n e s t a b -

    l i sh e d t h a t t h e s o d i u m i o n s i n f a u j a s i t e h a v e a t l e a s t

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    5/11

    Zeoli te , faujas i te , subst i tut ional ser ies : a review with new d ata

    383

    t w o d i f f e r e n t c r y s t a l l o g r a p h i c p o s i t i o n s . F o r e x a m -

    p l e , in h i g h - A l - f a u j a s i t e s , 1 6 N a i o n s a r e l o c a t e d

    w i t h i n t h e h e x a g o n a l p r i s m s [ t y p e ( i ) ] o f t h e

    d o u b l e -5 m e m b e r o x y g e n r in g s , a n d 3 2 N a i o n s a r e

    a s s o c i a t e d w i t h t h e s i n g le - 6 m e m b e r o x y g e n r i n g s

    [ t y p e ( ii )] . T h e r e s t o f t h e N a i o n s h a v e b e e n a s -

    s u m e d t o r e s i d e o n t h e s u r f a c e o f t h e l a r g e c a v i t i e s ,

    p r o b a b l y a s s o c i a t e d w it h t h e fo u r m e m b e r o x y g e n

    r i n g s [ t y p e ( i i i ) ] . S i m p l e e l e c t r o s t a t i c c a l c u l a t i o n s

    r e v e a l * t h a t i o n - f r a m e w o r k c o u l o m b i c i n t e r a c t i o n s

    f o r s o d i u m i o n s l o c a t e d i n th e s e t h r e e d i s c r e t e c r y s -

    t a l l o g r a p h i c l o c a t i o n s ( s p e c i f i c a l ly , t h e i n t e r a c t i o n

    o f an N a i o n a s s o c i a t e d w i t h a d o u b l e 6 - m e m b e r o x -

    y g e n r i n g , a s i n g l e 5 - m e m b e r r i n g a n d a 4 - m e m b e r

    o x y g e n r i n g ) s h o u l d b e c o n s i d e r a b l y d i ff e r e n t

    ( D e m p s e y , 1 9 6 8 ) .

    B y s y n t h e s i s o f a s e r i e s o f z e o l i t e s , t h e c a t i o n

    d e n s i t y c a n b e u n i f o r m l y d e c r e a s e d b y d e c r e a s e i n

    t h e A 1 s u b s t i t u t i o n . I n t h i s w a y , t h e c a t i o n p o p u l a -

    t i o n o f o n e o r m o r e o f t h e t h r e e c a t i o n s i t e s m e n -

    t i o n e d a b o v e c a n b e p r e f e r e n t i a l l y d e p l e t e d . A c o r -

    r e s p o n d i n g v a r i a t i o n s h o u l d o c c u r i n t h e a c t i v a t i o n

    e n e r g y r e q u i r e d f o r t h e o v e r a l l c o n d u c t i o n p r o c e s s .

    B r i e fl y , N a i o n s l o c a t e d o n t h e s u r f a c e o f t h e l a r g e

    c a v i t i e s ( a s s o c i a t e d w i t h t h e 4 - m e m b e r o x y g e n

    r i n g s ) a r e t h e l e a s t s t r o n g l y b o u n d a n d w i l l t h e r e -

    f o r e r e q u i r e t h e l e a s t a m o u n t o f e n e r g y t o m i g r a t e .

    I n z e o l i t e s w i t h h i g h c a t i o n d e n s i t i e s , t h e r a t e d e t e r -

    m i n i n g p r o c e s s f o r t h e m i g r a t i o n o f th e c u r r e n t c a r -

    r i e r s i n a n e x t e r n a l e l e c t r i c f ie l d i s d u e t o s u c h

    w e a k l y b o u n d c a t i o n s . A s t h e c a t i o n d e n s i t y i s

    d e c r e a s e d t o w a r d s t h e h i g h s i li c a e n d o f th e s e r i e s ,

    t h e l o w e n e r g y c a t i o n s i t e s a r e d e p l e t e d , a n d t h e

    m o r e s t r o n g l y b o u n d c a t i o n s s t a r t t o c o n t r i b u t e a n d

    h e n c e d e t e r m i n e t h e r a te o f t h e c o n d u c t i o n p r o c e s s .

    C o n s e q u e n t l y , t h e c h a n g e i n t h e a c t i v a t i o n e n e r g y

    f o r c o n d u c t i o n i s a d i r e c t m e a s u r e o f t h e d i f f e r -

    e n c e s i n t h e e n e r g y a s s o c i a t e d w i t h t h e d i f f e r e n t

    k i n d s o f c a t i o n / c a t i o n - s i t e p a i rs .

    *A s implified model of the locat ion of ca t ions in the unit

    cell is considered ; namely, the associat ion of Na ions with

    double 5-member oxygen r ings, s ingle 5-member o xygen

    r ings and 4-member oxygen r ings . However , project ion

    through the sodali te unit and the supercage results in

    actua l sites of type. ( i) and (ii) , locate d within th e sod alite

    unit. Typ e ( i) located in th e hex agonal pr ism, typ e ( i i) lo-

    cated in the supercage an d ty pe ( i i i) a lso in the supercage.

    In par t icular , we are concerne d here with th e dif ference in

    the bon ding energy of the Na ions in the type ( i i i) locat ion

    which is the leas t s table posi t ion (due mainly to the v ery

    small coulombic interact ion) as compared to the bonding

    energy at th e typ e ( i) and ( ii ) s i tes which are consid erably

    more s table , with higher energy of interact ion.

    tThis pr obably i s the aver age of the ind iv idua l cont r ibu-

    t ions , such as coulom bic, repuls ive, polar izat ion and small

    amounts due to steric effects.

    I n z e o l i t e s w i t h lo w c a t i o n d e n s i t i e s , t h e N a i o n s

    a r e p r i m a r i l y a s s o c i a t e d w i t h t h e s i n g l e a n d d o u b l e

    6 - m e m b e r o x y g e n r i n g s ; t h e r e f o r e , t h e a c t i v a t i o n

    e n e r g y i s c o n s i d e r a b l y h i g h e r . T h i s s i t u a t i o n w a s

    s h o w n i n t h e r e s u l t s p u b l i s h e d e a r l i e r ( s e e F i g . 3, o f

    F r e e m a n a n d S t a m i r e s , 1 96 1) w h i c h i l l u s t ra t e t h e

    u n i f o r m c h a n g e i n e n e r g y t a s s o c i a t e d w i t h

    c a t i o n / c a t i o n - s i t e p a i r s a m o n g t h e d i f f e re n t c r y s t a l -

    l o g r a p h i c s i t e s . I t w a s o n t h i s b a s i s t h a t a p h y s i c a l

    m o d e l w a s d e v e l o p e d a n d o n p u r e l y e n e r g e t ic c o n -

    s i d e r a t i o n s i t w a s p o s s i b l e t o d i f f e r e n t i a t e t h e

    c a t i o n s i n t h e s y n t h e t i c f a u j a s i t e i n t o t h r e e t y p e s .

    H o w e v e r , B r e c k ( 1 9 6 4 ) a n d B r e c k a n d F l a n i g e n

    (1 96 8) h a v e c o n c l u d e d t h a t t h e s e d a t a p r o v i d e e v i -

    d e n c e f o r d i v i d i n g t h e s u b s t i t u t i o n a l s e r i e s a t a n

    S / A o f t h r e e i n t o t w o s u b - g r o u p s , d e s i g n a t e d a s X

    a n d Y . I n f a c t , t h e r e i s a s m o o t h v a r i a t i o n in t h e

    a c t i v a t i o n e n e r g y w i t h S / A , w i t h n o d e t e c t a b l e d i s -

    c o n t i n u i t y . T h e i n f le c t i o n p o i n t ( t h e p o i n t w h e r e t h e

    a c t i v a t i o n e n e r g y c h a n g e s m o s t d r a s t i c a l l y w i t h c a -

    t i o n d e n s i t y ) i n t h e c o n d u c t i v i t y - A 1 c o n t e n t p l o t i s

    c l o s e t o a n S / A o f 4 , n o t 3 . T h i s p o i n t i s c o n v i n c -

    i n g l y i l l u s t r a t e d i f t h e f i r s t d e r i v a t i v e o f t h e a c t i v a -

    t i o n e n e r g y i s p l o t t e d a g a i n s t t h e S / A .

    I n F i g . 2 th e a c t i v a t i o n e n e r g y ( A H ) a n d i t s fi rs t

    d e r i v a t i v e a r e p l o t t e d a g a i n s t S / A . T h e a r b i t r a r y d i -

    v i s i o n a t a r a t i o o f 3 i s a l s o i n d i c a t e d . T h e s e d a t a

    c l e a r l y s h o w t h a t s u c h a d i v i s i o n i s n o t j u s t i f i e d .

    3 0

    d [ ~ H l

    2 .O

    0 . 2

    0

    No

    Fig. 2. Faujas i te conductivi ty as a function of

    s i l ica-alum ina rat io, Freem an an d Stamires (1961). The

    broken l ine represents the plot of the f ir s t der ivat ive of

    (AH) w ith respec t to SiOJA1203 mole rat io.

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    384

    DENNIS N STAMIRES

    F u r t h e r m o r e , t h e d is t in c t io n o f X f r o m Y a s t w o

    d i f f e r e n t z e o l i t e s p e c i e s w h e r e X a n d Y r e f e r t o

    c o m p o s i t i o n a l r a n g e s ) , c e r ta i n l y i s n o t s u g g e s t e d b y

    t h e r e s u lt s . I f o n e h a d t o u s e t h e c o n d u c t i v i t y d a t a

    t o d i v i d e a r b i tr a r i l y t h e s e r i e s i n t o t w o g r o u p s , t h e n

    a n S / A o f a p p r o x i m a t e l y 4 w o u l d b e a l o g i c a l

    c h o i c e , s i n c e i n t h i s r e g i o n t h e c o n d u c t i o n p r o c e s s

    c h a n g e s m o s t d r a s t i c a l l y w i t h c a t i o n d e n s i t y .

    A s i n t h e c a s e o f s t e a m s t a b i l i t y , t h e e l e c t r o n i c

    p r o p e r t i e s o f s y n t h e t i c f a u j a s i t e s a l s o v a r y

    u n i f o r m l y a n d c o n t i n u o u s l y w i t h c o m p o s i t i o n .

    Adsorp t ion proper t i es

    A m o s t i m p o r t a n t p r o p e r t y , w h i c h h a s b e e n u s e d

    e x t e n s i v e l y t o c h a r a c t e r i z e t h e v a r i o u s z e o l i t e

    s p e c i e s , is th e a d s o r p t i o n o f g a s e s a n d v a p o r s .

    T r i e t h y l a m i n e a d s o r p t i o n h a s b e e n u s e d b y B r e c k

    t o d i s t i n g u i s h c a l c i u m - e x c h a n g e d Z e o l i t e X f r o m

    s i m i la r l y t r e a t e d Z e o l i te Y . F u r t h e r , W r i g h t , R u p e r t

    a n d G r a n q u i s t 1 9 69 ), h e r e a f t e r r e f e r r e d t o a s

    W R G , h a v e r e p o r t e d s i m il ar e x p e r i m e n t s u s i n g t h e

    N a f o r m s o f t w o s y n t h e t i c f a u j a s i t e s w i t h S / A o f

    2 .4 and 4 .8 .

    I n th e p r e s e n t w o r k , t h e m e a s u r e m e n t s h a v e

    b e e n e x t e n d e d t o c o v e r t h e w h o l e r an g e o f S / A a n d

    t o i n c l u d e a s a m p l e o f n a t u r a l f a u j a s i t e i n i t s

    s o d i u m f o r m . E q u i l ib r i u m d a t a w e r e o b t a i n e d f r o m

    e x p e r i m e n t s w h e r e t h e a d s o r p t i o n o f t r i e th y l a m i n e

    a t r o o m t e m p e r a t u r e w a s m e a s u r e d a s a f u n c t i o n o f

    v a p o r p r e s s u r e . E q u i l i b r iu m w a s r e a c h e d , a t t h e

    l o w e r v a p o r p r e s s u r e s , a f t e r 8 - 1 0 h r . I n o r d e r t o

    c o m p a r e

    W R G

    a n d p r e s e n t r e s u l t s , t h e s a m e e x -

    p e r i m e n t a l c o n d i t i o n s w e r e u s e d . T h e d a t a a r e

    c r o s s - p l o t t e d i n F i g . 3 . A l l t h e s a m p l e s s t u d i e d a d -

    s o r b e d a b o u t t h e s a m e a m o u n t o f tr i e th y l a m i n e ,

    w i t h i n e x p e r i m e n t a l e r r o r . S i n c e t h e s i z e o f t h e u n i t

    c e l l d e c r e a s e s w i t h S / A , a d s o r p t i o n w o u l d b e e x -

    p e c t e d t o d e c r e a s e w i th i n c r e as i n g S / A . P r o b a b l y

    t h e v a r i a t i o n i n t h e n u m b e r a n d d i s t r i b u t i o n o f t h e

    c a t i o n s i n t h e u n i t ce l l o f f s e t s t h i s t re n d . T h e i m p o r -

    t a n t p o i n t t o n o t e h e r e i s t h a t a l l t h e s a m p l e s , i n c l u d -

    i n g n a t u r a l f a u j a s i t e , s h o w w i t h i n e x p e r i m e n t a l

    e r r o r) a b o u t t h e s a m e a d s o r p t i v e c a p a c i t y . T h e tw o

    m e a s u r e m e n t s r e p o r t e d e a r l ie r b y W R G a r e i n

    a g r e e m e n t w i t h t h e p r e s e n t r e s u l t s .

    A c c o r d i n g l y , a d i v i s i o n b a s e d o n t h e a d s o r p t i o n

    o f t r ie t h y l a m i n e o f t h e s u b s t i t u t i o n a l s e r i e s a t a n y

    S / A i n t h e r a n g e 2 - 6 i s n o t j u s t i f i a b l e . F u r t h e r ,

    n a t u r a l f a u j a s i t e c a n n o t b e d i s t i n g u i s h e d a s a d i f fe r -

    e n t t y p e o f z e o l i t e o n t h e b a s i s o f s u c h d a t a . S i m i -

    l a r ly , t h e a d s o r p t i v e c a p a c i t i e s o f th e s u b s t i t u t io n a l

    s e r i e s a n d n a t u r a l f a u j a s i t e f o r o x y g e n a n d w a t e r a t

    - 1 8 3 ~ a n d a t r o o m t e m p e r a t u r e re s p e c t i v e l y a t

    t h e s a m e v a p o r p r e s s u r e s ) , w i t h in t h e e x p e r i m e n t a l

    R E S E N T D T

    D N A T U R A L F A U J A S I T E

    s ~ o

    ~ - ~ . . . . . . . . o )

    Fig. 3. Equilibrium capa city for triethylamine adsorption

    at 3 tort and ro om temperature as a function o f the

    SiO2/A1203mo le ratio.

    e r r o r , w e r e f o u n d t o b e a b o u t t h e s a m e . T h u s , t h e

    p o r e v o l u m e , a s i n d i c a t e d b y t h e s e a d s o r p t i v e

    c a p a c i t i e s , i s a b o u t t h e s a m e i n t h e s y n t h e t i c a n d

    n a t u r a l m e m b e r s o f t h e f a u j a s i t e g r o u p .

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    p h y s i c o c h e m i c a l p r o p e r t i e s o f t h e s u b s t i t u t i o n a l

    s e ri e s o f f a u ja s i te s t o u s e t h e s a m e h o m o c a t i o n i c

    f o r m s i n t h e e x p e r im e n t s . T h e t y p e o f c a t i o n s i ze s

    a n d c h a r g e ) a n d t h e p e r c e n t e x c h a n g e a f f e c t d r a s t i -

    c a l l y t h e a d s o r p t i o n c h a r a c t e r i s t i c s o f t h e z e o l i t e

    c r y s t a l s . T h e d a t a p r e s e n t e d b y B r e c k 1 9 64 ) o n th e

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    s t r u c tu r e h a s b e e n d i s c u s s e d b y B r e c k 1 96 4). F r o m

    s i m p le g e o m e t r i c a l c o n s i d e r a t io n s o f t h e S i - O a n d

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    a n d F l a n i g e n 1 9 68 ), h e r e a f t e r r e f e r r e d t o a s B F

    w h o e x a m i n e d 3 7 s a m p l e s o f s y n t h e t i c f a u j a s i te s o f

    v a r y i n g S / A . T h e y h a v e s h o w n b y a l e a s t s q u a r e f it

    t h a t a v a r i e s l i n e a r ly w i t h t h e n u m b e r o f A 1 a t o m s

    in t he un i t c e l l . B F r e p o r t e d a n e x p e r i m e n t a l e r r o r

  • 7/23/2019 Zeolite faujasite

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    Zeoli te , faujas i te , subst i tut ional

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    a l u m i n a c o n t e n t s .

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    s y n t h e t i c fa u j a s i t e s s y n t h e s i z e d f r o m h y d r o u s

    s o d i u m s y s t e m s s i m i la r t o t h o s e u s e d b y B F . T h e

    e s t i m a t e d p r o b a b l e e r r o r in t h e d a t a o f W R G w a s

    + 0 . 0 1 i n a a n d - +- 0.0 0 5 ~ i n t h e m o l e f r a c t i o n o f

    A I O 2- . I n t h e p a p e r o f F r e e m a n a n d S t a m i r e s

    ( 19 6 1 ), s e v e r a l a v a l u e s w e r e a l s o g i v e n f o r s y n t h e -

    t i c f a u j a s i t e s . T h e s e d a t a w e r e o b t a i n e d i n t h e v e r y

    e a r l y s t a g e s o f f a u j a s i t e s y n t h e s i s a n d t h e t e c h n i -

    q u e s f o r a a n d S / A d e t e r m i n a t i o n w e r e n o t y e t w e l l

    r e f i n e d ; t h e r e f o r e , t h e e x p e r i m e n t a l e r r o r w a s

    l a r g e r , c l o s e t o - 4 :0 . 2 i n t h e S / A v a l u e s .

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    t h e r e s u l ts o f t h e s e f o u r i n d e p e n d e n t g r o u p s . T h e s e

    s t u d i e s r e p r e s e n t w o r k d o n e o v e r a t l e a s t t h e l a s t

    1 0 y r , w i t h v a r i o u s a n a l y t i c a l t e c h n i q u e s a n d l e v e l s

    o f s o p h i s t i c a t i o n .

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    ( 1 9 6 8 ) r e p o r t e d p r e c i s i o n

    m e t h o d s f o r d e t e r m i n i n g a w h i c h a r e u s e d

    r o u t i n e l y t o i d e n t i f y f a u j a s i t e s a m p l e s .

    B F a l s o p r e s e n t e d d a t a o n a v a l u e s o f d e h y d -

    r a t e d c a l c i u m - e x c h a n g e d s y n t h e t i c f a u ja s i t e s . I n

    c o n t r a s t t o t h e h y d r a t e d s o d i u m f o r m s , a i n t h i s

    c a s e d i d n o t v a r y l i n e a r l y w i t h S / A , a n d t h e d a t a

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    385

    d i s p l a y e d t w o d i s c o n t in u i t e s , a t a p p r o x i m a t e l y 6 2

    a n d 7 7 A 1 p e r u n i t c e l l. T h e s e d i s c o n t i n u i t i e s w e r e

    i n t e r p r e t e d b y B F a s d u e t o f r a m e w o r k d i s t o r t i o n

    a s s o c i a t e d w i t h m o v e m e n t o f C a i on s . D e h y d r a t i o n

    c a u s e s t h e c a l c i u m i o n s t o m o v e t o s t r u c t u r a l p o s i -

    t i o n s w h i c h a r e m o r e f a v o r a b l e e n e r g e t i c a l l y . T h e

    m e c h a n i s m r e s p o n s i b l e f o r th e s e d i s c o n t i n u i t i e s

    m a y b e m u c h m o r e c o m p l i c a t e d t h a n d e s c r i b e d ,

    s i n c e t h e s a m p l e s c o n t a i n e d a p p r e c i a b l e a m o u n t s

    o f r e s i d u a l N a , a n d s i n c e h e a t i n g i n a i r a t 40 0 ~ i s

    n o t t h e b e s t w a y t o a c t i v a t e c a l c i u m - e x c h a n g e d

    z e o l i t e s . A l s o , if a v a l u e s f o r N a a n d C a f o r m s o f

    t h e s a m e s a m p l e s a r e c o m p a r e d , a a l s o c h a n g e s a s

    N a i s e x c h a n g e d f o r C a i n s a m p l e s c o n t a i n i n g t h e

    s a m e a m o u n t o f A 1. T h i s d e p e n d e n c y i n t r o d u c e s

    a n o t h e r v a r i a b l e , d e g r e e o f i o n e x c h a n g e , i n t o t h e

    d e t e r m i n a t i o n o f a . H o w e v e r , t h e i m p o r t a n t f a c t o r

    t o b e n o t e d h e r e i s t h a t t h e t e c h n i q u e s u s e d b y

    B F

    w e r e s e n s i t i v e a n d q u i t e r e l i a b l e i n o r d e r t o b e a b l e

    t o e s t a b l i s h t h e s e d i f f e r e n c e s i n th e a v a l u e s .

    D e s p i t e t h e a g r e e m e n t s h o w n i n F i g . 4 , a c o m p l i -

    c a t i o n i s i n t r o d u c e d b y t h e r e s u l t s o f D e m p s e y ,

    K f i h l a n d O l s o n ( 1 96 9 ), h e r e a f t e r r e f e r r e d t o a s

    D K O w h o h a v e a l s o s t u d i e d t h e v a r i a t i o n o f a w i t h

    A I c o n t e n t f o r h y d r a t e d N a - f a u j a s i t e . I n c o n t r a s t t o

    a l l p r e v i o u s l y p u b l i s h e d d a t a , D K O f o u n d t h r e e

    d i s c o n t i n u i t i e s i n a , n e a r 5 2 , 64 , a n d 8 0 A 1 a t o m s p e r

    u n i t c e l l . D K O s u g g e s t e d t h a t a t l e a s t t h r e e d i f f e r-

    e n t f a u j a s i t e p h a s e s e x i s t i n t h e S / A r a n g e s t u d i e d .

    T h e d i s c o n t i n u i ty o b s e r v e d a t t h e h i g h e s t S i co n -

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    in the hydra ted sodium (homocationic) form . Data o f Breck and Flanigen (1968) ; Wright , Ruper t and

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    are shown enclosed in a c ircle for em phasis .

  • 7/23/2019 Zeolite faujasite

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    386 DENNIS N.

    a m o r p h o u s s il ic a o c c l u d e d i n t h e s a m p l e s . DKO d o

    n o t d e s c r i b e t h e t e c h n i q u e s u s e d i n s y n t h e s i z i n g

    t h e ir s a m p l e s . H o w e v e r , i f th e y u s e d t h e t e a c h i n g s

    o f B a r r e r ( 1 9 59 ) a n d B r e c k ( 19 6 4) f o r t h e s y n t h e s i s

    o f f a u ja s i te s , t h e n t h e i r d a ta w o u l d b e e x p e c t e d t o

    be s im i l a r t o t he r e su l t s , i n F ig . 4 , o f BF WRG a n d

    t h e p r e s e n t p a p e r . F u r t h e r , i t i s h i g h l y i m p r o b a b l e

    t h a t t h e i r o b s e r v e d d i s c o n t i n u i t i e s r e p r e s e n t e x p e r i -

    m e n t a l a r t i f a c t s . T h e s e i r r e g u l a r i t i e s p r o b a b l y r e -

    p r e s e n t r e a l e ff e c t s c h a r a c t e r i s t i c o f t h e n a t u r e o f

    t h e DKO s a m p l e s . I n t h e a b s e n c e o f a d d i t io n a l i n -

    f o r m a t i o n , i t m u s t b e c o n c l u d e d t h a t t h i s d i s c r e -

    p a n c y i s d u e t o d i f f e r e n c e s i n t h e

    DKO

    s a m p l e s

    c a u s e d b y v a r i a t i o n s i n s y n t h e s i s a n d p r e p a r a t i o n

    t e c h n i q u e s .

    DKO e x p l a i n t h e s e d i s c o n t i n u i t e s o n t h e b a s i s o f

    v a r i a t i o n s i n ( St, A 1 ) o r d e r i n g . S i n c e s u c h o r d e r i n g

    w i l l t e n d t o d e c r e a s e a , t h e f a c t t h a t a l l t h e

    DKO

    d a t a l i e b e l o w t h e s t r a i g h t l i n e o f F i g . 4 s u g g e s t s

    t h a t th e s a m p l e s u s e d b y BF WRG a n d t h e p r e s e n t

    a u t h o r c o r r e s p o n d t o h i g h e r ( S i, A I ) o r d e r i n g .

    F u r t h e r , t h e a d a t a i n d i c a t e t h a t n a t u r a l f a u j a s i t e

    h a s t h e h i g h e s t o r d e r . T h r e e p r e v i o u s l y r e p o r t e d

    v a l u e s o f a f o r t h e n a t u r a l m i n e r a l a n d t h e p r e s e n t

    m e a s u r e m e n t a r e s h o w n i n F i g . 4 . T h e p r e s e n t r e -

    s u l t w a s o b t a i n e d o n h y d r a t e d h o m o c a t i o n i c

    N a - f a u j a s i t e c r y s t a l s w h i c h w e r e u s e d i n th e o t h e r

    e x p e r i m e n t s d e s c r i b e d i n t h is p a p e r . S / A w a s f o u n d

    t o b e 4 . 5 5 - + 0 . 0 1 a n d t h e c u b i c l a t t i c e p a r a m e t e r a ,

    2 4- 66 _+ 0 . 0 0 5 . ~; t h e s e v a l u e s w e r e e s t a b l i s h e d a f t e r

    s e v e r a l d e t e r m i n a t i o n s . T h e s e v a l u e s a r e v e r y c l o s e

    t o t h o s e o f

    BF

    a n d B e n n e t t a n d S m i t h ( 1 9 7 2 ) . A l l

    f o u r v a l u e s a r e p r e s e n t e d i n F i g . 4 , e n c l o s e d i n a

    c i rc l e f o r e m p h a s i s . T h e BF v a l u e o f a l i e s c l o s e t o

    t h e s t r a i g h t li n e o b t a i n e d f r o m t h e a v a l u e s f o r t h e

    s y n t h e t i c s a m p l e s . I n a l l c a s e s , t h e n a t u r a l c r y s t a l s

    a p p e a r t o b e m o r e ( S t, A 1 ) o r d e r e d t h a n t h e s y n t h e -

    t i c m a t e r i a l , p r o b a b l y d u e t o m o r e i d e a l n a t u r a l

    g r o w t h c o n d i t io n s . A l t h o u g h r e a s o n a b l e , t h e r e i s n o

    d i r e c t e x p e r i m e n t a l e v i d e n c e t o s u b s t a n t i a t e t h i s

    p o s t u l a t e d o r d e r i n g .

    T h e a v a l u e s s h o w n i n F i g . 4 r e p r e s e n t a b o u t 6 0

    s a m p l e s s y n t h e s i z e d a n d a n a l y z e d i n d e p e n d e n t l y

    b y f o u r o r f iv e g r o u p s o f w o r k e r s a t d i f f er e n t t im e s .

    I t c a n b e c o n c l u d e d t h a t w h e n f a u j a s i t e s a r e s y n -

    t h e s i z e d b y s t a n d a r d p r o c e d u r e s ( B a r r e r , t 9 5 9 ,

    B r e c k , 1 9 64 ), t h e n t h e a v a l u e s v a r y l in e a r l y a n d

    c o r r e l a t e q u i t e w e l l w i t h t h e a l u m i n u m c o n t e n t o f

    t h e c r y s ta l s . T w o o u t o f th e f o u r r e p o r t e d v a l u e s o f

    a f o r n a t u r a l f a u j a s i t e a r e , w i t h i n t h e e x p e r i m e n t a l

    e r r o r , c l o s e t o t h e s t r a i g h t l i n e o b t a i n e d f o r t h e

    s y n t h e t i c s a m p l e s . N e v e r t h e l e s s , t o a f i r s t o r d e r

    a p p r o x i m a t i o n i n s o f a r a s t h e v a r i a t i o n o f a w i t h A 1

    c o n t e n t i s c o n c e r n e d , i t c a n b e c o n c l u d e d t h a t t h e

    ST MIRES

    d i f fe r e n c e b e t w e e n n a t u r a l a n d s y n t h e t i c s a m p l e s i s

    qu i t e sm a l l .

    T h e l o c a t i o n o f t h e c h a r g e - b a l a n c i n g c a t i o n s i n

    t h e s t r u c t u r e , t h e ( S t , A 1 ) o r d e r i n g , a n d t h e d i s t r i b u -

    t io n o f t h e a d s o r b e d m o l e c u l e s m a y b e d i f f e re n t i n

    t h e n a t u r a l a n d s y n t h e t i c s a m p l e s .

    F r o m a s t a t i s t i c a l p o i n t o f v i e w , t h e d a t a p r e -

    sen t ed i n F ig . 4 (pa r t i cu l a r l y t he

    BF

    a n d p r e s e n t r e -

    s u l t s ) a p p e a r t o b e i n a c c o r d . D e s p i t e t h i s a c c o r d ,

    t h e c o n f l i c t in g DKO r e s u l t s s h o w t h a t t h e v a r i a t i o n

    o f a w i t h c o m p o s i t i o n i s n o t a c l o s e d i ss u e . F u r t h e r

    e x p l o r a t i o n i s n e c e s s a r y t o y i e l d a d e f i n i t i v e

    a n s w e r .

    Catalytic properties

    C a t a l y t ic b e h a v i o r , a l t h o u g h c o m p l i c a t e d t o a s -

    c e r t a i n , is a n o t h e r c h a r a c t e r i s t i c p r o p e r t y o f t h e

    s u b s t i t u t i o n a l s e r i e s . T h e m a i n f a c t o r s w h i c h d e t e r -

    m i n e t h e p e r f o r m a n c e o f a z e o l i t e c a t a l y s t a r e :

    s i l i c a - a l u m i n a r a t i o ; p e r c e n t e x c h a n g e a n d n a t u r e

    o f th e e x c h a n g e c a t i o n ; m e t h o d o f p r e p a r a t i o n ; a n d

    t y p e o f m a t r i x ( t h e z e o l i t e i s u s u a l l y c o n t a i n e d i n

    s u p p o r t i n g m a t r i x ) . G o o d c a t a l y s t s h a v e b e e n p r e -

    p a r e d f r o m f a u j a s i t e s w i t h b o t h h i g h - a n d l o w - A 1

    c o n t e n t s .

    K i m b e r l i n a n d G l a d r o w ( 1 9 6 1 ) d e m o n s t r a t e d e x -

    c e l l e n t c a t a l y t i c p r o p e r t i e s o f z e o l i t i c c a t a l y s t s

    u s i n g s y n t h e t i c f a u j a s i t e w i t h S / A o f 2 . 7 . S u b s e -

    q u e n t l y , R a b o et al. (1966) pub l i shed r e su l t s on

    c a t a l y t i c p r o p e r t i e s o f s y n t h e t i c f a u j a s i t e s w i t h S / A

    i n t h e r a n g e 3 - 6 , a n d c l a i m e d t h a t t h e c a t a l y t i c

    p r o p e r t i e s o f th e s e z e o l i te s w e r e u n i q u e a n d d i f f e r-

    e n t f r o m t h o s e s t u d ie d b y K i m b e r l i n a n d G l a d r o w

    ( 19 61 ). T h i s a s s e r t i o n w a s i n l in e w i t h B r e c k s c o n -

    c e p t t h a t Y z e o l i t e i s d i f f e r e n t f r o m 3 ( . B o t h o f

    t h e s e g r o u p s o f w o r k e r s f a i le d t o i n d i ca t e t h e p e r -

    c e n t e r r o r i n v o l v e d i n t h e S / A u s e d i n t h e i r c l a im s .

    A s i s s h o w n i n F i g . 5 , t h e c a t a l y t i c a c t i v i t y , f o r

    c r a c k i n g c u m e n e a t 4 0 0~ o f a s er ie s o f M g e x -

    c h a n g e d f a u j a s i t e c a t a l y s t s v a r i e s s m o o t h l y w i t h

    S / A . T h e t e c h n i q u e s u s e d f o r t h e s e c a t a l y t i c m e a s -

    u r e m e n t s w e r e s i m i l a r t o t h o s e o f e a r li e r s t u d i e s

    ( T u r k e v i c h , N o z a k i a n d S t a m i r e s , 1 9 6 4) w h e r e

    o t h e r t y p e s o f z e o li t e c a t a l y s t s w e r e i n v e s t i g a t e d . A

    d i s c u s s i o n o f t h e m e c h a n i s m i n v o l v in g t h e e f fe c t o f

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    t h i s p a p e r a n d w i l l b e p r e s e n t e d e l s e w h e r e ( S t a -

    m i r e s , t o b e p u b l i s h e d ) . T h e i s s u e c o n s i d e r e d h e r e

    i s t h e f a c t t h a t c a t a l y t i c a c t i v i t y f o r c u m e n e c r a c k -

    i n g ( w i t h i n t h e e x p e r i m e n t a l e r r o r ) v a r i e s a l m o s t

    l i n e a r ly w i t h S / A i n t h e r a n g e o f 2 - - 4 . S i m i l a r ly , a

    l i n e a r v a r i a t i o n i s o b s e r v e d i n t h e r a n g e o f 4 - 6 . A l -

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    samples were activated at 450~ prior to catalytic measurements.

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    p r o x i m a t e l y a t S / A o f 4 .

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    t h e o t h e r p r o p e r t i e s d i s c u s s e d e a r l ie r . C a t a l y t i c a c -

    t iv i ty f o r o t h e r t y p e s o f h y d r o c a r b o n r e a c t io n s m a y

    s h o w a d i f f e r e n t t y p e o f d e p e n d e n c e o n t h e S / A ;

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    range i s un l i ke ly .

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    o f c u m e n e .

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    u n r e s o l v e d . A d d i t i o n a l w o r k a t a sti ll h i g h e r l e v e l o f

    soph i s t i c a t i on wi l l be r equ i red fo r a de f in i t i ve

    a n s w e r .

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    l a r h y d r o t h e r m a l t e c h n i q u e s s h o w c o ; n si s te n t a v a l-

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    w i t h t h e a l u m i n u m c o n t e n t o f t h e c r y s t a l s .

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    tha t t he ex i s t i ng a r t i f i c i a l d iv i s ion o f t he f au j a s i t e

    s e r ie s a t a S / A o f 3 b e e l i m i n a t e d , a n d a n e w

    n o m e n c l a t u r e a d o p t e d . T h i s n e w n o m e n c l a t u r e

    s h o u l d b e c a p a b l e o f r e p r e s e n t i n g p r e c i s e l y o n e

    p a r t i c u l a r c o m p o s i t i o n , r a t h e r t h a n t h e w i d e r a n g e

    o f c o m p o s i t io n s e n c o m p a s s e d b y t h e t r ad e n a m e s

    p r e s e n t l y i n u s e . F u r t h e r , t h i s n e w n o m e n c l a t u r e

    , shou ld c l ea r ly r e f l e c t t he ac tua l s im i l a r i t i e s and t he

    s m o o t h g r a d u a l v a r i a t i o n i n t h e m o s t i m p o r t a n t

    p h y s i c o c h e m i c a l p r o p e r ti e s o f t h e c o n t i n u o u s

    se r i e s and t he c lose s im i l a r i t i e s wi th t he i r na tu ra l

    c o u n t e r p a r t f a u j a s i t e .

    S u c h a u n i f o r m s y s t e m f o r n a m i n g t h e v a r i o u s

    z e o l i t e m e m b e r s i n t h e c o n t i n u o u s s u b s t i t u t i o n a l

    f a u j a s i t e s e r i e s c o u l d b e o n e s i m i l a r t o th a t a l r e a d y

    s u g g e s t e d b y W R G .

    R E F E R E N E S

    Barter, R. M., Baynham, J. W., Bulti tude, F. W. and

    Meier, W. M , (1959) Hydrothermal chemistry o f si l i-

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    aluminosil icates and of some gall ium and germanium

    analogues:

    J. Chem. Soc. Lond.)

    195-208.

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    the rm ale , le s pa ram~ tres de r6sea u , le s p ropri6 t6s d 'ads orp t ion e t le s p ropri6 t6s 61ec tr iques e t ca ta ly t t -

    q u e s d ' & h a n t i l l o n s d e f a u ja s i t e s y n th 6 t iq u e e t n a tu re ll e . L e s c o n c e p t s a c tu e l s c o n c e r n a n t l a n a tu re

    e t l e s r e l a t io n s e x i s t a n t e n t r e l a f a u ja s i t e s y n th 6 t iq u e e t l a f a u ja s i t e n a tu re l l e s o n t r e p r i s p o u r 6 t r e e n

    a c c o rd a v e c l e s p re u v e s e x p 6 r im e n ta l e s e t l e m o d u le p h y s iq u e d 6 v e lo p p 6 . L e s p ro p r i6 t6 s s t ru c tu ra l e s

    e t p h y s ic o -c h im iq u e s p r in c ip a le s r e f l~ te n t d e s s im i l i t u d e s & ro i t e s e t d e s g ra d a t io n s r6 g u l ib re s q u e l ' o n

    p e u t a t t e n d re e n t r e d e s t e rm e s d e s u b s t i t u tio n q u i fo rm e n t u n e s 6 ri e c o n t in u e . O n d iv i s e a c tu e l l e -

    m e n t l e d o m a in e d e s r a p p o r t s m o la i r e s S IO 2/A 12 0 3 (S /A ) , q u i s ' 6 t e n d d e 2 ~ t 6 , h l a v a l e u r 3 ; c e t t e

    d iv i s io n e n d e u x s o u s d o m a in e s d e c o m p o s i t io n a p pa ra i't n o n ju st i f i6 e e t r i s q u e p lu t6 t d ' i n d u i re e n

    e r re u r . L e s c o m p o s i t io n s in d iv id u e l l e s p r i s e s d u n s c e s d e u x s o u s d o m a in e s n e r e p r6 s e n te n t p u s d e s

    ty p e s d e z 6 o l i t e s d i s t in c t e m e n t d i f f6 re n t s ; e n r e a l i t 6 , o n d 6 m o n t re q u ' i l s ' a g i t d e t e rm e s d ' u n e s & ie

    c o n t in u e , a v e c d e s p ro p r i6 t6 s c h a n g e a n t g ra d u e l l e m e n t s u r t o u te l ' 6 t e n d u e S iO J A l2 0 3 & u d i6 e . C e r -

    t a in e s d e s p ro p r i& & d e l a f a u ja s i t e n a tu re l l e o n t 6 t6 t ro u v 6 e s t r~ s s e m b la b le s h c e l l e s d ' a n a lo g u e s

    s y n th 6 t iq u e s a y a n t l e m ~ m e ra p p o r t m o la i r e S iO 2 /A 1 2 0. v

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    Z e o l i t e , f a u ja s i t e , s u b s t i t u tio n a l s e r i e s : a r e v ie w w i th n e w d a ta

    F in a le m e n t , o n e x p r im e l e v o e u q u e s o i t c r~ 6e u n e n o m e n c la tu re u n i fo rm e q u i s e rv i r a h id e n t if i e r

    d e s c o m p o s i t io n s s p 6 c i f iq u e s (u n iq u e s ) a u l i e u d e d o m a in e s d e c o m p o s i t io n s ~ r e n d re c o m p te d e l a

    con t inu i tY, des s imil i tudes ~ tro i te s e t des in te rre la t ions da r ts le s p ropri~ t~s s t ruc tu ra les e t phys ico-

    c h im iq u e s p r in c ip a le s A id e n t if i e r ~ g a le m e n t l e s c a ra c t~ r i s tiq u e s d u g ro u p e d e l a f a u ja s i t e .

    389

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    d e r a d s rp t iv e n , e l e k t r i s e h e n u n d k a ta ly t i s c h e n E ig e n s c h a f t e n y o n s y n th e t i s c h e m u n d n a t i i r l i c h e m

    F a u ja s i t w e rd e n m i tg e te i lt . G e g e n w i i r t i g e V o rs t e l lu n g e n , d i e d i e N a tu r u n d d a s V e rh i i l t n is y o n s y n -

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    n i s s e n u n d d e m e n tw o f fe n e n p h y s ik a l i s c h e n Mo d e l l b e fu n d e n . D ie w ic h t ig s t e n s t ru k tu re l l e n u n d

    p h y s ik o c h e m is c h e n E ig e n s c h a f t e n s p ie g e ln d i e g rofS e A h n l i c h k e i t u n d d e n f l i e g e n d e n l ]b e rg a n g w id e r ,

    d i e f i i r d ie S u b s t i tu t io n s g l i e d e r e in e r k o n t in u ie r l ic h e n R e ih e z u e rw a r t e n s ind . D ie b e s t e h e n d e A u f -

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    e i c h e d e r Z u s a m m e n s e tz u n g w i rd a l s u n g e re c h t fe r t ig t u n d e h e r i r r e f f ih re n d h in g e st e l i t. D ie in d iv id u e l-

    l e n Z u s a m m e n s e tz u n g e n in n e rh a lb d i e s e r b e id e n U n te rb e re i c h e s t e l l e n k e in e e in d e u t ig v e r s c h ie d e n e n

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    Glie der e ine r kon t inu ie r l ichen R e ihe m it fl ie l?,end wec hse lnd en E igensc haf ten shad .

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    (E in z e l- ) Z u s a m m e n s e tz u n g e n ( a n S te l l e d e r Z u s a m m e n s e tz u n g s b e re i c h e ) z u id e n t i fi z i e re n , d i e K o n -

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