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Pure A p p / . Chem. Vol. 61, No. 11, pp. 1977-1980, 1989.Printed in Great Britain.@ 1989 IUPAC

Effect of hydro thermal dealuminat ion o f a synthet icfaujasite by IR spectroscopySOP. ZhdmOVI nsti tute of Si l i cate Chemstry of the USSR Academy ofSci ences, Nab. Makarov 2, Leni ngrad 199164, USSRTI. Ti tova and L.S. Koshel evaI nsti tute of Physi cal Chemstry of the USSR Academy ofSci ences, Leni nsky prospect, 31, Moscow 117915, USSRW LuteCentral I nst i tute of Physi cal Chemstry of the GDR Academyof Sci ences, Rudower Chaussee, 5, Berl i n 1199, GDRAbstract Crystal st ructure of a fauj asi te deal umnatedhydrothermal l y t o di f ferent degrees has been studi ed bymeans of the FT-SR spectroscopy. I t has been f ound that i nearl y stages of deal umnati on, a part i al hydrol ysi s of thef ramework al umni umoccurs, whi ch causes a Si -0 symmetri cstretch at 66 cmol t o become acti ve i n the I R spectrumf i nal stages of deal umnati on, expul si on of al umni umf romthe f ramework has been det ect ed as reveal ed i n the dramati cdecr ease i n absorbance at 720-740 anDq characteri sti c ofA1 -0 f ramework bonds, al ong w th the appearence of thebands at 527, 612, 832, and 973 cm l , whi ch were assi gned toA1 -0 non- f ramework speci es. Expul si on of al umni umisaccompani ed by the l ocal rearrangement of the crystalf ramework produci ng sp-hybri di zed si l oxane bonds associ atedw th the bands at 485, 1170 and 1200 cmI.

In

IvVI

Modi f i cati on of zeol i tes by hydrothermal deal umnati on i s known t o be basi ct o the producti on of a wde vari ety of ul trastabl e mol ecul ar si eves andcatal ysts, and i s the subj ect of much research ref. 1-3). At the sameti me, the mechani smof zeol i tes deal umnati on i s under di scussi on t i l l nowref. 15.To contri bute t o the cl ari f i cati on of thi s questi on, an attempt was made i nthe present work t o ref i ne the assi gnment of the bands i n the I R l att i cevi brati on spectra of fauj asi te sampl es deal umnated by BdcDaniel and Maherprocedure ref. 6 7) t o di f ferent degrees, due t o i nvoki ng the i nterpretedspectra of l ayered and skel eton al umnosi l i cates as cl osel y rel ated systems,as wel l as due to correl ati ng the IR spectral behavi or of the sampl es i nves-ti gated t o the correspondi ng 29Si NMR one.usi ng 0.5 XBr pl atel ets on a Bruker IFS-115c Model FT- I R spectrometer overI R spectra were recorded

1977

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1978 S. P. ZHDANOV et a/.

the range o f 400-1400 cm-under a resolution of 4 cm.sp ec tr a were measured and kin dly put a t o u r d i s p o s a l by Dr. J. Xlinowski.Characteris t ics o f the samples inves tig ate d and spec if ic at io n of themodification conditions are given i n Table.

29Si MAS NMR

TABLE .Ch ara cte ris tic s of the samples investiga ted.Sample Produced by performing S i / A l a S i / A l btotal framework

indust r ia l synthes isi n i t i a l NaY sample)1 2.37 2.4

primary NHi-exchange on 1, 2.37 3.1873K steaming9739 steaming

l O 2 3 K steaming0.1 N H C 1 treatment o f 4

secondary NBg-exchange on 2, 2-57 14.034 secondary NHi-exchange on 2, 2-37 18.05

analyaed chemically, bassessed by 29Si NMR due t o ref . ).I R transmittance spectra o f the samples investigated are shown i n Figure.Dealumination of the i n i t i a l N a Y sample a t 873K i s seen t o cause a high-frequency HF) shift of most str uct ure -se nsi tiv e bands ref. 7 9), resul -t i n g f r o m the decreased average length and ionic character o f 1 0 bonds,with T = S i , A l ref. 10).i n the spectrum 2 and exhibits a HF s h i f t to 675-678 cm a t higher degreeso f dealumination spectra 3 and 4). Since this band a t t r ibu ted to the Si-0symmetric stretch i s known t o manifest a HF s h i f t and increase i n in tens i tyon decreasing the content on tetrahedrally coordinated aluminium o f layeredand ske let on alu min osi lic ate s framework ref. 10 I ? ) , i t i s reasonable t oassociate the appearence o f t h i s band i n s p ec t ra o f dealuminated faujasitesamples with ar is in g aluminium-deficiency i n t h e i r framework.i n the character o f A 1 4 framework bonds may be direct ly detected by thechanges i n the sp ec tr al region o f 720-780 cm-, whereby t h e higher thefrequency o f a band i n t h i s region and the greater the in tens i ty o f i t , thestronger covalent character has the corresponding 81 0 bond and the greateri s the extent o f those i n the a lumhosi l ica te framework,correspondingly

ref. 12). In t h i s respect, the s h i f t o f the band f r o m 718 t o 741 cm anda s l i g h t decrease in intensi ty indicates a lowering o f the extent o f covalentbonding o f aluminium to the framework oxygen, simu lating the so-ca lledaluminium-deficiency e ff ect ; whereas no pr in ci pa l dif fer enc es between thespect ra 1 and 2 strongly suggest that aluminium remains a framework substi-tuent i n th i s s tage o f dealurnination.

Additionally, a s l i g h t band a t 664 cm appears

The changes

Dealumination o f the sample 2 at

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lR study o f fau jasi te dealuminat ion 1979

h i g h e r t e m p e r a t u r e s c a u s e s d r a s t i c ch an ge s in t h e c o r r e s p o n d i n g s p e c t r a 3and 4.i n d i c a t e s that p a r t i c i p a t i o n o f a lu min iu m i n b u i l d i n g up the f ramework i se x t r e m e l y l i m i t e d , i.e*, aluminium i s e x p e l l e d from t h e f ramework. Itp ro du ce s t h e i n c r e as e i n t h e r e l a t i v e i n t e n s i t y o f t h e TO4 bending band a t65 cmol, accompanied by t h e development of th e bands a t 427, 612, nd832 cm-, on t h e on e hand, and the appearance of the 482 cm- band accompa-n i e d b y t h e HF s h i f t a nd r e s o l v i n g of t h e highes t f r e q u e n c y s h o u l d e r at

1155 cm- i n t o 1168 and 1198 om, on t h e o t h e r hand.

The d r a m a t i c d e c re a s e i n i n t e n s i t y of the 741 cm- band d i r e c t l y

465

B

-90 -100 -110PPM FROM TYLS

F i g u r e I R l a t t i c e v i b r a t i o n ) and 29Si l yL s N R B )s p e c t r a of t h e s am p l es i n v e s t i g a t e d t h e n um bers o f s p e c t r ar e f e r t o t h e l i s t i n g of t h e sam ples i n Table ) *

The f i r s t group of spectra l changes i s a n al og o u s t o tha t o bs er ve d i n s p e c t r ao f l a y e r e d and s k e l e t o n a l u m i n o s i l i c a t e s ( r ef . 10 11) on A1Iv O-AlV1 Ot r a n s i t i o n s , w h e r e b y the a b s o r b a n c e at 524 cm- has b e e n c o n s id e r e d c h a r a c -t e r i s t i c of A1 -0 s p e c i e s . It is thu s r ea sonab le t o assume t h a t the ana-logous bands i n s p e c t r a o f d ea lu m in at ed f a u j a s i t e s r e p r e s e n t v i b r a t i o n s o fnon-framework A1 -0 s p e c i e s as well. I n s e n s i t i v i t y 01 p o s i t i o n s o f t h ebands a t 527, 612 and 832 cm- t o t h e de gr ee o f the f ramework oxygen charged i s b a l a n c e o c c u r r i n g o n d e a l u m i n a t i o n , as w e l l as the i n c r e a s e i n i n t e n s i t yo f t h o s e with t h e d e g r e e of d e a l u m i n a t i o n (co mp are s p e c t r a 3 and 4), andt h e d e t e c t a b l e d e c r e a s e i n t h e same a f t e r the a c i d t r e a t m e n t ( sp e ct ru m 5a r g u e no doubt i n f av o r of s u c h i n t e r p r e t a t i o n .

V I

VI

Hereby, t h e removal of

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198 S. . ZHDANOV eta /most non- framework a lumin ium by ac id t r ea tm en t ena b le s one t o ob se rve t heThe s e c on d g ro u p of s p e c t r a l c h an g e s i s t o b e c o n s id e r e d i n d i c a t i v e of area r rangemen t o f the c r y s t a l fra me wo rk at h i g h d e g re e s o f d e a l u m i n a t i o n ,whereby ce n te r in g of new bands at 485 an d 12 00 cm- , wi th t he l a t t e r be in gc h a r a c t e r i s t i c of t h e asym metric s t r e t c h of c l o s e t o l i n e a r s i l o x a n e b onds( r e f . lo), i n d i c a t e s of t h e f o r m a t i o n o f n orm ala t s i t e s o f aluminium expu l s ion . So, t h e IR l a t t i c e v i b r a t i on s p e c t r a ofh i g h l y d ea lu m in at ed f a u j a s i t e s r e p r e s e n t a s u p e r p o s i t i o n o f s p e c t r a o fc i e s .T o a s c e r t a i n the a b o v e c o n c l u s i o n s , t h e 29Si MAS NMR s p e c t r a o f the samesamples were analyzed. In t h e c o r r e sp o n d i n g s p e c t r a of F i g u r e , t h e Si nA1)s i g n a l s with n = 0, I , 2 3 denoting the number of framework aluminium atomsl i n k e d t o a g i v e n s i l i c o n ( r e f . 8) a r e d e s ig n a t e d a , b , c , d , r e s p e c t i v e l y .R e d i s t r i b u t io n of i n t e n s i t i e s of Si nA1) s i g n a l s i n t h e s pe ct ru m 2 as compa-red t o t he i n i t i a l s p e c t ru m 1 i n d i c a t e s of t h e c hange i n t h e s t a t e o f alumi-n ium a f t e r t he 873K t rea tme n t , wh i l e remain ing of t h e Si nA1) s i g n a l s i nt h i s s p e c t r u m r e v e a l s tha t aluminium remains a f r a m e w o r k s u b s t i t u e n t , f o rext ra-framew ork a luminium would no t be d et ec te d by t h i s method (ref. 8).I n t h i s r e s p e c t , t h e d e c re a s e i n i n t e n s i t y o f t h e Si nA1) s i g n a l s t o n e g li -g i b l e v al u es and t h e c o n t r a s t i n g i n c r e a s e i n that o f t h e Si(oA 1) s i g n a l a f t e rthe 973 and 1023K t r e a t m e n t s ( s p e c t r a 3 and 4) i n d i c a t e the e x p u l s i o n o fa lu m in iu m f ro m t h e f ra m ew ork, a nd s t r o n g l y s u p p o r t t h e a bo ve i n t e rp re t a -t i o n o f t h e I R s p e c t r a o f h i g h l y d e a l um i n a te d f a u j a s i t e s am ple s.

band a t 973 cm-I a ss igne d t o th e A 1V I a s y m m e t r i c s t r e t c h ( r e f , 10).

s p -h y b r id i z e d s i l o x a n e b on ds

h i g h l y s i l i c e o u s r e a r r a n g e d f ram ew ork a n d tha t of non-framework A 1V I 0 spe-

RE FE RE NCE S

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10. 1.1. P l u s n i n a , I n f r a k r a s n s e S DektrY S i l i c a t o v . MGU l ~ ,1967).11. Ju.1. Ta ras ev ic h , S t ro en ie K h i m i j a P o v er k h no s ti S l o i s t y k h S i l i k a t o v ,12. V.A. Kolesova, Optika i S p e k t r o s k o p i j a , g 38-43 (1959)*

Naukova Dumka ,E 1988)