Acidity of Mordenite - ACS Symposium Series (ACS Publications)

9

Acidity

of M o r d e n i t e

G. H. KÜHL

Downloaded by AUBURN UNIV on March 2, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0040.ch009

Mobil Research and Development Corp., Paulsboro, N.J. 08066

ABSTRACT The acidity of hydrogen mordenite was determined by treatment with 0.1N NaOH and back-titration of the excess, and by t i t r a t i o n of the extract obtained by successive batch treatments with 2N NaCl or O.1N AgN0 . The results show that acid-exchanged mordenites are true hydronium forms. The degree of dehydroxylation of thin-layer calcined NH -mordenites can be estimated from the different results obtained by the two methods. 3

4

Introduction When a true hydrogen zeolite Y i s contacted with O.lN NaOH solution, the sodium form of the zeolite i s obtained (1). Sorbing water on hydrogen zeolite Y probably produces the hydronium form of the zeolite; the structure collapses upon dehydration of hydronium zeolite Y (1). It i s not clear whether any frameworkAl hydrolyzes upon contact of HY with water, but since the heat of hydration of a proton i s considerable, p a r t i a l hydrolysis i s l i k e l y to occur. Similar reactions can be expected upon contact of HY with NaCl solution. When a stabilized hydrogen zeolite Y is treated with O.lN NaOH solution, cationic aluminum i s removed from the zeolite and replaced by Na ions (1). Contact of stable hydrogen zeolite Y with 2n NaCl solution also causes removal of cationic aluminum i n exchange for sodium, while the pH of the i n i t i a l l y neutral solution drops to about 3 and the S1O2/AI2O3 ratio of the remaining solid increases (2). Refluxing of a stabilized hydrogen zeolite Y with several batches of sodium chloride solution resulted i n a gradual increase of the pH in sequential batches: 2.7-3.0-3.23.35-3.5 (2). It was also found that most of the exchangeable aluminum was removed in the f i r s t treatment. The number of sodium ions introduced into the zeolite per aluminum ion removed was close to 3.0 in the f i r s t exchange and decreased i n subsequent +

96

In Molecular Sieves—II; Katzer, James R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9.

Acidity

KUHL

of

Mordenite

97 3 +

steps. I t t h e r e f o r e , appears t h a t A l ions are exchanged f i r s t , f o l l o w e d by A l ( O H ) and A l ( O H ) 2 . In a few samples we found t h a t the r a t i o N a i n / A l t dropped below 1, i n d i c a t i n g the p o s s i b l e r

2 +

+

o u


presence o f a dimeric i o n such as { H O - A T ^ ^ A I } * . S i m i l a r r e a c t i o n s occur w i t h most z e o l i t e s . A notable excep t i o n i s mordenite. When hydrogen mordenite i s t r e a t e d w i t h NaCl s o l u t i o n a t ambient temperature, hydronium ions are exchanged from the z e o l i t e , unless the c o n t a c t i s prolonged, no aluminum c a t i o n s appear i n s o l u t i o n ; i t i s l i k e l y t h a t hydrated •aluminum ions are so l a r g e a t ambient temperature t h a t they cannot e a s i l y migrate out o f the c a v i t i e s . T h i s behavior permits easy determination o f exchangeable hydrogen ions by t i t r a t i o n and may be u s e f u l as a model f o r o t h e r z e o l i t e s . Since t h i s work was done, B a r r e r and Klinowski (3) r e p o r t e d on the exchange of Na-mordenite w i t h ΗβΟ" " ions and on the reverse r e a c t i o n . They a l s o reported r e s u l t s w i t h H-mordenite prepared by c a l c i n a t i o n o f NH4-mordenite. Therefore, we s h a l l l i m i t t h i s paper t o those p a r t s o f our work t h a t w i l l p r o v i d e a d d i t i o n a l con t r i b u t i o n s t o the understanding o f hydrogen mordenite. 1

Experimental M a t e r i a l s , Two samples o f commercial hydrogen mordenite and three samples o f commercial sodium mordenite were obtained from Norton Company; the compositions were ( i n wt. % ) : Hydrogen Mordenite

Si0 A1 0 Na 0 2

2

3

2

Sodium Mordenite

A

Β

A

Β

86.4 13.0 0.39

85.5 12.1 0.66

78.7 13.35 7.45

C

78.8 13.6 7.4

77.4 12.9 7.6

Three samples o f hydronium mordenite were prepared by i o n exchange o f sodium mordenite w i t h O.lN HC1 a t ambient temperature. T h e i r compositions were: Hydronium Mordenite From Na-Mordenite Dried Si0 A1 0 Na 0 2

2

3

2

A

Β A

Heat Lamp

Heat Lamp

Β Room Temp

70.9 10.9 0.21

70.9 11.7 0.33

69.9 11.6 0.34

NH -mordenite was prepared by s u c c e s s i v e ion-exchange o f sodium mordenite C w i t h 2N NH4CI s o l u t i o n a t r e f l u x temperature. The composition was 65.2% S i 0 , 10.7% Al C>3, 0.30% Na 0, 2.69% N. 4

2

2

2


MOLECULAR


98

SIEVES—II

Procedures. The thermal a n a l y s i s was c a r r i e d o u t w i t h a DuPont Model 950 thermogravimetric a n a l y z e r . Ammonia appearing i n the e f f l u e n t helium was determined by p a s s i n g the gas through a s o l u t i o n c o n t a i n i n g 2 ml o f aqueous 4% b o r i c a c i d and 50 ml o f water, and t i t r a t i n g w i t h sulfamic a c i d u s i n g an automatic titrator. Three methods f o r determining the a c i d hydrogen were used: a) Approximately l g o f z e o l i t e i s t r e a t e d w i t h 20-25 ml o f O.lN NaOH and s t i r r e d f o r one hour. The s l u r r y i s then f i l t e r e d and washed w i t h water. The excess o f NaOH i s b a c k - t i t r a t e d w i t h O.lN HC1 t o determine the ml O.lN NaOH consumed. Methyl p u r p l e was used as i n d i c a t o r . b) Approximately l g o f z e o l i t e i s t r e a t e d w i t h 150 ml o f 2N NaCl s o l u t i o n and s t i r r e d f o r f i f t e e n minutes. The s l u r r y i s f i l t e r e d on a f r i t t e d d i s k f u n n e l and the r e s i d u e washed w i t h water. The f i l t r a t e i s t i t r a t e d w i t h O.lN NaOH. Methyl p u r p l e was used as i n d i c a t o r t o o b t a i n a very d i s t i n c t end p o i n t , but other i n d i c a t o r s can be used. The s o l i d i s r e s l u r r i e d with 150 ml o f 2N NaCl s o l u t i o n and the treatment repeated u n t i l t h e amount o f t i t r a n t r e q u i r e d i s o n l y 0.1 ml f o r the l a s t batch. The accumulated ml o f O.lN NaOH i s p l o t t e d over the number o f treatments and e x t r a p o l a t e d . c) S i n c e mordenite, l i k e o t h e r z e o l i t e s , has a h i g h a f f i n i t y f o r A g i o n s , 2N NaCl can be replaced by O.lN AgN0 s o l u t i o n . To prevent p r e c i p i t a t i o n o f A g 0 d u r i n g the t i t r a t i o n , NaCl s o l u t i o n i s added t o each f i l t r a t e (AgN0 + NaCl+AgCl+ + NaN0 ) before t i t r a t i n g w i t h O.lN NaOH. No aluminum was e x t r a c t e d by these treatments i n the g r e a t m a j o r i t y o f determinations. I n a few experiments, n e g l i g i b l e t r a c e s o f aluminum were observed. The percentage o f aluminum p o t e n t i a l l y a s s o c i a t e d w i t h hydrogen ions ( " e f f e c t i v e " aluminum) was c a l c u l a t e d by s u b t r a c t i n g the percentage o f aluminum a s s o c i a t e d w i t h sodium o r ammonium from the t o t a l aluminum content. From t h i s f i g u r e and t h e t i t r a t i o n r e s u l t the atomic r a t i o o f a c i d hydrogen p e r e f f e c t i v e aluminum, H / e f f . A l , was determined. X-ray d i f f r a c t i o n o f a few s e l e c t e d samples showed f u l l r e t e n t i o n o f c r y s t a l l i n i t y . +

3

2

3

3

+

Results and D i s c u s s i o n When a mordenite sample c o n t a i n i n g hydrogen ions i s cont a c t e d w i t h sodium c h l o r i d e s o l u t i o n , an exchange HM + NaClr* NaM + HCl takes p l a c e . The extent o f t h e exchange i s governed by the exchange isotherm (3). Repeated NaCl treatments remove more and more hydrogen i o n s , t h e t o t a l amount o f a v a i l a b l e a c i d hydrogen being approached a s y m p t o t i c a l l y . I f the accumulated a c i d removed i s p l o t t e d over the number o f treatments, the curve obtained w i t h f i v e t o seven treatments can be e x t r a p o l a t e d t o


9.

Acidity

KUHL

of

99

Mordenite


determine the t o t a l amount o f hydrogen removable by t h i s t r e a t ment. Z e o l i t e s u s u a l l y have a p a r t i c u l a r l y high a f f i n i t y f o r s i l v e r i o n s . Therefore, f o r more p r e c i s e determinations, s i l v e r n i t r a t e may be used i n s t e a d o f sodium c h l o r i d e . Such a treatment g i v e s a steeper curve t h a t can be e x t r a p o l a t e d w i t h g r e a t e r accuracy (Figure 1 ) . The r e s u l t s obtained by these two procedures are g e n e r a l l y i d e n t i c a l . Both have the advantage o f short c o n t a c t times p r a c t i c a l l y e l i m i n a t i n g the r i s k o f aluminum ion-exchange. F i n a l l y , a hydrogen mordenite can be t r e a t e d w i t h a known amount o f d i l u t e NaOH according t o HM + NaOH + NaM + H2O. The excess i s then b a c k - t i t r a t e d i n the f i l t r a t e . T h i s procedure i s very f a s t and accurate. Commercial Hydrogen Mordenite. I n c o n t r a s t t o the f i n d i n g s o f B a r r e r and Klinowski (3), the two samples o f commercial hydro gen mordenite (see experimental section) we had r e c e i v e d c o u l d not be converted completely t o the sodium form by treatment w i t h O.lN NaOH. Instead we found H+/eff.Al A Β

after 15 min. a t 25°C 1 hour a t 25°C

0.545 0.590

0.660 0.668 +

Repeated NaCl treatments gave 0.268 (A) and 0.305 (B) H / e f f . A l . When heated t o 550°C, a c i d hydrogen was l o s t from sample B: Time

Method

H*/eff . A l .

3 hours 16 hours

NaCl AgN0

0.290 0.055

3

When a s l u r r y o f sample A i n d i l u t e NaCl s o l u t i o n was t i t r a t e d p o t e n t i o m e t r i c a l l y w i t h O.lN NaOH, a smooth s i n o i d a l curve was obtained w i t h an i n v e r s i o n p o i n t a t pH 6.5 corresponding t o 0.440 H / e f f . A l (Figure 2 ) . The t i t r a t i o n i s very slow as the mixture has t o be p e r m i t t e d t o reach e q u i l i b r i u m a f t e r each a d d i t i o n o f NaOH. The curve has c h a r a c t e r i s t i c s o f both a strong and a weak a c i d . However, the base, known t o be s t r o n g , shows the same strong and weak aspects. Such a behavior can be explained by the e f f e c t o f the system +

H

3+ 20 + A10H 2

Al

+

H 0 +H ·> A1(0H) 4" +

2

H 0 •+ A l ( O H ) + H Ψ 2

2

+ H Ψ

The hydrogen ions a r e exchanged f o r N a H +

z

+

N a +

s *

N a +

z

+

3

+

(1)

ions, H +

s


(2)


100

MOLECULAR

0

Figure 1. Comparison of Ag and Na exchange of H-mordenite

1

2

3

4

SIEVES—Π

5

Number of Treatments

12

Figure 2. Titration of H-mordenite. 1.0982g H-mordenite A + 10 ml satu rated NaCl solution + 100 ml H O. t

5

10

15

ml 0.1 Ν NaOH


20

9.

KUHL

Acidity

of

101

Mordenite

and n e u t r a l i z e d upon l e a v i n g t h e z e o l i t e . The e q u i l i b r i u m pH a f t e r every a d d i t i o n o f NaOH depends on t h e two coupled r a t e r e a c t i o n s , h y d r o l y s i s o f c a t i o n i c A l ( l ) and ion-exchange(2). The p o i n t s corresponding t o t h e r e s u l t s o b t a i n e d by t h e NaCl method(b) and by the NaOH method(a) are marked i n F i g u r e 2. I t seems l i k e l y , t h e r e f o r e , t h a t f r e e hydrogen i o n s and those generated by Al

3 +

+ H 0 - A10H

2+

+ H

2

+

(3)


are determined by procedure b ) , whereas the sum o f these hydrogen ions and those generated by t h e r e a c t i o n s A10H

2+

Al(OH)

+ H 0 = Al(OH) 2

+ 2

+

+ H 0 = Al(OH) 2

+ H

2

3

+

+ H

and

(4)

+

(5)

i s obtained by procedure a ) . The r e s u l t s obtained i n d i c a t e t h a t commercial hydrogen mordenites — o r a t l e a s t t h e two samples i n v e s t i g a t e d by us — are n o t t r u e hydrogen z e o l i t e s . T h e i r s t r u c t u r e appears t o be c o n s i d e r a b l y more complex. Our next g o a l was, t h e r e f o r e , t o prepare a t r u e hydrogen form o f mordenite. A mordenite c o n t a i n i n g hydrogen i o n s as t h e o n l y source o f a c i d i t y should g i v e t h e same r e s u l t s w i t h both procedures, u n l e s s a secondary r e a c t i o n , such as h y d r o l y s i s o f framework-aluminum, o c c u r s . An a c i d form o f mordenite can c o n c e i v a b l y be prepared by a) ion-exchange w i t h an a c i d , b) c a l c i n a t i o n o f ammonium mordenite. Hydronium Mordenite. Ion-exchange o f sodium mordenite w i t h 0.1N HC1 produced hydronium mordenite, i n agreement w i t h Shikunov, L a f e r and Yakerson (4). The a n a l y t i c a l data show a s m a l l i n c r e a s e i n the S1O2/AI2O3 r a t i o f o r samples Β and C, a somewhat g r e a t e r i n c r e a s e f o r sample A. The r e s u l t s suggest t h a t treatment w i t h 0.1N HC1 e x t r a c t s some aluminum from the z e o l i t e , i n agreement with the f i n d i n g s o f B a r r e r and K l i n o w s k i (3). The amount o f a c i d used t o prepare sample A was g r e a t e r than f o r Β and the product contained l e s s sodium and aluminum. Sodium c h l o r i d e e x t r a c t e d 0.601 H / e f f . A l from hydronium mordenite A. The t r e a t e d z e o l i t e sample had a Na/Al atomic r a t i o o f 0.595, i n e x c e l l e n t agreement with t h e r e s u l t o f the t i t r a t i o n . Another sample o f hydronium mordenite (sample B) was examined a f t e r twelve years o f storage. Treatment w i t h 0.1N NaOH n e u t r a l i z e d 0.481 H+/eff.Al, and NaCl treatment e x t r a c t e d 0.482 H / e f f . A l . The p e r f e c t agreement o f t h e r e s u l t s i n d i c a t e s t h a t the o n l y a c i d i t y p r e s e n t i n t h e z e o l i t e was t h a t o f H30 i o n s . But t h e absolute number found i s very low suggesting t h a t H 0 ions disappeared, e i t h e r i n the d r y i n g procedure o r i n storage, without generating other p o t e n t i a l a c i d i t y , such as t h a t o f +

+

+

+

3


102

MOLECULAR

SIEVES—II

aluminum c a t i o n s . Determination o f a c i d hydrogen i n hydronium mordenite C gave 0.648 H / e f f . A l w i t h NaOH and 0.663 H / e f f . A l w i t h NaCl, i . e . p r a c t i c a l l y i d e n t i c a l r e s u l t s by the two methods, again i n d i c a t i n g the absence o f a c i d i t y o t h e r than H30 . F i n a l l y , ammonium mordenite was exchanged w i t h O.lN HC1 but the product was not d r i e d a f t e r washing. Treatment o f t h i s sample w i t h O.lN NaOH and b a c k - t i t r a t i o n o f the excess showed the presence o f 0.802 H / e f f . A l , c a l c u l a t e d on the assumption t h a t the small percentage o f Na d i d not change during t h e HCl exchange. An i d e n t i c a l l y t r e a t e d sample was contacted w i t h NaCl and the r e l e a s e d a c i d t i t r a t e d y i e l d i n g 0.776 H / e f f . A l by t h i s determinat i o n , again i n agreement w i t h the r e s u l t o b t a i n e d by NaOH treatment. The h i g h e r H / e f f .Al o f t h i s sample compared w i t h the d r i e d m a t e r i a l s agrees w i t h the statement o f Shikunov and co-workers (5) t h a t the presence o f molecular water i s r e q u i r e d f o r the e x i s t e n c e o f the hydronium i o n . A l l samples o f hydronium mordenite gave the same r e s u l t s by the two methods employed. T h i s can o n l y happen i f hydronium i o n s are the only source o f a c i d i t y i n the z e o l i t e . In p a r t i c u l a r , aluminum c a t i o n s o f any composition cannot be p r e s e n t . I t i s i n t e r e s t i n g t h a t the a c i d treatment d i d e x t r a c t small amounts o f aluminum from the framework, but a l l intermediate c a t i o n i c aluminum was then removed by ion-exchange. The always low H /A1 r a t i o s suggest t h a t some non-ionic A l i s p r e s e n t , p o s s i b l y s t i l l attached t o the framework through two oxygen i o n s and c a r r y i n g one f r e e hydroxyl group. +

+

+

+

+


+

+

H-Mordenite Obtained by C a l c i n a t i o n o f NHa-Mordenite. The decomposition p a t t e r n o f ammonium mordenite i s shown i n F i g u r e 3. A helium atmosphere was used t o avoid temperature excursions upon o x i d a t i o n o f NH3 i n a i r , as observed, e.g., by Weeks and coworkers (6). The f i g u r e contains the thermogravimetric a n a l y s i s a t 5°/min. heating r a t e (corroborating the r e s u l t s o f Benesi (7) and Shikunov and co-workers ( 8 ) ) , the weight o f ammonia r e l e a s e d and the weight o f water g i v e n o f f . A l s o i n c l u d e d are the r a t e s a t which ammonia and water are l i b e r a t e d ( i n a r b i t r a r y units)· The temperature a t which ammonia begins t o escape i s about the same as f o r z e o l i t e Y Ç9). Whereas the r e l e a s e o f ammonia from NH Y i s p r a c t i c a l l y complete a t 460°C (9), i t reaches i t s h i g h e s t r a t e f o r mordenite a t 480 C, and i s e s s e n t i a l l y complete a t 6 2 0 ° C The h i g h e s t r a t e o f dehydroxylation o f mordenite i s a t t a i n e d a t about the same temperature as w i t h z e o l i t e Y, about 6 7 0 ° C However, whereas dehydroxylation o f z e o l i t e Y occurs w i t h i n a narrow temperature range (9), t h i s r e a c t i o n i n mordenite i s drawn out from 525 t o 880°C. I t i s evident t h a t the deammoniation and dehydroxylation r e a c t i o n s o v e r l a p i n the range o f 525 t o 620°C. For t h i s reason, i t i s very d i f f i c u l t , i f not impossible, t o prepare a pure hydrogen mordenite by c a l c i n a t i o n o f ammonium mordenite. The best chances appear t o be i n the range 480-525°C 4

e


9.

Acidity

KUHL

of

103

Mordenite

H e a t i n g Rate: 5

C/Min.

Flowing Helium,

150 c c / M i n .

TGA


NH _ . _

3

Liberated

Rate of NH3 R e l e a s e ( A r b i t r a r y H 0 2

Rate of H 0 ?

0

100

Units)

Released Release ( A r b i t r a r y

200

300

Units)

400 Temperature,

Figure 3.

500 C

600

700

800

900

(Corrected)

Thermo gravimetric analysis of

NH mordenite r


1000

104

MOLECULAR

SIEVES—II

In order t o prevent h y d r o l y s i s of framework-aluminum, i t i s mandatory to remove gaseous r e a c t i o n products f a s t . S e v e r a l attempts to prepare a pure hydrogen mordenite are o u t l i n e d i n Table I . TABLE I . - Attempts to prepare pure H-mordenite


Sample No. 1 2 3 4 5 6 7 8

Muffle Cold

Sample in

Heating Rate

Crucible T h i n Bed

II

l°/min 3°/ "

II

II

II

II

II

II

II

II

II

II

1°/

"

II

II

II

Crucible

II

II

Hot

II

II

II

•Contains 0.156

-

Time a t Highest Temp.

Highest Temp,

8 hrs 3 " 1 hr 3 hrs

480°C II II

500°C 515°C 550°C 480°C 550°C

II

II

II

II

II

II

•1

II

+

H /eff.Al NaOH NaCl 0.539 0.795 0.855* 0.816 0.539 0.508 0.669 0.479

0.344 0.559 0.695* 0.631 0.453 0.189 0.518 0.250

+

r e s i d u a l NH /A1, a l l other samples A10H} +

(Α1 0 0Η ) η

Ζ

ο

Ζ

(A10 · JLo 1 c

)

o

Ζ

+

i s assumed:

H

+ 5

2

I t i s q u e s t i o n a b l e whether hydrogen ·b/

ions can c o e x i s t w i t h the d i m e r i c c a t i o n , and o t h e r explanations may be p o s s i b l e . Dealuminized Mordenite. The number of a c i d s i t e s i n a hydro gen mordenite can be reduced by mere c a l c i n a t i o n o r steaming. However, oxy- and hydroxy-aluminum c a t i o n s and p o s s i b l y aluminum oxide are d e p o s i t e d i n the channels of the z e o l i t e . These m a t e r i a l s , which may b l o c k passage o f hydrocarbons i n c a t a l y t i c a p p l i c a t i o n s , can be removed by a c i d e x t r a c t i o n . Prolonged heating o f any hydrogen mordenite t o a temperature o f about 480°C o r higher causes a decrease o f the H /A1 r a t i o by dehydroxylation (Table I I ) . +

TABLE I I . - Dehydroxylation o f hydrogen +

Sample, S i 0 2 / A l 2 0 H-Mordenite B,

3

H /A1 after drying a t 120°C

12.0

+

mordenite

H /A1

after calcination a t 550°C f o r 3 hours 16 hours

0.31

0.29

0.06

14.8

a

0.65

0.50

0.12

H-Mordenite, 23.8

b

0.63

0.53

0.14

H-Mordenite,

a)

Prepared by r e f l u x i n g Na-mordenite C with two batches o f

20%

D f o r f o u r h r s . each, H SO>| 2

b)

4

Prepared by r e f l u x i n g NH4-mordenite A with 6N HC1 f o r e i g h t h r s ,


106

MOLECULAR

SIEVES—II

+

The data f o r H /A1 i n t h i s t a b l e were obtained from NaCl t r e a t ments; t h i s procedure was chosen because i t does not e x t r a c t H generated by h y d r o l y s i s o f hydroxylated aluminum c a t i o n s , and the data obtained i n t h i s way should be more meaningful. +

TABLE I I I . - Dealuminized mordenite E f f e c t o f steaming and a c i d treatment


Starting Material SiO^/Al.O 23.8 38 23.8 11. 3 75 11. 3 62 10. 2 59 a) b) c) d) e)

a

a

b

Steamed hours °C 24 24

-2 -2

24 b

d

760 760

538 538

760

Refluxed with hours 8 8 24 6x8 4x8 5x8 5x8 6x8 3x8

IN 6N 6N 6N 6N 6N 6N 6N 6N

HC1 HC1 HC1 HC1 HC1 HC1 HC1 HC1 HC1

Product H /A1 SiOVAl.O +

38 41.5 47 75 102 62 112 59 125

0.05 0.02 0.56 0.58 0.29 0.69 0.46 0.62 0.39

c

e

e

See Table I I . Hydrogen mordenite Α.* A f t e r two-hour c a l c i n a t i o n a t 480°C. Sodium mordenite C. A f t e r two-•hour c a l c i n a t i o n a t 540°C.

Table I I I contains r e s u l t s obtained by NaCl treatment of dealumi n i z e d mordenites; the e f f e c t o f steam treatment on the hydrogen content was examined. When a mordenite o f 23.8 S1O2/AI2O3 was steamed a t 760°C f o r a day, a c i d hydrogen was almost completely l o s t . The same treatment decreased the H / A l r a t i o o f a 75 S1O2/ AI2O3 sample by only 50%. Steam treatment a t lower temperature (538°) (11) and f o r a s h o r t e r p e r i o d (two hours) r e t a i n e d considerably more H /A1 i n the p r e p a r a t i o n o f h i g h - s i l i c a dealuminized mordenite. The r e s u l t s i n d i c a t e t h a t high-temperature steaming o f hydrogen mordenite causes removal o f aluminum from the framework and d e p o s i t i o n w i t h i n the z e o l i t e as polymeric oxoaluminum c a t i o n s o f low charge and probably even as n e u t r a l aluminum o x i d e . These species appear to have a low r a t e o f d i s s o l u t i o n a t a hydrogen i o n c o n c e n t r a t i o n present i n the z e o l i t e channels and cannot be e x t r a c t e d very r e a d i l y . +

+

Acknowledgment The v a l u a b l e a s s i s t a n c e of Mr. G. R. Landolt i n the e x p e r i mental procedures o f the thermal a n a l y s i s i s g r a t e f u l l y acknowledged.


9. kuhl

Acidity of Mordenite

107

Literature Cited 1. 2. 3. 4. 5.


6. 7. 8.

9. 10.

Kerr, G. T., J. Catal. (1969), 15, 200. Kühl, G. H., unpublished results. Barrer, R. Μ., and Klinowski, J., J. Chem. Soc., Farad. Trans. I, (1975), 71, 690. Shikunov, Β. I., Lafer, L . I., and Yakerson, V. I., Dokl. Akad. Nauk SSSR (1971), 200, 1119. Shikunov, Β. I., Lafer, L . I., Yakerson, V. I., and Rubinshtein, Α. Μ., Izv. Akad. Nauk SSSR, Ser. Khim. 1971, 1595. Weeks, T. J., Jr., H i l l e r y , H. F., and Bolton, A. P . , J. Chem. Soc., Farad. Trans. I, (1975), 71, 2051. Benesi, Η. Α . , J. Cat. (1967), 8, 368. Shikunov, Β. I., Mishin, I. V . , Piloyan, G. Α . , Klyachko-Gurvich, A. L., Lafer, L . I., Yakerson, V. I., and Rubinshtein, Α. Μ., Izv. Akad. Nauk SSSR, Ser. Khim. 1973, 767. Kerr, G. T., and Chester, A. W., Thermochimica Acta (1971), 3, 113. Kühl, G. H., "A Study of Aluminum Coordination in Zeolites Using the K Line", Recent Progress Report, Proceedings of the Third International Conference on Molecular Sieves, page 227 (1973). F u l l paper in preparation. Chen, Ν. Y., and Smith, F . Α . , Inorg. Chem. (1976), 15, 295. ß

11.


Acidity of Mordenite - ACS Symposium Series (ACS Publications)

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