NMR Relaxation of Water in Zeolite 13-X - ACS Publications

37 N M R Relaxation of Water in Zeolite 13-X

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch037

H. A. RESING and J. K. THOMPSON Naval Research Laboratory, Washington, D. C. 20390

The nuclear magnetic resonance relaxation times for the protons of water adsorbed to saturation in a high-purity specimen of zeolite 13-X have been measured between 200° and 500°K. The data can be accounted for by the model of an intracrystalline fluid which is about 30 times as "viscous" as bulk water at room temperature, shows a broad distribu tion of molecular mobilities, and is about as dense as liquid water. The median correlation time (time between molecu lar flights) is -12

τ* = 2.8 Χ 10

ttTntracrystalline

fluid"

exp [417/(T - 189)]

is t h e t e r m chosen b y B a r r e r to d e s c r i b e t h e

state o f w a t e r a n d other m o l e c u l e s c o n d e n s e d i n t h e pores of zeolites ( 1 ) . T h i s r e p o r t presents a d e t e r m i n a t i o n of t h e fluidity of w a t e r a d s o r b e d t o s a t u r a t i o n i n zeolite 1 3 - X . A s a m e a s u r e of t h e fluidity, t h e t i m e b e t w e e n m o l e c u l a r j u m p s or c o r r e l a t i o n t i m e , r , is e m p l o y e d ; i t has b e e n d e r i v e d f r o m measurements of n u c l e a r m a g n e t i c resonance ( N M R ) r e l a x a t i o n times via the t h e o r y of B l o e m b e r g e n , P u r c e l l , a n d P o u n d ( B P P ) ( 2 ) . F o r a b u l k l i q u i d , this c o r r e l a t i o n t i m e is r e l a t e d t o t h e v i s c o s i t y , η, b y a n e q u i v a l e n t of t h e D e b y e e q u a t i o n ( 2 ) : τ =

χ η α / ( 6 kT) 3

(1)

w h e r e a is t h e m o l e c u l a r d i a m e t e r . F o r m a l l y , a viscosity f o r t h e i n t r a c r y s t a l l i n e fluid c o u l d b e d e f i n e d thus, b u t w o u l d b e w i t h o u t o p e r a t i o n a l significance; f u r t h e r d i s c u s s i o n of

fluidity,

therefore, w i l l b e c a r r i e d o u t

i n terms o f T . T h e z e o l i t e s p e c i m e n u s e d i n t h e present studies w a s p r e p a r e d f r o m zone-refined a l u m i n u m a n d s i l i c o n ; its f e r r i c i o n i m p u r i t y content of < 6 p p m is l o w e n o u g h to ensure that o n l y " i n t r i n s i c " N M R r e l a x a t i o n is observed

( I I ) a n d that t h e effects of p a r a m a g n e t i c i m p u r i t i e s , w h i c h

t r o u b l e d p r e v i o u s studies (4, 6, 8, 10), are c o m p l e t e l y suppressed. T h e 473 In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

474

MOLECULAR SIEVE ZEOLITES

1

b r o a d - l i n e N M R a b s o r p t i o n studies of K v l i v i d z e ( 5 ) , w h i c h w e c a l l u p o n for s u p p o r t i n this p a p e r , w e r e d o n e o n samples of u n s p e c i f i e d p u r i t y . Arguments given previously

(10),

however,

i n d i c a t e that at the

low

temperatures of h e r e x p e r i m e n t s , the presence of p a r a m a g n e t i c i m p u r i t i e s w o u l d n o t affect her interpretations to a n y significant extent. T h e s p e c i m e n u s e d i n this s t u d y w a s a l l o w e d to c o m e to e q u i l i b r i u m w i t h w a t e r v a p o r at a r e l a t i v e pressure P / F =

1. T h e t o t a l w e i g h t was 0.2886 g r a m ,

0

of w h i c h 0.0766 g r a m is H 0 . 2

T h e p u l s e d N M R a p p a r a t u s (12 M H z ) a n d m e t h o d s of Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch037

h a v e b e e n d e s c r i b e d p r e v i o u s l y (JO, 13). T, 2

procedure

T h e spin—spin r e l a x a t i o n t i m e ,

e q u i v a l e n t to the inverse a b s o r p t i o n l i n e w i d t h , is a t i m e constant

for the e x p o n e n t i a l d e c a y s p i n system.

t o w a r d i n t e r n a l e q u i l i b r i u m i n the n u c l e a r

T h e s p i n - l a t t i c e r e l a x a t i o n t i m e , T i , is the t i m e constant

for the e x p o n e n t i a l d e c a y t o w a r d e q u i l i b r i u m b e t w e e n the n u c l e a r spins a n d a l l other degrees of f r e e d o m of the system. T h e d a t a are p r e s e n t e d i n F i g u r e 1. N o t e t h a t at h i g h e r temperatures T

500 10

τ (-κ)

300

400

250

2

is m u c h l o w e r t h a n Τχ.

200

τ. H

H 0 on Z E O L I T E 13-X 2

I I I 3.0 Itf Τ

I L 4.0 (°Κ"') I

J_JL 5.0

Figure 1. T and T vs. reciprocal temperature at ω = 12 MHz for water in zeolite 13-X t

2

m = τ* ο = τ, 0 = =

T of Kvlividze Best fit of theoretical expres sions to data 2

In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

37.

NMR

RESiNG AND T H O M P S O N

Rehxation

of

Water

475

T h i s effect is g e n e r a l i n s o l i d - w a t e r a d s o r p t i o n systems ( 8 ) a n d is c a u s e d at least i n some cases b y a n exchange process b e t w e e n the protons surface h y d r o x y l groups a n d the protons of w a t e r m o l e c u l e s

(15).

a b o u t 4 0 0 ° K , the h f e t i m e of a w a t e r m o l e c u l e p r o t o n w i t h respect exchange i n t o this other phase is a b o u t =

of At to

T , i.e., 10 msec. W e i n t e n d to 2

discuss this m o r e t h o r o u g h l y i n a f u t u r e p u b l i c a t i o n , a n d i n this p a p e r w e r e s t r i c t o u r d i s c u s s i o n of T

2

to t e m p e r a t u r e s s u c h t h a t 1 0 / T > 3

I n the l o w - t e m p e r a t u r e r e g i o n , a r o u n d 1 0 / T = of T

2

3.6.

5 ( F i g u r e 1) 2 v a l u e s

3

are i n d i c a t e d for a g i v e n t e m p e r a t u r e ; h e r e the " T " process 2

was


d e s c r i b a b l e as a s u p e r p o s i t i o n of 2 decays, t h e r e l a t i v e i n t e n s i t y v a r y i n g w i t h temperature. ( g i v e n as T

2

E q u i v a l e n t l y , the a b s o r p t i o n l i n e of K v l i v i d z e

(5)

i n F i g u r e 1) w a s c o m p o s e d of a b r o a d a n d n a r r o w c o m

p o n e n t i n this t e m p e r a t u r e i n t e r v a l . T h i s is the " a p p a r e n t p h a s e t r a n s i t i o n effect" c a u s e d b y a b r o a d d i s t r i b u t i o n of c o r r e l a t i o n t i m e s ( 8 ) , as w i l l be e x p l a i n e d . The

fluidity

of associated l i q u i d s i n g e n e r a l is r e p r e s e n t e d w e l l b y

the free v o l u m e m o d e l (3), a c c o r d i n g to w h i c h τ* = τ exp [A/(Τ

-

0

T )]

(2)

0

where T a n d A depend on molecular parameters, a n d where T 0

0

is the

t e m p e r a t u r e at w h i c h free v o l u m e d i s a p p e a r s . S u c h a m o d e l is consistent w i t h the d a t a of this study. A n a d d e d a s s u m p t i o n w h i c h m u s t b e m a d e , h o w e v e r , is t h a t at a n y t e m p e r a t u r e , τ is s p r e a d o v e r a b r o a d r a n g e of v a l u e s ; the d i s t r i b u t i o n f u n c t i o n a s s u m e d is the often u s e d l o g - n o r m a l distribution

(9) Ρ(τ)άτ

=

(B/Vk)

exp ( -

B Z*)dZ

(3)

2

Ζ = In (τ/τ*) Β = α (Τ -

(4)

To)

(5)

w h e r e Β is a s p r e a d p a r a m e t e r d e p e n d e n t o n t e m p e r a t u r e a n d τ* is the m e d i a n of the d i s t r i b u t i o n . T h i s b r o a d d i s t r i b u t i o n is necessary to e x p l a i n the a p p a r e n t " t w o - p h a s e " r e l a x a t i o n d e s c r i b e d a b o v e B P P (2)

(9).

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

field b y the t r a n s l a t i o n a n d r o t a t i o n of m o l e c u l e s is a n effective n i s m for besides

relaxation.

mecha

T h e other i m p o r t a n t p a r a m e t e r i n t h e i r t h e o r y

the c o r r e l a t i o n t i m e is the s e c o n d

n u c l e a r d i p o l a r field seen b y a n u c l e u s ( σ ) 0

2

moment

or m e a n

squared

(14):

σο» = | γ * Α » / ( / + 1 ) Σ ΐ - ο · -

β

(6)

w h e r e the s u m is t a k e n over a l l i n e i g h b o r i n g n u c l e i . B e c a u s e the n u c l e a r s e p a r a t i o n r is r a i s e d to the s i x t h p o w e r , the s e c o n d m o m e n t is a sensitive i ;


476


1

m e a s u r e of the d e n s i t y of m o l e c u l a r p a c k i n g . W e assume t h a t i t is n o t necessary to d i s t i n g u i s h b e t w e e n r o t a t i o n a l j u m p s ( w h i c h m o d u l a t e the i n t r a m o l e c u l a r field) a n d t r a n s l a t i o n a l j u m p s ( w h i c h m o d u l a t e the e x t r a molecular

field).

I n a n associated l i q u i d , b o t h processes s h o u l d h a v e

r o u g h l y the same r a t e ; thus, b o t h fields are i n c l u d e d i n E q u a t i o n 6.

The

r e l a x a t i o n t i m e d a t a s h o w s e v e r a l features i n a c c o r d w i t h the B P P t h e o r y : there is a m i n i m u m i n T

a n d at l o w t e m p e r a t u r e s T

2

decreases as the

t e m p e r a t u r e is l o w e r e d . H o w e v e r , the r a t i o of T i to T

2

a n d the v a l u e of

u

T i at the m i n i m u m are inconsistent w i t h t h e i r theory.

Further, their

t h e o r y does n o t p r e d i c t the t w o - p h a s e T b e h a v i o r . A l l of these d e p a r t u r e s Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch037

2

f r o m the B P P t h e o r y c a n b e t a k e n i n t o a c c o u n t b y a l l o w i n g a b r o a d d i s t r i b u t i o n of c o r r e l a t i o n times ( 9 ) .

A t h i g h temperatures, exchange

b e t w e e n sites of different τ is sufficiently r a p i d t h a t a n " a v e r a g e " T o b s e r v e d ( 16).

2

is

A t l o w t e m p e r a t u r e s , the a v e r a g i n g is n o l o n g e r effective;

t h e r e are 2 values of T — t h e m o b i l e T 2

a n d the r i g i d lattice T , — a n d as

2

2

the t e m p e r a t u r e is l o w e r e d f u r t h e r , the f r a c t i o n of n u c l e i i n the m o b i l e state

(f ) m

(1 — f ) m

decreases w i t h

a complementary

increase i n the f r a c t i o n

of n u c l e i i n the r i g i d state. T h e effect of the d i s t r i b u t i o n o n Γι

is o n l y to b r o a d e n the m i n i m u m a n d to raise the e x p e c t e d v a l u e of T i at the m i n i m u m ; n o b r e a k - d o w n i n a v e r a g i n g occurs, i n contrast to T . 2

equations u s e d are

The

(9) 00

r , - ' = l «'{tL-fïpW*

+f [J£^

—00

+ ^] T

PMdj (7)

?

—CO

(8)

/« = jp{t)dx

CO

—00

T

2r

=

T = c

where t

c

(σο )" 2

(σο )~ 2

(10)

1 / 2

(11)

1/2

is the cut-off a b o v e w h i c h a v e r a g i n g i n T

2

n o l o n g e r occurs.

T h e t o t a l n u m b e r of p a r a m e t e r s i n the m o d e l is 5: 3 to fit the free v o l u m e m o d e l for τ, 1 to c h a r a c t e r i z e the d i s t r i b u t i o n w i d t h , a n d the s e c o n d moment.

T h e i n t r o d u c t i o n of the d i s t r i b u t i o n of c o r r e l a t i o n times i n t r o

duces o n l y 1 n e w p a r a m e t e r , the w i d t h p a r a m e t e r , b u t i t explains s e v e r a l d e p a r t u r e s f r o m the B P P t h e o r y .

Equations 7 and 9 were

fitted


simul-


37.

NMR Relaxation

RESiNG AND THOMPSON

I0 l ι 20 4

ι

ι I ι 3.0

ι

ι

I ι ι 4.0 IOVT (°K")

of

ι 1 ι 5.0

477

Water

ι

J 6.0

Figure 2. Median molecular jump rate (3τ*)~* vs. reciprocal temperature for liq uid water, water in charcoal pores, and water in zeolite 13-X Circles at about 10 represent the respective Ti minima. Those at about 10 represent the points at which only half the water remains in the respective mobile phases. 7

5

t a n e o u s l y to the d a t a of F i g u r e 2 b y a least squares r o u t i n e w h i c h also c a l c u l a t e d n u m e r i c a l l y the necessary integrals ( 1 0 ) . T h e "best-fit" t h e o r e t i c a l curves are g i v e n i n F i g u r e 2 a n d agree q u i t e w e l l w i t h the e x p e r i m e n t a l d a t a . T h e s e c o n d m o m e n t e x t r a c t e d f r o m the d a t a is 2.0 Χ 1 0 rad sec~ , w h i c h is r o u g h l y e q u a l to the 2.29 Χ 1 0 2

2

1 0

rad sec" 2

1 0

found by

2

K v l i v i d z e ( 5 ) f r o m the l o w - t e m p e r a t u r e b r o a d - l i n e N M R studies; these results c o n c u r i n s h o w i n g t h a t the n u m b e r of nearest n e i g h b o r

water

m o l e c u l e s is, o n t h e average, less t h a n i n i c e . T h e values of the m e d i a n j u m p t i m e , τ*, are p r e s e n t e d i n F i g u r e 2 i n the f o r m ( 3 τ * ) — i . e . , as _1

j u m p i n g r a t e s — a n d these are c o m p a r e d

w i t h the same q u a n t i t i e s for

w a t e r i n c h a r c o a l pores a n d f o r b u l k w a t e r ( h y p o t h e t i c a l ) temperatures. fitting

at v a r i o u s

T h e hypothetical curve for b u l k water was obtained b y

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

t e m p e r a t u r e to E q u a t i o n 2 ( 7 , 1 2 ) . A t r o o m .temperature, the j u m p i n g rate ( p r o p o r t i o n a l to

fluidity)

is a b o u t 100 times h i g h e r f o r b u l k w a t e r

a n d f o r w a t e r i n c h a r c o a l pores (dia 25 A ) t h a n f o r t h e z e o l i t i c " i n t r a crystalline-fluid" water.

N e v e r t h e l e s s , t h e z e o l i t i c w a t e r protons are at


478


least 1000 times m o r e m o b i l e t h a n t h e protons i n i c e at 0 ° C .

1

This and

the fact that the free v o l u m e m o d e l a p p l i e s to this system s h o w t h a t t h e w a t e r a d s o r b e d i n zeolite 1 3 - X is t r u l y a n i n t r a c r y s t a l l i n e fluid. Literature


(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)

Cited

Barrer, R. M., Ber. Bunsen Ges. Phys. Chem. 1965, 69, 786. Bloembergen, N., Purcell, Ε. M., Pound, R. V., Phys. Rev. 1948, 73, 679. Cohen, M . H., Turnbull, D., J. Chem. Phys. 1963, 39, 2783. Cohen-Addad, J. P., Farges, J. P., J. Phys. (Paris) 1966, 27, 739. Kvlividze, V. I., Kiselev, V. F., Serpinski, V. V., Dokl. Akad. Nauk SSSR 1965, 165, 1111. Pfeifer, H., Przyborowski, F., Schirmer, W., Stach, H., Z. Phys. Chem. (Leipzig) 1967, 236, 345. Pryde, J. Α., Jones, G. O., Nature 1952, 170, 685. Resing, Η. Α., Advan. Mol. Relaxation Processes 1968, 1, 109. Resing, Η. Α., J. Chem. Phys. 1965, 43, 669. Resing, Η. Α., Thompson, J. K., Ibid., 1967, 46, 2876. Resing, Η. Α., Thompson, J. K., Proc. Colloque Ampere XV, North Hol land, Amsterdam, 1969, p. 237. Saxton, J. Α., "Meteorological Factors in Radio Wave Propagation," p. 278, The Physical Society, London, 1946. Thompson, J. K., Krebs, J. J., Resing, Η. Α., J. Chem. Phys. 1965, 43, 3853 Van Vleck, J. H., Phys. Rev. 1948, 74, 1168. Woessner, D. E., J. Chem. Phys. 1963, 39, 2783. Zimmerman, J. R., Brittin, W. E., J. Phys. Chem. 1957, 61, 1328.

RECEIVED February 13,

1970.

Discussion N . G . Parsonage ( I m p e r i a l C o l l e g e , L o n d o n ) : Is there a n y u s e f u l i n f o r m a t i o n w h i c h c a n b e o b t a i n e d b y d e l i b e r a t e l y u s i n g zeolites w h i c h h a v e b e e n i o n - e x c h a n g e d so as to c o n t a i n almost s t o i c h i o m e t r i c amounts of p a r a m a g n e t i c ions? H . A . Resing: Effects of p a r a m a g n e t i c ions i n zeolites o n r e l a x a t i o n times h a v e b e e n

only cursorily examined

(Ducros,

Cohen, - A d d a d —

theses, U n i v e r s i t y of G r e n o b l e ) w i t h not too m u c h success.

L a r g e effects

c e r t a i n l y o c c u r , b u t m u c h i n t e r p r e t i v e w o r k appears to be r e q u i r e d . R. A . Munson ( B u r e a u of M i n e s , C o l l e g e P a r k , M d . 2 0 7 4 0 ) :

You

h a v e c o m p a r e d y o u r m o b i l i t i e s i n zeolites w i t h those i n p u r e w a t e r a n d ice. W o u l d i t n o t b e m o r e r e a l i s t i c to c o m p a r e w i t h electrolyte solutions of analogous concentration?

W h a t results w o u l d y o u expect for this case?

H . A . Resing: I b e l i e v e that electrolytes of s i m i l a r

concentration

w o u l d not l e a d to s u c h a 2 0 - f o l d l o w e r i n g of m o b i l i t y , b u t o n l y to a 2- or 3-fold effect at most.


37.

RESING A N D T H O M P S O N

NMR

Relaxation

of

Water

479

D . M . R u t h v e n ( U n i v e r s i t y of N e w B r u n s w i c k , F r e d e r i c t o n , N . B . , C a n a d a ) : I w a s i n t e r e s t e d i n the c o n c l u s i o n t h a t the d e n s i t y of i n t r a c r y s t a l l i n e w a t e r is s i m i l a r to that of the b u l k l i q u i d . T h i s agrees rather w e l l w i t h the conclusions of D u b i n i n et al. w h i c h are b a s e d o n e q u i l i b r i u m s o r p t i o n studies i n N a X zeolite a n d also i n other systems. H . A . R e s i n g : Such information based on adsorption and crystallog r a p h y is c e r t a i n l y m o r e definitive t h a n that a d d u c e d i n o u r p a p e r .

This

" e x t e r n a l " i n f o r m a t i o n is i n the n a t u r e of a b o u n d a r y c o n d i t i o n o n o u r i n t e r p r e t a t i o n of the N M R results; i.e., i t is a c h e c k o n the correctness of Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch037

o u r interpretations. P . B . V e n u t o ( M o b i l O i l , P a u l s b o r o , N . J . 0 8 0 3 4 ) : I w o u l d l i k e to r e i n f o r c e y o u r c o m m e n t c o n c e r n i n g the d e c r e a s i n g m o b i h t y of w a t e r at v e r y l o w i n t r a z e o l i t e concentrations b y c i t i n g the e x t r e m e l y h i g h isosteric heats of a d s o r p t i o n , @ 3 0 - 4 5 k c a l / m o l e , r e p o r t e d at l o w θ some t i m e ago for s o d i u m faujasite b y B a r r e r a n d c o w o r k e r s .


NMR Relaxation of Water in Zeolite 13-X - ACS Publications

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