Isomerization of

41 Isomerization of n-Hexane and n-Pentane over Various Bifunctional Zeolitic Catalysts I. Influence of the Structure Parameters of the Catalysts on the Activity and Selectivity G. BRAUN, F. FETTING,* and H . SCHOENEBERGER Institut für Chemische Technologie, ΤΗ Darmstadt, West-Germany and E . Gallei, BASF AG., 6700 Ludwigshafen, West-Germany

ABSTRACT H-mordenite and CaY-zeolite loaded with various noble and transition metals were tested. The bifunctional catalysts contai­ ning platinum or palladium were demonstrated to be the most active. The H-mordenite catalysts showed high activity and selectivity at temperatures as low as 573 K. The isomerization of n-hexane and n-pentane over Pt/CaY are possibly "structure sensitive" reactions. Kinetic studies showed that intraparticle mass transfer limita­ tions in the secondary pore system were significant for Pt/CaY but not for Pt/H-mordenite catalyst. Introduction Itie requirements f o r unleaded h i g h octane g a s o l i n e s have l e d to r e s e a r c h e f f o r t s , both i n d u s t r i a l and academic, i n the area o f p a r a f f i n i s o m e r i z a t i o n and other r e f o r m i n g r e a c t i o n s . Because o f the r e g u l a t i o n s r e g a r d i n g the emissions o f hydrocarbons, carbon monoxide, n i t r o g e n oxide and l e a d compounds from i n t e r n a l com­ b u s t i o n engines, l e a d a l k y l c o n c e n t r a t i o n s w i l l have t o decrease, r e s u l t i n g i n an i n c r e a s e d need f o r l i g h t hydrocarbons w i t h h i g h octane numbers, e.g. isomers o f n-hexane and n-pentane. In former s t u d i e s we i n v e s t i g a t e d the d e h y d r o c y c l i z a t i o n o f nhexane over commercial b i f u n c t i o n a l c a t a l y s t s ( 1 , 2 ) . The s t r u c ­ ture parameters o f these i n d u s t r i a l c a t a l y s t s were n o t completely a v a i l a b l e , so a d e t a i l e d statement concerning the c o r r e l a t i o n s between the s t r u c t u r e o f the c a t a l y s t s and t h e i r a c t i v i t y was not p o s s i b l e . I n a d d i t i o n , the i n f o r m a t i o n from the l i t e r a t u r e about reforming r e a c t i o n s over z e o l i t i c c a t a l y s t s i s scanty r e g a r d i n g the r e l a t i o n s between a c t i v i t y and s e l e c t i v i t y and s t r u c t u r a l pa­ rameters o f the employed c a t a l y s t s ( 3 - 1 0 ) . However, such c o r r e ­ l a t i o n s are important f o r c a t a l y s t o p t i m i z a t i o n . *To whom correspondence concerning t h i s paper should be addressed.

504

41.

BRAUN ET

Isomerization

AL.

of n-Hexane

and

n-Pentane

505

T h e r e f o r e , i n t h i s work the i n f l u e n c e of the c a t a l y s t s t r u c ­ ture parameters, e s p e c i a l l y o f the s t a t e of the m e t a l l i c phase, on the a c t i v i t y and s e l e c t i v i t y f o r the i s o m e r i z a t i o n of n-hexane and n-pentane was i n v e s t i g a t e d . As t e s t i n g r e a c t i o n s , the i s o m e r i z a t i o n r e a c t i o n s o f Q-hexane and n-pentane were s e l e c t e d mainly f o r two reasons: f i r s t , t h e i r low heats of r e a c t i o n prevent h i g h temperature p r o f i l e s i n the ca­ t a l y s t bed and second, a l l r e a c t i o n products can be q u a n t i t a t i v e l y a n a l y z e d . This f a c i l i a t e d e v a l u a t i o n of the k i n e t i c data, which was c a r r i e d out along with i n v e s t i g a t i o n s regarding mass t r a n s f e r l i m i t a t i o n s on the e x t e r n a l (gas to p a r t i c l e ) and i n t e r n a l s u r f a c e ( i n t r a p a r t i c l e ) of the c a t a l y s t p e l l e t s . Experimental M a t e r i a l s ; S t a r t i n g m a t e r i a l s f o r the c a t a l y s t s were NaY z e o l i t e powder (Linde SK-4o) and a commercial H-mordenite powder (Norton Zeolon l o o ) . Both m a t e r i a l s were f r e e of c l a y b i n d e r . CaY z e o l i t e was prepared from NaY by exchanging p a r t of the Na-ions (75#) by C a . The chemical compositions and the s t r u c ­ t u r a l parameters of the z e o l i t e s are given i n Table I . 2 +

^eolite

H-mordenite

NaY

CaY

64.3 21.9 13.8

65.0 22.1

87.9

3.5

1-5

parameter chemical composition [wt %]

Si0 A1 0 Na 0 CaO 2

2

3

2

s p e c i f i c s u r f a c e area [m pore volume [ml/g]

1250

/g] 0.60

secondary pores

ο·3ο -

primary pores

[X]

secondary pores

c r y s t a l s i z e [/*) Table I .

9 Λ

primary pores

mean pore diameter

I0.6

ΐ

500

ο .o6

0.57

o.o3

o.?7

9 4ooo

1.2

Chemical a n a l y s i s on anhydrous b a s i s and parameters of z e o l i t e s

7-8 loooo

6

structure

MOLECULAR SIEVES—II

506

Some o f these z e o l i t e s were loaded w i t h o.5# by weight o f v a r i o u s t r a n s i t i o n and noble metals ( l l _ ) by i o n exchange o r im­ pregnation a t room temperature. Noble metal loaded z e o l i t e s were reduced a t 573 Κ and z e o l i t e s c o n t a i n i n g N i ions a t 773 K. The s t r u c t u r e parameters, e.g. s p e c i f i c s u r f a c e area o f the z e o l i t e s and the pore s t r u c t u r e were determined by gas s o r p t i o n methods and mercury p e n e t r a t i o n (12). The composition o f the z e o l i t e s u r f a c e r e g a r d i n g the f u n c t i o n a l groups was i n v e s t i g a t e d by means of i n f r a r e d spectroscopy ( 1 3 ) . 2 +

Measurement o f the D i s p e r s i o n o f the M e t a l l i c Phase. The s t r u c t u r a l parameters o f the m e t a l l i c phase, f o r example the d i s p e r s i o n o f the metal on the c a r r i e r , the metal c r y s t a l l i t e s i z e and the s p e c i f i c s u r f a c e area o f the supported metal have been determined by chemisorption o f hydrogen f o r n i c k e l and platinum and o f carbon monoxide f o r palladium, u s i n g a m o d i f i e d Perkin-Elmer S h e l l Sorptometer model 212 B. The pulse flow ad­ s o r p t i o n method was employed. FOr a l l c a t a l y s t s good agreement was obtained between t h i s pulse technique and e l e c t r o n microscopy determinations o f the s t r u c t u r a l parameters o f the m e t a l l i c phase (1^). C a t a l y t i c A c t i v i t y Measurements ( R e a c t o r ) . I s o m e r i z a t i o n o f n-hexane and n-pentane was performed i n a flow apparatus w i t h a f i x e d bed r e a c t o r operated under isothermal and plug-flow con­ d i t i o n s and d i f f e r e n t i a l conversions ( < l o # ) . The downflow tube r e a c t o r had an inner diameter o f 2o mm and a l e n g t h o f 165 mm. The maximum l i q u i d f e e d f o r f l u i d hydrocarbons and hydro­ gen gas was 2oo ml/hr and I500 Nl/hr, r e s p e c t i v e l y . The c a t a l y s t p e l l e t s (3 χ 3ran)were contained i n the middle o f the r e a c t o r tube. I n e r t spheres were p l a c e d above and under the c a t a l y s t bed to o b t a i n b e t t e r m i x i n g . Before measuring the a c t i v i t y and s e ­ l e c t i v i t y , the c a t a l y s t p e l l e t s were a c t i v a t e d f o r 12 hours with hydrogen (2 N l / h r ) a t 623 Κ and a t 1 b a r . Feed mixtures o f hydrogen and hydrocarbons were preheated to the r e a c t o r temperature before e n t e r i n g the bed. Merck " a n a l y t i c a l grade" l i q u i d hydrocarbon was dosed by a "Burdosa" microdosing pump i n t o a heated stream o f hydrogen c o n t r o l l e d by a flowmeter. Beyond the c a t a l y s t bed a p a r t i a l stream o f products was removed and d i r e c t l y t r a n s f e r r e d t o a gas chromatograph equipped with a l o o m squalane c a p i l l a r y and a FID. T h i s d e s i g n allowed a continuous q u a n t i t a t i v e a n a l y s i s o f the p r o d u c t s . The main pro­ duct stream was cooled down and conducted i n t o a seperator and decompression v e s s e l . C a t a l y t i c A c t i v i t y Measurements (Procedure). The t e s t i n g procedure was dependent on the v a r i o u s problems t o be s o l v e d and v a r i e d i n the f o l l o w i n g range:

41.

BRAUN ET AL.

Isomerization

of n-Hexane

Temperature T Pressure Ρ R a t i o H /HC Weight of c a t a l y s t W L i q u i d feed F 2

and

n-Pentane

507

473 - 773 Κ 5 - 3ο bar 2 - 2ο mole/mole : o,5 - 2,5 gram ml/min. : o,2 - 1 , 2 : : :

R e s u l t s and D i s c u s s i o n . At f i r s t the z e o l i t i c c a t a l y s t s had to be t e s t e d r e g a r d i n g t h e i r a c t i v i t y and s e l e c t i v i t y f o r the i s o m e r i z a t i o n of n-hexane and n-pentane. As a measure f o r the a c t i v i t y was d e f i n e d the temperature dependency of the conversion and f o r the s e l e c t i v i t y the f r a c t i o n of the isomers of the t o t a l c o n v e r s i o n . Thereby had to be kept i n mind, t h a t the chemical e q u i l i b r i u m between n - p a r a f f i n s and i s o - p a r a f f i n s i s s h i f t e d to the isomers a t low temperatures. Therefore v a l u a b l e c a t a l y s t s should show h i g h a c t i v i t y and s e l e c t i v i t y already a t f a i r l y low temperatures. B i f u n c t i o n a l C a t a l y s t s . For the p r e p a r a t i o n of the b i ­ f u n c t i o n a l c a t a l y s t s the a c t i v e z e o l i t e s CaY and H-mordenite had been employed as supports. The c h a r a c t e r i s t i c p r o p e r t i e s of the c a r r i e r s were not changed d u r i n g metal l o a d i n g , as determined by i n f r a r e d spectroscopy and mercury p e n e t r a t i o n (12,15). The r e s u l t s obtained f o r the conversion of n-hexane over various b i f u n c t i o n a l c a t a l y s t s are shown i n Figure 1 and corresponding data are l i s t e d i n Table I I . catalyst

Re Ir Pt Pd

/ / / /

CaY CaY CaY CaY

activity [mole %]

4o,6 25,o 2o,7 36,2

the

selectivity

o,ol o,24 o,83 o,86

Table I I . A c t i v i t y and s e l e c t i v i t y f o r the conversion of n-hexane over v a r i o u s b i f u n c t i o n a l c a t a l y s t s with CaY z e o l i t e as support a t 673 K. Almost no i s o m e r i z a t i o n a c t i v i t y was found f o r the c a t a l y s t s with N i , Ru and Rh as m e t a l l i c components and C a Y - z e o l i t e as c a r r i e r . The i s o m e r i z a t i o n s e l e c t i v i t y of the Ir/CaY c a t a l y s t was moderate and t h a t of the Re/CaY was even lower (see Table I I ) . However, The Ru, Rh and N i c o n t a i n i n g c a t a l y s t s r e v e a l e d a h i g h hydroc r a c k i n g a c t i v i t y y i e l d i n g p r e f e r e n t i a l l y methane as product; and a r a p i d d e a c t i v a t i o n was observed. The r e s u l t s f o r i s o m e r i ­ z a t i o n of n-hexane over c a t a l y s t s w i t h H-mordenite as support and N i , Pd, or Pt as m e t a l l i c components are i l l u s t r a t e d i n

MOLECULAR SIEVES—II

508 Figure 2 and Table I I I . catalyst

Ni/H-mordenite Pd/H-mordenite Pt/H-mordenite

activity [mole JÈ] 51,9 11.9 25,4

selectivity

o,2o o,97

0,90

Table I I I . A c t i v i t y and s e l e c t i v i t y of b i f u n c t i o n a l c a t a l y s t s with H-mordenite as support a t 573 K. Contrary to the c a t a l y s t s with C a Y - c a r r i e r s , Pt/H-mordenite shows a higher a c t i v i t y than Pd/H-mordenite. The c a t a l y s t Ni/Ήmordenite i s very a c t i v e f o r hydrocracking as already r e p o r t e d f o r Ni/CaY. D i f f e r e n c e s , however, a r i s e i n the products produced over the Ni/H-mordenite or the Ni/CaY c a t a l y s t . Whereas over Ni/CaY methane i s produced as main product over Ni/H-mordenite the n-hexane conversion y i e l d s propane and butane as already r e p o r t e d i n l i t e r a t u r e (16). I t should be emphasized the low temperatures (493-573 K) a t which the c a t a l y s t s with H-mordenite supports show already h i g h a c t i v i t y . For a comparison of the a c t i v i t y and s e l e c t i v i t y o f one metal component on d i f f e r e n t c a r r i e r s i n Figure 3 are p l o t t e d the conversions and s e l e c t i v i t i e s as a f u n c t i o n of the temperature f o r the c a t a l y s t s Pt/CaY and Pt/H-mordenite. From Figure 3 i t i s shown, t h a t the h i g h ac­ t i v i t y and s e l e c t i v i t y f o r Pt/H-mordenite, which i s already ob­ served a t temperatures between 523 and 583 Κ i s reached with Pt/CaY f i r s t between 613 and 693 K. The same r e s u l t s were ob­ t a i n e d f o r the n-pentane c o n v e r s i o n . Influence of the D i s p e r s i o n of the Metal Phase. For a c l o s e r i n s i g h t i n t o the c a t a l y t i c p r o p e r t i e s of the m e t a l l i c components, the i n f l u e n c e of the metal d i s p e r s i o n on the conversion f o r the n-hexane and n-pentane i s o m e r i z a t i o n was i n v e s t i g a t e d . The c h a r a c t e r i s t i c s t r u c t u r e parameters are as already men­ t i o n e d the d i s p e r s i o n R, the s p e c i f i c metal s u r f a c e area S, and the mean metal p a r t i c l e diameter d. The d i s p e r s i o n R i s de­ f i n e d as the r a t i o of f r e e metal atoms on the s u r f a c e to the t o ­ t a l metal atoms on the c a r r i e r . A comparison of the methods of l o a d i n g , e.g. impregnation or ion-exchange f o r the c a t a l y s t Pt/CaY r e s u l t e d i n metal d i s ­ persions of R = 0.62 and o . 8 l , r e s p e c t i v e l y . The t e s t i n g of these c a t a l y s t s i n the r e a c t o r y i e l d e d a higher a c t i v i t y f o r the i o n exchanged c a t a l y s t , t h a t means a c t i v i t y and metal d i s p e r s i o n are i n t h i s range p r o p o r t i o n a l t o each o t h e r . More d e t a i l e d informa­ t i o n r e g a r d i n g the d i s p e r s i o n should be obtained by systematic s t u d i e s of s i n t e r i n g o f the metal phase f o l l o w e d by t e s t i n g o f these c a t a l y s t s f o r the n-hexane i s o m e r i z a t i o n a c t i v i t y . S i n t e r i n g

41.

BRAUN E T A L .

Figure 2.

Isomerization

of n-Hexane

and

n-Pentane

509

Conversion of n-hexane and yield of isomers as functions of temperature for bifunctional catalysts with H-mordenite as support

MOLECULAR SIEVES—Π

510

o f the metal phase decreases the s p e c i f i c metal s u r f a c e area and simultaneously increases the mean metal? p a r t i c l e s i z e . The c r y s ­ t a l l i n e s t r u c t u r e o f the z e o l i t i c supports was n o t damaged by the s i n t e r i n g procedure as checked by x-ray a n a l y s i s . The h y d r o x y l group c o n c e n t r a t i o n i s mainly a f u n c t i o n o f the a c t i v a t i o n tem­ perature and had a constant value f o r a l l c a t a l y s t samples as de­ termined by i r - s p e c t r o s c o p y . The s t r u c t u r e parameters o f a Pt/CaY sample s i n t e r e d a t 973 Κ f o r d i f f e r e n t times a r e l i s t e d i n Table If. catalyst Pt/CaY Pt/CaY Pt/CaY Pt/CaY

sintering

S L

2 hrs,973 Κ 5 hrs,973 Κ 16 Hrs,973 Κ

gr

Pt

J

d

[%]

189,0

11

39,o 25,o l4,o

60 95 163

Table IV. S t r u c t u r a l parameters o f the m e t a l l i c phase a f t e r s i n t e r i n g a t 973 Κ f o r d i f f e r e n t t i m e s . By n o r m a l i z i n g the obtained a c t i v i t i e s f o r the v a r i o u s s i n t e r e d c a t a l y s t s t o the corresponding s p e c i f i c s u r f a c e area S the spe­ c i f i c a c t i v i t y can be c a l c u l a t e d . I f the s p e c i f i c a c t i v i t y i s p l o t t e d a g a i n s t the mean metal c r y s t a l l i t e diameter d, the curves shown i n F i g u r e 4 are obtained f o r the i s o m e r i z a t i o n o f n-hexane. I d e n t i c a l r e s u l t s were obtained f o r the i s o m e r i z a t i o n o f n-pen­ t a n e . The graphs have a maximum f o r the s p e c i f i c a c t i v i t y a t metal p a r t i c l e diameters between 80-I00 X. These r e s u l t s l e n d m i l d support t o the c o n c l u s i o n t h a t the i s o m e r i z a t i o n o f η,-hexane and n-pentane i s a " s t r u c t u r e s e n s i t i v e " r e a c t i o n ; the p o s s i b l e mi­ g r a t i o n o f the c a t i o n s i n the z e o l i t e l a t t i c e d u r i n g the s i n t e r i n g steps could a l s o have s l i g h t l y i n f l u e n c e d the s p e c i f i c a c t i v i t y . The concept o f " s t r u c t u r e s e n s i t i v e o r i n s e n s i t i v e r e a c t i o n " has been proposed p r e v i o u s l y i n connection w i t h r e l a t i o n s , between c a t a l y t i c a c t i v i t y and s t r u c t u r e o f m e t a l l i c phase (l£). For a " s t r u c t u r e s e n s i t i v e " r e a c t i o n the conversion o f n-hexane or n-­ pentane becomes dependent on the arrangement o f metal atoms i n the i n d i v i d u a l metal c r y s t a l f a c e s . Such r e l a t i o n s a r e n o t y e t known i n l i t e r a t u r e f o r n-hexane and n-pentane i s o m e r i z a t i o n over Pt/CaY catalysts. f

K i n e t i c s . A f i r s t order k i n e t i c model w i t h k and k , the forward and reverse r e a c t i o n r a t e constants, r e s p e c t i v e l y , was based on the f o l l o w i n g r e a c t i o n n-paraffin ~

«

k

-

[ i-paraffin]

(1)

k

The r a t e o f r e a c t i o n , expressed as moles o f i-hexanes o r i pentanes produced per hour, per gram c a t a l y s t i s represented by

41.

B R A U N ET A L .

Isomerization

of n-Hexane

and

511

n-Pentane

- c o n v e r s i o n o f n-hexane

^

y i e l d o f isomers

Pt / H-mordenite / * Ft/CcY

χ : T[KJ

723

Figure 3. Conversion of n-hexane and yield of isomers as function of tempera­ ture for bifunctional catalysts with Pt as metallic component on CaY and Hmordenite support

Figure 4.

Specific activity as function of mean metal crystallite di­ ameter for the isomerization of n-hexane

MOLECULAR SIEVES—Π

512

C l i

x

i-hexanes

where [χ, , 1 stands f o r the mole f r a c t i o n of a l l i s o i-hexanes mers of η,-hexane and χ f o r the corresponding mole f r a c t i o n a t equilibrium. A f t e r i n t e g r a t i o n equation 2 can be used to determine values f o r . The dependency of k on the temperature i s used to evaluate the a c t i v a t i o n e n e r g i e s . Each s e t of data was l i n e a r l y regressed to o b t a i n k and the a c t i v a t i o n e n e r g i e s . The obtained k i n e t i c data are " o v e r a l l " values which are evaluated f o r a coupled r e a c t i o n system. Before the e v a l u a t i o n of the k i n e t i c data the i n f l u e n c e of g a s - t o - p a r t i c l e mass t r a n s f e r and i n t r a ­ p a r t i c l e d i f f u s i o n on the o v e r a l l r a t e had to be i n v e s t i g a t e d . I t was shown, t h a t g a s - t o - p a r t i c l e mass t r a n s f e r was an i n s i g ­ n i f i c a n t r e s i s t a n t to the o v e r a l l r a t e f o r both Pt/CaY and Pt/H-mordenite confirmed by the c r i t e r i o n of Mears (18). The i n f l u e n c e of i n t r a p a r t i c l e d i f f u s i o n i n the secondary pores was s t u d i e d by systematic v a r i a t i o n of the c a t a l y s t p e l l e t s i z e . A s m a l l i n f l u e n c e o f i n t r a p a r t i c l e mass t r a n s f e r l i m i t a t i o n was found f o r Pt/CaY but not f o r Pt/H-mordenite. The im­ portance of micropore d i f f u s i o n was not determined and the k i n e t i c r a t e s include any e f f e c t of d i f f u s i o n a l r a t e s i n micropores. The experimentally determined values f o r catalyst

effecti­ pellet veness size d=H[mm] f a c t o r

Pt/CaY Pt/CaY Pt/CaY Pt/CaY

4 3 o.7 o.5

Pt/H-mord. Pt/H-mord. Pt/H-mord. Pt/H-mord.

4 3 o.7 o.5

T=633 Κ ο .6o o.73 1 .oo 1 .oo T=543 Κ o.9o 0.94 1.00 1 .00

ε V

k

r

1

J

mole

J

r eff

L

66 .gî 76. l j 97 .οΐ 97.0-

7 8 lo lo

7.66 9.52 13.23 13.25

115 .οί 115.0Ϊ 120.012ο.οΐ

11 11 12 12

1.67 1.89 2.o6 2.o2

mole hr.gr c a t .

χ lo" χ " x " x "

-j J

3

-2

Table V. R e s u l t s of i n t r a p a r t i c l e mass t r a n s f e r

x lo χ " χ " χ " limitation

e f f e c t i v e n e s s f a c t o r s and the corresponding r a t e constants and a c t i v a t i o n energies are l i s t e d i n Table V. The almost constant values of the a c t i v a t i o n energies and e f f e c t i v e n e s s f a c t o r s f o r Pt/H-mordenite c a t a l y s t s i n d i c a t e t h a t no s i g n i f i c a n t mass t r a n s -

41.

BRAUN ET AL.

Isomerization

of n-Hexane

and

n-Pentane

513

f e r l i m i t a t i o n o c c u r s . However, with Pt/CaY c a t a l y s t a continuous increase o f e f f e c t i v e n e s s f a c t o r s and a c t i v a t i o n energies i s ob­ served i f the c a t a l y s t p e l l e t s are broken up i n t o small p i e c e s . These r e s u l t s i n d i c a t e the occurance o f i n t r a p a r t i c l e d i f f u s i o n l i m i t a t i o n i n the secondary pore system t h a t means i n the space between the z e o l i t e c r y s t a l s . A d d i t i o n a l support i s given by the s t r u c t u r a l parameters of the secondary pores o f Pt/CaY and Pt/Hmordenite (Table I ) . The average diameter o f the secondary pores of Pt/CaY has a value of 4ooo A and makes the d i f f u s i o n l i m i t a ­ t i o n much more probable than the appropriate pore diameter f o r Pt/H-mordenite which i s 2,5 times higher ( l o ooo A ) . S i m i l a r e f f e c t s concerning mass t r a n s f e r l i m i t a t i o n s have been obtained f o r the i s o m e r i z a t i o n of n-pentane. Q

Conclusions. The most a c t i v e b i f u n c t i o n a l i s o m e r i z a t i o n c a t a l y s t s are composed o f z e o l i t i c support l i k e H-mordenite or CaY and noble metals l i k e Pt or Pd. The c a t a l y s t s with H-mordenite as support show already a t temperatures as low as 573 Κ very high a c t i v i t y and s e l e c t i v i t y f o r the i s o m e r i z a t i o n . The i n v e s t i g a t i o n about the r e l a t i o n s between the s t r u c t u r a l parameters o f the m e t a l l i c phase and the a c t i v i t y r e v e a l e d t h a t the i s o m e r i z a t i o n of nhexane and n-pentane over Pt/CaY c a t a l y s t s i s p o s s i b l y " s t r u c t u r e s e n s i t i v e " . K i n e t i c s t u d i e s showed a s l i g h t i n t r a p a r t i c l e mass t r a n s f e r l i m i t a t i o n f o r Pt/CaY, but not f o r Pt/H-mordenite. Acknowledgement. The authors want t o thank H . L i t t e r e r und C.P.Halsig f o r experimental a s s i s t a n c e and h e l p f u l d i s c u s s i o n s . They are a l s o indebted t o the "Deutsche Forschungsgemeinschaft" and the "Bundesministerium f u r Porschung und Technologie" f o r sub­ s t a n t i a l f i n a n c i a l support. Literature Cited. 1. C r i s t o f f e l , E . , V i e r r a t h , H . , P e t t i n g , P . , 5th European, 2nd Int.Symp.Chem.Reaction Engng.,Amsterdam,(1972)2-49 2. Christoffel,E.,Fetting,Ρ.,Vierrath,Η., J.Catal.(1975)40,249 3. Hopper,J.R.,Voorhies,A.,Jr.,Ind.Eng.Chem.Proc.Des.Develop. (1972),11,294 4. Garanin,V.J.,Minacheν,Κh.Μ.,Isakova,Τ.A.,Neftekhimiya(1972), 12,501 5. Beecher,R.,Voorhies.A.,Jr.,Ind.Eng.Chem.Proc.Des.Develop. (1969)8,366 6 . Minachev,Kh.,M.,Garanin,V.J.,Piguzova,L.I.,Vitukhina,A.S., Izv.Aka.Nauk SSSR,Ser.Khim.(1966),6,1oo1 7. Rabo,J.A.,Pickert,Ρ.E.,Mays,R.L.,Ind.Eng.Chem.(1961 ),53,773 8. Kouwenhoven,H.W.,Adv.Chem.Ser.(1973 ),121,529 9. Lanewala,M.A.,Pickert,Ρ.Ε.,Bolton,A.Ρ.,J.Catal.(1967),9,95 10. Bolton,A.P.,Lanewala,M.A.,J.Catal.(1970),18,1

514

MOLECULAR SIEVES—Π

11. Gallei,E.,Eisenbach,D.,Ahmed,A.,J.Catal.(1974),22,62 12. Eisenbach,D.,Gallei,E.,Chem.Ing.Techn.(1975),45,1261 13. Gallei,E.,Eisenbach,D.,J.Catal.(1975),37,474 14. Braun,G.,Ph.D.Thesis,TH Darmstadt, in p r e p a r a t i o n 15. Eisenbach,D.,Ph.D.Thesis,TH Darmstadt,West-Germany,(1975) 16. Burbridge,B.W.,Advan.Chem.Ser.(1971),102,400 17. Boudait,M.,Advan.Catal.Rel.Subj.(1969),20,153 18. Mears,D.Ε.,Ind.Eng.Chem.Proc.Des.Develop.(1971),10,541