Ruthenium hydrogenation catalysts: Activation characterization application

Activation Characterization Application

P. G. J. Koopman

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Activation Characterization Application

Proefschrift ter verkrijging van

de graad van doctor in de

technische wetenschappen

aan de Technische Hogeschool Delft,

op gezag van de rector magnificus

Prof. Ir. B. P. Th. Veltman,

voor een commissie aangewezen

door het college van dekanen

te verdedigen op

woensdag 5 november 1980

te 16.00 uur door

Petrus Gerardus Joseph Koopman

scheikundig ingenieur

geboren te Amsterdam

^3, öija-NsfR.ioi /•?/

Dit proefschrift kwam tot stand onder

leiding van

Prof. Dr. Ir. H. van Bekkum, promotor,

en

Dr. Ir. A. P. G. Kieboom

Drawings: J. M. Dijksman and W. J. de Haas

Typing : Mrs. M. A. A. van der Kooij-van Leeuwen

CONTENTS I n t r o d u c t i o n I I n d u c t i o n e f f e c t s i n l i q u i d phase hydrogénation c a t a l y z e d by r u t h e n i u m on c a r b o n 5 S ummary 5 I n t r o d u c t i o n 5 E x p e r i m e n t a l 6 R e s u l t s 6 No prior treatment 6 Pretreatment in suspension 8

High temperature pretreatment 10 TGA and TPR experiments 12

Solvent effect 12

D i s c u s s i o n 14

Nature of the induction period 14

Hydrogen uptake 15 C o n c l u s i o n s 17 A d d i t i o n a l comments 18 L i t e r a t u r e 18 I I A c t i v a t i o n o f r u t h e n i u m on s i l i c a h y d r o g e n a t i o n c a t a l y s t s 21 Summary 21 I n t r o d u c t i o n 21 E x p e r i m e n t a l 22 R e s u l t s 22 Unsupported ruthenium 22 Supported ruthenium 23 Activity measurements 25 D i s c u s s i o n 25 A d d i t i o n a l comments 27 L i t e r a t u r e 29

V I I I I I I P r e p a r a t i o n and h i g h t e m p e r a t u r e a c t i v a t i o n o f r u t h e n i u m on c a r b o n hydrogénation c a t a l y s t s 31 S ummary 31 I n t r o d u c t i o n 31 E x p e r i m e n t a l 32 R e s u l t s and d i s c u s s i o n 32 Adsorption/Impregnation 32 Calcination 33 Reduction/Activation 34 Activity 36 A d d i t i o n a l comments 38 L i t e r a t u r e 39

IV Temperature programmed r e d u c t i o n . A p p a r a t u s and P r o c e d u r e 41

Summary 41 I n t r o d u c t i o n 41 E x p e r i m e n t a l 42 R e s u l t s 43 L i t e r a t u r e 45 V C h a r a c t e r i z a t i o n o f r u t h e n i u m c a t a l y s t s as s t u d i e d by t e m p e r a t u r e programmed r e d u c t i o n 47 Summary 47 I n t r o d u c t i o n 47 E x p e r i m e n t a l 48 R e s u l t s 49 Hydrogen desorption 49 Unsupported ruthenium (oxide) 51

Silica supported ruthenium (oxide) 54

D i s c u s s i o n 56 L i t e r a t u r e 60

VI S o l v e n t - r e a c t a n t - s u p p o r t i n t e r a c t i o n s i n l i q u i d phase h y d r o g e n a t i o n 63 Summary 63 I n t r o d u c t i o n 63 E x p e r i m e n t a l 64 Materials 64 Procedure 65 R e s u l t s 65

Rate and adsorption measurements 65 Effect of solvent/support combination 69

D i s c u s s i o n 72 A d d i t i o n a l comments 75 L i t e r a t u r e 76 V I I Mass t r a n s p o r t i n l i q u i d phase h y d r o g e n a t i o n 79 Summary 79 I n t r o d u c t i o n 79 Rate d e t e r m i n i n g s t e p s f o r t h e gaseous r e a c t a n t 81

Transport of hydrogen from the gasbubbles into the bulk

of the solvent 81 Transport of hydrogen from the bulk of the solvent to

the catalyst 83 Transport of hydrogen in the pores of the catalyst support 84

Rate d e t e r m i n i n g s t e p s f o r t h e d i s s o l v e d o r g a n i c r e a c t a n t 85

Transport of the organic reactant from the bulk of the

solvent to the catalyst 85 Transport of the dissolved liquid reactant in the pores

of the catalyst support 85 Transport of the product from the catalyst to the bulk of

the solvent 86 R e a c t i o n k i n e t i c s 86 C r i t e r i a f o r d e t e r m i n i n g t h e r a t e c o n t r o l l i n g s t e p 90 C a l c u l a t i o n o f mass t r a n s f e r r a t e s 91 E x p e r i m e n t a l 94 E x p e r i m e n t a l r e s u l t s and d i s c u s s i o n 94 L i t e r a t u r e 100 S ame n v a t t i n g 101

INTRODUCTION

H e t e r o g e n e o u s l y c a t a l y z e d l i q u i d phase hydrogénation i s an i m p o r t a n t t o o l f o r t h e r e d u c t i o n o f ( f u n c t i o n a l g r o u p s i n ) o r g a n i c compounds. By a p r o p e r c h o i c e o f t h e c a t a l y s t hydrogénation r e a c t i o n s c a n most o f t e n be c a r r i e d o u t

s u c c e s s f u l l y a t low p r e s s u r e and t e m p e r a t u r e . T h e r e i s a l a r g e number o f r e f e r e n c e s , r e v i e w e d i n a number o f books ( 1 - 1 3 ) , t h a t p e r t a i n t o t h e use o f c a t a l y t i c hydrogénation i n s y n t h e t i c o p e r a t i o n s .

A l t h o u g h t h e m a j o r i t y o f t h e t r a n s i t i o n e l e m e n t s p o s s e s s e s a t l e a s t some c a t a l y t i c a c t i v i t y , most hydrogénation r e a c t i o n s a r e p e r f o r m e d by t h e use o f m e t a l s from group V I I I . I n p a r t i c u l a r P t , P d , Rh, Ru, and N i have been a p p l i e d i n numerous hydrogénations.

A l t h o u g h t h e s e l e c t i o n o f t h e m e t a l i s o f c o u r s e e s s e n t i a l , t h e c h o i c e o f t h e s u p p o r t , t h e way o f c a t a l y s t p r e p a r a t i o n and t h e way o f c a t a l y s t a c t i v a t i o n a r e a l s o i m p o r t a n t f a c t o r s i n d e s i g n i n g a c a t a l y s t . F u r t h e r m o r e , t h e r e a c t i o n c o n d i t i o n s t o be a p p l i e d , i n c l u d i n g s o l v e n t , t e m p e r a t u r e , and hydrogen p r e s s u r e may be d e c i s i v e i n t h e o p t i m i z a t i o n o f t h e hydrogénation p r o c e s s .

Ruthenium, w h i c h has a s p e c i a l m e r i t as a c a t a l y s t f o r t h e hydrogénation o f a r o m a t i c r i n g s and c a r b o n y l g r o u p s , t a k e s an i n t e r m e d i a t e p o s i t i o n i n t h e group V I I I m e t a l s ; i t i s l e s s n o b l e t h a n e.g. P t , Rh, and P d , and more n o b l e t h a n e.g. N i . E x p e r i e n c e s i n o u r l a b o r a t o r y have l e a r n e d t h a t i n p a r t i c u l a r t h e use o f Ru as a c a t a l y s t i n l i q u i d phase hydrogénations was sometimes d i s a p p o i n t i n g f o r r e a s o n s w h i c h were n o t o b v i o u s . F o r i n s t a n c e , u n p r e d i c t a b l e i n d u c t i o n phenomena were f r e q u e n t l y met i n R u c a t a l y z e d l i q u i d phase h y d r o -génations and caused many c a t a l y s t s t o be d i s c a r d e d ( 8 ) . I n a d d i t i o n , Ru c a t a l y s t s were f o u n d t o be v e r y s e n s i t i v e t o s o l v e n t e f f e c t s , e.g. t h e p r e s e n c e o f w a t e r i s r e p o r t e d t o be e s s e n t i a l f o r i t s c a t a l y t i c a c t i v i t y ( 6 , 8, 9 ) .

2 d e v o t e d t o Ru c a t a l y s t s , namely: - t h e a c t i v a t i o n and c h a r a c t e r i z a t i o n o f s i l i c a and c a r b o n s u p p o r t e d Ru c a t a l y s t s ; - t h e b e h a v i o u r o f Ru c a t a l y s t s i n l i q u i d phase hydrogénations; - t h e r o l e o f s o l v e n t - s u p p o r t i n t e r a c t i o n s f o r R u - c a t a l y z e d hydrogénations i n b i n a r y s o l v e n t systems.

The r e s u l t s o f t h e i n v e s t i g a t i o n s , w h i c h were p e r f o r m e d from 1976 t o 1980 have been p u b l i s h e d o r have been s u b m i t t e d f o r p u b l i c a t i o n i n p a p e r s t o w h i c h w i l l be r e f e r r e d i n t h e f o l l o w i n g C h a p t e r s when a p p r o p r i a t e .

A s t u d y o f t h e o r i g i n o f t h e i n d u c t i o n p e r i o d , i . e . t h e t i m e t h e c a t a l y s t needs t o become a c t i v e when suspended i n t h e r e a c t i o n medium, i s d e s c r i b e d i n C h a p t e r I ( 1 4 ) . The c a t a l y s t s used i n t h e s e e x p e r i m e n t s were m a i n l y o f

c o m m e r c i a l o r i g i n . To c o n t r o l t h e p r e p a r a t i o n and t o p e r m i t t h e use o f v a r i o u s s u p p o r t m a t e r i a l s a l s o home-made c a t a l y s t s have been u s e d . The p r e p a r a t i o n and i n p a r t i c u l a r t h e h i g h t e m p e r a t u r e a c t i v a t i o n i n c l u d i n g t h e e f f e c t o f

c a l c i n a t i o n b e f o r e r e d u c t i o n o f b o t h Ru on s i l i c a and Ru on c a r b o n c a t a l y s t s are r e p o r t e d i n t h e C h a p t e r s I I (15) and I I I ( 1 6 ) , r e s p e c t i v e l y . F o r t h e c h a r a c t e r i z a t i o n o f t h e c a t a l y s t s p r e p a r e d a t e m p e r a t u r e programmed r e d u c t i o n

(TPR) a p p a r a t u s has been b u i l t (Chapter I V ) . The c h a r a c t e r i z a t i o n by means o f o x i d a t i o n / r e d u c t i o n o f t h e Ru c a t a l y s t s and by means o f hydrogen d e s o r p t i o n u s i n g TPR i s d i s c u s s e d i n C h a p t e r V ( 1 7 ) . The Ru c a t a l y s t s were a p p l i e d i n l i q u i d phase hydrogénations u s i n g d i f f e r e n t b i n a r y s o l v e n t systems. I n p a r t i c u l a r , t h e i n f l u e n c e o f t h e c o m b i n a t i o n o f t h e s o l v e n t system and t h e c a t a l y s t s u p p o r t on t h e s e l e c t i v i t y o f hydrogénation r e a c t i o n s i s d i s c u s s e d i n C h a p t e r V I ( 1 8 ) . Examples o f p a r a l l e l as w e l l as c o n s e c u t i v e r e a c t i o n s a r e g i v e n . C h a p t e r V I I (19) d e a l s w i t h mass t r a n s p o r t p r o c e s s e s d u r i n g h e t e r o -g e n e o u s l y c a t a l y z e d l i q u i d phase hydro-génation r e a c t i o n s i n o r d e r t o e s t i m a t e t h e i r p o s s i b l e e f f e c t s on t h e a c t i v i t y measurements o f t h e Ru c a t a l y s t s . L i t e r a t u r e

(1) A. S k i t a , Katalytische Reduktionen Organischer Verbindungen, F e r d i n a n d Enke V e r l a g , S t u t t g a r t , ( 1 9 1 2 ) .

(2) R. Bauer und H. W i e l a n d , Reduktion und Hydrierung Organischer

Verbindungen, O t t o Spamer, L e i p z i g , (1918).

(3) P. Saba t i e r . La Catalyse en Chimie Organique, C H . Ber a n g e r , P a r i s , (1920) .

(4) C. E l l i s , Hydrogénation of Organic Substances, George R o u t l e d g e , London, (1931) .

(5) D.V. S o k o l s k i i , Hydrogénation in Solutions, I s r a e l Program f o r S c i e n t i f i c T r a n s l a t i o n s , J e r u s a l e m , (1964).

(6) F. Z y m a l k o w s k i , Katalytische Hydrierungen, F e r d i n a n d Enke V e r l a g , S t u t t g a r t , (1965).

(7) R.L. A u g u s t i n e , Catalytic Hydrogénation, M a r c e l D e k k e r , New Y o r k , (1965). (8) P.N. R y l a n d e r , Catalytic Hydrogénation over Platinum Metals, Academic

P r e s s , New Y o r k , (1967).

(9) M. F r e i f e l d e r , Practical Catalytic Hydrogénation, John W i l e y , New Y o r k , (1971) .

(10) R . J . P e t e r s o n , Hydrogénation Catalysts, Noyes Data C o r p o r a t i o n , P a r k R i d g e , New J e r s e y , (1977).

(11) A.P.G. Kieboom and F. van R a n t w i j k , Hydrogénation and Hydrogenolysis

in Synthetic Organic Chemistry, D e l f t U n i v e r s i t y P r e s s , D e l f t , (1977).

(12) M. F r e i f e l d e r , Catalytic Hydrogénation in Organic Synthesis, John W i l e y , New Y o r k , (1978).

(13) P.N. R y l a n d e r , Catalytic Hydrogénation in Organic Syntheses, Academic P r e s s , New Y o r k , (1979).

(14) P.G.J. Koopman, A.P.G. Kieboom, and H. v a n Bekkum, s u b m i t t e d f o r p u b l i c a t i o n i n Colloids and Surfaces.

(15) P.G.J. Koopman, A.P.G. Kieboom, and H. van Bekkum, R e a c t . Kinet. Catal.

Lett. 8, 389 (1978).

(16) P.G.J. Koopman, A.P.G. Kieboom, H. v a n Bekkum, and J.W.E. Coenen, Carbon 17, 399 (1979),

(17) P.G.J. Koopman, A.P.G. Kieboom, and H. v a n Bekkum, s u b m i t t e d f o r p u b l i c a t i o n i n J. Catal.

(18) P.G.J. Koopman, H.M.A. Buurmans, A.P.G. Kieboom, and H. v a n Bekkum, s u b m i t t e d f o r p u b l i c a t i o n i n Reel. Trav. Chim. Pays-Bas.

(19) P.G.J. Koopman, A.P.G. Kieboom, and H. v a n Bekkum, Delft Prog. Rep. 24 (1980).

I INDUCTION EFFECTS IN LIQUID PHASE HYDROGENATION CATALYZED BY RUTHENIUM ON CARBON

Summary

I n d u c t i o n appears f r e q u e n t l y i n l i q u i d phase hydrogénations a t room t e m p e r a t u r e and a t m o s p h e r i c p r e s s u r e w i t h r u t h e n i u m c a t a l y s t s , i f used w i t h o u t p r i o r t r e a t m e n t . T h i s i s caused by a d s o r b e d oxygen and s u r f a c e o x i d e s p r e s e n t on t h e Ru. The s o l v e n t has an i m p o r t a n t e f f e c t on t h e i n d u c t i o n phenomenon. I n h y d r o -c a r b o n s o l v e n t s t h e r e d u -c t i v e oxygen r e m o v a l does n o t p r o -c e e d under t h e c o n d i t i o n s used (30 3 K, P ^ = 101 kPa) and t h e Ru c a t a l y s t r e m a i n s i n a c t i v e f o r hydrogénation. I n p o l a r s o l v e n t s an i n d u c t i o n t i m e i s f o u n d . P r e t r e a t m e n t o f t h e c a t a l y s t i n a hydrogen o r a n i t r o g e n atmosphere a t 473 K d i m i n i s h e s the i n d u c t i o n t i m e and r e s u l t s i n a c t i v e c a t a l y s t s i r r e s p e c t i v e o f t h e s o l v e n t used. O t h e r group V I I I m e t a l c a t a l y s t s ( b e i n g more n o b l e t h a n Ru) d i d n o t show t h e s e i n d u c t i o n e f f e c t s . Hydrogen u p t a k e i n e x c e s s o f t h e amount needed f o r the r e d u c t i o n o f t h e Ru s u r f a c e o x i d e s i s m a i n l y c o n n e c t e d w i t h t h e hydrogén-a t i o n o f oxygen hydrogén-a d s o r b e d on t h e c hydrogén-a r b o n s u p p o r t .

I n t r o d u c t i o n

Ru c a t a l y s t s a r e f r e q u e n t l y used f o r t h e l i q u i d phase hydrogénation o f a r o m a t i c and c a r b o n y l compounds ( 1 - 4 ) . Water, a c e t i c a c i d , a l c o h o l and m i x t u r e s t h e r e o f are commonly used as a s o l v e n t . These R u - c a t a l y z e d hydrogénations u s u a l l y show a v a r i a b l e and sometimes l o n g i n d u c t i o n p e r i o d ( 1 , 2, 5 - 7 ) , u n l e s s f r e s h l y p r e p a r e d c a t a l y s t s were used ( 8 ) . F u r t h e r m o r e , i t i s known t h a t s u p p o r t e d Ru l i k e o t h e r n o b l e m e t a l c a t a l y s t s as p l a t i n u m and p a l l a d i u m consumes h y d r o g e n i n e x c e s s o f a m o n o l a y e r , when t r e a t e d i n s u s p e n s i o n w i t h h y d r o g e n . Up t o now no a t t e n t i o n was p a i d t o t h e s e phenomena.

6

c a t a l y s t s a r e d i s c u s s e d , i n r e l a t i o n t o t h e ease o f o x i d a t i o n and r e d u c t i o n o f Ru. U s i n g c o m m e r c i a l Ru on c a r b o n c a t a l y s t s , s p e c i a l a t t e n t i o n was p a i d t o the e f f e c t o f p r e t r e a t m e n t o f t h e c a t a l y s t and t o t h e i n f l u e n c e o f t h e s o l v e n t a p p l i e d . F o r c o m p a r i s o n f r e s h l y p r e p a r e d Ru on c a r b o n as w e l l as some o t h e r c a r b o n s u p p o r t e d group V I I I m e t a l s have been i n c l u d e d . U s i n g t h e l i q u i d phase h y d r o g e n a t i o n o f benzene as a model r e a c t i o n , t h e r e l a t i o n between t h e i n d u c t i o n t i m e and t h e a c t i v i t y o f t h e c a t a l y s t has been i n v e s t i g a t e d .

E x p e r i m e n t a l

The c a t a l y s t s used were 5% Ru on c a r b o n (Ru/C ( A ) ) , o b t a i n e d from D r i j f h o u t 2 -1

Amsterdam, w i t h a t o t a l s u r f a c e a r e a o f 805 m g and 5% Ru on c a r b o n (Ru/C 2 -1

(B)) p r e p a r e d by i m p r e g n a t i o n o f c a r b o n (Degussa, 770 m g ) w i t h a s o l u t i o n o f r u t h e n i u m t r i c h l o r i d e h y d r a t e ( A l f a ) i n a c e t o n e ( 9 ) . The r e d u c t i o n o f t h e samples was c a r r i e d o u t i n a s t r e a m o f h y d r o g e n a t t e m p e r a t u r e s > 473 K. The 5% rhodium, 10% p a l l a d i u m and 5% p l a t i n u m on c a r b o n c a t a l y s t s were o b t a i n e d .from D r i j f h o u t . The 10% i r i d i u m on c a r b o n was p r e p a r e d by i m p r e g n a t i o n w i t h the m e t a l c h l o r i d e f o l l o w e d by r e d u c t i o n a t 573 K. The 10% osmium on c a r b o n was p r e p a r e d by t h e r e d u c t i o n o f osmium t e t r o x i d e i n t h e p r e s e n c e o f a s u s p e n s i o n o f c a r b o n i n 2 - p r o p a n o l a t 333 K and 8080 kPa hydrogen p r e s s u r e

(10) .

The h y d r o g e n a t i o n e x p e r i m e n t s were c a r r i e d o u t i n a t h e r m o s t a t t e d g l a s s r e a c t o r m o n i t o r i n g t h e hydrogen consumption c o n t i n u o u s l y ( 1 1 ) . The f o l l o w i n g s t a n d a r d c o n d i t i o n s were used: c a t a l y s t c o n c e n t r a t i o n : 7.5 g 1 *, benzene c o n c e n t r a t i o n : 0.17 mol 1 .» t e m p e r a t u r e : 303 K, h y d r o g e n p r e s s u r e : 101 k P a . The h y d r o g e n u p t a k e o f t h e c a t a l y s t i n s u s p e n s i o n i s e x p r e s s e d i n mol hydrogen p e r mol Ru and t h e a c t i v i t y o f t h e c a t a l y s t i n mol benzene p e r mol m e t a l p e r s e c o n d .

T h e r m o g r a v i m e t r i c a n a l y s e s were c a r r i e d o u t w i t h a t h e r m o b a l a n c e ( S a r t o r i u s 4104) i n f l o w i n g g a s . The t e m p e r a t u r e programmed r e d u c t i o n was c a r r i e d o u t i n an a p p a r a t u s w h i c h m o n i t o r e d t h e h y d r o g e n c o n s u m p t i o n o f a c a t a l y s t sample, h e a t e d a t c o n s t a n t r a t e ( 1 2 ) .

R e s u l t s

No prior treatment

A s t i r r e d s u s p e n s i o n o f c o m m e r c i a l Ru/C (A) i n 1-propanol a d s o r b e d hydrogen as shown by c u r v e 1 i n F i g . 1. The t i m e a t w h i c h t h e r a t e o f hydrogen

F i g . 1. Hydrogen u p t a k e versus t i m e o f 303 K, PH 2: 101 k P a ; c u r v e 1 -benzene: 0.17 mol 1 ; c u r v e 3 Ru/C (A) (7.5 g 1 ) i n 1 - p r o p a n o l , w i t h o u t o r g a n i c r e a c t a n t ; c u r v e 2 -- c y c l o h e x e n e : 0.15 mol 1 .

hydrogen u p t a k e amounted t o 3.3 mol o f h y d r o g e n p e r mol o f Ru. The c u r v e s 2 and 3 o f F i g . 1 d e m o n s t r a t e t h a t d u r i n g t h i s i n d u c t i o n p e r i o d t h e c a t a l y s t was i n a c t i v e f o r t h e h y d r o g e n a t i o n o f b o t h benzene and c y c l o h e x e n e . When

c a r b o n (7.5 g 1 was added t o t h e s u s p e n s i o n via a r e v o l v i n g t u b u l a r d e v i c e , a f t e r t h e hydrogen u p t a k e o f t h e Ru/C s u s p e n s i o n had been c e a s e d , an a d d i t i o n a l hydrogen u p t a k e o f about 2 mol p e r mol Ru was f o u n d . T h i s h y d r o g e n u p t a k e p r o v e d t o be p r o p o r t i o n a l t o t h e amount o f c a r b o n added. The hydrogen u p t a k e

-1 o f u n s u p p o r t e d Ru, w i t h a m e t a l d i s p e r s i o n ^ 0 .1, i n 1-propanol (3 g 1 ) amounted t o about 0.12 mol p e r mol Ru.

F o r c o m p a r i s o n , t h e h y d r o g e n u p t a k e and t h e a c t i v i t y i n t h e l i q u i d phase h y d r o g e n a t i o n o f benzene o f some o t h e r group V I I I m e t a l s on c a r b o n i n

1-propanol have been d e t e r m i n e d ( T a b l e I ) . I n c o n t r a s t t o Ru no i n d u c t i o n p e r i o d was o b s e r v e d w i t h t h e s e c a t a l y s t s .

8

TABLE I - Hydrogen u p t a k e and a c t i v i t y o f c a r b o n s u p p o r t e d group V I I I m e t a l c a t a l y s t s C a t a l y s t H u p t a k e A c t i v i t y -1 -3 (mol H /mol m e t a l ) (s 10 ) 5% Ru/C (A) 3 3 2 0 5% Rh/C 2 6 7 0 10% Pd/C 1 7 0 1 10% Os/C 6 4 0 9 10% I r / C 1 3 0 2 5% Pt/C 5 5 7 5 S o l v e n t : 1 - p r o p a n o l , c a t a l y s t : 7.5 g 1 , 303 K, PH : 101 k P a . -1 Benzene: 0.17 mol 1 Pretreatment in suspension

F l u s h i n g a s u s p e n s i o n o f Ru/C (A) i n 1-propanol w i t h n i t r o g e n a t 303 K d e c r e a s e d b o t h t h e i n d u c t i o n p e r i o d and t h e h y d r o g e n u p t a k e as compared t o t h e u n t r e a t e d c a t a l y s t ( F i g . 2, c u r v e s 1 and 2 ) . The r e v e r s e i s t r u e f o r

p r e t r e a t m e n t w i t h oxygen ( F i g . 2, c u r v e 3 ) .

A l t e r n a t e t r e a t m e n t o f a s t i r r e d s u s p e n s i o n o f Ru/C i n 1-propanol w i t h h y d r o g e n and a i r r e s u l t e d i n a hydrogen oxygen u p t a k e r a t i o c l o s e t o 2:1 as d e p i c t e d i n F i g . 3.

I n c o n t r a s t t o t h e r a p i d oxygen u p t a k e each hydrogen c o n s u m p t i o n s t a r t e d a f t e r an i n d u c t i o n p e r i o d o f ^ 5 min. T h i s t r e a t m e n t had no e s s e n t i a l i n f l u e n c e on t h e a c t i v i t y o f t h e c a t a l y s t i n t h e h y d r o g e n a t i o n o f benzene. I t may be n o t e d t h a t w i t h o t h e r r e a c t a n t s , f o r i n s t a n c e a l d e h y d e s , t h i s t r e a t m e n t had a b e n e f i c i a l e f f e c t on t h e c a t a l y t i c a c t i v i t y ( 8 ) .

I n a s t i r r e d s u s p e n s i o n o f 5% p l a t i n u m on c a r b o n i n 1-propanol a t t h e same c o n d i t i o n s such an o x i d a t i o n - r e d u c t i o n c y c l e was n o t r e v e r s i b l e , whereas t h e a c t i v i t y o f t h e c a t a l y s t d e c r e a s e d upon such a t r e a t m e n t .

H2u p t a k e ( m o l H2( m o l Ru)~1)

t (min)

F i g . 2. Hydrogen u p t a k e v e r s u s t i m e o f Ru/C (A) ( 7 . 5 g 1 ) i n 1 - p r o p a n o l , 3 0 3 K, P j ]9 : 1 0 1 k P a ; c u r v e 1 - no p r i o r t r e a t m e n t ; c u r v e 2 - s u s p e n s i o n -1 f l u s h e d w i t h n i t r o g e n f o r 4 h a t 1 1 h ; c u r v e 3 - s u s p e n s i o n f l u s h e d -1 w i t h oxygen f o r 0 . 5 h a t 1 1 h 3 H2 2 t — ^ ; a, 2 | 021 10 20 30 a, 2 | 021

r- ; ; ;

oS 3 o H2 2 £ 1 AO 50 60 * 2h 70 80 90

% °

2

' \r~—

— lA 0

t

3

t

1 100 110 120 730 1A<) 150 • t(min)

F i g . 3. Sequence o f a l t e r n a t e h y d r o g e n and oxygen u p t a k e v e r s u s t i m e o f Ru/C ( B ) ( 7 . 5 g 1_1) i n 1 - p r o p a n o l , 3 0 3 K, PH 2: 1 0 1 k P a , P Q2: 2 0 k P a .

10

High température pretreatment

A c o m p i l a t i o n o f d i f f e r e n t p r e t r e a t m e n t p r o c e d u r e s f o r Ru/C (A) t o g e t h e r w i t h t h e hydrogen u p t a k e o f t h e c a t a l y s t and t h e c a t a l y t i c a c t i v i t y i n t h e hydrogénation o f benzene i s g i v e n i n T a b l e I I .

TABLE I I - E f f e c t o f p r e t r e a t m e n t p r o c e d u r e on t h e b e h a v i o u r o f Ru/C (A)

a) a) a) ,

P r e t r e a t m e n t I n d u c t i o n t i m e H u p t a k e A c t i v i t y -1 -3 Gas Temp. (K) Time (h) (min) (mol H /mol Ru) (s 10 )

- - - 40 3.3 2.0 303 4 15 1.7 1.5 303 0.5 110 5.1 1.5 473 1 < 1 0.3 1.3 473 1 < 1 0.6 2 . 8f ; d) ,9) _{473 1 < 1 1.9 6.2} d),9) ₆₇₃ 1 < 1 2.2 3.7

<

>,9) 673 1 < 1 2.8 3.5 d)

M

₆₇₃ 1 7 2.8 2.0 673 1 4 2.8 2.1 A i r 403 16 74 4.2 1.1 A i r 403 70 148 1.8 0.03 A i r 403 336 > 300 0 < 0.01 a) S o l v e n t : 1 - p r o p a n o l , c a t a l y s t : 7.5 g 1 1, 303 K, PH, : 101 k P a . jb) — 1 Benzene: 0.17 mol 1 c) -1 S u s p e n s i o n o f t h e c a t a l y s t i n 1-propanol (7.5 g 1 ) f l u s h e d w i t h gas (1 1 h_ 1) a t 101 k P a . d , ) C a t a l y s t f l u s h e d w i t h gas (1 1 h ) . f) 9) h) i) Not exposed t o a i r . 0.25 v o l % w a t e r added.

Exposed t o a i r f o r 5 min a t room t e m p e r a t u r e . Exposed t o w a t e r vapour

Exposed t o oxygen.

Exposure o f t h e c a t a l y s t t o a i r c l e a r l y i n c r e a s e d b o t h t h e i n d u c t i o n t i m e and t h e h y d r o g e n uptake as shown i n F i g . 4.

H2 u p t a k e ( m o l H2(mol Ru) 1) 4 -»• t(min) F i g . 4. Hydrogen u p t a k e o f Ru/C ( A ) (7.5 g 1 ) i n 1 - p r o p a n o l , 303 K , P J J2 : -101 k P a ; c u r v e 1 - Ru/C, a t 473 K f o r 1 h , n o t exposed t o a i r , s o l v e n t deoxygenated; c u r v e 2 - Ru/C, o r a t 473 K f o r 1 h , exposed t o a i r f o r 5 min, s o l v e n t deoxygenated; c u r v e 3 - Ru/C, H2 a t

473 K f o r 1 h , exposed t o a i r f o r 1 d a y .

More d r a s t i c a g i n g o c c u r r e d upon h e a t i n g t h e c a t a l y s t i n a i r a t 403 K as shown by t h e i n c r e a s e o f t h e i n d u c t i o n time and the l o s s o f a c t i v i t y i n benzene h y d r o g e n a t i o n ( T a b l e I I ) .

The e f f e c t o f t h e r e d u c t i o n t e m p e r a t u r e o f RuCl^/C, l e a d i n g t o Ru/C ( B ) , on t h e i n d u c t i o n t i m e , t h e hydrogen u p t a k e i n s u s p e n s i o n and t h e a c t i v i t y i n benzene h y d r o g e n a t i o n i s d e p i c t e d i n T a b l e I I I . I t may be n o t e d t h a t t h e r e TABLE I I I - E f f e c t o f r e d u c t i o n t e m p e r a t u r e o n t h e b e h a v i o u r o f Ru/C ( B ) ^ b) b) . . b) ,c) R e d u c t i o n I n d u c t i o n t i m e H u p t a k e A c t i v i t y -1 -3 t e m p e r a t u r e ( K ) (min) (mol H2/ m o l Ru) (s 10 )

54 3 4.4 2 4 0 31

563 3.6 2 7 0 55

613 3.6 2 8 0 94

663 3.3 2 8 1 .2

723 2.1 3 1 2 6

a > A f t e r 2 h r e d u c t i o n exposed t o a i r f o r 5 min a t room t e m p e r a t u r e .

S o l v e n t : 1 - p r o p a n o l , c a t a l y s t : 7.5 g 1 , 303 K , P f j2: 101 k P a .

-1 Benzene: 0.17 mol 1

12

was a d i f f e r e n c e i n b e h a v i o u r , as t o t h e i n d u c t i o n p e r i o d , between c o m m e r c i a l and f r e s h l y p r e p a r e d c a t a l y s t s ; t h i s may be due t o t h e h i s t o r y o f p r e p a r a t i o n .

Comparable h i g h t e m p e r a t u r e p r e t r e a t m e n t o f p l a t i n u m and p a l l a d i u m on c a r b o n c a t a l y s t s d i d n o t r e s u l t i n a g a i n o f a c t i v i t y as found f o r Ru.

TGA and TPR experiments

The o x i d a t i o n and r e d u c t i o n o f u n s u p p o r t e d Ru were f o l l o w e d w i t h thermo-g r a v i m e t r i c a n a l y s i s . Upon h e a t i n thermo-g Ru powder i n a i r a t 6 K mln ^ we o b s e r v e d an u l t i m a t e g a i n i n w e i g h t c o r r e s p o n d i n g t o t h e f o r m a t i o n o f RuC^- The w e i g h t s t a r t e d t o i n c r e a s e a t ^ 393 K and became c o n s t a n t a t 973 K under t h e s e c o n d i t i o n s . Upon h e a t i n g o f RuO^ i n h y d r o g e n a t 6 K min * t h e w e i g h t l o s s s t a r t e d a t °v 373 K, i n c r e a s e d i n r a t e a t 433 K and was c o m p l e t e , c o r r e s p o n d i n g t o t h e f o r m a t i o n o f Ru m e t a l , a t 473 K.

The oxygen u p t a k e by r e d u c e d Ru c a t a l y s t s was a l s o d e m o n s t r a t e d by t h e hydrogen c o n s u m p t i o n , measured w i t h a t e m p e r a t u r e programmed r e d u c t i o n a p p a r a t u s , o f samples w h i c h were exposed t o a i r a t room t e m p e r a t u r e ( 1 2 ) . The oxygen, t a k e n up a t room t e m p e r a t u r e , c o u l d be p a r t l y (^ 60%) removed by h e a t i n g s u c h a sample i n n i t r o g e n a t 473 K f o r 0.5 h as shown by t h e d e c r e a s e d h y d r o g e n u p t a k e a f t e r t h i s t r e a t m e n t .

Solvent effect

I n t h e r e s u l t s g i v e n above 1 - p r o p a n o l was u s e d as t h e s o l v e n t . When Ru/C (A) was suspended i n n e a t benzene no h y d r o g e n c o n s u m p t i o n o c c u r r e d a t a l l (12 h a t 303 K and 101 kPa H2) . H y d r o g e n a t i o n c o u l d be a c h i e v e d by t h e a d d i t i o n

o f 1 - p r o p a n o l (10 v o l % o r more) o r when u s i n g a c a t a l y s t p r e r e d u c e d i n 1 p r o p a n o l o r when u s i n g f r e s h l y r e d u c e d c a t a l y s t s ( T a b l e I V ) . U s i n g c y c l o -hexane o r i s o o c t a n e as t h e s o l v e n t t h e Ru/C (A) was a l s o i n a c t i v e u n l e s s p r e r e d u c e d samples were u s e d ( T a b l e I V ) .

The e f f e c t o f t h e s o l v e n t on t h e i n d u c t i o n and t h e a c t i v i t y o f Ru/C (A) was f u r t h e r d e m o n s t r a t e d w i t h c y c l o h e x a n e / l - p r o p a n o l and 1 - p r o p a n o l / w a t e r m i x t u r e s ( F i g . 5 ) . I t i s n o t e w o r t h y t h a t t h e a d d i t i o n o f a s m a l l amount o f w a t e r t o 1-propanol i n c r e a s e d t h e i n d u c t i o n t i m e by a f a c t o r 3.

TABLE IV - E f f e c t o f p r e t r e a t m e n t o f Ru/C (A) w i t h hydrogen a t 473 K on t h e a c t i v i t y i n benzene hydrogénation i n d i f f e r e n t s o l v e n t s S o l v e n t P r e r e d u c t i o n a) A c t i v i t y -1 -3 (s 10 ) 1-propanol - 2.0 1-propanol + 6.2 c y c l o h e x a n e - < 0.01 c y c l o h e x a n e + 13 benzene - < 0.01 benzene + 20 a} C a t a l y s t : 7.5 g l~ , benzene: 0.17 mol 1 1, 303 K, PH : 101 k P a .

F i g . 5. I n d u c t i o n time (x) and a c t i v i t y (o) i n benzène hydrogénation f o r Ru/C -1

(A) (7.5 g 1 ) versus s o l v e n t c o m p o s i t i o n i n c y c l o h e x a n e / 1 - p r o p a n o l -1

m i x t u r e s (benzène: 0.17 mol 1 ) and 1-propanol/water m i x t u r e s (benzène: 0.017 mol 1_ 1) , 303 K, 101 kPa H2

-14

D i s c u s s i o n

Nature of the induction period

S i n c e i n d u c t i o n a p p e a r i n g i n l i q u i d phase h y d r o g e n a t i o n w i t h Ru c a t a l y s t s I s o b s e r v e d f o r c o m m e r c i a l as w e l l as f r e s h l y p r e p a r e d and r e d u c e d c a t a l y s t s w h i c h were s u b s e q u e n t l y exposed t o a i r , a p p a r e n t l y a c o n t a m i n a t i o n r e s u l t i n g from i n t e r a c t i o n o f t h e Ru m e t a l w i t h oxygen i s i n v o l v e d . A l t h o u g h Ru b e l o n g s t o t h e n o b l e m e t a l s , i t s s u r f a c e becomes r e a d i l y c o v e r e d w i t h an o x i d i c l a y e r on e x p o s u r e t o a i r a t room t e m p e r a t u r e ( 1 3 ) . The e x a c t c o m p o s i t i o n o f t h e s u r f a c e o x i d e i s n o t y e t c l e a r ; b o t h RuO^ and RuO have been p r o p o s e d from oxygen c h e m i s o r p t i o n measurements ( 1 4 - 1 6 ) , whereas n o n - d i s s o c i a t i v e c h e m i s o r p t i o n o f oxygen on Ru was a l s o s u g g e s t e d ( 1 7 ) . I t i s c l e a r , however, t h a t on f r e s h l y r e d u c e d Ru oxygen c h e m i s o r p t i o n w i l l t a k e p l a c e and t h a t upon p r o l o n g e d e x p o s u r e t o a i r s u r f a c e o x i d e s a r e formed:

Ru + x/2 0„ > RuO 2 x Upon t r e a t m e n t o f t h e c a t a l y s t i n s u s p e n s i o n w i t h h y d r o g e n t h e s u r f a c e o x i d e s a r e r e d u c e d by r e a c t i o n w i t h c h e m i s o r b e d h y d r o g e n : RuO + 2x RuH -* (2x + 1) Ru + x H„0 X 2 f o l l o w e d by hydrogen c h e m i s o r p t i o n on t h e Ru s u r f a c e formed: Ru + 1/2 H2 -* RuH.

The r e d u c t i o n o f RuO w i l l t h e r e f o r e be a c c e l e r a t e d by s u r f a c e m e t a l atoms, x

T h i s a u t o c a t a l y t i c b e h a v i o u r e x p l a i n s t h e s i g m o i d c u r v e s f o r t h e h y d r o g e n u p t a k e by t h e c a t a l y s t . The q u e s t i o n remains whether i n i t i a l l y m o l e c u l a r h y d r o g e n a t t a c k s t h e s u r f a c e o x i d e i n a s l o w r e a c t i o n ( 1 8 ) .

The s h o r t i n d u c t i o n t i m e s found f o r f r e s h l y r e d u c e d c a t a l y s t s , exposed t o a i r f o r o n l y a s h o r t t i m e , r e f l e c t a r a t h e r low oxygen c o v e r a g e o f t h e Ru s u r f a c e , i . e . x i s s m a l l . Thus t h e d i f f e r e n c e i n i n d u c t i o n between t h e c o m m e r c i a l and t h e f r e s h l y p r e p a r e d c a t a l y s t s i s c o n s i d e r e d t o be an a g i n g e f f e c t w h i c h o r i g i n a t e s from an i n c r e a s e d s u r f a c e o x i d e f o r m a t i o n upon exposure t o a i r ( 1 2 ) . H e a t i n g o f Ru/C i n n i t r o g e n a t 473 K l e d t o a d i m i n i s h i n g o f t h e i n d u c t i o n t i m e . T h i s i s due t o t h e t h e r m a l d e c o m p o s i t i o n o f t h e s u r f a c e o x i d e s , w h i c h was a l s o d e m o n s t r a t e d by t e m p e r a t u r e programmed r e d u c t i o n e x p e r i m e n t s .

I t i s known (13) t h a t , on h e a t i n g Ru m e t a l i n a i r , t h i c k e n i n g o f t h e o x i d e s k i n appears and u l t i m a t e l y complete b u l k o x i d e f o r m a t i o n o c c u r s . We o b s e r v e d t h i s o x i d a t i o n b o t h w i t h t h e r m o g r a v i m e t r i c a n a l y s i s and t e m p e r a t u r e programmed r e d u c t i o n . I t c a n e x p l a i n t h e i n c r e a s e i n i n d u c t i o n t i m e and u l t i m a t e

i n a c t i v i t y o f t h e c a t a l y s t under m i l d c o n d i t i o n s upon h e a t i n g i n a i r a t 403 K ( T a b l e I I ) .

For o t h e r group V I I I m e t a l s s u p p o r t e d on c a r b o n no i n d u c t i o n t i m e was f o u n d . S i n c e t h e s e m e t a l s do n o t show s u b s u r f a c e o x i d a t i o n , t h e c h e m i s o r p t i o n o f hydrogen on t h e s u r f a c e and t h e c o n c o m i t a n t r e d u c t i o n o f t h e c h e m i s o r b e d oxygen i s f a s t . T h i s d i f f e r e n t b e h a v i o u r i s u n d e r s t a n d a b l e i n v i e w o f t h e h i g h e r h e a t o f a d s o r p t i o n o f oxygen and the h i g h e r h e a t o f f o r m a t i o n o f t h e o x i d e f o r Ru (19, 2 0 ) .

I n t h e h i g h t e m p e r a t u r e p r e t r e a t m e n t e x p e r i m e n t s a d e c r e a s e o f t h e i n d u c t i o n p e r i o d i s c o n n e c t e d w i t h an i n c r e a s e i n a c t i v i t y o f t h e c a t a l y s t . T h i s may be due t o more a c t i v e o r more active c a t a l y t i c s i t e s w h i c h r e s u l t s i n b o t h a d e c r e a s e i n i n d u c t i o n t i m e , i . e . a f a s t e r r e d u c t i o n o f s u r f a c e o x i d e s and an i n c r e a s e i n a c t i v i t y , i . e . h y d r o g e n a t i o n o f t h e o r g a n i c r e a c t a n t . Under p r a c t i c a l c o n d i t i o n s t h e Ru c a t a l y s t s a p p l i e d c o n s i s t o f a ( p a r t i a l ) o x i d i c Ru s u r f a c e l a y e r on w h i c h w a t e r from t h e a i r w i l l be a d s o r b e d . We h a v e , t h e r e f o r e , t o t a k e i n t o a c c o u n t t h e a d s o r p t i o n e q u i l i b r i u m o f w a t e r on t h e c a t a l y s t s u r f a c e w h i c h w i l l be s h i f t e d t o the a d s o r b e d s t a t e when t h e h y d r o -p h i l i c c h a r a c t e r o f t h e s o l v e n t d e c r e a s e s . I n -p a r t i c u l a r w i t h h y d r o c a r b o n s o l v e n t s , t h e p r e s e n c e o f w a t e r , e i t h e r from m o i s t u r e o r from t h e r e d u c t i o n of Ru s u r f a c e o x i d e s , may r e s u l t i n a b l o c k a d e o f t h e Ru. An a n a l o g o u s e f f e c t i s o b s e r v e d i n t h e gas phase r e d u c t i o n o f m e t a l o x i d e s where a model has b e e n p r o p o s e d i n w h i c h t h e o x i d e r e d u c t i o n r a t e i s r e t a r d e d by t h e p r e s e n c e o f w a t e r vapour due t o t h e more d i f f i c u l t hydrogen a d s o r p t i o n on a h y d r o x y l a t e d

s u r f a c e ( 1 8 ) .

Hydrogen uptake

The hydrogen uptake o f Ru/C i n s u s p e n s i o n c a n o r i g i n a t e from t h e r e a c t i o n o f hydrogen w i t h t h e f o l l o w i n g oxygen s p e c i e s : a) Ru s u r f a c e o x i d e b) b u l k Ru o x i d e c) oxygen a b s o r b e d i n Ru d) oxygen a d s o r b e d on t h e c a r b o n e) oxygen d i s s o l v e d i n t h e s o l v e n t . In a d d i t i o n t o a) - e) hydrogen a d s o r p t i o n on t h e c a t a l y s t w i l l c o n t r i b u t e t o the o b s e r v e d u p t a k e .

16

ad a) I n c a s e o f a m e t a l d i s p e r s i o n 0.5 and an o x i d a t i o n s t a t e 2 f o r Ru, t h e r e d u c t i o n o f t h e s u r f a c e o x i d e as d i s c u s s e d above, w i l l cause a h y d r o g e n consumption o f 0.5 mol h y d r o g e n p e r mol Ru.

ad b) When t h e Ru i s o x i d i z e d c o m p l e t e l y t o t h e d i o x i d e , t h e r e d u c t i o n r e q u i r e s a h y d r o g e n consumption o f 2 mol p e r mol Ru. B u l k o x i d e f o r m a t i o n upon e x p o s u r e t o a i r a t room t e m p e r a t u r e i s n o t o b s e r v e d , however; h i g h e r t e m p e r a t u r e s a r e r e q u i r e d as shown by t h e t h e r m o g r a v i m e t r i c a n a l y s i s e x p e r i m e n t s .

ad c) K o r s c h (21) has f o u n d t h a t t h e a b s o r p t i o n o f oxygen i n a Ru f i l m a t room t e m p e r a t u r e a t 0.66 kPa amounted t o 0.1 mol oxygen p e r mol Ru; t h i s oxygen c o u l d be removed f a s t by a d m i s s i o n o f h y d r o g e n .

ad d) Oxygen c a n be b r o u g h t i n t o t h e s y s t e m b y t h e s u p p o r t . The c h e m i s o r p t i o n o f oxygen on c a t a l y s t s u p p o r t m a t e r i a l s a t room t e m p e r a t u r e arid 4 kPa i s s m a l l ( 1 4 ) ; r e l a t e d t o t h e Ru t o s u p p o r t r a t i o i t i s < 0.03 mol oxygen p e r mol Ru. P h y s i c a l l y a d s o r b e d oxygen on t h e s u p p o r t , a s s u m i n g a m o n o l a y e r c o v e r a g e , would a c c o u n t f o r 19 mol p e r mol Ru f o r t h e c a r b o n ( A ) . A d s o r p t i o n

3 -1

c o e f f i c i e n t s f o r oxygen on a c t i v a t e d c a r b o n o f 6-11 cm g were r e p o r t e d (22) which i s , r e l a t e d t o t h e Ru s u p p o r t r a t i o , 0.5-1.0 mol p e r mol Ru.

ad e) The s o l u b i l i t y o f oxygen i n 1 - p r o p a n o l ( 2 3 ) , r e l a t e d t o t h e p r e s e n t c o n d i t i o n s c a n a c c o u n t f o r maximal 0.45 mol oxygen p e r mol Ru.

The o r i g i n and t h e maximum amount o f oxygen p r e s e n t i n t h e s y s t e m a r e resumed i n T a b l e V t o g e t h e r w i t h t h e maximum t h e o r e t i c a l h y d r o g e n u p t a k e due t o t h e r e d u c t i o n o f t h e v a r i o u s oxygen s p e c i e s and t h e h y d r o g e n u p t a k e due t o chemi-s o r p t i o n on t h e Ru m e t a l . From t h e e x p e r i m e n t a l h y d r o g e n u p t a k e o f c a r b o n s u p p o r t e d and u n s u p p o r t e d Ru under v a r i o u s c o n d i t i o n s t h e c o n t r i b u t i o n o f t h e oxygen s p e c i e s c a n be e s t i m a t e d ( T a b l e V ) . I t can be c o n c l u d e d t h a t t h e major p a r t o f t h e h y d r o g e n u p t a k e i s due t o oxygen a d s o r b e d on t h e c a r b o n . E x p e r i m e n t a l e v i d e n c e f o r t h e h y d r o g e n a t i o n o f oxygen a d s o r b e d on t h e c a r b o n i s g i v e n by t h e a d d i t i o n a l u p t a k e o f h y d r o g e n upon a d d i n g c a r b o n t o t h e s u s p e n s i o n , t h e d i f f e r e n c e i n h y d r o g e n u p t a k e f o r r e d u c e d c a t a l y s t s i n d e g a s s e d s o l v e n t s when e x p o s e d t o a i r o r n o t and t h e d i f f e r e n c e i n h y d r o g e n u p t a k e f o r c a r b o n s u p p o r t e d and u n s u p p o r t e d Ru.

The e f f e c t o f d i s s o l v e d oxygen and oxygen a d s o r b e d on t h e c a r b o n on t h e h y d r o g e n u p t a k e and t h e i n d u c t i o n t i m e was d e m o n s t r a t e d by f l u s h i n g t h e s u s p e n s i o n w i t h n i t r o g e n and o x y g e n . The o b s e r v e d u p t a k e o f h y d r o g e n and oxygen upon t h e a l t e r n a t e t r e a t m e n t shows t h e r e v e r s i b i l i t y o f r e d u c t i o n and o x i d a t i o n o f Ru c a t a l y s t s .

TABLE V - Maximum amounts o f oxygen p r e s e n t i n t h e Ru/C (A) 1-propanol system and hydrogen u p t a k e caused by t h e v a r i o u s oxygen s p e c i e s

Maximum Maximum " E x p e r i m e n t a l " Oxygen s p e c i e s O^ c o n t e n t u p t a k e H2 u p t a k e

mol O^/mol Ru mol H^/mol Ru mol H^/mol Ru

a S u r f a c e o x i d e 0.5 0.5 b B u l k o x i d e 1.0 2 c A b s o r b e d 0^ 0.1 0.2 d O2 on c a r b o n 19 38 2C) e 0^ i n s o l v e n t 0 . 4 5d ; 0.9 0.55 c h e m i s o r p t i o n 0.25 0.25 O x i d a t i o n s t a t e 2. A m e t a l d i s p e r s i o n o f 0.5 i s assumed. Based on p r e s e n t Ru t o s u p p o r t r a t i o . 20 ml 1 - p r o p a n o l , 150 mg Ru/C. A s p i l l - o v e r mechanism (24) o f h y d r o g e n from t h e Ru t o t h e c a r b o n i s o f m i n o r i m p o r t a n c e i n v i e w o f t h e low hydrogen u p t a k e o f r e d u c e d c a t a l y s t s w h i c h were n o t exposed t o a i r .

Keren and S o f t e r (25) s t u d y i n g t h e r o l e o f w a t e r i n t h e p a l l a d i u m - c a t a l y z e d hydrogénation o f c a r b o n s u r f a c e s e x p l a i n e d t h e h y d r o g e n u p t a k e o f 1% p a l l a d i u m on c a r b o n i n an aqueous s y s t e m i n terms o f a s p i l l - o v e r mechanism i n w h i c h a p r o t o n was p r o p o s e d t o be t h e m i g r a t i n g s p e c i e s . These a u t h o r s n e g l e c t e d , however, t h e p o s s i b l e p r e s e n c e o f oxygen i n t h e i r system.

C o n c l u s i o n s The i n d u c t i o n p e r i o d o f t e n o b s e r v e d f o r R u - c a t a l y z e d l i q u i d phase hydrogénations i s c a u s e d by s u r f a c e o x i d a t i o n o f t h e Ru m e t a l due t o e x p o s u r e t o a i r a t ambient c o n d i t i o n s . These s u r f a c e o x i d e s c a n be s l o w l y r e d u c e d , i . e . the c a t a l y s t c a n be a c t i v a t e d f o r hydrogénation, i n p o l a r s o l v e n t s a t 303 K and Pfj2: k P a . P r e r e d u c t i o n i n h y d r o g e n a t t e m p e r a t u r e s o f about 473 K i s r e q u i r e d f o r Ru c a t a l y s t s t o be u s e d i n h y d r o c a r b o n s o l v e n t s . The hydrogen u p t a k e i n e x c e s s o f a monolayer i s n o t c a u s e d b y s p i l l - o v e r o f hydrogen b u t m a i n l y by hydrogénation o f oxygen a d s o r b e d on t h e s u p p o r t .

18

A d d i t i o n a l comments

I n d u c t i o n phenomena were a l s o o b s e r v e d w i t h 5% Ru/SiO^ c a t a l y s t s p r e p a r e d by i m p r e g n a t i o n o f s i l i c a w i t h a s o l u t i o n o f R u C l ^ h y d r a t e i n a c e t o n e f o l l o w e d by d r y i n g a t 393 K and r e d u c t i o n w i t h B^ a t 573 K t o 1073 K ( 2 6 ) . When Ru/Sic^ was exposed t o a i r (> 1 day) a f t e r r e d u c t i o n , i t s B^ u p t a k e i n 1-propanol s u s p e n s i o n r e s e m b l e d t h a t f o r t h e u n t r e a t e d c o m m e r c i a l Ru/C ( F i g . 1, c u r v e 1 ) . The u p t a k e , however, v a r i e d from 2-6 mol B^ p e r mol Ru a.o. depending on t h e r e d u c t i o n t e m p e r a t u r e o f t h e c a t a l y s t . When s i l i c a was added t o such a s u s p e n s i o n a f t e r t h e uptake o f Ru/SiC^ had been c e a s e d , no a d d i t i o n a l B^ uptake t o o k p l a c e , whereas t h e a d d i t i o n o f c a r b o n t o R u / S i C ^ s u s p e n s i o n showed a s l o w e x t r a u p t a k e . I n c o n t r a s t w i t h t h e phenomena on Ru/C t h e p r e s e n t e x p e r i m e n t a l d a t a c a n n o t e x c l u d e t h e p o s s i b i l i t y o f B.^ s p i l l - o v e r from Ru t o S i O j - A d d i t i o n a l i n f o r m a t i o n i s r e q u i r e d f o r t h e u n d e r s t a n d i n g o f t h e u p t a k e o f Ru/SiC^ c a t a l y s t s . L i t e r a t u r e

(1) P.N. R y l a n d e r , Engelhard Ind. Tech. Bull. 1, 133 (1961).

(2) P.N. R y l a n d e r , Catalytic Hydrogénation over Platinum Metals, Academic P r e s s , New York (1967).

(3) A.P.G. Kieboom and F. v a n R a n t w i j k , Hydrogénation and Hydrogenolysis in

Synthetic Organic Chemistry, D e l f t U n i v e r s i t y P r e s s , D e l f t (1977).

(4) M. F r e i f e l d e r , Catalytic Hydrogénation in Organic Synthesis, J o h n W i l e y , New York (1978).

(5) L.M. B e r k o w i t z and P.N. R y l a n d e r , J. Org. Chem. 24, 708 (1959).

(6) E. B r e i t n e r , E. R o g i n s k i , and P.N. R y l a n d e r , J. Chem. Soc. 2918 (1959). (7) F. Z y m a l k o w s k i , Katalytische Hydrierungen, F e r d i n a n d Enke V e r l a g ,

S t u t t g a r t (1965), p. 28.

(8) P.N. R y l a n d e r and J . K a p l a n , Engelhard Ind. Tech. Bull. 2, 48 (1961). (9) P.G.J. Koopman, A.P.G. Kieboom, H. v a n Bekkum, and J.W.E. Coenen, Carbon

17, 399 (1979).

(10) Y. T a k a g i a n d S. I s h i i , Bull. Chem. Soc. Japan £ 3 , 917 (1970).

(11) G.W.H.A. M a n s v e l d , A.P.G. Kieboom, W.Th.M. de G r o o t , and H. v a n Bekkum,

Anal. Chem. 4 2 , 813 (1970).

(12) P.G.J. Koopman, A.P.G. Kieboom, and H. v a n Bekkum, s u b m i t t e d f o r p u b l i c a t i o n i n J . C a t a J .

(14) N.E. Buyanova, O.N. Karnaukhov, N.G. K o r o l e v a , I.D. R a t n e r , and O.N. C h e r n y a v s k a y a , Kinet. Catal. 1_3, 1364 (1972).

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(1975), p. 169.

(19) H . A . B o r t n e r and G. P a r r a v a n o , Engelhard Ind. Tech. Bull. _3» 23 (1962). (20) I . Toyoshima and G.A. S o m o r j a i , Catal. Rev. Sei. Eng. 19_, 105 (1979). (21) D. K o r s c h , Z . Rngew. Phys. 28, 43 (1969).

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Wiss. Tech. j_5, 299 (1949).

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I I ACTIVATION OF RUTHENIUM ON S I L I C A HYDROGENATION CATALYSTS

Summary

A c t i v a t i o n o f R u C l ^ - i m p r e g n a t e d s i l i c a by h y d r o g e n t r e a t m e n t a t h i g h

t e m p e r a t u r e , up t o 700 C i s s u p e r i o r t o a p r o c e d u r e i n v o l v i n g a i r c a l c i n a t i o n o f t h e m a t e r i a l b e f o r e r e d u c t i o n . Upon d i r e c t r e d u c t i o n s i n t e r i n g h a r d l y o c c u r s , whereas t h e Ru m e t a l s u r f a c e , as measured by hydrogen d e s o r p t i o n , i n c r e a s e d a t h i g h e r a c t i v a t i o n t e m p e r a t u r e , due t o t h e r e m o v a l o f c h l o r i n e i m p u r i t i e s from t h e Ru s u r f a c e . A c t i v i t y measurements o f t h e Ru c a t a l y s t s f o r t h e l i q u i d phase h y d r o g e n a t i o n o f benzene r e f l e c t e d t h e f a v o u r a b l e e f f e c t o f t h e h i g h t e m p e r a t u r e r e d u c t i o n o f R u C l /SiO^-I n t r o d u c t i o n The p r e p a r a t i o n o f s u p p o r t e d m e t a l c a t a l y s t s g e n e r a l l y i n v o l v e s i m p r e g n a t i o n o f t h e s u p p o r t w i t h a m e t a l s a l t s o l u t i o n , d r y i n g , c a l c i n a t i o n i n a i r and a c t i v a t i o n w i t h h y d r o g e n t o r e d u c e t h e m e t a l p r e c u r s o r . I n t h e c a s e o f s u p p o r t e d Ru c a t a l y s t s , t h e r e d u c t i o n p r o c e d u r e s , as mentioned i n t h e l i t e r a t u r e ( 1 - 5 ) , show much d i v e r g e n c e i n b o t h t e m p e r a t u r e and time o f r e d u c t i o n . I n a d d i t i o n , t h e r o l e and p o s s i b l e advantages o f c a l c i n a t i o n o f the i m p r e g n a t e d s u p p o r t p r i o r t o r e d u c t i o n a r e n o t o b v i o u s .

I n t h i s p a p e r we r e p o r t on t h e i n f l u e n c e o f some v a r i a b l e s i n t h e p r e p a r a t i o n o f S i O ^ - s u p p o r t e d Ru c a t a l y s t s ( 6 ) . D e s o r p t i o n o f hydrogen from t h e c a t a l y s t s (7) was used as a measure f o r t h e Ru s u r f a c e o f t h e s u p p o r t e d c a t a l y s t s and e n a b l e d t h e c o m p a r i s o n o f t h e s p e c i f i c a c t i v i t i e s o f t h e Ru c a t a l y s t s i n t h e l i q u i d phase h y d r o g e n a t i o n o f benzene.

22

E x p e r i m e n t a l

The c a t a l y s t s were p r e p a r e d by i m p r e g n a t i o n o f a p o r o u s S i O (AKZO F2, s u r f a c e 2 - 1

a r e a 345 m g ) t o i n c i p i e n t wetness w i t h a s o l u t i o n o f R u C l ^ h y d r a t e ( A l f a ) i n a c e t o n e . S u b s e q u e n t l y , t h e i m p r e g n a t e d S i O ^ was d r i e d i n a i r a t 120 C f o r 2 h. The a c t i v a t i o n was p e r f o r m e d i n a gas s t r e a m u s i n g t h e f o l l o w i n g

p r o c e d u r e s . (A) T r e a t m e n t w i t h f o r 2 h a t a f i x e d t e m p e r a t u r e between 200 and 700 °C; h e a t i n g o f t h e sample t o t h e d e s i r e d t e m p e r a t u r e took p l a c e a t

10 °C min , (B) As A b u t w i t h p r i o r h e a t i n g o f t h e sample t o t h e d e s i r e d o t e m p e r a t u r e i n - (C) C a l c i n a t i o n i n a i r a t 400 C f o r 2 h f o l l o w e d by p r o c e d u r e A. (D) T r e a t m e n t w i t h N2 f o r 2 h a t a f i x e d t e m p e r a t u r e between 400 and 700 °C. U n s u p p o r t e d Ru was p r e p a r e d by t h e r e d u c t i o n o f R u C l ^ h y d r a t e a c c o r d i n g t o p r o c e d u r e A a t 200-600 C.

The a c t i v i t y o f t h e c a t a l y s t s was measured u s i n g t h e l i q u i d phase o

h y d r o g e n a t i o n o f benzene (0.26 g) i n 1-propanol (20 ml) a t 30 C and 101 k P a .H2, u s i n g t h e a p p a r a t u s d e s c r i b e d e a r l i e r ( 8 ) .

T h e r m o g r a v i m e t r i c a n a l y s e s were c a r r i e d o u t w i t h a s y m m e t r i c a l t h e r m o b a l a n c e ( S a r t o r i u s 4104) i n f l o w i n g g a s .

The d e s o r p t i o n o f from t h e Ru/SiO^ was p e r f o r m e d i n a t e m p e r a t u r e programmed r e d u c t i o n a p p a r a t u s , w h i c h w i l l be d e s c r i b e d e l s e w h e r e ( 7 ) . R e s u l t s

Unsupported ruthenium

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

R u C l3. X H20 i n H2 was a l r e a d y c o m p l e t e below 160 °C. A f t e r the l o s s o f 0.8 and

o o

3.0 mol o f w a t e r a t about 100 C and 125 C, r e s p e c t i v e l y , r a p i d r e d u c t i o n o f Ru ( I I I ) t o Ru (0) o c c u r r e d ( F i g . 1) . I n a i rRuCl - j was o x i d i z e d t o RuC>2 a t

350 C, whereas i n N2 t h e r e was a s l o w ( r e d u c t i v e ) d e c o m p o s i t i o n o f t h e m e t a l

complex. Subsequent t r e a t m e n t o f b o t h t h e a i r - o r ^ - t r e a t e d samples l e d t o Ru ( 0 ) . The r e d u c t i o n o f R u 02 took p l a c e a t ^ 170 °C ( 7 ) .

I n c r e a s e o f t h e r e d u c t i o n t e m p e r a t u r e o f RuCl^.XH^O ( p r o c e d u r e A) d e m o n s t r a t e d s e r i o u s s i n t e r i n g o f t h e u n s u p p o r t e d Ru as r e f l e c t e d by t h e m e t a l d i s p e r s i o n from n i t r o g e n a d s o r p t i o n measurements a t -196 °C ( F i g . 2 ) .

F i g . 1. T h e r m o g r a v i m e t r i c c u r v e s o f RuCl^.XH^O i n E^, a i r and N2; h e a t i n g r a t e ^ o . -1 2 c min 5C 40 30 20 10 F i g . 2. E f f e c t o f r e d u c t i o n t e m p e r a t u r e on s u r f a c e a r e a o f Ru powder; PH 2= k P a , 2 h. Supported ruthenium

The v a r i o u s a c t i v a t i o n p r o c e d u r e s and t h e i n f l u e n c e o f t h e S i O ^ s u p p o r t have been s t u d i e d by means o f t h e r m o g r a v i m e t r i c a n a l y s i s . The thermograms i n E^ and N,, f o r R u C l ^ / S i C ^ and f o r t h e SiC>2 as s u c h a r e g i v e n i n F i g . 3. The d e c r e a s e

i n w e i g h t o f R u C l ^ / S i O ^ was caused by d e s o r p t i o n o f w a t e r , d e h y d r a t i o n o f s i l a n o l groups and d e c o m p o s i t i o n o f t h e Ru complex. The c u r v e s showed t h a t r e d u c t i o n i n was a l m o s t complete a t 350 °C, whereas t h e d e c o m p o s i t i o n i n N2

24

86 Y

0 200 400 600

-°C

F i g . 3. T h e r m o g r a v i m e t r i c c u r v e s o f SiO,, i n ( 1 ) , RuCl^/SiO,, i n B.^ (2) and R u C l3/ S i 02 i n N2 ( 3 ) ; h e a t i n g r a t e 4 °C min . r e q u i r e d a much h i g h e r t e m p e r a t u r e . T h e r m o g r a v i m e t r i c a n a l y s i s o f t h e c a l c i n a t i o n o f RuCl^/SiO,, i n a i r showed t h a t f o r m a t i o n o f R u 02/ S i 02 t o o k p l a c e a t a b o u t 325 C ( F i g . 4 ) . Subsequent H2 t r e a t m e n t l e d t o f o r m a t i o n o f R u / S i 02 a t % 150 °C. 0 200 400 600 800 °C

F i g . 4. T h e r m o g r a v i m e t r i c c u r v e s o f RuCl /SiO i n a i r (1) and RuO / S i O i n H o — 1

Activity measurements

The e f f e c t o f t h e a c t i v a t i o n p r o c e d u r e on t h e a c t i v i t y o f R u / S i c ^ i n t h e l i q u i d phase hydrogénation o f benzene i s d e p i c t e d i n F i g . 5. The a c t i v i t y o f

O p r o c e d u r e A (0>> B ( X ) , C ( A ) , and D ( O ) . R u / S i c ^ o b t a i n e d v i a c a l c i n a t i o n ( p r o c e d u r e C) i s r a t h e r i n d e p e n d e n t o f t h e a c t i v a t i o n t e m p e r a t u r e , whereas t r e a t m e n t o f R u C l ^ / S i O ^ w i t h o r w i t h f o l l o w e d b y r e s u l t e d i n a r e m a r k a b l e enhancement o f t h e a c t i v i t y w i t h o i n c r e a s i n g a c t i v a t i o n t e m p e r a t u r e , even up t o 700 C. S i m i l a r , though l e s s pronounced, r e s u l t s were o b t a i n e d b y p y r o l y s i s i n N . I t may be n o t e d t h a t i m p r e g n a t i o n o f SiC>2 w i t h a s o l u t i o n o f R u C l ^ i n aqueous h y d r o c h l o r i c a c i d (0.24 M) gave a n a l o g o u s r e s u l t s . I m p r e g n a t i o n w i t h a n o n - a c i d i f i e d aqueous R u C l ^ s o l u t i o n , however, l e d t o l e s s a c t i v e Ru/Sic^ c a t a l y s t s . D i s c u s s i o n I t i s c l e a r l y d e m o n s t r a t e d t h a t u n s u p p o r t e d Ru s i n t e r s upon r e d u c t i o n a t o t e m p e r a t u r e s above 200 C. T h i s i s accompanied by a d e c r e a s e i n a c t i v i t y o f Ru f o r benzene hydrogénation. R e d u c t i o n o f s u p p o r t e d R u C l ^ needs a s u b s t a n t i a l h i g h e r t e m p e r a t u r e f o r complete b u l k r e d u c t i o n ( F i g . 1 and 3 ) . The

d e c r e a s e d r e d u c i b i l i t y w i l l be caused by t h e i n t e r a c t i o n o f t h e m e t a l complex w i t h t h e s u p p o r t .

2 6 The i n c r e a s e i n a c t i v i t y i n t h e h y d r o g e n a t i o n o f benzene a t i n c r e a s i n g r e d u c t i o n t e m p e r a t u r e o f t h e Ru/SiO^ c a t a l y s t p o i n t s t o an i n c r e a s e o f the a c t i v e m e t a l s u r f a c e . T h i s i s c o n f i r m e d by t h e measurement o f t h e Ru s u r f a c e by H2 d e s o r p t i o n ( T a b l e I) showing an i n c r e a s e i n m e t a l d i s p e r s i o n a t TABLE I - M e t a l d i s p e r s i o n o f R u / S i 02 p r e p a r e d by d i r e c t r e d u c t i o n and by c a l c i n a t i o n - r e d u c t i o n , a) , , <b) P r o c e d u r e H/Ru d (nm) a) H 2 390 o C 0 037 3 H2 490 o c 0 074 3.5 H 2 690 o c 0 17 4 A i rd ; 400 o C z H2 300 o C 0 035 A i r 400 °C H2 500 o c 0 043 8 A i r 400 o C H2 700 o c 0 040

3^ H/Ru d e t e r m i n e d from d e s o r p t i o n measurements.

From X-ray l i n e b r o a d e n i n g .

C > PH 2: 101 k P a , 2 h. d > P . : 101 k P a , 2 h.

a i r

i n c r e a s i n g r e d u c t i o n t e m p e r a t u r e . T h i s may be due t o t h e removal o f c h l o r i n e i m p u r i t i e s from t h e Ru s u r f a c e . T h i s a s p e c t i s d i s c u s s e d i n more d e t a i l i n a subsequent p a p e r ( 7 ) . Any s e r i o u s s i n t e r i n g o f t h e Ru c r y s t a l l i t e s , as w o u l d be e x p e c t e d a t t h e s e h i g h t e m p e r a t u r e s , does n o t o c c u r : X - r a y l i n e b r o a d e n i n g measurements show j u s t a s l i g h t i n c r e a s e o f t h e mean Ru m e t a l p a r t i c l e s i z e

(from 3 nm a t 3 9 0 °C t o 4 nm a t 6 9 0 °C) ( 7 ) . C a l c i n a t i o n o f i m p r e g n a t e d c a t a l y s t s i s u s u a l l y c a r r i e d o u t t o c o n v e r t t h e m e t a l p r e c u r s o r i n t o i t s o x i d i c s t a t e , w h i c h i s s u b s e q u e n t l y r e d u c e d t o t h e m e t a l . I t f o l l o w s from t h e a c t i v i t y measurements t h a t t h e r e d u c t i o n t e m p e r a t u r e o f R u 02/ S i 02 h a r d l y i n f l u e n c e s t h e c a t a l y s t s p e r f o r m a n c e and t h a t t h e a c t i v i t y o f a c a t a l y s t o b t a i n e d by d i r e c t h i g h t e m p e r a t u r e r e d u c t i o n o f R u C l ^ / S i C ^ i s s u b s t a n t i a l l y h i g h e r . The Ru s u r f a c e o f Ru/SiC>2, p r e p a r e d via t h e c a l c i n a t i o n

method, i s i n d e p e n d e n t o f t h e r e d u c t i o n t e m p e r a t u r e , whereas i t s average Ru p a r t i c l e s i z e amounted t o 8 nm. T h i s means t h a t t h e a c t i v i t y o f t h e Ru c a t a l y s t s e x p r e s s e d p e r exposed Ru atom i s i n d e p e n d e n t o f t h e a c t i v a t i o n p r o c e d u r e .

I n c o n c l u s i o n we may s t a t e t h a t ( i ) c a l c i n a t i o n o f R u C l ^ / S i O ^ i n a i r t o RuC^/SiC^ f o l l o w e d by H r e d u c t i o n p r o v i d e s a c a t a l y s t w i t h l a r g e r Ru m e t a l c r y s t a l l i t e s t h a n d i r e c t r e d u c t i o n o f R u C l ^ / S i C ^ . ( i i ) d i r e c t r e d u c t i o n o f R u C l ^ / S i O ^ r e s u l t s i n a p a r t l y ( c h l o r i n e ) p o i s o n e d Ru m e t a l s u r f a c e w h i c h c a n be c l e a n e d b y h i g h t e m p e r a t u r e a c t i v a t i o n i n A d d i t i o n a l comments

The e f f e c t o f pd C l2 as c a t a l y s t component on t h e a c t i v i t y o f Ru/SiC>2 was

s t u d i e d f o r c a t a l y s t s c o n t a i n i n g v a r i o u s m e t a l l o a d i n g s o f Ru and Pd. Pd/SiC>2

and PdRu/SiC>2 c a t a l y s t s were p r e p a r e d by i m p r e g n a t i o n o f s i l i c a w i t h s o l u t i o n s

o f P d C l2 and o f P d C l2 and R u C l3 h y d r a t e , r e s p e c t i v e l y , i n 0.24 M HC1 f o l l o w e d

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

I n some p r e l i m i n a r y e x p e r i m e n t s t h e a c t i v i t y o f 5% P d / S i 02 and 5% Ru/SiC>2

i n t h e h y d r o g e n a t i o n o f c y c l o h e x e n e and o f 0.5% Pd 4.5% Ru/SiC>2 and 2.5% Pd

2.5% Ru/SiC>2 i n t h e h y d r o g e n a t i o n o f benzene and c y c l o h e x e n e was s t u d i e d . The

e f f e c t o f t h e r e d u c t i o n t e m p e r a t u r e o f t h e s e c a t a l y s t s on t h e a c t i v i t y i s p l o t t e d i n F i g . 6, 7, and 8. I n c o n t r a s t w i t h Ru/SiC>2 t h e a c t i v i t y o f Pd/SiC>2

i n t h e h y d r o g e n a t i o n o f c y c l o h e x e n e d e c r e a s e d when i n c r e a s i n g r e d u c t i o n t e m p e r a t u r e s were a p p l i e d , w h i c h i s p r o b a b l y due t o an i n c r e a s e o f Pd m e t a l

F i g . 6. A c t i v i t y (mmol c y c l o h e x e n e mol m e t a l s ) v e r s u s r e d u c t i o n t e m p e r a t u r e o f 5% Ru/SiO ( X ) and 5% Pd/SiO ( A ) .

28

F i g . 7. A c t i v i t y (mmol r e a c t a n t mol m e t a l s ) versus r e d u c t i o n t e m p e r a t u r e o f 0.5% Pd 4.5% Ru/SiO ; c y c l o h e x e n e ( X ) and benzene ( O ) .

F i g . 8. A c t i v i t y (mmol r e a c t a n t mol m e t a l s ) versus r e d u c t i o n t e m p e r a t u r e o f 2.5% Pd 2.5% R u / S i 02; c y c l o h e x e n e ( X ) and benzene ( O )

-p a r t i c l e s i z e . F o r t h e PdRu c a t a l y s t s a b e h a v i o u r as f o r Ru/SiO^ was f o u n d . T h i s m i g h t i n d i c a t e t h a t Pd p l a y s no r o l e i n t h e r e d u c t i o n o f s u r f a c e R u - C l bonds. A d d i t i o n a l d a t a , amongst o t h e r s t h e s u r f a c e c o m p o s i t i o n o f t h e PdRu

c r y s t a l l i t e s , a r e r e q u i r e d , however, i n o r d e r t o e x p l a i n t h e e f f e c t o f t h e a d d i t i o n o f Pd t o Ru/SiO^. L i t e r a t u r e (1) H. K u b i c k a , J . Catal. \2_, 223 (1968). (2) J.H. S i n f e l t and D.J.C. Y a t e s , J . Catal. 8, 82 (1967). (3) K.C. T a y l o r , J . Catal. 38, 299 (1975). (4) G.P. Nowack and M.M. J o h n s o n , US P a t e n t , 3912787 (1975).

(5) B. C o u g h l a n , S. Narayanan, W.A. McCann, and W.M. C a r r o l l , Chem. Ind. 125 (1977).

(6) P a r t o f t h i s work was p u b l i s h e d i n a p r e l i m i n a r y c o m m u n i c a t i o n :

P.G.J. Koopman, A.P.G. Kieboom, and H. v a n Bekkum, React. Kinet. Catal.

Lett. 8, 389 (1978) .

(7) P.G.J. Koopman, A.P.G. Kieboom, and H. v a n Bekkum, s u b m i t t e d f o r p u b l i c a t i o n i n J . Catal.

(8) G.W.H.A. M a n s v e l d , A.P.G. Kieboom, W.Th.M. de G r o o t , and H. v a n Bekkum,

I I I PREPARATION AND HIGH TEMPERATURE ACTIVATION OF RUTHENIUM ON CARBON HYDROGENATION CATALYSTS Summary Treatment o f r u t h e n i u m on c a r b o n s u p p o r t i n a i r ( c a l c i n a t i o n ) o r i n h y d r o g e n ( r e d u c t i o n ) a t t e m p e r a t u r e s o f 4 0 0 - 5 0 0 °C i s n o t a s u i t a b l e s t e p i n t h e c a t a l y s t p r e p a r a t i o n p r o c e d u r e because o f t h e c a t a l y t i c a c t i v i t y o f r u t h e n i u m i n t h e o x i d a t i o n and hydrogénation o f c a r b o n . No s u b s t a n t i a l m e t h a n a t i o n o f the c a r b o n s u p p o r t o c c u r s , however, when t h e r e d u c t i o n w i t h h y r o g e n i s p e r f o r m e d a t h i g h t e m p e r a t u r e s ( 7 0 0 8 0 0 °C) f o r s h o r t c o n t a c t t i m e s . C a l c i n a t i o n i n n i t r o g e n i n c o m b i n a t i o n w i t h t h i s h i g h t e m p e r a t u r e r e d u c t i o n p r o c e -dure r e s u l t s i n c a t a l y s t s w i t h h i g h a c t i v i t y i n t h e l i q u i d phase hydrogénation o f benzene. I n t r o d u c t i o n R e c e n t l y , we r e p o r t e d on t h e f a v o u r a b l e e f f e c t o f h i g h t e m p e r a t u r e r e d u c t i o n of r u t h e n i u m on s i l i c a c a t a l y s t s ( 1 ) . Though r u t h e n i u m c h l o r i d e i s r e d u c e d a t 160 °C i n h y d r o g e n , s u p p o r t e d on s i l i c a i t r e q u i r e d a t e m p e r a t u r e o f 3 5 0 °C to be r e d u c e d . R e d u c t i o n a t h i g h t e m p e r a t u r e , up t o 7 0 0 °C, r e s u l t e d i n h i g h l y a c t i v e " hydrogénation c a t a l y s t s . S i n c e c a r b o n i s o f t e n used as a s u p p o r t , p a r t i c u l a r l y i n l i q u i d phase hydrogénation ( 2 ) , t h e p o s s i b l e use o f t h e h i g h t e m p e r a t u r e a c t i v a t i o n f o r r u t h e n i u m on c a r b o n c a t a l y s t s m e r i t s i n v e s t i g a t i o n . O b v i o u s l y , t h e p r o b l e m o f m e t h a n a t i o n o f t h e c a r b o n w i l l a r i s e when t h e

a c t i v a t i o n i s c a r r i e d o u t a t a h i g h t e m p e r a t u r e ( 3 , 4 ) .

I n t h e p r e p a r a t i o n o f a group V I I I m e t a l on a c a r b o n s u p p o r t , t h e r e d u c t i o n of t h e m e t a l p r e c u r s o r i s u s u a l l y c a r r i e d o u t a t low t e m p e r a t u r e s i n s u s p e n -s i o n . F o r m i c a c i d and formaldehyde i n aqueou-s a l k a l i n e -s o l u t i o n ( 5 , 6 ) , m e t h a n o l ( 7 ) , sodium b o r o h y d r i d e ( 8 ) , h y d r a z i n e ( 9 ) , and h y d r o g e n ( 1 0 ) have