PHYSICOCHEMICAL ASPECTS
OF
SUPPORTED LIQUID PHASE RHODIUM
CATALYSTS
Het onderzoek werd uitgevoerd met financiële steun van de Nederland Organisatie voor Zuiver Wetenschappelijk Onderzoek, als onderdeel va het programma van de Stichting Scheikundig Onderzoek in Nederland
PHYSICOCHEMICAL ASPECTS
OF
JPPORTED LIQUID PHASE RHODIUM
CATALYSTS
"he Hydroformylation of the Butenes
PROEFSCHRIFT
ter verkrijging van de graad van doctor in de technische wetenschappen aan de Technische Hogeschool Delft,
op gezag van de Rector Magnificus, Prof. Dr. J.M. Dirken, in hel openbaar te verdedigen ten overstaan van het College van Dekanen op
donderdag 7 februari 1985 te 14.00 uur
door
HENDRIK LEENDERT PELT
geboren te Rotterdam scheikundig ingenieur
DELFT UNIVERSITY PRESS 1985
Dit proefschrift is goedgekeurd door de promotoren Prof. dr. J.J.F.Scholten,
Prof. dr. W. Drenth.
Aan mijn ouders Aan Rixta, Bart en Jaap
1. INTRODUCTION 1 1.1 The hydroformylation reaction 1
1.2 Heterogenization of the homogeneous catalyst 2
1.3 Scope of the present thesis 5
References 5
2. ADSORPTIVE WITHDRAWAL OF RhHCOfPPl^^ IN SUPPORTED LIQUID PHASE HYDROFORMYLATION CATALYSTS
Summary 9 1. I n t r o d u c t i o n 10 2 . E x p e r i m e n t a l 11 2 . 1 M a t e r i a l s 11 2.2 C h a r a c t e r i z a t i o n 12 2 . 2 . 1 T e x t u r e of t h e s u p p o r t s 12 2 . 2 . 2 Chemical a n a l y s i s of t h e s u p p o r t s 12 2 . 2 . 3 P r e - t r e a t m e n t of t h e s u p p o r t s 12 2 . 3 D e t e r m i n a t i o n of t h e a d s o r p t i o n i s o t h e r m s of KhHC0( PPt^)j d i s s o l v e d i n e x c e s s of t r i p h e n y l p h o s -p h i n e on v a r i o u s s u -p -p o r t s 13 3 . R e s u l t s 14 4 . D i s c u s s i o n 20 4 . 1 A d s o r p t i o n of RhHCOCPPhg)^ on t h e m a c r o r e t i c u l a r r e s i n XAD-2 20 4 . 2 A d s o r p t i o n on a l u m i n a 21 4 . 2 . 1 I n t r o d u c t i o n 21 4 . 2 . 2 A d s o r p t i o n on low t e m p e r a t u r e m o d i f i c a t i o n s of a 1 umi na 22 4 . 2 . 3 A d s o r p t i o n on a - a l u m i n a 24 4 . 3 A d s o r p t i o n on s i l i c a 2 5 4 . 4 I n f l u e n c e of t h e t e m p e r a t u r e of a d s o r p t i o n 26 4 . 5 I n f l u e n c e of t h e rhodium complex a d s o r p t i o n on t h e rhodium c o n c e n t r a t i o n i n t h e t r i -p h e n y l -p h o s -p h i n e m e l t i n t h e SLPC 27
X - — — __: ■_
._2__.^.-5. Conclusions 28 Acknowledgements 29 List of symbols 29 References 30 H Y D R O F O R M Y L A T I O N OF ALKENES WITH SUPPORTED LIQUID
PHASE RHODIUM CATALYSTS
The influence of the d i s s o l u t i o n of the produced
alkanals on the catalytic p e r f o r m a n c e 3 2
Summary 32 1. I n t r o d u c t i o n 33 2 . E x p e r i m e n t a l 35 2 . 1 M a t e r i a l s 35 2.2 S o l u b i l i t y d e t e r m i n a t i o n s 35 2 . 3 D e t e r m i n a t i o n of ads o r p t i o n i s o t h e r m s 35 3 . R e s u l t s and d i s c u s s i o n 36 3 . ! The s o l u b i l i t y of n - p e n t a n a l i n t r i p h e n y l p h o s p h i n e 36 3.2 The s o l u b i l i t y of t h e h y d r o f o r m y l a t i o n r e a c t a n t s H-?, CO and b u t e n e - 1 , i n t r i p h e n y l p h o s p h i n e a s i n f l u e n c e d by a d m i x t u r e of n - p e n t a n a i 39 3.3 The i n f l u e n c e of a c o - s o l v e n t on t h e complex a d s o r p t i o n a t t h e s o l i d - l i q u i d i n t e r f a c e i n a Rh-SLPC 41 3.4 The a c t i v i t y and s e l e c t i v i t y of t h e rhodium com
p l e x e s i n t h e SLPC, as i n f l u e n c e d by t h e d i s s o l u t i o n of n - p e n t a n a l i n t h e c a t a l y t i c s o l u t i o n 42 3.5 The i n f l u e n c e of t h e d e g r e e of p o r e f i l l i n g on t h e c a t a l y t i c a c t i v i t y of rhodium SLP c a t a l y s t s 43 4 . C o n c l u s i o n s 47 Acknowledgements 47 L i s t of symbols 48 R e f e r e n c e s 48
HYDROFORMYLATION OF BUTENE-1 AND BUTENE-2 OVER RHODIUM SLP CATALYSTS, AS COMPARED WITH THE HYDROFORMYLATION OF ETHENE AND PROPENE
The i n f l u e n c e of t h e d e g r e e of p o r e f i l l i n g on t h e p e r f o r m a n c e Summary 1. Introduction 2. Experimental 2.1 Materials 2.2 C a t a l y s t p r e p a r a t i o n 2 . 3 C a t a l y s t c h a r a c t e r ! z a t i o n 2.4 H y d r o f o r m y l a t i o n equipment 3 . R e s u l t s 3.1 I n t e r c o m p a r l s o n of t h e h y d r o f o r m y l a t i o n r a t e s of e t h e n e , propene and b u t e n e - 1 o v e r a Rh-SLPC 3.2 The l i n e a r t o b r a n c h e d r a t i o s ( 1 / b ) 3 . 3 C a t a l y t i c b e h a v i o u r of monolayer c a t a l y s t s 3.4 H y d r o f o r m y l a t i o n of b u t e n e - 1 , b u t e n e - 2 , and m i x t u r e s t h e r e o f 4 . D i s c u s s i o n Acknowledgements L i s t of symbols R e f e r e n c e s
THE KINETICS OF THE HYDROFORMYLATION OF BUTENE-1 OVER RHODIUM SUPPORTED LIQUID PHASE CATALYSTS, AS INFLUENCED BY THE DEGREE OF PORE FILLING
S umma r y 1. I n t r o d u c t i o n 2 . E x p e r i m e n t a l 2.1 M a t e r i a l s 2 . 2 C a t a l y s t p r e p a r a t i o n 2 . 3 The h y d r o f o r m y l a t i o n a p p a r a t u s 2 . 4 S p e c t r o s c o p y
3 . R e s u l t s and d i s c u s s ! o n 71 3.1 The k i n e t i c s of b u t e n e - 1 h y d r o f o r m y l a t i o n 71 3.2 S i d e , p a r a l l e l and c o n s e c u t i v e r e a c t i o n s 7 5 3.3 IR and 31P-NMR s t u d y of t h e rhodium SLP c a t a l y s t 79 3 . 3 . 1 S p e c t r a of s o l i d RMIC0(PPh3)3 79 3 . 3 . 2 S p e c t r a of t h e rhodium complex i n t h e SLPC 81 4 . C o n c l u s i o n s 83 Acknowledgements 8 4 L i s t of symbols 85 R e f e r e n c e s 85
THE THERMAL AND CHEMICAL STABILITY LIMITS OF SUPPORTED LIQUID PHASE RHODIUM CATALYSTS IN THE HYDROFORMYLATION
OF PROPENE 87 Summary 8 7 1. I n t r o d u c t i o n 88 2 . E x p e r i m e n t a l 89 3 . R e s u l t s and d i s c u s s i o n 90 3.1 C a t a l y s t s t a b i l i t y i n t h e h y d r o f o r r a y l a t i o n of p r o p e n c 90 3 . 2 D e a c t i v a t i o n of Lhe c a t a l y s t 93 3 . 3 The i n f l u e n c e of a d m i x t u r e of OPPh^ on the c a t a l y t i c
p e r f o r m a n c e 95 3.4 The i n f l u e n c e of water on t h e p e r f o r m a n c e of t h e SLPC 9 6 4 . C o n c l u s i o n s Acknowledgements 98 L i s t of symbols 99 R e f e r e n c e s 99 Appendix 1
CATALYST PREPARATION AND CATALYTIC HYDROFORMYLATION
EXPERIMENTS 101 Catalyst preparation 101 Hydroformylation experiments 102
References 105 Appendix 2
SOLUBILITY OF HYDROGEN, CARBON, MONOXIDE AND BUTENE-1 IN
TRIPHENYLPHOSPHINE + N-PENTANAL MIXTURES 106
Summary 106 1. I n t r o d u c t i o n 107 2 . E x p e r i m e n t a l 107 2.1 M a t e r i a l s 107 2 . 2 S o l u b i l i t y of n - p e n t a n a l i n PPh3 107 2 . 3 S o l u b i l i t y of H2, CO and b u t e n e - 1 i n Pph3 108 3 . R e s u l t s 109 3.1 S o l u b i l i t y of n - p e n t a n a l i n PPh3 109 3.2 D e t e r m i n a t i o n of H e n r y ' s c o n s t a n t s of t h e r e a c t a n t s h y d r o g e n , c a r b o n monoxide and b u t e n e - 1 i n PPh3 and
n - pent a n a l m i x t u r e s 1 4 . D i s c u s s i o n 113 5. Conclusions 117 Acknowledgements 1 ] List of symbols 1 ] References 1 S umma r y Samenvatting Naschrift Curriculum vitae 120 123 126 127
C H A P T E R
INTRODUCTION
1.1 The h y d r o f o r m y l a t i o n r e a c t i o n
H y d r o f o r m y l a t i o n i s t h e c a t a l y t i c f o r m a t i o n of a l k a n a l s ( a l d e h y d e s ) from t h e r e a c t i o n of a l k e n e s w i t h e q u i m o l a r amounts of h y d r o g e n and c a r b o n m o n o x i d e :
RCH - CH - CHO l i n e a r a l k a n a l H? + CO + RCH = CH2 ^ ' "' ( n - a l d e h y d e )
^ ^ RCH - CH. b r a n c h e d a l k a n a l CHO ( i s o - a l d e h y d e ) The h y d r o f o r m y l a t i o n r e a c t i o n was d i s c o v e r e d by Roeien [1] i n 1938, d u r i n g h i s i n v e s t i g a t i o n s on t h e F i s c h e r - T r o p s c h s y n t h e s i s of h y d r o c a r bons . From t h i s d i s c o v e r y on, many r e s e a r c h has been d e v o t e d t o t h i s r e a c t i o n . I n i t i a l l y , h y d r i d o c o b a l t t e t r a c a r b o n y l , HCo(CO)^, was used as a c a t a l y s t , but l a t e r on o t h e r t r a n s i t i o n m e t a l complexes were a p p l i e d . Up t o now t h e b e s t and most f r e q u e n t l y a p p l i e d c a t a l y s t i s a rhodium com p l e x . Osborn, W i l k i n s o n and Young [2] and Slaugh and M i l l i n e a u [3] found h y d r i d o c a r b o n y l t r i s ( t r i p h e n y l p h o s p h i n e ) r h o d i u m ( I ) , RhHCO(PPh.3)3, d i s s o l ved i n t o l u e n e t o be an e x c e l l e n t homogeneous c a t a l y s t . I t s a c t i v i t y i s a b o u t 10 t o 10 t i m e s h i g h e r t h a n t h e c o b a l t - b a s e d c a t a l y s t s . By a d d i t i o n of an e x c e s s of t r i p h e n y l p h o s p h i n e (PPh->) s i d e r e a c t i o n s l i k e d o u b l e bond i s o m e r i z a t i o n and a l k e n e h y d r o g e n a t i o n a r e s u p p r e s s e d t o a l a r g e e x t e n t . A h i g h molar p h o s p h i n e t o rhodium complex r a t i o i n c r e a s e s t h e l i n e a r t o b r a n c h e d a l k a n a l ( a l d e h y d e ) r a t i o ( 1 / b ) , i n c r e a s e s t h e c a t a l y s t s t a b i l i t y , and d e c r e a s e s t h e r e a c t i o n r a t e [ 4 ] .
H y d r o f o r m y l a t i o n w i t h rhodium c a t a l y s t s has been t h o r o u g h l y i n v e s t i g a t e d and has been r e v i e w e d by v a r i o u s a u t h o r s [ 5 - 8 ] . The r e a c t i o n me c h a n i s m , p o s t u l a t e d by W i l k i n s o n [ 9 - 1 1 ] , on t h e a n a l o g y of t h e c o b a l t mechanism p r o p o s e d by Heck and Breslow [ 1 2 ] , i s e s s e n t i a l l y s t i l l a c c e p t e d .
The h y d r o f o r m y l a t i o n of p r o p e n e w i t h rhodium complexes i s i n d u s t r i a l l y a p p l i e d i n t h e s o - c a l l e d Low P r e s s u r e Oxo p r o c e s s (LPO p r o c e s s ) . I t was d e v e l o p e d by Union C a r b i d e , Davy Power Gas and J o h n s o n M a t t h e y [ 1 3 ] ,
C H A P T E R
INTRODUCTION
1.1 The h y d r o f o r m y l a t i o n r e a c t i o n
H y d r o f o r m y l a t i o n i s t h e c a t a l y t i c f o r m a t i o n of a l k a n a l s ( a l d e h y d e s ) from t h e r e a c t i o n of a l k e n e s w i t h e q u i r a o l a r amounts of hydrogen and c a r b o n m o n o x i d e :
RCH - CH - CHO l i n e a r a l k a n a l
' ^ " ( n - a l d e h y d e )
^"** RCH - CH b r a n c h e d a l k a n a l ' ' ( i s o - a l d e h y d e ) The h y d r o f o r m y l a t i o n r e a c t i o n was d i s c o v e r e d by Roeien [ 1 ] i n 1938, d u r i n g h i s i n v e s t i g a t i o n s on t h e F i s c h e r - T r o p s c h s y n t h e s i s of h y d r o c a r bons . From t h i s d i s c o v e r y on, many r e s e a r c h has been d e v o t e d t o t h i s r e a c t i o n . I n i t i a l l y , h y d r i d o c o b a l t t e t r a c a r b o n y l , HCo(CO)^, was used as a c a t a l y s t , but l a t e r on o t h e r t r a n s i t i o n m e t a l complexes were a p p l i e d . Up t o now t h e b e s t and most f r e q u e n t l y a p p l i e d c a t a l y s t I s a rhodium com p l e x . Osborn, W i l k i n s o n and Young [2] and Slaugh and M i l l i n e a u [ 3 ] found h y d r i d o c a r b o n y l t r i s ( t r i p h e n y l p h o s p h i n e ) r h o d i u m ( I ) , RhHC0( P P h ^ ^ , d i s s o l ved i n t o l u e n e t o be an e x c e l l e n t homogeneous c a t a l y s t . I t s a c t i v i t y i s a b o u t 10 t o 10 t i m e s h i g h e r t h a n t h e c o b a l t - b a s e d c a t a l y s t s . By a d d i t i o n of an e x c e s s of t r i p h e n y l p h o s p h i n e (PPh-j) s i d e r e a c t i o n s l i k e d o u b l e bond i s o m e r i z a t i o n and a l k e n e h y d r o g e n a t i o n a r e s u p p r e s s e d t o a l a r g e e x t e n t . A h i g h m o l a r p h o s p h i n e t o rhodium complex r a t i o i n c r e a s e s t h e l i n e a r t o b r a n c h e d a l k a n a l ( a l d e h y d e ) r a t i o ( 1 / b ) , i n c r e a s e s t h e c a t a l y s t s t a b i l i t y , and d e c r e a s e s t h e r e a c t i o n r a t e [ 4] .
H y d r o f o r m y l a t i o n w i t h rhodium c a t a l y s t s has been t h o r o u g h l y i n v e s t i g a t e d and has been r e v i e w e d by v a r i o u s a u t h o r s [ 5 - 8 ] . The r e a c t i o n me c h a n i s m , p o s t u l a t e d by W i l k i n s o n [ 9 - 1 1 ] , on t h e a n a l o g y of t h e c o b a l t mechanism p r o p o s e d by Heck and Breslow [ 1 2 ] , i s e s s e n t i a l l y s t i l l a c c e p t e d .
The h y d r o f o r m y l a t i o n of p r o p e n e w i t h rhodium complexes i s i n d u s t r i a l l y a p p l i e d i n t h e s o - c a l l e d Low P r e s s u r e Oxo p r o c e s s (LPO p r o c e s s ) . I t was d e v e l o p e d by Union C a r b i d e , Davy Power Gas and J o h n s o n Matthey [ 1 3 ] ,
and the f i r s t plant is in production since 1975. From that time on more and more plants are constructed for the hydroforraylation with rhodium c a t a l y s t s . The hydroformylation process for the production of butanal (butyraldehyde) from propene operates at mild reaction conditions: at temperatures from 353 to 393 K (80-110°C) and t o t a l pressures from 1.3 Co 2.7 MPa. The linear to branched alkanal r a t i o is about 8 to 16. The rhodium complex has been dissolved in a mixture of butanal and high-boiling aldol condensation products obtained from alkanal t r i m e r i z a t i o n , and an excess of PPh.3 is added to the solution (P/Rh ■ 100).
Generally speaking, the linear product is i n d u s t r i a l l y far more im portant than the branched one. Normal butanal, for instance, ts the well known monomer from which, via condensation and e s t e r i f i c a t i o n , d i - o c t y l phtalate (DOP), an important p l a s t i c i s e r , is produced. The i n t e r e s t in the branched product is increasing due to i t s possible application as an intermediate in the production of automotive fuel a d d i t i v e s .
Other companies, like Exxon [14], have exerted t h e i r strength to the development of a rhodium-based hydroformylation process, s u i t a b l e for the hydroformylation of butene-1.
By applying special ligands, the s t a b i l i t y of the c a t a l y t i c system has been increased, by which higher reaction temperatures, up to 413 K
(140"C), are made possible. Further development is s t i l l in the stage of research [ 15-17].
1.2 Heterogenization of the homogeneous catalyst
Due to the very high price of rhodium, and the problem of c a t a l y s t recycling in the homogeneous operation [18, 19], effort is taken to he-terogenize the homogeneous c a t a l y s t s . At Delft University of Technology, several methods of heterogenization were investigated: physical adsorp tion of the rhodium complex on a support by Spek [20, 21] and by Tjan [22, 23], chemical anchoring of the rhodium complex to an organic sup port by de Munck [24-27], and rhodium catalysts in the Supported Liquid Phase form (SLPC) by Gerritsen [28-35], by de Munck [24, 36, 37] and by Herman [38]. In other laboratories rhodium-based SLPC for the hydrofor mylation were developed too [39-46]. From research in our laboratory i t can be concluded that rhodium SLP catalysts are a t t r a c t i v e as an a l t e r native for the homogeneous c a t a l y s t s .
A Supported Liquid Phase Catalyst consists of a liquid phase, d i s persed in a porous support. The gaseous reactants diffuse through the r e s i d u a l , non l i q u i d f i l l e d , pore space as well as through the dispersed liquid phas e, and undergo a homogeneous c a t a l y t i c reaction in the liquid phase and/or a heterogeneous reaction at the gas-liquid i n t e r f a c e . Next, the produced v o l a t i l e products are transported by diffusion out of the porous support. In such a hybrid c a t a l y s t , the advantages of homogeneous and heterogeneous c a t a l y s i s are combined. Besides t h e i r s t a b i l i t y and product s e l e c t i v i t y at r e l a t i v e l y mild operational conditions, typical of homogeneous c a t a l y s t s , they also have the q u a l i t i e s of heterogeneous c a t a l y s t s like convenient handling, a large gas-liquid i n t e r f a c i a l area and consequently small diffusion path, and ease of separation of the ca t a l y s t from the products. Use can be made of normal fixed bed reactors like multi tube r e a c t o r s , as contrasted with the homogeneous processes, where use is made of, for example, a s t i r r e d gas-liquid r e a c t o r , and where the feed as well as the reactant stream may be in the liquid or gaseous phase. The SLPC process is applicable with gaseous reactants and products only.
Models describing the c a t a l y t i c performance of SLP catalysts are published by Rony [39, 40, 47], Rinker [48-51], Livbjerg [52-54], Kheifets [55] , and Boreskov [56]. The change in the c a t a l y t i c a c t i v i t y as a function of the degree of pore f i l l i n g (6) is explained by these authors by taking into account the change in diffusional r e t a r d a t i o n as a function of 6.
The SLP c a t a l y s t s we are dealing with in t h i s t h e s i s , consists of the rhodi um complex, RhHCOf PPh^)3, diss olved in one of i t s l i g a n d s , PPh3, and c a p i l l a r y condensed in the pores of a support.
Gerritsen investigated the preparation of such c a t a l y s t s [28-30]. The parameters which are Important for the c a t a l y t i c performance a r e : the type of the support, the degree of pore f i l l i n g , the rhodium complex concentration, and the molar PPh3 to rhodium complex r a t i o . From mea sured diffusions constants, s o l u b i l i t y data, and reaction r a t e s , Ger r i t s e n calculated t h a t , at least in his experiments, diffusional r e t a r dation of the reaction r a t e was absent. On the other hand, he was able to prove that adsorption of rhodium complexes at the s o l i d - l i q u i d i n t e r face in many cases decreases the degree of rhodium u t i l i z a t i o n . G e r r i t sen also concluded that the hydroformylation reaction exclusively takes
place at the gas-liquid interface, but the validity of this view was al ready doubted by Herman [38], especially when working with high conver sion per pass. The adsorptive withdrawal of rhodium complexes, together with the surface area of the gas-liquid interface, are influenced by the degree of pore filling (6) and therefore the activity per rhodium com plex molecule depends on 6.
Gerritsen's rhodium SLP catalysts show an excellent catalytic per formance. The activity per mole of rhodium is comparable with (but lower than) the activity of the catalyst in the LPO process [28]. The selecti vity for the hydroformylation products was, at the very low conversions he worked with, nearly 100%, and the linear to branched alkanal ratio may be increased to values as high as forty, when the carbon monoxide partial pressure is lowered appreciably. In the hydroformylati on of pro pene, at 363 K (90°C) and at a total pressure of 1.6 MPa, no loss of ac tivity was observed after runs of 800 hours; this points to a very good catalyst stability [28].
Herman [38] investigated the industrial-technological aspects of the propene hydroformylation over rhodium SLP catalysts. In a bench scale reactor, he showed the SLPC to perform satisfactorily, applying catalyst particle diameters up to a few mm, and a rhodium concentration of 100 raol/m . The maximum allowable temperature was fixed at 383 K (110°C). Also the problem of the gradual evaporation of the solvent li ga nd PPh3 was discussed by him. Finally, Herman presented the design of an industrial chemical reactor suitable for SLPC hydroformylation.
Gas-phase hydroformylation of propene and allyl alcohol was inves tigated by de Munck [24-27, 36, 37], He applied both chemically anchored phosphine rhodium complexes and Supported Liquid Phase Rhodium Cata lysts. In the hydroformylation of propene, highly dispersed rhodium com plexes, dissolved in PPl^, over the surface of a macroreticular resin of polystyrene-divinylbenzene were very successful catalysts, with respect to a high activity per rhodium complex molecule. SLP catalysts appeared to be suitable to hydroformylate substituted alkenes, like allyl alco hol. The selectivity to the linear product is far higher than obtained in homogeneous processes.
1.3 Scope of t h e p r e s e n t t h e s i s .
The aim of t h e p r e s e n t t h e s i s i s t o deepen our i n s i g h t s i n t o t h e p h y s i c o c h e m i c a l a s p e c t s of t h e rhodium SLPC ( c h a p t e r 2 and 3 ) . As e x p l a i n e d i n s e c t i o n 1.2, a d s o r p t i v e w i t h d r a w a l of rhodium complexes a t t h e s o l i d - l i q u i d i n t e r f a c e changes t h e c a t a l y t i c a c t i v i t y as a f u n c t i o n of t h e d e g r e e of p o r e f i l l i n g . This a s p e c t was s t u d i e d f u r t h e r , t a k i n g I n t o a c c o u n t t h e i n f l u e n c e of d i s s o l u t i o n of t h e p r o d u c e d a l k a n a l s on t h e e x t e n t of complex a d s o r p t i o n t o o . F u r t h e r m o r e , t h e l o c a t i o n of t h e c a t a l y t i c s i t e s i n a SLPC i s r e c o n s i d e r e d , and G e r r i t s e n ' s view ( h y d r o -f o r m y l a t i o n t a k e s p l a c e e x c l u s i v e l y a t t h e g a s - 1 1 q u i d i n t e r -f a c e ) i s r e j e c t e d . A second o b j e c t i v e of t h i s s t u d y i s t o i n v e s t i g a t e t h e h y d r o f o r m y -l a t i o n of t h e v a r i o u s b u t e n e s over rhodium SLP c a t a -l y s t s ( c h a p t e r 4 and 5 ) . I t i s t o be e x p e c t e d t h a t t h e r e a c t i v i t y of b u t e n e - 1 d i f f e r s c o n s i d e r a b l y from t h a t of b u t e n e - 2 ( c i s and t r a n s ) , and from I s o b u t e n e . T h e r e f o r e h y d r o f o r m y l a t i o n of m i x t u r e s of b u t e n e s i s a l s o i n t e r e s t i n g , as i t o f f e r s t h e p o s s i b i l i t y of a s i m u l t a n e o u s s e p a r a t i o n of b u t e n e - 1 and b u t e n e - 2 and h y d r o f o r m y l a t i o n of b u t e n e - 1 . In c h a p t e r 6 t h e l i m i t s of t h e t h e r m a l s t a b ! l i t y of t h e SLPC a r e shown.
We have not performed a m e c h a n i s t i c s t u d y , a l t h o u g h t h e k i n e t i c s ( c h a p t e r 5) can be e x p l a i n e d by t h e mechanisms g i v e n I n t h e l i t e r a t u r e .
The l i n e a r h y d r o f o r m y l a t i o n p r o d u c t of b u t e n e 1 , n p e n t a n a l ( n v a -l e r a -l d e h y d e ) i s an i n t e r m e d i a t e i n t h e p r o d u c t i o n of a p -l a s t i c i s e r w i t h low v o l a t i l i t y , d i l s o d e c y l p h t a l a t e (DIDP). H y d r o f o r m y l a t i o n of b u t e n e -2 , t h o u g h d i f f i c u l t due t o lower r e a c t i v i t y of t h e i n t e r n a l d o u b l e bond l e a d s t o t h e f o r m a t i o n of 2 - m e t h y l b u t a n a l ( i s o - v a l e r a l d e h y d e ) . A c c o r d i n g t o a p a t e n t p u b l i s h e d r e c e n t l y [ 5 8 ] , 2 ^ m e t h y l b u t a n a l can d i r e c t l y be d e h y d r a t e d t o i s o p r e n e .
REFERENCES
1. 0 . Roeien (Ruhrchemie AG), German P a t e n t 8 4 9 , 5 4 8 ( 1 9 3 8 ) .
2 . J . A . Osborn, G. W i l k i n s o n , J . F . Young, Chem. Commun. , 2 (1965) 1 7 . 3 . L.H. S l a u g h , R.D. M i l l i n e a u ( S h e l l O i l C o . ) , US P a t e n t 3 , 2 3 9 , 5 6 6
4 . J . H . Craddock, A. Hershman, E . E . P a u l i k , I n d . Eng. Chem. P r o d . R e s . D e v . , 8 ( 3 ) (1969) 2 9 1 .
5 . J . F a l b e , New S y n t h e s i s w i t h Carbon Monoxide, S p r i n g e r V e r l a g , B e r l i n , FRG ( 1 9 8 0 ) .
6 . F . E . P a u l i k , C a t a l . Rev. - S c i . E n g . , 6 (1972) 4 9 . 7. R.L. P r u e t t , Adv. Organomet. Chem., 17 (1979) 1.
8 . P. P i n o , F . P i a n c e n t i , M. B r i a n c h i , O r g a n i c S y n t h e s i s v i a Metal C a r -b o n y l s , v o l . 2, eds . I . Wendern, P. P i n o , John W i l e y , New York, USA ( 1 9 7 7 ) .
9. D. Evans, J . A . Osborn, G. W i l k i n s o n , J . Chem. Soc. A, (1968) 3 1 3 3 . 10. G. Yagupsky, C.K. Brown, G. W i l k i n s o n , J . Chem. Soc. A, (1970) 1392. 1 1 . C.K. Brown, G. W i l k i n s o n , J . Chem. Soc. A, (1970) 2753.
12. R . F . Heck, D . S . B r e s l o w , J . Am. Chem. S o c , 8 3 ( 1 ) (1961) 1097. 1 3 . R. F o w l e r , H. Connor, R.A. B a e h l , Chem. Eng. ( N . Y . ) , 8 4 ( 2 ) , December
5 , (1977) 110.
14. I . Huang (Exxon R e s e a r c h and Eng. C o . ) , PCT WO 8 0 / 0 1 6 9 1 ( 1 9 8 0 ) . 15. A.A. Oswald (Exxon R e s e a r c h and Eng. C o . ) , PCT W0 8 0 / 0 1 6 9 0 ( 1 9 8 0 ) . 16. M. Matsumoto, M. Tamura, J . Mol. C a t a l . , 16 (1982) 209.
17. M. Matsumoto, M. Tamura, J . Mol. C a t a l . , 19 (1983) 3 6 5 .
18. M. Matsumoto, M. Tamura ( K u r a r a y Co. L t d . ) , B r i t . P a t e n t Appl. 2 , 0 5 6 , 8 7 4 ( 1 9 8 1 ) .
19. D.G. M o r e l l , P.D. Sherman (Union Carbide C o r p . ) , US P a t e n t 4 , 2 6 0 , 8 2 8 (1981) 2 0 . Th.G. Spek, J . J . F . S c h o l t e n , J . Mol. C a t a l . , 3 ( 1 9 7 7 / 7 8 ) 8 1 . 2 1 . Th.G. Spek, Ph.D. T h e s i s , D e l f t , The N e t h e r l a n d s ( 1 9 7 6 ) . 2 2 . P.W.H.L. T j a n , J . J . F . S c h o l t e n , P r o c . S i x t h I n t . Congr. C a t a l . , The Chem. S o c , London, (1977) 4 4 8 . 2 3 . P.W.H.L. T j a n , Ph.D. T h e s i s , D e l f t , The N e t h e r l a n d s ( 1 9 7 6 ) . 24. N.A. de Munck, Ph.D. T h e s i s , D e l f t , The N e t h e r l a n d s ( 1 9 8 0 ) . 2 5 . N.A. de Munck, M.W. V e r b r u g g e n , J . J . F . S c h o l t e n , J . Mol. C a t a l . , 10
(1981) 3 1 3 .
2 6 . N.A. de Munck, M.W. V e r b r u g g e n , J . E . de L e u r , J . J . F . S c h o l t e n , J . Mol. C a t a l . , 11 (1981) 3 3 1 .
2 7 . N.A. de Munck, J . J . F . S c h o l t e n , Eur. P a t e n t Appl. 4 0 , 8 9 1 ( 1 9 8 1 ) .
6
28. L.A. Gerritsen, Ph.D. Thesis, Delft, The Netherlands (1979). 29. L.A. Gerritsen, A. van Meerkerk, M.H. Vreugdenhil, J.J.F. Scholten,
J. Mol. Catal., 9 (1980) 139.
30. L.A. Gerritsen, J.M. Herman, W. Klut, J.J.F. Scholten, J. Mol. Catal. , 9 (1980) 157.
31. L.A. Gerritsen, J.M. Herman, J.J.F. Scholten, J. Mol. Catal., 9 (1980) 2 4 1 .
3 2 . L.A. G e r r i t s e n , W. K l u t , M.H. V r e u g d e n h i l , J . J . F . S c h o l t e n , J . Mol. C a t a l . , 9 (1980) 2 5 7 .
3 3 . L.A. G e r r i t s e n , W. K l u t , M.H. V r e u g d e n h i l , J . J . F . S c h o l t e n , J . Mol. C a t a l . , 9 (1980) 2 6 5 .
3 4 . L.A. G e r r i t s e n , J . J . F . S c h o l t e n (ZWO), N e t h e r l a n d s P a t e n t Appl. 7 , 7 0 0 , 5 5 4 ( 1 9 7 7 ) , 7 , 7 1 2 , 6 4 8 (1977) and 7 , 9 0 2 , 9 6 4 ( 1 9 7 9 ) .
3 5 . L.A. G e r r i t s e n , J . J . F . S c h o l t e n ( S t a r o i c a r b o n BV), Germ. P a t e n t A p p l . 2 , 8 0 2 , 2 7 6 ( 1 9 7 8 ) , US P a t e n t 4 , 1 9 3 , 9 4 2 ( 1 9 8 0 ) , US P a t e n t 4 , 2 9 2 , 1 9 8 ( 1 9 8 1 ) and B r i t . P a t e n t Appl. 1 , 5 5 1 , 6 0 1 ( 1 9 7 9 ) .
36. N.A. de Munck, J . P . A . Notenboom, J . E . de L e u r , J . J . F . S c h o l t e n , J . Mol. C a t a l . , 11 (1981) 2 3 3 .
3 7 . N.A. de Munck, J . J . F . S c h o l t e n , E u r . P a t e n t A p p l . 3 8 , 6 0 9 ( 1 9 8 1 ) , and N e t h e r l a n d s P a t . A p p l . 8 , 0 0 2 , 3 4 2 ( 1 9 8 0 ) . 3 8 . J.M. Herman, Ph.D. T h e s i s , D e l f t , The N e t h e r l a n d s ( 1 9 8 3 ) . 3 9 . P.R. Rony, J . C a t a l . , 14 (1969) 142. 4 0 . P.R. Rony, J . F . R o t h , J . Mol. C a t a l . , 1 ( 1 9 7 5 / 7 6 ) 1 3 . 4 1 . W. S t r o h m e i e r , B. G r a s e r , R. Marcec, K. H o l k e , J . Mol. C a t a l . , 11 (1981) 2 5 7 . 4 2 . W. S t r o h m e i e r , M. M i c h e l , J . C a t a l . , 69 (1981) 2 0 9 . 4 3 . J . H j o r t k j a e r , J . Mol. C a t a l . , 5 (1979) 3 7 7 . 4 4 . J . H j o r t k j a e r , M.S. S c u r r e l l , P. Simonsen, J . Mol. C a t a l . , 6 ( 1 9 7 9 ) 4 0 5 . 4 5 . J . H j o r t k j a e r , M.S. S c u r r e l l , P. Simonsen, J . Mol. C a t a l . , 10 (1981) 127. 4 6 . J . H j o r t k j a e r , M.S. S c u r r e l l , P. Simonsen, J . Mol. C a t a l . , 12 (1981) 179.
4 7 . P . R . Rony, Chem. Eng. S c i . , 23 (1968) 1 0 2 1 . 4 8 . R. Abed, R.G. R i n k e r , J . C a t a l . , 31 (1973) 1 1 9 . 4 9 . O.T. Chen, R.G. R i n k e r , Chem. Eng. S c i . , 33 ( 1 9 7 8 ) 1 2 0 1 . 5 0 . R. D a t t a , Ph.D. T h e s i s , Santa B a r b a r a , USA ( 1 9 8 1 ) .
1. INTRODUCTION
Supported Liquid Phase Catalysts (SLPC) are used in the oxidation of SO9 [1-3], the dimerlzation of alkenes [4], the Wacker oxidation [5-7] and the hydroformylation of alkenes
[8-26]-Gerritsen et al. [9-16], de Kunck et al. [25] and Herman [26] de veloped a number of rhodium SLP catalysts which were successfully applied in the hydroformylation of ethene, propene and allyl alcohol. In these catalysts the Wilkinson complex, RhHCOC PPbo)3, has been dissolved in triphenylphosphine (the so-called solvent-ligand). The solution has been capillarily condensed in the pores of vari ous supports,
One of the characteristics of SLP catalysts is the dependence of their activity on the degree of pore filling (6).
Rony [21, 22], who Investigated the hydroformylation of propene by butylphtalate solutions of RhClCO( PPh.3) 3 capillarily condensed in the pores of silica, found an opLinurn In the conversion (expressed in units of reactor vol urne) versus the degree of pore filling at about 5 = 0.5. The existence of an optimum loading is, according to Rony, due tc a gradual change of the dispersion of the liquid in the pores by which the length of the liquid diffusion path increases with increasing degree of pore filling. "Hence the supposition is made that diffusion of the re act ants determines the observed reaction rat e. The theories of Villadsen et al. [1-3] and of Abed, Chen and RInker [27, 29] are based on the same supposition: the observed reaction rate is determined by the diffusion of the reactants.
From the investigations by Gerri tsen et al. [10, 11] it appears that the plot of the reaction rate (expressed in cm ai ke n e/ (gp,h*s)) ver sus the degree of pore filling depends on the type of support material used: sometimes an optimum is found, but a gradual decrease of the con version with increasing degree of pore filling is observed too. It was discovered furthermore, by measuring adsorption isotherms of rhodium complex in molten triphenylphosphine on some supports, that adsorptive withdrawal of the complex from the solution occurs. The extent of the adsorption in a SLPC is a function of the degree of pore filling. In their theoretical treatment diffusional retardation of the reaction rate is rejected, and arguments are given that the catalytically active sites are located at the gas-liquid interface only. In their view, the change
of the alkene conversion as influenced by the degree of pore filling may be des cribed by taking Into account two aspects: the decrease of the meniscus surface area wi th increasing degree of pore f i llir.g and the simultaneous decrease of the percentage of complex molecules withdrawn from the solution by adsorption.
It is the aim of this chapter to extend our knowledge of the ad sorption of the rhodium complex from a triphenylphosphine melt on vari ous supports and to describe the nature of the adsorptive bond. Starting from an experimentally determined adsorption isotherm, a calculation is made of the concentration of dissolved rhodium complexes as a function of the degree of pore filling.
2. EXPERIMENTAL
2.1 Materials
RhHCO(PPh3)3 was p r e p a r e d by t h e method of Ahmad et a l . [ 3 0 ] . T r i p h e n y l p h o s p h i n e (Merck, West Germany, 98%) was used as r e c e i v e d . A 5 0 / 5 0 m i x t u r e (99.5%) of hydrogen and c a r b o n monoxide was o b t a i n e d from Air P r o d u c t s , USA. The s u p p o r t s used and t h e i r s u p p l i e r s a r e shown i n T a b l e 1. They were c r u s h e d i f n e c e s s a r y , and s i e v e d to t h e d e s i r e d f r a c t i o n . T a b l e 1. S u p p o r t s and t h e i r s u p p l i e r s . s u p p o r t code s u p p l i e r raacroretlcular r e s i n s t y r e n e - d i v i n y l b e n z e n e s 111 ca Y~alumlna 3 - a 1 umi na a - a l u m i n a XAD-2 000-3E S, H Dl 1-11 000-1,5E 000-3P 004-1,5E SA 5202 K 10 S e r v a , West Germany AKZO, The N e t h e r l a n d s DSM, The N e t h e r l a n d s ( n o n - c o m m e r c i a l ) BASF, West Germany AKZO, The N e t h e r l a n d s AKZO, The N e t h e r l a n d s AKZ0, The N e t h e r l a n d s N o r t o n , U.K.
5 1 . H.D. W i l s o n , R.G. R l n k e r , J . C a t a l . , 42 (1976) 2 6 8 . 5 2 . H. l i v b j e r g , J . V i l l a d s e n , Chem. Eng. S c i . , 27 (1972) 2 1 . 5 3 . H. L i v b j e r g , K . F . J e n s e n , J . V i l l a d s e n , J . C a t a l . , 45 (1976) 216. 5 4 . H. L i v b j e r g , B. S o r e n s e n , J . V i l l a d s e n , Chem. R e a c t . Eng. I I , Adv.
Chem. S e r . 133 (1974) 2 4 2 . 5 5 . L . I . K h e l f e t s , A.V. Neimark, K i n e t . C a t a l . ( E n g l . T r a n s ! . ) , 21(1) (1980) 109. 56. G.K. B o r e s k o v , V.A. D r i s ' k o , D.V. T a r a s o v a , K i n e t . C a t a l . ( E n g l . T r a n s l . ) , 11(1) (1970) 144. 5 7 . J . V i l l a d s e n , H. K l v b j e r g , C a t a l . Rev. - S c i . E n g . , 17(2) (1978) 2 0 3 . 5 8 . D. F o s t e r , G.E. Barker (Memsanto C o . ) , E u r . P a t e n t Appl. 8 0 , 449
( 1 9 8 3 ) .
8
•
C H A P T E R 2
ADSORPTIVE WITHDRAWAL OF RhHCO(PPh3)3 IN SUPPORTED LIQUID PHASE HYDRO-FORMYLATION CATALYSTS*-5
by
H.L. P e l t , G. van der Lee and J . J . F . S c h o l t e n ,
Department of Chemical T e c h n o l o g y , D e l f t U n i v e r s i t y of T e c h n o l o g y , J u l i a n a l a a n 136, 2628 BL D e l f t , The N e t h e r l a n d s . SUMMARY In S u p p o r t e d L i q u i d P h a s e C a t a l y s t s (SLPC) t h e d e g r e e of p o r e f i l l i n g may s t r o n g l y i n f l u e n c e t h e c a t a l y t i c a c t i v i t y . This i s , f o r I n s t a n c e , t h e c a s e when d e a l i n g w i t h Rh-SLP c a t a l y s t s i n which t h e complex RhHCOf PPh-j) 3 , d i s s o l v e d i n PPh^, i s d i s p e r s e d i n t h e p o r e s of a s u p p o r t mat e r i a 1 .
One of t h e f a c t o r s which c a u s e s t h e change of t h e a c t i v i t y p e r u n i t weight of r h o d i u m , i s t h e v a r i a b l e e x t e n t of a d s o r p t i v e complex w i t h d r a w a l a t t h e l i q u i d - s o l i d I n t e r f a c e i n t h e p o r e s . The amount of com p l e x e s a d s o r b e d ( t h e p e r c e n t a g e of d i s s o l v e d complexes withdrawn from t h e l i q u i d PPh3 by a d s o r p t i o n ) a p p e a r s , among o t h e r s , t o depend s t r o n g l y on t h e d e g r e e of p o r e f i l l i n g ( 6 ) .
In view of t h e f o r e g o i n g we d e t e r m i n e d a d s o r p t i o n I s o t h e r m s of RhHCOC PPh^) 3 , d i s s o l v e d i n PPÏ13, on v a r i o u s s u p p o r t m a t e r i a l s l i k e s i l i c a , v a r i o u s c r y s t a l l o g r a p h i c m o d i f i c a t i o n s of a l u m i n a , and on p o r o u s Am b e r l i t e , t y p e XAD-2. Most i s o t h e r m s a r e measured a t 3 63 K, t h e t e m p e r a t u r e a t which t h e c a t a l y s t s a r e u s u a l l y a p p l i e d .
The n a t u r e of t h e a d s o r p t i v e bond i s d i s c u s s e d ; i n some c a s e s we a r e d e a l i n g w i t h p h y s i c a l a d s o r p t i o n , i n o t h e r s t h e r e i s s t r o n g e v i d e n c e f o r c h e m i s o r p t i o n of t h e complex on t h e s u p p o r t .
Paper a c c e p t e d f o r p u b l i c a t i o n i n J o u r n a l of M o l e c u l a r C a t a l y s i s .
2 . 2 C h a r a c t e r i z a t i o n
2 . 2 . 1 T e x t u r e of t h e s u p p o r t s
Pore volume d i s t r i b u t i o n s of t h e s u p p o r t s were d e t e r m i n e d from n i t r o g e n c a p i l l a r y c o n d e n s a t i o n a t 77 K [ 3 1 ] , a p p l y i n g a C a r l o Erba 1800 " S o r p t o m a t i c " , or by mercury p o r o s i m e t r y [ 3 2 ] , a p p l y i n g an " A u t o p o r e 9200" a p p a r a t u s from M i c r o m e r i t i c s (USA).
BET s u r f a c e a r e a s were c a l c u l a t e d from n i t r o g e n or methane a d s o r p t i o n i s o t h e r m s a t 77 K, measured w i t h a micro-BET a p p a r a t u s p r o v i d e d w i t h a MKS B a r a t r o n p r e s s u r e g a u g e , t y p e 170M-25B.
2 . 2 . 2 Chemical a n a l y s i s of t h e s u p p o r t s
The sodium c o n t e n t of t h e s u p p o r t s ( b u l k c o m p o s i t i o n ) was d e t e r mined by n e u t r o n a c t i v a t i o n a n a l y s i s , u s i n g t h e s i n g l e c o m p a r a t o r me t h o d , w i t h z i n c a s a r e f e r e n c e [ 3 3 ] .
The rhodium c o n t e n t of t h e s o l i d s o l u t i o n s ( t h e rhodium complex d i s s o l v e d i n t r i p h e n y l p h o s p h i n e ) was d e t e r m i n e d by q u a n t i t a t i v e X - r a y f l u o r e s c e n c e a n a l y s i s , u s i n g a P h i l i p s PW 1450/20 ADP s e q u e n t i a l a u t o m a t i c X - r a y s p e c t r o m e t e r .
The alumina s u p p o r t s were c r y s t a l l o g r a p h i c a l l y c h a r a c t e r i z e d by X-r a y d i f f X-r a c t i o n a n a l y s i s [ 3 4 , 3 5 ] . We employed a P h i l i p s PW 1050 X - X-r a y d i f f r a c t o m e t e r w i t h Cu K-a r a d i a t i o n .
For some s u p p o r t s s u r f a c e a n a l y s i s was performed by Xray P h o t o -e l -e c t r o n S p -e c t r o s c o p y (XPS) [ 3 6 ] , -employing a L -e y b o l d - H -e r a -e u s LHF-10-XPS/AES s p e c t r o m e t e r . A Mg K-a e x c i t a t i o n s o u r c e ( e n e r g y 1253.6 eV) was a p p l i e d a t t h e o p e r a t i n g c o n d i t i o n of 13 kV and 20 mA. Samples were p r e -t r e a -t e d i n vacuo i n a p r e p a r a -t i o n chamber c o n n e c -t e d -t o -t h e XPS/AES cham b e r v i a a v a l v e l e s s UHV-lock.
2 . 2 . 3 P r e - t r e a t m e n t of t h e s u p p o r t s
C a l c i n a t i o n of t h e y~alumina 0 0 0 - 1 , 5 E s u p p o r t was c a r r i e d out i n
a i r a t t e m p e r a t u r e s between 773 and 1473 K f o r 16 h o u r s .
a-Alumina K 10 was p u r i f i e d by t h r e e - f o l d washing w i t h s t r o n g a c i d (10 w% HNO3) a t 343 K f o r 2 h o u r s , f o l l o w e d by t e n - f o l d e x t r a c t i o n w i t h
water at 293 K for one hour, and dried at 393 K. XPS measurements were carried out to investigate the effect of this treatment.
Rehydroxylation of hydrofobic silica, silica H, was performed by Immersing the support in water at 353 K for 16 hours. From the measure ment of water adsorption isotherms it appeared that the hydrophylicity was retained.
2.3 Determination of the adsorption isotherms of RhHCO(PPh^)^ dissolved in excess of triphenylphosphine on various supports
The adsorption isotherms were determined as follows:
H2 / C O F i g u r e 1. A d s o r p t i o n a p p a r a t u s A m f i l t e r B = s u s p e n s i o n of t h e s u p p o r t i n PPh-i c o n t a i n i n g t h e d i s s o l v e d rhodium complex C = h e a t i n g j a c k e t .
V a r y i n g amounts of RhHC0(PPh3)3 ( 0 . 0 1 - 0 . 0 9 g) and a b o u t 4 g of PPI13 and 1.5 g of t h e s u p p o r t were b r o u g h t i n t o t h e a p p a r a t u s shown i n F i g u r e I . The s u p p o r t s were p r e - d r i e d i n vacuo a t 773 K f o r 16 h o u r s , e x c e p t f o r t h e m a c r o r e t i c u l a r r e s i n XAD-2 which was p r e - d r i e d a t a m b i e n t p r e s s u r e
at 393 K for 16 hours. A mixture of hydrogen and carbon monoxide (50/50) was continuously bubbled through the solution. After two hours, when ad sorption equilibrium was reached, the solution and the support, totally filled with liqui d, were separated in situ by filtration. The amount of adsorbed complex was calculated from the change in rhodium concentration in the triphenylphosphine solution due to adsorption up to equilibrium. Equilibrium time was experimentally determined by changing the adsorp tion time with Y-alumina 000-1,5 E and with silica 000-3E as a support material. Using an ads orption time longer than two hours, no significant change in the amount of adsorbed rhodium was observed.
Whereas most isotherms were determined at 36 3 K some were obtained at temperatures between 353 and 393 K. From DSC measurements [10] it follows that during all adsorption experiments the PPh.3 was in the li quid state,
3. RESULTS
Information on the texture of the supports and on their sodium con tent is presented in Table 2. The differences in the BET surface areas are relatively large. The pore radii, which correspond with the maxima in the pore volume distributions, are presented as rp m a x. From the to tal pore volume distributions it follows that all pores are easily ac cessible f or the rhodium complex, for example y-alumina 000-1,5E as sup port material. From the pore volume distribution it was found that 80% of the surface area is formed by pores with a diameter less than 14 nm. Moreover it was found that pores with a diameter between 5 and 8 nm at tributed to 20% of the surface area. As the diameter of a rhodium com plex molecule is about 1.3 nm, it follows that all pores are accessible to the complex. The same reasoning is valid for other supports; see for instance the pore size distribution of XAD-2 in ref. [38].
The influence of the calcination temperature on the surface area of alumina 000-1,5E is given in Figure 2. The crystallographic composition of this alumina at different calcination temperatures, determined by X-ray analysis, is plotted in the same Figure. The composition at each temperature was calculated by means of the relat ive intensities of the diffraction lines of the various alumina modifications, given by van Dijk [35] .
u
Table 2. Texture and sodium content of the supports.
XAD-2 silica sodium content O /g) (cm3/g) (nm) wt % at % 000-3E S H H rehydr. D 11-11 alumina 000-1,5E 000-3P 004-1,5E SA 5202 K 10 K 10 (washed) 203 101 46 5 120 203 240 101 1.1 0.8 4 0.85 a 1.05 a 0.44 b c 0.87 a 0.51 a 0.55 a 0.52 a 0.34 b 0.185b' c) 5.7 17.9 c)
0
15.1 5.5 4.5 10.5 630 463 c) 0.49 0.0036 0.001 0.001 0.10 0.0003d'1 0.09 d) 0.10 d ) 0.26 0.33 c) c) c) 0.0 c) c) c) c) c) 8.6 5.0 0.0 d)calculated from N, capillary condensation (2 nm < r < 50 n m ) . measured by mercury porosimetry (3.75 nm < r < 75,000 n m ) . not measured.
200 100
o
(m2/g) v /j 1 1 i > ^ , i % modification RhQ d sx106 .(mol/m2 ) 600 1000 K 0 0 — T ( K ) F i g u r e 2 . I n f l u e n c e of t h e c a l c i n a t i o n t e m p e r a t u r e of y a l u -tnina 0 0 0 - 1 , 5 E on t h e s u r f a c e a r e a , o n t h e c r y s t a l l o g r a p h i c c o m p o s i t i o n and on t h e e x t e n t of a d s o r p t i o n a t [Rh] = 2 . 5 mol/ra3 a t 363 K. 1 = "ï-alumina , 2 - 9-alumi na , 3 = a - a l u m i n a . 0 2 01 -— -— [Rh] ( m o t / m3]F i g u r e 3 . A d s o r p t i o n i s o t h e r m of RhHCOCPPh3>3 o n XAD-2, a t 363 K, from a PPh.3 s o l u t i o n .
The adsorption isotherms of RhHC0(PPh3)3 at 363 K from a PPh3 melt on the various supports are given in Figures 3-5. In these Figures the amount of adsorbed rhodium complex, expressed in mol Eh per m , is plot
ted as a function of the equilibrium rhodium complex concentration, in mol Rh per m PPÏ13. The coverage (9) is calculated assuming the cross-sectional area of the adsorbed rhodium complex to be 1.35 nm2. From iso therms 5 and 6 in Figure 4 it follows that, at least at the a-aluminas SA 5202 and K 10, this assumption is untenably. Apparently the rhodium complex is adsorbed as a complex with less ligands.
F i g u r e 4 , A d s o r p t i o n i s o t h e r m of RhHCO(PPh3)3 on v a r i o u s a l u minas a t 363K from a PPh3 m e l t . 1. Y-alumina 0 0 0 - 1 , 5 E 2 . Y-alumina 0 0 0 - 3 P 3 . 9 - a l u m i n a 0 0 4 - 1 ,5E 4 . a - a l u m i n a K 10 washed 5 . a - a l u m i n a SA 5202 6. ct-a 1 umi na K 10
02
0.1
0
0 10 20 30 E = — [Rh]e ( m o l / m3]
Figure 5. Adsorption isotherms of RhHCO(PPh^)3 on various s i l i c a s , at 363 K, from a PPh^ s o l u t i o n . 1. s i l i c a 000-3E 2. s i l i c a S 3. s i l i c a Dl 1-1 1 4. s i l i c a H 5. s i l i c a H, rehydroxylated
In Table 2 i t is seen that the a-aluraina samples SA 5202 and K 10 show a r e l a t i v e l y high sodium surface concentration. It is possible that the sodium causes destruction of the ads orbed rhodium complex. Isotherms 5 and 6 in Figure 4 show that the coverages calculated on the basis of the cross-sectional area of RhHC0( PPh.3) 3 exceed the maximum coverage of 6 = 1. Otherwise, on well purified, sodium-free a-alumina K 10 (washed) a maximum coverage of one is arrived a t .
The beneficial effect of HNO3 washing on the surface purity of a-alumlna is demonstrated in Table 3. In this table the composition of the two outermost layers of alumina K 10 and K 10 (washed) i s given. This is
determined by XPS analysts. By extending the depth of analysis, it was found that O-alumina K 10 (washed) is free of Ma en Ca over at least 10 atomic layers.
The strong influence of the alumina modification on the extent of complex adsorption is demonstrated in Figure 2, whereas Figure 6 demon strates the influence of the temperature of adsorption.
0 3 0 2 01 Rh , x1C ads ( mol/m? )
R h
Q d sx 1 0 <
( mol / m ' )
« 5Figure 6.Amount of adsorbed rhodi um complex as a function of the adsorption temperature, at an equilibrium concentration of 20
3
mol Rh/m in the PPh3 s o l u t i o n . 1. s i l i c a 000-3E
2. Y-alumina 000-1,5E 3. a-alumina SA 5202
Table 3 . S u r f a c e c o m p o s i t i o n of a - a l u m i n a K 10 i n atom %, from XPS a n a l y s i s . K 10 K 10 (Washed) Na ( I s ) 5.0 0 . 0 0 ( I s ) 5 8 . 5 5 9 . 5 Ca ( 2 p ) 0 . 4 0 . 0 Al ( 2 s ) 3 1 . 0 3 5 . 5 C ( I s ) 0 . 9 0-7 Si ( 2 s ) 2 . 9 2 . 2 Ti C2p) 1.3 1.7 4. DISCUSSION 4 . 1 A d s o r p t i o n of RhHCOtPPh^^ on t h e m a c r o r e t i c u l a r r e s i n XAD-2
The a d s o r p t i o n i s o t h e r m of t h e rhodium complex on t h e m a c r o r e t i c u l a r r e s i n XAD-2 ( F i g u r e 3) shows t h a t a t 363 K h a r d l y any a d s o r p t i o n t a k e s p l a c e . XAD-2 i s a copolymer of s t y r e n e and d i v i n y l b e n z e n e ( 4 : 1 ) . The s u r f a c e of t h i s s u p p o r t i s composed of a r y l , a l k y l and v i n y l g r o u p s . De Munck [37] proved h0% of t h e v i n y l groups t o be u n p o l y m e r i z e d . We a s sume t h e s m a l l amount of a d s o r b e d rhodium complex t o be it bonded t o t h e v i n y l g r o u p s , as d e s c r i b e d by De Munck [38] ( F i g u r e 7 ) . I t a p p e a r s t h a t rhodium a d s o r b s o n l y on 3% of t h e u n p o l y m e r i z e d v i n y l g r o u p s . In a SLPC, t h e v i n y l groups of t h e s u p p o r t may be h y d r o f o r m y l a t e d . However t h i s i s u n l i k e l y i n t h e s e a d s o r p t i o n e x p e r i m e n t s .
c = c _ + c = c
+ R h H L3 H R h L3
F i g u r e 7. Rhodium complex a d s o r p t i o n on XAD-2. L = PPh3 or CO.
I n view of t h e l a r g e m o l e c u l a r w e i g h t of t h e rhodium complex one might e x p e c t i t s p h y s i c a l a d s o r p t i o n t o be s t r o n g e r t h a n t h a t of t r i p h e -n y l p h o s p h i -n e . However, due t o t h e l a r g e e x c e s s of t r i p h e -n y l p h o s p h i -n e , t h e thermodynamic p o t e n t i a l of t h e d i s s o l v e d complex i s t o o low t o i n c r e a s e i t s c o v e r a g e i n c o m p e t i t i o n w i t h p h y s i c a l t r i p h e n y l p h o s p h i n e a d s o r p t i o n . If t h e a d s o r p t i v e w i t h d r a w a l of t h e complex from t h e t r i p h e n y l p h o s -p h i n e s o l u t i o n i s harmful f o r t h e c a t a l y t i c a c t i v i t y of t h e SLPC, XAD-2 i s an e x c e l l e n t s u p p o r t w i t h r e s p e c t t o maximum c a t a l y t i c u t i l i z a t i o n of r h o d i u m . We r e t u r n t o t h i s q u e s t i o n i n a s e q u e n t c h a p t e r . 4 . 2 A d s o r p t i o n on a l u m i n a 4 . 2 . 1 I n t r o d u c t i o n Before d i s c u s s i n g t h e r e s u l t s of t h e a d s o r p t i o n e x p e r i m e n t s w i t h t h e a l u m i n a s , t h e s t r u c t u r e of t h e a l u m i n a s u r f a c e i s s h o r t l y r e v i e w e d . Alumina s u r f a c e s c o n t a i n OH g r o u p s (BrfSns t e d a c i d s i t e s ) , a n i o n v a c a n c i e s (Lewis a c i d s i t e s ) and 0 i o n s [ 3 9 ] . The c o n c e n t r a t i o n of each of t h e s e s i t e s d e p e n d s on t h e t e m p e r a t u r e a t which t h e a l u m i n a i s p r e t r e a -t e d . A low -t e m p e r a -t u r e -t r e a -t m e n -t r e s u l -t s i n a s u r f a c e m a i n l y c o v e r e d w i t h OH g r o u p s and a h i g h t e m p e r a t u r e t r e a t m e n t r e s u l t s i n a d e h y d r o x y -l a t e d s u r f a c e , w i t h o u t any B r ^ n s t e d a c i d s i t e s . a-A-lumina has n e i t h e r Lewis nor B r ^ n s t e d a c i d s u r f a c e s i t e s .
R e c e n t l y Knözinger e t a l . [40] i n t r o d u c e d a n o t h e r t y p e of s u r f a c e s i t e s on t h e low t e m p e r a t u r e m o d i f i c a t i o n s of a l u m i n a , t h e s o c a l l e d X-s i t e ( F i g u r e 8 ) . The Brf$nX-sted a c i d p a r t of t h e X - X-s i t e w i l l become X-s t r o n g e r a c i d i c a f t e r a d s o r p t i o n on t h e Lewis a c i d p a r t of a m o l e c u l e w i t h a l o n e p a i r , l i k e t r i p h e n y l p h o s p h i n e . F l o c k h a r t e t a l . [41] a l s o d e s c r i b e t h e i n c r e a s e d a d s o r p t i o n of e l e c t r o n a c c e p t o r m o l e c u l e s i n t h e p r e s e n c e of e l e c t r o n donor m o l e c u l e s .
From t h e r a t i o of t h e amounts of y, 9 and a m o d i f i c a t i o n i n a l u m i n a 0 0 0 - 1 , 5 E a t v a r i o u s c a l c i n a t i o n t e m p e r a t u r e s , combined w i t h t h e e x t e n t of rhodium complex a d s o r p t i o n ( F i g u r e 2 ) , we c a l c u l a t e d t h e e x t e n t of rhodium complex ads o r p t i o n on t h e d i f f e r e n t m o d i f i c a t i o n s a t a rhodium c o n c e n t r a t i o n i n t h e l i q u i d of 2 . 5 mol/m . For "f-alumina was found 9 = 0 . 0 4 , f o r 8 - a l u m i n a 8 = 0.07 and f o r a - a l u m i n a 6 = 0 . 4 1 . This i s i n good
D
OH
i l A l A l F i g u r e 8 . X - s i t e s on a l u m i n a , a c c o r d i n g t o KnÖzinger e t a l . [40J . O i n d i c a t e s an a n i o n v a c a n c y . a g r e e m e n t w i t h t h e r e s u l t s ( F i g u r e 4) f o r y - a l u m i n a 000-3P ( 9 = 0 . 0 3 ) , f o r 0 - a l u m i n a 0 0 4 - 1 , 5 E ( 9 = 0 . 0 8 ) and f o r ct-alumina K 10 (washed) ( 9 = 0 . 3 6 ) . A p p a r e n t l y t h e c r y s t a l l o g r a p h i c m o d i f i c a t i o n s t r o n g l y d e t e r m i n e s t h e e x t e n t of complex a d s o r p t i o n . The e x t e n t of a d s o r p t i o n depends on t h e a d s o r p t i o n s t r e n g t h of t h e rhodium complex, on t h e number of a d s o r p t i o n s i t e s p e r m , and on t h e s t r e n g t h and e x t e n t of t r i p h e n y l p h o s p h i n e c o - a d s o r p t i o n . 4 . 2 . 2 A d s o r p t i o n on low t e m p e r a t u r e m o d i f i c a t i o n s of alumina The a d s o r p t i o n of t r i p h e n y l p h o s p h i n e on y - a l u m i n a was s t u d i e d by Spek [ 4 2 ] . A c c o r d i n g t o Spek, PPh^ m o l e c u l e s w i l l f i r s t a d s o r b on t h e Lewis a c i d s i t e s and a f t e r t h a t p o s s i b l y r e a c t w i t h OH or 0 s u r f a c e groups ( F i g u r e 9 ) . From IR m e a s u r e m e n t s , t h e f o r m a t i o n of t r i p h e n y l p h o s p h i n e o x i d e i s p r o v e d . a OH 0 P P h OH 0 l i t i 3 i i Al Al Al + P P h „ + A l Al A l + OH I Al F i g u r e 9. A d s o r p t i o n of t r i p h e n y l p h o s p h i n e on y - a l u m i n a , a c c o r d i n g t o Spek [ 4 2 1 ; o i n d i c a t e s an a n i o n v a c a n c y . The s t r o n g l y c h e m i s o r b e d PPh-^ w i l l c o v e r t h e s u r f a c e t o a l a r g e e x t e n t a n d , on t h e o t h e r hand, w i l l i n t e n s i f y t h e a d s o r p t i o n of t h e r h o dium complex on t h e X - s i t e s ( F i g u r e 1 0 ) , i f no t r i p h e n y l p h o s p h i n e a d s o r p t i o n o c c u r s on t h e B r e a s t e d a c i d p a r t of t h e X - s i t e . OH PPh OH i i 3 i Al Al + PPh„ + RhHL -*• Al Al + RhHL ■»F i g u r e 1 0 . C o a d s o r p t i o n of rhodium complex and t r i p h e n y l p h o s p h i n e on y -and 8 - a l u m i n a ; L a PPh3 or CO.
A c c o r d i n g t o K n ö z i n g e r e t a l . [ 3 9 ] t h e c o n c e n t r a t i o n of t h e X - s i t e s on t h e s u r f a c e of y and n a l u m i n a ( n a l u m i n a has t h e same X s i t e c o n c e n
-■
9-.-31 7
The maximum e x t e n t of complex a d s o r p t i o n , t a k e n from t h e a d s o r p t i o n i s o t h e r m s ( F i g u r e 5 ) , i s i n a g r e e m e n t w i t h t h i s s i t e c o n c e n t r a t i o n , p r o v i ded one complex m o l e c u l e i s a d s o r b e d per s i t e . These maximum a d s o r p t i o n s a r e 4-6 x 10 complexes p e r m f o r Y-alumina and 1.8 x 10 complexes per m f o r 6-alumina a t an e q u i l i b r i u m rhodium c o n c e n t r a t i o n of 20 mol Rh/m . The good c o r r e s p o n d e n c e between K n b ' z i n g e r ' s s i t e c o n c e n t r a t i o n s and t h e c o n c e n t r a t i o n s of a d s o r b e d complexes found by us may be f o r t u i t o u s , but i s not i n c o n t r a d i c t i o n w i t h t h e bonding p r o p o s e d i n F i g u r e 12, which was p r o p o s e d by H j o r t k j a e r e t a l . [24] t o o .
F u r t h e r e v i d e n c e f o r t h i s k i n d of complex a d s o r p t i o n i s found from G e r r i t s e n ' s a d s o r p t i o n i s o t h e r m on a s t r o n g l y a c i d i c s i l i c a - a l u m i n a s a m p l e [ 1 1 ] . This i s o t h e r m p o i n t s t o s t r o n g complex c h e m i s o r p t i o n on a r e l a t i v e low number of s i t e s per m .
A n o t h e r p o s s i b l e rhodium complex a d s o r p t i o n i s g i v e n by Spek [ 4 2 , 44] ( F i g u r e 1 1 ) . Spek i n v e s t i g a t e d , by means of IR, t h e a d s o r p t i o n of R h (ï ïC3H5) C 0 ( P P h3)2 on y - a l u m i n a w i t h o u t an e x c e s s of t r i p h e n y l p h o s p h i n e .
L I © H - R h
Figure 11. Adsorption of rhodium complex on 0 surface s i t e s of alumi na. L = PPh3 or CO.
In excess of triphenylphosphine t h i s kind of complex adsorption i s less probable, due to the strong chemisorption of PPb.3 on these s i t e s (Figure
2—
9 ) . The complex adsorption on the Lewis basic surface 0 groups is fur ther discussed i n 4 . 2 . 3 .
4.2.3 Adsorption on a-alumina
The extent of rhodium complex adsorption on a-alumina i s much high er than on low temperature modifications of alumina (Figure 4). Chemi-sorption of PPhrj cannot take place on a-alumina due to the absence of Lewis and Br^nsted acid s i t e s . The observed high extent of rhodi urn com plex adsorption has to be the result of strong physical adsorption or chemisorption of the complex, otherwise the complex could not compete with the physical adsorption of the triphenylphosphine.
In Figure 11 we have already given a representation of rhodium com plex adsorption on the Lewis basic s i t e s . On a-alumina there is no com p e t i t i o n on these s i t e s between rhodium complex and triphenylphosphi ne. Recent experiments by Kruissink [45] , point the 0 -surface groups on the surface of a-alumina to be Lewis basic s i t e s . This offers the p o s s i b i l i t y of replacing an unknown number of triphenylphos phine ligands by 0 -ligands (Figure 12). Such an adsorption does not necessarily mean an elimination of a c a t a l y t i c centre. We return to this in a sequent chapter.
0 ©
•
CO-
-v.
/
H R h -IV,
Figure 12. Alternative representation of rhodium complex adsorption on a-alumina. L = PPb.3 or CO.
4.3 Adsorption on s i l i c a
The adsorption isotherms on s i l i c a supports are presented i n Figure 5. We see that the extent of adsorption is low. The nature of the s u r face of the support has only a small effect on the adsorption. Silica H, a hydrofobic s i l i c a , and the hydroxylated s i l i c a H, which i s h y d r o f i l i c , show about the same coverage.
Triphenylphosphine adsorption on s i l i c a was studied by Spek [42]. He concluded from his IR-investigations that the chemisorption takes place by p a r t i a l proton transfer to the lone pair of the phosphor and the ÏÏ electron system of the phenyl group (Figure 13).
P/
OH ISi
OH I Si Figure 13. Adsorption of PPh^ on s i l i c a .Due to the excess of triphenylphosphine and its relatively strong adsorption via hydrogen bridges, the extent of the rhodium complex co-adsorption is low. Adjacent sllanol groups are known to exhibit stronger acidity than the isolated singletons. Hence such groups are the most at tractive candidates for the adsorption of triphenylphophine, described above, and for adsorption of the rhodium complex like the adsorption on hydroxylated alumina surfaces (Figure 14).
RhL. i 5
OH 0 Si + RhHL3 - - S i + H 2
Figure 14. Adsorption of rhodium complex on silica; L = PPl^ or CO.
Total dehydroxylation of silica results in a surface covered with siloxane bridges. Isotherm 4 in Figure 5 (silica H) shows the adsorption of the rhodium complex (in excess of triphenylphosphine) on this surfa ce. We suppose the siloxane bridges will open during rhodium complex ad sorption as it occurs at the rehydroxylation of these surfaces.
4.4 Influence of the temperature of adsorption
The extent of adsorption of the rhodium complex from a triphenyl-phosphine solution is influenced by the adsorption temperature (Figure 6). In the case of a-alumina as an adsorbent, a decrease of adsorption with increasing temperature Is observed, in accordance with expectation. The enthalphy of the rhodium complex adsorption was calculated to be about -70 kj/mol.
With y-alumina and silica another result is arrived at. The adsorp tion increases with increasing temperature. We think this is due to the gradually increasing replacement of triphenylphosphine by the rhodium complex in the competitive adsorption at higher temperatures. The pro posed adsorption on y, 8-alumina and silica is a co-adsorption of tri phenylphosphine and of the rhodium complex. The competition of the tri phenylphosphine adsorption makes it impossible for the rhodium complex to adsorb at all desired sites. The triphenylphosphine adsorption will decrease with increasing temperature, and hence the complex adsorption will increase.
4.5 Influence of the rhodium complex adsorption on the rhodium concen tration in the triphenylphosphine melt in the SLPC
It appears that the complex adsorption Isotherms presented in Figu res 3-5 may be described by the Langmuir equation, except Isotherm 6 in Figure 4 :
[Rb]
Kj . K, . [ R h ]E
ads = 1 + K [Mi] ( 1 )
where [Rh] i s complex concentration in PPI13 at equilibrium, [Rh]acjs the surface concentration of complex, Ki the equilibrium constant and Kg the maximum rhodium adsorption concentration. We performed t h i s only for mathematical reasons, i t has no physi cal or chemical meaning.
0 0 2 0.4 0.6 0 8 1.0
— 5
Figure 15. Relation between the percentage of rhodium complex retained in solution and the degree of pore filling, at different
initial complex concentrations, for silica H as a support. 1. [Rh]c 5 mol/ra
2. [Rh] - 25 mol/m 3. [Rh], 50 mol/m
From t h e Langrauir r e l a t i o n combined w i t h t h e mass b a l a n c e f o r r h o dium, we c a l c u l a t e d t h e c o n c e n t r a t i o n of d i s s o l v e d rhodium complex i n a SLPC as a f u n c t i o n of t h e d e g r e e of pore f i l l i n g . The r e s u l t s f o r s i l i c a H as an a d s o r b e n t , f o r v a r i o u s i n i t i a l c o n c e n t r a t i o n s of t h e rhodium complex, a r e p l o t t e d i n F i g u r e 1 5 . N o t w i t h s t a n d i n g t h e r e l a t i v e low e x t e n t of complex a d s o r p t i o n on s i l i c a H, F i g u r e 15 d e m o n s t r a t e s t h e e x t r e m e l y high i n f l u e n c e of t h e d e g r e e of p o r e f i l l i n g on t h e c o n c e n t r a t i o n of d i s s o l v e d c o m p l e x e s . To what e x t e n t t h e a d s o r p t i v e w i t h d r a w a l w i l l i n f l u e n c e t h e c a t a l y t i c p e r f o r m a n c e as a f u n c t i o n of t h e d e g r e e of p o r e f i l l i n g , depends on t h e r e l a t i v e c o n t r i b u t i o n of a d s o r b e d and d i s s o l v e d rhodium complexes t o t h e c a t a l y t i c a c t i v i t y . F u r t h e r m o r e , d i s s o l u t i o n of t h e p r o d u c t s ( a l k a n a l s ) i n t o t h e s o l v e n t l i g a n d t r i p h e n y l p h o s -p h i n e may i n f l u e n c e t h e e x t e n t of t h e rhodium com-plex a d s o r -p t i o n t o o . This w i l l be d i s c u s s e d i n t h e f o l l o w i n g c h a p t e r .
5 . CONCLUSIONS
1. On m a c r o r e t i c u l a r r e s i n p o l y s t y r e n e - d i v i n y l b e n z e n e (XAD-2) t r i p h e n y l phos p h i n e i s p h y s i c a l l y a d s o r b e d . The a d s o r p t i o n of t h e W i l k i n s o n complex cannot compete w i t h i t .
2 . The e x t e n t of a d s o r p t i o n of t h e W i l k i n s o n complex on Y and B-alumina , i n t h e p r e s e n c e of e x c e s s t r i p h e n y l p h o s p h l n e , i s v e r y l o w .
T r i p h e n y l p h o s p h l n e , a s t r o n g Lewis b a s e , i s p h y s i c a l l y a d s o r b e d , b u t a l s o bound t o t h e Br(4nsted a c i d i c OH-groups. The W i l k i n s o n complex may compete w i t h t r i p h e n y l p h o s p h l n e a d s o r p t i o n v i a s t r o n g b o n d i n g t o f r e e 0 - g r o u p s a n d / o r v i a bonding t o Bryinsted a c i d OH-groups.
3 . The s u r f a c e 0 - g r o u p s i n a - a l u m i n a a r e s t r o n g l y Lewis b a s i c . T h i s i s t h e r e a s o n why t h e a d s o r p t i v e w i t h d r a w a l of t h e rhodium complexes i s s t r o n g and e x t e n d e d . The s t r o n g b o n d i n g , I n c o m p e t i t i o n w i t h p h y s i c a l t r i p h e n y l p h o s p h i n e a d s o r p t i o n , i s t h o u g h t t o be due t o l i g a n d e x change between t r i p h e n y l p h o s p h l n e l i g a n d s and 0 - s u r f a c e g r o u p s a n d / o r a d s o r p t i o n of t h e CO l i g a n d t o t h e 0 - s u r f a c e g r o u p s .
4 . As t h e s u r f a c e s i l a n o l g r o u p s on s i l i c a a r e weakly B r ^ n s t e d a c i d i c , t r i p h e n y l p h o s p h l n e i s s t r o n g l y a d s o r b e d . C o m p e t i t i v e a d s o r p t i o n of t h e W i l k i n s o n complex i s r e l a t i v e l y low and might be a s c r i b e d t o I n t e r a c t i o n w i t h t h e s i l a n o l groups of h i g h e s t a c i d i t y . 5 . T h e c a t a l y t i c p e r f o r m a n c e of a r h o d i u m SLPC i s a f u n c t i o n of t h e d e g r e e of p o r e f i l l i n g [ 1 1 ] . T h e q u e s t i o n , t o w h a t e x t e n t t h e a d s o r p t i v e w i t h d r a w a l of c o m p l e x e s i s i n v o l v e d i n t h i s e f f e c t w i l l b e d i s c u s s e d i n a s e q u e n t c h a p t e r . ACKNO WLEDGEMENTS We t h a n k M r . J . T e u n i s s e a n d M r . N. v a n W e s t e n f o r c a r r y i n g o u t t h e a d s o r p t i o n e x p e r i m e n t s a n d t h e t e x t u r e m e a s u r e m e n t s , M r . A . P . P i j p e r s ( D e p a r t m e n t P h y s i c a l C h e m i s t r y , C e n t r a l L a b o r a t o r i e s , DSM, G e l e e n , T h e N e t h e r l a n d s ) f o r t h e XPS m e a s u r e m e n t s a n d M r . J . P . G . R o u s s e a u ( D e p a r t m e n t A n a l y t i c a l C h e m i s t r y , C e n t r a l L a b o r a t o r i e s , DSM, G e l e e n , T h e N e t h e r l a n d s ) f o r t h e X - r a y f l u o r e s c e n c e a n a l y s i s . T h e i n v e s t i g a t i o n s w e r e s u p p o r t e d ( i n p a r t ) by t h e N e t h e r l a n d s F o u n d a t i o n f o r C h e m i c a l R e s e a r c h ( S O N ) w i t h f i n a n c i a l a i d f r o m t h e N e t h e r l a n d s O r g a n i z a t i o n f o r t h e A d v a n c e m e n t of P u r e R e s e a r c h ( Z W O ) . L I S T OF SYMBOLS
radi at maximum in pore volume di tribution
adsorbed rhodium complex concentration rhodium complex in BET surface area
temperature pore volume
degree of pore filling ( Vp p h /Vp) rhodium coverage (Sp^ / SB E T) .8-PPh3 nm 2 mol/m mol/m-' m2/g K cm /g
-REFERENCES
1. H. L i v b j e r g , B. S o r e n s o n , J . V i l l a d s e n , Chem. R e a c t . Eng. I I , Adv. Chem. S e r . 133 (1974) 2 4 2 .
2 . H. L i v b j e r g , J . V i l l a d s e n , Chem. Eng. S c i . , 27 (1972) 2 1 . 3 . H. L i v b j e r g , K . J . J e n s e n , J . V i l l a d s e n , J . C a t a l . , 45 (1976) 2 1 6 . 4 . G. E g l o f f , I n d . Eng. Chem., 28 (1968) 1 4 6 1 .
5. G. K a t z , L.M. Pismen, Chem. Eng. J - , 18 (1979) 2 0 3 . 6 . H. Komiyama, H. I n o u e , J . Chem. Eng. J p n . , 8 ( 4 ) (1975) 3 1 0 . 7. H. Komiyama, H. I n o u e , J . Chem. Eng. J p n - , 10(2) (1977) 1 2 5 . 8 . J . C . B a i l e r , C a t . R e v . - S c i . E n g . , 10(1) (1974) 1 7 .
9. L.A. Gerritsen, A. van Meerkerk, M.H. Vreugdenhil, J.J.F. Scbolten, J. Mol. Catal., 9 (1980) 139.
10. L.A. Gerritsen, J.M. Herman, W. Klut, J.J.F. Scholten, J. Mol. Catal., 9 (1980) 157.
11. L.A. Gerritsen, J.M. Herman, J.J.F. Scholten, J. Mol. Catal., 9
(1980) 241.
12. L.A. Gerritsen, W. Klut, M.H. Vreugdenhil, J.J.F. Scholten, J. Mol. Catal-, 9 (198C) 257.
13. L.A. Gerritsen, J.J.F. Scholten (ZWO), Netherlands Pat. Appl. 7700554 (1977), 7712648 (1977), 7902964 (1979).
14. L.A. Gerritsen, J.J.F. Scholten (Stamicarbon B.V.), German Pat. Appl. 2802276 (1978).
15. L.A. Gerritsen, J.J.F. Scholten (Stamicarbon B.V.), US Pat. 4193942 (1980), 4292198 (1981).
16. L.A. Gerritsen, J.J.F. Scholten (Stamicarbon B.V.), Brit. Pat. Appl. 155169 (1969).
17. J. Hjortkjaer, J. Mol. Catal., 5 (1979) 377.
18. J. Hjortkjaer, M.S. Scurrell, P. Simonsen, J. Mol. Catal., 6 (1979) 405.
19. W. Strohmeier, H. Michel, J. Catal., 69 (1981) 209.
20. W. Strohmeier, B. Graser, R. Maréec, K. Holke, J. Mol. Catal., 11 (1981) 257.
2 1 . R . P . Rony, Chem. Eng. S c i . , 23 (1968) 1 0 2 1 . 2 2 . R . P . Rony, J . C a t a l . , 14 (1969) 142.
23. J. Villadsen, H. Livbjerg, Catal. Rev.-Sci. Eng., 17(2) (1978) 203.
30
24. J. Hjortkjaer, M.S. Scurrell, P. Simonsen, J. Mol. Catal., 10 (1981) 127.
25. N.A. de Munck, J.P.A. Notenboom, J.E. de Leur, J.J.F. Scholten, J. Mol. Catal., 11 (1981) 233.
26. J.M. Herman, Ph.D. Thesis, Delft, The Netherlands (1983). 27. R. Abed, R.G. Rinker, J. Catal., 31 (1973) 119.
23. H.D. Wilson, R.G. Rinker, J. Catal., 42 (1976) 268. 29. 0.T. Chen, R.G. Rinker, Chen. Eng. Sci., (1978) 1201.
30. N. Ahmad, S.D. Robinson, M.F. Uttler, J. Chem. Soc. Dalton Trans, (1972) 843.
31. J.C.P. Broekhoff, Ph.D. Thesis, Delft, The Netherlands (1969). 32. L.A. de Wit, J.J.F. Scholten, J. Catal., 36 (1975) 36.
33. P.J.M. Korthoven, M. de Bruin, J. Radioanal. Chem., 35 (1977) 127. 34. II.P. Klue, L. Alexander, X-ray Diffraction Procedures for Polycrys-talline and Amorphous Materials, chapter 5, 7, 2nd ed., John Wiley & Sons, New York, USA (1974).
35. J. van Dijk, Ph.D. Thesis, Delft, The Netherlands (1975).
36. T.A. Carlson, Photoelectron and Auger Spectroscopy, 1st ed., Plenum Press, New York, USA (1975).
37. N.A. de Munck, M.W. Verbruggen, J.J.F. Scholten, J. Mol. Catal., 10 (1981) 313.
38. N.A. de Munck, Ph.D. Thesis, Delft, The Netherlands (1980). 39. H. Knözinger, P. Ratnasamy, Catal. Rev.-Sci. Eng., 17(1) (1978) 31. 40. H. Knözinger, H. Krietenbrink, H.D. Muller, W. Schultz, Proc. Sixth
Int. Congr. Cat., The Chem. Soc. London, (1977) 145.
41. B.D. Flockhart, J.R. Leith, R.C. Pink, J. Catal., 9 (1967) 45. 42. Th.G. Spek, Ph.D. Thesis, Delft, The Netherlands (1976).
43. G.D. Gatta, B. Fubini , G. Ghiotti, C. Morterra, J. Catal., 43 (1976) 90.
44. Th.G. Spek, J.J.F. Scholten, J. Mol. Catal., 3 (1977/78) 81. 45. E.C. Kruissink, Appl. Catal., 9 (1984) 145.
