JOURNAL OF CATALYSIS 112, 329-336.(1988)

Deactivation of Platinum Catalysts by Oxygen

1. Kinetics of the Catalyst Deactivation Consultan Inc.ts, Ali TranTech Amirnazmi,

E

Received September 17, 1985; revised August 21, 1987

A study has been made of the kinetics of deactivation of a commercial Pt/C catalyst being used in an aqueous slurry for the oxidation of D-gluconate to D-glucarate at 50°C. It appears that the deactivation of the catalyst is an independent process, governed by the coverage of the platinum surface by oxygen atoms. Under steady-state conditions an exponential decay is observed. A mathematical model is presented, based on the processes occurring at the platinum surface, which describes the experimental results very well. © 1988 Academic Press, inc.

INTRODUCTION oxidation of ammonia with oxygen, while

iiaZjiiii a.iiu uuuuoi i \i j) c u o u 1 wuiiva a. Catalyst deactivation is an important loss of catalyst activity during the decom-

problem, especially in the case of large- position of nitrogen oxide over P t /Al 2 0 3 . scale production. Well-known causes of catalyst deactivation are sintering, irrevers-

Deactivation of platinum catalysts also oc-curs during oxidation processes in the liq-

ties in the feed, and deposition of carbona-ceous material on active sites. Irreversible

et al. in oxidizing ethylene glycol (3, 4) and Dirkx et al. in oxidizing D-glucose to D-glu-

catalyst deactivation is of particular impor-tance in the case of the application of noble m j=»tQl r"sitc»1\/ctc h p r ^ i i K P n f th**ir h i o h in i t ia l

carate (8-10). Also, patents have been pub-lished (14, 15) concerning the activity of rvlatirmm r*QtQl\/ctc Hurmo r w i r l a t i n n nrn.

costs. Platinum catalysts are often used both for

cesses in the liquid phase. The oxidation of D-gluconate (obtained

hydrogenation/dehydrogenation reactions and for oxidation reactions. Important ap-nhV.atinns of nlatirmm catalysts in the field

by oxidation of D-glucose) to D-glucarate involves a reaction intermediate, L-gulu-ronate Thft main reaction sp.rmp.nrp. is

of oxidation are the complete combustion of automotive exhaust gases (7) and the

given in Fig. 1. The compounds D-glu-conate and L-guluronate possess weak re-

oxidation ot ammonia (I, 2). Ihe oxidation of alcohols (3-6), aldehydes (6, 7), and suears (8-12) mav serve as examples of

ducing properties. Ihe overall selectivity to D-glucarate is about 50%. The remaining products are carboxvlic acids of a lower

platinum-catalyzed oxidation reactions in the liquid phase.

T-V .1 1 1

molecular weight (as D-tartrate, tartronate, glycolate, D-erythronate, and oxalate)

uuring tnese processes a sirong aeac-tivation of the platinum catalysts often oc-curs due to the presence of oxygen. Oster-

iormea oy c-

riTTlf flu A A P FT AT

kept at a constant temperature. A mixture of oxygen and nitrogen is supplied to the reactor containing the aqueous catalyst *1

slurry is measured with an oxygen probe (Ingold 533 sterilizable electrode) which

D-glucos* D-gluconate L-guluronat» D-g'ucarite

F I G . 1. Reaction sequence in the oxidation of D-

displays the equivalent saturation pressure of the oxygen dissolved in the slurry. The

cose to disodium-D-glucarate. oxygen pressure in me siurry, ro 2 , is con-trolled by a continuous adjustment of the stirrer speed. In this way a dynamic equilib-

A possible new application is the use of num is obtained between the amount of D-glucarate as a substitute for polyphos- oxygen transferred from the gas phase to phates in detergents (79, 20). the slurry and the amount ot oxygen con-

A serious problem for the production of sumed by reaction. ^ ~i — „ i „ - , w * r ^ ^ i A The nH of the slurrv is kent at a constant JJ-giUL.cliaic un a laigc stait 13 nit iapu * j 1

deactivation of the Pt/C catalyst under the level by titration with a solution of sodium reaction conditions used. An investigation hydroxide, in order to neutralize the sugar on this subject has been started because information in the literature concerning this

acids formed during the oxidation process. Simultaneously a solution of sodium-D-glu-r-nncitp ic QHHP>H ir% tVif* c l n r n ; in Q p n n c t a n t

pnenomenon is scarce, special auenuun is given to the influence on the deactivation process of the oxygen pressure, D-elu-

& L J UUUW I V J LliV J1U1 1 J 111 W\-f 11J LUUt

proportion with the amount of alkali added (the production of 1 mole disodium-D-glu-

conate concentration, pH, and temper- carate from sodium-D-gluconate requires 1 a t u r e mole of alkali). The rate of deactivation of

EXPERIMENTAL

The catalyst used in this study was com-alkali consumption as a function of time. In this way the reaction conditions remain

mercially available 5% platinum on acti-vated charcoal (Degussa F 196 RA/W).

constant in time except for the catalyst

Utner types or support were testea in me past but charcoal appeared to be prefer-able The same conclusion was drawn bv other authors oxidizing various alcohols under comparable reaction conditions (21,

A first requisite to study catalyst deac t i v o t i r m ic tr\ m a i n t a i n t h e rp.nr.tinn rondi tions at a constant level as a function of time. Batch experiments in which the deac-tivation proceeds along with conversion of D-gluconate cannot provide useful informa-

deactivation process. Therefore an appara-tus has been built (Fig. 2) to study the F I G . 2. Apparatus for continuous oxidation. (1) continuous oxidation of sodium-D-glu conate under steady-state conditions.

Keacior, muuuun vessel, \ 3 j pn iiicasuitmciiu control, (4) measurement/control of partial pressure of oxygen in the liquid, (5) feed of alkali, (6) feed of

1: -i J . - / T \ /o\ +u „ A iiv ±±±i±±u f u i t j V/A v^w^uivnv ^ SOUlum-D-glUCUnau;, V'7 pump, VA* uicnuv&iav,

reactor and the filtration vessel which are sampling system.

330 DIJKGRAAF ET AL.

D.~I"CO‘. 0-9I"CO".t* L.9YIYrm.t. D-~I"car.t*

FIG. 1. Reaction sequence in the oxidation of D-glu- case to disodium-n-glucarate.

A possible new application is the use of D-glucarate as a substitute for polyphos- phates in detergents (19, 20).

A serious problem for the production of o-glucarate on a large scale is the rapid deactivation of the Pt/C catalyst under the reaction conditions used. An investigation on this subject has been started because information in the literature concerning this phenomenon is scarce. Special attention is given to the influence on the deactivation process of the oxygen pressure, D-glu- conate concentration, pH, and temper- ature .

EXPERIMENTAL

The catalyst used in this study was com- mercially available 5% platinum on acti- vated charcoal (Degussa F 196 RA/W). Other types of support were tested in the past but charcoal appeared to be prefer- able. The same conclusion was drawn by other authors oxidizing various alcohols under comparable reaction conditions (22, 22).

A first requisite to study catalyst deac- tivation is to maintain the reaction condi- tions at a constant level as a function of time. Batch experiments in which the deac- tivation proceeds along with conversion of o-gluconate cannot provide useful informa- tion on the factors which influence the deactivation process. Therefore an appara- tus has been built (Fig. 2) to study the continuous oxidation of sodium-D-glu- conate under steady-state conditions.

The main parts of the equipment are the reactor and the filtration vessel which are

kept at a constant temperature. A mixture of oxygen and nitrogen is supplied to the reactor containing the aqueous catalyst slurry. The concentration of oxygen in this slurry is measured with an oxygen probe (Ingold 533 sterilizable electrode) which displays the equivalent saturation pressure of the oxygen dissolved in the slurry. The oxygen pressure in the slurry, PO*, is con- trolled by a continuous adjustment of the stirrer speed. In this way a dynamic equilib- rium is obtained between the amount of oxygen transferred from the gas phase to the slurry and the amount of oxygen con- sumed by reaction.

The pH of the slurry is kept at a constant level by titration with a solution of sodium hydroxide, in order to neutralize the sugar acids formed during the oxidation process. Simultaneously a solution of sodium-D-glu- conate is added to the slurry in a constant proportion with the amount of alkali added (the production of 1 mole disodium-D-glu- carate from sodium-D-gluconate requires 1 mole of alkali). The rate of deactivation of the catalyst is determined by recording the alkali consumption as a function of time. In this way the reaction conditions remain constant in time except for the catalyst

FIG. 2. Apparatus for continuous oxidation. (1) Reactor, (2) filtration vessel, (3) pH measurement/ control, (4) measurement/control of partial pressure of oxygen in the liquid, (5) feed of alkali, (6) feed of sodium-D-gluconate, (7) pump, (8) thermostat, (9) sampling system.

F»F A T T T V A T T O M O F PT ATTXTTT1U P AT AT Y55TS1 1 ' U l

concentration which slightly decreases by dilution with the solutions of alkali and sodium-D-gluconate. This is compensated •y penuuicaiiy pumping ctouui J/C UI me slurry to the filtration vessel followed by partial filtration. The resulting slurry is pumped back to the reactor. The filtrate is analyzed by high-speed liquid chromatogra-

1 1 " 1 1 1 T̂ V f+ I S ^% \ pny as aescriDea oy LnjKgraai et at. \ZJ).

Al l experiments were performed at temperature of 50°C. a D H of 9. and catalyst concentration of 10 kg/m 3 unless mentioned otherwise. In all experiments

time Us)

FIG. 4. Activity of the catalyst as a function of time nH nH (+\ nH 7 (C)\ nH 8 ( x ) nH Q

the conversion or sodium-D-gluconate in the reactor was kept at the same low level nf nlimit 5% t

310 n T T W n P A A P T7T A T

4 i reactor or stopping the stirrer for a few minutes (the rate of deactivation of the catalyst after resuming the experiment, I1UWCVCI, IS l l l g l lC l i i u s i c a v u v c t i i u i i

is accomplished by reducing compounds in the reaction mixture which reactivate the deactivated platinum sites at the catalyst surface. Using a similar procedure, regen-eration or a platinum catalyst was acnievea in the case of the oxidation of other com-nounds such as ethvlene elvcol (3. 4). am-

FIG. 5. Deactivation constant as a function of partial monia (2), and sugar acids (8-10). This regeneration process at the platinum sur-

pressure 01 UAygeu anu suuiuiii-D-giui-uuiiic luuic i i -tration. Sodium-D-gluconate concentrations: (O) 0.25 mole/liter, (x) 0.5 mole/liter, (•) = 1.0 mole/liter, ( + )

face will also occur during normal oxidation experiments. However, deactivation then Hr\mir»Qt(=»c ctnr\ ihf> npt rpcn l t ic a ornHiml

decrease in the catalyst activity. Equation (1) can also be derived starting

platinum catalysts during the oxidation of D-gluconate can be ascribed entirely to the

from the three elementary processes that take place on the catalyst surface, namely,

have been performed using a constant con-centration of D-gluconate and different oxy-

ation. Because of these general starting points the proposed model does not have to

gen pressures. The deactivation constants refer only to the oxidation of D-gluconate. belonging to these experiments are given in It may possibly also hold for other oxida-tig. J as a runction or tne oxygen pressure and the D-gluconate concentration. It is striking that the deactivation constant de-

iion processes using precious meiai caia-lysts under comparable reaction condi-tions, during which (weak) reducing

pends on both parameters and decreases using a lower oxygen pressure or a higher

compounds are converted to their ac-cessory products. The three elementary

D-gluconate concentration, rrom this result steps will now be discussed in some detail, the assumption arises that the coverage of The oxidation reaction. As reported by thf* nlntinum

nC A P T n / A T T r i M H P DT AXTXTTTA4 P A T A T V Q T C 1 S *J

tivated, 1 - the rate of oxidation is the platinum surface at infinite time and described by equals, k d f 0 / ( k d f 0 + k r f A ) , */,o is the deac-

tivated fraction of the platinum surface at / r„M) = A O X / A / O H - Xi(t)). (2) r\ _ 1 rs- * i i J ±: _ ^ „ A ^

The deactivation reaction. The deac tivation of the catalvst is caused by disso

u, anu A D is ine ueaciivauun cuiisictiu "') and equals ( k d f 0 + k r f A ) / S . Wolf and Petersen (28) derived a similar

ciative chemisorption of oxygen followed type of relation for a reaction with a self by penetration of oxygen atoms into the poisoning parallel reaction due to an irre-platinum lattice, the nature ot trie deac-tivation is described in more detail in Part 2 (?4\ Tt is verv likelv that the rate of the

versible interaction ot a reactant adsorbed on an active site. The introduction of a regeneration reaction as in our case.

deactivation reaction depends on the frac-tion of platinum sites at the surface which is

however, does not result in a greatly differ-ent expression.

not yet deactivated, 1 - Xi(t), and the The total rate of reaction is obtained by fraction of sites which is covered with the summation of Eqs. (2) and (4). Equation

reaction also contributes to the conversion of the organic reactant into products:

The regeneration reaction. The interac-tion between a reducing compound A and a deactivated site may result in a regenera-tion of this site. The rate of regeneration

} ib aisu ULUCUIICU uy LUC 1I1U1L1(J1IL;

I'XA mnicii> A A TH F T A T

very likely. As regards the equilibrium con-dition for adsorption, it is very likely that the Langmuir theory is applicable. CA

i n e ucacuvciiiuii uuiisuuu can nuvv uc written as O 4

S(l + (KnCn.)05 + KACA + ZKXCX) n

(8) 40 50 60

T ( ° C >

The oxygen concentration in the slurry is proportional to the partial pressure of oxy-

FIG. 7. Deactivation constant as a iunction or tem-perature (P0l = 1 bar, C G 0 Z = 0.5 mole/liter).

gen m trie reaction mixture ^Co2 may oe obtained by multiplication of Po2 with the Henrv coefficient which is determined as a

£d(^o,C 0 ,) 0 , 5 . From Eqs. (3) and (4) it then follows that the regeneration reaction is

function of the concentration of several compounds). Hence the deactivation con-

much less signmcant than the deactivation reaction. All together Kb may be simplified to

stant is proportional to (Po2) as long as it holds that

0.5

c /1 _i_ ir r< (10)

(K0lCof -5 < 1 + KACA + ZKXCX. (9) From Eq. (9) it follows that the fraction of

According 10 tne resuus in rig. d 11 was found that a linear relationship exists be-tween and CPn.)05. Aooarentlv the con-

uie piaimiun suiiciL-c uuvcicu uy uAygcn atoms must be rather low. This means that in view of the high rates of deactivation of

dition as given by Eq. (9) is fulfilled. In Fig. 5 the interception of all lines with the KD

the catalyst observed during our experi-ments, the reaction rate constant k& in Eq.

axis is located m the origin, lhis means that (3) is quite mgn. the term ^ / A C A in the numerator of Eq. (8) In Fig. 6 the deactivation constant is ic vprv Qmall rnmnarprl tn the other term nlotted as a function of the sodium-D-elu-

conate concentration (all these experiments were performed using a reaction mixture saturated with oxygen at 1 bar). I he path 01 the curve corresponds with the general formula oivf»n hv P n (\(W Thp Hftar-

tivation constant at a zero concentration of D-gluconate in Fig. 6 was obtained by batch experiments as described under Experi-mental.

1,0 2.0 r fmolR r 1 l

constant appears to decrease linearly with increasing temperature (all experiments

wGOZ

FIG. 6. Deactivation constant as a function of so-

were performed using a reaction mixture saturated with oxygen at 1 bar). Ostermaier s>t n / ctnH\/ino tin* 1rv\x/_t**fTmf»ratiirf*

IV • T V V 111 i-* %r A. U t U l ^

334 DIJKGRAAF ET AL.

very likely. As regards the equilibrium con- dition for adsorption, it is very likely that the Langmuir theory is applicable.

The deactivation constant can now be written as

K D

= kti + krfi S

kd(Ko,Co2)0~5 + k&CA

= S(l + (Ko,Co,)O.’ + KACA + XK,G)

(8)

The oxygen concentration in the slurry is proportional to the partial pressure of oxy- gen in the reaction mixture (Co, may be obtained by multiplication of Pq with the Henry coefficient which is determined as a function of the concentration of several compounds). Hence the deactivation con- stant is proportional to (PO,)‘.’ as long as it holds that

(Ko,CO,)~.~ + 1 + KACA + XK,C,. (9)

According to the results in Fig. 5 it was found that a linear relationship exists be- tween Kn and (PO,)‘.‘. Apparently the con- dition as given by Eq. (9) is fulfilled. In Fig. 5 the interception of all lines with the Kn axis is located in the origin. This means that the term krfACA in the numerator of Eq. (8) is very small compared to the other term

0 1.0 2.0

cGoz (mole I-‘)

FIG. 6. Deactivation constant as a function of so- dium-D-ghconate concentration (Ps = 1 bar).

6.

‘; ”

% .-

2 4

2

oL----- 40 50 60

T(“C)

FIG. 7. Deactivation constant as a function of tem- perature (PO2 = 1 bar, Co,, = 0.5 mole/liter).

kd(KO,CO,)o~S. From Eqs. (3) and (4) it then follows that the regeneration reaction is much less significant than the deactivation reaction. All together KD may be simplified to

h(Ko co >O” KD =

S(1 + KACy +’ XK,C,)’ (10)

From Eq. (9) it follows that the fraction of the platinum surface covered by oxygen atoms must be rather low. This means that in view of the high rates of deactivation of the catalyst observed during our experi- ments, the reaction rate constant kd in Eq. (3) is quite high.

In Fig. 6 the deactivation constant is plotted as a function of the sodium-D-glu- conate concentration (all these experiments were performed using a reaction mixture saturated with oxygen at 1 bar). The path of the curve corresponds with the general formula as given by Eq. (10). The deac- tivation constant at a zero concentration of D-gluconate in Fig. 6 was obtained by batch experiments as described under Experi- mental.

As illustrated in Fig. 7, the deactivation constant appears to decrease linearly with increasing temperature (all experiments were performed using a reaction mixture saturated with oxygen at 1 bar). Ostermaier et al. (2), studying the low-temperature

n F A P T T V A T T O N OF PT ATTNTTTM P AT AT V S T S 1 11*

oxidation of N H 3 , also noted a decreasing A C K N O W L E D G M E N T S extent of deactivation with increasing tem- T he authors gratefully acknowledge financial sup-perature. They ascribed this effect to an port from the Dutch Foundation for Applied Techno-

of N H 3 at elevated temperatures. It is diffi-cult, however, to predict in the light of Eq.

I V g l V U l 1WOVU1 V U . M. * T T • / X \ J X U l l O L^l V J V V L ^ *. X i -V «/ X / -

The authors also thank Degussa for supplying the catalysts.

(10) what kind of relation exists between the deactivation constant and the tempera-mre. A H rates or reaction ana adsorption equilibria presumably depend on the tem-perature to a different extent, while it is

/. " Kirk-Othmer Encyclopedia of Chemical Tech-nology," 3rd ed. Wiley, New York, 1978.

impossible to determine the influence of the temperature on all rate and adsorption con-

i. ustermaier, j . j . , Katzer, j . K., ana Manogue, w. H . , 7 . Catai 41, 277 (1976).

3. Khan, M. I. A . , Miwa, Y . , Morita, S., and Okada, stants. J., Chem. Fharm. Bull. 31, 1141 (1983).

Khan, M. I. A . , Miwa, Y . , Morita, S., and Okada, J., Chem. Pharm. Bull 31, 1827 (1983).

APPENDIX: N O M E N C L A T U R E

rate of reaction (mol g

5. Morozov, L. G. , and Druz, V. A . , Kinet. Katal. 21, 1071 (1980).

6. Nagal, M . , and Gonzalez, R. D. , Ind. Eng. Chem. initial rate of reaction (mol g

r o t a n f ror»r*tiAti o f 11 rv* c%

Prod. Res. Dev. 24, 525 (1985). 7. Franklin, T. C , and Miyakoshi, Y . , Swrf. Tech-

nol. 5, 119 (1977).

(mol g"1 s"1) KD deactivation constant (s_1)

8. Dirkx, J. M. H . , and van der Baan, H . S., J Catal. 67, 1 (1981).

9. Dirkx, J. M. H . , and van der Baan, H. S., J time (s) rate of oxidation reaction

Catal. 67, 14 (1981). 10. Dirkx, J. M. H . , van der Baan, H. S., and van den

Broek, J. M. A. J. J., Carbohydr. Res. 59, 63

rate constant of oxidation re-action (mol e"1 s - 1)

(1977). Alper, E . , Wichtendahl, B . , and Deckwer, W. D., Chem. Ens. Commun. 10. 369 (1981).

r& rate of deactivation reaction 12. Tsukamoto, T., Morita, S., and Okada, J., Chem. (mol g" 1 S" 1) Pharm. Bull. 28, 2188 (1980).

1 . . . . . . /.?. Amirna7mi. A and Rnnrlart M 1 C.ntnl V)_ /cd rate constant or tne deac-

tiyation reaction (mol g 1 / 4 Neth. Appl. Patent, N L 7,106,590 (1970) to Hoff-

rate of regeneration reaction 15. U.S. Patent, US 4,190, 605 (1980) to Muench, w (mol g" 1 S~ !) C., Strand, G. O., and Hormel, T. S.

rate constant of the regenera-tion reaction (mol g 1 s 1 )

tntal amnnnt nf nlatirmm citpc

Inorg. Nucl. Chem. 38, 889 (1976). 17. Velasco, J. G. , Allyon, S., and Sancho, J

J AT 7 *t 1 A T C / 1 (\1C\\

per gram of catalyst (mol -•)

inufg. lyutt. Ksiivm. f i , I U / J \ i y / y j . 18. Wilham, C. A . , and Mehltretter, C. L . , J. Amer.

Oil Chem. Soc. 48, 682 (1971). j n M « * L A 1 r * „ 4- A. X T i -f ^ t c i o n /1 r \ i a \ *. _

the inactive fraction of the platinum sites

o t i n i i m o i l * *

Heesen, J. G. 20. Dijkgraaf, P. J. M . , Verkuylen, M. E. C. G. , and

face covered by compound * i

van aer wieie, K. , Carbohydr. Kes. lbJ, 12/ (1987).

27. U.S. Patent, US 3,407,220 (1968) to Shell Oil Co.,

Ko2, KA, Kx adsorption constants Po2 partial oxygen pressure in the

rsew I OFK. 22. German Patent, DE 2836327 (1980) to Fiege, H . ,

and Wademeyer, K. LUjKgraar, v. j . M . , vernaar, L. A . , in . , Lrroen-

DEACTIVATION OF PLATINUM CATALYSTS, 1 335

oxidation of NH3, also noted a decreasing ACKNOWLEDGMENTS extent of deactivation with increasing tem- The authors gratefully acknowledge financial sup- perature. They ascribed this effect to an port from the Dutch Foundation for Applied Techno- increasing reduction (regeneration) ability logical Research (S.T.W.) for-this project (1 l-20-318). of NH3 at elevated temperatures. It is diffi- The authors also thank Degussa for supplying the

cult, however, to predict in the light of Eq. catalysts.

(10) what kind of relation exists between the deactivation constant and the tempera- ture. All rates of reaction and adsorption equilibria presumably depend on the tern- ‘. perature to a different extent, while it is impossible to determine the influence of the

2,

temperature on all rate and adsorption con- 3. stants.

R Ro

R,

KD

t

rox

k ox

rd

kd

APPENDIX: NOMENCLATURE

rate of reaction (mol g-’ s-9 initial rate of reaction (mol g-l

SF’) rate of reaction at infinite time

(mol g-’ SC’) deactivation constant (s-l) time (s) rate of oxidation reaction

(mol g-’ s-l) rate constant of oxidation re-

action (mol g-’ SC’) rate of deactivation reaction

(mol g-’ ss’) rate constant of the deac-

tivation reaction (mol g-’ s-l)

rate of regeneration reaction (mol g-’ SC’)

rate constant of the regenera- tion reaction (mol g-’ ss’)

total amount of platinum sites per gram of catalyst (mol s-9

the inactive fraction of the platinum sites

fraction of the platinum sur- face covered by compound

4.

5.

6.

7.

8.

9.

10.

II.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

Ko,, KA, K, adsorption constants PO, partial oxygen pressure in the

22.

slurry 23.

ERENCES

“Kirk-0thmer Encyclopedia of Chemical Tech- nology,” 3rd ed. Wiley, New York, 1978. Ostermaier, J. J., Katzer, J. R., and Manogue, W. H., J. Catal. 41, 277 (1976). Khan, M. I. A., Miwa, Y., Morita, S., and Okada, J., Chem. Pharm. Bulk 31, 1141 (1983). Khan, M. I. A., Miwa, Y ., Morita, S., and Okada, J., Chem. Pharm. Bull. 31, 1827 (1983). Morozov, L. G., and Druz, V. A., Kinet. Katal. 21, 1071 (1980). Nagal, M., and Gonzalez, R. D., Ind. Eng. Chem. Prod. Res. Dev. 24, 525 (1985). Franklin, T. C., and Miyakoshi, Y., Surf. Tech- nol. 5, 119 (1977). Dirkx, J. M. H., and van der Baan, H. S., J. Catnl. 67, 1 (1981). Dirkx, J. M. H., and van der Baan, H. S., J. Catnl. 67, 14 (1981). Dirkx, J. M. H., van der Baan, H. S., and van den Broek, J. M. A. J. J., Carbohydr. Res. 59, 63 (1977). Alper, E., Wichtendahl, B., and Deckwer, W. D., Chem. Eng. Commun. 10, 369 (1981). Tsukamoto, T., Morita, S., and Okada, J., Chem. Pharm. Bull. 28, 2188 (1980). Amirnazmi, A., and Boudart, M., J. Cutnl. 39,383

(5 eth. Patent, NL 7,106,590 (1970) to Hoff- man-La

.Patent,

US 4,190, 605 (1980) to Muench, W. C., Strand, G. O., and Hormel, T. S. Velasco, J. G., Ortega, J., and Sancho, J., J. Inorg. Nucl. Chem. 38, 889 (1976). Velasco, J. G., Allyon, S., and Sancho, J., J. Inorg. Nucl. Chem. 41, 1075 (1979). Wilham, C. A., and Mehltretter, C. L., J. Amer. Oil Chem. Sot. 48, 682 (1971). Neth. Appl. Patent, NL 7,215,180 (1974) to Heesen, J. G. Dijkgraaf, P. J. M., Verkuylen, M. E. C. G., and van der Wiele, K., Carbohydr. Res. 163, 127 (1987). U.S. Patent, US 3,407,220 (1968) to Shell Oil Co., New York. German Patent, DE 2836327 (1980) to Fiege, H., and Wademeyer, K. Dijkgraaf, P. J. M., Verhaar, L. A., Th., Groen-

nUVni? A AT7 r?T AT

land, W. P. T., and van der Wiele, K . , J. Chroma- 26 Heyns, K . , Paulsen, H . , Rudiger, G. , and Weyer, togr. 329, 371 (1985).

24. Dijkgraaf, P. J. M . , Duisters, H. A. M . , Kuster, B. F. M . , and van der Wiele ; K . , J. Catal. 112, 337

J., Fortschr. Chem. Forsch. 11, 285 (1969). 27. Dijkgraaf, P. J. M . , submitted for publication. 28. Wolf, E. E . , and Petersen, E. E . , J. Catal. 47, 28

(1988). 25. Heyns, K . , and Paulsen, H . , Adv. Carbohydr.

Chem. 17, 169 (1962).

(1977). 29. Sarkany, J., and Gonzalez, R. D., Appl. Catal. 5,

85 (1983).

336 DIJKGRAAF ET AL.

land, W. P. T., and van der Wiele, K., J. Chroma- 26. Heyns, K., Paulsen, H., Rudiger, G., and Weyer, togr. 329, 371 (1985). J., Fortschr. Chem. Forsch. 11, 285 (1969).

24. Dijkgraaf, P. J. M., Duisters, H. A. M., Kuster, B. 27. Dijkgraaf, P. J. M., submitted for publication. F. M., and van der Wiele. K., J. Caral. 112, 337 28. Wolf, E. E., and Petersen, E. E., J. Catal. 47,28 (1988). (1977).

25. Heyns, K., and Paulsen, H., Adu. Carbohydr. 29. SPkhny, J., and Gonzalez, R. D., Appl. Catal. 5, Chem. 17, 169 (1962). 8.5 (1983).