Journal of Catalysis 185, 378385 (1999)

Article ID jcat.1999.2475, available online at http://www.idealibrary.com on

Characterization and Catalytic Pro

mceV

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MCmal trtechninatedwas dwas noused iboth tin theing ischannisomeof theisopenversioconclu

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0021-95CopyrigAll righDealuminated MP. Meriaudeau,1 Vu A. Tuan, Vu T. Nghie

IRC/CNRS, 2 Avenue Albert Einstein, 69626 Villeurbanne, Fran43, Boulevard du 11 Novembre, 69626

Received November 26, 1998; revised February

M-22 has been synthesized and dealuminated by hydrother-eatments. The resulting solids were characterized by differentques in order to know how the acid properties of the dealumi-solids were modified. It appears that the number of acid sitesecreased by hydrothermal treatments but the acid strengtht modified. Nondealuminated and dealuminated solids were

n the n-octane hydroconversion. Results suggested that forypes of solids the hydroisomerization is mainly occurring10-membered ring (MR) channels whereas the hydrocrack-mainly coming from acid sites located in 12-membered ring

SibeenframordeconsNMable

SunateBrn(els. According to the observed distribution of monobranched

rs, MCM-22 shows some shape-selective character typicalpentasil family, whereas, according to the absolute yield oftane in the hydrocracked products at low hydrocracking con-ns, MCM-22 behaves more like a 12 MR zeolite (6). Similarsions were proposed in (7). c 1999 Academic PressWords: MCM-22; dealumination; hydroconversion.

INTRODUCTION

olite MCM-22 was recently patented as a useful cata-r alkylation and isomerization reactions and for con-n of methanol or olefins to hydrocarbons (13). Moretly, it has been shown that the porosity of MCM-22 isosed of two independent 10-ring channels, with onese channels containing large supercages of 12-ring (4,om n-decane hydroisomerization studies (6, 7) it wasuded that MCM-22 presents shape-selective proper-f both 10- and 12-membered ring (MR) zeolites, de-ng on the particular criterion used: according to theved distribution of monobranched isomers, MCM-22s some shape-selective character typical of the pen-family, whereas, according to the absolute yield ofntane in the hydrocracked products at low hydroc-g conversions, MCM-22 behaves more like a 12 MR

e (6). Similar conclusions were proposed in (7).

whom correspondence should be addressed.

OH

(10).Th

dealuon th

Zeoli

Ththoseand 0solutof H2ethylresulsteel11 dacalcinoxyge

ThexchaThis

That di10 kPactorsired773 Kfor 3

17/99 $30.00ht c 1999 by Academic Pressts of reproduction in any form reserved.

378perties of HydrothermallyCM-22, F. Lefevbre, and Vu T. Ha

; and COMS/CPE, Universite Claude Bernard,illeurbanne, France

1, 1999; accepted March 6, 1999

l4 treatments (8) or hydrothermal treatments (9) haveshown as an effective way to dealuminate the zeolitework. The dealumination studies were performed into remove most of the Al in the framework and as aquence to have a much better resolution for the 29Sispectrum. Using this procedure, the authors were

o distinguish experimentally seven distinct Si sites.ccinct characterization of the acidity of the dealumi-

and nondealuminated solids was reported (510);sted acid sites were observed by using IR spectroscopyD 3620 cm1), all of which were accessible for pyridine

e aim of this work is to report on the hydrothermalmination of MCM-22 and its effect on the acidity ande catalytic properties in n-octane hydroconversion.

EXPERIMENTAL

te Synthesis and Dealumination

e zeolite synthesis conditions used here are the same asdescribed earlier (11): 0.55 g of NaAlO2 (Carlo Erba).59 g of NaOH were dissolved in 60 g of H2O. To this

ion, 6 g of silica (Degussa), 0.16 g of H2SO4, and 10 gO were added under stirring; finally, 3.6 g of hexam-eneimine (Aldrich) and 10 g of H2O were added. Theting gel was introduced into a PTFE-lined stainless-autoclave rotated at 60 rpm and heated at 423 K forys. To remove the template, the synthesized solid wased for 48 h at 810 K under nitrogen containing 5 vol%

n.

e ammonium form was prepared via a threefold ionnge at 350 K with a 1 N aqueous solution of NH4Cl.

batch was used to prepare dealuminated samples.e parent zeolites were hydrothermally dealuminatedfferent temperatures, H2O pressure being fixed ata. The sample was loaded in a dynamic microflow re-(1 g of sample) and heated under a flow of N2 at the de-temperature and then N2 was replaced by (N2CH2O):for D 773 MCM-22 for 2 h, 973 K for D2 973 MCM-22

h, and 973 K for D3 973 MCM-22 for 3 days.

PROPERTIES OF DEALUMINATED MCM-22 379

Characterization

The 13C, 27Al, 29Si MAS-NMR spectra were recorded ona Bruker DSX-300 spectromeerenced to the classical extern[Al(H2O)6]3C for Al. Cross-p27Al MAS-NMR spectra wereof 1 s ( /6) and a recycle de

The chemical compositiondetermined by AES (atomic

The X-ray powder diffracttained with a Philips W1050 pter. The samples were stored iof water at ambient temperattion of X-ray diffraction patt

Morphology and particle sining electron microscopy (Hspectra were recorded with Ptrometer; the solids were preand activated after having beeallowing thermal treatments

Catalytic Tests

The n-octane hydroisomerdealuminated and dealuminthe supports were loaded wi

d

(wet impregnation technique); the metal precursors werePt(NH3)4(OH)2 and Pd (NH3)4(OH)2 (Johnson Matthey).Solids were calcined under an oxygen flow from room tem-

n, and thenemperature4 h at this523 K.ow reactorbeing fixedspace velo-

to vary the

chromatog-a capillaryom Altech,alysts wereal catalysts:

negligiblethe inverse).

value (15.4ed sample isFIG. 1. XRD patterns of (a) MCM-22 anter. Chemical shifts were ref-al standards : TMS for Si andolarization was used for 13C.obtained using a pulse lengthlay of 1 s.of the MCM-22 (H form) wasemission spectroscopy).ion (XRD) patterns were ob-owder diffraction spectrome-n a desiccator, in the presenceure for 2 days before registra-erns.zes were estimated from scan-

itachi S800 apparatus). IRerkin-Elmer 580 FT IR spec-

ssed in small wafers (20 mg)n mounted in a special IR cell

under controlled atmosphere.

ization was studied over non-ated solids. For this purpose,th 0.5 wt% Pt and 1 wt% Pd

perature to 573 K for 12 h, flushed with nitrogereduced under a flow of hydrogen, with the tincreased to 773 K (ramping 1 K/min). Aftertemperature, the temperature was decreased to

The reaction was carried out in a fixed-bed flworking at atmospheric pressure, temperatureat 523 K. The H2/C8 molar ratio was 54 and thecity was varied from 0.5 to 8 h1 in orderconversion.

Reactant and products were analyzed by gasraphy, chromatographs being equipped withPona column and with a Unibed column (both frFrance). For all solids, the metal-loaded catchecked to ensure that they are true bifunctionamong the cracked products C1 and C2 are inamounts and the n-octane conversion varied asof the hydrogen pressure (see Catalytic Results

RESULTS

Chemical Analysis

Si/Al (atomic) was found close to the expectedcompared to 15). The XRD pattern of the calcin(b) D3 973 MCM-22.

380 MERIAUDEAU ET AL.

FI973 M

giveto thX-ra

OhighAgaintetalli

SEM

Tdiffe0.5 pho

IR R

IRammMC

Bfirst

Tare2c (D

In3747

to silanols groups (3747 cm1), AlOH (Al belonging to ex-traframework Al, see below), and Si(OH)Al Brnsted acid

i

aahs

sga

pa

a

t

d

GppG. 2. Infrared spectra of MCM-22 (a), D 773 MCM-22 (b), and D2CM-22 (c).

n in Fig. 1. It appears that the diffractogram is identicalat expected for an MCM-22 structure (4) and no othery line due to impurity is observed.n the same figure the XRD pattern obtained for thely dealuminated sample D3 973 MCM-22 is given.in the MCM-22 structure is still present but a reducednsity of the different lines suggests that a loss of crys-nity has occurred.

he MCM-22 zeolite is composed of thin plates havingrent morphologies with the largest dimension close tom and the thickness less than 0.1 m. The same mor-

logies were reported previously (5, 11).

esults

studies were performed on the nondealuminatedonium-exchanged MCM-22 and on two dealuminated

M-22 samples.efore registration of the IR spectrum, the sample wasthermally treated at T D 773 K for 12 h under vacuum.he spectra recorded for the three samples under studygiven in Figs. 2a (MCM-22), 2b (D 773 MCM-22), and

2 973 MCM-22).these figures, three different vibrations are observed at, 3664, and 3622 cm1. These vibrations are attributed

sitestainsthisplatesonvibrthegesthydrcrea

Fivibran incomof frAl. Avibrber odue

Inpyritemp

FIadsoradsor(11). Figure 2a indicates that the MCM-22 already con-extraframework Al before dealumination treatment;s attributed to partial dealumination during the tem-removal as suggested by Corma et al. (11). Compari-mong Figs. 2a2c indicates that the absorbance of thetion at 3622 cm1 is decreasing when the severity ofydrothermal treatment is increasing. This result sug-that part of framework Al is extracted because of the

othermal treatment and by consequence causes a de-e in Si(OH)Al group concentration.ures 2 also indicates a change of the absorbance oftion at 3664 cm1 with the hydrothermal treatment:crease of this vibration is observed for D 773 MCM-22ared to MCM-22. This increase is due to the extractionmework Al forming highly dispersed extraframeworkmore severe dealumination causes a decrease of both

tions at 3622 and 3664 cm1; the decrease of the num-f OH groups linked to extraframework Al is probablyo the growth of Al2O3 extraframework particles.order to characterize the OH groups described above,ine was adsorbed at RT and desorbed at increasingeratures. Figures 3 and 4 show the vibrations observed

. 3. Infrared spectra (38003500 cm1) of MCM-22 after pyridinetion and desorption at increasing temperatures (1) before pyridinetion.

PROPERTIES OF DEALUMINATED MCM-22 381

FIG.pyridinepyridine

in the rin the

Theof Brcomple

Figuvibrati1540 aand ofrespec

Fordine atthe vibbrationcarefudesorpfully reobservBrnstthat ofservatistill exto pyri

From Figs. 57, one can also deduce the change in thepyridine ion absorbances as a function of desorption tem-

etp

3h

eka

e2

.n4. Infrared spectra (38003500 cm1) of D 773 MCM-22 afteradsorption and desorption at increasing temperatures (1) beforeadsorption.

ange 38003500 cm1 and Figs. 57 for the vibrations17001400 cm1 range.pyridine adsorption causes the complete vanishingnsted acid sites vibrating at 3622 cm1 and a nearlyte vanishing of the vibration at 3664 cm1.

res 57 show that upon pyridine adsorption someons appeared (17001400 cm1 range): IR bands atnd 1450 cm1 are characteristics of pyridinium ionspyridine coordinatively bonded to Lewis acid sites,

tively (11).all samples, it is observed that the desorption of pyri-increasing temperatures causes a strong decrease ofrations at 1540 and 1450 cm1 and that initial OH vi-s at 3622 and 3664 cm1 are partially restored. A

l examination of Fig. 4 indicates that for pyridinetion at 573 K, the OH vibrations at 3664 cm1 arestored whereas OH vibrations at 3622 cm1 are noted. This result indicates that the acid strength ofed OH groups vibrating at 3664 cm1 is weaker thanthe OH groups vibrating at 3622 cm1. From this ob-on, it can also be deduced that the pyridinium ionsisting after desorption at 573 K are exclusively duedine having reacted with OH groups at 3622 cm1.

peraturfor nonance ofdisappeMCM-2(OHDples is t

NMR R

The 1

MCM-2and 163to hexaother pthe peacarbonbond. Eshow thof the t

Thesampleat ca 50

FIG. 5adsorptio. This has been plotted in Fig. 8 which indicates thatreated MCM-22 and D 773 MCM-22 the disappear-yridinium ions follows the same trend whereas this

arance occurs at a lower temperature for D2 9732. In other words, the acid strength of OH groups622 cm1) for MCM-22 and D 773 MCM-22 sam-e same, while that of D2 973 MCM-22 is weaker.

esults3C CP-MAS-NMR spectrum of the as-synthesized2 displays numerous peaks at 26.8, 47.5, 56.4, ca 130,.4 ppm. If some of these peaks can be attributedmethyleneimine and to the corresponding cation,aks cannot be due to these species. In particular,s at 130 and 163.4 ppm can only be assigned to sp2toms coordinated or not to nitrogen via a doubleven if these species are in a minor amount, theyat during the synthesis a partial dehydrogenationmplate occurred.7Al MAS-NMR spectrum of the as-synthesizedshows only one signal at 54 ppm with a shoulderppm corresponding to tetrahedrally coordinated

Infrared spectra (17001400 cm1) of MCM-22 after pyridineand desorption at increasing temperatures.

382 MERIAUDEAU ET AL.

FIpyrid

alumAftspodinationtheshapmincomintetrumbroalumcomsignis aminat 97andin thcan

T

(1traf

Gin

os)

n

GleG. 6. Infrared spectra (17001400 cm1) of D 773 MCM-22 afterine adsorption and desorption at increasing temperatures.

inum in the framework of the MCM-22 sample (Fig. 9).er calcination a new sharp peak appears at 0 ppm corre-nding to isolated aluminum ions in an octahedral coor-tion, located outside the framework. After dealumina-at 773 K the 27Al NMR spectrum has slightly changed:

intensity of the peak at 0 ppm has increased, while thee of the peak corresponding to the tetrahedral alu-

um atoms has been modified; the shoulder has increasedpared to the signal at 54 ppm and now has the samensity. After dealumination at 973 K for 3 h, the spec-

becomes broader: the sharp peak at 0 ppm is nowadened, due to the formation of polymeric octahedral

inum atoms as in alumina. The signal at 54 ppm haspletely disappeared and has been replaced by a broadal centered at ca 48 ppm. One can also think that therebroad signal at ca 30 ppm due to extraframework alu-um in a tetra- or pentacoordinate. After dealumination3 K for 3 days the broadening of the peaks has increasedthe peak corresponding to tetrahedral aluminum atomse framework has continued to shift to lower ppm. Onenow distinguish two peaks at ca 49 and 39 ppm.hese results show the following:

) If in the as-synthesized material there is no ex-ramework aluminum, the calcination leads to the for-

FIpyrid

matispon

(2extragatio

FIsamp. 7. Infrared spectra (17001400 cm1) of D2 973 MCM-22 aftere adsorption and desorption at increasing temperatures.

n of some isolated octahedral aluminum species, re-ible of the infrared band at 3664 cm1.Dealumination at 773 K increases the number of theseframework aluminum atoms without sensible aggre-

.

. 8. Change in relative pyridium ion absorbances for differents at increasing desorption temperatures.

PROPERTIES OF DEALUMINATED MCM-22 383

FIG.(b) MCMCM-2

(3) Dthe octhen to

(4)framewportanin ourcal shiably reminumThesethe petortedever, othe frahigh.

Theare givshowsand 1creasesharp pthe sambroadders anponen

(11) for the ITQ-1 zeolite or in (9) for highly dealuminatedMCM-22.

i

r

ro

tMic

sy

n

p

1M9. 27Al MAS-NMR spectra of (a) as-synthesized MCM-22,M-22 after calcination, (c) D 773 MCM-22, and (d) D2 9732.

ealumination at 973 K results in an aggregation oftahedral extraframework aluminum atoms, leading

a decrease of the corresponding AlOH groups.The chemical shift of the aluminum atoms in the

ork decreases when the dealumination is more im-t. Such an effect is well known in the literature butcase the variation is more important as the chemi-ft varies from 54 to 39 ppm. This decrease is prob-lated to the increasing distortion around the alu-atom when the Si/Al (framework) ratio increases.

results show that the attribution previously made ofak at ca 30 ppm in dealuminated species to a dis-tetrahedral aluminium atom is probably true. How-ur results show that such a species can be found inmework when the Si/Al (framework) ratio is very

29Si MAS-NMR spectra of the various samplesen in Fig. 10. The spectrum of the initial materialonly three relatively broad signals between 10320 ppm. New peaks appear when the Si/Al ratio in-

s and in the final material one can easily distinguisheaks at108,113.7,116.2, and120.2 ppm withe intensity and the same linewidth and a relatively

signal between 111 and 113 ppm with two shoul-d corresponding probably to the sum of three com-

ts. This spectrum is quite similar to that reported in

Catalyt

TheC5) andare in tactionstudiedthe mePd MC

In Foctaneselectivappearlectivitdistribunated aTable 1was co

It isis com

FIG.(b) MCMCM-22c Results

eaction of n-octane produced cracked products (C3C8 isomers. Among the cracked products, C1 and C2ace amounts, indicating that the hydrogenolysis re-ver metal function was negligible. For both samplesit has been checked by varying H2/HC ratios thatal and acid functions are well balanced and that Pt

-22 behaves like a true bifunctional catalyst (13).g. 11 is reported the isomerization yield versus n-onversion. The isomerization selectivity as well the

ity toward monomethyl isomers is also reported. Itthat even for low conversion the isomerization se-reached was relatively low. In Table 1 the product

tion obtained at low conversion for non dealumi-nd dealuminated MCM-22 is listed. Figure 11 andshow clearly that the catalytic behavior of MCM-22siderably modified upon dealumination.

known from the literature that MCM-22 porosityosed of two nonintersecting porous systems, one

0. 29Si MAS-NMR spectra of (a) as-synthesized MCM-22,-22 after calcination, (c) D 773 MCM-22, and (d) D2 973

.

384 MERIAUDEAU ET AL.

FImericonv

havpoc

Itarering48 (andhydporaboderi

TsioncomclosSAPberedericonacidlarg

n-O

Reac

MCMD 77SAPZSM

a,b

By contrast, the high values obtained for 2MC7/3MC7and 25 DMC6/24 DMC6 indicated that for hydroisomer-

e7

nnb

t

s

.Celert

t

siedni

dsft

uin

Mc-atn

CG. 11. Reaction of n-octane: change in isomerization yield (s), iso-zation selectivity (h), and monomethyl isomer selectivity (4) versusersion. Open symbols, MCM-22; black symbols, D 773 MCM-22.

ing a 10-T ring and the other a 10-T ring channel withkets of 12-T rings (4).is also known from the literature that the linear alkanesvery selectively hydroisomerized over 10-memberedpore zeolites like ZSM-22 (14), ZSM-23 (15), and ZSM-16) or medium pores SAPOs (SAPO-11, SAPO-31,SAPO-41(17) (18)): at high conversions (8090%) theroisomerization selectivity was always very high. Thee architecture of MCM-22 which is constituted, as statedve, by 10- and 12-membered ring channels, was furtherved from study of the n-decane reaction (6, 7).he results we have obtained for n-octane hydroconver-also reveal that the catalytic behavior of MCM-22 is

plex: from Table 1 it is observed that the iC4/C4 ratio ise to that obtained for large molecular pore sieves such asO-5 (19) but different from that obtained for 10-mem-d ring zeolites; the same remark is true when consi-ng the (C3CC5)/C4 ratio. These results suggest that thetribution to hydrocracking of surface acid sites and/or ofsites located in large pores having 12-membered rings is

er than that of acid sites located in 10-membered rings.

TABLE 1

ctane and 2MC7 Hydroconversion (Distribution of ProductsObtained at Low Conversion (10%))

n-Octane 2MC7

tants/solid IC4/C4iC5C5

C3CC5C4CiC4

2MC73MC7

25DMC624DMC6 3MC7/n-C8

-22 1.75 10 0.86 1.6 3 1.153 MCM-22 1.65 7 0.88 1.8 3.2 1.10O-5a 2.4 6 0.87 0.8 0.85 8-23b 0.93 1.9 1.1 2.1 2.2 0.8

From Ref. (19).

izatioligibl3MCparechanmem

Duets (can bporeDMCthe laturesinto iof thwith

Thof sumoucompratioselecof suacidlocat

Th22 inlumidistrfied bposeTheas athatThisbe dandchan

Finoveris delargemediconsC3, a

Mnatedmentsitespyridn the contribution of pores with large pockets is neg-. In line with this conclusion is the low value of the/n-C8 ratio obtained with 2MC7 as a reactant (19). Ap-tly those C8 molecules reaching 12-membered ringels were preferentially cracked while those in 10-ered rings were preferentially isomerized.

e to the peculiar shape of pores having 12-ring pock-hese pockets are linked via 10-ring apertures (5)) ite assumed that n-octane will be able to enter in suchand be transformed in these large pockets into MC7,6, and TMC5. MC7, DMC6, and TMC5 isoolefins inrge pockets would have to diffuse across 10-ring aper-Highly branched isomers will be formed and cracked4 and possibly C4 and C3C iC5 (and/or C5). Thus most

cracked products will reflect the contribution of poresarge pockets.results of Table 1 also indicated that the contribution

face acid sites and/or of acid sites located at the poreh of pores with 12-membered pockets is negligible asared to that of all acid sites because the 3MC7/n-C8obtained with 2MC7 as a feed clearly indicates a shape-ivity effect (19). This could be due to a small numberrface acid sites as compared to the total number ofites and/or to their small intrinsic activity due to theiron.

results obtained with MCM-22 and D2 973 MCM-icated that the isomerization yield is lower on dea-ated solid. Within the cracked products formed the

bution of light alkanes (C3C5) was not deeply modi-y dealumination, indicating that the explanation pro-above for MCM-22 is still valid for D 773 MCM-22.

light increase of the 2MC7/3MC7 ratio with n-octaneeed and of n-C8/3MC7 with 2MC7 as a feed suggestshe porosity constraint is reinforced by dealumination.reduced porosity of 10-membered ring pores coulde to the extraction of aluminum of the frameworkts deposit as very small alumina debris, inside theels.ally, it is observed that at high conversion (fi > 60%)

CM-22 and D 773 MCM-22, the isomerization yieldreased as expected: this phenomenon is general forpore zeolites were the dimethyl and trimethyl inter-tes formed in large amount due to the lack of spatial

raint, these products being hydrocracked to form C4,d C5 alkanes.

CONCLUSIONS

M-22 zeolite has been synthesized and dealumi-by hydrothermal treatments. Dealumination treat-causes a decrease in the number of Brnsted acid

but the acid strength is not modified as observed byine TPD studies for MCM-22 and D 773 MCM-22.

PROPERTIES OF DEALUMINATED MCM-22 385

For highly dealuminated zeolite D2 973 MCM-22, the acidstrength of Brnsted acid sites is weaker.

Studies of n-octane hydroconversion indicate thatmost of the hydroisomerization products are formed in10-T-membered ring channels whereas the hydrocrakingis mainly occurring on acid sites located in 12-memberedring channels. Comparison of product distribution betweenMCM-22 and dealuminated MCM-22 suggested that alu-minum debris located in the porosity reinforced the shapeselectivity.

REFERENCES

1. Huss, A., Kirker, G. W., Keville, K. M., and Thomson, R. T., U.S. Patent4 992 615, 1991.

2. Del Rossi, K. J., and Huss, A., U.S. Patent 5 107 047, 1992.3. Chu, C. T., U.S. Patent 4 956 514, 1990.4. Leonowicz, M. E., Lawton, J. A., Lawton, S. L., and Rubin, M. K.,

Science 264, 1910 (1994).5. Lawton, S. L., Leonowicz, M. E., Partridge, R. D., Chu, P., and Rubin,

M. K., Microporous Mesoporous Mater. 23, 109 (1998).

6. Corma, A., Corell, C., Llopis, F., Martinez, A., and Perez-Pariente, J.,Appl. Catal. A 115, 121 (1994).

7. Souverijns, W., Verrelst, W., Vanbustsele, G., Martens, J. A., and Jacobs,P. A., J. Chem. Soc. Chem. Commun., 1671 (1994).

8. Hunger, M., Ernst, S., and Weitkamp, J., Zeolites 15, 188 (1995).9. Kennedy, G. J., Lawton, S. L., and Rubin, M. K., J. Am. Chem. Soc.

116, 11000 (1994).10. Corma, A., Corell, C., Fornes, V., Kolodziejski, W., and Perez-Pariente,

J., Zeolites 15, 576 (1995).11. Corma, A., Corell, C., and Perez-Pariente, J., Zeolites 15, 2 (1995).12. Camblor, M. A., Corma, A., and Dias-Cabanas, M. J., J. Phys. Chem.

B 102, 44 (1998).13. Meriaudeau, P., Tuan, Vu. A., Lefebvre, F., Nghiem, Vu. T., and

Naccache, C., Microporous Mesoporous Mater., in press.14. Martens, J. A., Parton, R., Uytterhoeven L., Jacobs, P. A., and Froment,

G., Appl. Catal. 76, 95 (1991).15. Ernst, S., Kumar, R., and Weitkamp, J., Catal. Today 3, 1 (1988).16. Meriaudeau, P., Tuan, Vu. A., Nghiem, Vu. T., Sapaly, G., and

Naccache, C., J. Catal. 185, 435 (1999).17. Miller, S. J., U.S. Patent 5, 135, 638 (1992).18. Miller, S. J., Microporous Mater. 2, 439 (1994).19. Meriaudeau, P., Tuan, Vu. A., Sapaly, G., Nghiem, Vu. T., and

Naccache, C., 12th International Zeolite Conference, Baltimore, July510 1998, in press.

INTRODUCTIONEXPERIMENTALRESULTSFIG. 1.FIG. 2.FIG. 3.FIG. 4.FIG. 5.FIG. 6.FIG. 7.FIG. 8.FIG. 9.FIG. 10.FIG. 11.TABLE 1

CONCLUSIONSREFERENCES