Proceedings of ZEOCAT 90

701 Pages·1991·17.406 MB·iii-xiii, 1-718\701

by  G. Öhlmann, H. Pfeifer and R. Fricke (Eds.)

Studies in Surface Science and Catalysis
Advisory Editors: 6. Delmon and J.T. Yates
Vol. .65
CATALYSIS AND
ADSORPTION BY
ZEOLITES
Proceedings of ZEOCAT 90, Leipzig, August 20-23, 1990
Editors
G. Ohlmann
Zenrralinsrirur fur Physikalische Chemie, Rudower Chaussee 5,
Berlin Adlershof, 0- 1 7 99 FRG
H. Pfeifer
Universirar Leipzig, Sekrion Physik, Linnhstrasse 5, Leipzig, 0- 70 10 FRG
and
I?.F ricke
Zenrralinstirur fur Physikalische Chemie, Rudo wer Chaussee 5,
Berlin Adlershof, 0- 1 199 FRG
ELSEVIER Amsterdam - Oxford - New York - Tokyo 1991
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XI
PREFACE
There is a permanently growing interest, worldwide, in zeolite
science and technology. Especially in Europe it has become an
established tradition to hold specialized zeolite meetings which
occur sandwiched in between the large International Zeolites
Conferences. The ZEOCAT 90 Conference held in Leipzig, is the latest
in a series of successful European zeolite conferences which have
been held previously in Wurzburg, Nieuwpoort, Siofok, Prague and
Bremen.
The range of synthesized zeolites and zeolite-related molecular
sieve materials is constantly expanding. The variety of structures
comprises high- and low-silica zeolites, micro-porous metallo-
silicates, alumino-phosphates and crystalline silica polymorphs.
These newly developed, modified or improved zeolites and other
molecular sieves have opened up new horizons by their application as
shape-selective catalysts and adsorbents, as cation exchangers or as
high-tech materials. Current topics of interest are the newly
developed catalytic applications of zeolites in the synthesis of fine
chemicals, the use of zeolites as a new material for sensors or solid
electrolytes and the setting up of sophisticated zeolite-based
separation processes including molecular sieve membranes. In order
to master the promising potential offered by the new zeolites, the
links between the various fields of molecular sieve research are
growing closer. This is especially true for merging synthesis and
characterization by such powerful methods as solid state NMR and X-
ray or neutron diffraction, as well as for adsorption, diffusion and
catalytic studies. A new trend is the growing interest in the use of
computational and theoretical approaches to explain synthesis,
sorption, diffusion and catalytic data.
ZEOCAT 90 was comprised of the many different and diverse aspects
of the rapidly expanding field of zeolite science and technology. The
invited plenary lectures of this conference summarize our current
knowledge and address topical areas of zeolite research. New
interesting findings produced by fundamental research have led to new
industrial applications and these developments have, in their turn,
inspired new directions for fundamental research.
The deliberate control of crystallization processes has led to the
production of many zeolites which do not occur naturally. Chemically
XI1
and physically controlled treatments have been used to tailor shape-
selective zeolite catalysts and adsorbents for industrial use. Newly
developed physical and chemical spectroscopic and diffraction methods
have given us new insights into the exciting world of molecular
interactions of solid surfaces.
The editors are convinced that ZEOCAT 90 contributed, like its
European predecessors, to the successful interdisciplinary
exploration of zeolites and to finding new pathways for their
application in science and technology.
G. dhlmann, H. Pfeifer, R. Fricke (Editors)
XI11
ZEOCAT 90 - Leipzig
International Scientific Committee
R.M. Barrer, London W.M. Meier, Zurich
D. Barthomeuf, Paris W.J. Mortier, Heverlee
H. K. Beyer , Budapest C. Naccache, Villeurbanne
H. Bremer, Berlin L.V.C. Rees, London
P. Fejes, Szeged W. Schirmer, Berlin
J.P. Fraissard, Paris G. Schulz-Ekloff, Bremen
J. Haber, Krakow J. Weitkamp, Stuttgart
P.A. Jacobs, Heverlee B. Wichterlova, Prague
H.G. Karge, Berlin S.P. Zhdanov, Leningrad
V.B. Kazansky, Moscow
National Orsanizina Committee
Chairmen: G. Ohlmann, H. Pfeifer
Secretary: H. Miessner, B. Staudte
H. Bremer, Berlin W. Schirmer, Berlin
M. Bulow, Berlin R. Schollner, Leipzig
D. Freude, Leipzig H. Stach, Berlin
R. Fricke, Berlin K.-H. Steinberg, Leipzig
J. Karger, Leipzig J. Volter, Berlin
H. Lieske, Berlin
SI)onsors
AKZO Chemicals B.V.
BASF AG
BAYER AG
Chemie AG Wolfen-Bitterfeld
Degussa AG
Deutsche Shell AG
EXXON Chemical Holland-BCT
Hoechst AG
Intern. Zeolite Ass. (IZA)
Leuna-Werke AG
PCK AG Schwedt
PQ Corp.
G. Ohlmann et al. (Editors), Catalysis and Adsorption by Zeolites 1
0 1991 Elsevier Science Publishers B.V.. Amsterdam
G OHLMANN, H.-b.JtHSCHKEWlIL, b.LlSCHKt, H.ECKtLT, b.PARLIIL,
t SCHRklER. B /IKROWiIIS. 6 InFFLER
CentraJ Institute ot Phvsical Chemistry of the Academy of Sciences
R:idower umissep 5. 11'JY MRL IN-ADLtRSHOF
AbS1 RAL!
Modirvins (J teinplcite-tree synthesized and hydrothermally dealu-
minuted LSIY-5 tvoe zeolite with orthophosDhoric acid vields cata-
lysts tor the high-temperature MIO-reaction which are superior to
the niei'ely aealuniiiiot t'cl zeolites i n respect of Cz-Cd-olef i n selec-
tivi.tiec nncl deactivation times. Formation of methane, aromatics
ond coke is :;ti-onyIv suppressed. Ihe mechanism of the P-modificn-
rton 35 char;ic,teriz;ld by on nt lenst partially reversible chemical
intei-ili.tiui1 oi phlisEtjoi'lc acid with the sti-onq acid sites and by n
ct~ii:ye i.11 ;.oncentrutinn and nature ot weak acid sites which also
contrtbute fo catalysis. After P-modification, dealumination of
the zeolite tramework by steoiaing is inhibited.
';inre the work nt Kciedinq and Rutter (1) who first hnvp shown
the positive etfrct of the PhosDhOrus moditication of ZSM-5 cata-
lvrts on their rrr:alvtic properties i n the MIO-process and sonie-
what later on tile Poco-selective alkyiation ot toluene with metho-
no1 (L), numeruus studies have been aevoted to the problem ot the
niec;huiiisin ot ttiis iaodirication(3 - 11).
KUt?dillg uiicl Butte1 pruposed i n their Paper bonding ot PhosPhorLls
to the zeolite framework through oxygen what formally is equiva-
lent to the reoiacpinent of the hridged hydroxyl groups hv a HZP04-
QI'OUD bv means ot IPD mensuremmts of NHs they tound a signifi-
rantlv inrreasftl number of acid sites. which are weaker i n
strenuth compared tilth those in the unmodi tied zeolite.
Vedrine et a1 (4) stzted that Phosphorus neutralizes acid sltes
primarilv ut tne entrant-e at the LSM-5 channels whereas the stron-
aest ncia sites ore not modiiied. Consequentlv tor explanation ot
the observed incrense nf C2-C4-.nlefin selectivities. o slight
aocl; :ir.atinn in chnnnel r;ize und increased turtuositv due to phos-
~hoi~ii:;c omooirnd is prefered, compared to changes i n acid strength.
Uerewinski und Haber (6) found by NHZ-lPD that modification with
r I. inie t n y 1p iio 5 uii i t e ond d iilmmon i umh yd r agenp hos p ha t e e 1i minat es the
Hrrjn:;ted acirl si.tes and also s i ~ n I f I c a n tdl ~ec reases the content
u r WC~CIKC~Ir.i cic'l SI tes
B~isecl on P~IISC~I~~I~Y experiments with quinoline and trimethylphos-
pliite Nunoil et oi (L,j r;ont:liirierl, that the most important effect of
unos~h~~I:r; ~~rh; t:o oir,oning nt the strnng ocirf site:, on the exter-
riol :;urtnr.f rit the i'.r,vstals.
K:IIl. Maiiit~c~a rid Yii;hinio ( iiJ) studied the shupe selective alkylution
nt ethvlhenzene WIt ll ethanol or1 P-modified ZSM-5 catalvsts and
claim thnt the SLIPP~~SSIOo~ i Para-di.ethvlbenzene Lsomerization i s
achieved by I'eduLing the amount ot strons acid sites rather tnan
tiy re~~ucintah e ettective pnre diameter of LSM-5.
Shiueru Ik(i1 et ril. (12) orepnred a catalyst for methanol conver-
sion (;oIir;i?,t inu ot H'-LSM-5 oel letized and moditied with
onrl HPU4&- According to their conclusion the binder
reduces the acid sites an the external siirtuce CJt the
serves 0s a source of gradual supply of HPUqA-, which
ocirl sites arid retards dealumination. Most comprehen-
problein of the mechanism of P-modification has been
the wnrks nt lercher et n l (7.8.14,15). In their wr-
I :FI- w,i; 1 , (8) tl;ev hnd develooed a concept of controlled decrease
L. i*. ;;i- -i,.; .?,i:-~r,athh v cnnversinn of strong acid sites into weakely
ii( id oiler,. uitlloiii alteration nt the OVel-all acid-base Properties.
111 tti, L: i;r:est publications they come to the conclusion, thut
ti eu(ine:i~o i tile zeolite with H3PU4 and triinethulphasphite decrea-
~e!t,ir e CcjiiLenti'ution OT strotis aciu sites esseiitiuily by dealunii-
rxiTinii, In the case nt trimethylphosphine as the modifying agent
thev rniiiid (15) ('I hl.ocking of stronq acid sites up to u reaction
teinc;t?rotiir~C it 0OOnC. Ahc,ve this temperature the phosphine is de-
?,rjrtji?<j. ir?qciieroI 1 . i ~th e original acidic propertj.es of HI -LSM-5.
Lumniar-iziriy this overview i t may be stated, that decreuse ot
;troriy iliiility atiJ i't'auction of pore diameter are inostly discussed
i n ui'tJei tc, explain the etiect ot phosphorus modification. the
I eicli~vt' 1lllIJlJI~t~iloLr~ these roctors is aitrerently evaluated and
rfww-ids GII the sttidied reaction. Contradictory are the views of
vnrioiis nilthrbrs on the wov. i.n which strong acid sites are decren-
3
sed, by interaction with the bridged hydroxyl groups, or by uar-
tial deaiumination.
in this paper we describe the combined effect of hydrothermal
dealumination and phosphorus modification on the selectivities and
deactivation rimes i n the high-temperature MTO-reaction. For a l l
experiments the ZSM-5 type. template-free synthesized zeolite
HS-30 of Chemie AG Bitterfeld, has been used. TPD of ammonia, IR-
and :*1P--.27AI-MAS-NMR soectroscopy were employed to get deeper
insight into the mechanism of the zeolite modification by ortho-
ptiosplioric acia. lhe work was part of a cooperation with the
Researcn and Uevelopment Division of Leuna-Werke-AG.
freParorion v t soimles
Pentasil type LSM-5 zeolite (HS-30, Si/Al=19, Chemie AG Bitter-
teld) is converted Into the H*-form by a four times repeated
treatment with a 0.2 N so1.ution of HN03 i n a simule batch Proce-
diire. For deulusination. samples of the H+-form are exposed to a
stream ot air and steam (pwater.=90 kPa) at 400, 410 and 700°C.
Framework aluminiirm ( A h ) i s determined using the ammonium exchon-
ge method. For partial extraction of non-framework aluminium
tA11.i~) torined during deUlUminatiOn, samples are treated with 2 N
HN03 at 105°C for two hours. Extracted aluminium was determined
onalyticallv in the solution of the extracting agent. Catalyst
particles were oreoared by mixinq the HS-30 samples with Aero-
sil-ZGO and water and subsequent extruding, the ready made extru-
dates (d = 1 to 2 mm) containing 65% by weight ot zeolite. P-modi-
rication was carried out by impregnation with aqueous phosphoric
acid. ihe content of phosphorus for catalysts based upon extracted
HS-30 was hela somewhat lower taking into consideration their
di.minished contents of total. alilminium. Finally catalyst samples
were conditioned by steaming at 700°C for 1 hour.
Ammonium exchange
lhe HI-ions ot LSM-5 zeolites are exchanged by NH4*-ions by
treatment with an aqueous solution of an ammonium salt. For this
Purpose the sample is placed on a 64 slas trit (approx. 4s) and
exposed to CI tiow of 50u ml ot an aqueous 0,2 N NH4(CHaCOO) solu-
tion tor b Iluurs at /c) to 80°C. Atter careful washing, the content
4
of ammonium is determined by the Kjeldahl method.
Determination of ahasphorus in o wou s solutions
Ihe suiiif device as i n the ammonium exchanse is used to analyze
phosphorus removed from P-modified samples by elution with hot
water. Quantitative determination of the extracted Phosphorus i s
based on the photometric molvbdo-vanada-phosphoric acid method.
Temper atwrogrammed des orption of am0 nia (NH 3-TPD)
Atter- cleaning zeolite samples by heating to 500°C i n an He 9ns
stream (v = 3 ml/s) for one hoirr, ammonio i s odsarbed at 120°C
from a He gas stream containing 3 Vo1.-I of NH3. After fltrshing by
pure He at 120°C for two ho:irs, desorption of ammonia up to 500°C
1s started crlow fate of helium: 1 ml/s; heat rate lPC/min). Ihe
concentration ot NH3 i n the exit gas i s determined using a thernio-
conducrivity cell. Ihe curve of the desorptogram is recorded DY a
conventionol device. Additionally ammonia i s absorbed from the
exit acts stream SY on 0.1 N HaS04 solution. Its total amount i s
determined by back tjtration of excess sulfuric ocicl.
TR Soectroscooy
LSM-5 zrolite samples are compacted to thin self supporting
waTe1-s tiouohlu 7 mg/cmz) and placed i n a quartz 1R cell. The
worers ore curcinea at 400°C in vacuo. After cooling to 200°C,
pyrioine vapour is uailiitted into the system for 30 minutes. After-
wur~ts, tlie cell 1s degusbecl and evacuated to eliminute phvsisorbed
Pvridln f
Transmission spectra are recorded i n the range from 4000 to
3300 cm-' both hetore and after pyridine ndsorptinn. using o
SDecord M 85 spectrometer of Carl Zeiss Jena with a 4 cm-l resolu-
t ion.
Diffuse retlectance spectra are recorded with the t-T-1H technique
using u special aevice, the resolution of which i s 4 cm-I. The
zeolite Powdei is pretreated for tour hours at 450°C and at
10- ' Po
L7A l- and P-MAS-NMK--measurement s
Ihe NMK spectra were obtained on a BRUCKER MSL4OO multinuclear
spectronieter operating at u field ot 9,4 r with a standard BRUCKER
double-bearing MAS probe, Ihe zirkoniu oxide rotors were spun near
5
5 kHz wirh ary nitrogen as driving gas. About 200 my of sample
material are filled i n the inner rotor volume of about 0.35 cm:’.
Typically, 1500 to 1800 free induction decays (FID’s) were ac-
cumulated per sample for both nuclei. The pulse widths were 3.9 11s
(n/U-pulse) with repetition times between 5 to 30 s and 0.6 11s
(n/l2-puise) with a repetition time of 1 s for at 362 MH7 and
for 27Al at 104 MHz, respectively. The chemical shifts are given
on the d scale with a maximum uncertainty of fl Ppm.
In order to obtain reliable quantitative results by the L’7Al-MAS;-
NMR measurements, the samples were hyarated i n an exsiccator i n an
atmosphere saturated wi.th water for more than 20 hours. Ihct ah-
solute intensjtv mode (AI-mode of the DISMSL-software package) was
used tor experimental data analysis.
La t alvsi s
Catalytic experiments were carried out i n a tubular fixed bed
(6
reactor = 12 mm) using a mixture of methanol/Nz (molecular
ratio= 1:l) as reaction feea (conditions of reaction see table 1).
Products were analyzed DY an on-line operated guscnromotogrophic
device Calculation of the concentrntinn from analvtical data i s
based on individual calibration of the components
lABLE I: Parameters of reaction
- ~ _ _
~
t enipe ratu r e : 560°C
concentration ot methanol: 50 Val-%
catalyst volume: 12 m l
catalyst mass (average): 5.b 9
teed t-are (inixrure) : 4.0 ml/s (Sir)
charge
GHSV (mixture) . 1200 ml/mlca t I vs t *h
LHSV(methano1): 1 m 1/ ml a t I I. * h
Ihe time on stream when methanol first appears i n the exit gas of
the reactor is clenGted as t 1 m e o t d e a c t i v a t i o n
Catalysts are named according to the general formula DXPv. x
denoting the bi/Al~ ratio and Y the content ot pnosphorus us
weight percent.