ZSM-5 type zeolites:
Synthesis and use in gasphase reactions with ammonia
ZSM-5 type zeolites:
ZSM-5"type zeolites:
Synthesis and use in gasphase reactions with ammonia
Proefschrift
ter verkrijging van de graad van doctor aan de
Technische Universiteit Delft, op gezag van de
Rector Magnificus, prof.dr. J.M. Dirken, in
het openbaar te verdedigen ten overstaan van
een commissie door het College van Dekanen
daartoe aangewezen, op 14 december 1987 te
16.00 uur, door
Frederik Jan van der Gaag,
geboren te Delft
scheikundig ingenieur,
TR diss ï
1595
STELLINGEN
1. Thermische degradatie van polyvinylchloride (PVC) wordt tegengegaan door toevoegen van metaalzepen (bv. Ca-, Ba-, of Zn-stearaat). Gezien het werkingsmechanisme lijkt de benaming stabilisator voor verbetering vatbaar.
2. Het refereren naar artikelen door het overnemen van referenties zonder de literatuur zelf te lezen kan de nodige gevaren opleveren en ook tot kettingeffecten aanleiding geven. Zo leidt een klein verschil in
paginanummers ertoe dat de MeAPO-molekulaire zeven niet als een recente vinding, doch als één van de oudst beschreven zeolieten gezien zouden moeten worden.
D.W. Breek, "Zeolite Molecular Sieves, structure, chemistry and use", J. Wiley & Sons, New York 1974, p. 27.
A. Damour, Ann. Mines, 17, (1840), 191. A. Damour, Ann. Mines, 17, (1840), 202.
3. Het door Ohrui en medewerkers gegeven mechanisme voor de werking van galactose-oxidase is aan bedenking onderhevig.
H. Ohrui, Y. Nishida, H. Hori, H. Meguro, Abstr. 4th Eur. Carbohydr. Symp, Eds. F.W. Lichtenthaler, K.H. Neff, (1987), p. B 11.
4. De door Fukui en Tanaka voorgestelde racemisatie van (+)-menthol is chemisch niet eenvoudig uitvoerbaar.
S. Fukui, A. Tanaka, Enzyme Eng., 6, (1982), 191.
5. Het gebruik van elektronische apparatuur in een chemisch laboratorium vraagt om bijzondere maatregelen in verband met corrosieproblemen.
6. Gezien de ervaringen met de fonnosereactie dient bij het onderzoek naar een eerste stap bij de methanolconversie over ZSM-5 type zeolieten (de Methanol-to-Gasoline reactie) ook rekening gehouden te worden met autokatalyse via sporen Cz-verbindingen.
A. Butlerow, Justus Liebigs Ann. Chem., 120, (1861), 295. R. Breslow, Tetrahedron Lett. 1959, 22.
R.F. Socha, A.H. Weiss, M.M. Sakharov, J. Catal., 67, (1981), 207. A.P.G. Kieboom, H. van Bekkum, Reel. Trav. Chim. Pays-Bas, 103. (1984), 1
7. Het gebruik van apparatuur voor de versnelde (foto-)degradatie van bv. kunststoffen (bv. "Weather-O-Meters") als model voor de natuurlijke veroudering heeft nog enkele duistere kanten.
8. Het Europarlement zou, naar voorbeeld van internationale
wetenschappelijke congressen, het Engels als voertaal dienen aan te wijzen.
9. Het valt op dat de elementkleuren (waterstof, zuurstof en stikstof) van molekuuIraode11en en van gasflessen niet in harmonie met elkaar zijn.
term "pressure sensitive adhesive" ("drukgevoelige lijm") is een betere omschrijving.
11. In octrooiliteratuur inzake zeolietsynthese wordt veelal ten onrechte niet expliciet vermeld of er al dan niet geroerd wordt tijdens de kristallisatie.
S.T. Wilson, B.M.T. Lok, E.M. Flanigen, Eur. Pat. EP 0.043.562 (1981). H.W. Grose, E.M. Flanigen, US Pat. 4.061.724 (1977).
F.J. van der Gaag 14 december 1987
CONTENTS
1. Introduction 1
History 1
Structure 5
Synthesis 8
Analysis 10
ZSM-5 special properties 13
Literature 16
2. Identification of ZSM-type and other 5-ring containing
zeolites by i.r. spectroscopy 18
Introduction 18
Experimental 19
Results and discussion 19
References 24
3. Template variation in the synthesis of zeolite ZSM-5 26
Introduction 26
Experimental 27
Results and discussion 29
References 35
4. Isomorphous substitution in zeolite ZSM-5 37
Introduction 37
Experimental 38
Results and discussion 38
Conclusions 43 '
and the particle size of ZSM-5 zeolites 45
Introduction 45
Experimental 45
Results and discussion 47
Literature 49
6. Ammoxidation of toluene over modified ZSM-5 type
catalysts
Introduction
Experimental
Results and discussion
Literature
7. Reaction of Ethanol and Ammonia to Pyridines
over Zeolite ZSM-5
Introduction
Experimental
Results
Discussion
Conclusions
References
8. Reaction of Ethanol and Ammonia to Pyridines
over ZSM-5-Type Zeolites
Introduction
Experimental
Results
Discussion
Conclusions
References
50
50
51
53
60
61
61
62
63
68
70
70
72
72
73
73
76
78
78
9. The formation of 2,6-lutidine from acetone, methanol
and ammonia over zeolite ZSM-5 79
Introduction 79
Experimental 80
Results and discussion 81
Mechanistic experiments and considerations 87
Literature 93
10. Exploratory work on silicon aluminum phosphate
molecular sieves and related materials 94
Introduction 94
Experimental 98
Results and discussion 99
Conclusions 104
Literature 105
Summary 106
Samenvatting 108
Dankwoord 111
Curriculum vitae
112
I n t r o d u c t i o n 1 HISTORY
I N T R O D U C T I O N
HISTORY
The first zeolitic species, stilbite, was described in 1756 by Cronstedt
[1]. This type of new materials, crystalline aluminosilicates, was named
zeolites, due to its behaviour upon heating (see Figure 1). The crystals
produced water vapor when heated in a blowpipe.
Figure 1: Zeolite powder appears to be boiling upon heating.
The next important event in zeolite science was the discovery of the
reversible hydratation-dehydratation character of zeolites by Damour
[2], almost a century later (1840). This property provided one of the more
important uses of zeolites both in industry and in the laboratory, namely
as a drying agent for liquids and gases. = » 3 0 2 ■ . i —■ ■ — r i
-Ccttc experience réitérée sur Ie mémc échan-E S S A I S tillon , et sur un autre morceau d'opale de Hon-grie pesiint o5 r,3135 , m'a toujours présenté des
Sur quelques mmêrnux connus sous Ie nom resul ia Is ideittiques et qui ne m e laissent aucun de .quartz résirüte; d o u l c s u r l a propiiété que possècle 1'opale de
pci-ihe et d'absorber f'acilement une notablequanlité
r-ar M. A. DAMOUR. d'eau.1
Figure 2: Extract form the original literature.
Some decades later another important property of zeolites, the cation
exchange capacity, was discovered (Eichhorn, 1858). This property opened a
new world of applications, ranging from the removal of cations from
aqueous solutions (e.g. as Ca binder in washing powder or capture of
radioactive ions by exchange) to the modification of the adsorptive and
In 1896 the idea was advanced that the structures of zeolites consist of
open spongy frameworks. Friedel [3] observed that various liquids such as
alcohol, benzene, chloroform and carbon disulfide were occluded by
zeolites. Grandjean [4], who studied the adsorption of gases, observed
that the zeolite chabazite adsorbs ammonia, air, hydrogen, carbon
disulfide, hydrogen sulfide, iodine and bromine. However, vapors of
acetone, diethyl ether and benzene were essentially not adsorbed. McBain
suggested the expression molecular sieve to describe this phenomenon of
selective adsorption. Barrer et al. performed much of the pioneering
work on this property of zeolites [5]. The often encountered high
selectivity of zeolite adsorbents is based on two principles:
a) separations based upon size of the adsorbates in relation to the
zeolite's pore size.
b) separations based on the different strength of adsorption due to
different polarizability of the adsorbates and/or different
strength of cation coordination in relation to the zeolite's polarity
and cations.
The number and available amounts of natural zeolites of consistent
quality were limited. This has led to a search for synthetic zeolites, in
which Barrer also played an important role. The search resulted in the
large scale preparation of the zeolite types A and Y by the Union Carbide
Corporation in the 1950's [6,7].
The almost unlimited availability of synthetic zeolites induced an
enormously increased effort in zeolite research. Soon zeolites were
discovered as catalysts. Especially in acid-catalyzed reactions zeolites
are powerful after exchange of the cations for ammonium, hydronium or rare
earth (HE) ions. In 1959 the first industrial application of a zeolite
catalyst was introduced by the Union Carbide Corporation with a zeolite Y
isomerization catalyst [8]. Three years later the industrial use of
zeolite catalysists really started off with the introduction of a rare
Introduction 3 HISTORY
developments are the dealuminated Y type zeolites, which share a high
stability and high acid strength. Nowadays most cracking units use zeolite
catalysts.
Another field of fast growing interest is hydroisomerization. Here
straight-chain hydrocarbons are converted into their branched isomers.
Zeolite catalysts containing Pt or Pd (e.g. Pt(0)-containing H-Mordenite
in the Shell Hysomer process [10]) are ideal for the reaction. A further
development of this process is the Shell-Union Carbide Total Isomerization
Process (TIP, see Figure 3)[11], in • which linear hydrocarbons are
isomerized in a first stage and then separated in a branched and a linear
fraction over another zeolite (A-type) column. The linear hydrocarbons are
recycled to the isomerization step. Here two applications of zeolites are
used: as a catalyst and as a selective adsorbent.
The increase in branched hydrocarbons is very important in view of the
use as gasoline, where a higher octane number is required. Branched
hydrocarbons have a higher octane number than the linear isomers. A TIP
plant can increase the octane number of the Cs, C6 fraction of gasoline by
as much as 20 points, so the addition of lead can be reduced. This is
important in those cases where an exhaust catalyst is used, since even
small traces of lead deactivate the catalyst completely. In 1985 over 20
TIP plants were in operation.
H2 PURGE PLUS NORMALS
A relatively recent important discovery in the zeolite field is the
invention of the so-called "pentasil"-type zeolites, of which ZSM-5
[12](1972) is the bestknown member. The reaction for which ZSM-5 is most
frequently cited is the MTG (Methanol-To-Gasoline) reaction which converts
a methanol feed to a hydrocarbon fraction containing aliphatic as
well as aromatics compounds (<= Cio) in the gasoline boiling range and
with good gasoline properties. An installation using this process has
recently been started up in New Zealand. Other important applications
include catalytic dewaxing and p-xylene technology (see later).
Present consumption volumina of the various uses of zeolites are shown
schematically in Figure 4.
s u b d i v i s i o n c a t a l y s t s s u b d i v i s i o n c a t a l y s t s
a: detergent builders; b: catalysts; c: adsorbants; d: desiccants; e: new applications.
Catalysts subdivided in: f: miscellaneous; g: aromatics processing; h: isomerization; i: hydrocracking; j : catalytic cracking.
Figure 4: Use of synthetic zeolites in 1986 and 1990 (*1000 tons).
The latest inventions in the zeolite field include the A1PO-, SAPO-,
MeAPO- and MeAPSO- molecular sieves [13,14]. These materials have a
lattice consisting of Al and P tetrahedra (A1P0) with incorporation of
secondary or tertiary ions like Si (SAPO), Co, Mg and/or Mn (MeAPO and
MeAPSO sieves). This family of molecular sieves includes novel structures
as well as pore structures which have an analogon in the families of
zeolite molecular sieves.
This thesis deals mainly with pentasil-type zeolites, so in the
following part of this introduction particularly properties of ZSM-5 will
Introduction 5 HISTORY
STRUCTURE
Zeolites are crystalline aluminosilicates, which contain in their
natural forms ions of Group IA and Group H A elements such as Na, K, Mg
and Ca. The structure is composed of tetrahedra of an Al3+ or Si4+ ion
surrounded by four 02 - ions. The Al and Si atoms are referred to by the
term "T-atoms" because of their tetrahedral coordination. Each 02" ion is
shared between two neighbouring tetrahedra, so an average formula of TO2
results. In the case of a. Si tetrahedron this will give an electrically
neutral unit, whereas an Al tetrahedron bears a negative charge. This
charge has to be compensated to yield electrically neutral crystals. The
zeolite contains cations to neutralise the charge on the Al tetrahedra.
Thus, zeolites are represented by the general formula:
Mx/n [(Al02)x(Si02)y] .WH20
n is the valence of the charge balancing cation M, w is the number of
water molecules per unit cell, and the sum of x and y are the total number
of tetrahedra per unit cell. The Si/Al ratio (y/x) ranges from 1 to 5 for
the classical zeolites. Pentasil type zeolites have a higher Si/Al ratio,
e.g. 11 or higher for ZSM-5. The Si/Al ratio cannot be lower than 1. In
that case the Loewenstein rule (no adjacent Al tetrahedra) will be
violated.
It may be noted that lattice defects, e.g. hydroxyl nests in ZSM-5, may
occur in as synthesized zeolites, as shown in recent investigations [15].
Other ions can also be incorporated as T-atom in a zeolite lattice;
phosphorus(V), germanium(IV), gallium(III) and boron(III) are
well-known examples. A prerequisite is that the T-atoms (ions) can to. adopt a
tetrahedral configuration in an oxidic lattice. In these cases the strict
definition of a zeolite no longer applies: a zeolite should be an
aluminosilicate. Samples containing other T-atoms than Si and Al will have
The alternative lattice ions can be incorporated during synthesis, but in recent years it has become clear that in principle all ions in a zeolite can be exchanged. Well-known are for instance dealumination procedures in which the Al ions are replaced by Si by treatment with SiCl4 vapour [16]. Von Ballmoos showed that the oxygen ions are also subject to
exchange reactions using H 21 80 at 95°C [17]. Especially hydroxyl-oxygens
show fast exchange; bridging (T-O-T) oxygens exchange 40 times slower. The TO2 tetrahedra are the primary building units. In these units the differences between Al and Si are neglected. These primary building units are linked through the oxygen ions to form larger building blocks, the secondary building units (see Figure 5 ) . Linking the secondary building
a O O
SIR D4R
T,0„ 4-1 T.O„ 5-1 T „ 0 »
4-«-Figure 5: Building units in zeolite structures.
units together yields the smallest unit of the lattice bearing all properties of this lattice: the unit cell. The zeolite structure can be generated by translating the unit cell in the crystallographic directions. A unit cell of zeolite ZSM-5 is shown in Figure 6. The secondary building
(b)
Figure 6: The ZSM-5 structure, view in the straight channel (left, SBU and 5-ring chain).
Introduction 7 STRUCTURE
unit for ZSM-5 is the T12O20 block also shown in Figure 6. The ZSM-5 unit cell contains 96 T-atoms (with an observed maximum of 8 Al atoms (Si/Al>ll), cf. Chapter 3) and 192 O-atoms.
The complete zeolite structure does not fill the complete space. It contains cavities in the form of cages and channels. These pores will contain the adsorbed species when the zeolite is filled with an adsorbate. The intracrystalline space is substantial: a zeolite can have a void volume of up to 0.48 ml/ml (0.31 ml/g for H2O adsorption in CaA zeolite, [1], p.428). Zeolite ZSM-5 has a pore system as shown in Figure 7: it
Figure 7: Channel structure of ZSM-5.
consists of a system of intersecting straight and sinusoidal channels. For clarity, the channels in the schematic drawing in Figure 7 are drawn with a smaller diameter than actually is the case. In the photograph the channels are shown in the right scale. The void volume of this zeolite is 0.17 ml/g, so this zeolite has a higher structural density than for instance zeolite A. The channels in ZSM-5 have a diameter of 0.50 to 0.56 nm, leaving enough space to allow passage of aromatic nuclei like benzene, (p-)xylene and pyridine(s). Figure 8 shows a drawing of the top view of the intersections in the ZSM-5 structure. Note that many figures given in literature do not give the proper geometry. The diameter at the intersections is much larger, reaching in some directions 1 nm, thus allowing reactions to occur with intermediates or transition states with diameters larger than 0.6 nm.
Figure 8: Top view of ZSM-5 channels showing large space at the
intersections
SYNTHESIS
Several zeolites (analcime, mordenite and stilbite) occur naturally.
Some natural zeolites have also been synthesized, important
representatives being mordenite and X and Y (isostructural with the
natural faujasite). Several zeolites which are industrially interesting
(e.g. types A and ZSM-5) are synthetic without a natural counterpart.
The synthesis of zeolites is usually performed under hydrothermal
conditions: a silica source, an alumina source and an exchangeable cation
are dissolved in water and the crystallization of the zeolite is effected
by heating the resulting gel (80-200°C) for a period of time. To obtain
good dissolution of all chemicals a high pH is applied by adding a base
(e.g. NaOH). The so-called "low-silica"-zeolites (A, X, Y) can be
synthesized as described above. The synthesis of the
"high-silica"-zeolites like ZSM-5 is more difficult: an organic
structure-directing agent generally has to be added to obtain the desired
product. For the synthesis of ZSM-5-type zeolites a range of "templates"
has been reported (table 1, [18]). The effectivity of some of these
Introduction 9 SYNTHESIS
TABLE 1: Templates reported for the synthesis of zeolite ZSM-5.
Tetrapropylammonium halide Tetraethylaramonium halide Tripropylamine Diprbpylamine Propylamine 1,6-diarainohexane 1,6-hexanediol 1,5-diaminopentane Ethanolamine Propanolamine Pentaerythritol Methylquinuclidine Morpholine Ethylenediamine Diethylenetriamine Triethylenetetraamine Dipropylenetriamine Dihexamethylenetriamine Di-n-butylamine Ethanol Ethanol + ammonia Glycerol
The template is believed to play two roles in directing zeolite
synthesis: firstly by promoting the formation of the desired building
blocks in the gel [19], and secondly by acting as a hydrophobic pore
filler to prevent dissolution and recrystallization of already formed
crystals [20]. Several analysis methods show that in the as-synthesized
sample the pores are almost completely filled with the template molecules
(see Figure 9 ) .
S p a c * filling drawing of T P A ' i n flr»t i i i a n t a l l o n * ho win o tha packing tn tha linuaoldai channal (van d*r W a a l * r a d i i uaad).
Figure 9: TPA in ZSM-5 (light atoms: zeolite lattice, dark atoms:
TPA), from [22].
Some of the templates shown in Table 1 will be locked in the zeolite
pores after synthesis. In these cases the as-synthesized zeolites have to
be activated before application. Activation requires a high temperature
water from the pores. In some cases the high temperature may damage the
zeolite structure. Recently an alternative technique was developed in
this laboratory by Maesen et al. [21] using a rf-plasma. Here the
temperature is low (less than 100°C) and activation is effected by the
combined action of low pressure and reactive plasma.
ANALYSIS
In zeolite science two types of analysis have to be distinguished:
regarding the resulting crystal structure and as to the chemical
composition. In most cases another separation can be made: between the
as-synthesized and the activated (calcined) samples, as sometimes small
lattice changes can be observed during calcination.
Structural analysis.
Structural analysis is performed by X-ray diffraction. This technique
gives direct information about the crystal structure of the sample. For
zeolite samples it is usual to apply a powder technique, because synthetic
zeolites generally are powders of 1-10 urn particle diameter. Special
synthesis methods allow the preparation of large (>200 urn) crystals which
can be analysed in more detail using a single crystal technique.
Thus a recent X-ray structural analysis of as-synthesized ZSM-5 gives
details on the lattice and on the location and conformation of the TPA
template [22]. X-ray diffraction data give a way of determining the
crystalline species present in a sample, but amorphous impurities cannot
be detected. It should be stressed that X-ray diffraction techniques need
a minimum crystal size to detect the structure. This size is in the order
of 4 times the unit cell dimension (e.g. for ZSM-5 in the order of 8 nm)
[23]. A compilation of computer-simulated X-ray diffraction powder
patterns is given by Von Ballmoos [24]. The XBD pattern of ZSM-5 is shown
Introduction 11 ANALYSIS
A second method, infrared spectroscopy, allows a quick identification of
some zeolites. This analysis method is treated in detail later in this
thesis. Infrared spectroscopy gives information about the occurrence of
specific structures in the lattice. These structures are absent in
amorphous phases, thus giving a way of estimating the amount of
amorphous impurities. For infrared spectroscopy the minimum particle size
needed for the detection of the zeolite structures is smaller than
required in X-ray analysis. This technique has been used to show the
presence of ZSM-5 type particles in an X-ray amorphous material [23]. A
crystal size of a few unit cells (2-4 ■ nm) has been mentioned. The IR
spectrum of ZSM-5 is shown in Figure 10.
Another method, MAS-NMR[25], allows to focus in principle on all nuclei
having a magnetic moment in the zeolite. Frequently reported are the use
of 13C-NMR to study the template or occluded organic species, the use of
e.g. 23Na-NMR to study the exchangeable ions and the use of 27A1 and
29Si-NMR to study the T-atoms in the lattice. The last two techniques
(27A1 and 29Si-NMR) allow an estimation of the chemical composition (Si/Al
ratio) of the sample by integration of the peaks obtained for Si
surrounded by 0 Al and 4 Si, by 1 Al and 3 Si and so on. A more accurate
way of determining the Al content of the zeolite lattice is by . use of
27Al-nutation-MAS-NMR [26]. In this method tetrahedrally coordinated
(lattice-) Al and octahedrally coordinated (extra-lattice-) Al can be
distinguished. Combined with the results from the chemical analysis this
yields an accurate Si/Al ratio. Detailed studies are reported by Fyfe et
al. [27,28]. At high Si/Al ratios the 2 9Si NMR spectrum of ZSM-5 shows
substantial fine structure for the Si(OAl) peak (see Figure 10). The
observed multiplicity arises from crystallographically non-equivalent
tetrahedral units of Si(OAl) silicons. This may be explained by assuming
no less than 24 non-equivalent Si sites in the unit cell. X-ray
diffraction shows either 12 (orthorombic structure) or 24 unique locations
treatment [29] or by adsorbing or desorbing e.g. ammonia. XHD NMR
UwlluUiu
30 28 — I — 40 SUOAI) (SI,A | ) = Si (IAD/ 6 0 ~i 1 1 1 r -i 1 1 1 r,J\
—i 1 i i 1 -i 1 1 1 1— - 8 0 - 9 0 -100 -110 -120 150 100 50 O - 5 0 ppm from TMS ppm f r o m A I ( H20 ) | * —i 1 1 1 1 - 8 0 - 9 0 - 1 0 0 -110 -120 ppm I r o m TMS ~i 1 1 1 — T -150 100 50 0 - 5 0 ppm from AI(H20)J* IRT o o b t a i n =~~~. inflation about"
materials .ie zeolite sample cheml
exact
b u
üt
ln rour work two basic /o d s w e r e u s e d : A A S (atonlic
md XRF (X-ray uorracence spectrometry).
Predecomposition' jf tte-^sample- For AAS the sample is decoü
hydrofluoric acid yie>'ins a s o l u t i o n uPo n which analysis is
The XRF method y^ss discs prepared by decomposing the zeolite aï
n i« h temperature'' li t h i u m borate mixtures. The results obtained by both
methods are co^arable. It will be clear that not all elements can be
analysed by ea c h method: it will, for instance, be impossible to analyse
for boron using the XRF method.
C . .
ZSM-5 S P E C I A L PROPERTIES
Zeolite ZSM-5 is a special type of zeolite. It is a
"high-silica"-zeolite, which gives it most of its special properties. Zeolite ZSM-5 is
moderately hydrophilic to highly hydrophobic (depending on the Si/Al
ratio), whereas zeolites like the types A, X and Y are very hydrophilic.
The number and type of cations compensating the lattice charge are an
important factor as to this property. Zeolite ZSM-5 has a very high
temperature (>1000°C) and acid stability (down to pH=3). The last property
makes it possible to obtain the hydrogen form directly by exchanging the
zeolite in a dilute hydrochloric acid solution without large Al-losses. To
convert the "low-silica"-zeolites to the hydrogen form they have to be
exchanged with an ammonium salt solution and then calcined to decompose
the ammonium ions.
The ZSM-5 structure allows the introduction of alternative T-atoms (B,
Ga, Fe etc.) during synthesis. The structural properties of the zeolite
remain unchanged, just the unit cell dimensions change slightly (see
Figure 11 for the relation between cell dimensions and B content of a
aat the acid strength in
Al content of the sample. The
Les where the Next Nearest Neighbour
Ps not an Al tetrahedron. For ZSM-5 this
for all permissible Si/Al ratios (Si/Al > 11).
tie special pore structure (the channel diameter is
the same as the diameter of an aromatic ring) this yields an
'combination of activity, selectivity and stability in numerous
üatalytic reactions. Some examples are: the conversion of methanol [32]
(and/or ethanol [33] or higher alcohols [34]) to a hydrocarbon fraction in
the gasoline range or to ethene, the alkylation of toluene with methanol
to form (p-)xylene[35], the disproportionation of toluene to benzene and
(p-)xylene[35,36] and selective cracking paraffins [37].
Among these applications of zeolite ZSM-5 two are especially noteworthy:
the (p-)xylene formation and the catalytic "dewaxing" of gas-, fuel- or
lubricating oil. Both applications show the shape-selective properties of
the catalyst.
It has been mentioned that the channels of ZSM-5 allow the passage of
aromatic nuclei. Para-substituted benzenes like p-xylene will also pass
Introduction 14 Z S M T 5 SPECIAL PROPERTIES
properties will be significantly modified. ThusA so-called T-atom
substitution during synthesis renders a powerful tool to tailor the
catalytic activity of a ZSM-5-type zeolite.,
5380 =< 5360 | 5 3 4 0 1 5 3 2 0 | S 3 0 0 .= 5280 D 5260 5240 = 20.12 20.08 20.04 \ • < 20.00 ■ \ £ 19.96 - \ S 19.92 \ " 19.88 \ 19.84 \ 19.80 i
!
■ :\
b^ ^
-\ ^
O ^ O ^ _ & b t 1 \ 1 1 ■ 13.34 c< / 13.32 „• (f 13.30 0 1 2 3 4 5 0 1 2 3 4 5 B/unii cell B/unit cellFigure 11: Variation of (a) unit cell volume and (b) individual cell
parameters as function of boron content [30].
\
Due to the low aluminium content the acid sites in H-ZSM-5 have a very
high acid strength. Barthomeuf [31] shows that the acid strength in
zeolite-type materials is related to the Al content of the sample. The
acid strength is maximal for samples where the Next Nearest Neighbour
(NNN) of an Al tetrahedron is not an Al tetrahedron. For ZSM-5 this
condition is fulfilled for all permissible Si/Al ratios (Si/Al > 11).
Together with the special pore structure (the channel diameter is
approximately the same as the diameter of an aromatic ring) this yields an
unique combination of activity, selectivity and stability in numerous
catalytic reactions. Some examples are: the conversion of methanol [32]
(and/or ethanol [33] or higher alcohols [34]) to a hydrocarbon fraction in
the gasoline range or to ethene, the alkylation of toluene with methanol
to form (p-)xylene[35], the disproportionation of toluene to benzene and
(p-)xylene[35,36] and selective cracking paraffins [37].
Among these applications of zeolite ZSM-5 two are especially noteworthy:
the (p-)xylene formation and the catalytic "dewaxing" of gas-, fuel- or
lubricating oil. Both applications show the shape-selective properties of
the catalyst.
It has been mentioned that the channels of ZSM-5 allow the passage of
w
~Y
•
Introduction Chemical composition.ƒ /
1 , 13 STRUCTURETo obtain exact information about the fractions of the starting
materials built in in the zeolite sample chemical analysis is required. In
our work two basic methods were used: AAS (atomic absorption spectrometry)
and XRF (X-ray fluorescence spectrometry). Both methods require a
predecomposition of the sample. For AAS the sample is decomposed using
■ /
hydrofluoric acid, yielding a solution upon which analysis is performed.
The XRF method uses'glass discs prepared by decomposing the zeolite at
high temperature/in lithium borate mixtures. The results obtained by both
methods are comparable. It will be clear that not all elements can be
analysed by, each method: it will, for instance, be impossible to analyse
for boron using the XRF method.
ZSM-5 SPECIAL PROPERTIES
Zeolite ZSM-5 is a special type of zeolite. It is a
"high-silica"-zeolite, which gives it most of its special properties. Zeolite ZSM-5 is
moderately hydrophilic to highly hydrophobic (depending on the Si/Al
ratio), whereas zeolites like the types A, X and Y are very hydrophilic.
The number and type of cations compensating the lattice charge are an
important factor as to this property. Zeolite ZSM-5 has a very high
temperature (>1000°C) and acid stability (down to pH=3). The last property
makes it possible to obtain the hydrogen form directly by exchanging the
zeolite in a dilute hydrochloric acid solution without large Al-losses. To
convert the "low-silica"-zeolites to the hydrogen form they have to be
exchanged with an ammonium salt solution and then calcined to decompose
the ammonium ions.
The ZSM-5 structure allows the introduction of alternative T-atoms (B,
Ga, Fe etc.) during synthesis. The structural properties of the zeolite
remain unchanged, just the unit cell dimensions change slightly (see
Figure 11 for the. relation between cell dimensions and B content of a
Introduction 15 ZSM-5 SPECIAL PROPERTIES
easily, whereas the transport of e.g. o- and m-xylene will be slower.
Passage of higher substituted aromatics (when formed at an intersection)
is even more limited, so these will probably be converted before leaving
the zeollte[38]. Therefore, alkylatipn. of toluene with methanol . and
disproportionation of toluene will yield a xylenes mixture with a higher
p-xylene content than the thermodynamic equilibrium.
The catalytic dewaxing of heavy oil fractions is a (hydro-)cracking
process in which only the linear ("waxy") hydrocarbons are involved.
Branched hydrocarbons are too large to enter the zeolite's pores. The
products of a dewaxing unit are a fraction with a boiling range comparable
to that of the feed fraction 'and a gasoline fraction. The pour point of
the gas-, fuel- or lubricating oil will be lowered (e.g. for a lubricating
oil from 7°C to -12°C and for a middle distillate ' from 32°C to -18°C
[39]), which drastically improves the properties of these oils at low
temperatures. Dewaxing of gas oil (diesel fuel) lowers the temperature at
which "fogging" occurs. This phenomenon is encountered during the winter
when the linear paraffins form clouds and plug the fuel lines of the car.
In this thesis the unique catalytic properties of ZSM-5 type zeolites
will be demonstrated in two . new gas phase reactions, namely the
conversion of ethanol and ammonia to pyridines (Chapters 7 and 8) and the
ammoxidation of toluene to benzonitrile (Chapter 6). Further chapters
describe the detection and analysis of ZSM-5 zeolites using infrared
spectroscopy (Chapter 2) and experiments on the synthesis of zeolite ZSM-5
using a range of templates (Chapter 3) and a range of substituting T-atoms
introduced during synthesis (Chapter 4). In Chapter 10 some data will be
given on experiments with molecular ..' sieves from the SAPO- and MeAPO
group, as these systems might offer the possibility of synthesizing
materials with anion exchange properties (here the lattice has to carry a
surplus of positive charge). It will be shown that the SAPC— type materials
can be effectively used in the catalytic ammoxidation of toluene (cf.
LITERATURE
1. D.W. Breck, "Zeolite Molecular Sieves, structure, chemistry and use", J. Wiley & Sons, New York 1974.
2. A. Damour, Ann. Mines, 17, (1840), 202.
3. G. Friedel, Bull. Soc. Fr. Mineral. Cristallogr., 19, (1896), 14, 96. 4. F. Grandjean, Compt. Rendu, 149, (1909), 866.
5. R.W. Barrer, "Zeolites and Clay Minerals as Sorbent and Molecular Sieves", Academic Press, London 1978.
6. R.M. Milton, U.S. Patent 2.882.243 (1959). 7. R.M. Milton, U.S. Patent 2.882.244 (1959).
8. R.M. Milton, in "Molecular Sieves", Soc. Chem. Ind., London, (1968), p.199.
9. C.J. Plank, E.J. Rosinski, W.P. Hawthorne, Ind. Eng. Chem., Prod. Res. Dev., 3, (1964), 165.
10. H.W. Kouwenhoven, Mol. Sieves Int. Conf. 3rd, Adv. Chem. Ser., 1973, (121), 529.
11. I.E. Maxwell, Proc. Shell Zeol. Catal. Conf., (1986), 2. 12. R.J. Argauer and G.R. Landolt, US Patent 3.702,886 (1972).
13. S.T. Wilson, B.M. Lok, C A . Messina, T.R. Cannan, E.M. Flanigen, ACS Symp. Ser., 218, (1983), "Intrazeolite Chemistry", G.D. Stucky, F.G. Dwyer. Eds., p.79.
14. E.M. Flanigen, B.M. Lok, R.L. Patton, S.T. Wilson, Pure & Appl. Chem., 58, (10), (1986), 1351.
15. G. Boxhoorn, A.G.T.G. Kortbeek, G.R. Hays, N.C.M. Alma, Zeolites 1984, (4), 15.
16. J. Klinowski, J.M. Thomas, M.W. Anderson, C A . Fyfe, G.C. Gobbi, Zeolites 1983. (3), 5.
17. R. von Ballmoos, W.M. Meier, J. Phys. Chem., 1982, (86), 2698. 18. B.M. Lok, T.R. Cannan andC.A. Messina, Zeolites, 1983, (3), 282. 19. G. Boxhoorn, O. Sudmeijer, P.H.G. van Rasteren, J.C.S., Chem. Coramun.,
1983, 1416.
20. J. Keijsper, M. Mackay, J. v.d. Berg, A.G.T.G. Kortbeek, M.F.M. Post, Prep. KNCV Katal. Symp., 1986, 39.
21. Th. L. Maesen, J.C.S., Chem. Commun., in press.
22. H. van Koningsveld, H. van Bekkum, J.C. Jansen, Acta Cryst., B43, (1987), 127.
23. P.A. Jacobs, E.G. Derouane, J. Weitkamp, J.C.S., Chem. Commun., 1981. 591.
24. R. von Ballmoos, "Collection of Simulated XRD Powder, Patterns for Zeolites", Butterworth, Guildford, (1985).
25. J.M. Thomas, J. Klinowski, Adv. Catal., 33, (1985), 199-374.
26. A. Samoson, E. Lippmaa, G. Engelhardt, U. Lohse, H.G. Jerschkewitz, Chem. Phys. Lett., 134. (1987), (6), 589.
27. C.A. Fyfe, G.C. Gobbi, G.J. Kennedy, J. Phys. Chem., 1984. (88), 3248.
Introduction 17 LITERATURE
28. C.A. Fyfe, G.C. Gobbi, J. Klinowski, J.M. Thomas, S. Ramdas, Nature, 296. (1982), 530.
29. H. van Koningsveld, J.C. Jansen, H. van Bekkum, Zeolites, in press. 30. B.L. Meyers, S.H. Ely, N.A. Kutz, J.A. Kaduk, E. van den Bossche, J.
Catal., 91, (1985), 352.
31. D. Barthomeuf, Mat. Chem'. Phys., 1987, (17), 49.
32. e.g. T. Mole, J.A. Whiteside, D. Seddon, J. Catal., 82, (1983), 261. 33. e.g. J.C. Oudejans, P.F. van den Oosterkamp, H. van Bekkum, Appl.
Catal., 3, (1982), 109.
34. e.g. O.A. Anunziata, O.A. Orio, E.R. Herrero, A.F. Lopez, C.F. Perez, A.R. Suarez, Appl. Catal., 15, (1985), 235.
35. e.g. L.B. Young, S.A. Butter, W.W. Kaeding, J. Catal. , 76, (1982), 418.
36. e.g. N.R. Meshram, S.G. Hegde, S.B. Kulkarni, Zeolites 1986. (6), 37. e.g. R.B. Borade, S.G. Hegde, S.B. Kulkarni, P. Ratnasamy, Appl.
Catal., 13, (1984), 27.
38. I.E. Maxwell, J. Inclusion Phenom., 1986. 4, (1), 1-29.
IDENTIFICATION OF ZSM-TYPE AND OTHER 5-RING CONTAINING ZEOLITES BY I.R. SPECTROSCOPY
J.C. Jansen, F.J. van der Gaag, and H. van Bekkum
Laboratory of Organic Chemistry. Delft University of Technology, Julianalaan 136, 2628 BL Delft. The Netherlands
ABSTRACT
The mid i.r. spectra have been recorded of the pentasil family, of the mordenite group, of ZSM-39 and Melanophlogite, and of the structurally unknown ZSM-34 and ZSM-35. It is concluded that i.r. spectroscopy enables fast differentiation of ZSM-type zeolites.
INTRODUCTION
During a current investigation program on the synthesis of ZSM-type zeolites a fast method to achieve a first differentiation of products including both the identification and the estimated purity was required. For this purpose i.r. spectroscopy and X-ray powder diffraction (XRD) were selected. Occasionally also scanning electron microscopy (SEM) and X-ray fluorescence (XRF) were applied.
For a more precise characterization of the known i.r. spectra of some
2-4 -1 ZSM-zeolites the mid infrared spectra (1500-400 cm ) of a series of
five-membered ring containing zeolites were recorded including both synthetic and natural materials. In this paper we present i.r. data on the members of the pentasil family, i.e. Silicalite, ZSM-5, ZSM-11, and
9
Boralite; of the mordenite group , i.e. Mordenite, Ferrierite, Epistilbite, Dachiardite, and Bikitaite, of the clathrate group, i.e. ZSM-39 and the natural polymorph Melanophlogite, and of the structurally unknown zeolites ZSM-34 and ZSM-35. Especially the absorption bands near 1200 and 550 cm assigned by Jacobs et al. and Vedrine et al. to the presence of five-membered ring systems, were studied.
fi—R
Based on the known crystal structures of most of the above mentioned zeolites it was attempted to acquire an empirically consistent assignment of the near 1200 and the 550 cm absorption bands.
19
For the determination of the estimated purity.of especially ZSM-5 the i.r. optical density ratio of the 550 and 450 cm • bands of the pentasil products
4 was examined since different values have'been published .
EXPERIMENTAL
Materials
For the synthesis of ZSM-type zeolites Aerosil (type 200 Degussa) as the silica source was added to aqueous solutions of organic template. Subsequently an aqueous solution of sodium aluminate was added under vigorous stirring. The gel being formed almost instantaneously was heated at 453 K and stirred in 30 ml autoclaves for 48 h. The solid product was washed three times with distilled water and dried at 373 K for four hours. Subsequently the zeolites were heated at a rate of 1 K/min to 773 K and calcined at this temperature overnight. The natural zeolites, which were obtained from several mineral collections, were air dried.
Methods and apparatus
The mid infrared spectra were recorded on a Perkin Elmer 521 spectrometer using the KBr pellet technique. To identify all zeolite samples used the X-ray powder diffraction data were obtained with a Type II Guinier de Wolff camera. Only zeolitic materials which were pure according to X-ray analysis were used in the present i.r. work. The silica alumina ratio of ZSM-5 was determined by XRF using a PW 1400 PHILIPS Röntgen spectrometer. The crystallinity and the particle size of the ZSM-species SEM was studied with a Jeol Jxa-50A electron microanalyser.
RESULTS AND DISCUSSION
o
The members of the pentasil family together with the complete mordenite g
group , their origin and silica.alumina ratio are listed in Table 1. The common secondary building unit (SBU) in these zeolite types is the 5-1 unit giving five-membered rings of T-sites in the framework
5 ~ structures . The five-membered rings of the synthetic ZSM-39 and the natural polymorph Melanophlogite of the clathro group are part of the polyhedra building units as depicted in Figure 1. The crystal structures of ZSM-34 and ZSM-35 are unknown. In column four and five of Table 1 the space group of the structures is given and the number of 2-fold screw axes per unit cell able to generate chains of five-membered rings from a typical motif of
T-sites indicated by dots in Figure 2. The last column of Table 1 contains the type of typical five-membered ring blocks as presented in Figure 3 and the number of blocks per unit cell.
T a b l * 1 Chemical and structural data of zeolites c o n t a i n i n g Springs
Zeolite type and o r i g i n Si/AI Space g r o u p 2, axes" N u m b e r ofc
chainsV2i 4 4 4 4 1 1
—
I 1 5-ring° blocks/UC 8 A. 8 B 8 A, 8 B 8 A, 8 B 8 A. 8 B 8 8 8 8 4 3 4 B 4 C Silicalite l' Z S M - 5 ' Boraltte' Z S M - 1 1 ' M o r d e n i t e (Fasatal, It.)' Ferrierite (Vincenza, It.) Epistilbite IGanagawa, Jpn.t Dachiardite (Niigata, Jpn.) Bikitaite (Bikitaite, Hhod.) Z S M - 3 9 ' M e l a n o p h l o g i l e ( G i r g e n t i , It.) Z S M - 3 4 ' Z S M - 3 5 ' X 17.4 13.9* 13.8» 5.0 5.0 3.0 4.0 2.0 X x 13.4» 9 . 0 ' 5 5 5 5 5 5 5 5 5 n n u u 1 Pnma 1 Pnma 1 r^nrna 1 Mm2 1 Cmcm 1 Immm 1 C2/m 1 C2Jm 1 P2, a. F d 3 m a. P67mm u. u. 4 4 4 4 4 4—
2 2 n.a n.a u. u. 'Secondary b u i l d i n g unit"Only the 2-fold screw axes w h i c h arrange f i v e - m e m b e r e d rings i n t o chains ' N u m b e r of f i v e - m e m b e r e d rings per 2! axis [Figure 2)
" N u m b e r and t y p e s of five-ring blocks per unit cell as depicted in Figure 3 "Si/B ratio
'Synthesized in this laboratory " A t o m i c reactant ratio
Figure 1 Polyhedra building units of Z S M - 3 9 la.c) and M e l a n o p h l o g i t e (a.b)
The most important i.r. data in the framework absorption region of the zeolite types are given in Table 2. As examples the spectra of ZSM-5, Epistilbite, Dachiardite, Bikitaite and ZSM-39 are shown in Figure 4. Especially the structure sensitive absorptions around 1200 and 550 cm are of interest to differentiate the zeolite types. The external asymmetric stretching vibration around 1225 cm is clearly present in the i.r. spectra of either the structures with four chains of five-membered rings arranged around a 2-fold screw axis as in the pentasil family or with one chain of five-merabered rings on the 2-fold screw axis as in the mordenite group, shown in Figure 2a and b ^ respectively. Although the space group of the Epistilbite structure indicates the presence of 2-fold screw axes, in this structure no five-membered ring chains are generated. However, the presence
21
of pseudo-five-membered ring chains might be the cause of the shift of the near 1200 cm absorption band to 1175 cm
In the Dachiardite structure the absorption band at 1210 cm could be caused by the presence of five-membered ring chains, containing 2-fold screw axes. A large shift compared to the other members of the mordenite group is seen in the spectrum of Bikitaite: though 2-fold screw axes are present the absorption band of the chains is found at 1105 cm . Perhaps this shift is due to the low silica alumina ratio
No absorption was found near 1200 cm in the i.r. spectrum of ZSM-39 and Melanophlogite. According to the structure data no five-membered ring chains are present in these structures.
In the unknown structure of ZSM-35 chains of five-membered rings are possible since the absorption at 1232 cm was demonstrated in the i.r. spectrum of the structure whereas the reverse is true for the also unknown ZSM-34.
Z.
Figure 2 (a) Four f i v e - m e m b e r e d ring chains arranged a r o u n d 2-fold screw axis; m o t i f of 12 f-sites is indicated by dots, (b) One f i v e - m e m b e r e d ring chain o n 2-fold screw axis; m o t i f of 3 T-sites is indicated by dots
Table 2 l.r. data between 1500-400 c m " ' of zeolites containing five rings Zeolite types Lit. data* Silicalite 1 Z S M - 5 8 o r a l i t e Z S M - l l M o r d e n i t e Ferrierite Epistilbile Dachiardite Bikitaite Z S M - 3 9 M e l a n o p h l o g i t e Z S M - 3 4 Z S M - 3 5 Aerosil A s y m . s t r e t c h ' External" 1150-1050 1225(shl 1225lshl 1228(sh) 1225lshl 1223(shl 1218lsh| 1175lshl I210lsh) 110S(sh)
—
—
—
1232(sh)—
Internal 1250-950 10931s) 10931s! 10961s) 10931s) 1045UI 10601s) 10501s) 1050(s) 968{s) 10901s) 11181s) 1060(s) 1070(sl llOOIs) Sym. s t r e t c h ' External 820-750 790(wl 790|wl 8 0 0 l w l 790lwl 800|w) 7 8 0 M 7 9 5 M 775(w) 7 8 2 l w l 790|w| 795(w> 7851ml 7 9 0 M 810(w) Internal 720-650—
—
—
—
720(wl 6 9 5 M 690lw) 670lw) 6801m)—
—
—
—
—
Double* " r i n g 650-500 5501m) S50(m) 550tml 5501ml 580. 5 6 0 M 5 6 3 M 563(wl 558lwl—
—
—
635. 580. 5 5 0 ( w l 5901ml—
TO' b e n d 500-420 4501s! 450lsl 4S0IS) 4 5 0 l s l 4501s) 4551s) 455(s) 4401s) 4601s) 4601s) 465(S| 4651s) 4601s) 4681s!'l.r. assignments according to Flanigen era/."
bFive-membered ring block vibrations according to Jacobs et a/, and Vedrine ef at.3'
According to Jacobs et al. and Vedrine et al. the second structure sensitive absorption band in the pentasil structures at 550 cm is caused by double five-membered ring blocks of Type A as depicted in Figure 3. Type A is a 5-5 block containing two parallel faces of nearly planar five-membered rings. However, in the pentasil structures also five-membered ring blocks are present of Type B (Figure 3) which is a 5-3 block with four faces of puckered five-membered rings in the envelope mode. The absorption band at 550 cm in the pentasil structures is therefore tentatively assigned to the
Figure 3 Types of five-membered ring blocks; A, 5-5 block; B. 5-3 block; C, 5-3-1 block
presence of a combination of Type A and Type B blocks. For the mordenite group an absorption is observed near 560 cm which is in the range
3 4
reported ' for structures with Type B blocks. An exception is Bikitaite, which zeolite shows no absorption near 550 cm . Bikitaite does not contain five-membered ring blocks of Type A and B. A five-membered ring containing block present in the Bikitaite structure is depicted in Figure 3 and called a 5-3-1 block. The 5-3-1 block is a 5-3 block with one additional T-site resulting into two five-membered ring faces in the envelope mode and two six rings. Another difference between Bikataite and the other members of the mordenite group is the relatively strong absorption band at 680 cm in the
23
i.r. spectrum of Bikitaite.
Absorptions near 550 cm were also absent in the i.r. spectra of ZSM-39 and Melanophlogite. This is in agreement with the absence of Type A and Type B
like blocks in these structures.
The weak absorptions at 635 cm , 580 cm and 550 cm in the spectrum of ZSM-34 are considered to be related to the presence of Type B blocks in the structure. The spectrum of the ZSM-35 structure is almost a pentasil-like spectrum except for the large shift of the 550 cm absorption band to 590 cm which could probably be related to the presence of Type A blocks in the structure.
It can be concluded that the presence of the near 1200 and 550 cm i.r. bands is indeed related to five-membered ring chains and blocks, respectively. The frequency shift of the i.r. bands is depending upon the particular zeolite type. Thus fast differentiation of zeolites containing five-membered rings via i.r. spectra is of great importance.
.o
a
1500 1000 5 0 0 v/crrr
Figure 4 I.r. spectra IKBr pellets) of Z S M - 3 9 ( I I , Z S M - 5 (2). Dachiardiie (3). Epistilbue (4) and Bikitaite 15)
The influence of very small crystals, d < 2 pm, must be sorted out because of a bad solution of the structure sensitive bands near 1200 and 550 cm and the poor X-ray diffraction pattern.
Furthermore, a remark can be made regarding the use of i.r. spec.troscopy in determining the purity of zeolite ZMS-5 samples. The most important impurity
in the pentasils, amorphous silica, has an absorption band at 450 cm and
-1 4 does not show a band at 550 cm . Therefore, as earlier reported , the
optical density ratio of the 550 and 450 cm bands could indicate if pure and well crystallized samples are present. Upon measuring physical mixtures of pure ZSM-5 and Aerosil we found this ratio to decrease linear with increasing amounts of amorphous silica present. According to earlier
2 3
investigators ' and our present findings the optical density ratio of the 550 and 450 cm bands is 0.8 for all pure pentasil samples (calcined at 823
4
K ) . This value contradicts the proposal of other workers that each pentasil member has a different ratio value. A constant ratio is consistent with the fact that all pentasil members (cf. Table 1) contain the same type and number of five-membered ring blocks per unit cell. It may be noted that the presence of organic template or adsorbed molecules influences the optical density ratio. Thus proper activation is required.
In conclusion the i.r. technique allows an estimate of the purity of the pentasil samples and gives valuable information regarding the structure of five-membered ring containing zeolites.
ACKNOWLEÜEMENT
We wish to thank Mr. N.M. van de Pers and Mr. J.F. van Lent of the Laboratory of Metallurgy for making the Guinier de Wolff photographs and Mr. D.P. Nelemans of the same laboratory for the SEM photographs. Mr. G.F. Herlaar is thanked for discussions. We are grateful to Prof. K. Koopmans and Mr. Th.W. Verkroost of the Department of Mining Engineering for the X-ray analysis of ZSM-5 and to Mr. C. Blotwijk of the same department for supplying the specimen of Bikitaite and Melanophlogite. We thank Dr. L.P. van Reeuwijk of the ISRIC (the former International Soil Museum) for supplying the specimen of Epistilbite.
REFERENCES
1. Gaag, F.J. van der, Jansen, J.C., and Bekkum, H. van, A p p l . C a t a l . , i l . ( 1 9 8 5 ) , 2 6 1 .
25
2. Ballmoos, R. von, PhD Thesis, E.T.H. Zurich, 1981.
3. Jacobs, P.A., Beyer, H.K. , and Valyon, J. , Zeolites, 1981, .1, 161.
4. Coudurier, G. , Naccache, C., and Vedrine, J.C., J. Chem. Soc. Chem. Comm.. 1982, 1413.
5. Meier, W.M. and Olson, D.H., 'Atlas of Zeolite Structure Types', Juris Druck and Verlag AG, Zurich, 1978.
6. Schlenker, J.L., Dwyer, F.G., Jenkins, E.E., Rohrbaugh, W.J., Kokotailo, G.T., and Meier, W.M., Nature, 1981, 224, 340.
7. Smith, J.V., Fifth Int. Conf. on Zeolites - Recent Prog. Rep. and Disc, (Eds., Seriale, R. , Colella, C., and Aiello, R.), Heyden, London, 1981, 228.
8. Kokotailo, G.T. and Meier, W.M., Chem. Soc. Spec. Publ., 1980, 33, 133. 9. Breek, D.W., 'Zeolite Molecular Sieves: Structure, Chemistry and Use',
John Wiley and Sons, New York, 1974, 122.
10. Gramlich-Meier, R. and Meier, W.M., J. of Solid State Chemistry. 1982, 44, 41.
11. Flanigen, E.M., 'Zeolite Chemistry and Catalysis', (Ed. Rabo, J.A.), Adv. Chem. Ser.. 1976, 171, Ch. 2.
TEMPLATE VARIATION IN THE SYNTHESIS OF ZEOLITE ZSM-5
F . J . VAN DER GAAG, J . C . JANSEN, and H. VAN BEKKUM
Laboratory of Organic Chemistry, D e l f t U n i v e r s i t y of Technology, . Julianalaan 136, 2628 BL Oei f t , The Netherlands.
(received 25 February 1985, accepted 22 March 1985)
ABSTRACT
The a b i l i t y of several organic template molecules i n the synthesis of ZSM-5 type z e o l i t e s was studied under standard conditions of temperature and time using s t a r t i n g Si/Al r a t i o s ranging from 4 to » (19.2 t o 0 A l / u c ) . 1,6Hexaned i o l , 1,6hexane1,6Hexanediamine, 1propanol, 1propanamine, p e n t a e r y t h r i t o l an1,6Hexaned t e t r a -propylammonium bromide (TPA-Br) were used as templates. The z e o l i t e s obtained were analyzed by X-ray. d i f f r a c t i o n a n d . i n f r a r e d spectroscopy f o r c r y s t a l l i n i t y and by X-ray fluorescence for chemical composition. Scanning e l e c t r o n m i c r o graphs were made of selected samples.
The range of the s t a r t i n g Si/Al r a t i o s g i v i n g pure ZSM-5 product increases ih': the f o l l o w i n g template order: alcohols < amines < t e t r a p r o p y l ammonium b r o
mide. Both 1,6-hexanediamine and TPA-Br give good r e s u l t s f o r low s t a r t i n g S i / A l r a t i o s .
The observed maximum content of 8 Al/uc of ZSM-5 i s discussed i n terms of special Al s i t e s connecting s i l i c a l a y e r s .
INTRODUCTION
In general z e o l i t e ZSM-5 i s synthesized in a hydrothermal system c o n t a i n i n g an alumina source, a s i l i c a source and an organic template molecule. The t e t r a propyl ammonium ion (TPA) was the f i r s t organic molecule which was reported [1] t o be capable of inducing ZSM-5 f o r m a t i o n . Later i n v e s t i g a t i o n s showed t h a t the use of TPA allows the synthesis of ZSM-5 z e o l i t e s w i t h a S i / A l r a t i o ranging from 11 to °° (which corresponds t o 8 t o 0 Al/uc) [ 2 ] .
Other organic molecules reported to induce ZSM-5 formation a r e , for example, 1,6-hexanediol [ 3 ] and 1-propanol [ 4 ] . A review on the use of d i f f e r e n t tem plates i n z e o l i t e synthesis has r e c e n t l y been given by Lok et a l . [ 5 ] . Derouane and Gabelica and coworkers [ 6 , 7 , 8 ] i n v e s t i g a t e d the process of forming the ZSM-5 phase and the role of the a l k a l i metal c a t i o n s , using the templates TPA-Br and tetrabutylammonium bromide.
ZSM-5 z e o l i t e s have a number of properties which are not dependent on the chemical composition, i . e . the Si/Al r a t i o of the sample, l i k e c r y s t a l s t r u c t u r e , pore size and pore volume, X-ray d i f f r a c t i o n p a t t e r n and r e f r a c t i v e index [ 9 ] . Many other properties of ZSM-5 do vary w i t h the c o m p o s i t i o n . In d i f f e r e n t a p p l i c a t i o n s of ZSM-5 c e r t a i n ranges of composition a r e , t h e r e f o r e , favoured or r e q u i r e d . Ion exchange c a p a c i t y , c a t a l y t i c a c t i v i t y and hydrophobicity are examples of composition-dependent p r o p e r t i e s .
27
In our l a b o r a t o r y the e f f e c t of varying Si/Al r a t i o on the e f f i c i e n c y of ZSM-type c a t a l y s t s i n e . g . ammoxidation [ 10J and aromatization [11] is under i n v e s t i g a t i o n .
In order t o o b t a i n knowledge of the templating potency of d i f f e r e n t organic molecules a series of ZSM-5 samples has been synthesized, s t a r t i n g out w i t h d i f f e r e n t S i / A l r a t i o s and d i f f e r e n t organic template molecules. Standard con d i t i o n s [ 5 ] of temperature and r e a c t i o n time were chosen. The organic molecules used were: TPA-Br, 1,6-hexanediol, 1,6-hexanediamine, 1-propanol, 1-propan-amine, and p e n t a e r y t h r i t o l , a t e t r a o l which resembles TPA as to s t r u c t u r e . Two s i l i c a sources, a e r o s i l and waterglass, were applied i n t h i s study.
EXPERIMENTAL
The ZSM-5 samples were prepared according to the general d i r e c t i o n s given by Casci et al . [ 3 ] .
The c r y s t a l l i z a t i o n was performed i n s t a i n l e s s steel (type 316) autoclaves (35 ml volume) a i r t i g h t e n e d by a t e f l o n r i n g and containing t e f l o n - c o a t e d mag n e t i c s t i r r e r b a r s . Nine autoclaves were placed i n an e l e c t r o n i c a l l y c o n t r o l l e d heated aluminum carrousel equipped w i t h magnetic s t i r r e r d r i v e s , as shown i n Figure 1 .
Figure 1 . S t a i n l e s s steel autoclave and alu.ninum carrousel used f o r ZSM-5 syn thesis experiments.
Chemicals.
Reagents were: a e r o s i l s i l i c a (S1O2, A e r o s i l 200, Degussa), sodium hydroxide (NaOH.H20, Merck Suprapur), sodium aluminate (NaA102, 41 wt% Na20, 54 wt%
Al2°3» Riedel-de Haehn), 1,6-hexanediol ( A l d r i c h ) , 1,6-hexanediamine ( A l d r i c h and Merck), 1-propanol (Merck), 1-propanamine (Merck), tetrapropylammonium b r o mide ( A l d r i c h ) , p e n t a e r y t h r i t o l (BOH), waterglass (sodium s i l i c a t e s o l u t i o n , 26.7 w U S1O2, 8.1 w t t Na20, Lamers & Indemans), s u l f u r i c acid (96 wt% H2S04,
Lamers & Indemans) and aluminum s u l f a t e (Al2(S04)3.18H2O, .Merck).
Aerosil as s i l i c a source
Each autoclave was charged w i t h 1.55 g (25.8 mmole) a e r o s i l suspended i n 20 ml demineralized water. To t h i s suspension a s o l u t i o n c o n t a i n i n g sodium hydrox i d e , sodium aluminate and organic template was added under s t i r r i n g . The t o t a l amount of NaOH i n the s o l u t i o n was kept a t 8.11 mmole. The amount of NaA102 was
adjusted to obtain a range of S i / A l r a t i o s i n the g e l , which u s u a l l y formed w i t h i n a few seconds. The amount of template was 8.57 mmole ( 1 , 6 - h e x a n e d i o l , 1.013 g ; 1,6-hexanediamine, 0.993 g; p e n t a e r y t h r i t o l , 1.167 g ; 1-propanol, 0.515 g; 1-propanamine, 0.506 g; TPA-Br, 2.29 g ) . The molar composition of the gel (as oxides) was: 1.00 S i 02: 0 - 0 . 1 4 A l203: 0 . 3 3 3 template:0.157'Na20:48.8 H20.
Waterglass as s i l i c a source
Each autoclave was charged w i t h a mixture of 7.44 g (30.38 mmole S i 02. 2.18
mmole Na20) waterglass and 6.67 g demineralized water, t o which a s o l u t i o n of
0.261 g (2.55 mmole) 96% s u l f u r i c a c i d , 11.76 mmole template ( 1 , 6 - h e x a n e d i o l , '.";', i . 3 9 ' g ; 1,6-hexanediamine, 1.37 g; p e n t a e r y t h r i t o l , 1.60 g; 1-propanol, 0.707 g ; 1-propanamine,; 0.695 g ; TPA-Br, 3.13 g) and aluminum s u l f a t e i n 10.67 ml water was added u n d e r . . - s t i r r i n g . The amount of aluminum s u l f a t e was adjusted t o obtain, a range of Sï/Al r a t i o s i n the g e l , which u s u a l l y formed w i t h i n a few ,. seconds. The molar composition of the gel (as oxides) was: 1.00 S i 02: 0 - 0 . 1 1
Al203:0.382 tempi ate :0 .208 Na20:31.7 H20 . ":
In both procedures the autoclaves were closed and s t i r r e d a t 448 K f o r 44 hours. After c o o l i n g , the s o l i d s were c o l l e c t e d by f i l t r a t i o n and washed three times with demineralized water. The samples were dried overnight at 373 K and analyzed by i n f r a r e d spectroscopy ( I R ) a n d X-ray d i f f r a c t i o n (XRD). A number of ' samples was analyzed as well by X-ray fluorescence (XRF) for chemical
composi-: , t i o n ,and by scanning e l e c t r o n micrography (SEM) for morphology. IR spectra were
recorded on. a Perkin-Elmer 521 spectrometer, using KBr p e l l e t s . XRD analyses were performed using an Enraf-Nonius Type I I Guinier-de Wolff camera and CuKa
r a d i a t i o n . XRF analyses were made on a P h i l i p s PW 1400 rbntgen spectrometer using l i t h i u m borate glass p e l l e t s containing the disclosed sample. SEM m i c r o graphs were made using a Jeol JXa-50A e l e c t r o n microanalyser.
29
RESULTS AND DISCUSSION
A number of samples which were pure ZSM-5 according to XRD and IR were submitted to XRF analyses. The analysis data are p l o t t e d in Figure 2 .
10 Al/uc (prod) 8 6 4 2 0 0 2 4 6 8 10 — A l / u c (gel)
Figure 2 . XRF analysis data, p l o t t e d as Al/uc i n synthesis gel v s . Al/uc i n ZSM-5 product, s i l i c a source waterglass: x: 1,6-hexanediamine; +: 1,6-hexane-d i o l ; s i l i c a source A e r o s i l : v : TPA-Br; o: 1,6-hexanediamine; • :
1,6-hexane-d i o l .
Figure'2 shows t h a t the r a t i o (Al/uc p r o d u c t ) / ( A l / u c gel) i s somewhat l a r g e r than u n i t y for a l l compositions except one. Thus i t can be concluded t h a t a l u minum i s preferably incorporated i n the s o l i d m a t e r i a l . This is i n agreement w i t h the r e s u l t s of Romannikov et a l . [12] and Gabelica et al . [ 8 ] .
In the s o l i d s t a t e Al-NMR spectrum [13] recorded from a sample c o n t a i n i n g 7.46 Al/uc ( i n the product, synthesis from A e r o s i l and TPA) no signal of o c t a
-29
hedral Al was observed. Furthermore from Si-NMR spectra of the same sample a l a t t i c e Si/Al r a t i o of 13 (6.9 A l / u c ) was e s t i m a t e d . I t can be concluded t h a t a l l Al i n the sample is incorporated i n the z e o l i t e l a t t i c e .
SEM micrographs i n d i c a t e d the growth of larger c r y s t a l s when using a synthe s i s mixture w i t h a lower aluminum c o n t e n t , as shown i n Figure 3. This has also been observed by Gabelica et al . [8] and Romannikov et al . [;12]. The l a t t e r authors suggest an increase in c r y s t a l l i z a t i o n rate with an increase of S i / A l r a t i o . When A e r o s i l was used as s i l i c a source, the c r y s t a l s were u s u a l l y b e t t e r shaped compared to the c r y s t a l s formed w i t h waterglass as s i l i c a source. This is assumed to be caused by a lower rate of c r y s t a l growth i n the case of Aero s i l .
t e m p l a t e : TPA
a e r o s ï l
5 «
S i / A l * 35
S i / A l ■ 174
S i / A l = oo
Figure 3. SFM micrographs showing the effect of variation in Si/Al r a t i o on crystal size.
31
The p u r i t y of the samples was judged from the recorded IR s p e c t r a , e s p e c i a l l y from the bands a t 1220, 550 and 450 c m "1. The bands a t 1220 and 550 cm"1 a r e
s t r u c t u r e - s e n s i t i v e peaks [14] a r i s i n g from 5-ring chain and 5 - r i n g block v i b r a t i o n s , r e s p e c t i v e l y . The p u r i t y of the sample can be estimated from the o p t i c a l density r a t i o of the 550 and 450 cm bands, which should be 0.8 f o r pure
ZSM-5 [ 1 4 ] . X-ray diffractograms were also used for ZSM-crystall i n i t y e s t i m a t i o n and i d e n t i f i c a t i o n of i m p u r i t i e s . Main i m p u r i t i e s were alpha quartz ( s i l i con-rich f o r m u l a t i o n s ) , mordenite and natroalumite ( N a A ^ t S O ^ t O H ^ ) ( a l u m i num-rich f o r m u l a t i o n s , waterglass method) and near-kenyaite ( c f . [ 3 ] ) . In F i gure 4 the estimated ZSM-5 p u r i t i e s of the various products obtained are p l o t ted versus the c a l c u l a t e d number of aluminum atoms per u n i t c e l l [ 1 5 ] .
Figure 4 c l e a r l y shows t h a t amines allow a wider range of Al/uc-values t o be used to prepare ZSM-5 i n a pure state than the corresponding a l c o h o l s . TPA p r o vides the widest range o f pure ZMS-5 products, ranging from 0 t o 8 A l / u c . The small templates (propanol, propanamine) give better r e s u l t s when a double molar amount of these templates i s used. TPA allows the use of smaller amounts o f t h i s template, e . g . h a l f the molar amount (of the standard formulations given i n the experimental s e c t i o n ) . The use of waterglass as s i l i c a source gives a higher c r y s t a l l i n i t y compared to Aerosil . Similar r e s u l t s were obtained by Derouane, Gabelica and coworkers [ 6 ] , who determined the time f o r 100% ZSM-5 c r y s t a l l i n i t y for a c t i v e s i l i c a to be approximately six times the time for wa t e r g l a s s . I t is obvious t h a t waterglass gives a higher c r y s t a l l i z a t i o n r a t e .
The precise r o l e of the organic template molecules i n z e o l i t e synthesis i s s t i l l a matter of much dispute ( c f . [ 5 ] ) . The good performance of TPA as a tem p l a t e has been r e l a t e d by Boxhoorn et a l . t o the i n t e r a c t i o n and reordering of i n i t i a l l y formed complex s i l i c a t e anions by the TPA c a t i o n [ 1 6 ] . Other elements i n the TPA templating potency may be i t s charge and the e f f i c i e n t f i l l i n g o f the z e o l i t e l a t t i c e . When the pores of ZSM-5 are completely f i l l e d with TPA, the z e o l i t e contains 4 TPA/uc. Additional counter charge can be i n the form o f sodium (higher number of A l / u c ) or hydroxide ions (lower number of A l / u c ) . I t is obvious that a p o s i t i v e l y charged species is the best complexant for an a n i o n . Perhaps template a c t i o n of non-charged organic molecules may also be r e l a t e d i n f i r s t instance t o i n t e r a c t i o n w i t h the complex s i l i c a t e anions. In t h i s view amines are b e t t e r templates because they easier form H-bond complexes w i t h the Si-OH terminal groups of the s i l i c a t e anion, compared t o a l c o h o l s . In the synthesized z e o l i t e s the neutral templates are expected to a c t as l i g a n d s for sodium ions s i t u a t e d a t c r o s s - s e c t i o n s . The resemblance of Na(template)4 t o
TPA i s clear t h e n .
Figures 2 and 4 show a maximum aluminum content o f approximately 8 A l / u c . This maximum number is also mentioned i n the l i t e r a t u r e [ 2 ] . The exact c r y s t a l -lographic p o s i t i o n s of the aluminum Ions i n the ZSM-5 l a t t i c e are s t i l l under d i s c u s s i o n . F r i p l a t et a l . [17] conclude from non-empirical mechanical c a l c u l a t i o n s t h a t the Al atoms w i l l be p r e f e r e n t l y located at p o s i t i o n s T2 and T12
&
e synthesis of ate [ 5 ] , the ^nge of app .ia amines 4.v'
< u:.<**
^
W
1 * > <c A ^ 49'»*°
fcV
^
/ ' a n d H. va ^ - - c a t a l . , ^ ' 9 8 3 (D. 01 s 536. ..i^Oosterkamp, and H. > .el. M a s t i k h i n , S. Hocevar, ^.-ormed by Dr. N.C.M. Alma (Shell Rese ^uer Gaag, J . C . Jansen, and H. van Bekkunhe direct (two-step-)conversion of synthesis
e-containing ZSM-5-type zeolites show a
raction [5].
s the . synthesis and analysis of ZSM-5 type
ther than Al and Si present in the synthesis
ized in sealed glass containers in an oven at
ing for 2 weeks. Two methods were used: the,
uPont) as the silica source, and the second
. In all experiments tetrapropylammoniuni bromide
the template. The molar gel composition was:
20 TPA-Br; 1500 H2O when using Ludox, and 100
5 TPA-Br; 1950 H2O when using waterglass. The
added in the form and the amount given in Table
as performed,using X-ray diffraction and infrared
olume was measured thermogravimetrically by the
t ca. 40°C) in a calcined sample (550°C) of the
ies of the samples were determined by NH3-TPD on
subsequently calcined sample.
ntroduction, an as-synthesized T-atom substituted
the non-Na and non-TPA cations incorporated in
e the following characteristics:
tructure according to spectroscopie techniques,
kept in mind.that the T-atoms should fit in a
rdination, whereas their size should not introduce
