Zeolite SSZ-53: An extra-large-pore zeolite with interesting catalytic properties

Article abstract of DOI:10.1002/anie.200701634

(Figure Presented) Wide pores for wide applications: The catalytic properties of SSZ-53, an extra-large-pore high-silica zeolite, were explored by using ethylbenzene disproportionation and the isomerization and hydrocracking of n-decane as test reactions. High activity together with a very open channel system render this zeolite an attractive candidate as catalyst for applications in petroleum refining.

Full text of DOI:10.1002/anie.200701634

Communications
DOI: 10.1002/anie.200701634
Zeolite Catalysts
Zeolite SSZ-53: An Extra-Large-Pore Zeolite with Interesting
Catalytic Properties**
Supak Tontisirin and Stefan Ernst*
Dedicated to Süd-Chemie on the occasion of its 150th anniversary
Zeolites have found widespread use as catalysts in petroleum
refining and petrochemistry and as selective adsorbents in
separation and purification. A special class of zeolites
comprises high-silica zeolites with extra-large pores (the
term “extra-large” encompasses zeolites with pore openings
delimited by rings with more than 12tetrahedral (SiO or
4
AlO4) centers)). Although such materials possess consider-
able potential in catalysis (and adsorption) with larger
molecules, their catalytic potential has only scarcely been
explored so far. One of the more recently discovered extra-
large-pore zeolites is SSZ-53, which was discovered in the
Chevron laboratories.[1,2] Its pore system consists of linear,
non-interconnected channels with pore openings formed from
elliptical 14-rings with an approximate size of 0.65 ”
0.85 nm2.[3] The framework topology of SSZ-53 has been
assigned the three letter code SFH by the Structure Com-
mission of the International Zeolite Association.[4] Herein, we
report on the hydrothermal synthesis of zeolite SSZ-53 and on
its catalytic properties in the acid-catalyzed disproportiona-
tion of ethylbenzene and the conversion of n-decane on a
bifunctional form of the zeolite.
Figure 1. X-ray powder patterns of B-SSZ-53 in its as-synthesized and
calcined form and of protonated Al-SSZ-53 (HSSZ-53).
The X-ray powder pattern of the as-synthesized B-SSZ-
53, its calcined form, and the acid form of Al-SSZ-53 are
depicted in Figure 1. From a comparison with published
data,[1–3] it can be deduced that the as-synthesized sample of
B-SSZ-53 is of good crystallinity and does not contain
amorphous or crystalline impurities. The modification steps
applied to the as-synthesized B-SSZ-53 apparently do not
alter the structural integrity of the material.
The typical crystallite size and morphology of SSZ-53 can
be seen from the scanning electron micrograph shown in
Figure 2. The needlelike crystallites are around 1 to 2 mm
long, and there are no indications for the presence of
amorphous materials or other crystalline phases in the
sample. Chemical analysis reveals that the Al-containing
form of SSZ-53 prepared in the present study has a nSi/nAl
ratio of 55:1. Moreover, N2 adsorption at 77 K (BET
Figure 2. Scanning electron micrograph of calcined B-SSZ-53.
440 m2 gÀ1 and a specific pore volume of about 0.19 cm3 gÀ1.
These values are in good agreement with previously published
data.[1–3]
The disproportionation of ethylbenzene to benzene and
the three diethylbenzene isomers was first introduced by
Karge et al. as a catalytic test reaction for the properties of
acid zeolite catalysts.[5,6] Moreover, it has been demonstrated
that this reaction can be exploited to distinguish between
medium- and large-pore zeolites, based on the reaction
selectivities.[7] More recently, the Catalysis Commission of
the International Zeolites Association also has recommended
the disproportionation of ethylbenzene as a test reaction for
the characterization of acid zeolites.[8] The results with HSSZ-
53 as the catalyst in the disproportionation of ethylbenzene
are depicted in Figure 3. Already at a reaction temperature as
measurement) yields
a specific surface area of about
[*] M.Sc. S. Tontisirin, Prof. Dr.-Ing. S. Ernst
Fachbereich Chemie, Technische Chemie
Technische Universität Kaiserslautern
Erwin-Schroedinger-Strasse 54, 67663 Kaiserslautern (Germany)
Fax: (+49)631-205-4193
E-mail: ernst@chemie.uni-kl.de
[**] Financial support of this work by the Stiftung Rheinland-Pfalz für
Innovation, Paul and Yvonne Gillet-Stiftung, and Fonds der
Chemischen Industrie is gratefully acknowledged.
7304
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 7304 –7306

Angewandte
Chemie
benzene to triethylbenzenes (TEB) and benzene. Indeed,
triethylbenzenes were found in small amounts and at
relatively high conversions over zeolite HSSZ-53 as catalyst
(cf. Figure 4). Moreover, also a slow deactivation is observed,
which is tentatively attributed to the formation of carbon-rich
residues on the catalyst (“coke”).
The catalytic properties of the bifunctional form of SSZ-
53 (0.27Pd/HSSZ-53; Pd content: 0.27 wt%) were explored
in the isomerization and hydrocracking of n-decane. This
reaction has been frequently used for probing the effective
pore width of zeolite catalysts.[9,10] The conversion of n-decane
and the yields of isomers and hydrocracked products as a
function of the reaction temperature are depicted in Figure 5.
It can be seen that conversion starts already at about 1708C
and is virtually complete at 3008C.
Figure 3. Disproportionation of ethylbenzene over HSSZ-53 at different
temperatures (Wcat/FEB =290 ghmolÀ1; Wcat =290 mg).
low as 1508C, conversions around 15% are achieved. In
addition, an induction period is initially observed (i.e. during
the first two hours) during which the conversion increases and
then levels-off into a quasi-stationary stage. All this is typical
for large-pore zeolites.[5–7] With increasing reaction temper-
atures, ethylbenzene conversion increases; however, the
induction period shortens or disappears completely (in
agreement with literature reports).[7,8] Moreover, catalyst
deactivation, that is, a decrease of conversion with time-on-
stream, is observed with increasing reaction temperature. This
is most probably due to coke formation as a result of
undesired side reactions.
Figure 4 shows the conversion of ethylbenzene and the
observed product yields at a reaction temperature of 2008C as
a function of time-on-stream. Ideally, pure ethylbenzene
disproportionation should result in the formation of equal
molar amounts of benzene and diethylbenzenes. It has,
however, repeatedly been observed with large-pore zeolites
that the molar ratio of diethylbenzenes to benzene is not
strictly 1:1. Rather, a small diethylbenzene deficit is found,
resulting in diethylbenzene/benzene ratios around 0.9:1.[7,8]
This discrepancy (viz. the “loss” of ethylene groups) has been
attributed to the formation of higher alkylated aromatics that
are strongly adsorbed on the zeolite and/or to consecutive
disproportionation of diethylbenzenes (DEB) with ethyl-
Figure 5. Influence of the reaction temperature on the conversion of n-
decane (n-De), as well as on the yields of the isomers and hydro-
cracked products over 0.27Pd/HSSZ-53 as catalyst (pH ꢀ101.3 kPa;
2
n
H /nn-De ꢀ100; Wcat/Fn-De =400 ghmolÀ1).
2
As usually observed, skeletal isomerization of linear n-
decane to branched isoalkanes is the sole reaction at very low
conversions. Moreover, monobranched isomers appear ini-
tially in the product and are, with increasing conversion,
converted to dibranched isomers. Among the monobranched
species, the different (2-, 3-, 4-, and 5-) methylnonanes
predominate with selectivities around 70 to 80%. The
selectivity ratio of 2- and 5-methylnonane formed at low
conversion is about 1.7:1 and is therefore typical for very-
large-pore zeolites.[9,10] The remaining monobranched isomers
consist of 3- and 4-ethyloctane (20 to 30%) and minor
amounts of 4-propylheptane (up to ca. 1%). All this is again
typical for very-large-pore zeolites.[9,10] Moreover, the forma-
tion of these large amounts of monobranched isomers with
side chains longer than methyl groups could be of advantage
in, for example, dewaxing by isomerization, leading to
improved cold flow properties of the dewaxed oil.
Hydrocracking already starts at low conversions and
consumes the branched C10 isomers (Figure 5). The generally
low yield of isomers together with an unsymmetrical distri-
bution of the hydrocracked products (Figure 6), is typical for
zeolites with one-dimensional pores (e.g., mordenite) and has
been rationalized with a hindered diffusion of C10 moieties in
the unidimensional channels, leading to enhanced hydro-
Figure 4. Conversion and product yields in the disproportionation of
ethylbenzene over HSSZ-53 (TR =2008C, Wcat/FEB =290 ghmolÀ1
,
Wcat =290 mg).
Angew. Chem. Int. Ed. 2007, 46, 7304 –7306
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
7305

Communications
added to a mixture of NaOH (0.047 g) and sodium borate decahy-
drate (0.1 g). The resulting mixture was stirred until the solid
dissolved. Subsequently, Cab-O-Sil M5 (1.5 g, 97 wt% SiO2, 3 wt%
water) were slowly added and the resulting gel stirred for another
0.5 h. The gel was then transferred to a 25-mL stainless-steel
autoclave with a Teflon-liner. Crystallization was achieved in the
rotating autoclave (40 revolutions per min) at 1608C over seven days.
The obtained crystalline solid was washed with distilled water and
then heated (1.58CminÀ1) to 5408C in a flow of N2. Then the gas flow
was switched to air and the temperature was kept constant for 5 h.
The sample was then heated to 5948C and kept there for 5 h. From the
calcined B-SSZ-53, acidic Al-SSZ-53 was obtained by ion-exchanging
the calcined form for 12h at 95 8C in an excess of a 1n aluminum
nitrate solution, followed by filtration and washing the resulting solid
with distilled water. After drying at 1008C for 12h and a final
calcination at 5408C in a flow of N2, the acid (H-) form of Al-SSZ-53
(HSSZ-53) was obtained. The bifunctional form of this material was
prepared by ion-exchange with an appropriate amount of an aqueous
solution of [Pd(NH3)4]Cl2 such as to obtain a final palladium loading
of 0.27 wt%. Prior to the catalytic experiments on the disproportio-
nation of ethylbenzene, the H-form of the catalyst was calcined in situ
in the reactor at 4008C in N2 for 12h. For the bifunctional conversion
of n-decane, the Pd-loaded catalyst was calcined at 4008C in N2 for
12h, at 300 8C in air for 7 h, and then reduced at 3008C in H2 for 10 h.
The catalytic experiments were conducted under atmospheric pres-
sure in a fixed-bed flow-type apparatus with on-line analysis using
temperature-programmed capillary gas chromatography. For the
disproportionation of ethylbenzene, N2 was used as carrier gas with
a partial pressure of the feed pEB of 1 kPa. For the bifunctional
conversion of n-decane, hydrogen was used as carrier gas and the
partial pressure of n-decane amounted to 1 kPa.
Figure 6. Distribution of cracked products from n-decane over 0.27Pd/
HSSZ-53 at Xn-De ꢀ43% and Ycr. ꢀ33%.
cracking.[10,11] With increasing conversion, hydrocracking
starts and consumes the branched C10 isomers. A typical
distribution of the hydrocracked products is shown in
Figure 6. It can be seen that C1 and C2 as well as C8 and C9
hydrocarbons are absent. This suggests that hydrogenolysis,
namely hydrocracking at the noble metal, is absent and the
predominating reaction mechanism is really a bifunctional
one.[12] From the slightly asymmetric shape of the distribution
of the hydrocracked products, it can be deduced that some
minor contribution of secondary cracking occurs. Moreover,
branched isomers predominate in the C4 to C7 fractions, which
indicates that hydrocracking starts from highly branched
intermediates. This reflects the large space available in the
channels of the extra-large-pore zeolite SSZ-53. In particular,
the molar amount of isopentane formed from 100 moles of
hydrocracked n-decane (at ca. 35% yield of cracked prod-
ucts) has been shown to be a valuable measure for the space
available around the catalytic sites. A value of 58 is found for
zeolite SSZ-53 which is comparable to values of about 54 for
Y-type zeolites with their large intracrystalline supercages of
about 1.3 nm in diameter.[10,11]
In conclusion, it has been shown that zeolite SSZ-53 is a
highly active extra-large-pore zeolite. The results of the test
reactions for probing its effective pore width under catalyti-
cally relevant conditions are in agreement with its crystallo-
graphic structure. Due to its high hydrocracking activity and
its large effective pore size, SSZ-53 seems to be particularly
suitable for the hydrocracking of more bulky molecules. This
makes it an attractive candidate for applications in petroleum
refining.
Received: April 13, 2007
Revised: June 1, 2007
Published online: September 6, 2007
Keywords: heterogeneous catalysis · microporous materials ·
.
SSZ-53 · zeolites
[1] S. Elomari (Chevron Research and Technology Company), WO-
A1 01/9992155, 2001.
[2] S. A. Elomari, S. I. Zones in Studies in Surface Science and
Catalysis, Vol. 135(Eds.: A. Galarneau, F. Di Renzo, F. Fajula, J.
Vedrine), Elsevier, Amsterdam, 2001, pp. 479 – 486.
[3] A. Burton, S. Elomari, C.-Y. Chen, R. C. Medrud, I. Y. Chan,
L. M. Bull, C. Kibby, T. V. Harris, S. I. Zones, E. S. Vittoratos,
Chem. Eur. J. 2003, 9, 5737 – 5748.
[4] http://www.iza-online.org/databases/.
[5] H. G. Karge, J. Ladebeck, Z. Sarbak, K. Hatada, Zeolites 1982, 2,
94 – 102.
[6] H. G. Karge, K. Hatada, Y. Zhang, R. Fiedorow, Zeolites 1983, 3,
13 – 21.
[7] J. Weitkamp, S. Ernst, P. A. Jacobs, H. G. Karge, Erdoel Kohle
Erdgas Petrochem. 1986, 39, 13 – 18.
[8] D. E. De Vos, S. Ernst, C. Perego, C. T. OꢀConnor, M. Stꢁcker,
Microporous Mesoporous Mater. 2002, 56, 185 – 192.
[9] J. A. Martens, M. Tielen, P. A. Jacobs, J. Weitkamp, Zeolites
1984, 4, 98 – 107.
[10] J. A. Martens, P. A. Jacobs, Zeolites 1986, 6, 334 – 348.
[11] M. M. Olken, J. M. Garces in Proceedings from the Ninth
International Zeolite Conference, Vol. II (Eds.: R. von Ballmoos,
J. B. Higgins, M. M. J. Treacy), Butterworth-Heinemann, Stone-
ham, 1993, pp. 559 – 566.
Experimental Section
Zeolite SSZ-53 was initially synthesized as borosilicate (B-SSZ-53)
and then converted to the catalytically more active and more stable
aluminosilicate form by post-synthetic treatments. B-SSZ-53 was
synthesized according to a modified procedure derived from the
literature.[1,2] The structure-directing agent required for the synthesis
step (N,N,N-trimethyl-[1-(4-fluorophenyl)cyclopentyl]methylammo-
nium hydroxide was prepared as described previously.[1] In a typical
synthesis, an aqueous solution of the template (concentration:
0.965 molkgÀ1) was diluted with distilled water (15 g) and then
[12] J. Weitkamp, S. Ernst in Guidelines for Mastering the Properties
of Molecular Sieves (Eds.: D. Barthomeuf, E. G. Derouane, W.
Hꢁlderich), Plenum, New York, 1990, pp. 343 – 353.
7306 www.angewandte.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 7304 –7306