Al-RUB-41: A shape-selective zeolite catalyst from a layered silicate

Article abstract of DOI:10.1039/c0cc03895d

A new zeolite catalyst, Al-RUB-41, was synthesized for the first time. It was tested as a catalyst in methanol amination, and showed a shape-selective performance that results in a highly favorable product distribution. The shape-selective nature was also evidenced by using Pt-Al-RUB-41 as a bifunctional catalyst for decane hydroconversion. With its unique pore architecture and remarkable shape-selective character, Al-RUB-41 presents a significant commercial potential in industrial catalysis.

Full text of DOI:10.1039/c0cc03895d

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Al-RUB-41: a shape-selective zeolite catalyst from a layered silicatew
a
a
b
b
c
d
Bilge Yilmaz,* Ulrich Muller, Bart Tijsebaert, Dirk De Vos, Bin Xie, Feng-Shou Xiao,
¨
g
e
f
f
g
Hermann Gies, Weiping Zhang, Xinhe Bao, Hiroyuki Imai and Takashi Tatsumi
Received 15th September 2010, Accepted 22nd November 2010
DOI: 10.1039/c0cc03895d
A new zeolite catalyst, Al-RUB-41, was synthesized for the first
time. It was tested as a catalyst in methanol amination, and
showed a shape-selective performance that results in a highly
favorable product distribution. The shape-selective nature was
also evidenced by using Pt-Al-RUB-41 as a bifunctional catalyst
for decane hydroconversion. With its unique pore architecture
and remarkable shape-selective character, Al-RUB-41 presents
a significant commercial potential in industrial catalysis.
variety of starting materials. We also demonstrate the use of
this new zeolite as a catalyst in methanol amination, which is
an important test reaction since methylamines are critical
intermediates in chemical industry and are extensively used
4
for the synthesis of fine and specialty chemicals.
In a recent liquid phase separations investigation, all-silica
RUB-41 was shown to possess an intriguing pore architecture,
5
which results in a unique shape-selective character. The two-
dimensional pore system is situated in the interlayer space
formed via topotactic condensation of the RUB-39 layers. The
dimensions of these intersecting 8- and distorted 10-membered
ring channels were determined by structural analysis as
Zeolites represent an important class of heterogeneous catalysts
as they not only offer superior activity with high surface areas,
but also provide shape/size selectivity. As a well-established
family of nanoporous crystalline materials, zeolites are of
paramount importance for the chemical industry, since
shape/size selectivity is a vital consideration for many industrial
2
,3
˚
˚
˚
˚
5.8 A Â 4.1 A and 5.9 A Â 4.1 A, respectively.
In the literature the standard recipe for synthesis of all-silica
RUB-39 takes 21 days at 150 1C using dimethyldipropyl-
ammonium hydroxide as the structure directing agent (SDA).
1
3
catalytic processes. Zeolites with small- and medium-pore
systems (i.e., 8MR and 10MR pore openings) are of great
interest for the chemical industry due to the commercial
potential they present in many processes dealing with molecules
in this size regime. However, in the last couple of decades there
was only limited success in the quest for new framework
topologies with small- and medium-pores. Topotactic transfor-
mation of layered silicates into zeolitic frameworks offers
promise as a prolific strategy for obtaining new framework
Controlled calcination of the resulting product results in the
RUB-41 zeolite. In order to incorporate Al into the frame-
work, we first developed a direct-synthesis recipe, where Al
was introduced into the starting synthesis mixture as an
additional ingredient. After 21 days of crystallization at 150 1C
and subsequent calcination, a zeolite product with RRO
topology could be obtained; however, characterization of the
product revealed that the Al incorporation into the structure
was limited. In order to increase Al incorporation and decrease
crystallization duration —and thus increase productivity— a
new synthesis procedure was developed where RUB-39 seed
crystals were utilized. This seeding approach was first carried
1
topologies. One of the recent zeolite structures discovered via
2
this approach is RUB-41. It is an all-silica zeolite obtained
through the conversion of novel layered silicate RUB-39 into a
three-dimensional zeolitic framework, which was assigned the
3
structure code RRO. Each new zeolite framework has the
out using synthesis mixtures with SiO
/Al O = 200 and
2 2 3
potential to offer unique features that can be beneficial for
industrial applications; however, for applications in catalysis
incorporation of functional T-atoms such as Al is essential. In
this communication we describe the synthesis of Al-RUB-41
for the first time, where Al is introduced into the RRO
framework following various methodologies and using a
SiO /SDA = 2. After 15 days of crystallization at 140 1C
2
and subsequent calcination, Al-RUB-41 was obtained.
Powder X-ray diffraction (XRD) patterns of Al-RUB-39 and
Al-RUB-41 are presented in Fig. 1. Elemental analysis showed
that for this Al-RUB-41 product Si/Al is 120. Nitrogen
adsorption/desorption experiments on Al-RUB-41 showed a
2
À1
3
À1
high surface area (477 m g ) and pore volume (0.36 cm g ),
indicating the presence of an open micropore system
a
BASF SE, Chemicals Research and Engineering, 67056,
Ludwigshafen, Germany. E-mail: bilge.yilmaz@basf.com
Centre for Surface Chemistry and Catalysis, K.U. Leuven, 3001,
Leuven, Belgium
State Key Laboratory of Inorganic Synthesis and Preparative
Chemistry, Jilin University, 130012, Changchun, China
Department of Chemistry, Zhejiang University, 310028, Hangzhou,
China
Institute of Geology, Minerology and Geophysics,
Ruhr-University Bochum, 44780, Bochum, Germany
State Key Laboratory of Catalysis, Dalian Institute of Chemical
Physics, 116023, Dalian, China
Chemical Resources Laboratory, Tokyo Institute of Technology,
226-8503, Yokohama, Japan
(
Fig. S1, ESIw).
By slightly modifying the synthesis mixture composition
b
(
SiO /Al O = 30) with same synthesis procedure, Al-RUB-41
2 2 3
c
product with a higher Al content (Si/Al E 8) could also be
obtained (Fig. S2, ESIw). Characterization of the products
d
2
7
resulting from this seeded-synthesis approach using Al
NMR showed that Al was successfully incorporated into
the framework and is exclusively present as tetrahedrally
coordinated species (Fig. S3, ESIw). However, the crystalli-
zation duration was still considerably long, and therefore
productivity was quite low for this synthesis recipe, especially
considering potential scale-up of production for utilization in
commercial applications. In order to overcome these obstacles
e
f
g
w Electronic supplementary information (ESI) available: Detailed synth-
esis, characterization and catalytic testing procedures, XRD patterns,
27
2
N -isotherms, Al NMR results. See DOI: 10.1039/c0cc03895d
1
812 Chem. Commun., 2011, 47, 1812–1814
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Fig. 1 Powder XRD patterns of Al-RUB-39 and Al-RUB-41
prepared via the direct crystallization route (synthesis mixtures with
2 2 3 2
SiO /Al O = 200 and SiO /SDA = 2).
for industrial realization, a new two-step synthesis recipe was
developed.
In the first step of this two-step procedure the silicate
precursor, which also contains the SDA and the RUB-39 seed
2
crystals (3–5% wt based on SiO ), was prepared. The first
crystallization step was conducted at 150 1C typically for
durations between 12–48 hours. In the second step, the
aluminium precursor was mixed with the silicate precursor
obtained from the first step. The second crystallization step
was performed at temperatures between 140–150 1C and the
duration was between 24–48 hours. Detailed descriptions of
typical synthesis procedures are available as ESIw; Powder
XRD analyses before and after calcination, confirmed Al-RUB-39
and Al-RUB-41 topologies, respectively (Fig, S4, ESIw).
The FE-SEM image of Al-RUB-41 presented in Fig. 2 depicts
the typical platelet morphology observed for RUB-41.
Local order and structural attributes of the new Al-RUB-41
Fig. 3 HR-TEM images (top and bottom-left) and ED pattern
(
bottom-right) of Al-RUB-41 obtained from the topotactic condensa-
tion of Al-RUB-39 prepared via the two-step crystallization route.
zeolite were also investigated using HR-TEM (Fig. 3). These
findings suggest that Al incorporation did not markedly alter
the textural and morphological features of the RRO-type
material.
In Fig. 4 results of the methanol amination reaction on the
H-form of the Al-RUB-41 catalyst obtained from the two-step
crystallization route are presented. These preliminary reaction
tests were performed at 340 1C with a NH /CH OH ratio
3
3
of 2, and demonstrated that the Al-RUB-41 catalyst is highly
active and shape-selective. After one hour methanol conversion
was 83%, and the product selectivities were 49% monomethyl-
amine (MMA), 40% dimethylamine (DMA) and 11% tri-
methylamine (TMA). In methanol amination thermodynamics
favor TMA formation, and under these reaction conditions
the thermodynamic equilibrium results in 20% MMA, 27%
6
DMA and 52% TMA. Using the shape-selective Al-RUB-41
catalyst, a much more favorable product distribution is
obtained since the worldwide demand for MMA and DMA
4
is significantly higher than the TMA demand.
Shape selectivity was also evidenced by using Pt-loaded
Al-RUB-41 (0.5 wt% Pt) as a bifunctional catalyst for
À1
decane hydroconversion (WHSV = 2252 kg s mol
pressure = 4.5 bar, H
,
Fig. 2 FE-SEM image of Al-RUB-41 obtained from the topotactic
condensation of Al-RUB-39 prepared via the two-step crystallization
route.
H
2
2
/decane = 300). A maximum
isomerisation selectivity of 19% was obtained at 230 1C at
This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 1812–1814 1813

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Fig. 4 Synthesis of methylamines at 340 1C with a NH
of 2 on Al-RUB-41 catalyst obtained from the two-step crystallization
route.
3
/CH
3
OH ratio
Fig. 6 Methylnonane distribution at various decane conversion levels
on Al-RUB-41 loaded with 0.5 wt% Pt (Al-RUB-41 obtained from the
two-step crystallization route).
In conclusion, we have synthesized Al-RUB-41 for the first
time. We have also demonstrated the use of this new zeolite as
a catalyst in methanol amination and decane hydroconversion.
It was verified that Al-RUB-41 is a highly active, stable
and shape-selective catalyst. Additional experimental work
on synthesis of methylamines is being performed using
Al-RUB-41 catalysts with varying Si/Al ratios. Incorporation
of other functional T-atoms such as Ga, Zn, B and Ti into the
RUB-41 framework is also being carried out. Findings from
these investigations will be reported in detail elsewhere.
This work was performed under the framework of the
INCOE (International Network of Centers of Excellence)
project coordinated by BASF SE. The authors would like to
thank Prof. Pierre Jacobs and Ir. Mathieu Henry for their help
in hydroconversion experiments.
Fig.
5 Results of hydroconversion of decane experiments on
Al-RUB-41 loaded with 0.5 wt% Pt (Al-RUB-41 obtained from the
two-step crystallization route).
Notes and references
1
2
B. Yilmaz and U. Mu
Y. X. Wang, H. Gies, B. Marler and U. Mueller, Chem. Mater.,
005, 17, 43–49.
Y. X. Wang, H. Gies and J. H. Lin, Chem. Mater., 2007, 19,
4181–4188.
¨
ller, Top. Catal., 2009, 52, 888–895.
8
3% decane conversion (Fig. 5). The methylnonane isomer
distribution gives an insight on the spaciousness of the pore
structure (Fig. 6). If methylnonane formation from decane
2
3
were statistical, one would obtain the following distribution:
7
-MeC 17%, 3-MeC 33%, 4-MeC 33%, 5-MeC 17%. In
4 D. R. Corbin, S. Schwarz and G. C. Sonnichsen, Catal. Today,
997, 37, 71–102.
5
2
9
9
9
9
1
zeolites with smaller cavities and 10-membered ring pores, the
formation of 2-MeC is favored at the expense of especially
- and 5-MeC . The ratio 2-MeC /5-Me-C for ZSM-5 is
B. Tijsebaert, C. Varszegi, H. Gies, F.-S. Xiao, X. Bao, T. Tatsumi,
U. Mueller and D. De Vos, Chem. Commun., 2008, 2480–2482.
A. B. van Gysel and W. Musin, in Ullmann’s Encyclopedia of
Industrial Chemistry, ed. B. Elvers, S. Hawkins and G. Schultz,
VCH, Weinheim, 5th edn., 1990, Vol. A16, p. 535.
9
6
4
9
9
9
between 6.8–9.4, for zeolite Beta between 1.4–2.9 and for
Mordenite 1.8. The ratio for Al-RUB-41 is around 4, clearly
demonstrating the shape-selective properties of this catalyst.
7
J. A. Martens, M. Tielen, P. A. Jacobs and J. Weitkamp, Zeolites,
1984, 4, 98–107.
1
814 Chem. Commun., 2011, 47, 1812–1814
This journal is c The Royal Society of Chemistry 2011