Facile Synthesis, Characterization, and Catalytic Behavior of a Large-Pore Zeolite with the IWV Framework

Article abstract of DOI:10.1002/chem.201504717

Large-pore microporous materials are of great interest to process bulky hydrocarbon and biomass-derived molecules. ITQ-27 (IWV) has a two-dimensional pore system bounded by 12-membered rings (MRS) that lead to internal cross-sections containing 14MRS. Investigations into the catalytic behavior of aluminosilicate (zeolite) materials with this framework structure have been limited until now due to barriers in synthesis. The facile synthesis of aluminosilicate IWV in both hydroxide and fluoride media is reported herein using simple, diquaternary organic structure-directing agents (OSDAs) that are based on tetramethylimidazole. In hydroxide media, a zeolite product with Si/Al=14.8-23.2 is obtained, while in fluoride media an aluminosilicate product with Si/Al up to 82 is synthesized. The material produced in hydroxide media is tested for the hydroisomerization of n-hexane, and results from this test reaction suggest that the effective pore size of zeolites with the IWV framework structure is similar to but slightly larger than that of ZSM-12 (MTW), in fairly good agreement with crystallographic data. Microporous materials: Synthesis of aluminosilicate IWV under industrially relevant conditions has been demonstrated, and the material can be produced in both fluoride and hydroxide media across a wide composition range. The zeolite demonstrates catalytic activity in the hydroisomerization of n-hexane (see figure).

Full text of DOI:10.1002/chem.201504717

DOI: 10.1002/chem.201504717
Full Paper
&
Heterogeneous Catalysis |Hot Paper|
Facile Synthesis, Characterization, and Catalytic Behavior of
a Large-Pore Zeolite with the IWV Framework
[
a]
[b]
[a]
[b]
Joel E. Schmidt, Cong-Yan Chen, Stephen K. Brand, Stacey I. Zones, and
Mark E. Davis*
[
a]
Abstract: Large-pore microporous materials are of great
interest to process bulky hydrocarbon and biomass-derived
molecules. ITQ-27 (IWV) has a two-dimensional pore system
bounded by 12-membered rings (MRs) that lead to internal
cross-sections containing 14 MRs. Investigations into the cat-
alytic behavior of aluminosilicate (zeolite) materials with this
framework structure have been limited until now due to
barriers in synthesis. The facile synthesis of aluminosilicate
IWV in both hydroxide and fluoride media is reported herein
using simple, diquaternary organic structure-directing
agents (OSDAs) that are based on tetramethylimidazole. In
hydroxide media, a zeolite product with Si/Al=14.8–23.2 is
obtained, while in fluoride media an aluminosilicate product
with Si/Al up to 82 is synthesized. The material produced in
hydroxide media is tested for the hydroisomerization of n-
hexane, and results from this test reaction suggest that the
effective pore size of zeolites with the IWV framework struc-
ture is similar to but slightly larger than that of ZSM-12
(MTW), in fairly good agreement with crystallographic data.
Introduction
as further modification by post-synthetic treatments) often
delivers adequate performance in a given application means
that the development of new microporous material frame-
works and compositions is an area of considerable research
Microporous crystalline materials are solids with pores of less
than 2 nm. They are formed from three dimensional networks
of oxide tetrahedra, and offer shape- and size-selective envi-
ronments for catalysis, absorption and ion exchange in materi-
als that often exhibit robust hydrothermal stability. There are
currently over 200 distinct microporous material frameworks
that differ in pore shape, size and dimensionality, presence or
[
4,6–10]
efforts.
Some of the strategies employed in recent years in the
quest for new materials include: new organic structure-direct-
ing agents (OSDAs), the use of fluoride as a mineralizing agent
coupled with low-water syntheses and germanium as a frame-
[1]
[11]
absence of internal cages, and composition. One of the most
important distinctions between frameworks is the size of the
pores, which are defined by the number of tetrahedral
work element.
Among these strategies, the use of new
OSDAs has received a great amount of attention. Although
computational guidance has been used in some limited cases
to predict OSDAs for desired phases a priori, the majority of
(
(
T-atoms) that border them. Pores defined by eight T-atoms
8 MR) are considered small-pore materials, 10 MR are medium
[
12–16]
discoveries are made through serendipity.
OSDAs are gen-
pore materials, and 12 MR are termed large-pore materials. Ma-
terials with large pores are of great interest to process bulky
erally quaternary alkylammonium molecules, though OSDAs
[
7,11,17–20]
[21]
based on phosphonium
and sulfonium chemistry are
[2]
hydrocarbon and biomass-derived molecules. The commer-
cial market for zeolites is dominated by five frameworks, *BEA,
FAU, FER, MFI, and MOR, and of these, three are large-pore ma-
terials (*BEA, FAU, and MOR), and a single large-pore material,
FAU, dominates 95% of the synthetic zeolite market, as it is
also known. Phosphonium OSDAs are especially advantageous
as they do not undergo Hoffman degradation, making their
use under severe crystallization conditions possible. However,
a potential drawback of phosphonium OSDAs is that phospho-
rous remains in the materials after calcination. One of the first,
new microporous materials discovered using phosphonium
OSDAs is ITQ-27 (IWV), that consists of a 2D pore system
[3–5]
used for fluidized catalytic cracking.
Although such market
dominance may seem to imply research stagnation in the field,
the fact that only a single framework and composition (as well
[
17,22]
limited by 12 MRs, but containing internal 14 MRs.
was discovered by using dimethyldiphenylphosphonium
as the OSDA and synthesis composition of
SiO :0.014Al O :0.50Me Ph POH:0.50HF:(3–4.2)H O. The prepa-
ITQ-27
[
a] Dr. J. E. Schmidt, S. K. Brand, Prof. M. E. Davis
Chemical Engineering, California Institute of Technology
Pasadena, CA 91125 (USA)
a
2
2
3
2
2
2
ration was reported to take 59 days to form the product (the
addition of seeds only shortens this by one week). While
a broad compositional range was claimed for ITQ-27 in the
E-mail: mdavis@cheme.caltech.edu
[
b] Dr. C.-Y. Chen, Dr. S. I. Zones
Chevron Energy Technology Company, Richmond, CA 94802 (USA)
[
22]
patent literature , the product was only reported as having
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201504717.
a Si/Al=29.5.
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We have recently been examining the use of diquaternary
OSDAs, and have reported products such as *BEA, CIT-7, CIT-8P,
CIT-10, STF, and STW by using a wide-range of inorganic condi-
intact (Figure 1). The TGA analysis shows a mass loss of
19 wt% (Figure 2), similar to values obtained for other large-
29
pore microporous materials. The Si MAS NMR of the calcined
[
23–25]
tions.
In these publications, we disclosed IWV as a product,
material shows the presence of Si(OSi) environments, as well
4
but did not discuss the material further. Herein, we report the
synthesis and characterization of aluminosilicate IWV across
a broad compositional range in both fluoride and hydroxide
media, as well as titanogermanosilicate IWV in fluoride media.
These materials are made using easily prepared OSDAs. Addi-
tionally, we have characterized IWV and assessed its catalytic
activity for the hydroisomerization of n-hexane.
as Si(OSi) (OAl) environments (Figure 3), which is consistent
3
with an aluminosilicate material.
Results and Discussion
Synthesis and characterization of IWV
Recently, we have demonstrated that tetramethylimidazole-
based diquats of varying linker length are capable of synthesiz-
ing a diverse range of microporous material frameworks in-
cluding 8, 10, and 12 MRs in a variety of pore dimensionalities
and containing cages. We have found many competing
phases, and have primarily used seeding as a method to
reliably synthesize desired frameworks. In addition to *BEA and
MTW, we have found IWV as a third large-pore product.
1
3
2
Figure 1. C liquid NMR of OSDA in D O (lower, methanol added as internal
13
standard), C CPMAS NMR of IWV prepared in hydroxide media (middle,
sample 1), and C CPMAS NMR of IWV prepared in fluoride media (upper).
Herein, screening reactions were run with diquats of varying
linker lengths in both hydroxide and fluoride-mediated synthe-
ses across a wide range of inorganic conditions, and results are
given in Tables S1 and S2, Supporting Information. In our previ-
ous work, we mentioned that IWV was found as a product
under certain conditions, but did not expand on its synthe-
13
[23,24]
sis.
Interestingly, we have found that IWV can be prepared
under both hydroxide- and fluoride-mediated aluminosilicate
reactions, as well as a titanogermanosilicate composition in
fluoride-mediated conditions. Based on the synthesis results in
Table S1 and S2, Supporting Information, the five-carbon
diquat is the most strongly directing towards IWV, but the
framework can also be prepared with the four- and six-carbon
diquats.
Hydroxide-mediated syntheses
In hydroxide-mediated syntheses IWV could be prepared using
a variety of sources of inorganics, both amorphous and crystal-
line, at a gel composition of Si/Al=10-30 (atomic ratio; see the
Experimental Section for an explanation). The characterized
products had Si/Al=14.8–23.2. Although this composition
range appears somewhat narrow, it is significant for several
reasons: 1) It is the first demonstration of aluminosilicate IWV
prepared under hydroxide-mediated conditions (most large-
scale zeolite preparations are conducted in hydroxide media;
thus, this method makes IWV available for realistic production
and testing) and 2) the product Si/Al range is favorable for
producing materials with a sufficient number of acid sites to
demonstrate catalytic activity, but also in a range that can
allow for robust hydrothermal stability.
Figure 2. TGA analysis of IWV prepared in hydroxide media (black, sample 1)
and fluoride media (gray).
Two samples of IWV produced in hydroxide media were se-
lected for further catalytic testing, and additionally character-
27
ized by PXRD, SEM, EDS, nitrogen adsorption, and Al MAS
NMR. The sample designations, inorganic sources, product Si/
Al ratios, and nitrogen micropore volumes are given in Table 1.
The PXRDs of the materials in ammonium form are illustrated
in Figure 4, and show that both samples are pure-phase IWV.
27
The Al MAS NMR spectra of the samples in ammonium form
are given in Figure 5 and both show only tetrahedral (frame-
work) aluminum. The SEM images of the samples are illustrat-
ed in Figure 6. Both samples show a plate-like morphology but
the crystallites of sample 1 are larger than sample 2.
13
With the as-made material prepared in hydroxide media,
C
CPMAS NMR results demonstrate that the organic is occluded
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29
Figure 3. Si NMR of calcined aluminosilicate IWV prepared in hydroxide
media (lower, gel Si/Al=15, product Si/Al=14.8, sample 1) and fluoride
media (upper, gel Si/Al=200, product Si/Al=82).
Table 1. H-IWV samples used for catalytic testing.
Sample
Inorganic
source
Product
Si/Al
Nitrogen micropore volume
[cc/g]
Figure 6. SEM images of 1 (lower) and 2 (upper) in ammonium form.
1
2
CBV720
CBV760
14.8
23.2
0.237
0.193
Fluoride-mediated syntheses
Results of the screening reactions in fluoride media are given
in Table S1. In fluoride media, the five carbon diquat was the
most strongly directing to IWV. It was able to produce alumi-
nosilicate IWV with a product Si/Al as high as 82 (gel Si/Al=
2
00). Additionally, it was also possible to prepare titanogerma-
nosilicate IWV, which is a potential large-pore Lewis acid cata-
lyst. Interestingly, it was necessary to have aluminum or ger-
manium to form IWV, and even with seeds present it was not
possible to prepare pure-silica IWV in fluoride media. The abili-
ty of germanium to help direct towards IWV agrees with the
structure of IWV, as it contains double four rings (d4rs); how-
ever, if the germanium content is too high, STW forms instead.
A representative SEM image of IWV prepared in fluoride media
is shown in Figure 7. As is typical for samples prepared in
fluoride media, the crystal size is larger than that observed
in hydroxide media.
Figure 4. PXRD of sample 1 (lower) and 2 (upper) in ammonium form.
Spectra have been normalized to the highest intensity peak.
19
The F NMR spectrum of the as-made material prepared in
fluoride media is shown in Figure 8 and contains a single reso-
nance at d=À35.5 ppm, consistent with fluoride occluded in
13
d4rs. C CPMAS NMR of the as-made material demonstrates
that the organic is occluded intact (Figure 1) and that the ma-
terial was not prepared from a decomposition product. The
TGA analysis shows a mass loss of 19 wt%, similar to values
29
obtained for other large-pore materials (Figure 2). The Si MAS
4
NMR of the calcined material shows the presence of Q ,
3
Si(OSi) , environments as well as Q , Si(OSi) (OAl), environments
4
3
(
Figure 3), which is consistent with an aluminosilicate zeolite.
The fluoride-mediated reactions show a novel method to
prepare high-silica IWV as well as Lewis acidic IWV. However, as
these samples are prepared in fluoride media, making them
27
Figure 5. Al MAS NMR of 1 (lower) and 2 (upper) in ammonium form.
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selectivity to hydroisomerization products increase initially,
proceed to a maximum, and then decrease. The distribution of
the C isomers reveals how the hydroisomerization proceeds
6
versus temperature. n-Hexane is isomerized only to 2- and 3-
methylpentane at low temperatures. As the temperature in-
creases, 2- and 3-methylpentane are further isomerized to 2,2-
and 2,3-dimethylbutane toward the thermodynamic equilibri-
um. The cracking products, although the yield and selectivity
are fairly low, consist predominantly of propane because the
formation of methane and pentanes, as well as ethane and bu-
tanes, involves primary carbenium ions and are energetically
less favorable than the formation of propane.
When comparing the shape selectivities of these zeolites in
a catalytic test reaction, it is always important to refer the cata-
lytic properties to a certain reaction parameter at the same or
similar value level. We found that the distributions of the
branched isomers of n-hexane at the maximum isomer yields
Figure 7. SEM image of calcined IWV prepared in fluoride media from gel.
Si/Al=200.
(
in contrast to e.g., 10 or 20 mol% conversion of n-hexane)
provide a very useful platform for correlating the shape selec-
tive properties of n-hexane hydroisomerization with the effec-
[
26,27]
tive pore/channel structures of zeolites.
Therefore, such re-
sults from ITQ-27 and some selected zeolites are summarized
in Table 2, together with the thermodynamic equilibrium
distributions of isomers calculated according to reference [28].
Zeolite Y, beta, and mordenite are the representatives of
1
2 MR zeolites with wide pore/channel openings and behave
similarly in n-hexane hydroisomerization. The effective pore/
channel sizes do not appear to have spatial restrictions to the
formation of the two relatively bulky dibranched isomers, 2,2-
and 2,3-dimethylbutane, leading to a yield ratio of 2,2- to 2,3-
dimethylbutane of roughly 2:1 at their maximum isomer
yields, while the yield ratio of dibranched isomers (2,2- and
1
9
Figure 8. F NMR of as-made IWV prepared in fluoride media.
difficult to scale up, they were not selected for further charac-
terization.
2
3
,3-dimethylbutane) to the monobranched isomers (2- and
-methylpentane) is approximately 0.5:1.
Hydroisomerization of n-hexane
ZSM-12 (MTW) is a one-dimensional, 12 MR zeolite with
The hydroisomerization of n-hexane was selected as a test re-
action to probe the effective pore-size of the materials. As de-
scribed in references [26,27], n-hexane cracks only slowly
under the conditions applied in this work by secondary carbe-
nium ions due to its short carbon–carbon chain, leading to
a high selectivity to hydroisomerization of n-hexane (kinetic di-
ameter: 4.3 Š) to form only four paraffinic isomers of different
molecular sizes, that is, 2-methylpentane (5.0 Š), 3-methylpen-
tane (5.0 Š), 2,2-dimethylbutane (6.2 Š), and 2,3-dimethylbu-
tane (5.8 Š). This provides a relatively simple case for studying
the shape-selective properties of zeolites that have effective
pore sizes close to the molecular kinetic dimensions of these
C6 isomers. The results from n-hexane hydroisomerization over
two ITQ-27 samples (1 and 2) loaded with 0.27 wt.% Pd are
shown in Figure 9 and compared to those of other zeolites in
Table 2.
a fairly narrow ring opening. Its yield ratio of 2,2- to 2,3-dime-
thylbutane is 1.7:1 and the yield ratio of dibranched isomers
(2,2- and 2,3-dimethylbutane) to the monobranched isomers
(2- and 3-methylpentane) is ~0.35:1 at the maximum isomer
yield, in good correlation with its effective pore size, which lies
between those of the 10 MR zeolite ZSM-5 and 12 MR zeolites
Y, beta and mordenite. In contrast to these large-pore zeolites,
the formation of the bulky 2,2- and 2,3-dimethylbutane is
essentially hindered by the narrow pores in the 10 MR zeolite
ZSM-5.
The two ITQ-27 catalysts show very similar results in spite of
the difference in reaction temperature. The curves depicted in
Figure 9 essentially overlap with each other when shifting the
curves of the lower Si/Al ITQ-27 by ~58C toward the higher
temperature region. Since these two ITQ-27 materials have
similar crystal morphology and size, this temperature differ-
ence is most likely attributed to the difference in acidity that is
associated with their different Si/Al ratios. At the maximum
isomer yield of ~75.5 mol%, the yield ratio of 2,2- to 2,3-
dimethylbutane for ITQ-27 is ~1.7:1 and the yield ratio of
dibranched isomers (2,2- and 2,3-dimethylbutane) to the
monobranched isomers (2- and 3-methylpentane) is ~0.4:1.
The conversion of n-hexane increases with the increasing
reaction temperature. At low temperatures, hydroisomerization
is the only reaction. When the reaction temperature increases,
the hydrocracking reaction takes off and its yield and
selectivity go up progressively. With the competing cracking
reaction occurring, as the temperature increases, the yield and
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Figure 9. Hydroisomerization of n-hexane over Pd/H-ITQ-27 with Si/Al=14.8 (sample 1, top) and Pd/H-ITQ-27 with Si/Al=23.2 (sample 2, bottom) at
À1
1
70–3008C, 1480 kPa, 1.0 h LHSV and 6:1 H
2
/n-hexane.
The results obtained from this catalytic test reaction suggest
that the effective pore size of ITQ-27 is similar to but slightly
larger than that of ZSM-12, in fairly good agreement with the
crystallographic data.
pore size of ITQ-27 is similar to but slightly larger than that of
ZSM-12, in fairly good agreement with the crystallographic
data. IWV materials can also be produced in fluoride media, as
an aluminosilicate with Si/Al up to 82, and as a titanogermano-
silicate material.
Conclusion
The facile synthesis of aluminosilicate IWV (ITQ-27) in both
hydroxide and fluoride media has been demonstrated using
simple, diquaternary OSDAs based on tetramethylimidazole. In
hydroxide media, a product with Si/Al=14.8–23.2 was found,
and all the aluminum was in framework (tetrahedral) positions.
The materials showed good microporosity. The solids produced
in hydroxide media were tested for the hydroisomerization of
n-hexane, and this test reaction suggests that the effective
Experimental Section
OSDA synthesis: The diquaternary imidazolium OSDAs used in this
work were synthesized by reacting 1,2,4,5-tetramethylimidazole
(
200 mmol; TCI Chemicals) with dibromoalkane (100 mmol) (all
from Aldrich) at reflux in methanol overnight. The solvent was
then removed using rotary evaporation and the product washed
with ether. The products were verified using C NMR in D O with
13
2
methanol added as an internal standard. Carbon NMR shifts are
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given in Table 3. The OSDAs were
then converted from bromide to hy-
droxide form using Dowex Maratho-
n A hydroxide exchange resin and
then titrated to determine final con-
centration using
a Mettler–Toledo
DL22 autotitrator with 0.01m HCl as
the titrant.
Microporous material synthesis: A general synthesis procedure
for the microporous materials can be found below. In all situations
the samples were spun at 43 rpm in a rotating oven. For all micro-
porous material syntheses, aliquots of the material were taken peri-
odically (generally every 3—4 days) by first quenching the reactor
in water and then removing enough material for PXRD. Syntheses
were considered to be finished when a crystalline product was ob-
served via PXRD and the broad peak indicative of amorphous ma-
terial, between 20 and 308 2q, had disappeared. If incomplete crys-
tallization or no crystalline product was observed in PXRD, the syn-
theses were replaced in the oven.
In this work all atomic ratios are on an atom basis, thus all compo-
sitions are given in terms of Si/Al ratios. In zeolite publications,
both Si/Al ratio and silica to alumina ratio (SAR, SiO /Al O ) are
2
2
3
used; the SAR numerical value is twice the Si/Al ratio.
Fluoride-mediated reactions: A general procedure for a fluoride-
mediated synthesis was as follows. Tetraethylorthosilicate (TEOS)
and aluminum isopropoxide (if necessary) were added to the
OSDA in its hydroxide form in a Teflon Parr reactor liner. The con-
tainer was closed and stirred for at least 12 h to allow for complete
hydrolysis. The lid was then removed and the alcohol and an ap-
propriate amount of water were allowed to evaporate under
a stream of air. The composition was monitored gravimetrically.
Additional water was added as necessary, and then aqueous HF
(
Aldrich) was added and the mixture was stirred by hand until a ho-
mogenous gel was obtained. (Caution: Use appropriate personal
protective equipment, ventilation and other safety measures when
working with HF.) The final molar ratios of the gel were:
(
1Àx)SiO :xAl:0.5ROH:0.5HF:yH O. The parameters x and y were
2
2
varied depending on the synthesis and the desired composition
and can be found in Table S1, Supporting Information. For low-
water syntheses, a final evaporation step was used after the addi-
tion of HF to reach the desired water ratio. The Teflon-lined Parr re-
actor was sealed and placed in a rotating oven at 160 or 1758C.
Complete results are given in Table S1, Supporting Information.
The titanogermanosilicate material was prepared using germani-
um(IV) ethoxide and titanium(IV) butoxide.
Hydroxide-mediated reactions: For the hydroxide syntheses, sev-
eral variations on gel Si/Al as well as the sources of silica and alu-
mina were used. Specific synthesis preparations are reported
below. For all hydroxide-mediated reactions, seeds were added
after 1 day at reaction temperature, once a decrease in pH was ob-
served. Normally seeds were added as a homogeneous aliquot of
the contents of a previous, completed reaction (less than 0.3 mL)
as these were found to be more active than seeds that had been
washed. Aliquots were taken periodically, and crystallization was
monitored by both PXRD and pH, as an increase in pH was gener-
ally observed when the product crystallized. After the product crys-
tallized, the material was washed with DI water and then collected
by centrifugation. This process was repeated at least three times,
and a final wash was performed using acetone. The product was
dried at 1008C in air.
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13
Table 3. C NMR shifts for the diquats used in this work.
1
3
Dibromoalkane
2
CNMR shifts (D O)
1
1
1
1
1
,4-dibromobutane
,5-dibromopentane
,6-dibromohexane
,8-dibromooctane
,10-dibromodecane
7.56, 9.35, 21.21, 25.88, 30.17, 44.14, 124.60, 126.00, 141.89
7.76, 7.82, 9.61, 22.82, 28.58, 31.42, 44.72, 124.84, 126.03, 141.95
7.88, 7.95, 9.72, 25.42, 28.88, 31.51, 44.97, 124.96, 126.08, 142.01
7.55, 7.59, 9.30, 25.46, 28.10, 28.76, 31.10, 44.83, 124.67, 125.70, 141.70
7.66, 7.71, 9.45, 25.55, 28.21, 28.41, 28.83, 31.22, 44.92, 124.71, 125.73, 141.73
Sodium aluminate and Ludox AS-40 as an alumina and silica source:
The OSDA in its hydroxide form, sodium hydroxide (if necessary),
any necessary water, and sodium aluminate (Pfaltz & Bauer) were
combined in a Teflon Parr reactor liner and stirred until the sodium
aluminate completely dissolved. Ludox AS-40 (Aldrich) was then
added and stirred until a homogenous gel was obtained. The gel
pH was measured, and then the Teflon-lined Parr reactor was
placed in a rotating oven at 1608C. Molar ratios used are given in
Table S2, Supporting Information.
termined from nitrogen adsorption measurements using a Micro-
meritics Tristar 3000. All samples were heated at 4008C in nitrogen
for 24 h and then degassed for 0.5 h prior to measurement. SEM
images were acquired on a ZEISS 1550 VP FESEM, equipped with
in-lens SE. EDS spectra were acquired with an Oxford X-Max SDD
X-ray Energy Dispersive Spectrometer system.
Hydroisomerization of n-hexane: The hydroisomerization of n-
hexane was used as a catalytic test reaction to investigate the cata-
lytic properties of ITQ-27. Each NH -ITQ-27 sample was loaded with
4
0
0
.27 wt.% Pd via ion exchange. The 24–42 Tyler mesh (0.35–
.71 mm) particles of the calcined catalysts were used for the cata-
CBV720 as an alumina and silica source: OSDA in its hydroxide
form (3 mmol) was mixed with 1m NaOH (1 g) and water was
added to bring the total mass to 7 g. Then, CBV 720 HY (Zeolyst,
Si/Al=15) (1 g) was added. The solution was heated at 1758C in
a rotating oven.
lytic experiments. The reactions were carried out in a flow-type
fixed bed reactor with pure n-hexane as a feed at temperatures be-
tween 170 and 3108C, pressure of 1480 kPa, LHSV (Liquid Hourly
À1
Space Velocity) of 1 h and molar H2 to n-hexane ratio of 6:1.
More details about the catalyst preparations and pretreatment and
[
26,27]
catalytic testing are described in our previous publications.
CBV760 as an alumina and silica source: OSDA in its hydroxide
form (3 mmol) was mixed with 1m NaOH (1 g) and water was
added to bring the total mass to 7 g. Then, CBV760 HY (Zeolyst,
Si/Al=30) (1 g) was added. The solution was heated at 1758C in
a rotating oven.
Each experiment was started at 1708C and the reaction tempera-
ture was then incrementally increased by 5.68C (=108F) toward an
end temperature of up to 3108C. At least five data points for each
temperature were collected to make sure that the results were
reproducible and the catalyst was stable. The products were ana-
lyzed by online GC every hour. Each GC analysis took ~45 min to
Calcination and ammonium exchange: All products were calcined
in breathing grade air. The material was heated to 1508C at
be sure that all the peaks (C –C cracking products as well as 2,2-
1 5
À1
À1
1
8Cmin , held for 3 h, then heated to 5808C at 18Cmin and
dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, 3-methyl-
pentane, and n-hexane) were well separated in GC analysis. In ad-
dition, we also ran the experiment at the maximum isomer yield
overnight, which is the best way to confirm the catalyst stability.
held for 6 h to assure complete combustion of the organic materi-
al. After calcinations, the materials produced in hydroxide media
were exchanged to ammonium form using 1m NH NO (100 mL of
4
3
solution per gram of catalyst) at 958C with stirring for 3 h, this was
done a total of three times per sample. After ammonium exchange
the materials were washed with water and dried in air at 1008C. Acknowledgements
Characterization: PXRD patterns were collected using a Rigaku
We would like to thank Chevron Energy Technology Company
Miniflex II diffractometer and Cu -radiation. Liquid NMR spectra
Ka
for providing funding for this work. J.E.S. would like to thank
the NDSEG for their support through a fellowship. We would
like to thank Dr. S. Hwang (Caltech) for his assistance with
NMR data collection.
1
3
19
27
29
were recorded with a 500 MHz spectrometer. C, F, Al, and Si
solid-state NMR were performed using a Bruker DSX-500 spectrom-
eter (11.7 T) and a Bruker 4 mm MAS probe. The spectral operating
frequencies were 500.2, 125.721, 470.7, 130.287, and 99.325 MHz
1
13
19
27
29
for H, C, F, Al, and Si nuclei, respectively. Spectra were refer-
enced to external standards as follows: tetramethylsilane (TMS) for
Keywords: heterogeneous catalysis · hydrothermal synthesis ·
isomerization · microporous materials · zeolites
1
29
13
H and Si, adamantane for C as a secondary external standard
1
9
relative to tetramethylsilane, CFCl for F and 1.0m Al(NO ) aque-
3
3 3
19
2
7
1
ous solution for Al. Samples were spun at 14 kHz for H, F, and
27
13
29
Al MAS NMR and 8 kHz for C and Si MAS and CPMAS NMR ex-
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Received: November 23, 2015
Published online on February 2, 2016
Chem. Eur. J. 2016, 22, 4022 – 4029
www.chemeurj.org
4029
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim