Verifying the mechanism of the ethene-to-propene conversion on zeolite H-SSZ-13

Article abstract of DOI:10.1016/j.jcat.2014.03.006

Several types of microporous molecular sieves with similar n _Si/n_Al ratios (except for SAPO-34) and different pore structures were prepared and applied as ethene-to-propene (ETP) catalysts. H-SSZ-13 zeolite consisting of chabazite cages connected via 8-ring windows possessed the highest adsorption capacity for ethene and exhibited the best activity in the ETP conversion. The decreasing amount of Bronsted acid sites after dealumination of H-SSZ-13 caused a prolonged lifetime of the catalyst in the ETP reaction. The reaction mechanism and deactivation behavior of H-SSZ-13 catalysts during the ETP process were investigated by in situ FT-IR, UV/Vis, GC-MS, TGA and ¹H MAS NMR methods. Ethene was rapidly oligomerized and converted into naphthalene-based carbenium ions, playing a significant role in the ETP reaction. The accumulation of these species lead to the formation of polycyclic aromatics, which are responsible for a total blocking of H-SSZ-13 pores, and cause the deactivation of the catalyst.

Full text of DOI:10.1016/j.jcat.2014.03.006

Journal of Catalysis 314 (2014) 10–20
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Verifying the mechanism of the ethene-to-propene conversion on zeolite
H-SSZ-13
a
b,
Weili Dai a, Xiaoming Sun a,b, Bo Tang a, Guangjun Wu a, Landong Li a, , Naijia Guan , Michael Hunger
⇑
⇑
a Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry, Nankai University, Tianjin 300071, PR China
b Institute of Chemical Technology, University of Stuttgart, 70550 Stuttgart, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Several types of microporous molecular sieves with similar nSi/nAl ratios (except for SAPO-34) and differ-
ent pore structures were prepared and applied as ethene-to-propene (ETP) catalysts. H-SSZ-13 zeolite
consisting of chabazite cages connected via 8-ring windows possessed the highest adsorption capacity
for ethene and exhibited the best activity in the ETP conversion. The decreasing amount of Brønsted acid
sites after dealumination of H-SSZ-13 caused a prolonged lifetime of the catalyst in the ETP reaction. The
reaction mechanism and deactivation behavior of H-SSZ-13 catalysts during the ETP process were inves-
tigated by in situ FT-IR, UV/Vis, GC–MS, TGA and 1H MAS NMR methods. Ethene was rapidly oligomerized
and converted into naphthalene-based carbenium ions, playing a significant role in the ETP reaction. The
accumulation of these species lead to the formation of polycyclic aromatics, which are responsible for a
total blocking of H-SSZ-13 pores, and cause the deactivation of the catalyst.
Received 10 January 2014
Revised 10 March 2014
Accepted 11 March 2014
Available online 19 April 2014
Keywords:
SSZ-13
Ethene-to-propene conversion
Framework dealumination
Brønsted acid sites
Ó 2014 Elsevier Inc. All rights reserved.
Naphthalene-based carbenium ions
1. Introduction
and propene selectivity (48%). More recently, Perea et al. [17] dis-
closed that the ethene conversion can be improved to about 80%
The production of propene has received broad attention in
recent years due to the increasing demand for propene derivatives,
especially polypropene [1]. To meet the increasing demand for pro-
pene, several strategies have been proposed for propene produc-
tion, e.g. the dehydrogenation of propane [2], the catalytic
cracking of C4 alkenes to propene [3,4], the metathesis of ethene
and 2-butene [5,6], and the conversion of methanol/ethanol to pro-
pene [7–10]. Recently, the direct conversion of ethene to propene
(ETP) without any addition of other hydrocarbons was proposed
as a new alternative to produce propene. This would be an interest-
ing reaction for the production of propene, particularly when it is
combined with the dehydration of ethanol/bio-ethanol to ethene,
a new alternative route to produce propene from renewable feed-
stock can be opened thereafter.
over Ni/AlMCM-41 with few acid sites, but the selectivity was
nearly not changed. Similar to Ni/AlMCM-41, also Ni/AlMCM-48
[18] was proved to be a good catalyst in the ETP reaction. Basset
and co-workers [19] found that the ETP reaction with high selectiv-
ity to propene (95%) can be obtained over tungsten hydride sup-
ported on
c-alumina, i.e. W(H)3/c-Al2O3, but the ethene
conversion starting with 40% drop to 10% after a time-on-stream
(TOS) of 20 h. In addition, several kinds of microporous molecular
sieves have been studied as possible ETP catalysts [20–24], and the
acidity and the pore structure of molecular sieves were proposed
to be key factors controlling the ETP reaction. SAPO-34, with
chabazite cages connected via 8-ring windows exhibits high selec-
tivity to propene in the ETP reaction, but the aluminosilicate ana-
logue H-SSZ-13 with stronger acidity was scarcely studied in the
ETP conversion. The relationship between acidity, ethene absorp-
tion ability, and ETP activity of microporous molecular sieves is
not clear until now and, therefore, is the goal of the present work.
In addition, the reaction mechanism of the ETP conversion has
been intensively studied in the past years, and a route was
accepted consisting of an ethene dimerization to form butene,
which is involved in a metathesis reaction with another ethene
molecules leading to propene [20,23,25–27]. However, to the best
of our knowledge, the reaction mechanism in the steady state of
the ETP reaction and the deactivation behavior of the catalysts,
The ETP reaction was first observed on olefin metathesis cata-
lysts, e.g. supported molybdenum [11] and tungsten catalysts
[12]. Recently, Iwamoto et al. [13–16] found that the ETP reaction
can be realized over Ni/MCM-41 catalysts prepared via template
ion exchange method, but with lower ethene conversion (68%)
⇑
Corresponding authors. Fax: +86 22 2350 0341 (L. Li). Fax: +49 711 685 64081
(M. Hunger).
E-mail addresses: lild@nankai.edu.cn (L. Li), michael.hunger@itc.uni-stuttgart.de
(M. Hunger).
http://dx.doi.org/10.1016/j.jcat.2014.03.006
0021-9517/Ó 2014 Elsevier Inc. All rights reserved.

W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
11
especially detailed spectroscopic investigations of the above-men-
tioned route of the ETP reaction, are missing until now and are,
therefore, also aims of this work.
atmosphere saturated with the vapor of an aqueous Ca(NO3)2 solu-
tion at ambient temperature.
Deuterated acetonitrile (CD3CN) was used as probe molecule to
measure the acid strength of the catalysts. The measurements were
performed with dehydrated samples by means of 1H MAS NMR
spectroscopy utilizing a Bruker Avance III 400WB spectrometer at
In this study, several types of microporous molecular sieves
with similar nSi/nAl ratios and different pore structures were pre-
pared and applied as ETP catalysts. The ethene adsorption abilities
of these catalysts were studied via dynamic breakthrough mea-
surements, and the ETP catalytic performances of the samples were
evaluated in a fixed-bed reactor. The effects of acid densities on the
catalytic performance were investigated by dealumination and
focused on H-SSZ-13, which exhibits the highest activity in the
ETP conversion. The organic intermediates formed on H-SSZ-13
catalysts during the different states of the ETP reaction were ana-
lyzed by in situ FTIR, ex situ UV/Vis, TGA, and GC–MS methods.
Specifically, the dynamic changes in the Brønsted acid sites and
carbenium ions during the ETP reaction are monitored by 1H
solid-state NMR spectroscopy using ammonia-loaded catalyst
samples. Based on the catalytic and spectroscopic results, the reac-
tion mechanism and the deactivation behavior of H-SSZ-13 cata-
lysts in the ETP reaction are discussed.
the resonance frequency of 400.1 MHz, with p/2 single pulse exci-
tation, the repetition time of 10 s, and the sample spinning rate of
8.0 kHz using a 4.0 mm MAS NMR probe. Before the 1H MAS NMR
studies of the catalysts, these materials were dehydrated at 673 K
in vacuum (pressure below 10À2 Pa) for 10 h. Then, the dehydrated
samples were loaded with 70 mbar acetonitrile-d3 (99.9% deuter-
ated) and, subsequently, evacuated at 298 K for 1 h to eliminate
physisorbed acetonitrile.
The experimental setup used for dynamic breakthrough mea-
surements is shown in Scheme S1. The downstream gas mixture
was monitored using an Omni Star TM mass spectrometer. In a
typical experiment, 0.2 g of the catalyst was treated at 673 K under
flowing He gas (20 mL/min) for 2 h. After the temperature was
decreased to room temperature, the gas flow was switched to an
ethene/helium mixture (ethene: 250 ppm) at the same total flow
rate. The complete breakthrough of ethene was indicated by reach-
ing a downstream gas composition equal to that of the feed gas. A
reference breakthrough experiment was recorded at the same con-
ditions without catalysts.
2. Experimental section
2.1. Preparation of the materials
A series of aluminosilicate zeolites in their Na-form with differ-
ent framework structures (MOR: Na-modenite, BEA: Na-Beta, MFI:
Na-ZSM-5, EUO: Na-EU-1, CHA: Na-SSZ-13) were provided by Sin-
opec, China. Then, the calcined Na-type aluminosilicate samples
were converted to their proton forms by refluxing three times in
0.1 M NH4NO3 solutions for 6 h, followed by drying at 343 K for
12 h and calcination at 873 K for 4 h. The SAPO-34 sample was syn-
thesized by a hydrothermal method using TEAOH (tetraethylam-
monium) as structure-directing agents, and the batch
composition was 1 Al2O3:1 P2O5:0.6 SiO2:0.5 TEAOH:77 H2O
[28,29]. Then, the as-synthesized SAPO-34 was calcined in flowing
synthetic air at 873 K for 4 h, and the parent H-SSZ-13 samples
were dealuminated by treatment in 13.0 M HNO3 solution at
373 K for 20, 40, and 60 h (20 mL gÀ1 zeolite), and named as
2.3. Catalytic studies of the zeolites under study
The ETP reaction was investigated in a fixed-bed reactor at
atmospheric pressure. Typically, 0.2 g of the catalyst (sieve frac-
tion, 0.25–0.5 mm) was placed in a stainless-steel reactor (5 mm
i.d.) and activated under flowing helium gas at 673 K for 1 h. After
the temperature was decreased to the desired reaction tempera-
ture, the reactant, i.e., C2H4, diluted with high purity helium was
introduced to start the reaction. The total flow rate (F) was
20 mL/min, and the partial pressure of C2H4, denoted as p(C2H4),
was 50.0 kPa. The products were analyzed by an on-line chromato-
graph HP5890/II with flame ionization detector (FID) and a packed-
column Porapak Q to separate the hydrocarbons.
deAl-SSZ-13(20),
respectively.
deAl-SSZ-13(40),
and
deAl-SSZ-13(60),
2.4. Characterization of entrapped organic compounds on the used
catalysts
2.2. Characterization of the materials
The nature of the organic compounds formed on the catalyst
during the ETP reaction was in situ monitored by Fourier transform
infrared (FTIR) spectroscopy. FTIR spectra were recorded in the dif-
fuse reflection mode on a Bruker Tensor 27 spectrometer, equipped
with a high sensitivity MCT detector cooled by liquid nitrogen and
an in situ reaction chamber. Prior to the FTIR studies, ca. 20 mg of
the catalyst materials were finely ground and placed in the FTIR
cell. The samples were activated in flowing helium gas at 673 K
for 1 h and a background spectrum was taken. Then, the reactant,
i.e., C2H4, diluted with high purity helium was introduced into
the reaction chamber with a flow rate of 2 mL/min and time-
resolved spectra were recorded with a resolution of 4 cmÀ1 and
an accumulation of 128 scans.
The amounts of entrapped organic compounds over the cata-
lysts after the ETP reactions performed with different time-on-
stream (TOS) were analyzed by thermogravimetric analysis (TGA)
on a Setram Setsys 16/18 thermogravmetric analyzer. In a typical
measurement, 0.1 g of the used catalyst materials were heated in
an Al2O3 crucible with a constant heating rate of 10 K/min and
under flowing synthetic air (30 mL/min).
X-ray diffraction (XRD) patterns of the calcined samples were
recorded on a Bruker D8 diffractometer with Cu K radiation
a
(k = 1.5418 Å) at 5–50° and with a scan rate of 2h = 6.0°/min.
The chemical compositions of the samples were determined by
inductively coupled plasma emission spectrometry (ICP-AES) on a
Thermo IRIS Intrepid II XSP atomic emission spectrometer.
The surface areas and nitrogen adsorption isotherms of the cal-
cined samples were measured by means of nitrogen adsorption at
77 K on a Quantachrome iQ-MP gas adsorption analyzer. Before the
nitrogen adsorption, samples were dehydrated at 473 K for 2 h. The
total surface area was calculated via the Brunauer Emmett Teller
(BET) equation and the microporous pore volume was determined
using the t-plot method.
The solid-state NMR investigations of the catalyst framework
were performed with hydrated samples on a Bruker Avance III
400WB spectrometer at the resonance frequency of 104.3 MHz
for 27Al nuclei. The MAS spectra were recorded upon
p/6 single
pulse excitation, with the repetition time of 0.5 s, and the sample
spinning rate of 8 kHz. To avoid hydrolyses of framework bonds,
the hydration of the samples was performed not longer than one
day before the NMR characterization by exposing them to an
The nature of occluded hydrocarbons in the catalysts after the
ETP reaction with different TOS was analyzed by ultraviolet–visible
spectroscopy
(UV–Vis)
and
gas
chromatography–mass

12
W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
spectrometry (GC–MS). The UV–Vis spectra of the fresh and used
samples (ca. 100 mg) were recorded in air against BaSO4 in the
region of 200–800 nm on a Varian Cary 300 UV–Vis spectropho-
tometer. For GC–MS analysis, typically, 0.1 g of the catalyst sam-
ples obtained after the ETP reaction were carefully dissolved in
1 M HF solution. This solution was treated with CH2Cl2 to extract
the organic compounds and the residual water was removed by
the addition of sufficient sodium sulfate solid. Then, 0.2 lL of the
organic extract was analyzed by GC–MS (GCMS-QP2010 SE) with
a RXI-5MS column (30 m, 0.25 mm i.d., stationary phase thickness
0.25 lm). The following temperature program was employed: Iso-
Brønsted acid sites with similar strengths are present in the alumi-
nosilicate zeolites under study, but a significantly lower acid
strength was observed for the silicoaluminophosphate SAPO-34.
The adsorption of ethene on the catalysts is one of the initial
steps of the ethene conversion and, thus, the adsorption behavior
is a very important property of ETP catalysts. However, the adsorp-
tion of ethene on the catalysts under reaction conditions is difficult
to measure, e.g. due to the fast coke formation. Therefore, low-tem-
perature breakthrough experiments at 298 K were performed to
extrapolate the adsorption of ethene on the catalyst materials.
Fig. 2 shows the breakthrough curves of an ethene/helium mixture
through a column filled with 0.2 g catalyst material at 298 K and
1 atm. For the blank experiment without catalyst, ethene immedi-
ately broke through the column and was monitored by mass spec-
trometry. In the case of catalyst-filled columns, ethene is adsorbed
on the catalysts until it breaks through the column after reaching
saturation. The breakthrough times in Fig. 2 hint to ethene adsorp-
tion capacities according to the sequence H-SSZ-13 (9.5 min) > -
SAPO-34 (7.0 min) > H-ZSM-5 (4.0 min) > H-EU-1 (2.5 min) > H-
Beta (1.5 min) > H-Mor (1.0 min). This sequence indicates that
the ethene adsorption properties of the catalysts under study are
highly influenced by their pore structure. H-SSZ-13 and SAPO-34
with large chabazite cages, directly connected via 8-ring windows,
have much higher adsorption capacities for ethene than H-ZSM-5
and H-EU-1 with medium 10-ring pores as well as H-Beta and H-
Mor with large 12-ring pores.
thermal heating at 313 K for 6 min, heating to 553 K with a rate of
10 K/min, and isothermal heating at 553 K for 10 min.
2.4.1. 1H MAS NMR characterization of surface sites
The Brønsted acid sites of the fresh and used samples were
characterized by means of 1H MAS NMR spectroscopy utilizing a
Bruker Avance III 400WB spectrometer at the resonance frequency
of 400.1 MHz, with p/2 single pulse excitation, the repetition time
of 10 s, and the sample spinning rate of 8.0 kHz using a 4.0 mm
MAS NMR probe. Before the 1H MAS NMR studies of the fresh
HSSZ-13 and deAl-SSZ-13 catalysts, these materials were dehy-
drated at 673 K in vacuum (pressure below 10À2 Pa) for 10 h. Sub-
sequently, the materials were sealed and kept in glass tubes until
their transfer into gas-tight MAS NMR rotors inside a glove box
purged with dry nitrogen gas. The used deAl-SSZ-13 catalysts were
obtained after quenching the ETP reaction and transferring them
into MAS NMR rotors without contact to air. The determination
of the number of accessible Brønsted acid sites was performed
upon adsorption of ammonia at room temperature and by evaluat-
ing the 1H MAS NMR signals caused by ammonium ions (d1H = 6.5–
7.0 ppm). For this purpose, the catalyst samples were loaded with
100 mbar ammonia and, subsequently, evacuated at 453 K for 2 h
to eliminate physisorbed ammonia. Quantitative 1H MAS NMR
measurements were performed by comparing the signal intensities
of the samples under study with the intensity of an external inten-
sity standard (dehydrated zeolite H, Na-Y with the cation exchange
degree of 35%). The decomposition and simulation of NMR spectra
were carried out utilizing the Bruker software WINFIT.
3.2. Investigation of the ETP conversion on the zeolite catalysts under
study
Table 1 gives a summary of the catalytic properties of the zeo-
lites under study characterized by different pore structures and
applied for the direct conversion of C2H4 at 673 K for TOS = 15 min.
The propene selectivity given in column 3 strongly depends on the
pore size of the various zeolite catalysts. Zeolites SAPO-34 and H-
SSZ-13 consisting of large chabazite cages connected via 8-ring
windows exhibit a significantly higher propene selectivity propene
(>59%) and lower butene selectivity (<9%) than zeolites H-EU-1 and
H-ZSM-5 with 10-ring pores as well as zeolites H-Mor and H-Beta
with 12-ring pores. The latter four catalysts exhibit propene selec-
tivities of <45% and butene selectivities of >20%. This finding may
hint to a product shape-selectivity of the zeolites under study since
butene with the larger kinetic diameter compared to propene can
more easily desorb via the 12-ring and 10-ring pores of H-Mor,
H-Beta, H-EU-1, and H-ZSM-5 than via the 8-ring windows of
SAPO-34 and H-SSZ-13. In addition, the sequence of the ethene
conversions over these catalysts is: H-SSZ-13 (82.9%) > SAPO-
3. Results and discussion
3.1. Physicochemical properties of the catalyst materials
Fig. S1 shows the powder XRD patterns of the calcined sample
materials under study. Typical diffraction lines corresponding to
MOR (H-Mor), BEA (H-Beta), EUO (H-EU-1), MFI (H-ZSM-5), and
CHA (HSSZ-13 and SAPO-34) framework structures are observed
[30], indicating that pure phases of these topologies were obtained
for the microporous catalysts under study.
34 > (62.4%) > H-ZSM-5
(57.2%) > H-EU-1
(30.3%) > H-Beta
(9.1%) > H-Mor (2.4%). These results fit well with the results of
breakthrough curves (vide supra), indicating that the ethene
adsorption abilities of the microporous catalysts strongly influence
their activities in the ETP conversion. The aluminosilicate-type H-
SSZ-13 catalyst with 3-dimensional structures and 8-membered
rings, has the strongest ethene adsorption capacity, consequently
exhibits the best activities in the ETP conversion. In order to get
more insight into the ETP reaction, more detailed studies were per-
formed on H-SSZ-13 catalyst.
Due to the low base strength of acetonitrile, the adsorption of
this probe molecule in the deuterated state (CD3CN) on zeolite cat-
alysts allows the discrimination of Brønsted acidic bridging OH
groups with different acid strengths. In this case, the adsorbate-
induced low-field shift
groups is utilized as a measure of the acid strength [31–34]. A
strong low-field shift d1H corresponds to a high acid strength.
D
d1H of the 1H MAS NMR signal of Si(OH)Al
D
The interaction of acetonitrile molecules with the Brønsted acidic
Si(OH)Al groups occurs via an OAHÁ Á ÁN-type hydrogen bonding
[33,34]. Fig. 1 shows the 1H MAS NMR spectra of dehydrated sam-
ples recorded before and after loading with CD3CN. Upon adsorp-
tion of acetonitrile, the signals of accessible Si(OH)Al groups
3.3. Effect of dealumination of H-SSZ-13 on the catalytic performance
Dealumination of the framework by liquid acids is an important
method to modify the catalytic properties of zeolites. Typically, the
removal of Al from the framework results in lower density of
Brønsted acid sites, but also in an enhanced acid strength. In order
to investigate the effects of Brønsted acid sites on the catalytic
(3.6–3.9 ppm) are low-field-shifted by
Dd1H = 6.5, 6.5, 6.5, 6.8,
7.3, and 5.6 ppm for zeolites H-Mor, H-Beta, H-SSZ-13, H-EU-1,
H-ZSM-5, and SAPO-34, respectively. This finding implies that
activities of H-SSZ-13 catalysts,
a
homologous series of

W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
13
Fig. 1. 1H MAS NMR spectra of dehydrated samples recorded before (bottom) and after (top) loading with deuterated acetonitrile (CD3CN).
dealuminated H-SSZ-13 zeolites due to the dealumination proce-
dures were investigated by X-ray diffraction (Fig. S2). The
unchanged diffraction lines clearly reveal that the framework
structure is well preserved after dealumination, which were fur-
ther confirmed by the similar type I adsorption/desorption iso-
therms in nitrogen physisorption for all H-SSZ-13 samples (Fig. S3).
The textural properties of the parent and treated H-SSZ-13 zeo-
lites are given in Table 2. After dealumination for 20 h, i.e. deAl-
SSZ-13(20), the nSi/nAl ratio slightly increased (column 2), while
the number of Brønsted acidic bridging OH groups (Fig. S4 and
Table 2, column 6) and the BET surface area (column 4) decreased.
However, with increasing time of acid treatment from 20 to 60 h,
i.e. deAl-SSZ-13(20) to deAl-SSZ-13(60), the nSi/nAl ratios, numbers
of Brønsted acid sites, and BET surface areas did not change, and
the degree of dealumination kept stable at about 14% (Table 2, last
column), which is also supported by the 27Al MAS NMR spectra in
Fig. S5. Both the spectra of the parent and acid-treated H-SSZ-13
zeolites are dominated by signals of tetrahedrally coordinated
framework Al atoms (58.1 ppm) within the CHA framework, and
only weak signals with similar intensities of few octahedrally coor-
dinated Al species (À2.1 ppm), corresponding to extra-framework
Al species, are present [35]. These results imply that the H-SSZ-
13 catalyst in this study has a high resistance to dealumination
by acid treatment, which agrees with an earlier report on ZSM-5
[36]. Similar to the observed framework dealumination of H-SSZ-
13, the lifetime of the catalyst obviously increased after acid treat-
ment for 20 h, but did not change obviously with the extension of
the acid treatment time from 20 h to 40 and 60 h (see Fig. S6).
In Fig. 3, the time-on-stream dependence of the ethene conver-
sion and product selectivities over the parent and dealuminated H-
SSZ-13 catalysts, determined in a fixed-bed reactor at 673 K, are
shown. The product distribution for deAl-SSZ-13(20) is almost sim-
ilar to that of parent H-SSZ-13. Although parent H-SSZ-13 exhib-
ited sufficient catalytic activity for the ETP conversion, it was
rapidly deactivated, and the lifetime with about 50% yield of pro-
pene was 4 h. This deactivation was probably caused by the large
amount of coke (25.4% weight loss after 12 h of the reaction, see
Fig. S7) formed on the catalyst. In contrast, zeolite deAl-SSZ-
13(20) exhibits a much longer lifetime of 7 h with about 50% yield
1.00
0.75
0.50
0.25
0.00
blank
H-Mor
H-Beta
H-EU-1
H-ZSM-5
SAPO-34
H-SSZ-13
0
10
20
30
40
Time / min
Fig. 2. Breakthrough curves of ethene of the ETP catalysts under study, recorded at
303 K.
Table 1
Ethene conversion and product selectivity during the ETP conversion on different
samplesa.
Catalystb
C2H4
Product selectivity (%)
Conversion (%)
C3H6
C4H8
C1AC3 alkane
others
H-Mor (11.2)
H-Beta (11.4)
H-EU-1 (10.3)
H-ZSM-5 (11.2)
SAPO-34 (0.1)
H-SSZ-13 (8.4)
2.4
9.1
30.3
57.2
61.4
82.9
38.5
43.4
32.3
40.1
68.3
59.5
21.2
20.8
22.3
21.5
7.7
25.8
25.7
26.5
18.3
22.4
27.9
14.5
10.1
18.9
20.1
1.6
9.8
2.8
Reaction conditions: W = 0.20 g, T = 673 K, P(C2H4) = 50.0 kPa, F = 20 cm3 minÀ1
Time on stream, 15 min.
The numbers in parentheses denote the nSi/nAl ratios for aluminosilicates and
the nSi/(nAl + nP + nSi) ratio for SAPO-34, determined by ICP-AES.
,
a
b
dealuminated sample was prepared by changing the time of acid
treatment (see Section 2.1). Possible structural changes in the

14
W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
Table 2
Chemical composition and surface area of the calcined H-SSZ-13 and deAl-SSZ-13 materials under study.
a
a
b
c
d
d
d
Samples
nSi/nAl
nAl (mmol/g)
SBET (m2/g)
Vmicro (cm3/g)
nSi(OH)Al (mmol/g)
nAl(OH) (mmol/g)
nSi(OH) (mmol/g)
DeAl-deg.e (%)
H-SSZ-13
8.4
9.5
9.4
9.5
1.58
1.37
1.36
1.36
823
774
764
746
0.28
0.26
0.25
0.24
1.17
0.96
0.99
0.97
0.40
0.36
0.35
0.38
0.25
0.27
0.28
0.35
-
deAl-SSZ-13(20)
deAl-SSZ-13(40)
deAl-SSZ-13(60)
13.3
13.9
13.9
a
b
c
Determined by ICP-AES.
Determined by N2-absorption.
Micropore volume was estimated by using the t-plot method.
d
e
Determined by 1H MAS NMR.
Calculated by the concentrations of Aluminum (column 3).
100
80
60
40
20
100
80
60
40
20
0
100
Conversion
C3=
C4=
=
=
Conv. of C
Select. to C
2
C1-C3 alkanes
others
3
80
60
40
20
H-SSZ-13
Select. to C1-C3 alkanes
=
Select. to C
4
Others
0
100
0
100
3h
573
623
673
723
=
Select. to C
3
80
60
40
20
80
60
40
20
0
Temperature / K
=
Conv. of C
2
deAl-SSZ-13(20)
Fig. 4. Ethene conversion and product distribution over deAl-SSZ-13(20) at
different temperatures (W = 0.20 g, p(C2H4) = 50.0 kPa, F = 20 mL/min, TOS = 1 h).
finding can be explained by an increasing tendency toward crack-
ing of heavier hydrocarbons to lighter fragments, i.e. ethene and
propene, with increasing reaction temperatures.
Select. to C1-C3 alkanes
=
Fig. 5 shows the change in the ethene conversion and product
distribution as a function of the weight of deAl-SSZ-13(20) applied
in the ETP conversion, which corresponds to a modification of the
contact time. Obviously, the longer contact time in the case of the
higher catalysts weight results in a higher ethene conversion, but
lower propene selectivity. Simultaneously, the selectivity to
C1AC3 alkanes strongly increases. This may be a hint that hydrogen
transfer reactions more easily occur if the main product propene
has longer contact time with active Brønsted acid sites on the
deAl-SSZ-13 catalyst. Consequently, the higher selectivity to
C1AC3 alkanes is expected and also obtained for reaction systems
with higher weight of catalyst.
Under optimum reaction conditions (vide supra), i.e. 0.2 g deAl-
SSZ-13(20) and a reaction temperature of 673 K, the possibility of
regeneration of used deAl-SSZ-13(20) catalysts was investigated
by calcination in synthetic air at 873 K for 4 h. The ethene conver-
sions and product selectivities in Fig. 6 show that the catalytic per-
formance could be well recovered for the regenerated catalysts.
After two reaction/regeneration cycles (Fig. 6, right), the catalytic
performance is the same as that of the fresh material (Fig. 6, left).
This indicates that carbon deposits are mainly responsible for the
deactivation of the deAl-SSZ-13(20) catalysts.
Select. to C
4
Others
0
0
2
4
6
8
10
12
Time-on-stream / h
Fig. 3. Ethene conversion over H-SSZ-13 and deAl-SSZ-13(20) sample (W = 0.20 g,
T = 673 K, p(C2H4) = 50.0 kPa, F = 20 mL/min, TOS = 12 h).
of propene during the ETP conversion, and it also showed a signif-
icantly lower coke formation (19.3% weight loss after 12 h of the
reaction, see Fig. S7). This lower tendency for coke formation is
probably caused by the decreased number of Brønsted acid sites,
indicating that dealuminated H-SSZ-13 is the better ETP catalyst
with prolonged life-time.
3.4. Effects of reaction conditions of the ETP conversion on the deAl-
SSZ-13(20) zeolite
Fig. 4 shows the ethene conversion and product distribution
over deAl-SSZ-13(20) at reaction temperatures of 573–723 K.
Clearly, ethene conversion gradually increases with increasing
reaction temperature up to 673 K, and it starts to decrease for
723 K. Simultaneously, the selectivity to propene gradually
increases, while the selectivities to larger products decrease. This
In order to get detailed information on the reaction mechanism
and the deactivation behavior of the deAl-SSZ-13 catalyst during
the ETP reaction, the nature of the organic deposits responsible
for the catalyst deactivation and the fate of active surface species

W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
15
100
80
60
40
20
0
Conversion
C1- C3 alkanes
others
=
=
C3
C4
0.1
0.2
0.3
0.4
Catalyst weight / g
Fig. 5. Ethene conversion and product distribution over deAl-SSZ-13(20) with different mass weight at 673 K (W = 0.1–0.40 g, p(C2H4) = 50.0 kPa, F = 20 mL/min, TOS = 1 h).
=
=
Ethene conversion
C1-C3 alkane
C3
Others
C4
100
80
60
40
20
0
100
80
60
40
20
0
2nd cycle
1st cycle
Fresh
0
2
4
0
2
4
0
2
4
Time-on-stream / h
Fig. 6. Catalytic properties of generated deAl-H-SSZ-13(20) zeolites used as ETP catalysts at 673 K (W = 0.20 g, p(C2H4) = 50.0 kPa, F = 20 mL/min, TOS = 4 h).
during the catalyst lifetime were investigated via in situ FTIR, ex
situ UV/Vis, TGA, GC–MS, and 1H MAS NMR spectroscopy in further
studies.
negative bands of terminal silanol groups at 3740 cmÀ1 and a neg-
ative shoulder at 3705 cmÀ1 can be observed, indicating interac-
tions between ethene and various types of silanol groups, in
accordance with the earlier studies of Wang et al. [24]. Positive
bands at 1424, 1485 and 3000–3120 cmÀ1 are attributed to CAH
bending vibrations and CAH stretching vibrations of weakly
adsorbed ethene, while bands at 1385 and 1460 cmÀ1 are due to
CAH bending vibrations of CH2 and CH3 groups, respectively, of
reaction products [34]. The latter bands indicate that oligomeriza-
tion of ethene occurs immediately after starting the ETP conversion
[38]. Subsequently, new bands at 1605, 1570, 1502 cmÀ1, and
2860–2930 cmÀ1 appear, which can be explained by skeletal C@C
3.5. In situ FTIR studies of the ETP reaction on deAl-SSZ-13(20)
The in situ FTIR spectra of the species adsorbed and occluded on
deAl-SSZ-13(20) under ETP reaction conditions at 673 K are shown
in Fig. 7 A. The appearance of negative bands at 3605 cmÀ1 after
starting the ethene flow indicates that reactants, such as ethene
or reaction products, gradually cover Brønsted acidic bridging OH
groups (Si(OH)Al) [37]. Simultaneously, the appearance of weak

16
W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
general, two obvious weight losses can be recognized: A low-tem-
perature weight loss, wlt, at <573 K and a high-temperature
weight loss, wht, at >673 K, which are ascribed to desorption of
(A)
D
D
volatile compounds and occluded coke compounds, respectively.
According to Fig. 8, the deAl-SSZ-13(20) samples obtained after
TOS = 0.25 h, 0.5 h, and 1.0 h show a similar low-temperature
2860-2930
60min
weight loss
TOS = 2.0 h, 4.0 h, 8.0 h, and 12 h are characterized by a signifi-
cantly lower weight loss wlt of ca. 3% in this temperature range.
Dwlt of about ca. 5%, while the samples obtained after
D
This finding indicates that much more volatile organic compounds
are formed up to TOS = 1 h compared to TOS P 2.0 h. In the high-
temperature range of 573 to 1073 K, the weight losses are
increased from 2.8% to 19.8% with the progress of the ETP conver-
sion from TOS = 0.25 h to 12 h, indicating the organic compounds
are gradually accumulated on the deAl-SSZ-13(20) catalyst. In
40min
0min
addition, the high-temperature weight loss
deAl-SSZ-13(20) catalyst obtained after TOS = 12 h is only 0.6% lar-
ger than the wht value of the active sample obtained after
TOS = 8 h. This finding indicates that only few coke deposits are
required to cause a significant deactivation of deAl-SSZ-13(20) in
the ETP conversion.
Dwht of the deactivated
4000 3600 3200 2800 1800 1650 1500 1350
Wavenumber / cm-1
D
(B)
Si(OH)Al
Organic species
-1
1605 cm
The nature of organic deposits formed on deAl-SSZ-13(20) dur-
ing the ETP conversion and after TOS = 0.25–12 h was investigated
by ex situ UV/Vis spectroscopy. According to Fig. 9, UV/Vis bands at
220, 276, and 400 nm occur during the initial 0.25 h. With the fur-
ther progress of reaction, the bands at 220 and 276 nm shift to 233
and 288 nm, and additional bands occur at 445–475 nm. Based on
earlier UV/Vis studies of organic compounds on acidic zeolite cat-
alysts [42–49], the band at 220 nm is assigned to UV/Vis sensitive
dienes, while the bands at ca. 276 nm may be due to aromatic spe-
cies or monoenylic carbenium ions [46]. The red shift of these
bands to 233 and 288 nm, respectively, for increasing TOS could
indicate that carbon chain growth or cyclization reactions occur
[47]. Bands at 350–420 nm hint to the formation of dienylic carbe-
nium ions and polycyclic aromatics [45,46,48]. The latter species
formed with two or three condensed aromatic rings occur at wave-
lengths lower than 400 nm, while those formed with four con-
densed aromatic rings occur at wavelengths slightly higher than
400 nm [49]. Broad bands occurring at 445–475 nm may be caused
by trienylic carbenium ions [47]. The concentrations of all organic
species, reflected as the intensities of corresponding UV/Vis bands,
change strongly with the progress of the ETP reaction. Upon
TOS = 1.0 h, the amount of dienes (220–233 nm) decreases, which
fits well with the performance of the low-temperature weight loss
C2= stopped
-1
3605 cm
C2= flow
0
10
20
30
40
50
60
Time-on-stream / min
Fig. 7. In situ FTIR spectra recorded during ethene conversion over deAl-SSZ-13(20)
at 673 K up to TOS = 1 h (A) and intensity of the Si(OH)Al band at 3605 cmÀ1 and the
band of organic deposits at 1605 cm-1 recorded during ethene conversion over
deAl-SSZ-13(20) at 673 K up to TOS = 1 h (B).
vibrations of aromatics and CAH stretching vibrations, respectively
[39–41]. These bands hint to a rapid formation of aromatics during
the ETP conversion on deAl-SSZ-13(20).
D
wlt during the TGA studies (Fig. 8, left). Simultaneously, the
After stopping the ethene flow and starting the purging with
helium, the bands at 1424–1485 and 3000–3120 cmÀ1 due to the
weakly adsorbed ethene disappeared, while the bands at 1605,
1570, 1502, 1460, and 1385 cmÀ1 still remain and keep stable.
Hence, the organic deposits formed during the ETP reaction are
very stable. The intensities of the bands of Brønsted acidic Si(OH)Al
groups at 3605 cmÀ1 and of aromatic species formed during the
ETP conversion at 1605 cmÀ1 are shown in Fig. 7 B. Clearly, the
Brønsted acid sites are gradually covered by ethene or reaction
products upon starting the ethene flow at reaction temperature,
while aromatic species are gradually formed simultaneously. After
stopping the ETP reaction by stopping the ethene flow, the cover-
age of Brønsted acid sites and the number of aromatic species grad-
ually keep stable.
100
3.0%
95
5.0%
2.8%
Δ
wlt
90
85
80
75
3.7%
5.1%
0.25 h
0.5 h
1.0 h
2.0 h
4.0 h
8.0 h
12 h
9.8%
Δ
wht
15.1%
18.7%
3.6. TGA, UV/Vis, and GC–MS analysis of organic deposits on the used
deAl-SSZ-13(20) catalysts
19.3%
1073
473
673
873
For quantifying the organic deposits formed on deAl-SSZ-13(20)
after the ETP conversion for TOS = 0.25–12 h, the weight loss was
determined by TGA in the temperature range of 293 to 1073 K. In
Temperature /K
Fig. 8. TGA curves of used deAl-SSZ-13 catalysts obtained after different TOS.

W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
17
naphthalenes, and anthracene become the dominating organic
compounds. At the same time, a deactivation of the deAl-SSZ-13
catalyst occurs, and the total deactivation can be observed at
TOS = 12 h. This may indicate that polymethyl-isopropylnaphtha-
lenes are the most active organic species in the ETP conversion,
from which propene can be split. Once the catalyst starts the deac-
tivation (TOS = 8.0 h), large coke compounds, e.g. anthracene, are
rapidly formed and block the cages and 8-ring windows of deAl-
SSZ-13(20), also the Brønsted acid sites, and no more poly-
methyl-isopropylnaphthalenes can be formed near the Brønsted
acid sites, resulting in the total deactivation of the catalyst.
12.0 h
8.0 h
4.0 h
2.0 h
1.0 h
0.5 h
0.25 h
fresh
370-410
445-475
288
233
3.7. 1H MAS NMR studies of the fate of Brønsted acid sites and
carbenium species during the ETP reaction
In order to investigate the fate of Brønsted acid sites and carbe-
nium-type organic species on deAl-SSZ-13 samples, the calcined
(TOS = 0 h) and used deAl-SSZ-13(20) samples obtained after
TOS = 0.5–12 h were investigated by 1H MAS NMR spectroscopy
with and without ammonia loading (Fig. 11, left and right, respec-
tively). The 1H MAS NMR spectrum of the calcined (TOS = 0 h)
deAl-SSZ-13(20) (Fig. 11, top, left) is dominated by a signal at
3.7 ppm caused by Brønsted acidic Si(OH)Al groups. Adsorption
of ammonia on accessible Brønsted acid site leads to the formation
of ammonium ions with a 1H MAS NMR signal at 6.1 ppm (Fig. 11,
top, right). After TOS = 0.5 h, strong signals at 1.7–2.2 ppm and 7.4–
9.7 ppm corresponding to hydrogen atoms bound to aliphatic and
aromatic carbon atoms [44], respectively, can be observed in the
1H MAS NMR spectrum. Meanwhile, the intensity of the signal at
3.7 ppm due to Brønsted acid site in deAl-SSZ-13(20) decreases
significantly. After ammonia loading at room temperature, a new
signal caused by the reaction of ammonia with organic deposits
occurs at 4.7 ppm. In a former study of the MTO conversion over
SAPO-34 zeolite, a signal at 5.1 ppm was explained by the forma-
tion of polyalkylphenylammonium ions by the reaction of ammo-
nia with polyalkylbenzenium ions [44]. According to the results
of in situ UV/Vis spectroscopy and GC/MS analysis of organic
deposits (Section 3.5), the aromatic-type carbenium ions formed
during the ETP reaction over deAl-SSZ-13(20) catalyst are probably
polyalkylnaphthalene-based carbenium ions. Upon adsorption of
ammonia, formation of amines occurs at these carbenium species
leading to a new signal at 4.7 ppm due to NH2 groups [50]. Caused
by the much stronger steric constrains of polyalkylnaphthalenes
compared to polyalkylbenzenes in the chabazite cages of HSSZ-
13 and SAPO-34, ammoniated polyalkylnaphthalenes cannot be
stabilized as carbenium ions, but form amines in the used and
ammonia-loaded deAl-SSZ-13(20) catalysts.
220 276
200
300
400
500
600
700
800
Wavenumber / nm
Fig. 9. Ex situ UV/Vis spectra of deAl-SSZ-13 catalysts obtained after different TOS.
amounts of aromatic species (276–288 nm) and polycyclic aromat-
ics (370–410 nm) increase with increasing TOS, which also agrees
very well with the high-temperature weight loss
right).
The chemical composition of the organic deposits occluded in
the used deAl-SSZ-13(20) samples was analyzed by ex situ GC–
MS and the results are shown in Fig. 10. Mainly, organic species
consisting of two or three aromatic rings, such as alkylnaphtha-
lenes and anthracene were detected. Typically, polymethyl-isopro-
pylnaphthalenes are observed as major organic species occluded in
the used catalyst samples obtained up to TOS = 4 h. According to
Fig. 10, the amounts of polymethyl-isopropylnaphthalenes (isopro-
Dwht (Fig. 8,
pylnaphthalenes,
monomethyl-isopropylnaphthalenes,
and
dimethyl-isopropylnaphthalenes) increase with increasing TOS
and reach a maximum at TOS = 4.0 h. Simultaneously, the deAl-
SSZ-13(20) catalyst exhibits a good activity in the ETP reaction
(Fig. 3). After TOS = 8.0 h, the number of polymethyl-isopropyl-
naphthalenes strongly decreases, while naphthalenes, 1-methyl-
12 h
In Fig. 12, the number of accessible bridging OH groups, nSiOHAl
,
8.0 h
and the number of polyalkylnaphthalene-based carbenium ions,
ncarbenium, which react with ammonia to a corresponding amine,
both determined by quantitative 1H MAS NMR spectroscopy, are
plotted as a function of TOS. The number of accessible Si(OH)Al
groups strongly decreases from 0.96 mmol/g for TOS = 0 h to
0.40 mmol/g after TOS = 0.5 h. At the same time (TOS = 0.5 h),
0.45 mmol/g naphthalene-based carbenium ions are formed. After
TOS = 2.0 h, the number of naphthalene-based ions increases to
0.69 mmol/g, while the number of Brønsted acid sites decreases
to 0.14 mmol/g. With the further progress of the reaction, the num-
ber of naphthalene-based ions starts to decrease and decreases to
0.46 mmol/g after TOS = 8.0 h, while the number of accessible
Brønsted acid sites reaches nearly a value of 0 mmol/g. Interest-
ingly, the deAl-SSZ-13(20) catalyst still exhibited an ETP activity
according to an ethene conversion of 40% at TOS = 8.0 h. After deac-
tivation of deAl-SSZ-13(20) at TOS = 12 h, neither accessible
Brønsted acid sites nor naphthalene-based carbenium ions can be
detected by 1H MAS NMR spectroscopy. This observation indicates
4.0 h
2.0 h
X5
1.0 h
C6-C8
0.5 h
X5
X5
0.25 h
10
15
20
25
30
35
40
Retention time / min
Fig. 10. GC–MS chromatograms of the extracts from used deAl-SSZ-13(20) catalysts
obtained after different TOS.

18
W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
1H MAS NMR
+ NH3
0h
0.5 h
1.0 h
+ NH3
+ NH3
+ NH3
+ NH3
2.0 h
4.0 h
+ NH3
+ NH3
8.0 h
12h
15.0
10.0
5.0
0.0
-5.0
15.0
10.0
5.0
0.0
-5.0
δ1Η / ppm
δ1Η / ppm
Fig. 11. 1H MAS NMR spectra of used deAl-SSZ-13(20) catalysts obtained after different TOS and recorded before (left) and after (right) adsorption of ammonia. From top to
bottom, the experimental spectra, the simulated spectra, and the signal components utilized for the simulation are shown.
ble Brønsted acid sites and naphthalene-based carbenium ions
leads to a complete deactivation of the deAl-SSZ-13(20) catalyst.
100
80
60
40
20
0
1.0
0.8
0.6
0.4
0.2
0.0
Conversion
nSiOHAl
ncarbenium
3.8. Reaction mechanism of ETP reaction over SSZ-13
In the present work, a number of complementary methods, such
as TGA, GC–MS, in situ FTIR, ex situ UV/Vis, and 1H MAS NMR spec-
troscopy, gave insights into different aspects of the ethene-to-pro-
pene conversion on dealuminated H-SSZ-13 zeolites including the
deactivation of this catalyst during the ETP reaction.
n
As demonstrated by in situ FTIR spectroscopy, ethene is rapidly
oligomerized and converted to aromatics after starting the conver-
sion at 673 K. With the progress of the ETP conversion, the aromat-
ics are gradually accumulated, and large aromatics with two to
three condensed aromatic rings are rapidly formed, which can be
supported by UV/Vis and GC–MS measurements. Naphthalene-
based carbenium ions, evidenced by quantitative 1H MAS NMR
spectroscopy, play the active reaction intermediates in ETP conver-
sion, to which ethene is added and from which propene are split in
a closed cycle (Scheme 1), similar to the hydrocarbon pool mecha-
nism in the MTO reaction [51–55]. Hence, in contrast to SAPO-34
forming hexylcarbenium ions and/or the 4-methyl-2-pentylcarbe-
nium ions during the induction period of the ETP reaction [23],
these organic species were not observed during the ETP conversion
on H-SSZ-13 catalyst. This finding indicates that hexylcarbenium
n
0
2
4
6
8
10
12
Time-on-stream / h
Fig. 12. Comparison of the ethene conversion and the numbers of Si(OH)Al groups
(nSiOHAl) and carbenium ions (ncarbenium), determined by quantitative 1H MAS NMR
spectroscopy.
that naphthalene-based carbenium ions play a key role as catalyt-
ically active organic compounds during the ETP conversion over
deAl-SSZ-13(20). Therefore, the total consumption of the accessi-

W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
19
Initial-state
Steady-state
Deactivated-state
Scheme 1. Reaction scheme.
ions and/or the 4-methyl-2-pentylcarbenium ions are rapidly con-
verted to larger naphthalene-based carbenium ions on H-SSZ-13.
Since these different catalytic properties of SAPO-34 and HSSZ-13
in the ETP reaction cannot be caused by different steric constrains
(both CHA-type zeolites), the above-mentioned different catalytic
properties may be due to the different strengths of their Brønsted
acid sites. This difference in the acid strength of zeolites SAPO-34
and HSSZ-13 was clearly evidenced by 1H MAS NMR spectroscopy
of the acetonitrile loaded materials (see Section 3.1 and Fig. 1).
Considering the Brønsted acidity as a key property of the H-SSZ-
13 catalyst for its application in the heterogeneously catalyzed ETP
reaction, 1H MAS NMR spectroscopy was applied to investigate the
fate of Brønsted acid sites during ETP conversion process. The num-
ber of accessible Brønsted acid sites of deAl-SSZ-13 strongly
decreased already after a short reaction time of 0.5 h. Interestingly,
already before the total deactivation of the deAl-SSZ-13 catalysts
under study occurred, nearly no accessible Brønsted acid sites
could be detected by 1H MAS NMR spectroscopy. On the other
hand, while the number of accessible Brønsted acid sites
decreased, the number of naphthalene-based carbenium ions
increased during the highly active reaction period of the deAl-
SSZ-13 catalyst. The above-mentioned observation indicates that
naphthalene-based carbenium ions play a key role as catalytically
active intermediates in the ETP conversion over H-SSZ-13. This
statement is supported by the absence of accessible naphthalene-
type carbenium species in the totally deactivated deAl-SSZ-13
catalyst.
sites and species non-accessible for further reactants, which was
demonstrated in our recently published PFG NMR study on ethene
diffusion in SAPO-34 used as MTO catalysts [43]. Compared with
the parent H-SSZ-13 zeolite, the dealuminated H-SSZ-13 (deA-
SSZ-13(20)) catalyst are characterized by a much slower coke for-
mation due to its lower Brønsted acid site density, making this
material an interesting catalyst with prolonged lifetime in the
ETP conversion.
4. Conclusions
In the present work, several types of microporous molecular
sieves with different pore structures were studied as ETP catalysts.
The aluminosilicate H-SSZ-13 catalyst with chabazite cages
directly connected via 8-ring windows and the strongest adsorp-
tion capacity for ethene exhibits the best activity in the ETP con-
version. After dealumination of the parent H-SSZ-13 zeolite,
prolonged lifetime could be obtained over deAl-SSZ-13 applied as
catalyst in the ETP conversion, since the velocity of coke formation
was reduced via decreasing the Brønsted acid site densities.
For elucidating the reaction mechanism and the deactivation
behavior of the deAl-SSZ-13 catalyst, in situ FT-IR, ex situ UV/Vis
spectroscopy, and GC–MS were employed to monitor the forma-
tion and nature of organic deposits during the ETP conversion.
The amounts of organic deposits formed during the ETP process
were determined by TGA. The nature and density of accessible
Brønsted acid sites and active organic species were investigated
as a function of the TOS by 1H MAS NMR spectroscopy. The reaction
mechanism and the deactivation behavior of the deAlH-SSZ-13(20)
catalyst investigated by the above-mentioned methods can be
described as follows:
In addition, because of the high reactivity of the carbenium spe-
cies, a surplus of these species in the SSZ-13 cages and pores is
accompanied with their rapid transformation, such as the forma-
tion of polycyclic aromatics as indicated by UV/Vis spectroscopy
(UV/Vis bands at ca. 400 nm). Finally, these polycyclic aromatics
cause a total blocking of the SSZ-13 pores, which strongly hinders
the diffusion of reaction products and make all catalytically active
(i) After starting the ethene conversion, a rapid oligomerization
occurs (FTIR) leading to the formation of dienes, aromatics,
and polycyclic aromatics (UV/Vis).

20
W. Dai et al. / Journal of Catalysis 314 (2014) 10–20
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these species strongly decrease upon the catalysts deactiva-
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strong decrease in the density of accessible Brønsted acid
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This work was supported by the National Natural Science Foun-
dation of China (21303089), China Postdoctoral Science Founda-
tion, 111 Project (B12015), the Collaborative Innovation Center of
Chemical Science and Engineering (Tianjin) and the Ministry of
Education of China (NCET-11-0251, IRT13022). Furthermore, M.H.
wants to thank for financial support by Deutsche
Forschungsgemeinschaft.
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jcat.2014.03.006.
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