A shaped binderless ZSM-11 zeolite catalyst for direct amination of isobutene to tert-butylamine

Article abstract of DOI:10.1016/S1872-2067(17)62756-6

A shaped binderless and two binder-containing ZSM-11 zeolite catalysts were prepared and characterized by powder X-ray diffraction, N₂adsorption-desorption, and pyridine adsorption-infrared measurements. The binderless catalyst was synthesized using a dry-gel conversion technique, in which 1,6-hexanediamine and tetrabutylammonium bromide were used as structure-directing agents and no other alkaline materials were added. The catalytic performance of the zeolites in the direct amination of isobutene to tert-butylamine was evaluated in a fixed-bed reactor. By virtue of its high crystallinity as well as its good mechanical strength, the shaped binderless ZSM-11 catalyst showed a higher rate of formation of tert-butylamine than did the binder-containing catalysts.

Full text of DOI:10.1016/S1872-2067(17)62756-6

Chinese Journal of Catalysis 38 (2017) 168–175
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
A shaped binderless ZSM‐11 zeolite catalyst for direct amination of
isobutene to tert‐butylamine
Wanshuo Zhang a,b,†, Shangyao Gao b,c,†, Sujuan Xie b, Hui Liu b,d, Xiangxue Zhu b, Yongchen Shang a,*,
Shenglin Liu b,#, Longya Xu b, Ye Zhang e
a College of Chemistry and Chemical Engineering, Harbin Normal University, Harbin 150025, Heilongjiang, China
b Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China
c University of Chinese Academy of Sciences, Beijing 100049, China
d Research and Development Center, Sinochem Quanzhou Petrochemical Co., Ltd., Quanzhou 362103, Fujian, China
e PetroChina Fushun Petrochemical Company, Fushun 113008, Liaoning, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A shaped binderless and two binder‐containing ZSM‐11 zeolite catalysts were prepared and char‐
acterized by powder X‐ray diffraction, N2 adsorption‐desorption, and pyridine adsorption‐infrared
measurements. The binderless catalyst was synthesized using a dry‐gel conversion technique, in
which 1,6‐hexanediamine and tetrabutylammonium bromide were used as structure‐directing
agents and no other alkaline materials were added. The catalytic performance of the zeolites in the
direct amination of isobutene to tert‐butylamine was evaluated in a fixed‐bed reactor. By virtue of
its high crystallinity as well as its good mechanical strength, the shaped binderless ZSM‐11 catalyst
showed a higher rate of formation of tert‐butylamine than did the binder‐containing catalysts.
© 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 20 October 2016
Accepted 22 November 2016
Published 5 January 2017
Keywords:
Binderless zeolite
ZSM‐11
Amination
Isobutene
Published by Elsevier B.V. All rights reserved.
Tert‐butylamine
1. Introduction
the case of the direct amination of isobutene, we found that
ZSM‐11 showed slightly higher activity than ZSM‐5 when using
Tert‐butylamine is an important raw material and pharma‐
ceutical intermediate, and the direct amination of isobutene
over zeolite catalysts to give tert‐butylamine has been reported
to be an environmentally benign and economical process. MFI
and BEA have been found to be superior to other materials
[1,2]. Zeolites ZSM‐5 and ZSM‐11 have similar framework den‐
sities and pore sizes, but differences in their channels result in
a higher selectivity for aromatics in the aromatization of
1‐hexene over ZSM‐11 compared with that over ZSM‐5 [3]. In
similar crystal size, SiO2/Al2O3 molar ratio and acidity.
Zeolites synthesized by conventional techniques are usually
obtained in powder form. However, for practical applications,
the zeolite powder should be formed into catalyst particles
with a certain shape, size, and mechanical strength by using
inert materials as binders [4]. Unfortunately, this causes the
reduction of the active zeolite component and blocks part of the
channel windows in the formed catalysts, which consequently
results in a considerable reduction in the catalytic performance
* Corresponding author. Tel: +86‐13936570503; E‐mail: yongchenshang@163.com
# Corresponding author. Tel: +86‐411‐84379968; E‐mail: slliu@dicp.ac.cn
† These authors contributed equally to this work.
This work was supported by K.C.Wong Education Foundation, Hong Kong (201611), and Youth Innovation Promotion Association, CAS (20120155).
DOI: 10.1016/S1872‐2067(17)62756‐6 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 38, No. 1, January 2017

Wanshuo Zhang et al. / Chinese Journal of Catalysis 38 (2017) 168–175
169
of the zeolites [5]. It would therefore be interesting to prepare a
mechanically stable and self‐supporting zeolite catalyst, in
which the active components are protected, namely, a binder‐
less zeolite catalyst [6].
All three samples (S1, S2, and S3) were converted to the
protonic form by conventional ion exchange in aqueous
NH4NO3 solution [14], followed by calcination (550 °C, 4 h, air).
The resultant samples were denoted Cat‐A, Cat‐B, and Cat‐C,
respectively.
Self‐bonded ZSM‐5 pellets are readily prepared at 170 °C
under hydrothermal conditions from a gel with the following
composition: a Li2O : b Na2O : 2b TPABr : b A12O3 : 150 SiO2:
490 H2O, with 8 ≤ a ≤ 9 and 14 ≤ b ≤ 16 (TPABr = tetraprop‐
ylammonium bromide). If the Li2O is replaced with Na2O or
K2O, only nonpelleted, powdered ZSM‐5 samples can be pre‐
pared, which underlines the role of the LiAlO2 binder in the
system [7]. Recently, shaped binderless ZSM‐5 zeolites have
been prepared from aluminosilicate extrudates using a dry‐gel
conversion (DGC) technique, in which the introduction of
amines into the steam favored the formation of nanosized
ZSM‐5 zeolite. Of particular note, the morphology of these alu‐
minosilicate extrudates was retained in the crystallization pro‐
cess [8]. Self‐bonded pellets of ZSM‐11 with high mechanical
resistance could also be obtained from initial gels with a com‐
position of 1 Li2O : (3.25–7.5) Na2O : (3.25–7.5) Al2O3 : 150 SiO2
: (0.65–1.5) TBABr : 490 H2O [9].
TPABr [10], tetrabutylammonium bromide (TBABr) [11]
and 1,6‐hexanediamine (HDA) [12] are suitable structure di‐
recting agents (SDAs) for the synthesis of ZSM‐5, ZSM‐11, and
ZSM‐5/ZSM‐11, respectively. However, ZSM‐11 synthesized
using TBABr and HDA as co‐SDAs has not yet been reported.
Here, a shaped binderless ZSM‐11 catalyst was prepared using
the DGC method, using TBABr and HDA as co‐SDAs in the syn‐
thesis and without adding other alkaline materials. The ob‐
tained sample was then employed for the direct amination of
isobutene. In addition, the performance of the binderless and
binder‐containing ZSM‐11 catalysts (HZSM‐11+Al2O3 and
HZSM‐11+SiO2) in the amination reaction was compared.
2.2. Characterization
The samples were characterized by powder X‐ray diffrac‐
tion (XRD), N2 adsorption‐desorption, temperature‐pro‐
grammed desorption of NH3 (NH3‐TPD), infrared spectrascopy
of adsorbed pyridine (Py‐IR), high‐resolution transmission
electron microscopy (HRTEM) and nuclear magnetic resonance
(NMR) techniques as described elsewhere [15]. The side‐pres‐
sure strength of the samples was tested using a ZQJ‐II intelli‐
gent particle strength tester.
2.3. Reaction
The direct amination of isobutene to tert‐butylamine was
carried out in a stainless‐steel fixed‐bed reactor and the mode
of operation was down‐flow. All the samples were pressed,
crushed, and sieved to give a particle size of 0.38–0.85 mm
before they were loaded into the reactor. Initially, 5 g of the
catalyst was loaded into the center of the reactor and pretreat‐
ed at 500 °C for 1 h in N2. The reactor was cooled to 250 °C, and
then liquid NH3 was pumped in from the top to fully fill the
reactor before isobutene was introduced. Ma et al. [16,17] have
reported that this feeding sequence is favorable for the reac‐
tion. After 2 h, it was confirmed that the NH3/i‐C4H8 molar ratio
remained stable at 4:1 by measuring the concentrations of the
educts, and the products were analyzed on‐line with an Agilent
7980B gas chromatograph equipped with a flame ionization
detector (FID) and a PONA capillary column.
2. Experimental
The isobutene conversion (Cisobutene), tert‐butylamine selec‐
tivity (Stert‐butylamine) and formation rate of tert‐butylamine (Vfor‐
mation) were calculated according to the following equations:
2.1. Preparation
xtert‐butylamine + xC
8
(1)
Cisobutene
=
× 100%
xisobutene + xtert‐butylamine + xC
Na‐ZSM‐11 zeolite powder with a framework SiO2/Al2O3
molar ratio of 61.6, and containing 2.33 wt% Na2O and 10.4
wt% TBABr was synthesized by following a previously report‐
ed procedure [3]. The powder was mixed with silica sol (SiO2:
30 wt%, Na2O: 0.31 wt%) to form a cylindrical extrudate that
was 1.8–2.2 mm in diameter and 3–7 mm in length. The dried
sample containing 30 wt% of silica was denoted S1. For com‐
parison, S2, which contained 30 wt% of alumina, was prepared
by using boehmite instead of silica sol as the binder.
S1 was recrystallized using the DGC method. First, 4 g S1
was placed in a stainless‐steel tube fixed and supported in a
horizontal position in a stainless‐steel autoclave with a Teflon
lining. Then 1.2 g HDA and 4 mL deionized water were poured
into the bottom of the Teflon‐lined autoclave taking care that
the solid sample did not come into direct contact with the liq‐
uid [13]. The autoclave was heated at 175 °C for 10.5 h, and
then cooled to room temperature. The solid sample was dried
at 120 °C for 2 h and then calcined in air at 540 °C for 5 h. This
sample was denoted S3.
8
xtert‐butylamine
(2)
Stert‐butylamine
=
× 100%
xtert‐butylamine + xC
8
ꢀꢁisobutene ꢂ Cisobutene ꢂ Stert‐butylamine
Vformation
=
× 106
(3)
ꢃcat
where xtert‐butylamine is the molar percentage of tert‐butylamine in
the products, xC8 is the molar percentage of C8 hydrocarbons in
the products, xisobutene is the molar percentage of isobutene in
the products, FM isobutene is the molar flow rate of isobutene
(µmol/h), and mcat is the mass of the catalyst (g).
3. Results and discussion
3.1. Synthesis of binderless ZSM‐11 zeolite catalyst
First, two binder‐containing ZSM‐11 samples (Cat‐A and
Cat‐B) were prepared, and their XRD patterns are shown in Fig.
1. The relative crystallinity (RC) of the sample was calculated

170
Wanshuo Zhang et al. / Chinese Journal of Catalysis 38 (2017) 168–175
-113
Si(4Si)
-106
-99
Si(3Si,1Al)
SiOH
Cat-C
Cat-C
HZSM-11
Cat-A
Cat-B
HZSM-11
Cat-A
-70
-80
-90
-100
-110
-120
-130
10
20
30
40
50
2/(o )

Fig. 1. XRD patterns of zeolite samples.
Fig. 2. 29Si MAS NMR spectra of three zeolite samples.
based on the areas of the diffraction peaks at 2θ = 7.9° ± 0.1°,
8.8° ± 0.1°, 23.0° ± 0.1°, 23.8° ± 0.1°, and 45.0° ± 0.1° using pure
ZSM‐11 in protonic form (HZSM‐11), which was assumed to
have 100% RC, as a standard. The RC of Cat‐A was 69.9%,
which is in good agreement with its composition, and that of
Cat‐B was 63.7%.
The DGC method uses steam to assist in heating the precur‐
sor and converting the amorphous structure to the crystalline
form [18]. Compared with hydrothermal synthesis, the impact
of diffusion on the zeolite growth rate is minimized in the DGC
method; this is attributed to the higher rate of diffusion for
gases than for liquids. In the DGC process, the solid sample was
not in direct contact with water; however, capillary condensa‐
tion of water vapor usually means that the surface of the
amorphous silica gel is covered with a thin layer of water dur‐
ing the steaming treatment [8]. In addition, seed addition can
be used for the rapid synthesis of zeolites with controllable
crystal size and morphology. Taking these ideas into considera‐
tion, we attempted to use the DGC method to prepare a binder‐
less ZSM‐11 zeolite catalyst.
proximately δ = −114, −106, and −100. These chemical shifts
correspond to Si(4Si), Si(3Si, 1Al), and Si(OH), respectively
[19,20]. Quantitative information regarding the percentages of
the different Si species was also obtained from these spectra.
The percentages of Si(4Si), Si(3Si, 1Al), and Si(OH) in HZSM‐11
were 85.0%, 13.0%, and 2.0%, respectively. After the DGC pro‐
cess, the percentage of Si(3Si, 1Al) changed from 13.0% (Cat‐A)
to 10.7% (Cat‐C), whereas that of Si(4Si) increased only slightly
(from 86.1% to 87.6%). The percentage of Si(OH) was between
1.0% and 2.0%. These results suggest that the amorphous SiO2
in Cat‐A was transformed into ZSM‐11 zeolite in Cat‐C, and this
resulted in the similar RCs for Cat‐C (101%) and HZSM‐11
(100%).
HRTEM images (Fig. 3) show that HZSM‐11 has relatively
regular crystal edges and does not contain any clearly visible
amorphous materials. A large amount of amorphous SiO2 was
observed around the ZSM‐11 in the Cat‐A sample, but this
phenomenon was hardly observed in Cat‐C. The Cat‐C sample
contained crystal particles with relatively clear and regular
shapes and no evidence of amorphous SiO2. The NMR and
The XRD pattern of the Cat‐C sample obtained from 4 g of a
mixture of ZSM‐11 and SiO2, 1.2 g HDA, and 4 mL H2O after
reaction at 175 °C for 10.5 h is shown in Fig. 1. It contains the
typical diffraction pattern of HZSM‐11 zeolite, and the RC of
Cat‐C was 101%, which is similar to that of HZSM‐11. The de‐
tailed crystallization mechanism will be explored in another
manuscript. It is worth noting that no other amines were added
to the system during the synthesis except for HDA and TBABr.
Generally, amines such as ethylamine and n‐butylamine should
be added into the DGC process; these amines have two func‐
tions: enhancing the alkalinity and acting as SDAs [8].
(b)
(a)
50 nm
(d)
20 nm
(c)
SiO2
To confirm the coordination state of the Si species and the
percentages of these species contained in the samples, 29Si MAS
NMR measurements were carried out and the spectra of vari‐
ous samples are given in Fig. 2. Deconvolution of the spectra of
the Cat‐A, Cat‐C, and HZSM‐11 samples showed that they each
contained three peaks with chemical shifts centered at ap‐
50 nm
Fig. 3. HRTEM images of zeolite samples. (a) HZSM‐11; (b) Cat‐A; (c)
Cat‐C; (d) Photograph of Cat‐C.

Wanshuo Zhang et al. / Chinese Journal of Catalysis 38 (2017) 168–175
171
442
800
600
400
200
0
239
Cat-B
Cat-C
Cat-A
HZSM-11
Cat-A
Cat-B
HZSM-11
Cat-C
200
300
400
500
600
0.0
0.2
0.4
0.6
0.8
1.0
Temperature (oC)
P/P0
Fig. 4. N2 adsorption‐desorption isotherms for zeolite samples.
Fig. 5. NH3‐TPD profiles of the zeolite samples.
HRTEM results are thus consistent with the XRD results. Based
on the results described above, it could be inferred that the
amorphous SiO2 binder in the extrudate was transformed into
ZSM‐11 in the DGC process, and the shaped binderless zeolite
catalyst was therefore synthesized successfully.
In comparison with HZSM‐11, Cat‐A and Cat‐B had lower
micropore surface areas and micropore volumes; this was a
result of the presence of the amorphous binder (silica or alu‐
mina). In contrast, HZSM‐11 and Cat‐C had similar micropore
surface areas and micropore volumes as a result of their similar
crystallinities.
The initial cylindrical shape of the catalyst was retained
during the DGC process; Fig. 3 shows a photograph of the Cat‐C
sample. The side pressure strengths of Cat‐A, Cat‐B, and Cat‐C
were 78, 110, and 94 N/cm, respectively, which indicates that
Cat‐C retained its high mechanical strength after recrystalliza‐
tion. This may be attributed to the formation of a matrix or
bridge structure, as reported in Ref. [21]. In this previous study
MFI with a low SiO2/A12O3 molar ratio of 80 was mixed with
amorphous SiO2 to give small crystals of MFI with a high
SiO2/A12O3 molar ratio of 900 using the DGC method. The sec‐
ond type of zeolite particles bound to the first type of zeolite
particles by adhering to their surface, thereby forming a matrix
or bridge structure. This resulted in zeolite particles with a high
mechanical strength.
The acidity of the catalysts was investigated using the
NH3‐TPD technique, and the spectra are shown in Fig. 5. Two
NH3 desorption peaks were observed in the tested temperature
range. The desorption peak temperatures for Cat‐B were cen‐
tered at approximately 250 and 423 °C, and correspond to
weak and strong acid sites, respectively. Those for the other
catalysts (HZSM‐11, Cat‐A, and Cat‐C) were centered at ap‐
proximately 239 and 442 °C. The total concentration of acid
sites followed the order: Cat‐B (486 µmol/g) > HZSM‐11 (453
µmol/g) > Cat‐C (395 µmol/g) > Cat‐A (362 µmol/g). The acid‐
ity of the sites was then further investigated with the Py‐IR
technique. The bands at approximately 1540 and 1450 cm−1
were integrated to determine the respective concentrations of
Brönsted and Lewis acid sites [23]. Conventionally, the total
acidity is determined when pyridine is desorbed at 150 °C (Fig.
6(a)), whereas medium and strong (M–S) acidity is obtained
when pyridine is desorbed at 300 °C (Fig. 6(b)). To determine
the concentration of Brönsted and Lewis acid sites (marked CB
and CL, respectively), we used the formulae CB = 1.88 IA (B)
R2/W and CL = 1.42 IA (L) R2/W [24]. The different strength CB
and CL values for each sample are listed in Table 1. Cat‐A
showed the lowest total and M–S CB; this is ascribed to the di‐
3.2. Physicochemical properties of ZSM‐11 catalysts
N2 adsorption‐desorption isotherms with a steep rise at
P/P0 < 0.01 are characteristic of microporous zeolites, and a
hysteresis loop at 0.44 < P/P0 < 1 corresponds to the existence
of dissimilar mesopores [22]. As shown in Fig. 4, all of the cata‐
lysts showed typical type I + IV isotherms. Data on the textural
properties of the catalysts are summarized in Table 1.
Table 1
Textural properties and acidity data for the zeolite samples.
ABET
(m2/g)
423
312
382
Vtotal
(m3/g)
0.425
0.360
0.519
0.328
Vmicro
(m3/g)
0.120
0.078
0.087
0.120
Vmeso
(m3/g)
0.305
0.282
0.433
0.208
Concentration of acid sites (µmol/g)
Amicro
(m2/g)
299
199
212
Sample
a
b
c
d
CB‐Py‐150
196
147
160
195
CL‐Py‐150
53
CB‐Py‐300
191
CL‐Py‐300
29
14
65
12
HZSM‐11
Cat‐A
Cat‐B
29
139
103
25
151
191
Cat‐C
399
303
a Brönsted acid concentration determined by Py‐IR at 150 °C.
b Lewis acid concentration determined by Py‐IR at 150 °C.
c Brönsted acid concentration determined by Py‐IR at 300 °C.
d Lewis acid concentration determined by Py‐IR at 300 °C.

172
Wanshuo Zhang et al. / Chinese Journal of Catalysis 38 (2017) 168–175
(a)
(b)
L acid
L acid
B acid
B acid
HZSM-11
HZSM-11
Cat-A
Cat-C
Cat-A
Cat-C
Cat-B
Cat-B
1550
1500
Wavenumber (cm1
1450
1400
1550
1500
1450
1400
Wavenumber (cm1
)
)
Fig. 6. Py‐IR spectra of the zeolite samples desorbed at 150 °C (a) and 300 °C (b).
luting effect of SiO2, which reduces the acidity. Owing to the
presence of Al2O3, Cat‐B displayed the highest CL, whereas
HZSM‐11 and Cat‐C possessed a similar CB. In comparison with
that of Cat‐A, the CB of Cat‐C was increased; this may be the
result of the small amount of additional Al being converted into
framework Al and replacing Si–OH in HZSM‐11.
°C, 5.2 MPa, and an NH3/i‐C4H8 molar ratio of 1, gave an isobu‐
tene conversion of 8.9% with a tert‐butylamine selectivity of
98% [25,26]. Furthermore, BASF have commercialized the BEA
zeolite catalyst for the direct amination of isobutene; however,
this process requires relatively harsh conditions of 270 °C, 28.0
MPa, and a NH3/i‐C4H8 molar ratio of 1.5. In addition the con‐
version of isobutene was only 22.67% [27].
3.3. Catalytic performance over ZSM‐11 catalysts by different
methods
As shown in Fig. 7, the formation rate of tert‐butylamine
changed very little over the 6 h reaction time. A similar phe‐
nomenon was observed for the MFI zeolites [2]. Furthermore,
as shown in Fig. 7, the formation rate of tert‐butylamine at TOS
= 6 h over the different zeolite samples decreased in the fol‐
lowing order: Cat‐C (1162 µmol h−1 g−1cat) ≈ HZSM‐11 (1152
µmol h−1 g−1cat) > Cat‐A (1083 µmol h−1 g−1cat) > Cat‐B (927 µmol
h−1 g−1cat). HZSM‐11 and Cat‐C showed similar performance in
the isobutene amination reaction, but HZSM‐11 is a powder
whereas Cat‐C is shaped and has high mechanical strength (94
N/cm). Cat‐C therefore has the potential for use in industrial
applications. Academic and fundamental research studies have
been neglected in this field [4] because the design of shaped
formulations is generally considered to be a technical process.
The performance of the Cat‐A, Cat‐B, Cat‐C, and HZSM‐11
catalysts in the direct amination of isobutene was compared,
and the isobuteneconversion and tert‐butylamine selectivity of
the four samples are summarized in Table 2.
Under reaction conditions of 250 °C, 5.0 MPa, weight hourly
space velocity (WHSV) of isobutene of 0.5 h−1, NH3/i‐C4H8 mo‐
lar ration of 4/1 and time‐on‐stream (TOS) of 6 h, the isobutene
conversion was in the range of 10.41%–13.04% over the cata‐
lysts employed. Cat‐A displayed higher isobutene conversion
than Cat‐B (12.16% vs 10.41%), and the conversions obtained
for the reactions over Cat‐C (13.04%) and HZSM‐11 (12.93%)
were similar. As shown in Table 2, the major product was
tert‐butylamine (> 99.9%), and the remaining trace compo‐
nents were C8 hydrocarbons. A small amount of oligomerization
and isomerization products were observed, but the selectivities
for both of these were less than 0.1%. This result is in good
agreement with those obtained with H‐FAU and H‐MOR zeo‐
lites. Reaction over these zeolites showed a tert‐butylamine
selectivity of more than 99% below 280 °C with a NH3/i‐C4H8
molar ratio of 2 [25].The H‐Y catalyst, under conditions of 260
1200
Cat-C
HZSM-11
Cat-A
1100
1000
Cat-B
Table 2
900
Catalytic performance of zeolite samples in isobutene amination.
Sample
Cat‐A
Cat‐B
Cat‐C
HZSM‐11
Isobutene conversion (%) Tert‐butylamine selectivity (%)
12.16
10.41
13.04
12.93
99.98
99.98
99.98
99.98
800
0
1
2
3
4
5
6
7
TOS (h)
Fig. 7. Formation rate of tert‐butylamine over zeolite samples as a func‐
tion of time. Reaction conditions: 250 °C, 5.0 MPa, WHSV (isobutene) =
0.5 h−1, NH3/i‐C4H8 = 4/1 (molar ratio).
Reaction conditions: 250 °C, 5.0 MPa, WHSV (isobutene) = 0.5 h−1,
NH3/i‐C4H8 = 4/1 (molar ratio), TOS = 6 h.

Wanshuo Zhang et al. / Chinese Journal of Catalysis 38 (2017) 168–175
173
However, a solid understanding of the relationship between
catalytic performance and catalyst structure and composition,
including formulation shape, is necessary for the development
of practical zeolite catalysts [28].
by a linear relationship and did not increase on increasing the
SiO2/Al2O3 molar ratio of the catalyst framework. This result is
not consistent with that reported in Ref. [30].
4. Conclusions
3.4. Relationship between physicochemical properties and
catalytic performance of ZSM‐11 catalysts
A shaped binderless ZSM‐11 zeolite catalyst was successful‐
ly prepared using the DGC method in its protonic form (Cat‐C).
When using suitable synthesis conditions, the concentration of
Brönsted acid sites in Cat‐C can approach the concentration in
HZM‐11. Compared with the binder‐containing catalysts (Cat‐A
The textural properties and acidity of ZSM‐11 may influence
its catalytic performance. First, we will discuss the effect of the
textural properties on catalytic performance. As shown in Table
1, ABET decreased in the order HZSM‐11 > Cat‐C > Cat‐B > Cat‐A,
whereas Amicro decreased in the order Cat‐C ≈ HZSM‐11 > Cat‐B
> Cat‐A. Vmicro followed the sequence HZSM‐11 = Cat‐C > Cat‐B >
Cat‐A, and Vmeso decreased in the order Cat‐B > HZSM‐11 >
Cat‐A > Cat‐C. Thus, the formation rate of tert‐butylamine does
not appear to show a clear relationship with the textural prop‐
erties of ZSM‐11. Li [29] reported that hierarchical nano‐ZSM‐5
zeolites with a high surface area showed little improvement in
catalytic performance compared with that of nano‐ZSM‐5 for
the direct amination of isobutene to tert‐butylamine. This
demonstrates that molecular diffusion is not the rate deter‐
mining step.
and Cat‐B), Cat‐C showed
a higher formation rate of
tert‐butylamine in the direct amination of isobutene. This was a
result of the higher concentration of Brönsted acid sites and
lower concentration of Lewis acid sites. Because of its high
crystallinity and good mechanical strength, the binderless
ZSM‐11 zeolite catalyst has potential for application in the di‐
rect amination of isobutene.
References
[1] W. F. Hoelderich, Catal. Today, 2000, 62, 115–130.
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255–261.
Second, we illustrate the effect of acidity on catalytic per‐
formance. In our study, the total acid site concentration (de‐
termined using NH3‐TPD) decreased in the order Cat‐B >
HZSM‐11 > Cat‐C > Cat‐A. As shown in Table 1, CB decreased in
the order HZSM‐11 ≈ Cat‐C > Cat‐B > Cat‐A, whereas the order
for CL was Cat‐B > HZSM‐11 > Cat‐A > Cat‐C, irrespective of the
total and M–S acid site concentrations. It could thus be specu‐
lated that the formation rate of tert‐butylamine is closely re‐
lated to CB [29–31]. However, CL should also be considered.
Even if a catalyst has a suitable CB, a high CL may inhibit the
formation of the ammonium cation, which reacts with gaseous
isobutene. The resulting cationic intermediate, the tert‐butyl
cation, then reacts with NH3, either adsorbed on the catalyst
surface or in the gas phase, and produces chemisorbed
tert‐butylamine [2,16].
ZSM‐5 is a common catalyst for the direct amination of iso‐
butene, and is considerably affected by the number and
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HZSM‐5 catalyst showed improved activity in the amination
reaction [31]. Chang et al. [32] reported that the catalytic per‐
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Wanshuo Zhang et al. / Chinese Journal of Catalysis 38 (2017) 168–175
Graphical Abstract
Chin. J. Catal., 2017, 38: 168–175 doi: 10.1016/S1872‐2067(17)62756‐6
A shaped binderless ZSM‐11 zeolite catalyst for direct amination of isobutene to tert‐butylamine
Wanshuo Zhang, Shangyao Gao, Sujuan Xie, Hui Liu, Xiangxue Zhu, Yongchen Shang *, Shenglin Liu *, Longya Xu, Ye Zhang
Harbin Normal University; Dalian Institute of Chemical Physics, Chinese Academy of Sciences; University of Chinese Academy of Sciences;
Sinochem Quanzhou Petrochemical Co., Ltd.; PetroChina Fushun Petrochemical Company
500
450
Binderless
ZSM-11
Isobutylene
400
+
350
Tert-butylamine
300
Ammonia
A shaped binderless ZSM‐11 catalyst was prepared by the dry‐gel conversion technique and showed superior performance in isobutene
animation reaction.
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both the English version and extended Chinese abstract of the paper. The
online version only has the English version. The pages with the extended
Chinese abstract are only available in the print version.