Silicoaluminophosphate molecular sieve DNL-6: Synthesis with a novel template, N,N″-dimethylethylenediamine, and its catalytic application

Article abstract of DOI:10.1016/S1872-2067(18)63122-5

DNL-6, a silicoaluminophosphate (SAPO) molecular sieve with RHO topology, was hydrothermally synthesized using a new structure-directing agent (SDA), N,N′-dimethylethylenediamine. The obtained samples were characterized by X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, scanning electron microscopy, and N₂ adsorption, which indicated that the synthesized DNL-6s have high crystallinity and relatively high Si content ranging from 20% to 35%. Solid-state magic-angle-spinning (MAS) nuclear magnetic resonance (¹³C, ²⁹Si, ²⁷Al, ³¹P, and ²⁷Al multiple-quantum (MQ)) was conducted to investigate the status of the SDA and local atomic environment in the as-synthesized DNL-6. Thermal analysis revealed the presence of a large amount of amines in the DNL-6 crystals (about 4.4 SDAs per α-cage), which was the reason for the formation of DNL-6 with an ultrahigh Si content (36.4% Si per mole). Interestingly, DNL-6 exhibited excellent catalytic performance for methanol amination. More than 88% methanol conversion and 85% methylamine plus dimethylamine selectivity could be achieved due to the combined contribution of strong acid sites, suitable acid distribution, and narrow pore dimensions of DNL-6.

Full text of DOI:10.1016/S1872-2067(18)63122-5

Chinese Journal of Catalysis 39 (2018) 1511–1519
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
Silicoaluminophosphate molecular sieve DNL‐6: Synthesis with a
novel template, N,N'‐dimethylethylenediamine, and its catalytic
application
Pengfei Wu a,b, Miao Yang a, Wenna Zhang a,b, Shu Zeng a,b, Mingbin Gao a,b, Shutao Xu a, Peng Tian a,*,
Zhongmin Liu a,#
a National Engineering Laboratory for Methanol to Olefins, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning,
China
b University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history:
DNL‐6, a silicoaluminophosphate (SAPO) molecular sieve with RHO topology, was hydrothermally
synthesized using a new structure‐directing agent (SDA), N,N'‐dimethylethylenediamine. The ob‐
tained samples were characterized by X‐ray diffraction, X‐ray fluorescence, X‐ray photoelectron
spectroscopy, scanning electron microscopy, and N2 adsorption, which indicated that the synthe‐
sized DNL‐6s have high crystallinity and relatively high Si content ranging from 20% to 35%. Sol‐
id‐state magic‐angle‐spinning (MAS) nuclear magnetic resonance (13C, 29Si, 27Al, 31P, and 27Al multi‐
ple‐quantum (MQ)) was conducted to investigate the status of the SDA and local atomic environ‐
ment in the as‐synthesized DNL‐6. Thermal analysis revealed the presence of a large amount of
amines in the DNL‐6 crystals (about 4.4 SDAs per α‐cage), which was the reason for the formation of
DNL‐6 with an ultrahigh Si content (36.4% Si per mole). Interestingly, DNL‐6 exhibited excellent
catalytic performance for methanol amination. More than 88% methanol conversion and 85% me‐
thylamine plus dimethylamine selectivity could be achieved due to the combined contribution of
strong acid sites, suitable acid distribution, and narrow pore dimensions of DNL‐6.
Received 7 May 2018
Accepted 2 June 2018
Published 5 September 2018
Keywords:
N,N'‐dimethylethylenediamine
SAPO molecular sieves
Synthesis
DNL‐6
Methanol amination reaction
© 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
SAPO‐34 with a CHA structure is an excellent catalyst for the
methanol‐to‐olefin (MTO) reaction [5,6] and its Cu2+
Silicoaluminophosphate (SAPO) molecular sieves, first re‐
ported by the Union Carbide Corporation in the 1980s, are im‐
portant microporous materials often used in industrial catalytic
processes [1–4]. The incorporation of Si atoms into neutral
aluminophosphate frameworks results in a moderate acidity
and high thermal and hydrothermal stabilities, which make
them suitable for many important applications. For example,
ion‐exchanged counterpart shows a superior catalytic perfor‐
mance and stability for the selective catalytic reduction (SCR)
of NOx [7,8]. Further, Pt/SAPO‐11 was used as a catalyst for
hydro‐isomerization due to its outstanding isomerization activ‐
ity and lower cracking activity [9,10].
The impressive properties and consequent important ap‐
plications of SAPO molecular sieves are mainly controlled by
* Corresponding author. Tel: +86‐411‐84379218; Fax: +86‐411‐84691570; E‐mail: tianpeng@dicp.ac.cn
# Corresponding author. Tel: +86‐411‐84379998; Fax: +86‐411‐84691570; E‐mail: liuzm@dicp.ac.cn
This work was supported by the National Natural Science Foundation of China (21476228, 21676262) and the Key Research Program of Frontier
Sciences, CAS (QYZDB‐SSW‐JSC040).
DOI: 10.1016/S1872‐2067(18)63122‐5 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 39, No. 9, September 2018

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Pengfei Wu et al. / Chinese Journal of Catalysis 39 (2018) 1511–1519
their Si distribution and morphology. Considerable efforts have
been put in over the past few decades to develop synthetic
strategies for SAPO molecular sieves. Generally, the synthesis of
SAPO molecular sieves is influenced by a number of parame‐
ters, such as the type of initial sources, solvent, crystallization
temperature, and time. The structure‐directing agent (SDA) is
one of the most important factors; it plays complicated roles in
the synthesis process, such as dissolving the raw materials,
orienting the structure, balancing the charges, and filling the
skeleton space [11]. Consequently, the crystalline phase, mor‐
phology, composition, and acidity of the final SAPO products
can be modified by template selection. Taking the synthesis of
SAPO‐34 as an example, low silicon SAPO‐34 can only be syn‐
thesized using a large organic amine template, such as trime‐
thylamine (TEA) or tetraethylammonium hydroxide (TEAOH),
because only one protonated template molecule can be ac‐
commodated in one CHA cage to balance the negative charge of
the framework. Meanwhile, SAPO‐34s synthesized by small
organic amines, such as diethylamine (DEA), piperazine (PIP),
and morpholine (MOR), have relatively high Si contents due to
their small volume and high charge density [12–14]. More in‐
terestingly, the SAPO‐34 product directed by TEAOH presents a
nano‐sized morphology, which exhibits an improved MTO cat‐
alytic performance. The strong alkalinity of TEAOH may induce
the dissolution of the silica source, which promotes nucleation
and small‐crystal formation [15,16]. Hence, discovering novel
SDAs is an effective way to modify the properties of SAPO mo‐
lecular sieves.
DNL‐6 is an SAPO molecular sieve with an RHO topology
(composed of α‐cages linked via double 8‐rings), which was
first reported by our laboratory. It was found accidentally dur‐
ing an investigation on the phase‐transformation processes of
SAPO molecular sieves [17]. Thereafter, the synthesis of DNL‐6
was accomplished by various strategies including surfac‐
tant‐assisted hydrothermal synthesis [18], dry‐gel conversion
[19], and aminothermal crystallization [20]. It is noteworthy
that DNL‐6 possesses strong Brønsted acid sites comparable to
those of HZSM‐5 or even stronger [21], over which hep‐
tamethylbenzenium cations (heptaMB+) were stabilized and
directly observed for the first time during a real MTO reaction
[22]. Moreover, the material can accommodate high concentra‐
tions of single Si(OAl)4 species, indicating huge potential for
CO2/CH4 and CO2/N2 adsorption/separation [19]. Optimized
synthesis of DNL‐6 is thus highly desired; it may provide op‐
portunities to develop new applications.
ic‐angle spinning nuclear magnetic resonance (solid‐state MAS
NMR). The sample with an ultrahigh silica content and acidity
shows excellent catalytic activity and a remarkable methyla‐
mine and dimethylamine selectivity in the methanol amination
reaction.
2. Experimental
2.1. Sample preparation
A typical hydrothermal synthesis procedure for DNL‐6 is as
follows. Orthophosphoric acid (85 wt%) and tetraethyl ortho‐
silicate were mixed with a solution of aluminum isopropoxide
and deionized water. After the synthesis solution was stirred
for 2 h, the template agent, N,N'‐dimethylethylenediamine, was
added and it was continually stirred for 4 h. Later, the synthesis
gel was transferred into a stainless steel autoclave and heated
at 200 °C for 12 h under rotation. After equilibrating for a cer‐
tain time period at this temperature for crystallization, the au‐
toclave was cooled down and the solid product was recovered
by filtration, washed three times with deionized water, and
dried at 110 °C overnight. Finally, the product was calcined at
550 °C for 4 h to remove organic species.
2.2. Characterization
Powder XRD patterns were recorded on a PANalytical X’Pert
PRO X‐ray diffractometer with Cu K radiation (λ = 1.54059 Å),
operating at 40 kV and 40 mA. SEM images were generated on
a Hitachi SU8020 electron microscope at 25 kV. The bulk and
surface compositions of samples were determined using a
Philips Magix‐601 XRF spectrometer and a VG ESCALAB MkII
XPS. N2 adsorption measurements were carried out on a Mi‐
cromeritics 2010 analyzer at –196 °C after the sample was de‐
gassed at 350 °C under vacuum. All solid‐state NMR experi‐
ments were performed on a Bruker Avance III 600 spectrome‐
ter equipped with a 14.1 T wide‐bore magnet and a 4 mm MAS
probe. The resonance frequencies at this field strength were
150.9, 156.4, 119.2, and 242.9 MHz for 13C, 27Al, 29Si, and 31P,
respectively. 13C cross polarization (CP)/MAS NMR spectra
were recorded with a contact time of 3 ms and recycle delay of
2 s at a spinning rate of 12 kHz. 27Al MAS NMR spectra were
recorded using one pulse sequence at a spinning rate of 12 kHz.
A total of 200 scans were accumulated with a π/8 pulse width
of 0.75 μs and a 2 s recycle delay. Chemical shifts were refer‐
enced to (NH4)Al(SO4)2·12H2O at –0.4 ppm. 29Si and 31P MAS
NMR spectra were recorded by high‐power proton decoupling.
29Si MAS NMR spectra were recorded with a π/4 pulse width of
2.5 μs and a recycle delay of 10 s at a spinning rate of 8 kHz.
Thus far, diethylamine (DEA) is the only known template to
synthesize DNL‐6. Moreover, the use of cationic surfactants is
important for the synthesis of DNL‐6. The strong adsorption of
cationic surfactant molecules on SAPO species protects DNL‐6
from dissolving, and inhibits its transformation to SAPO‐34
Chemical shifts were referenced to kaolinite at –91.5 ppm. 31
P
[23]. In this work, we report
a
new template,
MAS NMR spectra were recorded with a π/4 pulse width of
2.25 μs and a 10 s recycle delay. Chemical shifts were refer‐
enced to 85% H3PO4 at 0 ppm. Two‐dimensional (2D) 27Al mul‐
tiple quantum magic angle spinning (MQ‐MAS) NMR analysis
was performed on a 4 mm H‐X WVT probe at a spinning rate of
13 kHz. An rf field of 49.1 kHz was used for the creation (0Q →
±3Q) and ꢀirst conversion (±3Q → 0Q) pulses. The central tran‐
N,N'‐dimethylethylenediamine, to synthesize DNL‐6 molecular
sieves. Notably, a cationic surfactant is not necessary anymore.
The synthesized DNL‐6s were characterized by various tech‐
niques including X‐ray diffraction (XRD), X‐ray fluorescence
(XRF), X‐ray photoelectron spectroscopy (XPS), scanning elec‐
tron microscopy (SEM), N2 adsorption, and solid‐state mag‐

Pengfei Wu et al. / Chinese Journal of Catalysis 39 (2018) 1511–1519
1513
sition selective soft 90° pulse used for the last conversion step
(0Q → ±1Q) was 3.47 kHz. A shearing transformation was used
to achieve 2D Fourier transformation and obtain a pure ab‐
sorption‐mode 2D contour plot. The quadrupolar interaction
product, PQ (PQ is identical to the ‘‘second order quadrupole
effect (SOQE)’’ parameter used in various publications), and
isotropic chemical shift (δiso) values were calculated according
to procedures reported previously [24]. The 1H MAS NMR
spectra were recorded using a 4 mm MAS probe. The pulse
width was 2.2 μs for a π/4 pulse and 32 scans were accumu‐
lated with a 4 s recycle delay. The samples were spun at 12 kHz
and chemical shifts were referenced to adamantine at 1.74
ppm. Thermogravimetric analyses (TG‐DTG) were performed
on a TA Q600 analyzer. The sample was heated at a rate of 10
°C/min to 900 °C. Temperature‐programmed desorption by
NH3 (NH3‐TPD) experiments were conducted on an automated
characterization system (AutoChem 2920, Micromeritics) with
a TCD detector. The calcined sample (200 mg) was compressed
into pellets (40–60 mesh) and packed into a U‐tube reactor.
The packed column was initially purged with He flow and out‐
gassed at 600 °C. After pretreatment, the sample was cooled to
100 °C and saturated with ammonia. Physically adsorbed am‐
monia was swept by purging with He at a flow rate of 40
mL/min for 30 min. Finally, the packed bed was heated at a
rate of 10 °C/minto 600 °C under He flow (20 mL/min).
H-DNL-6
M-DNL-6
L-DNL-6
SP-D5
SP-D4
SP-D3
SP-D2
SP-D1
2.3. Catalytic test
5
10
15
20
25
30
35
40
2 ()
Fig. 1. XRD patterns of the as‐synthesized samples.
Methanol amination experiments were performed in a con‐
tinuous flow fixed‐bed reactor at atmospheric pressure. A 0.3 g
portion of the calcined sample (40–60 mesh) was loaded into
the reactor and pretreated in He (40 mL/min) at 500 °C for 1 h
prior to the reaction. The temperature of the catalyst bed was
cooled to reaction temperature (260 or 300 °C) in He. A NH3
flow of 6.2 mL/min was fed into the reactor by a mass‐flow
controller. Methanol was introduced into the system by passing
He (47 mL/min) through a methanol‐filled saturator (10 °C),
which resulted in a weight hourly space velocity (WHSV) of
0.813 h−1 and methanol/ammonia = 0.5 (mole). The products
were analyzed on‐line using an Agilent 6890 gas chromato‐
3. Results and discussion
3.1. Synthesis and characterization of DNL‐6
The detailed synthesis conditions including gel composition,
crystallization time, product crystalline phases, and composi‐
tion are listed in Table 1. The corresponding XRD patterns of
these products are shown in Fig. 1. When TEOS is absent
(SP‐D1), AlPO4‐21 with an AWO topology is the final product.
The AWO phase decreases and RHO phase increases with an
graph with
a flame ionization detector (FID) using a
CP‐Volamine column.
Table 1
Gel compositions and resultant products of hydrothermal syntheses.
Product composition
Gel composition
Sample a
Crystalline phase
TEOS/Al2O3/P2O5/R/H2O
0 /1.0/1.0/5.0/167.0
0.3 /1.0/1.0/5.0/167.0
0.6 /1.0/1.0/5.0/167.0
1.3/1.3/1.0/5.0/167.0
1.2/1.0/1.0/5.0/167.0
1.7/1.0/1.0/5.0/167.0
1.2/1.0/1.0/5.0/167.0
1.2/1.0/1.0/5.0/167.0
Bulk (XRF)
–
Surface (XPS)
SP‐D1
SP‐D2
SP‐D3
L‐DNL‐6
M‐DNL‐6
H‐DNL‐6
SP‐D4 b
SP‐D5 b
AWO
AWO + RHO
RHO + AWO
RHO
RHO
RHO
RHO + GIS
–
–
–
–
–
Si0.226Al0.475P0.230O2
Si0.286Al0.454P0.259O2
Si0.364Al0.414P0.222O2
Si0.231Al0.464P0.305O2
Si0.252Al0.466P0.282O2
Si0.262Al0.292P0.446O2
Si0.346Al0.421P0.233O2
Si0.462Al0.377P0.161O2
–
–
GIS + minor RHO
a The crystallization conditions are 200 °C and 12h. b The crystallization time is 68 h for SP‐D4 and 143 h for SP‐D5.

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Pengfei Wu et al. / Chinese Journal of Catalysis 39 (2018) 1511–1519
increase in the amount of TEOS. Pure DNL‐6 molecular sieves
cannot be synthesized unless the molar ratio of TEOS/Al2O3 is
1. Further, an amorphous phase appears along with DNL‐6
when the TEOS/Al2O3 molar ratio is greater than 1.7.
Pure‐phase DNL‐6s synthesized at TEOS/Al2O3 ratios of 1.0,
1.2, and 1.7 were denoted as L‐DNL‐6, M‐DNL‐6, and H‐DNL‐6,
respectively. Their Si contents range from 22.4% to 36.4%. It
should be noted that SAPO molecular sieves with such high Si
contents are rarely reported. Upon further prolonging the
crystallization time, the RHO phase gradually converts to a
dense GIS phase (68 h for SP‐D4 and 143 h for SP‐D5), indicat‐
ing the metastable characteristics of DNL‐6. Meanwhile, the Si
content of solid products is higher than that of M‐DNL‐6.
500
400
300
200
100
0
H-DNL-6
+200
+100 M-DNL-6
L-DNL-6
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
All pure DNL‐6 samples are present in the form of mi‐
cron‐sized particles, as shown in Fig. 2. The product morphol‐
ogy changes with an increase in the Si content; L‐DNL‐6 is
sphere‐like (Fig. 2(a) and (b)) and M‐DNL‐6 exhibits a truncat‐
ed rhombic dodecahedron morphology (Fig. 2(c) and (d)).
H‐DNL‐6 exhibits a spherical morphology with an average par‐
ticle size of about 4 μm, whose outer layer consists of small
cubic crystals of 50 nm size (Fig. 2(e) and (f)).
The textural properties of the obtained DNL‐6 samples were
characterized by N2 adsorption and are shown in Fig. 3 and
Table 2. The samples exhibit Type I adsorption‐desorption
isotherms with little mesopore volume, indicating that the in‐
ner regions of the particles are solid. All DNL‐6 samples exhibit
large Brunauer‐Emmett‐Teller (BET) micropore surface area
and volume, which verifies their high crystallinity. In particular,
owing to the rough surfaces of the particles, the external sur‐
face area of H‐DNL‐6 is larger than that of its analogs.
P/P0
Fig. 3. N2 sorption isotherms of DNL‐6 samples.
nance peaks at 44.1 and 32.9 ppm, corresponding to the meth‐
ylene and methyl groups of N,N'‐dimethylethylenediamine
template, respectively. The two weak split signals at about 55
ppm are caused by strong interactions between the methylene
groups of templates and the molecular sieve framework
[25,26]. These results verify the intact status of the organic
amine in the synthesized DNL‐6 crystals. Fig. 4(b) displays the
27Al NMR spectra of the samples, all of which show a broad
peak at 39 ppm; it can be assigned to the tetrahedrally coordi‐
nated Al species of the framework. The 31P NMR spectra (Fig.
4(c)) show a peak at –29 ppm attributable to the tetrahedral
PO4 group. The 29Si NMR spectra become complicated with
increasing Si content in DNL‐6, as shown in Fig. 4(d). L‐DNL‐6
shows a strong signal at –92 ppm and a very weak peak at –95
ppm indicating that Si(4Al) is the main environment for
L‐DNL‐6. Meanwhile, M‐DNL‐6 shows quadruple signals at –92,
–95, –99, and –104 ppm, indicating the appearance of a large
number of Si(3Al), Si(2Al) and Si(1Al) species. Regarding
H‐DNL‐6, a quintuplet of signals appears at –92, –95, –99, –104,
and –109 ppm. The signals at –95, –99, and –104 ppm are as
strong as the signal at –92 ppm, suggesting that the amount of
Si(3Al), Si(2Al), and Si(1Al) increased. In addition, the chemical
shift at –109 ppm indicates the existence of Si islands. The sur‐
face compositions of DNL‐6 products were evaluated by XPS, as
shown in Table 1. As expected, all the DNL‐6 samples contain
high Si contents on the crystal surface [27]. As the degree of Si
enrichment increases, the surface P and Al contents show a
corresponding decrease. Combining the XPS results and 29Si
NMR spectra, it is believed that the outer surfaces of DNL‐6
The chemical environments of the as‐synthesized DNL‐6s
were analyzed by solid‐state MAS NMR, as shown in Fig. 4. The
13C/CP MAS NMR spectra (Fig. 4(a)) show two strong reso‐
Table 2
Textural properties of the samples.
a
b
b
b
c
SBET
Smic
Sext
Vmic
Vmeso
Sample
(m2/g)
817
(m2/g)
772
(m2/g)
45
(cm3/g)
0.38
(cm3/g)
0.04
L‐DNL‐6
M‐DNL‐6
H‐DNL‐6
745
711
34
0.35
0.03
854
794
60
0.37
0.03
a Total surface area is determined by the BET equation. b Micropore
surface area, external surface area, and volume are determined by the
t‐plot method. c Mesopore volume is determined from the adsorption
isotherms by the BJH method.
Fig. 2. SEM images of calcined L‐DNL‐6 (a, b), M‐DNL‐6 (c, d), and
H‐DNL‐6 (e, f).

Pengfei Wu et al. / Chinese Journal of Catalysis 39 (2018) 1511–1519
1515
(b)
(a)
39 ppm
44.1 ppm
H-DNL-6
M-DNL-6
32.9 ppm
H-DNL-6
M-DNL-6
L-DNL-6
L-DNL-6
-20
120
100
80
60
40
20
0
-20
-40
-60
100
80
60
40
20
0
-40
ppm
ppm
(d)
(c)
-95 ppm
-99 ppm
-29 ppm
-92 ppm
-104 ppm
-109 ppm
H-DNL-6
H-DNL-6
M-DNL-6
M-DNL-6
L-DNL-6
L-DNL-6
-50
0
-10
-20
-30
-40
-60
-60
-70
-80
-90
-100
-110
-120
-130
-140
-150
ppm
ppm
Fig. 4. 13C (a), 27Al (b), 31P (c), and 29Si (d) MAS NMR spectra of the as‐synthesized samples.
crystals have more complex Si environments (more Si islands)
than the inner parts.
ppm, which are preliminarily attributed to Al(OP)4 (IVa),
Al(OSi)n(OP)(4−n) (n = 1, 2, and 3) (IVb and IVc), and Al(OSi)4 (IVd
and IVe), respectively [21,29]. The peak at 42 ppm is the
strongest, showing that Al(OSi)n(OP)(4−n) (n = 1, 2, and 3) cor‐
responding to Si atoms at the borders of Si islands, is a domi‐
nant chemical environment in H‐DNL‐6. On the basis of these
results, the distributions of Si concentration and Si environ‐
ments in the H‐DNL‐6 crystals are proposed and illustrated in
Fig. 6. Si content increases gradually from the inner part to the
exterior part of the crystals. The shell region of the crystals is
enriched with large Si islands and the region adjacent to the
shell contains a number of relatively small Si islands, both of
which provide Si(nAl) (n = 1, 2, and 3) environments. The inte‐
rior of H‐DNL‐6 crystals, which has a relatively low Si content,
is enriched with Si(4Al) species.
In order to further understand the atomic chemical envi‐
ronment of H‐DNL‐6, 27Al MQ‐MAS NMR analysis was con‐
ducted on calcined H‐DNL‐6 because Al atoms are the bridges
for Si and P atoms. As 27Al is a quadrupolar nucleus, the sin‐
gle‐pulse MAS NMR spectral line shape is often markedly
broadened, owing to residual second‐order quadrupolar inter‐
actions. 27Al MQ‐MAS NMR can effectively eliminate the sec‐
ond‐order quadrupolar interactions experienced by
half‐integer quadrupolar nuclei and thus narrow down asym‐
metric line shapes considerably [28]. The 27Al MQ‐MAS NMR
spectrum of calcined H‐DNL‐6 is shown in Fig. 5. The indirect
dimension (F1) displays five peaks at 34, 42, 48, 59, and 67
Thermal analysis was carried out to investigate the content
Fig. 5. 27Al MQ‐MAS NMR spectrum of calcined H‐DNL‐6.
Fig. 6. The distribution of Si concentration and Si environments in a
H‐DNL‐6 crystal.

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Pengfei Wu et al. / Chinese Journal of Catalysis 39 (2018) 1511–1519
and existing status of the N,N'‐dimethylethylenediamine tem‐
plate. The TG curves are shown in Fig. 7. The first weight loss
stage of ca. 5 wt % from room temperature to 200 °C corre‐
sponds to the desorption of physically adsorbed water. The
second weight loss of around 20 wt % between 200 and 800 °C
could be attributed to the decomposition of the template mol‐
ecules occluded within the crystals. The detailed weight loss
data of the three DNL‐6 samples are listed in Table 3. The
number of N,N'‐dimethylethylenediamine molecules per α cage
is calculated to be about 4.4, very similar to that of DNL‐6 di‐
rected by DEA (4.28 DEA per α cage) [18]. However,
N,N'‐dimethylethylenediamine has an obviously higher charge
density than DEA due to its low C/N ratio (2:1 vs. 4:1). This
means that it is possible for one N,N'‐dimethylethylenediamine
molecule to carry double positive charges, which can balance
more negative charges induced by greater Si incorporation.
This result is consistent with the high Si concentration of DNL‐6
samples.
CH3NH2 (MMA)
(CH3) 2NH (DMA)
(CH3) 3N (TMA)
CH3OH + NH3
Scheme 1. Synthesis of methylamines from methanol and ammonia.
the product distribution of the reaction obeys a thermodynam‐
ic equilibrium, producing trimethylamine (TMA) predomi‐
nantly instead of MMA and DMA. Thus, small‐pore molecular
sieve catalysts, such as RUB‐1 [32], RHO, SSZ‐16, and SAPO‐34
[33,34], have been investigated in order to optimize reaction
selectivity and meet commercial demands. The lack of strong
acid sites is one of the main drawbacks hindering the applica‐
tion of SAPO materials as amination catalysts, resulting in a
lower methanol conversion and much higher selectivity for
dimethyl ether than the corresponding aluminosilicate analogs
[33]. According to literature, DNL‐6 possesses very strong
Brønsted acid sites, similar to the aluminosilicate HZSM‐5.
Moreover, the pore dimensions of DNL‐6 (3.6 × 3.6 Å) are
smaller than the shortest dimension of TMA (3.9 Å), which may
help to suppress the formation of bulk TMA.
3.2. Catalytic performance
Methylamines, especially methylamine (MMA) and dime‐
thylamine (DMA), are important industrial chemicals for pro‐
ducing pesticides, pharmaceuticals, surfactants, and solvents.
Up to now, almost all methylamines are being produced by the
reaction of methanol and ammonia on an amorphous sili‐
ca‐alumina‐based catalyst [31]. The synthesis route of me‐
thylamines from methanol and ammonia is illustrated in
Scheme 1. It is mentioned that dimethyl ether, obtained by the
dehydration of methanol, can undergo the same reaction as
methanol with NH3, MMA, and DMA to produce methylamines
[31].
The catalytic performance of DNL‐6 samples was evaluated
in the methanol amination reaction at reaction temperatures of
260 and 300 °C, methanol WHSV of 0.813 h−1, and
n(ammonia):n(methanol) = 2:1. The steady‐state catalytic re‐
sults are illustrated in Table 4. The main products are MMA and
DMA with all DNL‐6 catalysts. Increasing the reaction temper‐
ature from 260 to 300 °C could greatly improve the catalytic
activity. However, the selectivity for MMA decreased obviously
accompanied by an increase in DMA and TMA, due to an en‐
hanced methylation reaction at elevated temperatures.
H‐DNL‐6, with its ultrahigh silica content, induces the highest
methanol conversion and selectivity for MMA plus DMA. Fig. 8
illustrates the changes in methanol conversion and product
selectivity with time on stream for H‐DNL‐6 at 300 °C. It is clear
that the reaction is stable during the investigated period; fur‐
ther, methanol conversion is higher than 88% and selectivity
for MMA plus DMA is greater than 85%.
One marked drawback of current industrial catalysts is that
100.0
0.14
0.12
97.5
95.0
92.5
90.0
87.5
85.0
82.5
80.0
77.5
75.0
72.5
70.0
0.10
0.08
0.06
0.04
0.02
0.00
Considering that acidity plays an important role in the
methanol amination reaction [33], NH3‐TPD was conducted to
investigate the acidity of DNL‐6 samples in order to better un‐
derstand the catalytic results. As shown in Fig. 9, there are two
desorption peaks corresponding to NH3 desorbed from weak
and strong acid sites. All the samples exhibit similar acid
strength, despite the different acid concentrations. A gradual
drop in strong acid sites can be observed following an increase
in Si concentration in the samples. Moreover, H‐DNL‐6 pos‐
sesses a small amount of super‐strong acid sites (the corre‐
sponding desorption temperature is higher than 550 °C), which
are absent in L‐DNL‐6 and M‐DNL‐6. Because the acidity of
different Si environments in SAPO molecular sieves follows the
order of Si(1Al) > Si(2Al) > Si(3Al) > Si(4Al), it is speculated
that the super‐strong acid sites are located at the borders of
larger Si islands in H‐DNL‐6 [6]. These acid characterization
results suggest that acid strength is more important than acid
density for the methanol amination reaction activity. Further‐
more, the Brønsted acid density of H‐DNL‐6 is determined by
100
200
300
400
500
600
700
800
900
Temperature (C)
Fig. 7. TG‐DTG curves of as‐synthesized M‐DNL‐6.
Table 3
Thermal properties of the samples.
Weight loss (%)
Sample
Moles of water Moles of R
per cage
per cage
RT–200 °C 200–800 °C
H‐DNL‐6
M‐DNL‐6
L‐DNL‐6
4.80
5.76
5.12
20.23
20.34
20.10
5.14
6.27
5.32
4.42
4.51
4.27

Pengfei Wu et al. / Chinese Journal of Catalysis 39 (2018) 1511–1519
1517
Table 4
Steady‐state conversion and product selectivity in the methanol amination reaction on DNL‐6 a.
Reaction temperature
(°C)
CH3OH conversion
(%)
Selectivity b (%)
Sample
CH4
0.52
0.19
0.61
0.20
0.56
0.27
0.20
DME
16.60
15.33
6.16
7.21
7.71
10.49
3.84
MMA
42.08
26.09
41.92
24.44
36.35
21.29
26.78
DMA
36.20
45.93
41.77
50.69
33.03
31.85
54.73
TMA
MMA+DMAc
H‐DNL‐6
260
300
260
300
260
300
380
49.68
88.32
33.26
79.99
35.52
82.86
82.00
4.60
12.46
9.54
94.45
85.26
89.77
81.13
75.63
59.54
84.94
M‐DNL‐6
L‐DNL‐6
SAPO‐34 d
17.47
22.36
36.11
14.46
a WHSV = 0.8131 h−1, NH3/CH3OH = 2.0, TOS = 146 min. b MMA, DMA, and TMA refer to monomethylamine, dimethylamine, and trimethylamine, re‐
spectively. Dimethyl ether is considered as a methanol resource.c (MMA + DMA) selectivity in the three methylamine products. d Sourced from our
previous work [34].
1H MAS NMR and a value of 0.69 mmol/g is obtained. This val‐
ue amounts to 67% of the total acid concentration (1.03
mmol/g), as determined by NH3‐TPD (NH3 desorption between
325–600 °C), implying the existence of Lewis acid sites with
strong acidity in H‐DNL‐6. This result is indeed consistent with
our previous work on the acidity of DNL‐6 with a composition
of Si0.182Al0.490P0.328O2 [21]. The generation of Lewis acid sites in
the structure is a result of the dehydroxylation of adjacent
Brønsted acid sites during the calcination process. Herein, con‐
sidering that amorphous acidic oxides (Al2O3 or SiO2‐Al2O3) can
act as effective catalysts in the industrial methanol amination
process, we speculate that the Lewis acid sites in DNL‐6 may
also contribute to the reaction. For comparison, the results of
methanol amination reaction on high‐Si SAPO‐34 from our
previous report [34] are also listed in Table 4. High‐Si SAPO‐34
contains a larger number of acid sites, but has a lower acid
strength than H‐DNL‐6; the position of the high‐temperature
NH3 desorption peak in the NH3‐TPD profile of SAPO‐34 was
located at 460 °C, whereas it was located at 492 °C for H‐DNL‐6.
From Table 4, it can be understood that a comparable methanol
conversion (82%) can only be achieved at a high reaction tem‐
perature of 380 °C when SAPO‐34 was used as the catalyst. This
confirms the effect of acid strength on the methanol amination
reaction activity.
H‐DNL‐6 exhibits a high selectivity for MMA plus DMA. This
may be related to the extremely high Si enrichment at the outer
shell of H‐DNL‐6 crystals, which causes a relatively low density
of strong acid sites. Therefore, for the product molecules, the
probability of consecutive reaction with methanol is reduced
when they diffuse out of the inner region to reach the outer
surface of the crystals.
4. Conclusions
DNL‐6
was
hydrothermally
synthesized
using
N,N'‐dimethylethylenediamine as a novel structure‐directing
agent. It is found that the crystalline region of the resultant
DNL‐6 products is wider than previously reported. About 4.4
amines are confined in one α‐cage, which implies that more
than 8 positive charges can exist simultaneously in one cage to
balance the negative charge framework caused by Si incorpora‐
tion; this explains the relatively high Si content of DNL‐6.
DNL‐6 with an ultrahigh silica content (36.4% Si per mole)
shows a remarkable catalytic performance for the methanol
amination reaction with a high methanol conversion (>88%)
and good selectivity for MMA plus DMA (>85%), implying that
DNL‐6 is a promising candidate for the synthesis of methyla‐
mines.
100
90
L-DNL-6
M-DNL-6
H-DNL-6
80
CH3OH
MMA
CH4
DME
TMA
70
60
50
40
30
20
10
0
DMA
0
50
100
Time (min)
150
200
100
150
200
250
300
350
400
C)
450
500
550
600
Temperature (

Fig. 8. Methanol conversion and product selectivity in the methanol
amination reaction on H‐DNL‐6 at 300 °C (NH3/CH3OH molar ratio =
2/1 and methanol WHSV = 0.813 h−1).
Fig. 9. NH3‐TPD profiles of DNL‐6 samples.

1518
Pengfei Wu et al. / Chinese Journal of Catalysis 39 (2018) 1511–1519
Graphical Abstract
Chin. J. Catal., 2018, 39: 1511–1519 doi: 10.1016/S1872‐2067(18)63122‐5
Silicoaluminophosphate molecular sieve DNL‐6: Synthesis with a novel template, N,N'‐dimethylethylenediamine, and its
catalytic application
Pengfei Wu, Miao Yang, Wenna Zhang, Shu Zeng, Mingbin Gao, Shutao Xu, Peng Tian *, Zhongmin Liu *
Dalian Institute of Chemical Physics, Chinese Academy of Sciences;University of Chinese Academy of Sciences
N,N'‐dimethylethylenediamine was used as a template to synthesize DNL‐6 with a high Si content, which showed excellent catalytic per‐
formance in the methanol amination reaction.
379–388.
[17] P. Tian, X. Su, Y. X. Wang, Q. H. Xia, Y. Zhang, D. Fan, S. H. Meng, Z.
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以N,N’-二甲基乙二胺为模板剂合成磷酸硅铝分子筛DNL-6及其在催化中的应用
吴鹏飞a,b, 杨 淼a, 张雯娜a,b, 曾 姝a,b, 高铭滨a,b, 徐舒涛a, 田 鹏a,*, 刘中民a,#
a中国科学院大连化学物理研究所, 甲醇制烯烃国家工程实验室, 辽宁大连116023
b中国科学院大学, 北京100049
摘要: 磷酸硅铝类分子筛由于其温和的酸性以及良好的热稳定性和水热稳定性在催化领域得到了广泛的应用. 例如
SAPO-34分子筛具有优异的催化甲醇制烯烃反应的催化活性, 经过铜离子交换后的Cu-SAPO-34分子筛在选择性催化还原
NOx过程中体现了良好的活性及稳定性. 在磷酸硅铝分子筛的合成过程中往往需要使用有机胺或铵盐作为有机结构导向
剂. 导向剂起到了溶解原料、导向结构、匹配电荷、填充骨架空间等复杂的作用, 因此开发新型的有机结构导向剂是调节
磷酸硅铝分子筛晶相、形貌以及酸性位点分布的最重要的手段. DNL-6分子筛是由本课题组首次报道的具有RHO拓扑结
构的磷酸硅铝分子筛, 由于其丰富的酸位点以及适宜的孔口尺寸在CO2/CH4和CO2/N2吸附分离过程中体现出良好的应用前
景. 此外由于DNL-6分子筛具有非常强的酸性(接近H-ZSM-5), 在DNL-6分子筛上首次发现MTO反应过程中的活性中间体
七甲基苯基碳正离子. 截止目前为止二乙胺是唯一被报道的成功导向DNL-6分子筛的有机胺模板剂, 在水热合成过程中必
须使用阳离子表面活性剂以防止DNL-6分子筛的溶解与转晶, 同时产品的组成调节困难。
本论文主要报道了一种新型的有机胺模板剂N,N’-二甲基乙二胺在水热条件下成功导向具有很高的结晶度与较高的
硅含量范围(20%–35%)的DNL-6分子筛, 对DNL-6产物进行X射线衍射、X射线荧光分析、X射线光电子能谱、扫描电镜以
及氮气物理吸附等一系列系统表征. 热重分析表明DNL-6分子筛α笼中较大的模板剂容纳量(单位α笼中容纳4.4个模板剂
分子)是成功得到具有超高硅DNL-6分子筛(硅摩尔含量达36.4%)的原因. 结合固体魔角旋转核磁(13C, 29Si, 27Al, 31P以及多
量子27Al)对分子筛骨架的原子配位环境的分析以及XPS表征表明超高硅DNL-6分子筛具有复杂的硅环境分布, 晶粒外表面
以酸密度很低的大面积硅岛为主, 沿晶粒半径方向向晶体内部硅含量逐渐下降同时硅岛面积逐渐减小, 晶粒中心的硅环境
主要以Si(4Al)为主. 由于超高硅DNL-6分子筛较强的酸强度、合适的酸位点分布以及狭窄的孔道尺寸在甲醇氨化反应中得
到了超过88%的甲醇转化率以及85%的甲胺+二甲胺选择性.
关键词: N,N’-二甲基乙二胺; 磷酸硅铝分子筛; 合成; DNL-6; 甲醇氨甲基化反应
收稿日期: 2018-05-07. 接受日期: 2018-06-02. 出版日期: 2018-09-05.
*通讯联系人. 电话: (0411)84379218; 传真: (0411)84691570; 电子信箱: tianpeng@dicp.ac.cn
#通讯联系人. 电话: (0411)84379998; 传真: (0411)84691570; 电子信箱: liuzm@dicp.ac.cn
基金来源: 国家自然科学基金(21476228, 21676262); 中国科学院前沿科学重点研究项目(QYZDB-SSW-JSC040).
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).