Download Full-Text PDF

crystals
Article
Synthesis, Characterization and Catalytic
Performance of Well-Ordered Crystalline
Heteroatom Mesoporous MCM-41
Jing Qin 1,2, *, Baoshan Li 1, * and Dongpeng Yan 1,3, *
1
2
3
*
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology,
Beijing 100029, China
Department of environmental protection and biological pharmacy, Beijing Industrial Technician College,
Beijing 100023, China
College of Chemistry, Beijing Normal University, Beijing 100875, China
Correspondence: [email protected] (J.Q.); [email protected] (B.L.); [email protected] (D.Y.);
Tel.: +86-10-6738-3433 (J.Q.)
Academic Editors: Helmut Cölfen and Mei Pan
Received: 27 February 2017; Accepted: 17 March 2017; Published: 23 March 2017
Abstract: Mesoporous heteroatom molecular sieve MCM-41 bulk crystals with the crystalline
phase were synthesized via a one-step hydrothermal method using an ionic complex as template.
The ionic complex template was formed by interaction between cetyltrimethylammonium ions
and metal complex ion [M(EDTA)]2− (M = Co or Ni)]. The materials were characterized by
X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy,
N2 adsorption-desorption isotherms, and X-ray absorption fine structure spectroscopy. The results
showed that the materials possess a highly-ordered mesoporous structure with a crystalline phase
and possess highly uniform ordered arrangement channels. The structure is in the vertical cross
directions with a crystalline size of about 12 µm and high specific surface areas. The metal atoms were
incorporated into the zeolite frameworks in the form of octahedral coordinate and have a uniform
distribution in the materials. The amount of metal complexes formed by metal ion and EDTA
is an essential factor for the formation of the vertical cross structure. Compared to Si-MCM-41,
the samples exhibited better conversion and higher selectivity for cumene cracking.
Keywords: bulk crystal mesoporous MCM-41; heteroatom molecular sieves; direct hydrothermal method
1. Introduction
By virtue of their high thermal and hydrothermal stability, microporous zeolites are widely
used in industries as heterogeneous catalysts, particularly as solid acid catalysts in the fields of oil
refining and petrochemistry [1]. Although the micropores of zeolites have often been described as
having excellent potential for chemical functions, their pore size often limits the reaction rate and thus
have an adverse effect on practical chemical processes [2–4]. In 1992, in an attempt to overcome this
problem, Mobil Oil Corporation synthesized a family of mesoporous solids named M41s [5] which
possess an ordered arrangement of larger pores with diameters of 2–10 nm. However, the use of these
materials as catalysts is hampered by their relatively low thermal stability and weak acid strength [6,7].
Therefore, it would be of great interest to synthesize a new type of material combining the advantages
of both mesoporous molecular sieves and zeolites [8,9]. Only a few studies have been published to date;
for example, Karlsson et al. prepared MFI/MCM-41 composites using two templates (C6 H13 (CH3 )3 NBr
and C14 H29 (CH3 )3 NBr), and optimized the template concentrations and reaction temperature [10].
In previous studies, we have reported the synthesis and characterization of composite molecular sieves
Crystals 2017, 7, 89; doi:10.3390/cryst7040089
www.mdpi.com/journal/crystals
Crystals 2017, 7, 89
2 of 11
M1 -MFI/M2 -MCM-41 (M1 , M2 = Ni, Co) and their catalytic properties for the hydrocracking of residual
oil [11] and the preparation of micro–mesoporous FeCo-MFI/MCM-41 composites which gave a clear
improvement in the hydrocracking of residual oil [12]. However, the resulting materials are composites
of zeolite crystallites embedded in a disordered mesoporous matrix. Kaliaguine et al. described
a general method for the production of a new type of material with semi-crystalline zeolite mesopore
walls [13]. Other attempts to crystallize the mesopore walls of mesostructure materials have resulted
in the formation of materials with increased thermal stability and catalytic activity. For example,
ITQ zeolites having a partially crystalline bimodal pore system with a combination of micropores
and mesopores have been synthesized by delaminating the layered zeolite precursors MCM-22 and
ferrierite [14]. However, none of these techniques yields a regular distribution of mesopores, let alone
an ideal channel system of mesopores structurally connected with the regular micropores of the zeolite.
Jiang et al. reported the synthesis of zeolite ITQ-43, which features a structurally hierarchical system of
connected mesopores and micropores. Although high-resolution transmission electron microscopy
(HRTEM) did not show the mesopore features, evidence for the presence of mesopores was provided
by automated electron diffraction tomography [15]. W. Chaikittisilp recently demonstrated a new
approach for the construction of hierarchically organized zeolites by sequential intergrowth; for the
first time, a complex and unusual morphology was observed for MFI zeolites [16].
In this paper, M-MCM-41 bulk crystal heteroatom molecular sieves with crystalline phase
have been synthesized using a direct hydrothermal method. The materials possess a crystalline
phase and highly uniform ordered arrangement channels. This is a new type of crystalline
mesoporous molecular sieve. Three-dimensional crystal mesoporous MCM-41 was obtained in typical
synthesis conditions.
2. Results
The samples were labeled as Cry-Ni and Cry-Co, and the metal heteroatom contents of the
samples measured by inductively coupled plasma (ICP) are listed in Table 1.
Table 1. Textural properties of the samples. ICP: inductively coupled plasma.
Sample
M Contents wt. % (by ICP)
SBET (m2 ·g−1 )
Pore Volume (cm3 ·g−1 )
Pore Diameter (nm)
Cry-Ni
Cry-Co
7.88
6.77
273
425
1.12
0.97
5.43
3.51
Low angle XRD patterns of the samples are presented in Figure 1. All samples show an intense
broad diffraction peak at very low 2θ angle of 0.7◦ –1.7◦ , with an overlapping broader feature at 2◦ –7◦ ,
which can be respectively attributed to the (1 0 0) diffraction peak and the overlapping pair of (1 1 0)
and (2 0 0) diffraction peaks, indicating that the samples have good structural order and the obvious
mesoporous structure of MCM-41 [17].
The particle size and shape of the samples were investigated using SEM, and the images are
shown in Figure 2a,b. The results show that the samples have well-defined morphologies with a crystal
structure (corresponding to the XRD results), and the crystalline sizes are about 12 µm with a uniform
distribution. It can be seen from the images that the two samples have good dispersion. In addition,
the materials possess a structure in the vertical cross direction. This is determined presumably by the
structure of the metal complex. The SEM-mappings of the samples are also shown in Figure 2a*,b*,
which display the composition and distribution of elements in the samples. It is clear that all samples
(Cry-Ni and Cry-Co) have uniform distribution of elements, and the metal atoms (Ni and Co) were
highly dispersed in the materials. It can be seen from Figure 2e,f that the two samples have good
dispersion. After grinding with a ball mill, the samples were tested by HRTEM, and the results
are shown in Figure 2c,d. The images indicate that the materials exhibit a uniform pore size with
a highly-ordered pore structure and the characteristic long-range ordered symmetry of a mesophase.
The ordered mesopores of the crystals can be easily observed in the HRTEM images.
Crystals 2017, 7, 89
3 of 10
with a highly-ordered pore structure and the characteristic long-range ordered symmetry of a
Crystals
2017,ordered
7, 89
3 ofimages.
11
mesophase.
The
mesopores of the crystals can be easily observed in the HRTEM
Crystals 2017, 7, 89
3 of 10
with a highly-ordered pore structure and the characteristic long-range ordered symmetry of a
mesophase. The ordered mesopores of the crystals can be easily observed in the HRTEM images.
Figure
1.
XRD patterns
patterns of
the
samples:
(a) Cry-Ni;
Cry-Ni; (b)
(b) Cry-Co.
Figure
1. XRD
the samples:
samples: (a)
Cry-Co.
Figure 1.
XRD
patterns
ofofthe
(a)
Cry-Ni;
(b) Cry-Co.
Figure 2. Cont.
Crystals 2017, 7, 89
4 of 11
Crystals 2017, 7, 89
4 of 10
Crystals 2017, 7, 89
4 of 10
Figure 2. SEM images, SEM-mappings, and high-resolution TEM (HRTEM) images of the samples:
Figure 2. SEM images, SEM-mappings, and high-resolution TEM (HRTEM) images of the samples:
Cry-Ni (a,a*,c,e) and Cry-Co (b,b*,d,f).
Cry-Ni
(a,a*,c,e)
and
Cry-Co
(b,b*,d,f). and high-resolution TEM (HRTEM) images of the samples:
Figure
2. SEM
images,
SEM-mappings,
Cry-Ni
(a,a*,c,e) and
Cry-Co
(b,b*,d,f).
The
handbook
of X-ray
photoelectron
spectroscopy (XPS) showed the binding energy of NiO
and CoO.
The binding
energy
peak of NiOspectroscopy
was between 854
eV and
855 eV.
peak ofenergy
CoO and
The
handbook
of X-ray
photoelectron
(XPS)
showed
theThe
binding
of NiO
The
handbook
of eV.
X-ray
photoelectron
spectroscopy
(XPS)
showed
the
binding
energyand
of NiO
Co
3
O
4
centered
at
780
Figure
3
shows
the
XPS
spectra
of
Cry-Ni
and
Cry-Co
samples,
the
and CoO. The binding energy peak of NiO was between 854 eV and 855 eV. The peak of CoO and
and CoO.
binding energyNi
peak
of NiO
was
between
854 eVAs
and
855 eV.
peak
CoO is
and
are The
the
de-convoluted
2p3/2
andXPS
Co spectra
2p3/2 spectra.
shown
in The
Figure
3a,ofthere
ainsets
Co3 Oinsets
at 780
eV. Figure 3 shows
the
of Cry-Ni
and
Cry-Co
samples,
and the
4 centered
Co
3O4 centered at 780 eV. Figure 3 shows the XPS spectra of Cry-Ni and Cry-Co samples, and the
predominant peak centered at 855.95 eV [18], indicating the strong interaction between nickel atom
are the
de-convoluted
Ni 2p3/2 and
Co 2p3/2
spectra.
shown
Figurein3a,Figure
there 3a,
is athere
predominant
insets
thebase,
de-convoluted
Co
2p3/2 As
spectra.
Asin
shown
is a
and
theare
silica
suggesting Ni
the2p3/2
nickeland
atoms
incorporating
into
the
silica framework
[19], which
peak predominant
centered at 855.95
eV [18],atindicating
the indicating
strong interaction
between
nickel
atom
andatom
the silica
peak
centered
855.95
eV
[18],
the
strong
interaction
between
nickel
corroborates the previous results; a peak centered at 781.55 eV in the Figure 3b is the characteristic
base,peak
suggesting
the
nickel
atoms that
incorporating
into
the silica
framework
[19],
which
corroborates
and
the
silica
base,
suggesting
nickel
atoms
incorporating
into
the silica
framework
[19],
which
of Co
2p2/3
[20],
indicatingthe
cobalt
atoms
were also incorporating
into
the silica framework.
corroborates
the previous
results; a peak
centered
eV in the
Figure
3b is the characteristic
the previous
results;
a peak centered
at 781.55
eV at
in781.55
the Figure
3b is
the characteristic
peak of Co
Co 2p2/3 [20],
that cobalt
were also incorporating
into the
silica framework.
2p2/3peak
[20],ofindicating
thatindicating
cobalt atoms
wereatoms
also incorporating
into the silica
framework.
Figure 3. X-ray photoelectron spectroscopy (XPS) spectra of the samples: (a) Cry-Ni; (b) Cry-Co.
Figure
4 3.
illustrates
the X-ray
absorption (XPS)
near-edge
structure
(XANES)
spectra
ofCry-Co.
Cry-Ms.
The
Figure
3. X-ray
photoelectron
spectroscopy
ofthe
thesamples:
samples:
Cry-Ni;
(b)
Cry-Co.
Figure
X-ray
photoelectron
spectroscopy
(XPS) spectra
spectra
of
(a)(a)
Cry-Ni;
(b)
corresponding spectra for metal oxides are given for comparison. The XANES pre-edge peak is
Figureto4the
illustrates
the X-ray
absorption
near-edge
(XANES)
spectra
of Cry-Ms.
The
attributed
1s-3d the
dipolar
forbidden
transition
[21]. structure
Principally,
this(XANES)
1s-3d
forbidden
transition
Figure
4 illustrates
X-ray
absorption
near-edge
structure
spectra
of Cry-Ms.
corresponding
spectra
for
metal
oxides
are
given
for
comparison.
The
XANES
pre-edge
peak
is
gains additional intensity when the metal center is in a non-centrally symmetric environment
The corresponding
spectra
for metal
oxides
are given
forPrincipally,
comparison.
The
XANES
pre-edge
peak is
attributed
to
the
1s-3d
dipolar
forbidden
transition
[21].
this
1s-3d
forbidden
transition
through mixing of 3d and 4p orbitals caused by the breakdown of inversion symmetry due to the
attributed
the 1s-3d
dipolarwhen
forbidden
transition
thissymmetric
1s-3d forbidden
transition
gains to
additional
intensity
the metal
center [21].
is in Principally,
a of
non-centrally
environment
structure
distortion.
Figure 4a illustrates
the XANES
spectra
NiO and Cry-Ni.
The nickel
atoms in
gainsthrough
additional
intensity
when
metalcaused
centerby
is the
in abreakdown
non-centrally
symmetric
environment
mixing
of 3d and
4pthe
orbitals
of inversion
symmetry
due to through
the
structure
distortion.
Figurecaused
4a illustrates
thebreakdown
XANES spectra
of NiO andsymmetry
Cry-Ni. The
nickel
atoms
in
mixing
of 3d and
4p orbitals
by the
of inversion
due
to the
structure
distortion. Figure 4a illustrates the XANES spectra of NiO and Cry-Ni. The nickel atoms in Cry-Ni
have similar pre-edge features to that of NiO, which indicates nickel exists as mainly Ni2+ in the
Crystals 2017, 7, 89
5 of 11
material.
Figure
Crystals
2017, 7, 4b
89 displays the XANES spectra of CoO, Co3 O4 , and Cry-Co. The cobalt 5atoms
of 10 in
Cry-Co have similar features to CoO, suggesting that Co2+ exists in the sample. Note that the peaks
Cry-Nishifted
have similar
pre-edge
features
to that
of NiO,samples
which indicates
exists
as mainly
Ni2+ shifts.
in
are slightly
to a longer
distance
than
standard
becausenickel
of the
scattering
phase
the material. Figure 4b displays the XANES spectra of CoO, Co3O4, and Cry-Co. The cobalt atoms in
Extended X-ray absorption fine structure (EXAFS) spectroscopy [22] is one of the most powerful
Cry-Co have similar features to CoO, suggesting that Co2+ exists in the sample. Note that the peaks
structural characterization methods, especially for interface-confined effects, due to its sensitivity to
are slightly shifted to a longer distance than standard samples because of the scattering phase shifts.
the three-dimensional
short-range order (typically 0–8 Å) and chemical state, including near-neighbor
Extended X-ray absorption fine structure (EXAFS) spectroscopy [22] is one of the most powerful
2
species,
distance
(R),
coordination
number
(N), and
disorder in bondeffects,
distance
4a* shows
structural characterization methods,
especially
for interface-confined
due(σto).itsFigure
sensitivity
to
3
the K the
-weighted
spectra of Cry-Ni
and order
NiO, which
are0–8
the Å)
Fourier
transformed
of Ni
K-edge
three-dimensional
short-range
(typically
and chemical
state,spectra
including
nearEXAFS
spectraspecies,
in the range
of k(R),
= 2–6
Å. The peaks
correspond
to the distance
a 2Ni
atom and
neighbor
distance
coordination
number
(N), and disorder
in bond between
distance (σ
). Figure
4a* shows the
K3-weighted
spectra
Cry-Ni
and NiO,reference
which arematerial),
the Fourier
transformed
spectra(–
of
1 )
5
its neighboring
atoms.
In the curve
of of
NiO
(a standard
there
are five peaks
Ni
K-edge
EXAFS
spectra
in
the
range
of
k
=
2–6
Å.
The
peaks
correspond
to
the
distance
between
a
2 Ni-O ,
3 Ni-Ni Ni-Ni-O, Ni-O-Ni-O, Ni-O ,
4 and Ni-Ni 5
that can be ascribed to Ni-O, Ni-Ni ,
Ni atom
and respectively.
its neighboringItatoms.
In the
of NiOof
(a Cry-Ni
standardisreference
material),
there
are five
scattering
paths,
is clear
thatcurve
the curve
different
from the
curve
of NiO,
peaks (①–⑤) that can be ascribed to Ni-O, Ni-Ni ②, Ni-O ③, Ni-Ni Ni-Ni-O, Ni-O-Ni-O, Ni-O ④,
1 and 2 of Cry-Ni are similar to the peaks 1 and 2 of NiO; a new peak
although
the two peaks and Ni-Ni ⑤ scattering paths, respectively. It is clear that the curve of Cry-Ni is different from the
1 and 2 of Cry-Ni presents, which is originated in the silicon atoms. The shape
between peaks curve of NiO, although the two peaks ① and ② of Cry-Ni are similar to the peaks ① and ② of
3 ,
4 and 5 are also different from that of NiO. The results show that the
,
and intensity
of
peaks
NiO; a new peak between peaks ① and ② of Cry-Ni presents, which is originated in the silicon
structure
forms
Ni atoms
in Cry-Ni
are different
from
in NiO.
Similar results
were
obtained
atoms.
The of
shape
and intensity
of peaks
③, ④, and
⑤ are
also different
from that
of NiO.
The in
the Cry-Co
4b* presents
Fourier
transforms
of k3 -weighted
Co
K-edge
EXAFS
results sample.
show thatFigure
the structure
forms of the
Ni atoms
in Cry-Ni
are different
from in NiO.
Similar
results
3-weighted
spectra
of Cry-Co,
Co3 O
(standard
reference
materials).
The
curve
of
Cry-Co
also
presents
were
obtainedCoO,
in theand
Cry-Co
sample.
Figure
4b*
presents
the
Fourier
transforms
of
k
Co
4
K-edge
ofare
Cry-Co,
CoO,
andthe
Co3peaks
O4 (standard
reference
materials).
curve
Cry1 EXAFS
2spectra
1 and
2 of the
two peaks
and ,
which
similar
with
curve ofThe
CoO,
butofare
much
Co also
presents
two of
peaks
①4 .and
which
are similar
with
the peaks
①
the curve
of
1 and
2and
different
from
the curve
Co3 O
The②,
small
peak
between
peaks
in ②
theofcurve
of Cry-Co
but are
different
from the
of Co
3O4. The small peak between peaks ① and ② in
is alsoCoO,
induced
bymuch
the silicon
atoms.
Thecurve
results
are
useful for estimation of the crystallinity of the
the curve of Cry-Co is also induced by the silicon atoms. The results are useful for estimation of the
samples, and the analytic results are listed in Table 2.
crystallinity of the samples, and the analytic results are listed in Table 2.
The XAFS results indicated that each metal center has a coordination number six with
The XAFS results indicated that each metal center has a coordination number six with an
an octahedral
coordination
atoms.The
Thebonds
bonds
M-O-Si
present
in the
Cry-Ms
octahedral
coordinationwith
with the
the surrounding
surrounding atoms.
of of
M-O-Si
present
in the
Cry-Ms
samples,
and
this
suggests
that
the
metal
atoms
are
incorporated
in
the
silica
framework
rather
samples, and this suggests that the metal atoms are incorporated in the silica framework rather thanthan
existing
as a separate
oxide
phase.
existing
as a separate
oxide
phase.
Figure 4. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure
Figure 4. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure
(EXAFS) of samples: (a,a*) Cry-Ni; (b,b*) Cry-Co.
(EXAFS) of samples: (a,a*) Cry-Ni; (b,b*) Cry-Co.
Sample
Coordination Type
N
R (Å)
σ2 (Å2)
Ni–O
6.0 ± 0.946
2.053 ± 0.031
0.00597 ± 0.0008
Ni–Ni
12.0 ± 0.556
3.091 ± 0.143
0.00833 ± 0.0008
Ni–O
6
2.084
12
2.948
Cry-Ni
Crystals 2017, 7, 89
NiO
Cry-Co
Ni–Ni
Co–O
Sample
CoO Cry-Ni
Co3O4
NiO
Cry-Co
Table 2. EXAFS fitting results for samples.
Co–Co
Coordination
Type
Co–ONi–O
Ni–Ni
Co–Co
Ni–O
Co–O
Ni–Ni
Co–Co
Co–O
Co–Co
6 of 11
6.0 ± 0.803
2.060 ± 0.073
0.00954 ± 0.0008
12.0 ±N0.398
3.116
± 0.099
R (Å)
0.00974
σ2 (Å2 ) ± 0.0008
6.0 ±
6 0.946
12.0 ± 0.556
2.053
± 0.031
2.133
3.091 ± 0.143
6
412
1.917
2.948
6 0.803
6.0 ±
12.0 ± 0.398
1.942
2.060
± 0.073
3.116 ± 0.099
12
3.017
0.00597 ± 0.0008
0.00833 ± 0.0008
2.084
0.00954 ± 0.0008
0.00974 ± 0.0008
The N2 adsorption-desorption isotherm method was employed to investigate the pore structur
Co–O
6
2.133
CoO
materials. The isotherms
of the Co–Co
samples obtained
at −196 3.017
°C are illustrated in Figure 5. It show
12
Co–O
4
at the isotherms of the
samples
are
type IV [23] and
possess 1.917
type H1 hysteresis loops. It is indicate
Co3 O
4
Co–Co
6
1.942
at the samples are typical mesoporous materials, exhibiting a sharp characteristic of capillar
ondensation at intermediate
partial pressures
(0.3 <was
P/P
0 < 0.5).
In the relative
pressure
range 0.90
The N2 adsorption-desorption
isotherm method
employed
to investigate
the pore structure
of
◦
materials.
isothermssharp
of the samples
at −196 C
illustrated
in Figure
5. It shows that
the
99, all samples
showThe
another
withobtained
the increase
ofarethe
nitrogen
adsorption
volume,
resultin
isotherms of the samples are type IV [23] and possess type H1 hysteresis loops. It is indicated that the
om filling thesamples
macropores
formed by interparticle spaces and untransformed amorphous silica. Th
are typical mesoporous materials, exhibiting a sharp characteristic of capillary condensation
xtural properties
of samples
listed
Table
1.InThe
pore diameters
the two
samples have littl
at intermediate
partial are
pressures
(0.3 in
< P/P
the relative
pressure range of
0.90–0.99,
all samples
0 < 0.5).
show another sharp with the increase of the nitrogen adsorption volume, resulting from filling
fference from each other, due to the different micelle diameter of [(C4H9)4N][M(EDTA)] caused b
the macropores formed by interparticle spaces and untransformed amorphous silica. The textural
2+
2+, which also influences the specific surface are
e difference properties
radius of
heteroatoms
of samples
are listed inNi
Table and
1. The Co
pore diameters
of the two samples have little difference
from each
to the different micelle diameter of [(C4 H9 )4 N][M(EDTA)] caused by the difference
ore volume, and
the other,
poredue
diameter.
radius of heteroatoms Ni2+ and Co2+ , which also influences the specific surface area, pore volume, and
the pore diameter.
Figure 5. N2 adsorption–desorption isotherms of the samples (inset: pore size distribution of the
samples: (a) Cry-Ni; (b) Cry-Co. isotherms of the samples (inset: pore size distribution of the
Figure 5. N2 adsorption–desorption
samples: (a) Cry-Ni; (b) Cry-Co.
The 0.5 g samples of Cry-Ni and Cry-Co were placed in 50 mL 1 mol/L NaOH solution, stirring
at room temperature for 2 h, then samples were filtered and dried. The morphological changes
The 0.5 g samples
of Cry-Ni
andunder
Cry-Co
were
placedand
in 50
1 mol/L
NaOH
solution,
stirrin
of the samples
were observed
electron
microscope,
the mL
morphology
of the
samples
is
shown infor
Figure
The crystal
structure
of filtered
the samples
treated
by sodium
hydroxide solutionchanges of th
room temperature
2 h,6.then
samples
were
and
dried.
The morphological
is shown. The samples covering the surface of the oxide dissolved by the lye treatment, and the
mples were observed
under
electron
and
the morphology
the samples
is shown i
crystal exhibits
relatively
completemicroscope,
form. Mesoporous
molecular
sieve material byof
traditional
alkali
treatment,structure
hole wall collapse
phenomenon
willtreated
appear. Inby
contrast,
the crystal
structure ofsolution
metal atomsis shown. Th
gure 6. The crystal
of the
samples
sodium
hydroxide
in the crystalline molecular sieve improves the alkali resistance of the molecular sieve.
mples covering the surface of the oxide dissolved by the lye treatment, and the crystal exhibit
latively complete form. Mesoporous molecular sieve material by traditional alkali treatment, hol
all collapse phenomenon will appear. In contrast, the crystal structure of metal atoms in th
ystalline molecular sieve improves the alkali resistance of the molecular sieve.
Crystals 2017, 7, 89
7 of 10
Crystals 2017, 7, 89
7 of 11
rystals 2017, 7, 89
7 of
Figure 6. SEM micrographs of the samples treated with NaOH solution: (a) Cry-Ni; (b) Cry-Co.
According to the above results, a possible mechanism was proposed that is revealed as Scheme
1. There are two nitrogen
atoms andoffour
carboxyl
oxygen
atoms
(marked
as A,
C, D, respectively)
6. SEM micrographs
the samples
treated
with NaOH
solution:
(a) Cry-Ni;
(b) B,
Cry-Co.
Figure 6. SEMFigure
micrographs
of the samples
treated
with NaOH
solution:
(a)
Cry-Ni;
(b) Cry-Co.
in the EDTA molecule which can coordinate with the metal ion to form the complex ion [M(EDAT)]2−
According
to the above
a possible
mechanism
was proposed
is revealed
Scheme
with an octahedral
structure.
Inresults,
the chelate
ion,
the carboxyl
oxygenthat
atoms
A, B,asand
two1.nitrogen
According
to
the
above
results,
a
possible
mechanism
was
proposed
that
is
revealed
as Schem
There
are
two
nitrogen
atoms
and
four
carboxyl
oxygen
atoms
(marked
as
A,
B,
C,
D,
respectively)
in vertical
atoms are at a flat surface, and the other two carboxyl oxygen atoms C and D are in the
2
−
the nitrogen
EDTA molecule which
can coordinate
with theoxygen
metal ion to
form the
complex ion
Theredirection
are two
and
fourthe
carboxyl
atoms
as[M(EDAT)]
A, B, C,was
D, respectivel
but not at aatoms
flat surface
with
two nitrogen
atoms.
As (marked
the complex
solution
added
with an octahedral structure. In the chelate ion, the carboxyl oxygen atoms A, B, and two nitrogen
2− [M(EDAT)]
+
n the EDTA
which
can coordinate
with
thesolution,
metal
ion
to form
the complex
ion
into themolecule
cetyltrimethyl
ammonium
ionic
atoms are at a flat
surface, andbromide
the other (CTAB)
two carboxyl
oxygenthe
atoms
C associate
and D are [M(EDAT)]
in the vertical (CTA )2
the special
structure
(Scheme
micelle
suspension
wastwo
mixed
direction
but not at amicelle
flat
withbe
theformed
two nitrogen
atoms.1).
AsAs
thethe
complex
solution
was
with anand
octahedral
structure.
In surface
thewould
chelate
ion,
the
carboxyl
oxygen
atoms
A,
B,added
and
nitroge
2− (CTA+ )
4−
4−
into
the
cetyltrimethyl
ammonium
bromide
(CTAB)
solution,
the
ionic
associate
[M(EDAT)]
withat
thea solution
of SiO4 and
formed
SiO2 and
of sodium
hydroxide,
ions
toms are
flat surface,
the by
other
twoplenty
carboxyl
oxygen
atoms SiO
C 4and
Dwould
are2 inrapidly
the vertic
and
the
special
structure
micelle
would
be
formed
(Scheme
1).
As
the
micelle
suspension
was
mixed
hydrolyze and polymerize around
the
micelle
which
possessed
a
structure
in
the
vertical
cross
irection but not
flat surface
the
nitrogen
As the complex
was adde
with at
theasolution
of SiO4 4−with
formed
by two
SiO2 and
plenty ofatoms.
sodium hydroxide,
SiO4 4 − ionssolution
would
direction. Additionally, the crystalline mesoporous zeolite precursors would grow along the vertical
2− (CTA+
rapidly hydrolyze
and polymerize
around(CTAB)
the micellesolution,
which possessed
aionic
structure
in the vertical
cross
nto thecross
cetyltrimethyl
ammonium
bromide
thethe
associate
[M(EDAT)]
2−
direction
in
the
following
hydrothermal
process.
Because
structure
of
the
[M(EDAT)]
direction. Additionally, the crystalline mesoporous zeolite precursors would grow along the vertical
nd thecomplex
specialcross
micelle
be
formed
(Scheme
1).theAs
the micelle
suspension
was
2 − same
isstructure
not
the same
in following
thewould
vertical
cross
direction,
micelle
structure
would
not be the
in mixe
direction
in the
hydrothermal
process.the
Because
structure of
the [M(EDAT)]
4−
is not
the
same
in by
the
vertical
cross
direction,
micelle structure
not
be4structures
theions
samewould
with thethe
solution
of SiO
44−
formed
SiOfactor
2 and
plenty
ofthesodium
hydroxide,
SiO
two complex
directions;
this
is the
main
causing
the
sample
to
havewould
different
in therapid
in
the
two
directions;
this
is
the
main
factor
causing
the
sample
to
have
different
structures
in
the
different
(Figure
2). A certain
amountwhich
of the complexes
by metalin
ionthe
andvertical
EDTA cro
ydrolyze
and directions
polymerize
around
the micelle
possessedformed
a structure
different directions (Figure 2). A certain amount of the complexes formed2−by metal ion and EDTA was
wasAdditionally,
essential in thethe
formation
of themesoporous
structure. Enough
[M(EDTA)]
could
ensure
the formation
2 precursors
− could ensure
irection.
crystalline
zeolite
would
grow
along theofvertic
essential in the formation
of the structure.
Enough [M(EDTA)]
the
formation
of single
single structural
micelleswith
with
the
vertical
structure,
which
is the prerequisite
of the
formation
structural
thehydrothermal
vertical
cross cross
structure,
which isBecause
the prerequisite
the formation
the
ross direction
in themicelles
following
process.
the ofstructure
ofof the
[M(EDAT)]
of the crystalline
zeoliteprecursors.
precursors.
crystalline zeolite
omplex is not the same in the vertical cross direction, the micelle structure would not be the same
he two directions; this is the main factor causing the sample to have different structures in th
ifferent directions (Figure 2). A certain amount of the complexes formed by metal ion and EDT
was essential in the formation of the structure. Enough [M(EDTA)]2− could ensure the formation
ngle structural micelles with the vertical cross structure, which is the prerequisite of the formatio
f the crystalline zeolite precursors.
Scheme
1. The
supposed formation
formation mechanism
of Cry-M.
Scheme
1. The
supposed
mechanism
of Cry-M.
The catalytic performance of the crystalline molecular sieves for cumene cracking was
investigated. The device diagram is shown in Figure 7. Before the reaction, the samples were activated
at 300 °C and nitrogen atmosphere for one hour. Reaction conditions were as follows: temperature,
30 °C; nitrogen atmosphere; mass ratio of raw material/catalyst, 100. After a certain reaction time, the
Crystals 2017, 7, 89
8 of 11
The catalytic performance of the crystalline molecular sieves for cumene cracking was investigated.
The device diagram is shown in Figure 7. Before the reaction, the samples were activated at 300 ◦ C
stals 2017, 7, 89 and nitrogen atmosphere for one hour. Reaction conditions were as follows: temperature, 30 ◦ C;
8 of 1
nitrogen atmosphere; mass ratio of raw material/catalyst, 100. After a certain reaction time, the results
are shown
in Figure 8.decreased
The first peak
is the20
cumene
peak,
the second peak
for small
molecule
mples were not
significantly
after
times,
indicating
thatisthe
samples’
recycling rate
hydrocarbon, the third peak is attributed to benzene homologues. It can be seen from the figure
e higher, andthat
themetal
highest
conversion
of 54.5%
anda catalytic
44.03%effect
was
cumene cracking
atoms in
the crystallinerate
molecular
sieves have
onreached.
the crackingThe
of cumene.
Figureacid
8a*,b* catalytic
for the catalytic
conversion
curves,
the silicon
catalytic efficiency
of Cry-Ni
and Cry-Co samples
action is a typical
reaction.
The
pure
Si-MCM-41
molecular
sieves have almos
were not significantly decreased after 20 times, indicating that the samples’ recycling rates are higher,
acid, so there is no catalytic function of the reaction. Comparing to Si-MCM-41, the sample
and the highest conversion rate of 54.5% and 44.03% was reached. The cumene cracking reaction is
hibited better
conversion
higher
selectivity
for molecular
cumenesieves
cracking.
The
better catalyti
a typical
acid catalyticand
reaction.
The pure
silicon Si-MCM-41
have almost
no acid,
so there is no catalytic
of the
reaction. Comparing
to Si-MCM-41,
the appropriate
samples exhibitedpore
betterdiameter, and
rformance is attributed
to thefunction
samples
possessing
uniform
channels,
Crystals 2017, 7, 89
8 of 10
conversion and higher selectivity for cumene cracking. The better catalytic performance is attributed
ive sites caused
bysamples
the introduction
of Ni
and Co
atomspore
intodiameter,
the framework
ofcaused
molecular
to the
possessing
uniform
channels,
appropriate
and
active sites
by the sieves.
samples were
not significantly
decreased
after
20 times, indicating
that the
samples’
recycling
rates
introduction
of and
Ni and
Co atoms
into therate
framework
of molecular
sieves.
are higher,
the highest
conversion
of 54.5% and
44.03% was
reached. The cumene cracking
reaction is a typical acid catalytic reaction. The pure silicon Si-MCM-41 molecular sieves have almost
no acid, so there is no catalytic function of the reaction. Comparing to Si-MCM-41, the samples
exhibited better conversion and higher selectivity for cumene cracking. The better catalytic
performance is attributed to the samples possessing uniform channels, appropriate pore diameter, and
active sites caused by the introduction of Ni and Co atoms into the framework of molecular sieves.
Figure
7. 7.
Diagram
forcumene
cumene
cracking.
Figure
Diagramof
ofthe
the apparatus
apparatus for
cracking.
Figure 7. Diagram of the apparatus for cumene cracking.
Figure
8. Chromatogram
(a,a*)and
andconversion
conversion (b,b*)
cumene
cracking
reaction.
Figure
8. Chromatogram
(a,a*)
(b,b*)curves
curvesofofthe
the
cumene
cracking
reaction.
3. Conclusion
Mesoporous heteroatom molecular sieves MCM-41s with crystalline phase were synthesized via
a one-step hydrothermal method. The resulting materials possessed a structure in the vertical cross
direction with a crystalline size of about 12 µm and high specific surface areas, and possess a highlyordered mesoporous structure and ordered arrangement channels. The elements in the samples have
a uniform distribution and are highly dispersed in the materials. A certain amount of metal
complexes formed by metal ion and EDTA is an essential factor for the formation of the vertical cross
Crystals 2017, 7, 89
9 of 11
3. Conclusion
Mesoporous heteroatom molecular sieves MCM-41s with crystalline phase were synthesized
via a one-step hydrothermal method. The resulting materials possessed a structure in the vertical
cross direction with a crystalline size of about 12 µm and high specific surface areas, and possess
a highly-ordered mesoporous structure and ordered arrangement channels. The elements in the
samples have a uniform distribution and are highly dispersed in the materials. A certain amount of
metal complexes formed by metal ion and EDTA is an essential factor for the formation of the vertical
cross structure. At the same time, the crystalline mesoporous heteroatom samples improve the alkali
resistance of the molecular sieves. Compared to Si-MCM-41, the samples exhibited better conversion
and higher selectivity for cumene cracking.
4. Materials and Methods
Nickel nitrate hexahydrate, Ni(NO3 )2 ·6H2 O (AR, Beijing Yili Fine Chemical Product Limited
Company, Beijing, China), was used as Ni source. Cobalt nitrate hexahydrate, Co(NO3 )2 ·6H2 O
(AR, Shantou Xilong Chemical Limited Company, Shantou, China), was used as Co source.
Cetyltrimethyl ammonium bromide (CTAB, AR, Tianjin Jinke Fine Chemical Institute, Tianjin, China)
was used as structure template. Ethylenediaminetetraacetate (EDTA, AR, Beijing Chemical Factory,
Beijing, China) was used as structure-directing agent. White carbon black (SiO2 , AR, Beijing Chemical
Factory, Beijing, China) was used as Si source, and sodium hydroxide (NaOH, AR, Beijing Chemical
Factory, Beijing, China) was used to adjust the pH.
The new crystalline sample of Cry-M (M = Ni, Co) was prepared through a direct hydrothermal
synthesis method, and the detailed process is as follows: a transparent solution of the ionic complex
[M(EDTA)]2− was made by dissolving disodium ethylenediaminetetraacetate solution and a certain
amount of M(NO3 )2 ·6H2 O in H2 O (10 g) and mixing well. CTAB (4.5 g, 12.3 mmol) was dissolved in
34 g of H2 O at 70 ◦ C. In another flask, 0.5 g (12.5 mmol) of sodium hydroxide dissolved in 15 g of H2 O
was mixed with 2.25 g (37.5 mmol) of SiO2 stirred for 0.5 h and then heated to 60 ◦ C. The ionic complex
[M(EDTA)]2− and CTAB solutions were then added to the silica solution, and the resulting mixture
was stirred for 0.5 h to form a homogeneous emulsion. After adjusting the pH to 11 using sodium
hydroxide solution, the mixture was stirred for another 12 h. The mixture was then transferred into
a Teflon-lined autoclave and heated at 160 ◦ C under autogenous pressure for 96 h. The resulting solid
was filtered and washed with water until the pH of the filtrate reached 7.0. After drying the sample
overnight at 100 ◦ C, the template was removed by calcination in air at 550 ◦ C for 5 h.
X-ray powder diffraction (XRD) patterns were recorded on a Philips X0 Pert diffractometer
equipped with a rotating anode using Cu Kα radiation (λ = 0.1541 nm). The pore morphology of the
samples was examined by high-resolution transmission electron microscopy (HRTEM) on a JEM-2100
microscope with an accelerating voltage of 200 kV. The crystal morphology was studied using a Hitachi
S-4700 scanning electron microscope (SEM). The chemical compositions of the samples were measured
by Optima 8000 inductively coupled plasma (ICP). Nitrogen adsorption–desorption isotherms were
obtained using a Quantachrome Autosorb-1 volumetric adsorption analyzer. The volume of the
adsorbed N2 was normalized to standard temperature and pressure. Prior to the measurements,
the samples were degassed at 300 ◦ C for 16 h. The X-ray photoelectron spectroscopy (XPS) analyses
were conducted on an ESCALAB 250 spectrometer equipped with an Al Kα X-ray source. The carbon
1 s peak at 284.6 eV was used as the reference for binding energies. X-ray absorption fine structure
(XAFS) spectroscopy of the M (Ni, Co) K-edge of the samples was performed on the U7C beamline at
the National Synchrotron Radiation Laboratory (NSRL) of China. The typical energy of the storage
ring was 0.8 GeV, with a maximum current of 250 mA. A Si (111) double crystal monochromator was
used. The data analysis of all the XAFS spectra was carried out using the IFEFFIT software (NSRL,
Beijing, China).
Crystals 2017, 7, 89
10 of 11
Acknowledgments: The work was supported by the National Natural Science of Foundation of China
(No. 21271017) and the Fundamental Research Funds for the Central Universities (YS1406), Beijing Engineering
Center for Hierarchical Catalysts. X-ray absorption fine structure spectroscopy was performed on the U7C
beamline of the National Synchrotron Radiation Laboratory (NSRL) of China.
Author Contributions: Jing Qin and Baoshan Li conceived and designed the experiments; Jing Qin performed
the experiments and analyzed the data; Baoshan Li and Dongpeng Yan contributed analysis tools; Jing Qin wrote
the paper; Dongpeng Yan modified the article.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
Kim, J.; Choi, M.; Ryoo, R. Effect of mesoporosity against the deactivation of MFI zeolite catalyst during the
methanol-to-hydrocarbon conversion process. J. Catal. 2010, 269, 219–228. [CrossRef]
Fang, Y.; Hu, H. An ordered mesoporous aluminosilicate with completely crystalline zeolite wall structure.
J. Am. Chem. Soc. 2006, 128, 10636–10637. [CrossRef] [PubMed]
Tao, Y.; Kanoh, H.; Kaneko, K. ZSM-5 monolith of uniform mesoporous channels. J. Am. Chem. Soc. 2003,
125, 6044–6045. [CrossRef] [PubMed]
Yang, Z.; Xia, Y.; Mokaya, R. Zeolite ZSM-5 with unique supermicropores synthesized using mesoporous
carbon as a template. Adv. Mater. 2004, 16, 727–732. [CrossRef]
Kresge, C.; Leonowicz, M.; Roth, W.; Vartuli, J.; Beck, J. Ordered mesoporous molecular sieves synthesized
by a liquid-crystal template mechanism. Nature 1992, 359, 710–712. [CrossRef]
Choi, M.; Na, K.; Kim, J.; Sakamoto, Y.; Terasaki, O.; Ryoo, R. Stable single-unit-cell nanosheets of zeolite
MFI as active and long-lived catalysts. Nature 2009, 461, 246–249. [CrossRef] [PubMed]
Sun, J.; Bonneau, C.; Cantín, Á.; Corma, A.; Díaz-Cabañas, M.J.; Moliner, M.; Zhang, D.; Li, M.; Zou, X.
The ITQ-37 mesoporous chiral zeolite. Nature 2009, 458, 1154–1157. [CrossRef] [PubMed]
Liu, Y.; Zhang, W.; Pinnavaia, T.J. Steam-stable MSU-S aluminosilicate mesostructures assembled from
zeolite ZSM-5 and zeolite beta seeds. Angew. Chem. Int. Ed. 2001, 11, 1295–1298. [CrossRef]
Li, X.; Li, B.; Xu, J.; Wang, Q.; Pang, X.; Gao, X.; Zhou, Z.; Piao, J. Synthesis and characterization of
Ln-ZSM-5/MCM-41 (Ln = La, Ce) by using kaolin as raw material. Appl. Clay Sci. 2010, 50, 81–86. [CrossRef]
Karlsson, A.; Stöcker, M.; Schmidt, R. Composites of micro-and mesoporous materials: Simultaneous
syntheses of MFI/MCM-41 like phases by a mixed template approach. Microporous Mesoporous Mater. 1999,
27, 181–192. [CrossRef]
Li, B.; Li, X.; Xu, J.; Pang, X.; Gao, X.; Zhou, Z. Synthesis and characterization of composite molecular
sievesM1-MFI/M2-MCM-41(M1 , M2 = Ni, Co) with high heteroatom contentand their catalytic properties
for hydrocracking of residual oil. J. Colloid Interface Sci. 2010, 346, 199–207. [CrossRef] [PubMed]
Li, B.; Xu, J.; Li, X.; Liu, J.; Zuo, S.; Pan, Z.; Wu, Z. Bimetallic iron and cobalt incorporated MFI/MCM-41
composite and its catalytic properties. Mater. Res. Bull. 2012, 47, 1142–1148. [CrossRef]
Trong On, D.; Kaliaguine, S. Large-pore mesoporous materials with semi-crystalline zeolite frameworks.
Angew. Chem. Int. Ed. 2001, 113, 3348–3351. [CrossRef]
Narkhede, V.; Gies, H. Crystal Structure of MCM-22 (MWW) and Its Delaminated Zeolite ITQ-2 from
High-Resolution Powder X-ray Diffraction Data: An Analysis Using Rietveld Technique and Atomic Pair
Distribution Function. Chem. Mater. 2009, 21, 4339–4346. [CrossRef]
Jiang, J.; Jorda, J.L.; Yu, J.; Baumes, L.A.; Mugnaioli, E.; Diaz-Cabanas, M.J.; Kolb, U.; Corma, A. Synthesis and
structure determination of the hierarchical meso-microporous zeolite ITQ-43. Science 2011, 333, 1131–1134.
[CrossRef] [PubMed]
Chaikittisilp, W.; Suzuki, Y.; Mukti, R.R.; Itabashi, K.; Shimojima, A.; Okubo, T. Formation of hierarchically
organized zeolites by sequential intergrowth. Angew. Chem. Int. Ed. 2013, 125, 3439–3443. [CrossRef]
Guo, X.; Lai, M.; Kong, Y.; Ding, W.; Yan, Q. Novel Coassembly Route to Cu-SiO2 MCM-41-like Mesoporous
Materials. Langmuir 2004, 20, 2879–2882.
Wu, N.; Zhang, W.; Li, B.; Han, C. Nickel nanoparticles highly dispersed with an ordered distribution in MCM-41
matrix as an efficient catalyst for hydrodechlorination of chlorobenzenem. Microporous Mesoporous Mater. 2014,
185, 130–136. [CrossRef]
Crystals 2017, 7, 89
19.
20.
21.
22.
23.
11 of 11
Qin, J.; Li, B.; Zhang, W.; Lv, W.; Han, C.; Liu, J. Synthesis, characterization and catalytic performance of
well-ordered mesoporous Ni-MCM-41 with high nickel content. Microporous Mesoporous Mater. 2015, 208, 181–187.
[CrossRef]
Jamshid, I.; Donald, O.; Hossein, T. Characterization of K2 CO3 /Co-MoS2 catalyst by XRD, XPS, SEM,
and EDS. Appl. Surf. Sci. 2001, 185, 72–78.
Sano, M.; Maruo, T.; Yamatera, H.; Suzuki, M.; Saito, Y. EXAFS studies on the origin of high catalytic activity
in nickel Y zeolite. J. Am. Chem. Soc. 1987, 109, 52–55. [CrossRef]
Guo, X.; Lai, M.; Kong, Y.; Ding, W.; Yan, Q. Novel coassembly route to Cu-SiO2 MCM-41-like mesoporous
materials. Langmuir 2004, 20, 2879–2882. [CrossRef] [PubMed]
Yang, Y.H.; Lim, S.; Du, G.A.; Chen, Y.; Ciuparu, D.; Haller, G.L. Synthesis and characterization of highly ordered
Ni-MCM-41 mesoporous molecular sieves. J. Phys. Chem. 2005, 109, 13237–13246. [CrossRef] [PubMed]
© 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).