Factors affect on the synthesis of silica-pillared zirconium phosphate with template-directing self-assembly method and its epoxidation catalytic performance

Article abstract of DOI:10.1007/s10562-014-1193-9

A series of silica-pillared zirconium phosphate materials with ordered structure were synthesized using hexadecylamine (HDA) as expanding agent, dodecyl dimethyl benzyl ammonium chloride (DDBAC) as template agent and tetraethyl orthosilicate (TEOS) as silica source. The textural properties of the materials can be effectively controlled by adjusting the dosage of HDA, DDBAC and TEOS. Furthermore, a template-directing self-assembly mechanism was proposed based on the synthesis. In the epoxidation of methyl soyate, the prepared materials showed excellent performance with 95.9 % conversion of double bonds and 84.7 % epoxy selectivity. This result is determined by the large surface area and the ordered interlayer structure. Graphical Abstract: Series silica-pillared zirconium phosphate materials with ordered structure were synthesized. The textural properties of the materials can be effectively controlled by adjusting the dosage of each reaction species. A template-directing self-assembly mechanism was proposed based on the synthesis. The materials show excellent catalytic performance on the epoxidation of methyl soyate.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-014-1193-9

Catal Lett (2014) 144:663–673
DOI 10.1007/s10562-014-1193-9
Factors Affect on the Synthesis of Silica-Pillared Zirconium
Phosphate with Template-Directing Self-Assembly Method and its
Epoxidation Catalytic Performance
•
Wenjin Liu Hongning Wang Mengyao He
•
•
•
Jing Zhong Ruoyu Chen
Received: 19 November 2013 / Accepted: 7 January 2014 / Published online: 4 February 2014
Ó Springer Science+Business Media New York 2014
Abstract A series of silica-pillared zirconium phosphate
materials with ordered structure were synthesized using
hexadecylamine (HDA) as expanding agent, dodecyl
dimethyl benzyl ammonium chloride (DDBAC) as tem-
plate agent and tetraethyl orthosilicate (TEOS) as silica
source. The textural properties of the materials can be
effectively controlled by adjusting the dosage of HDA,
DDBAC and TEOS. Furthermore, a template-directing
self-assembly mechanism was proposed based on the
synthesis. In the epoxidation of methyl soyate, the prepared
materials showed excellent performance with 95.9 %
conversion of double bonds and 84.7 % epoxy selectivity.
This result is determined by the large surface area and the
ordered interlayer structure.
of PCH include its poor thermal stability, weak acidity and
fast inactivation in reaction [5, 6]. Those features restrict its
application. In recent years, a-zirconium phosphate
(a-Zr(HPO4)2ꢀH2O, a-ZrP) has been extensively studied as
an ideal precursor for the preparation of pillared layered
materials due to its typical layered structure and out-
standing cation exchange capacity (6.67 mmol/g, which is
7*15 times of that of clay compounds [7] ). However, due
to the large charge density between layers, it cannot swell
in aqueous solution as clay does. Therefore, it could be
difficult to expand the layers for pillaring. This issue was
first solved by the insertion of polyhydroxy cations into
interlayer of a-ZrP and different types of pillared zirco-
nium phosphate materials were obtained and applied to
catalytic reactions [8–12]. Nonetheless, this method has the
following disadvantages such as unmanageable pillared
structure and wide pore size distribution, which limited the
applications in shape-selective adsorption and selective
catalysis.
Keywords Controllable synthesis ꢀ Silica-pillared ꢀ
Nanostructure ꢀ Self-assembly ꢀ Epoxidation
1 Introduction
In 2005, the self-assembly effect of template agent was
first utilized in the preparation of pillared zirconium
phosphate by Jimenez-Lopez [13]. Acetyltrimethyl
ammonium bromide (CTMA) expanded zirconium phos-
phate (CTMA–ZrP) was taken as raw material and the
hexadecylamine (HDA) was intercalated as template agent.
Then, the tetraethyl orthosilicate (TEOS) was intercalated
and hydrolyzed to form interlayer gallery. Finally, the
porous phosphate heterostructures (PPH) were obtained
after calcinations. Compared with the traditional pillaring
method using polyhydroxy cations, this method gives full
play to the self-assembly effect of template agent. It
achieves the controllable synthesis of PPH materials. A
high specific surface area is obtained as well. Based on the
methodology, a series of functional applications of PPH
materials were developed [14–19] and the properties of
Pillared layered materials represent a remarkable class of
materials which with regular pore sizes and ordered layer
structure, showing great advantages in many molecule-
selective catalysis [1]. In the last decade, the self-assembly
method using the template agent and functional guest had
been successfully used in the preparation of porous clay
heterostructure (PCH), permitting series applications in
heterogeneous catalysis [2–4]. However, the disadvantages
W. Liu ꢀ H. Wang ꢀ M. He ꢀ J. Zhong ꢀ R. Chen (&)
School of Chemistry and Chemical Engineering, Changzhou
University, 1 Gehu Road, Changzhou 213164, Jiangsu, People’s
Republic of China
e-mail: cxdcry@163.com
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W. Liu et al.
acid site of PPH materials were also been investigated [20].
Furthermore, this method is still imperfect since the prep-
aration of CTMA–ZrP provokes a worse orderliness than
that of the layered zirconium phosphate. The abundant
interlayer acid sites have not been fully exposed. This
might due to the regularity of the pore structures is defi-
cient. a-ZrP is composed of zirconium atoms in a semi-
planar arrangement bridged by phosphate groups above and
below the zirconium atom plane, which possess an integral
structure and high stability of layer. The interlayer elec-
trostatic interaction could be weakened by using some
alkyl-amine. Thus a starting material with appropriate
interlayer spacing and ordered layer structure could be
obtained. Then, the pillared zirconium phosphate with
uniform structure and more abundant acid sites would be
expected to be synthesized by interlayer molecular self-
assembly using suitable template agent and functional
guest, permitting potential applications in adsorption and
catalysis.
wise to the colloidal suspensions containing a-ZrP powders
and the liquid solid ratio of the final suspensions was about
5 L/g. The resulting mixtures were stirred at 50 °C for
about 24 h until HDAs were fully intercalated into the a-
ZrP inter-galleries. At last, the HDA intercalated a-ZrP
suspensions were filtered and subsequently washed with
plenty of distilled water and ethanol to remove HDA
molecules not intercalated. The obtained solid were dried
at 60 °C and denoted HDA-n-ZrP, where n is the molar
ratio of hexadecylamine/a-ZrP.
2.1.2 Silica-Pillared Zirconium Phosphate
The HDA-n-ZrP was first suspended in water. Then a
certain amount of 0.1 mol/L Dodecyl dimethyl benzyl
ammonium chloride (DDBAC) water solution was added.
Meanwhile tetraethyl orthosilicate (TEOS) was also drop-
ped slowly into the suspensions. The liquid–solid ratio of
the final mixtures was about 30 mL/g. After 2 h stirring,
the pH of the gel mixture was adjusted by ammonia solu-
tion to 10 and continued stirring for other 2 h at room
temperature. The product was recovered by filtration, dried
in oven at 60 °C. Subsequently it was calcined at 550 °C
for 6 h using programmed furnace in air (with increasing
temperature rate of 2 °C/min). The prepared solids were
denoted x-SPZHD-y, where x and y are the DDBAC/
HDA–ZrP and TEOS/HDA–ZrP molar ratios used in the
synthesis, respectively.
In this paper, a controllable synthesis of silica-pillared
zirconium phosphate is achieved by adjusting the dosage of
each reaction species. Alkylamine expanded zirconium
phosphate is first prepared and used for the intercalation of
surfactant and silica source. After adjusting the solution
pH, the silica galleries are formed via interlayer molecular
self-assembly. Based on the synthesis, a probable forma-
tion mechanism of the silica-pillared zirconium phosphate
is proposed. As for the catalytic performance, the epoxi-
dation of methyl soyate was chosen as probe reaction to
evaluate the effective acid–base and structure properties of
silica-pillared zirconium phosphate. It is an important
approach to obtain industrial products whit high commer-
cial significance [21]. Moreover, as a typical acid catalytic
reaction, it could distinguish the Lewis sites and Bronsted
sites of the catalyst sensitively [22] and the steric effect
arising from the long carbon chain of methyl soyate also
produces some structural requirements to the catalysts [23].
2.2 Characterization
The obtained solid products were characterized by X-ray
diffraction (XRD) on a Rigaku D/Max 2,500 VBZ?/PC
diffractometer using Cu Ka radiation (40 kV, 50 mA) in
the range between 0.5° and 10° 2h (low-angle range) and
Cu Ka radiation (40 kV, 200 mA) in the range between 3°
and 90° 2h (high-angle range). N2 adsorption isotherms
were obtained using a Micromeritics ASAP 2000 instru-
ment. The samples were outgassed at 200 °C for 8 h before
measurements. The specific surface area (SBET) was esti-
mated by the Brunauer–Emmett–Teller (BET) equation,
and the mesopore size distribution and mesopore analysis
were obtained from the desorption branch of the isotherm
using the Barrett–Joyner–Halenda method. Scanning elec-
tron microscopy (SEM) micrographs were obtained on a
HitachiS-4700 microscope operated at 30 kV. The trans-
mission electron microscopy (TEM) was done using JEOL-
2100 transmission electron micro-scope with an acceler-
ating voltage of 200 kV. Ammonia thermal programmed
desorption (NH3–TPD) was used to determine the total
acidity of the samples. Measurement was carried out by a
ASAP2920 (Thermo Electron Corporation). About 100 mg
of sample was treated at 600 °C in He for 1 h, cooled to
2 Experimental
2.1 Catalysis Synthesis
2.1.1 Hexadecylamine Intercalated a-ZrP
The synthesis of a-ZrP was performed with the method-
ology as described in the Ref. [24]. The hexadecylamine
(HDA) intercalated a-ZrP were prepared via the following
steps according to the published procedure [25]. First, a-
ZrP was suspended in a 50:50 mixture of H2O and ethanol
and the mixture was sonicated for about 10 min to obtain
well-dispersed colloidal suspensions. Second, various
amounts of HDA dissolved in ethanol were added drop-
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Factors Affect on the Synthesis of Silica-Pillared Zirconium Phosphate
665
Fig. 1 Left: representative
methyl soyate. Right:
epoxidized products of methyl
soyate
373 K and then exposed to a 1 vol% NH3/He stream for
20 min. Weakly adsorbed NH3 was removed by flushing
with He at 100 °C for 10 min. Finally, the treating tem-
perature was increased from 100 to 800 °C at a rate of
10 °C/min in a He flow of 20 cm3/min. Pyridine adsorption
coupled to FT–IR spectroscopy was employed to determine
the nature of the acid centres of the catalysts. The samples
were evacuated (380 °C, 10-2 Pa overnight), exposed to
pyridine vapour at room temperature, and then out-gassed
between 200 °C and 450 °C. FT–IR spectra were recorded
reported by the literature [27]. Corresponding computa-
tional formulas are listed as follows:
Conversion ð%Þ
½Iodine Numberꢁinitial ꢂ ½Iodine Numberꢁfinal
¼
ꢃ 100
ð1Þ
½Iodine Numberꢁinitial
½Oxirane Numberꢁ ꢃ PMI2
½Iodine Numberꢁ ꢃ PMO
Yield
Yield (%Þ =
ꢃ 100
ð2Þ
´
´
on a PROTEGE 460 spectrometer.
Selectivity (%Þ =
ꢃ 100
ð3Þ
Conversion
where Iodine Number is the grams of I2 that is taken up by
100 g of the oil; Oxirane Number is the grams of epoxydic
oxygen per 100 g of the oil; PMI2 is the molar weight of
I2 (g/mol); PMO is the molar weight of O (g/mol).
2.3 Catalytic Reaction
Methyl soyate was prepared by transesterification of
refined soybean oil with methanol by a standard procedure
using an alkali catalyst [26]. In a typical epoxidation
reaction, 10 g of methyl soyate was taken in a three-
necked, glass round-bottom flask (50 ml) fitted with a
water-cooled condenser and thermometer, then 1 g of
methanoic acid, 0.1 g of catalyst and 6.5 g of hydrogen
peroxide 30 wt% was added successively. The flask was
placed in a water-bath maintained at about 55 °C and the
reaction was conducted under reflux with magnetic stirring
for 5 h. The final solution was transferred to a separating
funnel and the aqueous layer was removed. The organic
layer was washed with 0.1 mol/L Na2CO3 solution three
times and then washed with distilled water until the pH was
7. Then the epoxidation of methyl soyate was obtained
from the supernatant after centrifugation.
3 Results and Discussion
3.1 The Controllable Synthesis of SPZHD Analysis
3.1.1 The Effect of HDA upon the Morphology
and Structure of SPZHD
First, several HDA-n-ZrP materials are obtained by
adjusting the dosage of HDA (Fig. 2). As shown in the
XRD patterns, when the molar ratio of HDA/a-ZrP is 0.2, a
relative weak peak at 2h = 2.95° (d001 = 3.00 nm) grows
out, it indicates HDA has been intercalated but the inter-
calated amount is small. As the ratio increases to 0.7, the
diffraction peak at 2h = 2.95° (d001 = 3.00 nm) becomes
sharp and it indicates an interdigitated layers structure of
intercalated HDAs occurs. Further increase the molar ratio
of HDA/a-ZrP to 2, a new distinct peak located at
2h = 2.05° (d001 = 4.30 nm) appears. It indicates the
formation of a well-ordered bilayer structure of intercalated
HDAs [21]. Using these HDA-n-ZrP and a-ZrP as starting
The representatives of methyl soyate are shown in Fig. 1
(left panel) and the possible epoxy products of methyl
soyate are depicted in Fig. 1 (right panel). The epoxy
products were analyzed to evaluate the double bond con-
version, through the determination of the Iodine Number,
and the epoxy selectivity, through the evaluation of the
Oxirane Number, according to the analytical methods
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W. Liu et al.
materials, series 0.2-SPZHD-3 materials are synthesized
via templating self-assembly method and examined by
SEM (Fig. 3). Different amount of co-precipitated silica
are observed on the surface or around the sheets of the
synthesized silicon pillared material. Dramatically, silicon
pillared material synthesized from HDA-0.7-ZrP exhibits a
clear layer morphology and the least co-precipitated silica.
In the corresponding XRD patterns (Fig. 4), each sample
exhibits different layer structural ordering. Among them,
silicon pillared material synthesized from HDA-0.7-ZrP
also presents the best layer structure and the least co-pre-
cipitated silica (the weakest diffraction at 2h = 20*25°
[28])
The results of SEM and XRD could be explained by
the expanding effects of HDA. When HDA is not used or
its intercalated amount is relative small, the subsequent
intercalation of DDBAC cationic and TEOS would be
hindered by the intense electrostatic interaction between
layers and the confined hydrophilic interlayer space also
Fig. 2 The small angle XRD patterns for HDA-n-ZrP
goes against the penetrate of TEOS, provoking
a
Fig. 3 SEM images for 0.2-SPZHD-3 obtained from a a-ZrP, b HDA-0.2-ZrP, c HDA-0.7-ZrP, d HDA-2-ZrP
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Factors Affect on the Synthesis of Silica-Pillared Zirconium Phosphate
667
Fig. 5 The small angle XRD patterns for a 0.2-SPZHD-2, b 0.2-
SPZHD-3, c 0.2-SPZHD-4, d 0.4-SPZHD-2, e 0.4-SPZHD-3, f 0.4-
SPZHD-4. The wide angle XRD patterns are shown in the insets
Fig. 4 The small angle XRD patterns for 0.2-SPZHD-3 obtained
from a a-ZrP, b HDA-0.2-ZrP, c HDA-0.7-ZrP, d HDA-2-ZrP. The
wide angle XRD patterns are shown in the insets
3.1.2 The Effect of Surfactant upon the Layer Structure
of SPZHD
tagraggery of co-precipitated silica and a-ZrP (Fig. 3a, b).
In this case, the amount of interlayer TEOS is insufficient
for the adequate formation of the galleries, leading to the
collapsed or disordered structure after calcinations
(Fig. 4a, b). If the amount of the interlayer HDA is rel-
atively large, most P–OH groups locating on the layers of
zirconium phosphate are neutralized while the retained
free P–OH are insufficient for the subsequent ion
exchange with DDBAC, TEOS also fail to intercalate
with DDBAC cationic by salvation [29]. Thus, large
number of TEOS hydrolysis on the layer surface after
adding ammonia solution (Fig. 3d) and a collapsed
interlayer structure is provoked after calcinations
(Fig. 4d). As the starting material is HDA-0.7-ZrP, the
amount of interlayer HDA is suitable. In this situation, all
the sheets of zirconium phosphate are expanded and the
electrostatic interaction between the layers is weakened
substantially. In addition, sufficient free P–OH groups are
retained, it ensures the ion exchange between DDBAC
cationic and H? of the P–OH. Thus, the prepared pillared
material presents well-ordered interlayer structure
(Fig. 3c) and clear layer morphology (Fig. 4c). Conse-
quently, it is deduced that the introducing of HDA
improves the intercalation of DDBAC cationic and TEOS
with ordered interlayer structure. One more thing to be
noted is that the intercalated amount of HDA must be
controlled to retain sufficient free P–OH groups as they
are keys of the intercalation of DDBAC cationic and
TEOS.
Using HDA-0.7-ZrP as starting material, several SPZHD
materials are synthesized by adjusting the molar ratios of
DDBAC/HDA-ZrP and TEOS/HDA-ZrP. Almost all the
prepared solids exhibit diffraction peaks with different
intensity at low angle and typical diffraction peaks of
a-ZrP at wide angle (Fig. 5). It indicates that interlayer
silica gallery with various structural ordering has formed
and the crystalline structure of the a-ZrP has not been
destroyed after calcinations. In addition, the co-precipitated
silica material was also obtained and it reflects a disordered
crystal structure which completely different from the typ-
ical pillared-layer structure of the pillared materials. This
fact assures the co-precipitated silica would not cause
interference to the structural characterization of pillared
materials. The interlayer spacing of all samples has been
calculated out and it is found that all of them fluctuate at
around 2.40 nm. Furthermore, several x-SPZHD-3 mate-
rials are synthesized by adjusting the molar ratio of
DDBAC/HDA–ZrP from 0 to 0.6. Corresponding behavior
of interlayer spacing is shown in Fig. 6. It can be seen that
the pillared structure doesn’t form until the molar ratio of
DDBAC/HDA–ZrP achieves 0.2. When the ratio exceeds
0.2, the interlayer spacing fluctuates at around 2.40 nm.
Thus it is possible to deduce that once the surfactant is
elected and the critical amount is achieved, the interlayer
spacing of SPZHD is stabilized. Otherwise, it should be
noted that the interlayer spacing of each sample is bigger
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W. Liu et al.
Fig. 6 The relationship between molar ratio of DDBAC/HDA–ZrP
and interlayer spacing. a 0-SPZHD-3, b 0.1-SPZHD-3, c 0.2-SPZHD-
3, d 0.3-SPZHD-3, e 0.4-SPZHD-3, f 0.6-SPZHD-3
Fig. 7 The small angle XRD patterns for silicon pillared materials
synthesized by a DDBAC, b BCDAC, c ODBAC. Relationship
between the interlayer spacing and the length of surfactants long
chain is shown in the insets
than length of DDBAC long chain (1.60 nm) and smaller
than the double of that (3.20 nm). By considerations sim-
ilar to those reported for the amine arrangements in zir-
conium phosphate [30, 31], it can be inferred that the
interlayer DDBAC cationic molecules are arranged as
molecular lamellar bi-layers with an oblique angle to the
layer plane, and the carbon chains of DDBAC cationic
molecules formed an inter-penetration phase [32]. To fur-
ther verify this conclusion, two more materials are syn-
thesized by using benzyl dimethyl hexadecyl ammonium
chloride (BCDAC) and octadecyl dimethyl benzyl ammo-
nium chloride (ODBAC), when the molar ratio of surfac-
tant/HDA–ZrP is 0.2 and TEOS/HDA–ZrP is 3. Low-angle
XRD patterns for the prepared solids show a single peak
corresponding to the d001 diffraction at 3.00 nm (Fig. 7b)
and 3.37 nm (Fig. 7c). Consistently, the interlayer spacing
of corresponding samples is still between the length of long
chain and double of it (the length of BCDAC long chain is
2.20 nm and the length of ODBAC long chain is 2.50 nm).
Interestingly, the relationship between the interlayer spac-
ing and the length of surfactants long chain is similar to
linearity.
3.1.3 The Effect of Tetraethyl Orthosilicate
upon the Porous Structure of SPZHD
Using HDA-0.7-ZrP as starting material, several SPZHD
materials are synthesized by adjusting the molar ratios of
DDBAC/HDA-ZrP and TEOS/HDA-ZrP. As can be seen
from the N2 adsorption–desorption isotherms and pore size
distributions (Fig. 8), all the samples are characterized as
hybrid type IV according to the BDDT (Brunauer–De-
ming–Deming–Teller) classification with a hysteresis loop,
whose features correspond to type B in Boer’s five types
representing the presence of open slit-shaped or cylindrical
pores formed in gallery regions [33–35]. From the pore size
distributions, it can be seen that the SPZHD materials
possess a relatively narrow pore size distribution, which is
typical for a well-ordered meso-structured material. The
interlayer spacing, pore size, pore volume and SBET of each
sample are summarized in Table 1. It can be seen that the
interlayer spacing of each sample is stabilized around
2.40 nm and it indicates that the effect of TEOS upon the
interlayer spacing of SPZHD is insignificant. However, all
the porous properties increases at first and then decreases
with the increasing of the dosage of TEOS. When the
molar ratio of TEOS/HDA-ZrP is 2, the relative small
amount of interlayer TEOS would provoke a low distri-
bution density of interlayer silica gallery and weak walls of
interlayer pores. In this case, a partial collapse of the
interlayer porous structure occurs throughout the
The preceding behaviors of the surfactant indicate that
the layer structure of silicon pillared materials can be
controlled directly by choosing the surfactant with required
length of long chain and adjusting the dosage of surfactant.
In this work, the 0.2-SPZHD-3 material synthesized from
HDA-0.7-ZrP exhibits ordered interlayer structure and the
largest interlayer spacing (2.52 nm).
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Factors Affect on the Synthesis of Silica-Pillared Zirconium Phosphate
669
Fig. 8 The N2 adsorption–desorption isotherms for SPZHD (Left) and the pore size distributions (Right). a 0.2-SPZHD-2, b 0.2-SPZHD-3, c 0.2-
SPZHD-4, d 0.4-SPZHD-2, e 0.4-SPZHD-3, f 0.4-SPZHD-4
Table 1 Textural properties of SPZHD
Material Interlayer Pore
facts, it is clear that the porous structure of SPZHD can be
controlled by adjusting the dosage of TEOS. In this work,
using HDA-0.7-ZrP as starting material, silicon pillared
material with the highest SBET and the largest pore size
could be synthesized when the molar ratio of TEOS/HDA-
ZrP is 3 and the molar ratio of DDBAC/HDA-ZrP is 0.2.
Pore volume SBET
spacing (nm) diameter (nm) (cm3/g)
(m2/
g)
0.2-SPZHD- 2.36
2
1.49
1.55
1.40
1.24
1.29
1.26
0.22
0.28
0.21
0.17
0.31
0.29
285.2
357.1
303.6
269.0
480.5
459.3
0.2-SPZHD- 2.52
3
3.1.4 Proposed Formation Mechanism of SPZHD
0.2-SPZHD- 2.41
4
Based on the synthesis, a possible formation mechanism of
SPZHD is proposed and shown in Fig. 9. In the first step,
HDA molecules are inserted into the interlayer by pro-
tonation, holding the zirconium phosphate sheets apart,
weakening the interlayer electrostatic interaction and
building a hydrophobic interlayer space. It would help to
improve the subsequent intercalation of DDBAC cationic
and TEOS. In the second step, the DDBAC cationic mol-
ecules intercalate into the interlayer by ion exchange, and
TEOS also intercalates with DDBAC cationic by solvation.
As the amount of intercalated DDBAC cationic increases
to the critical amount, HDA and DDBAC cationic mole-
cules in the gallery are arranged as molecular lamellar bi-
layers with an oblique angle, forming the interlayer
micelle. After adding ammonia solution, the interlayer
TEOS hydrolyzes quickly and assembles around interlayer
micelle, provoking an ordered pillared structure. As shown
in the formation mechanism, several factors are combined
such as the expanding effects expressed from HDA, ion
exchange property of a-ZrP, template-directing function of
DDBAC and solvation mechanism of TEOS. Above all, the
insertion of HDA significantly affects the morphology,
pore size and SBET of SPZHD material and the length of
DDBAC long chain directly controls the interlayer spacing
0.4-SPZHD- 2.37
2
0.4-SPZHD- 2.43
3
0.4-SPZHD- 2.40
4
calcinations and therefore the prepared silicon pillared
material exhibits less SBET and smaller pore size. When the
molar ratio of TEOS/HDA-ZrP is 4, the amount of inter-
layer TEOS is relatively large, provoking a filled interlayer
space and tightly arranged interlayer micelle molecules.
This leads to the decrease in SBET and pore size of the
prepared silicon pillared material. As the molar ratio of
TEOS/HDA-ZrP is 3, the suitable amount of interlayer
TEOS is achieved and it results a well distribution of
interlayer silica gallery, giving rise to a well-ordered
interlayer porous structure and the largest SBET and pore
size. It should be noted that the interlayer porous structure
also relates with the dosage of HDA closely, due to the
distribution of interlayer silica gallery depends on the
amount of available P–OH groups which participate the ion
exchange with DDBAC cationic. On the basis of preceding
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W. Liu et al.
Fig. 9 Models of formation mechanism of SPZHD materials
Fig. 10 SEM and TEM images for the 0.2-SPZHD-3 material. a, b SEM images for the 0.2-SPZHD-3 material; c, d TEM images for the
0.2-SPZHD-3 material
of SPZHD material. Therefore, the controllable synthesis
of SPZHD material could be achieved by regulating the
dosage of HDA, choosing suitable surfactant with expected
length of long chain and adjusting the dosage of surfactant
and TEOS. It gives rise to a chance for SPZHD material to
be used as a designable catalytic material which could be
adjusted according to the size of reactant molecules. In this
work, using HDA-0.7-ZrP as starting material, silicon pil-
lared material 0.2-SPZHD-3 has been synthesized. It
exhibits the largest interlayer spacing and the best porous
structure among the x-SPZHD-y series. From the SEM and
TEM images of 0.2-SPZHD-3, uniform ordered stacking of
disk-shaped platelets are observed (Fig. 10a, b) and the
distinct layered crystalline phases are also observed from
the edge of the sheets (Fig. 10c, d).
3.2 Evaluation of the Acidity and Catalytic
Performance
3.2.1 Evaluation of the Acidity
The 0.2-SPZHD-2 material, the 0.2-SPZHD-3 material and
a-ZrP are selected to examine the distribution of surface
acidity in SPZHD material by using NH3–TPD. According
to the profiles it can be seen that each sample shows two
desorption peaks placed at about 300 and 550 °C (Fig. 11).
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Factors Affect on the Synthesis of Silica-Pillared Zirconium Phosphate
671
Fig. 12 FT–IR spectra of adsorbed pyridine on a a-ZrP and b
0.2-SPZHD-3 at 200 and 450 °C, respectively
Fig. 11 The NH3–TPD patterns for a a-ZrP, b 0.2-SPZHD-3, c 0.2-
SPZHD-2
pillaring, the layers are expanded and the porous system
with large SBET is obtained. It generates a better adsorption
performance and provokes the accessible interlayer acid
sites for pyridine molecules. The result from the IR spectra
indicates that SPZHD material is a typical Lewis acid with
enhanced adsorption performance.
The peaking temperature of silicon pillared material is
slightly lower than the peaking temperature of a-ZrP,
which indicates the acid strength is reduced after pillaring.
This is because the interlayer silicon gallery would neu-
tralize or cover some interlayer P–OH groups providing
most acidity of zirconium phosphate and its derivatives
[36]. In addition, the silicon pillared materials with variant
pore structures and layer structures present similar behav-
iors in peaking temperature and peaking intensity. It indi-
cates that the total acid content of SPZHD material is
similar. Further characterization of a-ZrP and the 0.2-
SPZHD-3 material was carried out by FT–IR spectra of
adsorbed pyridine at 200 and 450 °C, respectively.
Figure 12 shows the IR spectra in the 1,400–1,700 cm-1
region, it can be seen that a-ZrP shows no bands at both
temperature and it indicates that the pyridinium ion is not
formed on the acid centre. At 200 °C, 0.2-SPZHD-3
material shows a characteristic band at 1,450 cm-1 corre-
sponds to pyridine coordinated to Lewis acid sites. When
the temperature is raised up to 450 °C, the band at
1,450 cm-1 still retains, it proposes a strong bonding
between pyridine molecules and acid centre [37]. Addi-
tionally, it should be noted that no bands are observed at
1,540 cm-1, it indicates that the Bronsted sites do not exist
in the SPZHD material [38, 39]. It is interesting that a-ZrP
exhibits a stronger acid strength in NH3–TPD test but
behaves oppositely in FT–IR spectra of adsorbed pyridine.
This result can be explained by the difference in adsorption
performance: the narrow interlayer spacing and low SBET
of a-ZrP leads to difficulty for pyridine molecules in
accessing large number of interlayer acid sites. After
3.2.2 Evaluation of Catalytic Performance
Table 2 lists the conversions of double bonds and the
selectivity of epoxy over the SPZHD material, a-ZrP and
the co-precipitated silica material. As can be seen, the
silica material shows a conversion of double bonds of
70.9 % and selectivity of epoxy of 62.5 %. a-ZrP shows a
conversion of double bonds of 77.8 % and selectivity of
epoxy of 68.7 %. In contrast, SPZHD materials exhibit a
substantially increase on catalytic effects: all conversions
of double bonds over SPZHD are more than 90 % and the
epoxy selectivities are more than 80 %. In parallel with
other solid acids, SPZHD material also exhibits an excel-
lent catalytic performance (the conversion of double bonds
reaches 95.9 % and the epoxy selectivity reaches 84.7 % in
5 h reaction time). Epoxy selectivity over hydrotalcite-like
compounds intercalated by 12-phosphorus tungsten het-
eropoly acid was only 59.4 % [23]. Ti grafted on silica
exhibited 80 % of epoxy selectivity [40]. Ti-MCM-41 was
reported to show better performance (both the conversion
of double bonds and the epoxy selectivity are more than
90 %), but it requires long reaction time of 25 h [41]. Same
level can be achieved over the sol–gel synthesized alumina,
which requires 20 h reaction time [42]. On the other hand,
the catalytic performance of each SPZHD material presents
123

672
W. Liu et al.
Table 2 Catalytic performance over a-ZrP and SPZHD materials
Materials
Double bond
conversion (%)
Epoxy
selectivity (%)
co-precipitated silica
a-ZrP
70.9
77.8
91.0
95.9
93.5
91.9
93.0
94.6
62.5
68.7
80.4
84.7
82.6
81.2
82.2
83.5
0.2-SPZHD-2
0.2-SPZHD-3
0.2-SPZHD-4
0.4-SPZHD-2
0.4-SPZHD-3
0.4-SPZHD-4
Fig. 14 The relationship between reaction time and the epoxy
selectivity
molecules, which is provoked by the larger interlayer
spacing.
Generally in the epoxidation of methyl soyate, an
intermediate peroxy acid is first obtained and then the
oxygen transfer from the peroxy acid to an olefin [43].
Based on this mechanism, a possible scheme of this
epoxidation is proposed. Performic acid is generated from
H2O2 and formic acid at first and then adsorbed into
interlayer. Meanwhile, the methyl soyate molecules are
also adsorbed into interlayer. With the catalyzing of basic
hydroxyl function locating on the layers of SPZHD,
epoxidation of the unsaturated carbon bonds occurs at
around the basic hydroxyl function. As can be seen in
Fig. 14, a rapid rise of epoxy selectivity is obtained in a
short time and then the rising of epoxy selectivity flattens
out gradually. It implies that an effect contact between the
catalysts and reactants is achieved quickly. The epoxy
selectivity is decreased as the reaction time is longer than
300 min because of the ring-opening of the epoxy pro-
ducts. Based on these facts, it can be inferred that the
chemical step controls the reaction process and not the
diffusion step, because macromolecular reactants can be
effectively adsorbed into interlayer and well diffused to the
basic hydroxyl function. The activation energy of reaction
is also calculated to be 30.1 kJ/mol, which is significantly
decreased compared with other catalytic system [44, 45].
Therefore, with the large surface area and the ordered
interlayer structure of SPZHD material, reactants and
active sites contact with each other adequately and a higher
catalytic performance is expressed over the SPZHD
material.
Fig. 13 The relationship between interlayer spacing and the epoxy
selectivity
some difference, 0.2-SPZHD-3 shows a maximum epoxy
selectivity of 84.7 % and 0.2-SPZHD-2 exhibits a mini-
mum epoxy selectivity of 80.4 %. Combining with the
results of the NH3–TPD (the total acid content of SPZHD
material with different layer structure is similar), it is
possible to deduce that the difference in catalytic perfor-
mance is provoked by the different layer structure of each
material. Based on this, the relationship between the
interlayer spacing and the epoxy selectivity is summarized
and shown in Fig. 13. It can be seen that with the
increasing of interlayer spacing, the epoxy selectivity keeps
improving. A rapid rise of epoxy selectivity is obtained
through the increasing of interlayer spacing from 0.76 to
2.52 nm, further increase the interlayer spacing to 3.37 nm,
the rising of epoxy selectivity flattens out gradually. This
result is consistent with the more accessible diffusion
pathway for the relatively large reactants and product
123

Factors Affect on the Synthesis of Silica-Pillared Zirconium Phosphate
673
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16. Leon M, Jimenez-Jimenez J, Jimenez-Lopez A, Rodrıguez-Cas-
tellon E, Soriano D, Lopez Nieto JM (2010) Solid State Sci
´
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4 Conclusions
´
12:996
A series of SPZHD materials with ordered structure were
successfully synthesized and the morphology, structure and
acidity of SPZHD were systematically studied. It was
found that the morphology, layered structure and porous
structure of SPZHD can be effectively controlled by
adjusting the dosage of HDA, DDBAC and TEOS, per-
mitting the use of designable material with potential
applications in adsorption and catalysis. Based on the
synthesis, a probable formation mechanism of the tem-
plate-directing self-assembly silicon gallery was described.
As a typical Lewis acid, SPZHD shows a maximum con-
version of double bonds of 95.9 % and epoxy selectivity of
84.7 % in the epoxidation of methyl soyate. Such an
excellent catalytic performance in parallel with other solid
acids may be consistent with the advantage of its structure.
´
17. Jimenez-Jimenez J, Algarra M, Rodrıguez-Castellon E, Jimenez-
Lopez A, Estevesda Silva JCG (2011) J Hazard Mater 190:694
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A, Rodrıguez-Castellon E, Nieto JM (2009) Appl Catal B Envi-
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Acknowledgments The authors acknowledge generous financial
support from National Natural Science Foundation of China
(21306012) and Innovation Project of Postgraduates in Jiangsu
Province (CXZZ11-0376).
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