Mesoporous Al-incorporated silica-pillared clay interlayer materials for catalytic hydroxyalkylation of phenol to bisphenol F

Article abstract of DOI:10.1039/c6ra15161b

A series of mesoporous, Al-incorporated, silica-pillared clay (Al-SPCs) interlayer materials with different Al content were prepared in the presence of cationic surfactant by a structure-directing method. The catalysts' structure, texture, and acidic properties were determined using XRD, BET, SEM, TEM, FT-IR, NH₃-TPD and Py-IR, respectively. Characterization results showed that these materials possess mesoporous structures with large specific surface areas. The incorporated Al leads to the increase and redistribution of Br?nsted and Lewis acid sites on SPC (silica-pillared clay). The Al-SPCs were used as catalysts for hydroxyalkylation of phenol to bisphenol F and gave a high product yield (95.4%) and selectivity (98.2%) to bisphenol F. Catalytic performance of the catalysts and characterization results proved that the catalytic activity of these catalysts depend on moderate acidity and the textural properties (specific surface areas), and the synergy of Br?nsted and Lewis acids is key for the hydroxyalkylation of phenol to bisphenol F. The reusability of the catalysts was studied, and they can be easily recovered and reused at least six times without significant loss of their catalytic activities. Finally, a plausible mechanistic pathway was proposed.

Full text of DOI:10.1039/c6ra15161b

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Mesoporous Al-incorporated silica-pillared clay interlayer
materials for catalytic hydroxyalkylation of phenol to bisphenol F
Xianzhang Wu, Xinnian Xia＊, You Chen and Yanbing Lu
Received 00th January 20xx,
Accepted 00th January 20xx
A series of mesoporous Al-incorporated silica-pillared clay (Al-SPCs) interlayer materials with different Al
content were prepared in the presence of cationic surfactant by structure-directing method. The catalysts
structure, texture, and acidic properties were determined using XRD, BET, SEM, TEM, FT-IR, NH3-TPD and Py-
IR, respectively. Characterization results showed that these materials possess mesoporous structure with
large specific surface areas. The incorporated Al leading to the increase and redistribution of Brönsted and
Lewis acid sites on SPC (silica-pillared clay). The Al-SPCs were used as catalysts for hydroxyalkylation of
phenol to bisphenol F, and give a high product yield (95.4%) and selectivity (98.2%) to bisphenol F. Catalytic
performance of the catalysts and characterization results proved that the catalytic activity of these catalysts
depended on moderate acidity and the textural properties (specific surface areas). Meanwhile, the synergy
of Brönsted acid and Lewis acid is key for hydroxyalkylation of phenol to bisphenol F. The reusability of the
catalyst was studied, which the catalysts can be easily recovered and reused for at least six times without
significant loss of their catalytic activities. Finally, a plausible mechanistic pathway was proposed.
DOI: 10.1039/x0xx00000x
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or MIL-101 material determined the isomers’ distribution of
bisphenol F. Even though the materials formed are good catalysts
for hydroxyalkylation of phenol to bisphenol F, the synthesis
1 Introduction
procedure is somewhat tedious. Garade et al.7 reported, for the
first time, that DTP/SiO2 was active for bisphenol F synthesis.
However, the yield of bisphenol F was only 34.2%, which the low
catalytic activity severely restricted its application. It is desirable to
With increasing demand and applicability in plastics, resins and
rubber industries, bisphenol F synthesis has been given an extensive
attention. Synthesis of bisphenol F via hydroxyalkylation of phenol
with formaldehyde is a typical acid-catalyzed reaction. Classically,
hydroxyalkylation of phenol with formaldehyde to bisphenol F
could be catalyzed by use of various conventional mineral acids,
such as phosphoric acid, hydrochloric acid, sulfuric acid or other
inorganic acids.1 Even though moderate to high bisphenol F yields
have been achieved, sustainable and economically viable routes for
develop
a cheaper and easier to synthesize catalysts for
hydroxyalkylation of phenol with formaldehyde to bisphenol F.
Pillared clay (PILC) is one of the most widely studied interlayer
materials, which have potentially wide applications in the areas of
8-10
bisphenol
F production in scalable quantities arose serious
adsorption and catalysis.
The introduction of oxide pillars into
challenges due to these are toxic, corrosive, and often hard to
remove from the reaction solution. Thus, it is keenly desirable to
develop new types of catalysts to replace them. The solid catalysts
were well recognized these days because of their ease of workup,
separation of products and catalysts, and economical advantages.
More importantly, it has unique properties including availability,
safety, nontoxicity, and insolubility in the vast majority of solvents.
Because of these properties, a number of studies have been
reported about the design of solid acid catalysts for bisphenol F
synthesis, which spans over a broad range of catalytic materials
including modified mesoporous silicas,2 clay,3 organometallic
framework,4 and zeolites5. Recently, Chen et al.6 reported the
metal−organic frameworks of MIL-100(Fe or Cr) and MIL-101(Fe or
Cr) encapsulated with Keggin phosphotungstic acid as a catalyst for
hydroxyalkylation of phenol to form bisphenol F. The studies
indicate that the nature of the transition metal Fe or Cr in MIL-100
the interlayer space results in a significant increase in surface area,
thermal stability, and microporosity. More importantly, by changing
the pillar oxide and raw clay, the acidity, layer space, and pore size
distribution of the PILCs can be regulated over relatively wide
ranges. Pillared clay are suited to be used in heterogeneous liquid
phase reactions, offering new opportunities for developing
environmentally benign and friendly processes. In this article, a
series of Al-SPC with different contents of Al were synthesized, and
catalytic performance of the Al-SPCs for hydroxyalkylation of
phenol to bisphenol
F was studied in detail. An Al-pillared
montmorillonite (Al-MMT) was also prepared and used as a catalyst
for comparative purposes. The experimental results are well
explained based on characterization by X-ray diffraction (XRD), FT-IR
using pyridine as
a probe (Py-IR), and NH3 temperature
programmed desorption (NH3-TPD).Also, the reusability of the
catalyst were investigated; As well, reaction parameters such as
catalyst weight, reaction temperature, reaction time and molar
ratio were optimized.
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2 Experimental
slowly added to MMT slurry of 2g/100 ml (10 mmol of Al per gram
of MMT). The final suspension was stirred at room temperature for
24 h, then was transferred to dialysis tubing and dialyzed in distilled
water for 3 days to remove C1−. The dialysis water was changed
each 24 h until the water-tested C1− free by the AgNO3 test. The
resultant mixture was subsequently separated from suspension by
filtration to obtain powders, dried in an air and calcined at 400 ℃
for 4 h.
2.1 Materials
Commercially available montmorillonite K10 as the raw Material
supplied by Sinopharm Chemical Reagent Co, Ltd, China. Analysis of
its mineralogy composition showed it to be 95% montmorillonite.
Its anhydrous structural (layer) formula, which was determined
previously11
is
as
[Si7.86Al0.14][Al2.84Fe0.30Mg0.86]O20(OH)4.
Montmorillonite K10, which is calcium-rich in commodities form
and was converted into the Na-MMT (denoted as MMT) by
treatment with NaCl (1 mol/L NaCl solution, 100 mL solution/g of
clay, 80℃ for 2 h); Dodecyl dimethyl benzyl ammonium chloride
(C12DMBACl) (A.R.),Tetraethoxysilane (TEOS) (A.R.), ammonia (25%)
Ethanol (99.7%) was purchased from Beijing Chemical Reagents
Company, China. phenol, formaldehyde (37–40%), aluminum
chloride hexahydratere (AlCl3·6H2O) were purchased from
Sinopharm Chemical Reagent Co, Ltd, China.
2.5 Catalytic activity tests.
Hydroxyalkylation of phenol with formaldehyde to bisphenol F was
performed in a magnetically stirred glass reactor fitted with a reflux
condenser and an arrangement for temperature control under
nitrogen atmosphere. Briefly, 82.86 mmol of phenol, 5.73 mmol of
formaldehyde and catalyst (0.12 g) were added into the glass
reactor. The reaction mixture was magnetically stirred and heated
to the required temperature. After a definite time interval, the
reaction is stopped and 0.03 g of the product is taken and is diluted
with 10 mL of methanol. The products were analyzed by a HPLC
2.2 Synthesis of SPC
SPC were synthesized in the presence of cationic surfactant by system with a Shimadzu LC-20AT system coupled with a SPD-20A
structure-directing method according to previous report.12 Typically, UV/Vis detector and a Phenomenex Luna C18 column (250 × 4.6
MMT (1.00 g) was added to 30 mL of water to form a clay mm, 5 μm) and Column oven temperature was 25℃, and mobile
suspension. C12DMBACl was dissolved in ethanol, and TEOS was phase was methanol : water with 65:35v/v. mobile phase whose
added and stirred for 0.5 h to form a clear solution. The solution flow was 0.6 mL/min.
was then slowly dropped into the clay suspension. The gel mixture
The reaction equation of phenol with formaldehyde to bisphenol
with a molar ratio of clay, surfactant, TEOS, ethanol and water at F is shown in Scheme 1.
1:2:30:1.2:250 was stirred for 0.5 h. Subsequently, the mixture was
filtered to remove the water and extra TEOS, and the product
obtained was C12DMBACl/TEOS-intercalated clay.
The C12DMBACl/TEOS-intercalated clay (2.g) was dispersed in 50
mL of ammonia solution and stirring for 2 h at room temperature.
The resultant mixture was subsequently separated from suspension
by filtration to obtain powders, dried in an air and calcined at 600
Scheme 1. Hydroxyalkylation of phenol with formaldehyde to
bisphenol F.
℃ for 3 h (at a heating rate of 2℃/min) to remove C12DMBACl. The
prepared sample was denoted as SPC.
The yield and selectivity of bisphenol F were calculated on the basis
of formaldehyde. The calculation equations are as follows:
2.3 Synthesis of Al-SPCs
Al-SPCs was prepared in the presence of cationic surfactant by
structure-directing method as follows:(i) MMT (1.00 g) was
suspended in 30 mL of water to form suspension A. (ii) AlCl3·6H2O
(1.2g) was added to a solution consisting of 2 mL of ethanol and 8
mL of TEOS to form suspension B. (iii) The suspension B was slowly
dropped into suspension A, and stirred for 1h to obtain a brown sol.
Then, 3 mL of ammonia solution was slowly dropped into the sol
and stirring for 3 h at room temperature. The resultant mixture was
subsequently separated from suspension by filtration to obtain
powders, dried in an air and calcined at 600 ℃ for 6 h using a
programmed furnace (at a heating rate of 2℃/min). The product
was denoted as Al-SPC-X, where the X represents the molar of Al in
per gram of MMT.
moles of bisphenolF
Yield(%) =
×100%
moles of HCHOcharged
moles of bisphenolF formed
Selectivity(%) =
×100%
∑ moles of alltheproducts
2.6 Catalyst Characterization.
Powder X-ray diffraction (XRD) patterns were recorded at room
temperature on a D8-Advance with Cu Kα radiation (λ = 0.1541 nm)
at 40 kV and 40 mA. Diffraction data were recorded in the 2 h range
from 1° to 8° and 10° to 80° with a scanning rate of 0.5° of 2θ/s and
2θ = 0.02°. Scanning electron microscopy (SEM) micrographs were
obtained on a Hitachi S-4800 microscope operated at 30 kV. The
chemical composition of the sample was determined by energy-
dispersive X-ray (EDX) analysis using an FEI QUANTA-200.
Transmission electron microscope (TEM) images were obtained
2.4 Synthesis of Al-MMT
Al-MMT was synthesized by intercalation of Na-MM with aluminum
hydroxy oligomeric solutions (Al solutions) according to our
previous reports.13 0.1 mol/L solution of NaOH was slowly added to
0.1 mol/L AlC13 solutions prepared from AlCl3·6H2O to obtain a final
hydrolysis ratio OH−/Al3+ = 2.4. Aging at 50℃for 24 h, the AlC13
solution was
using
a JEOL JEM-2100 microscope. The TEM samples were
prepared by dispersing nanoparticles in acetone to form
a
suspension. The suspension was sonicated for 20 min and was
2 | J. Name., 2012, 00, 1-3
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deposited onto Cu grid with lacey carbon coated.NH3-TPD analysis
was performed with a Micromeritics AutoChem II 2920 V3.05
instrument. Prior to analysis, the catalyst (100 mg) was enclosed in
a quartz tube and treated at 300
℃
under a helium flow of 30
under a flow
mL/min for 1 h. The sample was cooled down to 60
℃
of helium gas and then followed by adsorption of NH3 for 60 min,
which was maintained for 1 h. Subsequently, the catalyst was
heated to 700
℃ with a ramp of 10 ℃/min under a helium flow
rate of 30 mL/min. A thermal conductive detector (TCD) was used
to measure the desorption amount of NH3 which was quantified
based on the TCD calibration curve that had been obtained by
injecting NH3 pulses of known volume in the helium background
flow.
Pyridine adsorption monitored by in situ infrared FTIR spectra
(Py-IR) of the catalyst samples were recorded with a Brucker Vector
22 spectrometer in the absorption mode with a resolution of 4 cm-1.
Self-supporting wafers were made and loaded in an IR cell. The
wafers were pretreated at 400℃ under flowing oxygen for 2 h.
Background spectra were recorded after the sample was cooled to
room temperature. Adsorption of pyridine was then conducted
until saturation. Py-IR spectra were recorded after degassing for 0.5
h. The specific surface area was estimated according to the
Brunauer−Emmeꢀ−Teller (BET) equaꢁon. The pore size distribuꢁon
was calculated by the Barett−Joyner−Halenda (BJH) method by the
adsorption isotherm branch. Infrared spectra were recorded in the
wavelength range of 800–4000 cm-1 using a Bruker vector 22 FT-IR
spectrophotometer using KBr disk technique.
3 Results and discussion
3.1 Catalyst characterization
Fig. 1 XRD patterns of SPC, Al-SPCs and Al-MMT samples.
Fig. 1(A) shows small-angle XRD patterns of SPC, Al-SPCs and Al-
MMT. As can be seen in SPC and Al-SPCs, these reflections were
very similar, indicating that all of samples had similar basal spacings
and lamellar structures by this synthesis method.14 However, for Al-
MMT, the 001 reflection peak is shifted toward higher diffraction
angles, and exhibits lower intensity, illustrating that Al-MMT
prepared by Al pillared MMT has a smaller layer spacing than Al-
SPCs. The basal spacing values, for the montmorillonite component
in both the MMT, Al-SPCs and Al-MMT catalyst are shown in Table
1. The basal spacing increases from 1.7 nm in the MMT to 3.16 nm
in the Al-SPCs. This results is expected because of expansion of the
interlayer spacing in the MMT after pillaring treatment, indicating
that SiO2 has been successfully intercalated into the clay layers.15
The basal spacing of Al-MMT is 2.1 nm, which smaller than Al-SPCs.
Interestingly, no significant difference in the intensities among the
001 refraction peaks between SPC and Al-SPCs was observed,
suggesting that the amount of Al element used does not affect the
layered structure of Al-SPCs.
The wide-angle XRD patterns of MMT, SPC, Al-SPCs and Al-MMT
are presented in Fig. 1(B). All the samples shows the typical peaks
of the trioctahedral subgroup of 2:1 phyllosilicates, which are
ascribed to (110), (020), (004), (130), (200), (330) and (060)
diffractions.16 It is seen that there are no diffraction lines in Fig.
1(B), indicating that Al species well-dispersed in the interlayered
silica oxide framework and no long-range change in the crystalline
structure of clay.
Fig.
2
SEM image of SPC, Al-SPCs and Al-MMT samples.
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Table 1. Structural data of the samples.
samples
Surface area (m2 g-1) basal spacing (nm)
gallery height (nm)
Pore volume (cm3 g-1)
pore size (nm) Al content (wt %)
MMT
61
1.7
0.74
2.16
2.13
2.16
2.21
2.21
2.20
0.12
0.76
0.72
0.63
0.54
0.32
0.35
7.4
12.6
10.5
15.7
21.1
27.2
32.6
34.9
SPC
657.8
584.6
475.2
410.9
386.3
207.5
3.16
3.13
3.12
3.12
3.12
2.14
12.5
12.2
12.1
12.2
12.1
10.4
Al-SPC-1
Al-SPC-3
Al-SPC-5
Al-SPC-7
Al-MMT
The SEM micrographs were used to further study the structural
information of the catalyst. As shown in the Fig. 2. The MMT and Al-
MMT show a closer sheets structure, owing to that the MMT and
Al-MMT possesses ordered layered structure and small layer
spacing. The platelets in the SPC and Al-SPCs were unaffected by
hydrolysis, although they swelled slightly more than the MMT and
Al-MMT. All of the Al-SPCs derivatives synthesized using cationic
surfactants exhibited similar morphologies. Moreover, some small
particles can be observed around platelets of SPC and Al-SPCs. This
is due to the broken platelets and the forming of some compounds
in the extralayer regions of the clays.17 However, this platelet
destruction did not reflect SPC and Al-SPCs gallery structure
destruction .This result is confirmed by XRD Spectra.
FT-IR patterns of MMT, SPC, Al-SPCs and Al-MMT are shown in
Fig. 3. The absorption bands at about 3450 and 1658 cm−1 were
assigned to the stretching and bending vibrations of the O-H bond
in the clay and water molecules present in the interlayer.18 In all
curve, the band at around 3652 cm-1 is due to the vibration of Al-
OH. Typical bands of the silicate components appear between 1300
and 800 cm−1, and the absorption at 852 cm-1 is due to the Si-OH in
the tetrahedral layer.19 The band located at 1028 cm–1 was indexed
to the asymmetric stretching bonds of Si-O-Si.20 Compared to the
FT-IR spectra of pure MMT and SPC, significant increase of the
peaks intensity at 36542 cm-1 with increasing content of Al in Al-
SPCs, which is attributable to the appearance of Al-OH bending
vibration and the intensity is also enhanced. The above results
revealed that Al atoms were incorporated into the interlayered
framework of clay.
Fig. 3 FT-IR spectra of SPC, Al-SPCs and Al-MMT samples.
be observed, which is attributable to the clay layers.21 Furthermore,
the uniform gallery pores can be clearly observed between the dark
layers. Obviously, the Al-SPC-5 (Fig 4C) shows the uniform layered
structure, and has relative higher gallery height than MMT.
The N2 adsorption-desorption isotherms of the SPC, Al-SPCs and
Al-MMT are presented in Fig. 5(A) and average pore dimensions
and volumes obtained from the maxima (BJH) are presented in
Table 1.Irrespective of treatment method, the N2 isotherms of the
catalysts can be assigned to be a combination of types I and IV22
according to the BDDT (Brunauer, Deming, Deming, and Teller)
classification, and the features of hysteresis loop correspond to the
type B in Boer’s five types, suggesting that the presence of the open
slit-shaped capillaries with very wide bodies and narrow short necks
in the region between interlayers.23 Compared with MMT and Al-
MMT, the SPC and Al-SPCs have a significant increase in porosity
To get further insight into the layered structure of Al-SPCs,
HRTEM investigations were then conducted and the corresponding
images are shown in Fig 4.The HRTEM image (Fig 4A) of MMT shows
that the sheets keep together closely. From the image (Fig 4B and
4D) of the SPC and Al-SPC-7, clear solid dark lines and the pores can
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Fig 4. HRTEM images of (A) MMT, (B) SPC, (C) Al-SPC-5 and (D) Al-SPC-7 sample.
and surface area, which is attributable to the forming of rigid is closely related to the interlayer space height. This implies that the
intercalated porous structure when TEOS that as the pillaring interlayer surfactant plays an important structure-directing role in
precursors are converted to firm enough silica pillars. As shown in the synthesis of the intercalated silica. The surface area and pore
Fig. 4(A), the slight increase in the amount of N2 adsorbed with volume of the Al-SPCs decreased with increase in as the content of
increasing relative pressure from a low to a medium value (P/Po Al (Table 1), which is owing to the packing of small metal particles
=0.01−0.2) indicaꢁng that these materials possess supermicropores on the surfaces and pores.25
and small mesopores.24 In the P/Po region from 0.0 to 0.4, the
NH3-TPD analysis was performed in order to evaluate the
adsorption isotherm gives a good fit with the BET equation as well quantification of the catalysts acid density and the results are
as with the Langmuir equation; The above results indicates that the shown in Fig. 5. The amount of surface acid sites based on NH3
pores formed between parallel layers are quite open.
desorption are presented in Table 2. From Fig. 5, three types of
region was observed, which
The BJH-adsorption pore size distribution curves of the samples desorption peaks from 99 to 530
℃
are shown in Fig. 4(B). All the Al-SPCs studied displayed different could be denoted as weak, moderate and strong acid sites,
mesopore size distributions. The average pore size of Al-SPCs was respectively.26 The weak and moderate acid sites in the form of the
12.1-12.2 nm, which was slightly less than the average pore size of OH groups bonded to the pillars Al ions (Al–OH), and the strong acid
SPC, indicating that the interlayer frameworkthe are changed by sites is associated with the OH groups bonded to tetrahedrally
incorporation of Al. It might be owing to the extragallery Al2O3 coordinated Al ions (AlTd–OH). 27 As the Al content increased from 1
occupied the spaces of gallery channels and increased the thickness to 7, the total amount of acid sites of Al-SPCs significantly
of the pore walls, and resulting in a slightly decreased of the increased. Meanwhile, the amount of moderate acid sites of Al-
average pore size. These results were in great agreement with the SPCs enhanced considerably from 1.90 to
N2 adsorption–desorption isotherms. The average pore size of SPC
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Fig. 6 NH3-TPD profiles of SPC, Al-SPCs and Al-MMT samples.
assignable to coordinated pyridine species with Lewis acid sites.28
The band at 1544 cm−1 due to pyridinium ions bonded to Brönsted
acid sites. The band at 1490 cm−1 attributed to pyridine associated
with both Lewis and Brönsted acid sites.29-30 It can clearly found
that only small peaks corresponding to pyridine adsorbed on acidic
sites were observed for SPC, indicating that the surface acidities of
SPC were weak. Meanwhile, the amounts of Brönsted and Lewis
acid sites on Al-SPCs increased from 0.18 to 0.32 mmol g−1, and 0.13
to 0.53 mmol g-1 with increase in Al content from1 to 7,
respectively. Note that Al significantly affected the acidity of the
MMT materials and the addition of Al resulted in the increase and
redistribution of the two types of acid sites. Moreover, this results
shows that Al-SPCs, which was highly active for the reaction result
from higher L/B ratio. Therefore, the hydroxyalkylation of phenol to
bisphenol F is catalyzed by the synergy of Brönsted acid and Lewis
acid rather than a single one. This results was confirmed by Py-IR
results and is well consistent with the above NH3-TPD result.
Fig .5 N2 adsorption−desorpꢁon curves (A) and pore size
distributions (B) of SPC, Al-SPCs and Al-MMT samples.
3.19 mmol g-1. Interestingly, the amount of weak and strong acid
sites only shows a minor change. In addition, the highest amount of
moderate acid sites were found in Al-MMT, which may due to high
Al content for Al-MMT.
As shown in the Scheme 2, Al was incorporated in the silica-
framework between the interlayer regions of MMT.
3.2 Activity measurement
The catalytic activity of the prepared SPC, Al-SPCs and Al-MMT were
evaluated for the hydroxyalkylation of phenol. The results are
summarized in Table 3. As compared to MMT and SPC, Al-SPCs
shows of Aluminum species presence in the gallery silica
framework. Obviously, Al-SPC-5 had the highest activity (95.4%),
higher than that very high catalytic activity, indicating that catalytic
activity is a result
The acid properties of SPC and Al-SPCs and were evaluated by
FT-IR measurement for samples with adsorbed pyridine and the
results are shown in Fig. 7. The amounts of Brönsted and Lewis acid
sites are listed in Table 2. These peaks could be assigned to the
chemisorption of molecular pyridine at different type of surface
acidic sites. The band at 1447 cm−1 in the difference FT-IR spectra in
Fig. 7 is
Table 2. Acidic properties of various solid acid catalysts.
NH3-TPD amount of acidic sites (mmol g-1)
Acidity by type (mmol g-1)
Catalyst
SPC
Weak
0.49
0.50
0.51
0.54
0.56
0.62
Moderate
1.90
Strong
1.11
1.09
1.06
1.10
1.93
1.02
Total
3.50
3.64
3.84
4.56
5.68
6.24
Brönsted
0.18
0.25
0.27
0.29
0.32
－
Lewis
0.13
0.23
0.26
0.41
0.53
－
Lewis/Brönsted
0.72
0.92
0.96
1.41
1.66
－
Al-SPC-1
Al-SPC-3
Al-SPC-5
Al-SPC-7
Al-MMT
2.05
2.27
2.92
3.19
4.60
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indicating that the catalytic activity is good agreement with the
NH3-TPD analysis and the N2 adsorption- desorption isotherms,
indicating that the catalytic activity is dependent on the amount of
moderate acid sites and the specific surface area of catalyst for the
hydroxyalkylation of phenol. Al-SPC-5 exhibited the higher catalytic
performance than others.
Consequently, Al-SPC-5 was chosen as the catalyst for the
following study.
3.3 Recyclability of catalysts
Since Al-SPCs showed rather high catalytic activity and green
chemistry principle, its reusability appeared much more important.
After completion of the reaction, the catalyst was recovered by
filtration, washed with ethanol and acetone, and air-dried. The
recovered catalyst was reused in subsequent runs and the results
are listed in Table 4. It can be clearly found that only slight decrease
of bisphenol F yield were observed after the sixth run, indicating
that acid sites did not largely losses during the repeated process. In
order to confirm the above speculation, the recovered Al-SPC-5 was
explored using NH3-TPD, XRD, and FT-IR. XRD of the fresh and
recovered catalyst Al-SPC-5 after six times listed in Fig. 8 (A). It
clearly find that the intensity of 001 reflection peak is decrease.
Moreover, the 001 reflection peak is shifted toward higher
diffraction angles after the six cycle. The reason for this result may
be that reactants and trimer adsorbed on the clay layers after the
six cycle, and resulting in reduced basal spacings. NH3-TPD spectra
of sixth repeated used Al-SPC-5 were analyzed to further confirm
the acid property of recycled catalysts, and the results are
presented in Fig. 8 (B). As compared with the fresh catalyst, slight
decrease in the moderate acid sites’ peaks intensity of the
recovered catalyst Al-SPC-5 after six times was observed. It is
attributed to the acid site adsorption of some compounds, resulting
in a reduction in the amount of acid sites after the six cycle.
Fig. 7 Py-IR spectra of SPC and Al-SPCs samples.
of the Al-SPC-3 catalyst (72.8%). With the increase of Al content
from 1 to 5, the bisphenol F yield increasing from 36.5 to 95.4%.
This is attribute to enhanced amount of moderate acid sites and
higher L/B ratio resulted in higher catalytic activity, which is
confirmed the results of NH3-TPD and Py-IR (Table 2). When further
increase in Al content up to 7, there is a decrease of bisphenol F
yield (94.7%). This may be due to the Al-SPCs derivatives prepared
with high Al content contain mainly isolated tetracoordinated Al
species incorporated in the gallery silica structure, which leads to a
gradual reduction of quality of pore structure and of the pore
volumes and results in decline of specific surface areas.
Interestingly, the Al-MMT show the lower catalytic activity than Al-
SPC-5 and Al-SPC-7, although it has the higher amount of moderate
acid sites. This is attribute to the low specific surface areas of Al-
MMT. These experimental results were in good agreement with the
NH3-TPD analysis and the N2 adsorption- desorption isotherms,
Table 3. Catalytic activities of MMT, SPC, Al-SPCs and Al-MMT for bisphenol Fa
Isomer distribution/%
Catalyst
MMT
Yield/%
10.2
12.3
36.5
72.8
95.4
94.7
87.3
Selectivity/%
90.5
4,4'-Isomer
18.3
2,4'-Isomer
51.2
2,2'-Isomer
30.5
SPC
91.2
20.7
51.1
28.2
Al-SPC-1
Al-SPC-3
Al-SPC-5
Al-SPC-7
Al-MMT
97.6
27.4
51.3
21.3
97.2
29.1
50.8
20.1
98.2
29.6
50.2
20.2
98.1
29.3
50.1
21.6
90.4
32.2
48.5
19.3
a Reaction conditions: phenol/formaldehyde molar ratio, 15:1; catalyst concentration, 0.003 g/g; reaction temperature, 353 K; reaction
time, 40 min.
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Interlayered
MMT sheets
Hydrolysis
Calcination
Na+
Mixed gel of TEOS
and AlCl3
Cationic surfactant
Scheme 2. Schematic for preparation of Al-containing mesoporous silica-pillared clay.
Fig. 9 FT-IR spectra of fresh and recovered Al-SPC-5 after six times.
In order to further explain the superior recyclability of Al-SPCs,
the FT-IR spectrum of the sixth repeated used Al-SPC-5 was
compared with that of the fresh Al-SPC-5, and the results are shown
in Fig. 9. As compared with the spectrum of the fresh Al-SPC-5,
slight decrease of the peak intensity at 3652 cm-1 (corresponding to
the Al–OH, which is acid site) in the spectrum of the recovered Al-
SPC-5. This is well agreement with the result that the yield shows
slight decrease after the sixth run. These results clearly showed that
the Al-SPCs had the great potential to be effectively separated and
reused for the hydroxyalkylation of phenol.
3.4 Optimization of Reaction Parameters.
The effects of the phenol/formaldehyde molar ratio (3, 5, 10, 15,
and 20) on the yield, selectivity, and the isomers’ distribution of
bisphenol F over Al-SPC-5 are illustrated in Fig. 10. The product
yield is increased significantly from 48 to 95% with a change in the
phenol/formaldehyde ratio from 3 to 15; With further increase in
mole ratio of the phenol/formaldehyde to 20, both the yield and
selectivity of bisphenol F does not any significant changes. This was
Fig. 8 Small XRD patterns (A) and NH3-TPD profile (B) of fresh and
recovered Al-SPC-5 after six times.
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Table 4. Catalytic activities of Al-SPC-5 recycled different numbers of times.
Isomer distribution/%
Cycle no
Yield/%
95.4
94.1
93.3
93.1
92.0
91.4
91.2
Selectivity/%
98.2
4,4'-Isomer
27.3
2,4'-Isomer
50.6
2,2'-Isomer
22.1
0
1
2
3
4
5
6
97.5
27.5
50.2
22.3
97.1
28.2
51.3
20.5
97.0
28.4
50.5
21.1
97.0
29.1
50.8
20.1
96.4
28.6
50.1
21.3
96.4
28.1
50.7
21.2
mainly because of the blockage of active sites of the catalyst by
more phenol molecules present in excess amount for a mole ratio
of 20.32 Moreover, when increasing phenol concentration, the
formaldehyde molecules can be surrounded by phenol molecules
that resulting in the initially formed bisphenol F molecules to
almost not contact the formaldehyde molecule to form higher
homologues.33 The selectivity of the 4,4′ and 2,4′-isomer increases
from 26 to 28% and from 46 to49%, whereas the selectivity of the
2,2′-isomer decrease from 29 to 23% .Thus, the optimal molar ratio
was 15.
Fig. 11 shows the effect of catalysts concentration on the yield,
selectivity, and isomers’ distribution of bisphenol F. As shown in
Fig.11, the product yield dramatically increased from 75 to 95%
upon increasing the catalyst concentration increased from 0.0005
to 0.003 g/g. Nevertheless, further increase in catalyst
concentration, the product yield remained almost unchanged. This
may be attributed to this reason that overused catalysts were also
beneficial for accelerating the side-reaction to produce more
byproducts. Interestingly, No significant changed was observed in
the selectivity to bisphenol F and isomer distribution, as increase
the catalyst concentration from 0.0005 to 0.003 g/g. Thus, 0.003
g/g was selected as the suitable catalyst dose.
Fig. 11 Effect of catalyst concentration on the yield, selectivity and
isomers' distribution of bisphenol F. Reaction conditions: catalyst,
Al-SPC-5; mole ratio of phenol/formaldehyde, 15; catalyst
concentration, 0.0005–0.004 g/g; reaction time, 40 min; reaction
temperature, 343 K.
Results showing the effects of the reaction temperature on
product yield, selectivity to bisphenol F and isomer distribution over
Al-SPC-5 were investigated and presented in Fig. 12. It was clearly
observed that the product yield is significantly increased from 52 to
95%, while the bisphenol F selectivity just changes slightly, ranging
from 98 to 97% with increased temperature from 313 to 343 K.
However, further increase in temperature upon to 353 K, the
product yield show a contradictory decreasing trend. It has been
previously proved that an increase of the reaction temperature may
result in the formation of some undesired by products such as
trimer. In addition, the selectivity of the 4,4′-isomer decreased from
49 to 32%, However, the selectivity of 2,4′- and 2,2′-isomers
increased from 42 to 47% and 9 to 21% , respectively. Thus, 343 K
was chosen as the optimal reaction temperature.
A
The effects of reaction time on the products yield, bisphenol F
selectivity and isomers’ distribution was also studied and the results
are shown in Fig. 13. It was clearly observed that the product yield
increases rapidly from 65 to 95%, while remained almost
unchanged in bisphenol F selectivity with increased reaction time
from 10 to 40 min. When further prolonged reaction time to 50
min, the product
Fig. 10 Effect of phenol/formaldehyde molar ratio on yield,
selectivity and isomers' distribution of bisphenol F. Reaction
conditions: catalyst, Al-SPC-5; reaction time, 40 min; reaction
temperature, 343 K; catalyst concentration, 0.003 g/g.
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ion intermediate (A) by eliminate water. At the same time, the
carbenium ion were produced by the abstraction of H- over Lewis
acid sites of the catalyst. Subsequently, the carbenium ion may
attack phenol to form para or ortho hydroxy benzyl alcohol (B or
C).B or C was activated in the presence of Brönsted acid or Lewis
acid to form para or ortho hydroxy benzyl carbonium ion (D or E)
and released a water molecule simultaneously. Then, Species D or E
with strong electrophillicity attacked the para or ortho carbon atom
of an phenol molecule to form 2,2'-isomers, 2,4'-isomers, and 4,4'-
isomers of bisphenol F.
It can be found from the entire catalytic process that the
catalytic active sites of Al-SPCs are mainly from the hydrogen
proton (Brönsted acid) and coordinatively unsaturated Alm+ sites
(Lewis acid) in the pillars.31 Rataboul et al.36 measured Minimum-
activation energy required for catalysis by Brönsted and Lewis acid
sites, and manifested the protonation of formaldehyde is activated
by Lewis acid to capture H- from the reaction required activation
energy is more than Brönsted acid activation energy required.
Meanwhile, we find that catalysts with high Lewis to Brönsted acid
site ratios resulted in higher catalytic activity, which are confirmed
by the results of Py-IR. It means that the hydroxyalkylation of
phenol to bisphenol F is catalyzed by the synergy of Brönsted acid
and Lewis acid rather than a single one. These results are also in
qualitative agreement with the experimental work of Weingarten
and co-workers.37
Fig. 12 Effect of reaction temperature on the yield, selectivity and
isomers' distribution of bisphenol F. Reaction conditions: catalyst,
Al-SPC-5; phenol/formaldehyde, 15; reaction time, 40 min; reaction
temperature, 313–353 K; catalyst concentration, 0.003 g/g.
4. Conclusions
Mesoporous Al-SPCs with different Al content were prepared in the
presence of cationic surfactant by structure-directing method.
These materials possess mesoporous structure with large specific
surface areas. The incorporated Al leading to the increase and
redistribution of Brönsted and Lewis acid sites on SPC. These
catalysts show excellent catalytic activity and selectivity to
bisphenol F. The sufficient moderate acid sites and high surface
area are critical for achieving the highest yield and selectivity of
bisphenol
F in hydroxyalkylation of phenol. Moreover, the
reusability of the catalyst was studied, the results showed that the
catalysts can be recovered for at least six times without significant
loss of their catalytic activities. In addition, the influences of various
reaction parameters like mole ratio, catalyst concentration,
reaction temperature and reaction time on the product yield and
Fig. 13 Effect of reaction time on the yield, selectivity and isomers'
distribution of bisphenol F. Reaction conditions: catalyst, Al-SPC-5;
mole ratio of phenol/formaldehyde, 15; reaction time, 10–50 min;
catalyst concentration, 0.003 g/g.
selectivity to bisphenol
F were investigated and a plausible
mechanistic pathway was proposed.
yield and selectivity to bisphenol F only shows a minor change. This
is expected due to the bisphenol F conversion into a trimer as
longer reaction time. The selectivity of 4,4′- and 2,4′-isomer
decreased from 30 to 28% and 53 to 51%, however, the selectivity
of 2,2′-isomers increased from 17 to 20%, respectively. Based on
the results, we consider that 40 min is the reaction time for optimal
performance.
Acknowledgements
This research was financially supported by the National Natural
Science Foundation of China (no. 51378187, J1210040), Innovative
Research Team Development Plan-Ministry of Education of China
(no. IRT1238), the Key Project of Hunan Provincial Education
Department (no. 13CY001), and Hunan Provincial International
Cooperation Project of China (no. 2014WK3030).
3.5 Plausible mechanistic pathway.
On the basis of our group previous studies13 and some relative
literature,33 a plausible catalytic reaction mechanism was proposed
and is shown in scheme 3.The synthesis of bisphenol F via the
condensation reaction of phenol with formaldehyde is a typical
acid-catalyzed reaction.35 Following the adsorption of the
formaldehyde on the Brönsted acid sites, and to form a carbenium
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Scheme. 3 Proposed plausible mechanism for hydroxyalkylation of phenol and formaldehyde to bisphenol F.
1545-1550.
10 C. D. Keenan, M. M. Herling, R. Siegel, N. Petzold, C. R. Bowers, E.
A. Rossler, J. Breu and J. Senker, Langmuir., 2013, 29, 643-652.
11 H. Mao, B. Li, X. Li, L. Yue, J. Xu, B. Ding, X. Gao and Z. Zhou,
Microporous Mesoporous Mater., 2010, 130, 314-321.
12 S. Yang, G. Liang, A. Gu and H. Mao, Ind. Eng. Chem. Res., 2012,
51, 15593-15600.
13 X. Wu, X. Xia, R. Liu and Y. Chen, RSC Adv., 2016, 6, 34625-34632.
14 Q, Hao, G, Wang, Z, Liu, J, Lu, and Z, Liu, Ind. Eng. Chem.
Res.,2010, 49, 9004–9011.
Notes and references
1 M. Okihama and J. Kunitake, Patent JP 09067287, 1997.
2 S. K. Jana, T. Kugita, and S. Namba, Catal. Lett., 2003, 90,3-4.
3 R. Liu, X. Niu, X. Xia, Z. Zeng, G. Zhang and Y. Lu, RSC Adv., 2015,
62394-62401.
4 N. Maksimchuk, M. Timofeeva, M. Melgunov, A. Shmakov, Y.
Chesalov, D. Dybtsev, V. Fedin and O. Kholdeeva, J.Catal., 2008,
257, 315-323
5 K. Nowinska, W. Kaleta, Appl. Catal. A, 2000,203, 91–100.
6 M. Chen, J. Yan, Y. Tan, Y. Li, Z. Wu, L. Pan and Y. Liu, Ind. Eng.
Chem. Res., 2015, 54, 11804-11813.
7 A. C. Garade, V. S. Kshirsagar and C. V. Rode, Appl. Catal. A, 2009,
354, 176-182.
5
,
15 A. Gil, R. Trujillano, M. A. Vicente, and S. A. Korili, Ind. Eng.
Chem. Res., 2008, 47, 7226–7235.
16 H.Mao, B, Li, X Li, L. Yue, Z. Liu, and W. Ma, Ind. Eng. Chem. Res.
2010, 49, 583–591.
,
17 Y. Gao, Y. Guo and H. Zhang, J Hazard Mater., 2016, 302, 105-113.
18 F. Tomul, Ind. Eng. Chem. Res., 2011, 50, 7228-7240.
19 H. Mao, B. Li, X. Li, Z. Liu and W. Ma, Mater. Res. Bulletin., 2009,
44, 1569-1575.
20 Y. Han, H. Matsumoto, and S. Yamanaka, Chem. Mater., 1997, 9,
2013-2018.
8 M. A. De Leon, M. Sergio, J. Bussi, G. Ortiz de la Plata, A. E.
Cassano and O. M. Alfano, Ind. Eng. Chem. Res., 2015, 54, 1228-
1235.
9 J. Virkutyte and R. S. Varma, ACS Sustainable. Chem. Eng., 2014, 2,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
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Journal Name
21 H. Mao, B. Li, X. Li, Z. Liu, W. Ma, Materials Research Bulletin.,
2009,44, 1569–1575.
22 S. G.Hur, T. W. Kim, S.J. Hwang, S.H.Hwang, J. Yang, and J.H.
Choy, J. Phys. Chem. B, 2006, 110, 1599-1604.
23 J.H. Choy, H. Jung, Y.S. Han, J.B. Yoon, Y.G. Shul, and H.J. Kim,
Chem. Mater., 2002, 14, 3823-3828.
24 M. A. Vicente, C. Belver, M. Sychev, R. Prihod’ko, and A. Gil, Ind.
Eng. Chem. Res.,2009, 48, 406–414.
25 J. Valverde, A.Lucas, F. Dorado, A. Romero, and P. Garcı ´a, Ind.
Eng. Chem. Res., 2005, 44, 2955-2965.
26 M. Balaraju, V. Rekha, P. S. S. Prasad, B. L. A. P. Devi, R. B. N.
Prasad and N. Lingaiah, Appl. Catal. A, 2009, 354, 82-87.
27 G. Centi, S. Perathoner, F. Trifirb, J. Phys. Chem., 1992, 96. 2617-
2629.
28 F. Chambon, F. Rataboul, C. Pinel, A. Cabiac, E. Guillon and N.
Essayem, Appl. Catal. B,2011, 105, 171-181.
29 B. Devassy, F. Lefebvre and S. Halligudi, J. Catal., 2005, 231, 1-10.
30 A. M. Alsalme, P. V. Wiper, Y. Z. Khimyak, E. F. Kozhevnikova and
I. V. Kozhevnikov, J.Catal., 2010, 276, 181-189.
31 H. Mao, B. Li, L. Yue, L. Wang, J. Yang and X. Gao, Appl. Clay Sci.,
2011, 53, 676-683.
32 R. Liu, X. Xia, X. Niu, G. Zhang, Y. Lu, R. Jiang and S. He, Appl. Clay
Sci., 2015, 105-106, 71-77.
33D. Wang, Z. He, Z. Wu, Y. Tan, Y. Li and Y. Liu, Chinese. J. Chem. En
g, 2016.
34 J. Tian, H. An, X. Cheng, X. Zhao and Y. Wang, Ind. Eng. Chem.
Res., 2015, 54, 7571-7579.
35 Q. Wang, Z. M. Wu, Y. Li, Y. Tan, N. Liu and Y. Liu, RSC Adv., 2014,
4
, 33466- 33473.
36 F. Chambon, F. Rataboul, C. Pinel, A. Cabiac, E. Guillon and N.
Essayem, Appl. Catal. B, 2011, 105, 171-181.
37 R. Weingarten, G. A. Tompsett, W. C. Conner and G. W. Huber, J.
Catal., 2011, 279, 174-182.
12 | J. Name., 2012, 00, 1-3
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Mesoporous Al-incorporated silica-pillared clay interlayer materials for catalytic
hydroxyalkylation of phenol to bisphenol F.