Room-temperature production of bio-based aldehydes from vegetable oil-derived epoxide: via H2WO4?Al-MCM-41 as recyclable catalyst

Article abstract of DOI:10.1039/c9ra04348a

The oxidative cleavage of vegetable oils and their derivatives to produce bio-based aldehydes is a potentially useful process, although the aldehyde products are readily oxidized to carboxylic acids and thus seldom obtained in high yields. The present study developed a room-temperature method for the synthesis of bio-aldehydes via the oxidative cleavage of vegetable oil-derived epoxides, using H₂WO₄ as the catalyst, H₂O₂ as the oxidant, and t-BuOH as the solvent. Reactions were carried out at temperatures ranging from 25 to 35 °C for 3.5-10.5 h, and provided >99% conversion and >90% aldehyde yield. In particular, an approximately 97% yield was obtained at 25 °C after 10.5 h. As the reaction proceeded, the H₂WO₄ dissolved to form a W-containing anion. Several mesoporous Al-MCM-41 materials having different Si/Al ratios were hydrothermally synthesized and used as adsorbents to recover the catalyst by adsorbing these anions. The adsorption capacity of the Al-MCM-41 was found to increase with decreases in the Si/Al ratio. The Al-MCM-41 had little effect on the oxidative cleavage reaction at 25 °C, and thus could be directly added to the reaction system. The excellent anion adsorption performance of the Al-MCM-41 greatly improved the reusability of the H₂WO₄ catalyst. When using the Al-MCM-41 with the best adsorption performance, there was no significant decrease in the activity of the catalyst following five reuses.

Full text of DOI:10.1039/c9ra04348a

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Room-temperature production of bio-based
aldehydes from vegetable oil-derived epoxide via
Cite this: RSC Adv., 2019, 9, 23061
H2WO4@Al-MCM-41 as recyclable catalyst
*
and Jianbing Ji
Libo Peng, Qinglong Xie, Yong Nie,
Xuejun Liu, Meizhen Lu
The oxidative cleavage of vegetable oils and their derivatives to produce bio-based aldehydes is a potentially
useful process, although the aldehyde products are readily oxidized to carboxylic acids and thus seldom
obtained in high yields. The present study developed a room-temperature method for the synthesis of bio-
aldehydes via the oxidative cleavage of vegetable oil-derived epoxides, using H2WO4 as the catalyst, H2O2
as the oxidant, and t-BuOH as the solvent. Reactions were carried out at temperatures ranging from 25 to
35 ꢀC for 3.5–10.5 h, and provided >99% conversion and >90% aldehyde yield. In particular, an
approximately 97% yield was obtained at 25 ꢀC after 10.5 h. As the reaction proceeded, the H2WO4
dissolved to form a W-containing anion. Several mesoporous Al-MCM-41 materials having different Si/Al
ratios were hydrothermally synthesized and used as adsorbents to recover the catalyst by adsorbing these
anions. The adsorption capacity of the Al-MCM-41 was found to increase with decreases in the Si/Al ratio.
The Al-MCM-41 had little effect on the oxidative cleavage reaction at 25 ꢀC, and thus could be directly
added to the reaction system. The excellent anion adsorption performance of the Al-MCM-41 greatly
improved the reusability of the H2WO4 catalyst. When using the Al-MCM-41 with the best adsorption
performance, there was no significant decrease in the activity of the catalyst following five reuses.
Received 10th June 2019
Accepted 20th July 2019
DOI: 10.1039/c9ra04348a
rsc.li/rsc-advances
classic practice, the industrial scale epoxidation of vegetable oil,
such as unsaturated fatty acid methyl esters (UFAMEs), is
1. Introduction
Vegetable oils are an important biomass-derived energy source1
that can also be used in the food and chemical industries.
Historically, these oils have typically been employed as foods,
but more recently have been used to produce bio-based chem-
icals. This transition is due to concerns regarding limited
petroleum reserves and increased environmental awareness.
The American Oil Chemists' Society has assessed the usages of
nine major vegetable oils: coconut, cottonseed, olive, palm,
palm kernel, peanut, rapeseed, soybean, and sunower in
recent years.2 Interestingly, between 1999 and 2012, the portion
of such oils employed for applications other than human food
has increased from 10.5% to 23.9%.3
The vegetable oils not used for foods are typically processed
into high value-added bio-based products that are both biode-
gradable and nontoxic, oen based on epoxidation reactions.4
Epoxidized vegetable oils have numerous commercial applica-
tions, including as additives in lubricants, costabilizers and
plasticizers in polymers, stabilizers in chlorine-containing
resins, pharmaceutical components and biofuel additives.5,6
There are various approaches to the epoxidation of these oils. In
carried out by reacting the C]C double bonds in the oil with
a percarboxylic acid (generally peracetic acid or performic acid)
generated in situ during the reaction.7 Other methods involve
highly active catalytic systems, including Ti/silica,8 CoCuAl
double layered hydroxides,9 VO supported on Indion 130,10
Mo(O)2Cl2(H2biim) (H2biim ¼ 2,20-bisimidazole) supported on
an ionic liquid ([BMIM][PF6]),11 methyltrioxorhenium,12
tungsten-containing
H5PV2Mo10O40/Na2SO3 (ref. 15) and so on.
heteropolyacids,13
lipases,14
Vegetable oils can also be oxidatively cleaved into the cor-
responding aldehydes, which have various applications. As an
example, methyl oleate can be oxidized and cleaved to synthe-
size nonanal and methyl 9-oxononanoate. The nonanal can be
used as a spice or to prepare 100% bio-based surfactants via the
reductive alkylation of polyols,16,17 while the methyl 9-oxono-
nanoate can be converted to polymer monomers by hydroge-
nation or reductive amination.18 Normally, the oxidative
cleavage of UFAMEs is performed using ozonolysis and/or
a metal catalyst, such as Cr,19 Mo,20 Ru,21 Os22 or W.23
Although these methods provide excellent conversions, the
products are primarily carboxylic acids rather than aldehydes,
which tend to appear only as intermediates.2 This occurs
because the C]C bonds in UFAMEs are highly stable, such that
the oxidative cleavage of these compounds requires harsh
reaction conditions, including high temperatures, long
Institute of Chemical Engineering, Zhejiang University of Technology, Zhejiang
Province Key Laboratory of Biofuel, Biodiesel Laboratory of China Petroleum and
Chemical Industry Federation, No. 18 Chaowang Road, Hangzhou, Zhejiang
310014, China. E-mail: zjutluzhen@163.com; Fax: +86 571 88320043
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durations and strong oxidants such as O3, NaIO4 and KMnO4. ZnO) can be used to adsorb W-containing anions from the
Consequently, the as-formed aldehydes are easily further reaction products resulting from a mixture of H2WO4, H2O2 and
oxidized to carboxylic acids.24
EFAMEs.36,37
To obtain high yield of aldehydes from UFAMEs, it is vital to
Because H2O2 can be decomposed by most metal oxides,38 it
avoid or at least lessen the over-oxidation of aldehydes, and is benecial to disperse the metal oxide well to the solid that can
various novel strategies have been proposed for this purpose. coexist with H2O2 (just like SiO2) to reduce the amount of metal.
Louis et al.18 developed an oxydoreductive cleavage using PPh3 Among the various metal-doped SiO2 materials, Al-MCM-41 has
or H2 + Pd/C that reduces the ozonides of UFAMEs to generate been widely studied because its Al content is readily adjustable
aldehydes and gives complete conversion together with >90% and it has a suitable mesoporous structure.39 Due to their
aldehydes yield. Deruer et al.25 used a thiazolylidene catalyst to unique features, including high surface areas, large pores,
cleave the a-hydroxy ketone derived from methyl oleate into the narrow pore size distributions and high pore volumes, meso-
corresponding aldehydes at 150 ꢀC and reported a 60% porous materials such as Al-MCM-41 provide increased acces-
conversion and 40% yield. Other catalyst/oxidant systems with sibility of the reacting species to active sites on internal
high selectivity for aldehydes have also been designed, surfaces. Thus, these materials are of interest with regard to
including [Fe(OTf)2(mix-bpbp)](bpbp ¼ N,N0-bis(2-picolyl)-2,20- applications involving relatively large molecules such as long
bipyrrolidine)/H2O2 + NaIO4,26 niobium(V) oxide/H2O2,27 nano- chain alkanes and lipids.40
RuHAP(HAP ¼ hydroxyapatite)/NaIO4 (ref. 28) and alkylated
In the present investigation, methyl 9,10-epoxystearate (1)
polyethyleneimine/Na3{PO4[WO(O2)2]4}/H2O2.29 In previous derived from methyl oleate was used as a model to study the
work by our own group,30 epoxy fatty acid methyl esters oxidative cleavage of EFAMEs into bio-based aldehydes, using
(EFAMEs) were cleaved into the corresponding free aldehydes H2WO4 as the catalyst, H2O2 as the oxidant and t-BuOH as the
using WO3 and H2O2. The feedstock conversion obtained from solvent. To avoid side reactions and the thermal decomposition
ꢀ
this process was >99% at a reaction temperature of 80 C, but of H2O2, all reactions were performed at or close to room
the selectivity for aldehydes was approximately 80% and thus temperature. Subsequently, mesoporous Al-MCM-41 materials
unsatisfactory. Therefore, further research is required to having different PZC values (due to varying Si/Al ratios) were
improve the aldehyde selectivity associated with this technique. prepared via direct mixed-gel synthesis and used as adsorbents
To the best of our knowledge, the oxidative cleavage of epoxy to recover the catalyst.
group with W-based catalysts and H2O2 proceeds via the initial
hydrolysis of epoxy groups to vic-diols, followed by oxidation to
give aldehydes or carboxylic acids (Scheme 1(a)).2,31,32 Acidic
conditions enhance the oxidative cleavage of epoxides by
promoting the hydrolysis of epoxy groups (Scheme 1(b)).33,34
Thus, the use of H2WO4 instead of WO3 as the catalyst could
potentially provide better results. However, H2WO4 may also
react with H2O2 to form soluble W-containing anions,35 thus
reducing the extent to which the catalyst can be recovered. For
this reason, in prior work, dissolved W-containing anions were
adsorbed using mesoporous tin dioxide to regenerate catalyst.23
However, the pore structure in this dioxide is unstable, and this
material also has a low specic surface area and is costly to
prepare compared to more common mesoporous materials
such as SiO2. Typically, in the case that the point of zero charge
(PZC) of a mineral is higher (lower) than the pH of a solution,
the mineral will interact with hydrogen (hydroxide) ions in the
solution to generate positive (negative) charges on its surface
(Scheme 2), such that it is able to adsorb anions (cations). For
this reason, a mineral having a high PZC (such as Al2O3, MgO or
2. Experimental
2.1. Raw materials
The methyl oleate used in this work was provided by Shandong
Baiqian Chemical Co. The other reagents were purchased from
Aladdin Co. and were of analytical grade. The epoxide 1 was
prepared from methyl oleate through a previously reported
method.41 It was composed of epoxide 1 (about 80 wt%), methyl
octadecanoate (about 14 wt%) and methyl palmitate (about 6 wt%).
2.2. Oxidative cleavage of methyl 9,10-epoxystearate
10 mmol of epoxide 1, 0.17 mmol of H2WO4, 5 ml of t-BuOH and
100 mg of Al-MCM-41 were stirred at 25–35 ꢀC until uniform
followed by 12 mmol of H2O2 (30 wt%) was added dropwise. The
resulting mixture was continued to stir for 3.5–10.5 h. The
liquid products were then obtained by centrifugation to remove
Al-MCM-41 that adsorbed tungsten, and the solid was recovered
through washed with t-BuOH and dried at room-temperature.
Scheme 1 The mechanism of oxidative cleavage of epoxy group by tungsten catalysts and H2O2.
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Scheme 2 Interaction between mineral and H+ or OHꢂ in solution.
y ¼ 10, 30, 50, 70 and 90. In addition, the corresponding Al-free
sample, designated as MCM-41, was prepared as outlined in the
above procedure without the addition of aluminum isopropoxide.
2.3. Product analysis
Qualitative analysis of the product was performed by a gas
chromatography-mass spectrometry (GC-MS, Agilent 7890A/
5975C) equipped with a DB-5 capillary column (30 m ꢁ
0.25 mm ꢁ 0.25 mm). Helium with a purity of 99.99% was used
2.5. Characterization of Al-MCM-41
ꢀ
as the carrier gas. The oven temperature was held at 50ꢂ1C for
The actual Si/Al ratios of Al-MCM-41-y were measured using an
inductively coupled plasma mass spectrometer (ICP-MS) aer
dissolving the samples in hydrouoric acid.
Powder X-ray diffraction (XRD) patterns were obtained using
a PANalytical X'Pert Pro powder diffractometer with Cu Ka (l ¼
0.154056 nm, 40 kV, 40 mA) radiation.
ꢀ
ꢀ
3 min, and then raised to 150 C at a rate of 10 C min and
held for 1 min, and then raised to 220 ꢀC at a rate of 10 ꢀC minꢂ1
and held for 3 min, and nally raised to 280 ꢀC at a rate of
ꢂ1
ꢀ
10 C min and held for 10 min. All of the peaks were deter-
mined according to the National Institute of Standards and
Technology (NIST) library.
The specic surface area, pore volume and average pore size
were measured by N2 adsorption at 77 K using an Micromeritics
ASAP-2020-PLUS-HD88 instrument. Specic surface area was
calculated using the standard Brunauer–Emmet–Teller (BET)
model. The total pore volume was determined from the amount
of N2 adsorbed at a relative pressure p/p0 of 0.99. Pore size
distribution curve was calculated from the adsorption branch of
the isotherm using the Barrett–Joyner–Halenda (BJH) method.
The morphology and the pore structure information were
studied by transmission electron microscopy (TEM) using
a Tecnai G2 F30 S-Twin microscope. The sample was dispersed
in ethanol in an ultrasonic bath for several minutes before
deposited onto a Cu grid followed by being dried under an
infrared heat lamp.
The product was analyzed by a gas chromatograph (Shi-
madzu, GC-2014) equipped with a DB-5 capillary column (30 m
ꢁ 0.25 mm ꢁ 0.25 mm) and a ame ionization detector (FID).
The oven temperature was similar to the qualitative analysis of
the product using GC-MS. The quantication of feedstock and
product was conducted using the internal standard method
with undecanal as the internal standard. The feedstock
conversion and product yield were calculated using the
following equations:
Feedstock conversion ¼ (feedstock reaction amount/feedstock
feed amount) ꢁ 100%;
Product selectivity ¼ (amount of feedstock converted to the target
product/feedstock reaction amount) ꢁ 100%;
The contents of Brønsted and Lewis acid sites of MCM-41
and Al-MCM-41 were determined by the in situ Fourier trans-
form infrared spectroscopy of adsorbed pyridine (Py-FTIR)
using a Thermo sher Nicolet iS50 spectrometer. The sample
was pressed into a self-supporting disk and placed in a stain-
less-steel IR cell equipped with CaF2 windows. Initially,
sample was pretreated in He ow at 300 ꢀC for 2 h to remove any
adsorbed impurities, then the cell temperature was lowered to
50 ꢀC and a spectrum was recorded as background. Subse-
quently, pyridine was introduced and adsorbed on sample for
Product yield ¼ feedstock conversion ꢁ product selectivity.
2.4. Preparation of Al-MCM-41
According to the previous work,40 the Al-MCM-41 with different Si/
Al molar ratios from 10 to 90 were synthesized from a gel molar
composition of 1.00 Si : xAl : 0.25 CTAB : 0.20 TMAOH : 40H2O,
where x ¼ 0.1000, 0.0333, 0.0200, 0.0143 and 0.0111, correspond-
ing to Si/Al molar ratios of 10, 30, 50, 70 and 90, respectively. In
more detail, cetyltrimethylammonium bromide (CTAB, >99 wt%)
and tetramethylammonium hydroxide (TMAOH, >97 wt%) were
dissolved in distilled water under stirring at 35 ꢀC. Then, the
aluminum isopropoxide (>98 wt%) and tetraethyl orthosilicate
(TEOS, >98 wt%) were slowly added into the template solution
under stirring for 1 h. Aer further stirring for 1 h, the obtained gel
mixtures were aged for 72 h at room temperature. The solid
products were then ltrated, washed with distilled water until the
ꢀ
2 h at 50 C. Aer pyridine adsorption, sample was evacuated
for 1 h at 50 ꢀC to remove all physically adsorbed pyridine. Four
spectra were recorded under He ow at the following stagꢀes: (1)
ꢀ
aer 1 h evacuation at 50 C, (2) aer desorption at 150 C for
ꢀ
1 h, (3) aer desorption at 250 C for 1 h, and (4) aer desorp-
tion at 350 ꢀC for 1 h. The concentrations of Brønsted and Lewis
acid sites were calculated by integrating the absorption bands at
1545 cmꢂ1 and 1455 cmꢂ1, respectively and using the molar
extinction coefficients reported by Emeis.42
2.6. Determination of PZC values
ꢀ
pH of the ltrate was 7, and dried at 70 C for 12 h. Finally, Al-
MCM-41 were obtained aer calcining in air at 550 ꢀC for 8 h. The PZC values of MCM-41 and Al-MCM-41 were determined
The as-synthesized Al-MCM-41 were noted as Al-MCM-41-y, where using a salt titration technique.43 In each experiment, 2 g
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samples were placed in each of seven 50 ml glass tubes. subsequent cleavage to generate aldehydes 2 and 3.32 Notably,
Subsequently, deionized water was added and the pH values of aldehydes 2 and 3 were always generated in equimolar amounts
the resulting suspensions were adjusted to span the expected and no over-oxidized products (that is, carboxylic acids) were
pH0 value, using either 0.1 mol Lꢂ1 HC1 or 0.1 mol Lꢂ1 NaOH. obtained. As the reaction time was prolonged, the conversion of
In each case, the nal volume was 20 ml. Each sample was 1 and the aldehyde yields gradually increased to maximum
subsequently allowed to equilibrate for four days with occa- values and then remained basically unchanged. In addition,
sional stirring, aer which the equilibrium pH was recorded elevating the temperature was found to increase the reaction
and designated as pH1. Following this, 0.5 ml of a 2 mol Lꢂ1 rate. However, as the temperature was increased, the aldehydes
NaC1 solution was added and the tube was agitated using yield decreased from 97% at 25 ꢀC to 92% at 35 ꢀC, likely due to
a reciprocal shaker for 3 h, aer which the pH value was enhanced thermal decomposition of the H2O2 at the higher
recorded as pH2. For each tube, DpH (¼pH2 ꢂ pH1) was calcu- temperature. Typically, >99% conversion of epoxide 1 and >90%
lated and the DpH values were plotted versus pH1 to determine yields of the aldehydes were observed over the temperature
ꢀ
the point at which DpH ¼ 0. The corresponding pH equaled the range of 25–35 C for durations of 3.5–10.5 h. In past reports
PZC value for the sample.
concerning the oxidative cleavage of methyl oleate and its
derivatives to give aldehydes, Louis et al.18 and Ho et al.28 ob-
tained 90% and 13% isolated yields, respectively, while Deruer
et al.,25 Spannring et al.26 and Haimov et al.29 reported GC yields
(determined by gas chromatography) of 40%, 96% and 97%,
respectively. For comparison purposes, WO3 was also used as
a catalyst to promote the oxidation and cleavage of epoxide 1
under the same conditions, giving an approximately 86% yield
of the aldehydes following a reaction time of 10.5 h and >90%
yield aer 18 h. The WO3 exhibited weaker catalytic activity than
the H2WO4 primarily because the latter provided a more acidic
environment for the oxidative cleavage reaction.33,34
2.7. Adsorption of W-containing anions by Al-MCM-41
Experiments were performed to assess the adsorption of W-
containing anions by the Al-MCM-41. In these experiments,
1.7 mmol of H2WO4 and 120 mmol of H2O2 were combined and
stirred until the H2WO4 was completely dissolved, aer which
100 mg of Al-MCM-41 was introduced into the solution, fol-
lowed by continuous stirring for 4 h at ambient temperature.
Thereaer, the liquid and solid were separated by centrifuga-
tion, the solid was dried, and the W concentration of the solid
was determined using ICP-MS.
The degree of homogeneity of the H2WO4 during the H2O2-
based oxidative cleavage reaction of the EFAME was subse-
quently studied. As shown in Fig. 2(A1–A3), the H2WO4 was
mixed with H2O2 and the color of the resulting mixture was
tracked over time. The mixture was found to transition from
yellow to cyan over time to eventually produce a colorless
solution. In another experiment, epoxide 1 and t-BuOH were
also included in the mixture, to reproduce the oxidative
cleavage reaction solution. The color change of this mixture
over time is summarized in Fig. 2(B1–B3), which shows a similar
3. Results and discussion
3.1. Oxidative cleavage of methyl 9,10-epoxystearate
In the rst set of experiments, the effects of reaction time on the
conversion of epoxide 1 and the yields of the aldehyde products
(2 and 3) were investigated at temperatures ranging from 25 to
35 ꢀC, with the results shown in Fig. 1. During the reaction
process, epoxide 1 was rst hydrolyzed to vic-diol 4, followed by
oxidation to give the oxygen-rich products 5, 6, 7 and 8, with
Fig. 1 Effect of reaction time on 1 conversion and aldehyde products (2 and 3) yields in the temperature range of 25–35 ꢀC (10 mmol epoxide 1,
12 mmol H2O2, 0.17 mmol H2WO4, 5 ml t-BuOH).
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Fig. 3 The low angle XRD patterns of MCM-41 and Al-MCM-41.
Fig. 2 Study of homogeneity or heterogeneity of H2WO4 in the H2O2-
based EFAMEs oxidative cleavage reaction (25 ꢀC, 10 mmol epoxide 1,
12 mmol H2O2, 0.17 mmol H2WO4, 5 ml t-BuOH).
disturbs the long-range order of the MCM-41.46 Moreover, the
(100) reection shis to smaller angles as the Si/Al ratio
decreases, showing that the d100 spacing in the material became
wider. The d100 spacings of the MCM-41 and Al-MCM-41 are
summarized in Table 1. These data demonstrate that increases
in the Al concentration increased the (100) crystal plane spac-
ings from 3.33 nm in the pure MCM-41 to 3.86 nm in the Al-
MCM-41-10. This effect is attributed to increases in the wall
thickness (t ¼ a ꢂ dp, d100 ¼ a ꢁ sin 60ꢀ) and the replacement of
shorter Si–O bonds (0.160 nm) by longer Al–O bonds (0.175 nm)
in the Al-MCM-41 structure.47
trend to the experiment without the epoxide and solvent. The
changes in the color of the reaction mixture indicate that the
H2WO4 was dissolved during the reaction process, suggesting
that it functioned as a homogeneous catalyst. Therefore, addi-
tional work was required to assess separation and recovery of
the catalyst.
The nitrogen adsorption/desorption isotherms and pore size
distribution curves of the MCM-41 and Al-MCM-41 are depicted
in Fig. 4. All samples produced type IV isotherms, correspond-
ing to mesoporous materials according to the IUPAC classi-
cation system.48 In addition, the pore size distribution plots
(inset to Fig. 4) demonstrate that the pore size distributions of
both the MCM-41 and Al-MCM-41 were narrow and uniform.
The corresponding BET specic surface areas, average pore
sizes and pore volumes are summarized in Table 1. All samples
had high surface areas (1011–1518 m2 gꢂ1) and suitable average
pore sizes (2.68–3.34 nm). With increase in the Al concentra-
tion, the BET surface areas decreased while the average pore
sizes increased, because shorter Si–O bonds were replaced by
longer Al–O bonds.
3.2. Characterization of Al-MCM-41
The actual Si/Al molar ratios of the different Al-MCM-41
samples, as determined by ICP-MS, are provided in Table 1.
These ratios were relatively close to, although slightly lower
than, the corresponding feed ratios. Similar differences
between the actual and nominal Si/Al ratios have been previ-
ously reported. In one study, Al-MCM-41 prepared from
aluminum isopropoxide and pseudo boehmite showed Si/Al
molar ratios lower than the feed ratios.44
Fig. 3 presents the low angle XRD patterns generated by
MCM-41 and Al-MCM-41 materials. All samples produced peaks
characteristic of a typical mesoporous MCM-41 structure.45 The
characteristic reections of (100), (110) and (200) crystal planes
at 2q values of 2.5ꢀ, 4.3ꢀ and 4.9ꢀ are evident, indicating the
Fig. 5 presents TEM images of the MCM-41 and Al-MCM-41.
The MCM-41 evidently had a regular mesoporous structure with
a high degree of long-range order. Following the incorporation
of Al, the Al-MCM-41 was found to have a worm-like pore
structure with reduced long-range order, in agreement with the
presence of
a two-dimensional hexagonal lattice. With
decreases in the Si/Al ratio (that is, increases in the Al content),
the (110) and (200) reections become less intense and broader,
suggesting that the incorporation of Al into the silica framework
Table 1 Physiochemical properties of MCM-41 and Al-MCM-41
BET surface
area (m2 gꢂ1
Total pore volume
Average pore
diameter (nm)
Samples
Si/Al molar ratio
d100 (nm)
)
(cm3 gꢂ1
)
Al-MCM-41-10
Al-MCM-41-30
Al-MCM-41-50
Al-MCM-41-70
Al-MCM-41-90
MCM-41
7
29
46
66
85
—
3.86
3.65
3.59
3.50
3.48
3.33
1011
1181
1281
1279
1370
1518
0.88
0.88
1.00
0.97
0.98
1.04
3.34
2.95
2.88
2.91
2.78
2.68
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Fig. 4 The nitrogen adsorption/desorption isotherms and pore size distribution curves of MCM-41 and Al-MCM-41.
weaker (110) and (200) crystal planes reections in the low angle
XRD patterns of these materials (Fig. 3).
3.3. PZC values of Al-MCM-41 and W-containing anion
adsorption
The acidities of MCM-41 and Al-MCM-41 solids were
measured by thermoprogrammed desorption of Py followed by
FTIR spectroscopy, and quantitative data regarding Brønsted
and Lewis acid sites on the samples are provided in Table 2.
With increases in the Si/Al ratio, the acidity of the samples
decreased as a result of the lower Al concentrations. Assessing
pyridine desorption at different temperatures thus provided
useful information that allowed a qualitative evaluation of the
strengths of acid sites.49 All Al-MCM-41 samples lost approxi-
mately 80% of their Brønsted acid sites aer desorption at
350 ꢀC, showing that these materials possessed weak to
moderate Brønsted acidity. In contrast, approximately half of
the Lewis acid sites were retained in the Al-MCM-41 samples
aer desorption at 350 ꢀC, demonstrating the presence of
strong Lewis acid sites in these substances. The MCM-41 was
found to have only weak Lewis acidity.
Al2O3 typically has a high PZC value within a wide range from
5.0 to 9.6, while the PZC values of SiO2 materials are usually
below 4.0.36 Fig. 6(a) shows the effect of the Al content on the
PZC value of Al-MCM-41. With decreases in the Si/Al ratio, the
PZC value was increased. This PZC value was also closely related
to the anion adsorption performance of the material. Theoret-
ically, a higher PZC value will be associated with better
adsorption performance. Fig. 6(b) compares the W-containing
anion absorptions of the MCM-41 and Al-MCM-41, based on
determining the W levels in these materials aer adsorption,
using ICP-MS. As expected, the Al-MCM-41 exhibited better
adsorption performance than the MCM-41 and the quantity of
anions adsorbed by the Al-MCM-41 increased as the Si/Al ratio
decreased (that is, with increasing PZC values).
Table 2 Acidity of MCM-41 and Al-MCM-41 measured by FTIR of
adsorbed pyridine at different temperatures
Concentration of acid sites, mmolpyridine/gsupport
Brønsted sites
150 ꢀC 250 ꢀ
Lewis sites
Samples
C
350 ꢀ
C
150 ꢀ
C
250 ꢀ
C
350 ꢀ
C
Al-MCM-41-10 59
Al-MCM-41-30 40
Al-MCM-41-50 36
Al-MCM-41-70 31
Al-MCM-41-90 21
40
25
23
23
15
0
9
10
5
4
4
76
42
24
22
8
55
30
19
15
6
50
25
18
11
3
MCM-41
0
0
28
0
0
Fig. 5 TEM images of (a) MCM-41 and (b) Al-MCM-41.
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Fig. 6 (a) PZC values of MCM-41 and Al-MCM-41; (b) absorption performance of MCM-41 and Al-MCM-41 to tungsten-containing anion.
The addition of either MCM-41 or Al-MCM-41 to the reaction
mixture had no signicant effect on either the epoxide 1
conversion or the aldehydes yield (see Fig. 1). This lack of an
effect can possibly be attributed to the ability of the H2WO4 to
provide sufficient acidity for the reaction to proceed.
3.4. Effects of MCM-41 and Al-MCM-41 on the oxidative
cleavage of methyl 9,10-epoxystearate
In the experiments, MCM-41 and Al-MCM-41 as adsorbent were
directly added into the reaction mixture and were always
present until the end of the reaction, so the effect of MCM-41
and Al-MCM-41 on oxidative cleavage of epoxide 1 could not
be ignored. The potential for decomposition of the H2O2 by
these materials was assessed by mixing either the MCM-41 or Al-
MCM-41 with H2O2 and allowing the resulting mixture to stir at
ambient temperature, aer which a potassium permanganate
titration was used to determine the concentration of H2O2. As
shown in Fig. 7(a), aer 12 h, the H2O2 concentration was
essentially unchanged, indicating that neither the MCM-41 nor
the Al-MCM-41 promoted decomposition of the H2O2. In an
industrial operation, H2O2 is oen stored at room temperature
in aluminum tanks, because aluminum forms a hydrated
alumina lm in contact with the H2O2 solution. This lm
hinders the decomposition of H2O2 by separating the H2O2
from the bare metal. Moreover, The effect of the acidity of both
the MCM-41 and Al-MCM-41 on the oxidative cleavage of
epoxide 1 was studied, and the results are presented in Fig. 7(b).
3.5. Recycling of the catalyst
Fig. 8 summarizes the reusability of the H2WO4 catalyst aer
adding MCM-41 or Al-MCM-41 following the oxidative cleavage
of epoxide 1 into bio-based aldehydes. During the rst recycling
experiment, the H2WO4 and MCM-41, or Al-MCM-41, were
added together before the start of the reaction. During the
reaction, the H2WO4 was initially transformed into the peroxo-
W anion [WxOy(O2)z]nꢂ which acted as the active component
and then reduced to the soluble anion [WxOy]nꢂ aer reac-
tion.23,35,50 The hydroxyl groups on the MCM-41 and Al-MCM-41
surfaces would have interacted with hydrogen ions and so
carried positive charges, allowing these materials to absorb the
W-containing anions. The MCM-41 and Al-MCM-41 holding the
adsorbed
anions
(designated
H2WO4@MCM-41
and
H2WO4@Al-MCM-41) were separated from the reaction
Fig. 7 (a) Effect of MCM-41 and Al-MCM-41 on H2O2; (b) effect of the acidity of MCM-41 and Al-MCM-41 on epoxide 1 conversion and aldehyde
products (2 and 3) yields (25 ꢀC, 10.5 h, 10 mmol epoxide 1, 12 mmol H2O2, 0.17 mmol H2WO4, 5 ml t-BuOH, 100 mg MCM-41 or Al-MCM-41).
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Fig. 8 Recycle of catalyst after adding MCM-41 and Al-MCM-41 (25 ꢀC, 10.5 h, 10 mmol epoxide 1, 12 mmol H2O2, 0.17 mmol H2WO4, 5 ml t-
BuOH, 100 mg MCM-41 or Al-MCM-41).
solution, washed with t-BuOH, dried at ambient temperature immobilization of dissolved W species on these materials.
and reused in a subsequent reaction. The pure H2WO4 was Moreover, the catalyst reusability was increased as the Al
dissolved in the reaction solution and thus could only be used concentration in the Al-MCM-41 increased. When using Al-
once. The H2WO4@MCM-41 and H2WO4@Al-MCM-41 both MCM-41-10 or Al-MCM-41-30 as adsorbents, no W species
showed good reusability, primarily due to the adsorption and were detected in the liquid product during ICP-MS analyses,
and there was no signicant decrease in catalytic activity aer
ve recycling experiments.
The H2WO4@Al-MCM-41 was characterized using both XRD
and transmission electron microscopy (TEM). The resulting low
angle XRD pattern is presented in Fig. 9(a), which suggests that
the recovered H2WO4@Al-MCM-41 still has a good mesoporous
structure. The wide angle XRD pattern in Fig. 9(b) exhibits
peaks at 2q values of 16.49ꢀ, 24.16ꢀ, 25.62ꢀ, 26.63ꢀ, 33.24ꢀ,
34.04ꢀ, 35.02ꢀ, 49.63ꢀ, 52.71ꢀ, 56.18ꢀ, 57.20ꢀ and 61.23ꢀ, corre-
sponding to orthorhombic H2WO4 (ICDD-PDF no. 84-0886). The
TEM image of the recovered H2WO4@Al-MCM-41 in Fig. 9(b)
conrms that the pore structure of the Al-MCM-41 was not
signicantly modied aer adsorption of the H2WO4, and that
H2WO4 particles approximately 1 nm in size were uniformly
adsorbed and well dispersed on the Al-MCM-41.
4. Conclusions
H2WO4 was used as a catalyst to promote the oxidation and
cleavage of methyl 9,10-epoxystearate into the corresponding
free aldehydes, employing H2O2 as the oxidant with t-BuOH as
Fig. 9 The XRD patterns ((a) and (b)) and TEM images ((c) and (d)) of the
recovered H2WO4@Al-MCM-41-10.
the solvent. Using a 10/12/0.17 (on a mmol basis) mixture of
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epoxide/H2O2/H2WO4 and 5 ml of t-BuOH, >99% conversion 12 G. Du, A. Tekin, E. G. Hammond and L. K. Woo, J. Am. Oil
and >90% yield were obtained over the temperature range of 25–
35 C with durations of 3.5–10.5 h. The H2WO4 was found to 13 E. Poli, J. M. Clacens, J. Barrault and Y. Pouilloux, Catal.
Chem. Soc., 2016, 81, 477–480.
ꢀ
dissolve in the reaction mixture and thus showed the charac-
teristics of a homogeneous catalyst. A series of Al-MCM-41 14 E. Milchert, K. Malarczyk and M. Kłos, Molecules, 2015, 20,
materials having different Si/Al molar ratios (from 10 to 90) 21481–21493.
were prepared and introduced into the reaction system to allow 15 A. Rubinstein, R. Carmeli and R. Neumann, Chem. Commun.,
recovery of the catalyst by adsorption of dissolved W species. 2014, 50, 13247–13249.
Characterization by ICP-MS, XRD, BET, TEM and Py-FTIR was 16 M. Sutter, W. Dayoub, E. Metay, Y. Raoul and M. Lemaire,
performed to study the physiochemical properties of the Al- Green Chem., 2013, 15, 786–797.
MCM-41, and PZC values were also determined by salt titra- 17 Y. Shi, W. Dayoub, G. Chen and M. Lemaire, Green Chem.,
tion. The results show that each of the Al-MCM-41 materials 2010, 12, 2189–2195.
exhibited typical MCM-41 characteristics. The incorporation of 18 K. Louis, L. Vivier, J. Clacens, M. Brandhorst, J. Dubois,
Today, 2009, 140, 19–22.
´
Al disturbed the long-range order of the MCM-41 but increased
the PZC value. The Al-MCM-41-10 and Al-MCM-41-30 possessed
K. D. O. Vigier and Y. Pouilloux, Green Chem., 2014, 16, 96–
101.
the highest PZC values and showed the optimal W anion 19 P. H. Hoang, N. T. Nhung and L. Q. Dien, AIP Adv., 2017, 7,
adsorption performance. Aer adding the Al-MCM-41-10 or Al- 105311.
MCM-41-30, the catalyst could be reused ve times without 20 A. S. Ello, A. Enferadi-kerenkan, A. Trokourey and T. Do, J.
any signicant loss of activity.
Am. Oil Chem. Soc., 2017, 94, 1451–1461.
21 A. Behr, N. Tenhumberg and A. Wintzer, RSC Adv., 2013, 3,
172–180.
22 B. R. Travis, R. S. Narayan and B. Borhan, J. Am. Chem. Soc.,
2002, 124, 3824–3825.
Conflicts of interest
There are no conicts to declare.
23 M. Lu, L. Peng, Q. Xie, N. Yang, H. Jin, Z. Wu, Y. Nie, X. Liu,
X. Lu and J. Ji, Green Chem., 2019, 21, 560–566.
24 P. Spannring, P. C. A. Bruijnincx, B. M. Weckhuysen and
R. J. M. K. Gebbink, Catal. Sci. Technol., 2014, 4, 2182–2209.
Acknowledgements
This work was supported by the Zhejiang Science and Tech-
nology Plan Project (Fund number: 2017C37054). Thanks for 25 E. Deruer, N. Duguet and M. Lemaire, ChemSusChem, 2015,
nancial support by Zhejiang Ministry of Science and Tech- 8, 2481–2486.
nology. We also thank Liwen Bianji, Edanz Editing China 26 P. Spannring, V. Yazerski, P. C. A. Bruijnincx,
(www.liwenbianji.cn/ac), for editing the English text of a dra of
this manuscript.
B. M. Weckhuysen and R. J. M. KleinGebbink, Chem.–Eur.
J., 2013, 19, 15012–15018.
´
27 C. M. P. Cecchi, D. Cesarın-Sobrinho, A. B. B. Ferreira and
J. C. Netto-Ferreira, Catalysts, 2018, 8, 6.
28 C. Ho, W. Yu and C. Che, Angew. Chem., Int. Ed., 2004, 43,
3303–3307.
29 A. Haimov, H. Cohen and R. Neumann, J. Am. Chem. Soc.,
2004, 126, 11762–11763.
References
1 Y. Zhu, C. Romain and C. K. Williams, Nature, 2016, 540,
354–362.
2 A. E. Kerenkan, F. Beland and T. Do, Catal. Sci. Technol.,
´
2016, 6, 971–987.
3 AOCS lipid library, http://lipidlibrary.aocs.org/market/
nonfood.htm.
4 Z. Wu, J. Fang, Q. Xie, T. Zheng, L. Wu, M. Lu, L. Zhang,
Y. Nie and J. Ji, Ind. Crops Prod., 2018, 122, 266–276.
30 M. Lu, L. Peng, Q. Xie, Y. Nie, X. Liu, X. Lu and J. Ji, Eur. J.
Lipid Sci. Technol., 2018, 120, 1700415.
31 M. Wang, J. Ma, H. Liu, N. Luo, Z. Zhao and F. Wang, ACS
Catal., 2018, 8, 2129–2165.
32 E. Antonelli, R. D'Aloisio, M. Gambaro, T. Fiorani and
C. Venturello, J. Org. Chem., 1998, 63, 7190–7206.
33 P. Spannring, I. Prat, M. Costas, M. Lutz, P. C. A. Bruijnincx,
B. M. Weckhuysen and R. J. M. K. Gebbink, Catal. Sci.
Technol., 2014, 4, 708–716.
¨
5 A. Kockritz and A. Martin, Eur. J. Lipid Sci. Technol., 2008,
110, 812–824.
´
´
6 J. M. Fraile, J. I. Garcıa, C. I. Herrerıas and E. Pires, Synthesis,
2017, 49, 1444–1460.
7 Z. Wu, T. Zheng, L. Wu, H. Lou, Q. Xie, M. Lu, L. Zhang, 34 I. R. Piletic, E. O. Edney and L. J. Bartolotti, Phys. Chem.
Y. Nie and J. Ji, Ind. Eng. Chem. Res., 2017, 56, 5231–5238. Chem. Phys., 2013, 15, 18065–18076.
8 M. Guidotti, R. Psaro, N. Ravasio, M. Sgobba, E. Gianotti and 35 Y. Yoshimura, Y. Ogasawara, K. Suzuki, K. Yamaguchi and
S. Grinberg, Catal. Lett., 2007, 122, 53–56.
N. Mizuno, Catal. Sci. Technol., 2017, 7, 1662–1670.
9 S. Sankaranarayanan, A. Sharma and K. Srinivasan, Catal. 36 M. Kosmulski, J. Colloid Interface Sci., 2004, 275, 214–224.
Sci. Technol., 2015, 5, 1187–1197.
37 C. Sun and J. C. Berg, Adv. Colloid Interface Sci., 2003, 105,
10 P. K. Khatri, M. Aila, J. Porwal, S. Kaul and S. L. Jain, New J.
Chem., 2015, 39, 5960–5965.
151–175.
38 A. Hiroki and J. A. LaVerne, J. Phys. Chem. B, 2005, 109, 3364–
11 P. Neves, T. R. Amarante, A. A. Valente, M. Pillinger and
I. S. Gonçalves, Catal. Lett., 2016, 146, 841–850.
3370.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 23061–23070 | 23069

View Article Online
RSC Advances
Paper
39 H. Ziaei-Azad, J. M. Kolle, N. Al-Yasser and A. Sayari,
E. W. Sheppard, S. B. McCullen, J. B. Higgins and
Microporous Mesoporous Mater., 2018, 262, 166–174.
J. L. Schlenker, J. Am. Chem. Soc., 1992, 114, 10834–10843.
40 M. Lu, X. Liu, Y. Li, Y. Nie, X. Lu, D. Deng, Q. Xie and J. Ji, J. 46 X. Chen, L. Huang, G. Ding and Q. Li, Catal. Lett., 1997, 44,
Renew. Sustain. Energy, 2016, 8, 053103. 123–128.
41 Z. Wu, Y. Nie, W. Chen, L. Wu, P. Chen, M. Lu, F. Yu and J. Ji, 47 R. B. Borade and A. Cleareld, Catal. Lett., 1995, 31, 267–272.
Can. J. Chem. Eng., 2016, 94, 1576–1582.
48 K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou,
´
42 C. A. Emeis, J. Catal., 1993, 141, 347–354.
R. A. Pierotti, J. Rouquerol and T. Siemieniewska, Pure
43 K. Sakurai, Y. Ohdate and K. Kyuma, Soil Sci. Plant Nutr.,
1988, 34, 171–182.
44 K. M. Reddy and C. Song, Catal. Lett., 1996, 36, 103–109.
45 J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz,
C. T. Kresge, K. D. Schmitt, C. T.-W. Chu, D. H. Olson,
Appl. Chem., 1985, 57, 603–619.
49 H. Ziaei-Azad and A. Sayari, J. Catal., 2016, 344, 729–740.
50 E. Lassner, and W. Schubert, Tungsten: Properties, Chemistry,
Technology of the Element, Alloys, and Chemical Compounds,
Kluwer Academic/Plenum Publishers, New York, 1999, pp.
53–122.
23070 | RSC Adv., 2019, 9, 23061–23070
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