A novel synthetic approach for preparing dimethyl carbonate from dimethoxymethane and O2 over Cu-MCM-48

Article abstract of DOI:10.1016/j.apcata.2013.01.014

A new convenient method for the synthesis of dimethyl carbonate from dimethoxymethane and O₂ in the presence of catalytic amounts of Cu-MCM-48 was described. The XRD results indicate that the structure of Cu-MCM-48 is gradually distorted with the increase in the copper content, whereas the framework structure of Cu-MCM-48 is basically retained until the incorporated copper content reaches to 0.62 wt%. The SEM, TEM and N₂ adsorption studies show that copper content of 9.51 wt% completely changes the morphology and structure of Cu-MCM-48. Effects of the amount of the incorporated copper in catalyst, catalyst amount used and other reaction conditions on the catalytic activity are investigated in details to obtain the optimized reaction conditions. Short reaction time, easy recycling of the catalyst and excellent yields are the main advantages of this process.

Full text of DOI:10.1016/j.apcata.2013.01.014

Applied Catalysis A: General 455 (2013) 58–64
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
A novel synthetic approach for preparing dimethyl carbonate from
dimethoxymethane and O2 over Cu-MCM-48
Yongjie Dinga, Aiguo Konga,b,∗, Hengqiang Zhanga, Huanhuan Shena, Zhuodong Suna,
Songping D. Huangc, Yongkui Shana,∗
a Department of Chemistry, East China Normal University, Shanghai 200062, PR China
b Shanghai Key Laboratory of Molecular Catalysts and Innovative Materials, Fudan University, Shanghai 200433, PR China
c Department of Chemistry and Biochemistry, Kent State University, Kent, OH 44240, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 August 2012
Received in revised form 3 January 2013
Accepted 13 January 2013
Available online 7 February 2013
A new convenient method for the synthesis of dimethyl carbonate from dimethoxymethane and O2 in the
presence of catalytic amounts of Cu-MCM-48 was described. The XRD results indicate that the structure
of Cu-MCM-48 is gradually distorted with the increase in the copper content, whereas the framework
structure of Cu-MCM-48 is basically retained until the incorporated copper content reaches to 0.62 wt%.
The SEM, TEM and N2 adsorption studies show that copper content of 9.51 wt% completely changes the
morphology and structure of Cu-MCM-48. Effects of the amount of the incorporated copper in catalyst,
catalyst amount used and other reaction conditions on the catalytic activity are investigated in details to
obtain the optimized reaction conditions. Short reaction time, easy recycling of the catalyst and excellent
yields are the main advantages of this process.
Keywords:
Dimethyl carbonate
Dimethoxymethane
Molecular oxygen
Cu-MCM-48
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
viscosity also renders it useful in lithium ion battery applications
[3].
Many of the traditional industrial processes for preparing
fine and bulk chemicals are known to have negative impact on
human health and the environment due to the various disad-
vantages such as pollution, high costs, poor chemical selectivity,
long reaction times, high reaction temperatures, to name just a
few. Consequently, the search for clean, energy efficient, selec-
tive, and environmentally sustainable processes for such chemicals
is attracting considerable research attention. Dimethyl carbon-
ate (DMC) is a versatile compound that represents an attractive
eco-friendly alternative to methylhalides or dimethylsulfate in
methylation reactions and to poisonous phosgene (COCl2) in poly-
carbonate and isocyanate syntheses [1]. It is also considered as
an ideal additive for transportation fuels due to its higher oxygen
content (53.3%) and good blending properties with octane [2]. Addi-
tionally, DMC is also considered as a promising alternative to the
use of ketones and ester acetates in the field of paints and adhesives
due to a strong solvation power. The latter, combined with its low
There are several routes for DMC synthesis, such as phos-
genation of methanol, oxidative carbonylation of methanol,
transesterification and direct synthesis from carbon dioxide and
methanol [4–13]. However, the first two processes use toxic, cor-
rosive, flammable and explosive gases such as phosgene, hydrogen
chloride and carbon monoxide [14]. The transesterification route
has the disadvantages of high cost of the starting materials and
difficulty in the product separation [15]. DMC yield in carbon diox-
ide and methanol route is relatively low due to the fact that CO2
is highly thermodynamically stable and kinetically inert and due
to the deactivation of catalysts induced by water formation in the
reaction process [16,17].
DMC could be obtained from selective oxidation of
dimethoxymethane (DMM), as the following reaction equation:
CH2(OCH3)2 + O2 → C3H6O3 + H2O
In the reaction, the by-product is water; furthermore, DMM has
extremely low toxicity and can be produced on a large scale [18].
Compared to the conventional synthesis methods of DMC, the syn-
thesis process of DMC from selective oxidation of DMM is simple,
eco-friendly and high atom-economic. To the best of our knowl-
edge, although there have been a limited number of studies on the
synthesis of DMC by this route reported in the literature [19], they
suffer many disadvantages such as the tedious preparation process
∗
Corresponding authors at: Department of Chemistry, East China Normal Univer-
sity, 3663 Zhongshan Road North, Shanghai 200062, PR China.
Tel.: +86 21 62233503; fax: +86 21 62233503.
E-mail addresses: agkong@chem.ecnu.edu.cn (A. Kong),
ykshan@chem.ecnu.edu.cn (Y. Shan).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.01.014

Y. Ding et al. / Applied Catalysis A: General 455 (2013) 58–64
59
Table 1
C 1s (284.6 eV) was utilized as a reference to correct the bind-
ing energy. Temperature programmed reduction (TPR) with H2
were performed using a Belcat instrument. Typically, the U-tube
quartz microreactor was loaded with 50 mg catalyst along with
quartz wool and heated at a temperature ramp from 25 to 800 ◦C at
10 ◦C/min with a gas consisting of 5% H2 in Ar. The gas flow rate
was 30 ml/min. The H2 consumption (TCD signal) was recorded
automatically by TCD detection.
The adding amount of TEOS and Cu(NO3)2·3H2O in the preparation procedure and
the Cu content in Cu-MCM-48-X products.
Samples
Cu(NO3)2·3H2O (g)
TEOS (g)
Cu content in
products (wt%)
Cu-MCM-48-1
Cu-MCM-48-2
Cu-MCM-48-3
Cu-MCM-48-4
Cu-MCM-48-5
Cu-MCM-48-6
CuO/SiO2
0.02
0.05
0.10
0.25
0.50
1.00
0.16
8.6
8.6
8.6
8.6
8.6
8.6
3.5a
0.27 (0.21b)
0.62 (0.53b)
1.16 (1.05b)
2.75 (2.58b)
5.16 (5.00b)
9.51 (9.41b)
4.1 (4.0b)
2.3. Catalytic reaction
a
The calculated value in term of the conversion of 1.0 g SiO2 into TEOS.
The calculated Cu content in final product(CuO/SiO2 materials) according to the
The oxidative reaction of DMM with molecular oxygen was con-
ducted in a 100 ml stainless steel batch reactor. A typical reaction
process was as follows: 20 mmol DMM were dissolved into the
acetonitrile solvent (20 ml) in the reactor, and then 1 mmol N-
hydroxyphthalimide (NHPI) used as inducing agent and 1 mmol
chlorobenzene as the internal standard agent for quantitative anal-
ysis were added into the solution. After that, 0.5 g Cu-MCM-48
powders were added into the mixed solution above. Subsequently,
the reactor was sealed after adding the reaction mixtures and
purged with O2 for 5 min. Finally, the reactor with 2.0 MPa O2 was
heated to the setting temperature for the desired time under the
magnetic stirring. At the end of the reaction, the products were ana-
lyzed with a GC9890A Gas Chromatographer (GC) equipped with a
DB-WAX column and a flame ionization detector (FID).
b
adding amount of TEOS and Cu(NO3)2·3H2O.
of catalysts, the low selectivity on of DMC and the conversion of
DMM (YDMC/max = 35.4%).
In this paper, we introduce a new synthesis method of DMC
from DMM and O2 over copper modified mesoporous molecular
sieve Cu-MCM-48 in a batch reactor. The optimal reaction condi-
tions for DMC synthesis and a plausible mechanism for the selective
oxidation of DMM and O2 over Cu-MCM-48 catalyst was proposed.
2. Experimental
2.1. Catalyst preparation
3. Results and discussion
The samples were prepared with tetraethyl orthosilicate (TEOS)
as silica source, and cetyltrimethylammonium bromide (CTAB) as
a template [20]. In a typical synthesis, 0.79 g NaOH and 6.20 g CTAB
were dissolved in deionized water and the resulting solution was
stirred at 35 ◦C for about 40 min, and then 0.02 g Cu(NO3)2·3H2O
was added into the solution, followed by slow addition of 8.6 g
TEOS (Cu/Si = 0.002, mole ratio). The mixture was stirred for 1 h
before it was loaded into a Teflon-lined stainless steel vessel,
and kept at 110 ◦C for 3 days. The solid product was filtered,
washed with deionized water, dried in air at 110 ◦C for 1 day and
calcined at 550 ◦C for 6 h to obtain the solid catalysts. This syn-
thesized sample was designated as Cu-MCM-48-1 (1 is the sample
number). A similar procedure was followed for the synthesis of
the Cu-MCM-48-X (X = 2–6; the sample number) through adding
different amount of Cu(NO3)2·3H2O (Table 1) in the synthesis mix-
tures.
For comparison, a SiO2 supported CuO catalyst (CuO/SiO2)
with 4.0 wt% copper content was prepared by the tradi-
tional impregnation method. 1.0 g SiO2 powders (surface area,
270 m2/g) were added into 11 ml of aqueous solution containing
Cu(NO3)2·3H2O(0.06 M). After being aged at room temperature for
2 h, the samples were vaporized at 45 ◦C in the water bath. Finally,
the prepared sample was dried at 110 ◦C for 1 day, followed by
calcination at 550 ◦C for 6 h to obtain the SiO2-supported catalysts.
3.1. Characterization of Cu-MCM-48
The ICP analyses reveal that the copper amount in the prepared
samples can be tuned in the range from 0.27 to 9.51 wt% (Table 1)
by changing the content of Cu(NO3)2·3H2O in the reaction mix-
tures using the method described in the Section 2. The measured
amount of copper in these samples shows a slight higher value
than that in the synthesis mixtures, probably owing to the loss of
silicon-containing materials in the process of synthesis, which indi-
cates that all of Cu(NO3)2·3H2O in the synthesis mixture is almost
introduced into the prepared catalyst. Disappearance of the bands
at 2925 and 2854 cm−1 in the FI-IR spectra of Cu-MCM-48-Xsamples
calcined at 550 ◦C for 6 h showed that the template in the samples
had been effectively removed (see Supporting information, Fig. S1).
Fig. 1 shows the SEM and TEM images of Cu-MCM48-2 (a and
c) and Cu-MCM-48-6 (b and d), respectively. The Cu-MCM-48-2
containing 0.62 wt% copper retains the similar morphology and
structural integrity to that of MCM-48 [20] (Fig. 1a and c), whereas
the ordered channels in the structure of MCM-48 were not observed
in Cu-MCM-48-6 which contains a copper content of 9.51 wt%. On
the other hand, the TEM studies revealed that no obvious extra
phases of the copper species were presented in those samples
containing less copper, indicating that the copper species is well
dispersed in these samples. These results were also confirmed by
the XRD patterns of the samples (see Fig. 2B). No diffraction peaks at
2ꢀ = 36.18◦ and 38.78◦ corresponding to the crystalline CuO parti-
cles were presented in the high-angle XRD patterns for the prepared
Cu-MCM-48-X (X = 1–5) samples. However, two very weak diffrac-
tion peaks of CuO were observed for Cu-MCM-48-6 with higher
copper content corresponding to a thimbleful of the tiny crystalline
CuO. It can be seen from Fig. 2A that the stronger diffraction peaks at
2ꢀ = 2.7◦ and 2ꢀ = 3.2◦ corresponding to an ordered MCM-48 struc-
ture were observed for Cu-MCM-48-1 and 2, while these peaks
disappeared for Cu-MCM-48-4 and 6. These experimental results
illustrate that the content of copper precursors in the synthesis
mixtures has a remarkable effect on the morphology and structure
of the synthesized Cu-MCM-48-X.
2.2. Catalyst characterization
Powder X-ray diffraction patterns (XRD) were recorded on
a Rigaku D/Max-2500 diffractometer (40 kV, 40 mA) with CuK␣
radiation. TEM images were obtained on a JEM-2010 transmis-
sion electron microscope at an acceleration voltage of 200 kV. N2
adsorption/desorption measurements were carried out at 77 K on a
Micromeritics Tristar 3000 analyzer. FTIR spectra were collected on
a Thermo-Nicolet Nexus 670 FTIR spectrometer by using conven-
tional KBr pellet method. The Cu content of catalyst was determined
by an inductively coupled plasma-atomic emission spectrometer
(ICP-AES) (IRIS intrepid II XSP, Thermo). The X-ray photoelec-
tron spectra measurements were performed on the instrument
of Thermo ESCALAB 250 using Al K␣ radiation (1486.6 eV), and

60
Y. Ding et al. / Applied Catalysis A: General 455 (2013) 58–64
Fig. 1. SEM and TEM images of Cu-MCM48-2 (a and c) and Cu-MCM48-6 (b and d).
The N2 adsorption–desorption isotherms of the Cu-MCM-48-2,
structure for copper oxides with broad main peaks (Cu 2p3/2 and Cu
2p1/2) and typical shake-up satellites except that of Cu-MCM-48-1.
Electron binding energies of the Cu 2p3/2 peaks between 933.8 and
934.4 eV and typical shake-up satellites are observed for the sample
of Cu-MCM-48-X, which corresponds to divalent Cu [21,22]. Their
Cu 2p3/2 spectra can be deconvoluted into two individual peaks
as shown in Fig. 4. The binding energies at 934.4 (Cu-MCM-48-2),
934.1 (Cu-MCM-48-4) and 933.8 eV (Cu-MCM-48-6) are apparent
along with CuO on the surface of MCM-48, which is higher than
that of bulk CuO (933.7 eV). Such a shift of Cu 2p3/2 peak toward
high energy was believed from the better dispersion of CuO on
mesoporous silica. The other deconvolution peak for Cu-MCM-48-
X (X = 2, 4, 6) observed at around 936.1 eV indicates the existence
-4 and -6 belong to Type IV with H4 type of hysteresis loops (see
Fig. 3). The investigation results in Table 2 indicate that their BET
surface area, average pore size and pore volume decreased with
increasing copper content in the prepared samples. Cu-MCM-48-
2 (0.62 wt% copper) possesses a 343.0 m2/g surface area with a
pore size distribution centered at 2.7 nm. When the copper con-
tent of the sample (Cu-MCM-48-4) reaches to 2.75 wt%, its BET
surface area and average pore size decrease to 207.1 m2/g and
2.3 nm, respectively. These facts clearly indicate the copper mod-
ified mesoporous molecular sieve (Cu-MCM-48-2) containing the
incorporated copper content of 0.62 wt% still retains the ordered
structure of MCM-48 and the uniform dispersion of copper, and
the higher incorporated copper content can result not only in the
structure breakage of MCM-48 but also in the formation of CuO
in the Cu-MCM-48-X. Based on the investigation of XRD, TEM and
N2 adsorption–desorption isotherms, we conclude that the typi-
cal mesoporous structure of MCM-48 is gradually destroyed with
the increase of the incorporated copper content in the prepared
samples.
of Cu
O
Si O species [23,24]. It is interesting that only a weak
Si O were found in the
peak at 936.1 eV corresponding to Cu
O
Cu 2p3/2 spectrum of Cu-MCM-48-1with very low copper content
(0.27 wt%). These results testified that a part of copper species were
incorporated into the silica framework in the form of Cu
O Si O
in the Cu-MCM-48-X with the higher copper content, whereas all
the copper species were incorporated into the MCM-48 framework
in the Cu-MCM-48-X with very low copper content.
In ordered to explore the chemical environment of Cu elements
in the surface of the Cu-MCM-48-X catalysts, their X-ray photoelec-
tron spectroscopy (XPS) were measured. Fig. 4 depicts the Cu 2p
spectra of the different samples. All Cu 2p spectra show the typical
The reducibility of copper species in Cu-MCM-48 catalysts was
investigated by H2-TPR experiments. Fig. 5 shows TPR profile of
Cu-MCM-48-2 sample by H2. There are four reduction peaks for
Cu-MCM-48-2 sample observed in the range of 150–800 ◦C. The
peaks centered at around 265 and 482 ◦C are associated with the
reduction of Cu2+ to Cu+ and Cu+ to Cu0 as highly dispersed CuO,
respectively. This phenomenon is similar to the reduction of CuO
supported on the mesoporous MCM-41, MCM-48 and SBA-15 sil-
ica [21,25]. Nonetheless, peaks corresponding to around 638 and
720 ◦C may be ascribed to the reduction of Cu2+ to Cu+ and Cu+ to
Table 2
Textual properties of the prepared catalysts Cu-MCM-48-X.
Samples
BET surface
area (m2/g)
Average pore
size (nm)
Pore volume
(cm3 g−1
)
Cu-MCM-48-2
Cu-MCM-48-4
Cu-MCM-48-6
343.0
207.1
53.5
2.7
2.3
–
0.58
0.21
0.24
Cu0 in the Cu
work. The reduction feature of Cu2+ species at the high temperature
O Si O form incorporated into the MCM-48 frame-

Y. Ding et al. / Applied Catalysis A: General 455 (2013) 58–64
61
400
A
A
350
300
250
Cu-MCM-48-2
Cu-MCM-48-4
Cu-MCM-48-6
MCM-48
200
Cu-MCM-48-1
Cu-MCM-48-2
Cu-MCM-48-4
Cu-MCM-48-6
150
100
50
0
0.0
0.2
0.4
0.6
0.8
1.
2
4
6
8
10
P / P0
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
B
B
MCM-48
Cu-MCM-48-1
Cu-MCM-48-2
Cu-MCM48-2
Cu-MCM48-4
Cu-MCM48-6
Cu-MCM-48-4
Cu-MCM-48-6
0
2
4
6
8
10
12
14
16
18
20
Pore size / nm
30
40
50
60
70
80
Fig. 3. N2 adsorption–desorption isotherms and pore size distribution curves of
samples.
Fig. 2. The low-angle (A) and high-angle (B) XRD patterns of the MCM-48 and Cu-
MCM-48-X (X = 1, 2, 4, 6).
conversion increases with increasing copper content among differ-
ent samples with lower copper content. When the excessive copper
was included in the catalysts (i.e.Cu-MCM-48-6), the effective
can be attributed to the formation of Cu-containing stable materi-
als which are more difficult to be reduced than free CuO species
Cu
O Si O active sites were covered partially by the dispersed
[26]. It is consistent with the fact of formation of Cu
the prepared catalyst identified by XPS investigation.
O Si O in
CuO, which have a lower catalytic activity (see Fig. 6, CuO/SiO2),
thus leading to a poor performance. In addition, this experimental
result also indicates that the number of exclusive functional active
3.2. Catalytic oxidation reaction of DMM with O2
The systematic studies on the preparation of DMC from DMM
and O2 over Cu-MCM-48-X catalysts indicated that the reaction
conditions for the preparation of DMC and the use of different
catalysts apparently affect the yield of DMC.
Cu-MCM-48-6
Cu-MCM-48-4
The change in the amount of the incorporated copper in cata-
lysts did not profoundly influence the selectivity of DMC (Fig. 6).
However, The DMM conversion increased with the increase of
the amount of incorporated copper, reaching the maximum value
of 85.4% over Cu-MCM-48-2 catalyst with 0.62 wt% copper con-
tent, and then decreased to 67.8% over Cu-MCM-48-6 containing
9.51 wt% copper. But for all that, yield of DMC obtained over var-
ious Cu-MCM-48-X is much higher than that obtained over the
SiO2 supported CuO (CuO/SiO2) catalyst (see Fig. 6), on which non-
crystalline CuO was highly dispersed on SiO2 (see Fig. S2, XRD
diffraction pattern and XPS spectrum of CuO/SiO2). Based on these
experimental facts and the characterization results for Cu-MCM-
Cu-MCM-48-2
Cu-MCM-48-1
930
940
950
960
Binding energy(eV)
48-X mentioned above, it can be deduced that the Cu
linkage is the active center for the catalytic oxidation reaction of
DMM with O2. The number of Cu Si O active sites for DMM
O Si O
Fig. 4. Cu 2p XPS spectra of Cu-MCM-48-X (X = 1, 2, 4, 6). (For interpretation of the
references to color in figure legend, the reader is referred to the web version of the
article.)
O

62
Y. Ding et al. / Applied Catalysis A: General 455 (2013) 58–64
200
400
600
800
Temperature/
Fig. 5. H2-TPR profile of Cu-MCM-48-2.
sites in the prepared catalysts does change by the excessive copper.
For the Cu-MCM-48 catalysts, the optimal amount of incorporated
copper is 0.62 wt%.
Scheme 1. Mechanism for the oxidation reaction of DMM with O2 catalyzed by
Cu-MCM-48 catalyst in the presence of NHPI.
It was found that the yield and selectivity of DMC were about
1.6% and 23.5% without the use of Cu-MCM-48 catalyst, respec-
tively. When 0.1 g Cu-MCM-48-2 catalyst was used, the yield and
selectivity of DMC reached 55.3% and 81.6%, respectively (see
Fig. 7A). However, a further increase in the amount of catalyst used
did not obviously improve the yield and selectivity of DMC. These
phenomena provide a proof that Cu-MCM-48 plays a catalytic role
in selective oxidation of DMM with O2 as oxidant and indicate that
the rate of chemical reaction in which the catalysts were initially
involved is very fast.
The change of O2 pressure did not markedly change the selec-
tivity of DMC, but the effect of O2 pressure on the conversion of
DMM was obvious with the O2 pressure increasing from 1.0 to
3.0 MPa (Fig. 7B). When the O2 pressure was 2.0 MPa, the DMM
conversion reached the maximum value. If O2 pressure was further
increased, the DMM conversion decreased slowly. It is concluded
that the competitive adsorption between reactants DMM, O2 and
free radical initiator NHPI on the catalyst leads to the decrease of
DMM conversion under the exorbitant O2 pressure. Therefore, the
optimal O2 pressure is 2.0 MPa.
highest conversion of DMM and highest selectivity of DMC were
obtained at 180 ◦C. Furthermore, the results in Fig. 7D indicate that
the conversion of DMM and the selectivity of DMC are improved
dramatically with the increase of the reactive time in the initial
period of the reaction, and then kept unchanged beyond 2 h because
the thermodynamic equilibrium of this reaction had been reached
for 2 h at 180 ◦C.
In the absence of NHPI, the conversion of DMM and the selec-
tivity of DMC was very low (Fig. 7E). Only a small amount of NHPI
might extremely improve the yield and selectivity of DMC. The
effect of further increasing the NHPI amount on the selective oxi-
dation of DMM is negligible. From these phenomena it is inferred
that NHPI acts only as an initiator for the reaction and that the syn-
ergistic effect between NHPI and Cu-MCM-48 catalyst accelerates
the selective oxidation of DMM with O2.
Based on the above results, the reactive conditions for synthesis
of DMC from DMM with O2 were optimized. The highest the DMM
conversion (92.0%) and the DMC selectivity (88.9%) were obtained
over the 0.3 g Cu-MCM-48-2 catalysts containing 0.62 wt% copper
under 2.0 MPa O2 pressure at 180 ◦C for 2 h in presence of the ini-
tiator NHPI (1 mmol). These values are greatly superior to those
previously reported in the literature [19].
The conversion of DMM and the selectivity of DMC were greatly
improved with the increase in reaction temperatures ranging from
140 to 180 ◦C (Fig. 7C). Further increase in the temperature did not
cause obvious change of DMM conversion and DMC selectivity. The
The results in Fig. 7-F suggested the possibility of recycling Cu-
MCM48-2 under the optimal reactive conditions. In the five-time
recycling operations, no deactivation was observed, indicating that
the catalyst of Cu-MCM-48-2 is stable in the reaction system and
has a favorable potential for the large-scale production of DMC from
DMM and O2 in chemical industry.
100
Yield
Conversion
Selectivity
80
60
40
3.3. Suggested mechanism for the oxidation reaction of DMM
On the basis of the results of our studies and available published
literature data [27,28], a plausible mechanism for the selective oxi-
dation reaction of DMM with O2 in the presence of NHPI over
Cu-MCM-48 catalyst was proposed (Scheme 1).
The Scheme 1 shows the oxidation of DMM to DMC through
radical pathways. The initial stage of the reactive procedure
includes the reaction of NHPI with O2 to create the PINO• radi-
cal over Cu-MCM-48 [29], and then PINO• radical can abstract the
hydrogen atom from the DMM to produce the dimethoxymethyl
radical (DMM•) and regenerate the NHPI. The resulting carbon-
Catalyst
Fig. 6. The effect of the amount of incorporated copper on selective oxidation of
DMM. Reaction conditions: O2 pressure 2.0 MPa, temperature 140 ◦C, reaction time
2 h, catalyst 0.5 g, NHPI 1 mmol.
centered radical (DMM•) reacts with O2 to form
a peroxyl

Y. Ding et al. / Applied Catalysis A: General 455 (2013) 58–64
63
100
A
B
Selectivity of DMC
Conversion of DMM
Yield of DMC
Selectivity of DMC
Conversion of DMM
Yield of DMC
100
80
60
40
20
0
90
80
70
60
50
0.0
0.1
0.2
0.3
0.4
0.5
0.6
1.0
1.5
2.0
2.5
3.0
The catalyst amount (g)
O2 pressure (MPa)
100
100
95
90
85
80
75
70
65
60
C
D
Selectivity of DMC
Conversion of DMM
Yield of DMC
Selectivity of DMC
Conversion of DMM
Yield of DMC
90
80
70
140
150
160
170
180
190
200
1.0
1.5
2.0
2.5
Reaction time (h)
Reaction temperature ( C)
E
F 100
Selectivity of DMC
Conversion of DMM
Yield of DMC
Selectivity
Conversion
Yield
100
80
60
40
20
0
80
60
40
20
0
0.0
0.5
1.0
1.5
1
2
3
4
5
Reused times
The NHPI amount (mmol)
Fig. 7. The effect of reactive conditions on the selective oxidation of DMM. Reaction conditions: (A) O2 pressure 2.0 MPa, temperature 140 ◦C, reaction time 2 h, NHPI 1 mmol;
(B) temperature 140 ◦C, reaction time 2 h, catalyst 0.3 g, NHPI 1 mmol; (C) O2 pressure 2.0 MPa, reaction time 2 h, catalyst 0.3 g, NHPI 1 mmol; (D) O2 pressure 2.0 MPa,
temperature 180 ◦C, catalyst 0.3 g, NHPI 1 mmol; (E) O2 pressure 2.0 MPa, temperature 180 ◦C, reaction time 2 h, catalyst 0.3 g; (F) O2 pressure 2.0 MPa, temperature 180 ◦C,
reaction time 2 h, catalyst 0.3 g, NHPI 1 mmol.
radical (DMMOO•), which is further converted to DMC and a
hydroxyl radical (HO•) [30]. HO• radical can abstract hydrogen
from either NHPI or a molecule of DMM to form H2O and PINO• or
DMM•, respectively. Through the above-mentioned radical path-
ways, DMC is obtained by oxidizing the DMM with O2 over
Cu-MCM48.
new method for the preparation of DMC possesses the advan-
tages of short reaction time, easy recycling of the catalyst and
excellent yields. In addition, the oxidation reaction of DMM
with O2 over catalyst Cu-MCM-48 may proceed by a radical
pathway.
Acknowledgments
4. Conclusion
The authors are grateful to financial support from the key
project of Shanghai Science and Technology Committee (No.
11JC1403400, 08JC1408600) and the opening project of Shanghai
Key Laboratory of Molecular Catalysts and Innovative Materials
(No. 2011MCIMKF03)
The Cu-MCM-48 catalyst exhibits a very high catalytic activ-
ity for the synthesis of DMC by selective oxidation of DMM with
O2. DMM conversion of 92.0% and DMC selectivity of 88.9% are
achieved over the catalysts Cu-MCM-48-2, which are much higher
than those previously reported results. At the same time, this

64
Y. Ding et al. / Applied Catalysis A: General 455 (2013) 58–64
Appendix A. Supplementary data
[14] X.J. Wang, M. Xiao, S.J. Wang, Y.X. Lu, Y.Z. Meng, J. Mol. Catal. A: Chem. 278
(2007) 92–96.
[15] T.S. Zhao, Y.Z. Han, Y.H. Sun, Fuel Process. Technol. 27 (1998) 457–463.
[16] X.L. Wu, Y.Z. Meng, M. Xiao, Y.X. Lu, J. Mol. Catal. A: Chem. 249 (2006) 93–97.
[17] X.L. Wu, M. Xiao, Y.Z. Meng, Y.X. Lu, J. Mol. Catal. A: Chem. 238 (2005) 158–162.
[18] S. Satoh, Y. Tanigawa, US Patent 6,379,507.
[19] J.M. Dakka, S. Miseo, S.L. Soled, J.G. Santiesteban, J.E. Baumgartner, M.C.A.V.
Vliet, R.A. Sheldon, US Patent 7,718,564.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.apcata.
2013.01.014.
References
[20] 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, E.W. Sheppard, J. Am. Chem. Soc. 114 (1992) 10834–10843.
[21] A. Patel, P. Shukla, T. Rufford, S. Wang, J. Chen, V. Rudolph, Z. Zhu, Appl. Catal.
A: Gen. 409/410 (2011) 55–65.
[22] G. Ertl, R. Hierl, H. Knöinger, N. Thiele, H.P. Urbach, Appl. Surf. Sci. 5 (1980)
49–64.
[23] S. Bennici, A. Gervasini, N. Ravasio, F. Zaccheria, J. Phys. Chem. B 107 (2003)
5168–5176.
[24] Z.Y. Wu, Y.M. Wang, W.W. Huang, J. Yang, H.J. Wang, J.H. Xu, Y.L. Wei, J.H. Zhu,
Chem. Mater. 19 (2007) 1613–1625.
[25] X.Y. Hao, Y.Q. Zhang, J.W. Wang, W. Zhou, C. Zhang, S. Liu, Microporous Meso-
porous Mater. 88 (2006) 38–47.
[26] A. Gervasini, S. Bennici, Appl. Catal. A: Gen. 281 (2005) 199–205.
[27] F. Minisci, F. Recupero, G.F. Pedulli, M. Lucarini, J. Mol. Catal. A: Chem. 204/205
(2003) 63–90.
[28] R.A. Sheldon, I.W.C.E. Arends, J. Mol. Catal. A: Chem. 251 (2006) 200–214.
[29] P.J. Figiel, J.M. Sobczak, J. Catal. 263 (2009) 167–172.
[30] I. Hermans, J.F. Müller, T.L. Nguyen, P.A. Jacobs, J. Peeters, J. Phys. Chem. A 109
(2005) 4303–4311.
[1] P. Tundo, M. Selva, Acc. Chem. Res. 35 (2002) 706–716.
[2] M.A. Pacheco, C.L. Marshall, Energy Fuels 11 (1997) 2–28.
[3] N. Keller, G. Rebmann, V. Keller, J. Mol. Catal. A: Chem. 317 (2010) 1–18.
[4] P. Jessop, T. Ikariya, R. Noyori, Chem. Rev. 99 (1999) 475–494.
[5] S.N. Isaaca, B. O’Sullivan, C. Verhaelen, Tetrahedron 55 (1999) 11949–11956.
[6] U. Romano, R. Tesei, M.M. Mauri, P. Rebora, Ind. Eng. Chem. Prod. Res. Dev. 19
(1980) 396–403.
[7] S. Fang, K. Fujimoto, Appl. Catal. A: Gen. 142 (1996) L1–L3.
[8] S. Fujita, M. Bhalchandra, Y. Ikushima, M. Arai, Green Chem.
87–91.
[9] Q.H. Cai, C. Jin, B. Lu, H.J. Tangbo, Y.K. Shan, Catal. Lett. 103 (2005) 225–228.
[10] K.T. Jung, A.T. Bell, J. Catal. 204 (2001) 339–347.
[11] T.T. Li, L.B. Sun, L. Gong, X.Y. Liu, X.Q. Liu, J. Mol. Catal. A: Chem. 352 (2012)
38–44.
[12] J. Ren, S. Liu, Z. Li, K. Xie, Catal. Commun. 12 (2011) 357–361.
[13] L. Gong, L.B. Sun, Y.H. Sun, T.T. Li, X.Q. Liu, J. Phys. Chem. C 115 (2011)
11633–11640.
3 (2001)