Unraveling the mechanism of the oxidation of glycerol to dicarboxylic acids over a sonochemically synthesized copper oxide catalyst

Article abstract of DOI:10.1039/c8gc00961a

The utilization of low frequency ultrasound (US) offers a straightforward and powerful tool for the production of nanostructured materials, in particular for structurally stable, highly crystalline, and shape-controlled catalytic materials. Herein, we report an unconventional strategy for the synthesis of CuO nanoleaves within 5 min of US irradiation. The as-obtained CuO nanoleaves were found to be selective in the base-free aqueous oxidation of glycerol to dicarboxylic acids (78% yield of tartronic and oxalic acids), in the presence of hydrogen peroxide (H₂O₂) and under mild reaction conditions. Density Functional Theory (DFT) investigations revealed a synergy between the CuO catalyst and H₂O₂ in maintaining the structural integrity of the catalyst during the reaction, creating alternative efficient pathways for the selective formation of dicarboxylic acids. Isotope labeling experiments using H₂¹⁸O₂ further confirmed that oxygen from hydrogen peroxide, not from CuO, was preferentially incorporated into the dicarboxylic acid, significantly preserving the monoclinic structure of the CuO catalyst.

Full text of DOI:10.1039/c8gc00961a

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Unraveling the mechanism of the oxidation of glycerol to
dicarboxylic acids over a sonochemically synthesized copper oxide
catalyst
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Prince N. Amaniampong, a,# Quang Thang Trinh,b,# Jithin John Varghese,b Ronan Behling,c Sabine
Valange,c Samir H. Mushrif,d,e* Francois Jeromea,c*
www.rsc.org/
Correspondence to: FJ email: francois.jerome@univ-poitiers.fr; SHM email: SHMushrif@ntu.edu.sg
The utilization of low frequency ultrasound (US) offers a straightforward and powerful tool for the production of
nanostructured materials, in particular for structurally stable, highly crystalline, and shape-controlled catalytic materials.
Herein, we report an unconventional strategy for the synthesis CuO nanoleaves within 5 min of US irradiation time. The as-
obtained CuO nanoleaves were found to be selective in the base-free aqueous oxidation of glycerol to dicarboxylic acids
(78% yield in tartronic and oxalic acids), in the presence of hydrogen peroxide (H2O2) and under mild reaction conditions.
Density Functional Theory (DFT) investigations revealed a synergy between the CuO catalyst and H2O2 in maintaining the
structural integrity of the catalyst during the reaction, creating alternative efficient pathways for the selective formation of
dicarboxylic acids. Isotope labeling experiments using H218O2 further confirmed that oxygen from hydrogen peroxide, not
from CuO, was preferentially incorporated into the dicarboxylic acid, significantly preserving the monoclinic structure of
the CuO catalyst.
valuable dicarboxylic acids, particularly oxalic (OXA) and
tartronic acids (TAR), has been less thoroughly investigated.
Beside their promising utilization in the synthesis of renewable
INTRODUCTION
The utilization of biomass for the production of renewable
platform chemicals and fuels has become an important topic
aiming at accelerating the transition of our society into a more
sustainable development.1-5 Among bio-based chemicals,
glycerol, the main co-product of the vegetable oil industry, has
polymers,22, 23 these two dicarboxylic acids are also employed
for the extraction of rare earths from monazite, celluloid
production, leather manufacturing24 and for the synthesis of
pharmaceutical intermediates.25-27 World market for OXA rose
steadily at an annual rate of 3.15% from the year 2001 and the
consumption reached 278 thousand tons by the year 2010, as
stated in a report published by Global Industry Analysts, Inc.28
Particularly, the largest market for OXA is in Asia with an
annual growth rate of ~10% from 2012 to 2016. On the other
hand, applications of TAR as a high value-added chemical in
pharmaceutical disorder treatments such as osteoporosis and
obesity or in food industry as an anticorrosive and protective
agent are currently hindered due to the high cost of this
chemical (1564 US$/g),29 and therefore the development of
less expensive and greener methods to produce TAR is desired
(see SI, section 16).
attracted growing interest from the catalysis community.6-14
A
number of homogeneous and heterogeneous catalysts have
been investigated to convert glycerol to value-added chemicals
such as glyceric acid, lactic acid, propanediols,
dihydroxyacetone, acrolein, among others.15-20 In some
investigations, high yields of methanol from crude glycerol
were also reported.21 However, the conversion of glycerol to
a.INCREASE (FR CNRS 3707), Université de Poitiers, ENSIP, 1 rue Marcel Doré,
TSA41105, 86073 Poitiers Cedex 9, France
b.Cambridge Centre for Advanced Research and Education in Singapore (CARES),
Campus for Research Excellence and Technological Enterprise (CREATE), 1 Create
Way, Singapore 138602, Singapore.
Oxidation of glycerol has been shown achievable over several
noble metals, with Pt, Pd and Au being the most investigated
c. Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Université de
Poitiers,
catalysts.19, 30-32 Particularly, these noble metals supported on
d.School of Chemical and Biomedical Engineering, Nanyang Technological
University, 62 Nanyang Drive, Singapore 637459, Singapore.
e. Department of Chemical and Materials Engineering, University of Alberta, 9211-
116 St NW, Edmonton, Alberta T6G1H9, Canada.
30, 34
graphite, MgO,33 TiO2
and carbon nanotube (CNT)35 have
been documented to display high catalytic activity in the
presence of molecular oxygen (T: 30-80°C, 0.1-0.8 MPa O2, 2-4
pH), either under mild acidic or basic reaction conditions, with
glyceric acid often obtained as the prime product (Selectivity:
,#Authors contributed equally
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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30- 100 %) along with glycolic acid, lactic acid, ultrasound irradiation. This method involves short sonication
35
In some reports, synthesis time (5 min), the use of environmentally benign
dihydroxyacetone as co-products.33,
34, 36, 37
bimetallic33,
and trimetallic38 noble metals were reactants and does not require any surfactant, template or
employed for glycerol oxidation reactions, with the aim of calcination step as usual, thus simplifying the downstream
improving the catalyst activity, stability and product selectivity. procedure. The as-synthesized 2D CuO NLs were then
Unfortunately, in most of the reported studies, dicarboxylic characterized and tested as a catalyst in the oxidation of
acids such as TAR and OXA are formed in relatively low yields glycerol with H2O2, instead of molecular oxygen as usual which
(< 20 %). Very recently, Jin et al reported encouraging yields of raises safety issue at an industrial scale. Particularly, 2D CuO
TAR (64 %) and OXA (24%) from glycerol, in the presence of NLs not only produced OXA and TAR in an overall yield of 78%
molecular oxygen, using cobalt-based catalyst with specific but were also found more stable in water than CuO
activity depending on the catalyst preparation method.39 synthesized by a conventional route. A comparison of collected
Improved yield to TAR has been achieved over Au/HY (yield: results with those from the state of the art is provided in the
72%)27 and bismuth-promoted Pd/Carbon-support (yield: supporting information and shows the interest of CuO, in
79%)40 The use of non-precious supported-copper based particular in terms of yields in TAR and OXA (Table S1) Using
catalysts has also been attempted in the one-pot DFT calculations we reveal the detailed mechanism of glycerol
transformation of glycerol, albeit with lower selectivity activation and conversion to TAR and OXA on CuO NLs. We
towards TAR and OXA (total dicarboxylic acids yield < 10 %).41, also provide explanation for the role of hydrogen peroxide
42
Interestingly, layered double hydroxides (LDH) hosted (H2O2) in keeping the CuO structure intact during the reaction.
transition metal complexes (LDH-[MnSO3-salphen]) have been In agreement with DFT prediction, isotope labelling
peroxide-18O2
shown to exhibit preferential selectivity towards OXA (50.8 %), experiments
with
hydrogen
(H218O2)
although at low glycerol conversion (29.4 %), within 4 h at 60 demonstrated that oxygen from hydrogen peroxide, and not
°C.42 Conversely, the use of LDH-hosted sulphonato-salen from CuO, was preferentially utilized for the oxidation
Cr(III) complexes resulted in the selective formation of 1,3- reaction.
dihydroxyceton (59.3 % selectivity), at a glycerol conversion of
85.5 % at 60 °C, within 6 h.43
METHODS
To date, the best yields of TAR and OXA were obtained over
noble metals (Pd, Au), which poses significant problems as
Preparation of Copper (II) Oxide Nanoleaves (CuO NLs) under
regards availability and cost. Replacing precious metals by
ultrasound irradiation
cheap and accessible non-noble metals, while keeping high
All chemical reagents were used without further purification.
activity, selectivity and stability, is one of the biggest
In a typical synthesis method, 40 mL of 0.25 M NaOH aqueous
45
challenges faced by modern catalysis.44,
In this context,
solution was added to 10 mL of 0.5 M Cu(NO3)2 aqueous
solution and sky-blue suspension was obtained. This
suspension was subsequently exposed low frequency
metal oxides appear as an attractive alternative to noble metal
catalysts.46 Particularly, tailoring the morphologies and sizes of
these metal oxides contributes significantly to improve their
catalytic properties. Among these metal oxides, copper oxide
(CuO) has been extensively investigated and multiple synthesis
routes have been explored in the literature.47-51 Due to its
versatile properties and wide applications, hitherto, different
morphological structures such as ribbons, spheres, platelets,
dandelion and hollow structures have also been synthesized.52,
53 Although several synthetic methods have been explored, the
synthesis of highly pure and crystalline nanostructured CuO in
a fast and efficient one-pot method still remains a challenge;
particularly for aqueous phase reactions. Traditionally, the
synthesis of CuO involves surfactants, energy-consuming
synthesis time and high calcination temperatures (> 400°C) to
finally transform the synthesized Cu2O to CuO.54, 55 Recently,
sonochemistry has emerged as an attractive approach for
preparing nanostructured materials.56-59 The physical and
chemical effects induced by the implosion of cavitation
bubbles lead to an important improvement of reaction rates
and often allow nanostructured materials to be synthesized at
ambient temperatures, apace with in-situ pseudo-calcinations
of catalytic materials.
a
a
ultrasound irradiation. Ultrasound was generated by a Digital
Sonifier S-250D from Branson (power of standby Po = 27.0 W,
nominal electric power of the generator Pelec = 8.2 W). A 3.2
mm diameter tapered microtip probe operating at a frequency
of 19.95 kHz was used. The volume acoustic power of this
system was P
= 0.25 W.mL-1 in water (determined by
acous.vol
calorimetry measurements)60. The ultrasound probe was
immersed directly in the reaction medium and a Minichiller
cooler (Huber) was used to control the reaction temperature
at 25 oC. On completion of sonication at the desired time, the
dark blue or black precipitates were washed thoroughly with
distilled water and dried in an oven at 60 oC overnight.
Preparation of Copper (II) Oxide Nanoleaves (CuO NLs) under
Mechanical stirring
Copper (II) oxide nanoleaves synthesis procedure was adapted
following the procedure previously described by
Amaniampong et al.48 Briefly, 20 mL of 0.25 M NaOH aqueous
solution was added to 5 mL of 0.5 M Cu(NO3)2 aqueous
solution under stirring at room temperature and the mixture
was continuously stirred overnight. The solid sample was then
washed with deionized water several times and dried in an
oven at 60 oC.
Here, we report a fast and efficient synthesis route for the
production of highly crystalline, highly pure and uniform 2D
CuO nanoleaves (NLs) at 25 °C and under low frequency
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Catalyst Characterization
(PBE) functional64 were utilized for those simulations. To
correct the strong correlation and localization of 3d electrons
of Cu in CuO structure, the Hubbard term in the form of
GGA+U with Ueff = 7.0 ev was applied within the Dudarev’s
approach.65 This correction described well the bulk properties
(lattice parameters, band gap value and magnetic moment) of
Crystallographic analysis of the CuO NLs were performed by
means of XRD measurements in 2ϴ mode on a Bruker AXS D8
diffractometer with CuKα (λ = 0.154056 Å) radiation at 40 kV
and 20 mA. XPS was performed on a Thermo Escalab 250
spectrometer. The binding energy was calibrated using C1s
(284.6 eV) as a reference. The as-synthesized CuO nanoleaves
morphology was also studied by SEM (JEOL JSM 6700F field
emission), TEM and HR-TEM (JEOL JEM-2100F). Surface area
analysis was determined by nitrogen physisorption on a
Micromeritics TrisStar apparatus. The specific area was
calculated using the Brunauer-Emmett-Teller (BET) equation.
CuO and was successfully applied to simulate the activation of
glucose and methane on CuO surfaces.48,
51, 52
In this study,
CuO was modeled as periodic four-layer (4×2) slabs and a 20 Å
vacuum thickness above the top layer was used to prevent
interaction between repeated unit cells. Two top layers and
the adsorbates were allowed to fully relax while the bottom
two layers were fixed at the optimized bulk lattice parameters
to reduce the computational cost without influencing the
accuracy of simulations. Magnetic moment in the bulk-
ordering is applied for CuO(111) surface since it was found to
result in the most stable structure as reported by Mishra et
al.66 The 3×3×1 Monkhorst-Pack grid was used to sample the
Brillouin zone, and the tetrahedron method with Blöchl
corrections was employed for all calculations. Transition states
were searched using the Nudged Elastic Band (NEB) method,
and subsequently confirmed with the frequency calculations.
To get the free energies of the process, the entropy, zero-point
energy and enthalpy correction were computed from
statistical thermodynamics for all adsorbed structures, while
those values for gas-phase molecules were taken from the
standard thermodynamics NIST-JANAF table.44, 45, 67
Activity test and analytical methods
The general procedure for testing the catalytic oxidation of
glycerol over CuO NLs catalyst in the presence of H2O2 is briefly
described here. Typically, about 0.100 g of glycerol was
charged into a 25 mL capacity round-bottom flask and an
appropriate amount of CuO NLs catalyst (unless otherwise
stated) added. To this, 2 equivalent H2O2 and 2 mL of DI water
were added sequentially. The reaction mixture was heated in a
temperature controlled oil bath and heated to desired reaction
temperatures. Once the pre-set temperature of the oil bath is
attained, stirring rate was set at 250 rpm and reaction
proceeds until the desired reaction time. After the reaction,
approximately 05 mL of the reaction liquid sample was taken
and diluted and filtered before HPLC analysis. Oxalic acid,
tartronic acid, glycolic acid, formic acid and glyceraldehyde
were all confirmed using a Varian Pro Star HPLC equipped with
RESULTS AND DISCUSSION
an ICE-COREGEL 107H column 300
x 7.8 mm from
Transgenomic, a UV/Vis detector (Varian Pro Star, 210 nm) and
a refractive index detector (Varian 356-LC). A H2SO4 aqueous
solution (7 mM) was used as the eluent with a 0.4 mL min-1
flow rate. External calibration of the liquid chromatography
was performed using standards of oxalic acid, glycolic acid,
glycerol, tartronic acid, glyceraldehyde and formic acid was
quantified by the difference between the two HPLC analyses.
Noteworthy, the detected amount of formic acid reported in
our study is the solubilized fraction of it, although the volatized
amount of formic acid at the analyze condition is small
according to its corresponding Henry’s law coefficient.50 After
each set of reaction, the catalyst is filtered off, by washing
thoroughly with DI water, it is then dried in an oven at 60 °C
overnight. The recovered dried samples are weighed to
estimate the exact amount of recovered catalyst after
recycling. Typically, 90-85 % of the catalyst amounts are
recovered. All other reactant amounts are adjusted to the
amount of recovered catalyst in order to obtain uniform
reaction parameters throughout the experiment.
Synthesis and Growth Mechanism of 2D CuO NLs
CuO NLs were prepared by sonication of an aqueous solution
of copper nitrate (Cu(NO3)2) and sodium hydroxide (NaOH) at
19.95 kHz and at a controlled temperature of 25 °C. The
mechanism of the formation of CuO NLs was investigated by
XRD (Fig. 1).
Interestingly, it was observed that the initial sonication (1 to 3
min) of the reactant mixture (Cu(NO3)2 and NaOH) rapidly
formed a layered inorganic hybrid, herein identified as copper
(II) hydroxynitrate, (Cu2(OH)3NO3), also known as gerhardtite
(Fig. 1). The synthesis of gerhadtite on its own deserves crucial
attention since its synthetic analog is being used in vehicle
airbags due to its intrinsic mechanical and thermal properties.
Besides particle dispersions, ultrasound irradiation played a
crucial role in the further transformation of the formed
gerhardtite to CuO. The color of the reactant solution changed
from bright blue (after 1 min of sonication) to pale green (after
3 min of sonication) and finally to brown (from 5-30 min
sonication), in line with the formation of CuO (Fig. 1). We
postulate that in-situ generation of high temperatures,
pressures, shockwaves, microjets and hydroxide radicals
locally formed by the implosion of cavitation bubbles during
ultrasound irradiation, contributed to a rapid hydrolysis and
dehydration of intermediate copper (II) hydroxynitrate to CuO
nuclei, and to its subsequent crystal growth by Ostwald
ripening.56, 68 The CuO nuclei subsequently undergo self-
Computational Methods
All the spin-polarized DFT calculations were done using the
62
Vienna ab-initio simulation program (VASP).61, Plane-wave
basis set with a cut-off kinetic energy of 450 eV, the projector-
augmented wave (PAW)63 and the Perdew-Burke-Ernzerhof
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Fig. 1 XRD patterns showing CuO evolution at irradiation times 1, 3, 5, 10, 20 and 30
min. Images of reaction products recovered after each ultrasound irradiation time are
inserted in the XRD.
assembly along the same crystallographic orientation (like a
single crystal). The XRD patterns (Fig. 1) revealed that defects
and surface energy constraints of CuO nuclei drove the
assembly along [-1 1 1] and [1 1 1] direction with excellent
crystallographic orientation. This oriented attachment growth
mechanism goes through the entire reaction time (from 5 to30
min), as further confirmed in the XRD analysis (Fig. 1). The
major peaks centered at 2ϴ = 35.5 º and 38.8 º are indexed as
Fig. 2. (a) Low and (b) high magnification of SEM images of CuO nanoleaves
synthesized by low-frequency ultrasound (c) SEM images of CuO nanoleaves
synthesized by conventional method; (d) low magnification TEM; (e) high
magnification TEM image; (f) SAED pattern of CuO nanoleaves.
within 40
h
(Fig. 2c). For detailed morphological
characterization, TEM and HR-TEM were employed. TEM
images of the as-synthesized CuO NLs (Fig. 2d) were consistent
with the SEM observations, and revealed the leaf-like
morphology of the as-synthesized CuO. The HR-TEM revealed
that CuO NLs are composed of many small particles and the
assembly of the nanoparticles results in the formation of the
observed leaf-like morphology. A clear and continuous lattice
fringe with a lattice spacing between two neighboring fringes
of 0.23 nm (Fig. 2e) corresponded to the distance of the [111]
plane of the monoclinic CuO and confirmed the high-
crystalline nature of the leaf-like morphology with the same
crystallographic orientation.48 Figure 2f represents the
corresponding selected area electron diffraction (SAED
pattern) showing discrete spots and indicating the highly
crystalline and monoclinic structure of the synthesized CuO
NLs. The N2 adsorption-desorption isotherm of the CuO NLs
(Fig. S1) was in perfect agreement with the SEM and TEM
analysis, revealing a type II isotherm with a type H3 hysteresis
loop attributed to a macroporous material and the formation
of plate-like particles, respectively, according to the IUPAC
classification. A surface area of 20 m2g-1 was obtained for the
as-synthesized CuO NLs.
CuO [-1
1 1] and CuO [1 1 1], respectively, and are
characteristics of the pure phase monoclinic CuO crystallites.
Furthermore, no side products such as Cu(OH)2 and Cu2O were
detected from the XRD pattern, further indicating the
synthesis of highly pure leaf-like CuO nanostructures.
A stepwise reaction scheme for the formation of CuO, as
observed from XRD characterization analysis is as follows:
Morphological Characterization of CuO NLs
The as-synthesized CuO was first analyzed by SEM (Fig. 2). The
low magnification image illustrated that the leaf-shaped
nanostructure congregates to form large clusters (Fig. 2a). A
closer view of the leaf-shaped structure revealed that NLs of
CuO were uniformly formed (Fig. 2b) even at a short sonication
time (5 min) and were strikingly similar to the morphology
observed via the conventional synthesis method at 25 °C
XPS analysis of as-prepared CuO NLs confirmed the formation
of Cu2+ with the binding energy centered at 934.1 eV and
attributed to the core level of Cu 2p3/2 (Fig. 3a). The additional
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peaks observed at 935.3, 943.9 and 941.3 eV are due to the oxidation in the presence of H2O2 but without CuO NL did not
shakeup satellite peaks, and the analysis of the Cu LMM lead to any detectable product in the liquid phase (Table 1,
spectra revealed an intensity with kinetic energy of 917.1 eV69 entry 1), suggesting that a free OH radical mechanistic reaction
(Fig. S2, characteristic of a CuO nano-structured material), pathway is less likely to occur.72, 73 Glyceric acid (yield: 10 %)
ruling out the possibility of the existence of a Cu2O phase. The was observed for reactions performed over CuO NLs in the
O 1s spectra of the synthesized CuO revealed distinctive peaks absence of H2O2 within 4 h (Table 1, entry 2) but the complete
at 529-530 and 531-532 eV attributed to the bulk lattice reduction of CuO to Cu2O and Cu was observed by XRD at the
oxygen of CuO and surface adsorbed oxygen with low end of the reaction (Fig. S3). When the reaction was
70
coordination, respectively.52, The high intensity at 531-532 performed in the presence of H2O2 and CuO NLs,
eV suggests rich adsorbed dioxygen on the CuO surface. The characterization of the spent CuO NLs catalyst did not reveal
peak centered at 533-534 eV corresponds to the water any surface reduction, suggesting (i) the regeneration of the
molecule, which confirms the formation of CuO NL in the CuO NLs catalyst in the presence of H2O2 and (ii) both CuO NLs
hydrated form.71
and H2O2 are required for the transformation of glycerol to
OXA and TAR. Additionally, glycerol oxidation was performed
in labelled hydrogen peroxide-18O2 solution (H218O2). Analysis
of the reaction products by mass spectrometry revealed the
insertion of 18O into OXA (Fig. S4), demonstrating that H2O2 is
the preferred oxidizing agent for the reaction and CuO doesn’t
supply oxygen for the reaction, like that in the Mars van
Krevelen type mechanism.
After 4 h, 95% of glycerol was converted. Analysis of the
reaction mixture over time showed that glyceraldehyde and
glyceric acid were the primary products of the reaction. Their
yields reached a maximum of 36% (glyceric acid) and 18%
(glyceraldehyde) after 1h of reaction time (Table 1, entry 3).
When the reaction time was extended, the yield of
glyceraldehyde and glyceric acid decreased and,
concomitantly, OXA and TAR were produced with a maximum
yield of 56% and 22%, respectively after 4 h, i.e. an overall
yield in dicarboxylic acids of 78% (Table 1, entry 5). Glycolic
and formic acids were also detected but their amounts
remained rather low (< 5% yield). At 95% conversion of
glycerol, the carbon mass balance was 88%, suggesting that
gaseous products (mainly CO2), presumably from over
oxidation of glycerol and products, were also formed. The
kinetic data suggests that glycerol was first oxidized to
glyceraldehyde and then to glyceric acid. Glyceric acid is then
further oxidized to TAR. OXA would be produced via (1) C-C
bond cleavage after glyceraldehyde formation to give C1 and C2
precursors for formic acid and OXA, respectively; (2) C-C bond
cleavage of glyceric acid, releasing glycolic acid (further
oxidized to OXA) and formic acid and/or (3) decarboxylation of
TAR to glycolic acid followed by the oxidation to OXA (Scheme
1). At reaction temperatures higher than 80 °C (Table 1 entry
8), OXA yield decreased (from 56 to 35 %, at 100 ° C) and the
yield of C1 acids increased, suggesting additional C-C bond
cleavage. However, this increase in temperature (100 ° C) was
innocuous to the formed TAR, as its yield (20 %) was observed
to be somewhat stable.
Fig. 3. XPS analysis of CuO NLs. (a) Cu p3/2 peak fitting and (b) O 1s peak fitting
Catalytic oxidation of glycerol on CuO NLs
Glycerol oxidation of glycerol was performed over CuO NLs as
the catalyst, in the presence of H2O2 as an oxidizing agent, at
the reaction temperature of 80 °C and a reaction time span of
1-7 h (Table 1). The reaction conditions provided here were
optimized, as demonstrated in the Supplementary
Information. The reaction conditions provided here were
optimized, as demonstrated in the Supplementary
Information. It is important to mention here that glycerol
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Table 1: Reactant conversion and product yields for the CuO NL-catalyzed oxidation of glycerol. Glycerol amount = 0.100 g, Reaction temperature =80 °C, reaction time =1-7 h,
CuO catalyst = 0.05 g, volume of solvent (H2O) = 2mL . The optimum glycerol/H2O2 molar ratio is 0.5.
Yield (%)
Entry
% Conversion
Reaction time
OXA
TAR
Glyceric acid
Glyceraldehyde
Formic acid
( h)
4
1a
2b
3
< 2
10
0
0
0
10 ± 1.0
36 ± 3.1
30 ± 2.4
8 ± 0.5
0
0
0
0
4
0
0
0
70
1
0
2 ± 0.2
17 ± 1.5
22 ± 1.6
30 ± 2.2
27 ± 2.4
18 ± 1.8
6 ± 0.5
4 ± 0.3
2 ± 0.1
0
4
75
2
11 ± 0.9
56 ± 3.5
43 ± 2.6
39 ± 2.4
35 ± 3.2
10 ± 0.9
5
95
4
0
0
0
0
6
97
6
7
8c
98
7
0
0
100
4
20 ± 1.6
0
16 ± 1.0
a Oxidation of glycerol was performed in the presence of H2O2, without CuO catalyst. Oxidation of glycerol was performed in the presence of CuO catalyst, without
H2O2. c Reaction temperature = 100 °C
b
For benchmarking purposes, CuO synthesized via the corresponds to a total yield in dicarboxylic acid of 63%. This
conventional method, following a synthesis protocol reported yield is lower than the yield obtained with CuO NLs (78%),
earlier48 and denoted herein as CuO (CM) with a surface area after 4 h of reaction. It suggests that CuO NLs was not only
of 18 m2g-1, was also tested. Glycerol oxidation was conducted more selective but also more active than CuO (CM). The
under similar conditions with CuO NLs prepared by ultrasound presence of 13% of glycolic acid (reaction intermediate) at the
irradiation. Results obtained with both catalysts were collected end of the reaction with CuO (CM) suggests a lower oxidative
at iso-conversion (95 %). Results are summarized in Table 2. activity towards OXA.
Using CuO (CM) as the catalyst, OXA and TAR were produced
with 37% and 26% yields, respectively, after 6 h of reaction. It
Table 2. Product yields for the CuO-catalyzed oxidation of glycerol. Two different catalysts, CuO NLs and CuO (CM), were tested. Glycerol = 0.100 g, R. T = Reaction time, CuO
catalyst = 0.05 g, volume of solvent (H2O) = 2mL (Product yields were determined at an iso-conversion of 95 %)
O
O
O
O
O
H2O2, 80 °C
HO
HO
HO
O
HO
OH
HO
OH
O
OH
HO
OH
H
CuO, 95 % conv.
OH
OH
O
OXA
OH
TAR
Glycerol
Glyceric
acid
Glycolic acid Formic acid
Yield (%)
Catalyst
CuO NLs
CuO (CM)
Time (h)
OXA
TAR
Glyceric acid
8± 0.5
Glycolic acid
Formic acid
2± 0.1
4
6
56±3.5
37±2.7
22± 1.6
26±2.0
0
9±0.6
13±1.0
10±0.9
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To demonstrate the superior performances of highly ppm. In addition, FT-IR analysis (Fig. S5) revealed the
crystalline CuO NLs, the recycling of CuO NLs and CuO (CM) adsorption of organic compounds on spent CuO NLs. All
was then investigated at 80 °C, with a glycerol/H2O2 molar together, these factors contributed to the slight decrease in
ratio of 0.5. As shown in Fig. 4, a rapid decrease in OXA and catalytic activity of CuO NLs during recycling experiments. We
TAR yields was observed over CuO (CM) cycle after cycle. The further carried out
a hot filtration test to verify the
total yield of dicarboxylic acids dropped from 63% to only 7% heterogeneous nature of the reaction in the presence of CuO
after 6 catalytic cycles. Conversely, CuO NLs were more robust NLs. In this test, the CuO NLs catalyst was separated from the
than CuO (CM) and the total yield in dicarboxylic acids hot reaction mixture after 0.75 h (i.e. 50 % glycerol conversion)
remained higher than 70% up to the 5th catalytic cycle (vs 78% and the filtrate was heated at 80 °C for another 1 h. No
for the first cycle). The lower activity and stability of CuO (CM) increase in conversion was observed, thus confirming the
than those of CuO NLs could be a result of a lower purity, as heterogeneous nature of the catalytic process.
well as the presence of Cu vacancies on the surface of CuO
Reaction mechanism of the conversion of glycerol to dicarboxylic
(CM). Such vacancies may 1) affect the activation of glycerol
acids on CuO(111) and the role of H2O2
and hydrogen peroxide, thereby affecting the conversion of
glycerol and selectivity towards dicarboxylic acids and 2) may
Glycerol activation and oxidation on clean CuO(111) surface
accelerate the reduction of the copper oxide, leading to
To unravel the underlying reaction mechanism and to
changes in the crystalline structure of CuO, as presented in Fig.
investigate the role of H2O2 in enhancing the activity and
S6a. The presence of oxygen vacancies is known to make metal
oxides more amenable to reduction74. In addition, the pore
stability of CuO NLs, we performed density functional theory
(DFT) calculations. From the kinetic data presented in Table 1,
diameter and pore volume are slightly different between both
CuO samples (12 nm, 0.038 cm3/g and 9 nm, 0.019 cm3/g for
glyceric acid is suggested to be the primary product in the
initial stage of the reaction. The energy profile for the
CuO(US) and CuO(CM), respectively), which may also
oxidation of glycerol to glyceric acid on a clean CuO(111)
contribute to explain their difference of catalytic behavior.
surface is shown in Fig. 5.
Inductively coupled plasma with optical emission spectrometer
Under-coordinated O3 and Cu3 sites have been reported as
(ICP-OES) analysis of the filtrate collected after the 4th
active sites for C-H and N-H bond activations on the CuO
surface.51,
recycling with CuO NLs revealed a slight leaching of Cu of 20.6
52
On clean CuO(111) surface, glycerol is initially
activated via the abstraction of H from the primary OH,
facilitated by the surface O3 site, with the barrier of only 49
kJ/mol (TS1 in Fig.5b). All other competitive pathways
involving the C-H activation as the first step have barriers
greater than 130 kJ/mol (Supplementary Information, Fig.
S13). The preference of initial OH activation observed here is
also consistent with the recently reported results of Zhao et
al.,75. After the terminal OH is cleaved, the C-H bond can be
activated by the surface O3 site with the activation barrier of
63 kJ/mol (TS2, Fig.5c), forming glyceraldehyde. Adsorbed
glyceraldehyde is subsequently oxidized to glycerate via a two-
step process involving the formyl C-H bond activation with the
barrier of 74 kJ/mol (TS3, Fig 5d), followed by the
incorporation of the surface lattice oxygen into glyceraldehyde
(structure I5, Fig.5f). It is important to mention that the
incorporation of CuO lattice oxygen into glyceraldehyde
forming glycerate (step from I4 to I5) is energetically downhill
by -21 kJ/mol, similar to the oxidation mechanism of glucose
to gluconic acid, reported earlier.48 Glycerate is then
protonated by the surface hydrogen (has been confirmed by
both, calculations and isotope labelling study48) with the
Fig. 4. Recycle experiments over CuO NLs and CuO (CM) catalysts. Reaction conditions:
0.05 g of CuO (US), 0.1 g of glycerol, 80 oC reaction temperature, 2 mL of H2O, 4 h
reaction time and glycerol/H2O2 molar ratio of 0.5.
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and partially reducing the CuO structure, as was observed both
theoretically76 and experimentally.52, 77 In the absence of H2O2,
reduction of CuO to Cu2O and Cu over the reaction time results
in low conversion of glycerol (10%), as shown in Table 1, entry
2. The experimental results with and without H2O2 clearly
demonstrate that H2O2 plays a crucial role in achieving the high
conversion of glycerol and high yields of dicarboxylic acids, and
the role of H2O2 needs to be investigated.
The presence of H2O2 can generate OH groups adsorbed on the
CuO surface by the decomposition of H2O2 into two OH
fragments, catalyzed by CuO. The free energy change at the
reaction temperature of 80oC for the formation of adsorbed
OH species from H2O2 on CuO(111) is -28 kJ/mol and the
activation barrier is only 22 kJ/mol (Supplementary
Information, Fig. S16). The surface OH species from H2O2 can
react with the H on the O3 site to form water, with the barrier
of only 27 kJ/mol (Fig. S16c), thus, regenerating the active O3
site and enhancing the activity of the catalyst.
Next, we evaluated the involvement of surface OH, generated
from H2O2, in altering the mechanism of glycerol oxidation on
CuO. Activation barriers for the alternate pathway assisted by
surface OH are shown in Fig. 6.
Fig. 5. (a) Energy profile for the conversion of glycerol to glyceric acid on clean
CuO(111) surface; (b) Transition state for the initial primary O-H activation (TS1); (c)
Transition state for the subsequent C-H activation (TS2); (d) Transition state for the
formyl C-H activation (TS3); (e) Intermediate after the formyl C-H activation (I4); (f)
glycerate formation generating the surface lattice oxygen vacancy (I5) and (g) Transition
state for the protonation of glycerate to form glyceric acid (TS4). Activation barriers
(Ea) are indicated in kJ/mol. Big red and big salmon balls represent Oxygen (O) and
Copper (Cu) atoms of the CuO surface, respectively; while small white, grey and red
balls represent Hydrogen (H), carbon (C) and oxygen (O) atoms of glycerol/glyceric
acid, respectively.
barrier of 94 kJ/mol and finally is converted to glyceric acid
(TS4, Fig.5g). Our DFT results explain the formation of
glyceraldehyde and glyceric acid as initial products of the
reaction, as shown in Table 1. After glyceric acid is formed, it
reorients on the surface to a more stable configuration and
adsorbs on the surface via the primary OH (16 kJ/mol more
stable, Fig. S14). The oxidation of the other primary CH2OH
group in glycerol would proceed via the same mechanism,
resulting in the formation of tartronic acid (TAR). The
formation of oxalic acid (OXA) via C-C bond cleavage is
discussed later in section called C-C cleavage.
Fig. 6. Mechanism and energy profile of the conversion of glycerol to glyceric acid on
CuO(111), in the presence of H2O2; Activation barriers (Ea) are indicated in kJ/mol. Red
values are activation barriers for surface lattice oxygen catalyzed reaction steps and
green values are barriers for the surface OH facilitated reaction steps. Key transition
states are also shown. Big, blue arrows indicate the preferred reaction pathway. Color
code for atoms is the same as in Fig.5.
The role of H2O2
DFT calculations on the clean CuO surface reveal the activity of
CuO for glycerol oxidation. However, the surface lattice oxygen
is consumed during the reaction (Structure step from I4 to I5,
Fig.5), resulting in the reduction of CuO and the deactivation of
the catalyst.48,
50
Indeed, without the presence of H2O2 in
For comparison, the pathway catalyzed by the lattice oxygen
of CuO is also shown. Surface OH can activate the primary OH
group of glycerol with the barrier of only 14 kJ/mol (TS5, Fig.6),
much lower than the direct activation by the surface lattice O3
site (49 kJ/mol, TS1, Fig.5b), consistent with many earlier
studies.78-80 The subsequent C-H activation assisted by surface
OH has almost the same barrier (67 kJ/mol, Supplementary
Information, Fig. S17a) as that of the direct activation by the
experiments, CuO was reduced to Cu2O and Cu after the
reaction, as shown in Supplementary Information, Fig. S3.
Additionally, the surface O3 sites, as shown in TS1,2,3
(Fig.5b,c,d), will be blocked due to the strongly bound
dissociated
H atoms from C-H and O-H cleavages. At
sufficiently high coverage on the surface, these adsorbed
hydrogens would combine with the lattice oxygen, forming
water, thereby generating oxygen vacancies on the surface
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surface lattice O3 site (63 kJ/mol). However, the pathway also taken into account) are -212 kJ/mol and -342 kJ/mol,
assisted by the surface OH species leads to the “on-the-fly” respectively. This suggests that H2O2 can convert the partially
transfer of hydrogen from glycerol to the surface OH (TS5, reduced CunOn-1 surface to form 1) the hydrogenated surface
Fig.6), and does not generate any hydrogen on the active O3 CunOn—H (via reaction 3) or the original CuO(111) surface (via
site. This would prevent the surface reduction of CuO due to reaction 4). Structures relevant to reactions 3 and 4 are
the increased coverage of hydrogen, as discussed earlier. depicted in the Supplementary Information, Fig. S18.
Additionally, the oxidation of glycerol to glyceric acid on the To summarize, the presence of H2O2 can (i) compensate the
clean CuO surface involves the incorporation of lattice oxygen generated Oxygen vacancy and keep the structure of CuO and
of CuO into the acid product, resulting in the reduction of the its morphology intact, (ii) form surface OH groups and remove
catalyst.48,
50
This key step can also be avoided by the the H atoms that block the active O3 site on CuO surface and
assistance of surface OH, produced due to the dissociation of regenerate it, and most importantly (iii) provide an alternate
H2O2. The presence of surface OH on transition metals can lower energy barrier pathway to oxidize glycerol to acid
facilitate alcohol oxidation by an OH insertion mechanism into without utilizing the surface lattice oxygen of CuO.
the intermediate aldehyde, as reported by Zope et al.78 Using
C-C cleavage
DFT calculations and isotope labelling experiments, they
revealed that the added oxygen in the carboxylic acid The formation of glycolic acid, OXA and formic acid (Table 1),
originated from water (forming surface OH), instead of the requires C-C bond cleavage. Three possible routes for the C-C
dissolved molecular oxygen.78 Similarly, we show here that the cleavage are illustrated in Scheme 1, as were proposed in the
surface OH species originating from H2O2 combines with literature for the catalytic oxidation of glycerol to mono acids
glyceraldehyde to form an intermediate complex, with the and diacids.81,
82
They involve the C-C cleavage after
activation barrier of only 21 kJ/mol (TS6 in Fig.6). This complex glyceraldehyde formation (route 1), after glyceric acid
subsequently undergoes H-abstraction, preferably catalyzed by formation (route 2) and after tartronic acid formation (route
the surface lattice O3 site (TS7 in Fig.6) with the barrier of 27 3). DFT calculations were implemented to evaluate all these
kJ/mol to form the acid. The H-abstraction step assisted by the pathways and the transition states of C-C cleavages via these
surface OH is unlikely due to a relatively higher barrier of 92 routes are presented in Fig. 7.
kJ/mol (Supplementary information, Fig. S17b). The barrier for
the surface OH insertion into glyceraldehyde is much lower
than the value of 74 kJ/mol for the formyl C-H activation (TS3,
Fig.5d), which otherwise is the key step for its conversion to
acid. More importantly, this OH insertion pathway does not
require the insertion of a lattice oxygen from CuO for the
oxidation process, as described earlier, and therefore does not
generate any surface oxygen vacancy, keeping the structure of
CuO unchanged and intact after the reaction. This suggests
that H2O2 preferentially supplies oxygen for the reaction,
instead of CuO, via the aforementioned OH insertion pathway,
in excellent agreement with the observed experimental
isotope labelling study using H218O2. The most preferred
pathway for the oxidation of glycerol, in the presence of H2O2
on CuO, is highlighted by blue arrows in Fig.6. It involves the
surface OH assisted initial activation of the primary OH group
of glycerol, subsequent C-H activation to form glyceraldehyde
(could be either by surface lattice O3 or assisted by surface
Scheme 1. Different routes for the C-C cleavage.
OH), insertion of surface OH into glyceraldehyde and finally
deprotonation to glyceric acid facilitated by the surface lattice
O3 site of CuO.
In route 1 involving glyceraldehyde, the C-C bond cleavage is
Finally, we also evaluated the possibility of H2O2 providing
likely to be preceded by the activation of its primary OH group,
oxygen to compensate the generated oxygen vacancies on the
forming a structure which is adsorbed via both the terminal
surface. Two possible mechanisms for the replacement of
(1,3) oxygen atoms. The activation barrier for the C-C cleavage
lattice oxygen’s are:
in this precursor is 82 kJ/mol (TS8, Fig.7a) and forms C1 and C2
fragments which could be further oxidized to formic acid and
CunOn-1 + 0.5H2O2 ꢀ CunOn—H
CunOn-1 + H2O2 ꢀ CunOn + H2O
(3)
(4)
glycolic acid, respectively. Similarly, along route 2, the C-C
dissociation is also preceded by the abstraction of H from the
primary OH in glyceric acid to form a structure adsorbed via its
terminal oxygen (1,3) atoms. However, the C-C cleavage in this
precursor from glyceric acid has lower activation barrier of
The computed free energies of reactions (3) and (4) at 80oC
(the entropy, zero-point energy and enthalpy correction were
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only 58 kJ/mol (TS9, Fig7b). The precursor for the C-C cleavage yield of 78 % (OXA; 56 %, TAR acid; 22%) at 95 % conversion of
in route 3 is also a structure adsorbed via both the terminal glycerol was obtained. DFT calculations provided detailed
oxygen atoms (1,3), resulting from the H-abstraction of both insights into the reaction mechanism and identified the
the -COOH groups of tartronic acid. The H-abstraction of the synergistic role of H2O2 and CuO catalyst in the overall
terminal COOH groups proceeds with an activation barrier of oxidation reaction. The proposed CuO nanoleaves catalyst can
34 kJ/mol, as shown in the Supplementary Information Fig. eliminate disadvantages of using expensive noble metal
S15f. The C-C cleavage which is a decarboxylation reaction catalysts for oxidation reactions and the results shown here
(one of the fragments is CO2) has an activation barrier of 103 shed light, for the first time, on the synergistic role of CuO and
kJ/mol (TS10, Fig.7c). The C2 fragments in all three routes are H2O2 in the selective oxidative conversion of glycerol to
precursors for the formation of oxalic acid which is the dicarboxylic acids and in maintaining the stability of the
dominant product of the oxidation reaction. The activation catalyst.
barrier for C-C cleavage in route 3 is the highest among all
three routes and therefore the C-C cleavage in tartronic acid
Conflicts of interest
would be limited. This DFT result can explain why the amount
of tartronic acid is not reduced even when the oxalic acid is
formed in large yields, as shown in Table 1 (entry 5). The
activation barrier for C-C cleavages in route 2 (from glyceric
acid) is the lowest among all three routes. It is worth
mentioning that this activation barrier (58 kJ/mol) is even
lower than the barrier for the subsequent C-H activation (~63
kJ/mol, TS2, Fig.5c) in the minimum energy pathway indicated
in Fig.6 for the oxidation of glyceric acid to tartronic acid. This
implies that the formed glyceric acid would kinetically prefer
to undergo further decomposition to form C2 and C1
fragments, consistent with the higher yield of oxalic acid
(product of C-C cleavage) than that of tartronic acid (product
of oxidation), as observed in Table 1 (entry 5). Although the C-
Authors declare no competing financial interest.
Acknowledgements
Authors are grateful to the CNRS, the Ministry of Research and the
Région Aquitaine-Limousin-Poitou-Charentes for their financial
support. Funding from the International Consortium on Eco-
conception and Renewable Resources (FR CNRS INCREASE 3707)
and the chair “TECHNOGREEN” is also acknowledged. This research
is also supported by the National Research Foundation (NRF), Prime
Minister’s Office, Singapore under its Campus for Research
Excellence and Technological Enterprise (CREATE) program.
C
cleavage from glyceraldehyde is feasible at reaction
conditions, the activation barrier (82 kJ/mol) is higher than the
barrier for subsequent oxidation of glyceraldehyde (21 kJ/mol
for the OH insertion, TS6, Fig.6) and therefore results in the
formation of glyceric acid as the primary product in the initial
stage of the reaction (Table 1).
Notes and references
‡ Supplementary Information: Experimental details and conversion
and yield data. Effect of operating conditions on the conversion and
yield. Details of computational methods. DFT studies on adsorption
of glycerol on CuO(111) surfaces. Transitions states for the
oxidation of glycerol to glyceric acids and C-C cleavages from
different precursors. Surface OH adsorbed on CuO(111) surface, the
regeneration of active surface lattice O3 site and the compensation
of oxygen vacancies by H2O2.
1.
P. N. Amaniampong, K. Li, X. Jia, B. Wang, A. Borgna and Y.
Yang, ChemCatChem, 2014, 6, 2105-2114.
J. H. Clark, Nature Chemistry, 2009, 1, 12-13.
M. J. Climent, A. Corma and S. Iborra, Green Chemistry,
2011, 13, 520-540.
Fig. 7. Transition states (TS) for C-C cleavages from (a) glyceraldehyde, TS8, Route 1; (b)
glyceric acid, TS9, Route
2 and (c) tartronic acid, TS10, Route 3. Mechanisms
2.
3.
corresponding to routes 1, 2 and 3 for C-C cleavages are depicted in Scheme 1. Color
code for atoms is the same as in Fig.5. Activation barriers (Ea) are in kJ/mol and C-C
distances in the transition states are also indicated.
4.
5.
Q. T. Trinh, B. K. Chethana and S. H. Mushrif, The Journal
of Physical Chemistry C, 2015, 119, 17137-17145.
P. N. Amaniampong, A. Karam, Q. T. Trinh, K. Xu, H. Hirao,
F. Jérôme and G. Chatel, Scientific Reports, 2017, 7,
40650.
Y. Shen, S. Zhang, H. Li, Y. Ren and H. Liu, Chemistry-a
European Journal, 2010, 16, 7368-7371.
J. Ten Dam and U. Hanefeld, ChemSusChem, 2011, 4,
1017-1034.
CONCLUSIONS
In summary, the catalytic performances of non-noble CuO
prepared by a fast (5 min) and simple sonochemical approach
is reported in the oxidation of glycerol to OXA and TAR, in
base-free and mild conditions. A significant advantage of this
sonochemical synthesis technique is the incredibly fast
synthesis time along with in-situ pseudo-calcinations of the
CuO nanostructured material. An overall dicarboxylic acids
6.
7.
8.
C. H. Zhou, H. Zhao, D. S. Tong, L. M. Wu and W. H. Yu,
Catalysis Reviews, 2013, 55, 369-453.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
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Page 11 of 13
View Article Online
DOI: 10.1039/C8GC00961A
Journal Name
ARTICLE
9.
M. Morales, P. Y. Dapsens, I. Giovinazzo, J. Witte, C.
J. Hutchings, Angewandte Chemie International Edition,
2011, 50, 10136-10139.
J. Xu, H. Zhang, Y. Zhao, B. Yu, S. Chen, Y. Li, L. Hao and Z.
Liu, Green Chemistry, 2013, 15, 1520-1525.
Mondelli, S. Papadokonstantakis, K. Hungerbühler and J.
Pérez-Ramírez, Energy & Environmental Science, 2015, 8, 34.
558-567.
10.
11.
12.
13.
14.
H. J. Cho, C.-C. Chang and W. Fan, Green Chemistry, 2014, 35.
16, 3428-3433.
Y. Gu and F. Jérôme, Green Chemistry, 2010, 12, 1127- 36.
1138.
F. Jérôme, Y. Pouilloux and J. Barrault, ChemSusChem, 37.
2008, 1, 586-613.
J. Barrault and F. Jerome, European journal of lipid science 38.
and technology, 2008, 110, 825-830.
X. Ning, Y. Li, H. Yu, F. Peng, H. Wang and Y. Yang, Journal
of Catalysis, 2016, 335, 95-104.
D. Tongsakul, S. Nishimura and K. Ebitani, ACS Catalysis,
2013, 3, 2199-2207.
C. Xu, Y. Du, C. Li, J. Yang and G. Yang, Applied Catalysis B:
Environmental, 2015, 164, 334-343.
S. A. Kondrat, P. J. Miedziak, M. Douthwaite, G. L. Brett, T.
E. Davies, D. J. Morgan, J. K. Edwards, D. W. Knight, C. J.
Kiely, S. H. Taylor and G. J. Hutchings, ChemSusChem,
2014, 7, 1326-1334.
M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi and C. Della
Pina, Angewandte Chemie International Edition, 2007, 46,
4434-4440.
39.
X. Jin, M. Zhao, C. Zeng, W. Yan, Z. Song, P. S. Thapa, B.
Subramaniam and R. V. Chaudhari, ACS Catalysis, 2016, 6,
4576-4583.
15.
16.
17.
Y. Shen, S. Zhang, H. Li, Y. Ren and H. Liu, Chemistry – A
European Journal, 2010, 16, 7368-7371.
B. Katryniok, S. Paul and F. Dumeignil, ACS Catalysis, 2013, 40.
3, 1819-1834.
R. M. Painter, D. M. Pearson and R. M. Waymouth, 41.
Angewandte Chemie International Edition, 2010, 49,
H. Kimura, A. Kimura, I. Kokubo, T. Wakisaka and Y.
Mitsuda, Applied Catalysis A: General, 1993, 95, 143-169.
D. Liang, J. Gao, J. Wang, P. Chen, Y. Wei and Z. Hou,
Catalysis Communications, 2011, 12, 1059-1062.
T. Van Haasterecht, T. Van Deelen, K. De Jong and J.
Bitter, Catalysis Science & Technology, 2014, 4, 2353-
2366.
G. Wu, X. Wang, T. Jiang and Q. Lin, Catalysts, 2015, 5,
2039-2051.
Q. T. Trinh, A. Banerjee, Y. Yang and S. H. Mushrif, The
Journal of Physical Chemistry C, 2017, 121, 1099-1112.
Q. T. Trinh, J. Yang, J. Y. Lee and M. Saeys, Journal of
Catalysis, 2012, 291, 26-35.
9456-9459.
42.
18.
19.
20.
21.
L. S. Sharninghausen, J. Campos, M. G. Manas and R. H.
Crabtree, Nature Communications, 2014, 5, 5084.
A. Villa, G. M. Veith and L. Prati, Angewandte Chemie 43.
International Edition, 2010, 49, 4499-4502.
D. Roy, B. Subramaniam and R. V. Chaudhari, ACS 44.
Catalysis, 2011, 1, 548-551.
M. H. Haider, N. F. Dummer, D. W. Knight, R. L. Jenkins, 45.
M. Howard, J. Moulijn, S. H. Taylor and G. J. Hutchings,
Nature Chemistry, 2015, 7, 1028-1032.
P. Fordham, M. Besson and P. Gallezot, Applied Catalysis
A: General, 1995, 133, L179-L184.
A. Villa, C. Campione and L. Prati, Catalysis letters, 2007,
115, 133-136.
W. Riemenschneider and H. M. Bolt, in Ullmann's
46.
M. T. Le, V. H. Do, D. D. Truong, E. Bruneel, I. Van
Driessche, A. Riisager, R. Fehrmann and Q. T. Trinh,
Industrial & Engineering Chemistry Research, 2016, 55,
4846-4855.
Z. Wang, F. Su, S. Madhavi and X. W. Lou, Nanoscale,
2011, 3, 1618-1623.
22.
23.
24.
47.
Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag 48.
GmbH Co. KGaA, 2000, DOI:
10.1002/14356007.a09_565.pub2.
P. N. Amaniampong, Q. T. Trinh, B. Wang, A. Borgna, Y.
Yang and S. H. Mushrif, Angewandte Chemie International
Edition, 2015, 54, 8928-8933.
&
25.
M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi and C. Della 49.
Pina, Angewandte Chemie International Edition, 2007, 46,
J. Young Kim, J. Chan Park, H. Kang, H. Song and K. Hyun
Park, Chemical Communications, 2010, 46, 439-441.
P. N. Amaniampong, Q. T. Trinh, K. Li, S. H. Mushrif, Y. Hao
and Y. Yang, Catalysis Today, 2017, DOI:
https://doi.org/10.1016/j.cattod.2017.01.009.
J. J. Varghese, Q. T. Trinh and S. H. Mushrif, Catalysis
Science & Technology, 2016, 6, 3984-3996.
R. Singuru, Q. T. Trinh, B. Banerjee, B. Govinda Rao, L. Bai,
A. Bhaumik, B. M. Reddy, H. Hirao and J. Mondal, ACS
Omega, 2016, 1, 1121-1138.
4434-4440.
50.
26.
27.
28.
29.
C.-H. Zhou, J. N. Beltramini, Y.-X. Fan and G. Q. Lu,
Chemical Society Reviews, 2008, 37, 527-549.
J. Cai, H. Ma, J. Zhang, Z. Du, Y. Huang, J. Gao and J. Xu, 51.
Chinese Journal of Catalysis, 2014, 35, 1653-1660.
I.
Global
Industry
Analysts,
2008,
DOI: 52.
http://www.strategyr.com/PressMCP-2105.asp.
B. Katryniok, H. Kimura, E. Skrzynska, J.-S. Girardon, P.
Fongarland, M. Capron, R. Ducoulombier, N. Mimura, S. 53.
Paul and F. Dumeignil, Green Chemistry, 2011, 13, 1960-
B. Liu and H. C. Zeng, Journal of the American Chemical
Society, 2004, 126, 8124-8125.
1979.
54.
J. Rockenberger, E. C. Scher and A. P. Alivisatos, Journal of
the American Chemical Society, 1999, 121, 11595-11596.
W. Wang, Y. Zhan, X. Wang, Y. Liu, C. Zheng and G. Wang,
Materials research bulletin, 2002, 37, 1093-1100.
R. V. Kumar, Y. Diamant and A. Gedanken, Chemistry of
Materials, 2000, 12, 2301-2305.
30.
31.
G. Dodekatos and H. Tuysuz, Catalysis Science
Technology, 2016, 6, 7307-7315.
A. Villa, N. Dimitratos, C. E. Chan-Thaw, C. Hammond, L.
Prati and G. J. Hutchings, Accounts of Chemical Research, 56.
2015, 48, 1403-1412.
&
55.
32.
33.
S.-S. Liu, K.-Q. Sun and B.-Q. Xu, ACS Catalysis, 2014, 4, 57.
2226-2230.
G. L. Brett, Q. He, C. Hammond, P. J. Miedziak, N. 58.
Dimitratos, M. Sankar, A. A. Herzing, M. Conte, J. A. 59.
Lopez-Sanchez, C. J. Kiely, D. W. Knight, S. H. Taylor and G.
H. Xu, B. W. Zeiger and K. S. Suslick, Chemical Society
Reviews, 2013, 42, 2555-2567.
G. Chatel and J. C. Colmenares, Springer, 2017.
J. C. Colmenares, ChemSusChem, 2014, 7, 1512-1527.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
Please do not adjust margins

Please do not adjust margins
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Page 12 of 13
View Article Online
DOI: 10.1039/C8GC00961A
ARTICLE
60.
Journal Name
S. Koda, T. Kimura, T. Kondo and H. Mitome, Ultrasonics
sonochemistry, 2003, 10, 149-156.
61.
G. Kresse and J. Furthmüller, Computational Materials
Science, 1996, 6, 15-50.
62.
G. Kresse and J. Hafner, Physical Review B, 1993, 47, 558-
561.
63.
64.
P. E. Blöchl, Physical Review B, 1994, 50, 17953-17979.
J. P. Perdew, K. Burke and M. Ernzerhof, Physical Review
Letters, 1996, 77, 3865-3868.
65.
66.
67.
S. L. Dudarev, G. A. Botton, S. Y. Savrasov, C. J. Humphreys
and A. P. Sutton, Physical Review B, 1998, 57, 1505-1509.
A. K. Mishra, A. Roldan and N. H. de Leeuw, The Journal of
Physical Chemistry C, 2016, 120, 2198-2214.
Q. T. Trinh, A. V. Nguyen, D. C. Huynh, T. H. Pham and S.
H. Mushrif, Catalysis Science & Technology, 2016, 6, 5871-
5883.
68.
69.
70.
S. Sun and H. Zeng, Journal of the American Chemical
Society, 2002, 124, 8204-8205.
D. Tahir and S. Tougaard, Journal of Physics: Condensed
Matter, 2012, 24, 175002.
D. A. Svintsitskiy, T. Y. Kardash, O. A. Stonkus, E. M.
Slavinskaya, A. I. Stadnichenko, S. V. Koscheev, A. P.
Chupakhin and A. I. Boronin, The Journal of Physical
Chemistry C, 2013, 117, 14588-14599.
71.
72.
73.
74.
75.
I. G. Casella and M. Gatta, Journal of Electroanalytical
Chemistry, 2000, 494, 12-20.
C. Chen, C. Xu, L. Feng, Z. Li, J. Suo, F. Qiu and Y. Yang,
Advanced Synthesis & Catalysis, 2005, 347, 1848-1854.
V. F. Laurie and A. L. Waterhouse, Journal of agricultural
and food chemistry, 2006, 54, 4668-4673.
J. J. Varghese and S. H. Mushrif, The Journal of Physical
Chemistry C, 2017, 121, 17969-17981.
G. Zhao, F. Yang, Z. Chen, Q. Liu, Y. Ji, Y. Zhang, Z. Niu, J.
Mao, X. Bao and P. Hu, Nature communications, 2017, 8,
14039.
76.
77.
78.
79.
80.
81.
82.
Y. Maimaiti, M. Nolan and S. D. Elliott, Physical Chemistry
Chemical Physics, 2014, 16, 3036-3046.
J. Y. Kim, J. A. Rodriguez, J. C. Hanson, A. I. Frenkel and P.
L. Lee, J.AM.Chem.Soc, 2003, 125, 10684-10692.
B. N. Zope, D. D. Hibbitts, M. Neurock and R. J. Davis,
Science, 2010, 330, 74-78.
J. S. Yoo, T. S. Khan, F. Abild-Pedersen, J. K. Norskov and F.
Studt, Chemical Communications, 2015, 51, 2621-2624.
R. Kavanagh, X.-M. Cao, W. Lin, C. Hardacre and P. Hu, The
Journal of Physical Chemistry C, 2012, 116, 7185-7188.
B. N. Zope, S. E. Davis and R. J. Davis, Topics in Catalysis,
2012, 55, 24-32.
C. Len and R. Luque, Sustainable Chemical Processes,
2014, 2, 1.
12 | J. Name., 2012, 00, 1-3
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Glycerol was oxidized selectively to oxalic and tartronic acid in 78% yield over a highly crystalline CuO
catalyst prepared within few minutes by a sonochemical synthesis.