Highly Efficient Oxidation of Ethyl Lactate to Ethyl Pyruvate Catalyzed by TS-1 under Mild Conditions

Article abstract of DOI:10.1021/acscatal.7b03558

Highly efficient oxidation of ethyl lactate (ELA) to ethyl pyruvate (EP) was realized over TS-1 in the presence of aqueous H₂O₂ (30 wt %) at low temperature without other solvent. A 100% ELA conversion and 97.8% EP yield were obtained at 50 °C after 9 h. The conversion rate of ELA is sensitive to the reaction temperature. High reaction temperature (70 °C) leads to an increase in conversion rate of ELA but causes the fast hydrolysis and decarboxylation of EP to form byproducts of acetic acid and CO₂. On the basis of the characterization (pyridine-FTIR and UV-vis) and reaction results, active species of Ti(OOH) were proven. In addition, a nonradical mechanism for conversion of ELA to EP for this catalytic system was proposed. By kinetic analysis, the formation of Ti(OOH) is confirmed as the rate-determining step. The apparent activation energy (103.4 kJ mol^-1) was also obtained. Furthermore, TS-1 was highly stable for the oxidation of ethyl lactate. There were almost no change in ELA conversion and EP yield throughout 10 reaction runs.

Full text of DOI:10.1021/acscatal.7b03558

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Article
Highly Efficient Oxidation of Ethyl Lactate to Ethyl
Pyruvate Catalysed by TS-1 Under Mild Conditions
Tianliang Lu, Junpeng Zou, Yuzhong Zhan, Xiaomei Yang,
Yiqiang Wen, Xiangyu Wang, Lipeng Zhou, and Jie Xu
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b03558 • Publication Date (Web): 04 Jan 2018
Downloaded from http://pubs.acs.org on January 4, 2018
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Highly Efficient Oxidation of Ethyl Lactate to Ethyl
Pyruvate Catalysed by TSꢀ1 Under Mild Conditions
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Tianliang Lu , Junpeng Zou , Yuzhong Zhan , Xiaomei Yang , Yiqiang Wen , Xiangyu Wang ,
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Lipeng Zhou *, Jie Xu
a
School of Chemical Engineering and Energy, Zhengzhou University, 100 Kexue Road,
Zhengzhou 450001, People’s Republic of China
b
College of Chemistry and Molecular Engineering, Zhengzhou University, 100 Kexue Road,
Zhengzhou 450001, People’s Republic of China
c
State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian
Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian
1
16023, People’s Republic of China
ABSTRACT: Highly efficient oxidation of ethyl lactate (ELA) to ethyl pyruvate (EP) was
realized over TSꢀ1 in the presence of aqueous H O (30 wt%) at low temperature without other
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solvent. 100% ELA conversion and 97.8% EP yield were obtained at 50 C after 9 h. Conversion
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rate of ELA is sensitive to the reaction temperature. High reaction temperature (70 C) leads to
the increase of conversion rate of ELA, but causes the fast hydrolysis and decarboxylation of EP
to form byꢀproducts of acetic acid and CO . Based on the characterization (pyridineꢀFTIR and
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UVꢀvis) and reaction results, active species of Ti(OOH) were proven. Also, a nonꢀradical
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mechanism for conversion of ELA to EP for this catalytic system was proposed. By kinetic
analysis, the formation of Ti(OOH) is confirmed as the rateꢀdetermining step. Apparent
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activation energy (103.4 kJ mol ) was also obtained. Furthermore, TSꢀ1 was highly stable for
the oxidation of ethyl lactate. There were almost no change in ELA conversion and EP yield
throughout 10 reaction runs.
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KEYWORDS: Ethyl lactate; Ethyl pyruvate; TSꢀ1; Catalytic oxidation; Hydrogen peroxide
INTRODUCTION
Catalytic conversion of biomass to valuable chemicals has attracted much attention recently
due to the environmental benign and sustainable character. Pyruvic acid and its esters (pyruvate)
are important raw materials and chemical intermediates which are widely applied in food, plastic,
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pharmaceutical, and pesticidal industries. They can also be used as the precursors in the
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synthesis of bioactive substances. Nowadays, the commercial production of pyruvate is
realized by the dehydrative decarboxylation of tartaric acid. Excess KHSO as dehydrating agent
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is required in this process, leading to the low atom efficiency and environmental pollution.
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Pyruvate can also be produced by microbial fermentation of carbohydrates.
However, precise
regulation of the reaction conditions including pH value, temperature and so on, low spaceꢀtime
yield, high cost of product separation and purification limit the industrialization of this method.
Thus, development of a green, efficient, alternative route for the production of pyruvate is
necessary.
Lactic acid and esters (lactates) which can be produced readily from renewable biomass, such
as cellulose, starch, sugars and glycerol, are highly functionalized (hydroxyl and carboxyl groups)
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bioꢀbased feedstocks with great appeal.
Molecular structure of lactates is similar to that of
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pyruvates. Valuable pyruvates can be produced from lactates by dehydrogenation method.
Considering the excellent atom efficiency of this route, catalytic oxidative dehydrogenation
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strategies including vapour and liquid phase have been developed.
In vapour phase strategy,
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various metal catalysts including Fe O ꢀMoO , TeO ꢀMoO ,
NiꢀNbꢀO, MoVNbO , iron
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phosphate, and MoO ꢀTiO were investigated. For this strategy, high reaction temperature
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favors the activation of lactates and O (oxidant) on surface of catalysts. However, high reaction
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temperature (≥200 C) also leads to many side reactions, particularly decarboxylation of both
lactates and pyruvates. Furthermore, heavy energyꢀconsuming in this process would increase the
production cost. Thus, selective synthesis of pyruvates from lactates under lower temperature in
liquid phase is desired from the viewpoint of green chemistry.
Transition metal oxides and noble metals were usually used as catalysts for the conversion of
lactates to pyruvates in liquid phase. Haysshi’s group tested catalytic activity of various metal
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oxides on the conversion of lactates to pyruvates in liquid phase at 130 C. TiO , ZrO and
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SnO were proven to be highly selective catalysts for producing pyruvate. However, high
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selectivity can only be kept at a low lactate conversion. With the increase of reaction time and
lactate conversion, pyruvate selectivity decreased dramatically. So, in this catalysis system,
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pyruvate yield is low (<50%). RamosꢀFernandez and Shiju also applied metal oxides including
Fe O , TiO , V O /MgOꢀAl O , ZrO , CeO and ZnO as catalysts in dehydrogenation of lactates
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at 130 C, and found that TiO was the most efficient. By addition of activated carbon, side
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reaction of pyruvate polymerization was inhibited. This is an interesting and useful discovery for
improving the product selectivity. However, when the lactate conversion is high, the selectivity
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of pyruvate decreases leading to the low pyruvate yield (<50%). It is reasonable and necessary
to improve the pyruvate yield. Considering the effect of reaction temperature on the side
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reactions, further decreasing the reaction temperature would favor the increasing of pyruvates
yield. Noble metals with high dehydrogenation activity including Pd and Pt can be used in this
reaction at lower temperature. Sugiyama and coworkers developed Pd/C and TeꢀPd/C catalysts
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for the conversion of lactates to pyruvates at 85 C. The maximum yield of sodium pyruvate was
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8.2% on Te–Pd/C at 1.0 MPa O2. Ding and coworkers applied PbꢀPt/C to catalyze the
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oxidative dehydrogenation of lactates under 90 C, and about 61% pyruvate yield was given.
Indeed, lower reaction temperature is better for increasing pyruvate yield. On the other hand,
pyruvate selectivity decreased dramatically with increase of the reaction time. For Pd and Pt
based catalysts mentioned above, pyruvate yield is still lower than 70% even at optimized
conditions. Thus, it remains a great challenge to develop highly active catalyst for the green
dehydrogenation of lactate to pyruvate at low temperature.
Besides O , hydrogen peroxide, which has high active oxygen content (47%), is also a green
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oxidant with water as the only byproduct. As reported in previous literature, titanium oxide
systems are active and highly selective in many low temperature oxidation reactions with
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aqueous H O as the oxidant.
For example, epoxidation reaction can be catalysed by Ti
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substituted zeolites such as TSꢀ1
and TiꢀMWW ; oxidative degradation reaction can be
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realized over TiO2 or TiꢀCu oxide . As it is known, for oxidation reaction, reactive oxygen
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species generated on catalyst surface are important intermediates.
In H O /titanium oxide
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catalytic system, reactive oxygen species formed by the interaction of H O with Ti species.
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Microꢀenvironment of Ti could affect the interaction between Ti and H O . It is expected to
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fulfill the conversion of lactates to pyruvates at mild conditions with a high yield of product
using H O as oxidant over Tiꢀbased catalyst. Thus, in this study, we applied various titanium
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oxide systems including TiO , TSꢀ1, Ti/ZSMꢀ5, titanium hydrogenphosphate (TiHP) and
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phosphated TSꢀ1 (PꢀTSꢀ1) as catalysts and H O as oxidant for the conversion of ethyl lactate
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(
ELA) to ethyl pyruvate (EP). 100% ELA conversion with >95% EP yield can be given at 50 C
when TSꢀ1 was used as catalyst. By UVꢀvis and pyridineꢀFTIR, active centers and reactive
oxygen species were confirmed. Based on the characterization and catalytic test results, reaction
scheme was also proposed and discussed. Furthermore, TSꢀ1 applied in this work is recyclable.
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EXPERIMENTAL
Materials. ELA, EP and 30% H O aqueous solution were purchased from Sinopharm
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Chemical Reagent Co., Ltd. (China). TiO2 (anatase), tetrabutyl titanate (TBOT),
tetrapropylammonium bromide (TPABr) and tertꢀbutyl hydroperoxide were obtained from
Aladdin Chemical Reagent Corporation. Ethanolamine, hydroquinone, isopropanol, naphthalene,
colloidal silica, H SO , phosphoric acid, Na CO and Ca(OH) were used as received. NaZSMꢀ5
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was purchased from Nankai University Catalyst Co. (China).
Synthesis of TS-1. TSꢀ1 was synthesized by a hydrothermal method described in literature
with the molar composition of 1.0 SiO : 0.033 TiO : 0.1 TPABr: 0.5 ethanolamine: 30 H O.
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Colloidal silica was added to the mixture of ethanolamine, TPABr and deionized water in a
plastic beaker under stirring. After addition of TBOTꢀisopropanol solution, the isopropanol in the
mixture was removed by evaporation. After that, the obtained gel was crystallized in an
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autoclave under stirring at 175 C for 72 h. After the hydrothermal process, the solid was
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obtained by filtration, washing with deionized water, drying at 120 C overnight and calcination
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at 550 C for 6 h. To modify the product, the obtained solid was further treated in mixture of
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ethanolamine and TPABr at 175 C for 48 h followed by filtration, washing with deionized water,
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treating with dilute H SO and H O solution, drying at 120 C and calcination at 550 C for 6 h.
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Synthesis of Ti/ZSM-5. NH ꢀZSMꢀ5 was obtained from NaꢀZSMꢀ5 by ionꢀexchanging three
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times with 0.5 mol L NH NO solution (liquid: solid = 10 mL g ) at 80 C for 2 h. HꢀZSMꢀ5
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was then obtained by calcination of the NH ꢀZSMꢀ5 at 550 C for 5 h. Ti/ZSMꢀ5 (Si/Ti molar
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ratio = 31) was prepared by an impregnation method. 265 mg of TBOT was added to 10 mL of
ethanol in a plastic beaker. Then, 1.5 g of HꢀZSMꢀ5 was added into the mixture under stirring.
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After evaporation at room temperature for 24 h, the sample was dried at 100 C overnight, and
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finally calcined at 550 C for 5 h.
Synthesis of Titanium Hydrogenphosphate (TiHP). TiHP was synthesized by the method
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reported in the literature. 1.6 g of TiO and 2.45 g of H PO were added to 5 mL of deionized
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water. After stirring at 160 C for 8 h, the solid was filtered and washed with hot water to neutral.
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Then, the obtained TiHP was dried at 65 C for 4 h.
Synthesis of Phosphated TS-1 (P-TS-1). PꢀTSꢀ1 (5 wt% phosphate loading on TSꢀ1) was
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obtained by a postꢀtreatment method. 0.5 g of TSꢀ1 was added to 5 mL of H PO aqueous
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solution (0.043 mol L ). After stirring at room temperature for 4 h, evaporation of water was
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carried out by a water bath method at 50 C. Finally, the solid was dried at 80 C for 12 h and
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calcined at 600 C for 4 h.
Characterization. Powder Xꢀray diffraction (XRD) was carried out using a Panalytical X’pert
PRO powder diffractometer with CuꢀKα radiation (λ = 0.15418 nm) at tube voltage of 40 kV and
tube current of 40 mA. N adsorptionꢀdesorption isotherms were collected by a Quantachrome
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Autosorb at −196 C. Before measurement, samples were pretreated in vacuum at 300 C for 3 h.
Total surface area was calculated according to BrunauerꢀEmmetꢀTaller (BET) method, and pore
size distributions were calculated from the desorption branch of the isotherm based on Barrettꢀ
JoynerꢀHalenda (BJH) method. Ti content in the samples was analyzed by a Philips Margix Xꢀ
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ray fluorescence (XRF) spectrometer. Ti content in the reaction solution after reaction was
determined by induced coupled plasmaꢀatomic emission spectroscopy (ICPꢀAES). Scanning
electron microscopy (SEM) images were obtained with a Zeiss Auriga FIB SEM. Shimadzu UVꢀ
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600 spectrophotometer was applied to collect the UVꢀvis diffuse reflectance spectra in the
wavelength range from 800 to 200 nm. FTꢀIR spectra with pyridine adsorption were measured
on a Bruker Tensor Ⅱ spectrometer to characterize the acid properties of the catalysts. Before
measurement, water in the sample (9ꢀ15 mg) was removed by evacuation in the analysis pool at
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50 C for 3 h. After cooling down to 25 C, the IR spectrum of the catalyst was collected as
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background reference with a resolution of 4 cm . Then, pyridine gas was introduced to the
analysis pool. After about 15 min, the catalyst was saturated by adsorption of pyridine.
Subsequently, the pyridine was desorbed by evacuation at different temperature for some time,
followed by the recording of the FTꢀIR spectrum of the catalyst using the obtained IR spectrum
mentioned above as background.
Catalytic Tests. Catalytic oxidation of ELA was carried out in a threeꢀnecked roundꢀbottom
glass reactor (50 mL) with a reflux condenser. Typically, desired amount of ELA and 30% H O
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were charged to the reactor, followed by heating the reactor to desired temperature in a heated oil
bath under stirring. Then, the catalyst was added and the reaction was started.
Product Analysis. After desired reaction time, 0.25 mL of reaction mixture including reactant
and catalyst was taken out from the working reactor. After removing the catalyst by
centrifugation, the reaction mixture was analysed on Agilent 7890A GC with HPꢀ5 capillary
column and flame ionization detector using naphthalene as the internal standard. The products in
the reaction mixture were identified by Agilent 6890N GC/5973MS and comparison with the
authentic samples.
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Calculation of the Reaction Rate. In “Catalytic Results over TSꢀ1” section, ELA conversion
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rate at different concentration of L acid sites was calculated by the equation of RELA = c
ꢁ
ELA
ꢀ1
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XELA ꢁ t ,where RELA, c ELA, XELA and t represent the ELA conversion rate, ELA initial
concentration, ELA conversion and reaction time (2 h), respectively. TOF value for ELA
conversion at different H O concentration at reaction time of 2 h was calculated by the equation
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ꢀ1
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L
ꢀ1
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of TOF = c
ꢁ XELA ꢁ t ꢁ c , where c represents the concentration of L acid sites.
ELA
RESULTS AND DISCUSSION
Characterization. Figure S1 shows the XRD patterns of the synthesized samples. Anatase
phase of commercial TiO , typical MFI structure of prepared TSꢀ1, PꢀTSꢀ1 and Ti/ZSMꢀ5, and
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the crystalline characteristic of TiHP are confirmed. A peak at 25.3 was observed in the XRD
pattern of TiHP indicating the existence of some unconverted TiO in the synthesized TiHP. The
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textural properties of the samples were also investigated (Table 1). TSꢀ1 shows the highest
surface area and pore volume. Meanwhile, low external surface area and mesopore volume of
Ti/ZSMꢀ5, TSꢀ1, and PꢀTSꢀ1 indicate that the three samples are typical microporous zeolites.
TiO and TiHP showed much lower surface area as compared to the zeolite materials including
2
Ti/ZSMꢀ5, TSꢀ1, and PꢀTSꢀ1. Morphology of the samples was characterized by SEM (Figure 1).
All the samples are micronꢀsized. TSꢀ1, PꢀTSꢀ1 and Ti/ZSMꢀ5 have typical coffinꢀshaped
morphology of MFI zeolite. However, crystals of TSꢀ1 are more uniform than Ti/ZSMꢀ5 in
which some cracked crystals and many voids on the surface were observed. TiO sample consists
2
of irregular crystalline lumps with nonꢀuniform size. Mixture of flakes and lumps were observed
in TiHP samples.
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Table 1. Textural Parameters of the Samples
a
total pore volume
mesopore volume
2
−1
a
2
−1
sample
SBET (m g )
SExternal (m g )
−1
−1
(mL g )
(mL g )
TiO2
TiHP
77
20
0.25
0.11
0.27
0.22
0.17
77
14
45
42
29
0.25
0.11
0.10
0.08
0.03
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
TSꢀ1
380
316
294
PꢀTSꢀ1
Ti/ZSMꢀ5
a
SExternal = SBET – SMicropore; mesopore volume = total pore volume – micropore volume, where
the micropore surface area and volume were determined by the tꢀplot method at a relative
pressure of 0.05ꢀ0.70.
Figure 1. SEM images of TiO , TSꢀ1, Ti/ZSMꢀ5, TiHP and PꢀTSꢀ1.
2
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2
2
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2
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6
2
08
1
1
1
.6
.4
.2
3
13
TS-1
Ti/ZSM-5
TiO2
TiHP
P-TS-1
1.0
0.8
0.6
0.4
0
1
2
3
4
5
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8
9
0
1
2
3
4
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8
9
0
1
2
3
4
5
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0.2
.0
0
2
00
300
400
500
600
Wavelength (nm)
Figure 2. UVꢀvis spectra of TiO , TSꢀ1, Ti/ZSMꢀ5, TiHP and PꢀTSꢀ1.
2
Figure 2 shows the UVꢀvis spectra of the Tiꢀbased samples. The anatase TiO shows a wide
2
absorption profile with a ca. 420 nm of absorption edge indicating diversity of the chemical
41
states of Ti atoms. Ti/ZSMꢀ5 shows similar absorption feature to TiO . However, absorbance
2
of Ti/ZSMꢀ5 is weaker. This phenomenon implies that Ti species in Ti/ZSMꢀ5 are mainly in
TiO form but the concentration is lower. Meanwhile, the absorption edge of Ti/ZSMꢀ5 is shifted
2
toward short wavelength. Such a blue shift has been reported for dispersed TiO nanoparticles on
2
4
2
support due to the quantum size effect. A strong absorption with maximum at 208 nm and a
shoulder at 313 nm are observed in the UVꢀvis spectra of TSꢀ1 and PꢀTSꢀ1. The absorption band
at 208 nm originates from the charge transfer between the 2p electron of tetrahedral oxygen
4
+
29,43,44
ligand and the empty 3d orbital of framework Ti ion.
The presence of the absorption peak
4
5
centered at 313 nm is attributed to the existence of extraꢀframework anatase TiO2. As
determined by XRF method, the Si/Ti molar ratio of TSꢀ1 is 31. This Ti content is slightly higher
than the theoretical maximum (2.5%, molar fraction) of Ti that could be inserted into the
4
6
framework reported in literature. The excess Ti exists in the form of extraꢀframework anatase
TiO . The UVꢀvis spectrum of TiHP exhibited the characteristic absorption band of tetrahedrally
2
coordinated framework Ti at around 208 nm. Meanwhile, the absorption band centered at 313
nm indicates the presence of some TiO component, which is consistent with the XRD result.
2
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47
The band at around 280 nm was assigned to isolated hexaꢀcoordinated Ti species. So, there are
multifarious coordinated Ti species with different microꢀenvironments in TiHP.
o
5
1
0 C
o
00 C
150 C
1
445
o
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
491
TiO2
1
447
TS-1
P-TS-1
1
450
Ti/ZSM-5
1
580 1560 1540 1520 1500 1480 1460 1440 1420 1400
-1
Wavenumber
(
cm
)
Figure 3. FTIR spectra of the samples after pyridine adsorption and evacuation at 50, 100,
o
and 150 C for 30 min.
FTIR spectroscopy of absorbed base molecule was used to study the acidic properties
4+
of the Ti ꢀcontaining samples. Figure 3 shows the pyridineꢀFTIR spectra of TiO , TSꢀ1,
2
−
1
Ti/ZSMꢀ5 and PꢀTSꢀ1. Observation of bands at about 1550 cm in spectrum of Ti/ZSMꢀ
48,49
5 can be attributed to the pyridine adsorption on Brönsted (B) acid sites,
derived from bridging hydroxyl of Si(OH)Al group in Ti/ZSMꢀ5. IR bands at ~1447 cm
observed in the spectra of all the samples can be ascribed to pyridine adsorption on Lewis
which
−
1
48,49
−1
(
L) acid sites.
Appearance of bands at 1491 cm for TiO , TSꢀ1, and PꢀTSꢀ1 indicate
2
48,49
−1
pyridine adsorption on L acid sites.
For Ti/ZSMꢀ5, the IR band at 1491 cm was
48,49
ascribed to pyridine adsorption on both L and B acid sites.
According to the area of
−
1
the peak at ~1447 cm , the amount of L acid sites was calculated and listed in Table
50,51
2.
The amount of acid sites calculated according to the spectra after evacuation at 100
o
−1
C was applied for discussion. The amount of L acid sites on TiO is 277 ꢂmol g , which
2
−
1
is much lower than the theoretical surface Ti sites (1340 ꢂmol g ) on anatase TiO . The
2
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1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
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3
3
3
3
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4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
4+
reason is that only the coordinatively unsaturated Ti centers on the surface of TiO can
2
48
react with pyridine molecules. As described above, Ti species in Ti/ZSMꢀ5 are mainly
in TiO form (Figure 2). So, Ti only makes a small contribution to the formation of L acid
2
−
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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8
9
0
1
2
3
4
5
6
7
8
9
0
sites on Ti/ZSMꢀ5 (90 ꢂmol g ) which are mainly derived from Al species. This can be
confirmed by the pyridineꢀFTIR spectrum of HZSMꢀ5 (Figure S2), the amount of L acid
−
1
sites in HZSMꢀ5 is about 136 ꢂmol g . The amount of L acid sites on TSꢀ1 is 234 ꢂmol
−
1
g which is lower than the theoretical maximum framework Ti in TSꢀ1 (Si/Ti molar ratio
−1
=
40, 403 ꢂmol g ). In this work, the Si/Ti molar ratio is 31; the excess Ti exists in the
form of extraꢀframework TiO , and this makes small contribution to the formation of L
2
−
1
acid sites as mentioned above. For PꢀTSꢀ1, the amount of L acid sites (153 ꢂmol g ) is
lower than that of TSꢀ1. This might be caused by the blocking of L acid sites by P species.
No obvious band of pyridine adsorption on B acid sites is observed in pyridineꢀFTIR
spectrum of PꢀTSꢀ1. This is because that H PO may interact with surface OH group on
3
4
o
TSꢀ1. Dehydration would occur in the calcination at high temperature (600 C) leading to
the removal of hydroxyl groups of H PO . However, when PꢀTSꢀ1 was applied as catalyst
3
4
in aqueous solution, hydroxy groups can then be restored after interaction with water.
+
52
These restored hydroxy groups on H PO still have the ability to donate H . In this work,
3
4
+
we ascribed the restored H to the B acid sites of PꢀTSꢀ1. The amount of B acid sites of Pꢀ
+
TSꢀ1 (generated H in aqueous solution) can be easily measured by a titration method
(Table 2). The result means that when PꢀTSꢀ1 was applied as a catalyst, a large number of
+
−1
H (888 ꢂmol g catalyst) will be formed in the reaction solution (H O aqueous
2
2
solution). The pyridineꢀFTIR method is also invalid for TiHP because of the existence of
H O molecules in Ti(HPO ) ·H O (TiHP) which blocks the adsorption of pyridine
2
4 2
2
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molecules on the catalyst. Structure of TiHP would be destroyed in the process of sample
pretreatment (dehydration) before measure. As described in previous literature, there are
both L and B acid sites in TiHP. L acid property of this sample is difficult to be
characterized. The amount of B acid sites in TiHP can be measured by the titration
method (Table 2). It can be seen that there are a large number of B acid sites in TiHP (955
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
−
1
ꢂmol g ).
Table 2. Amount of Lewis and Brønsted Acid Sites of the Samples
Lewis acid sites
Brønsted acid sites
Brønsted acid sites
−1
a
−1 a
sample
(
ꢂmol g )
(ꢂmol g )
−
1 b
(
ꢂmol g )
o
o
o
o
o
o
5
0 C 100 C 150 C
50 C 100 C 150 C
TiO2
TiHP
344
277
ꢀ
215
ꢀ
0
ꢀ
0
ꢀ
0
ꢀ
0
ꢀ
955
0
TSꢀ1
336
295
209
234
153
90
128
83
57
0
0
0
PꢀTSꢀ1
Ti/ZSMꢀ5
ꢀ
ꢀ
ꢀ
888
196
101
86
85
a
50,51
Calculating by the equation given in literature
according to the pyridineꢀFTIR spectra after
o
evacuation at 50, 100 and 150 C for 30 min.
b
+
Measured by a titration method. Before titration, H in the sample was exchanged by NaCl
−
1
solution (2 mol L ) under stirring for 12 h.
Conversion of ELA to EP over Different Catalysts. Catalytic oxidative conversion
of ELA to EP was carried out over different Tiꢀbased samples. For comparison, a blank
reaction was also carried out. As anticipated, no ELA was converted without catalyst. As
shown in Figure 4, TiO and Ti/ZSMꢀ5 show low catalytic activity for the conversion of
2
ELA to EP. When TiHP was applied as a catalyst, 62.7% ELA conversion and 3.3% EP
yield were obtained. A large amount of lactic acid was detected in the reaction solution.
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2
2
2
2
2
2
2
2
2
3
3
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3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
So, the side reaction over TiHP is mainly the hydrolysis of ELA to lactic acid.
Surprisingly, TSꢀ1 is highly active for the conversion of ELA to EP, 100% ELA
conversion and 97.2% EP yield were given at the same reaction conditions.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Microenvironment of Ti species in these catalysts is different. In TiO , the coordinatively
2
4+
unsaturated Ti on the surface which formed L acid sites might be responsible for the
activity. For Ti/ZSMꢀ5, L and B acid sites are mainly derived from ZSMꢀ5. In TiHP, both
L and B acid sites exist in Ti(HPO ) ·H O structure. In TSꢀ1, there are only L acid sites
4
2
2
created by the framework Ti of Ti(OSi) without B acid sites. The presence of unitary
4
Ti(OSi) is responsible for the good catalytic performance of TSꢀ1. Oxidation of ELA
4
was also carried out with phosphated TSꢀ1 (PꢀTSꢀ1) as catalyst. As shown in Figure 4,
when P species were introduced, the catalytic activity of TSꢀ1 decreased dramatically.
This further confirmed the importance of unitary Ti(OSi) for the catalytic activity.
4
Further information about the active species in TSꢀ1 would be illustrated in the catalytic
mechanism section.
100
ELA conversion
EP yield
80
60
40
20
0
TiO2
TS-1
Ti/ZSM-5
Catalyst
TiHP
P-TS-1
Figure 4. Catalytic performance of the Tiꢀbased catalysts on conversion of ELA to EP.
Reaction conditions: 10 mL of ELA, 25 mL of 30% H O (molar ratio of H O to ELA =
2
2
2
2
o
2
.80), 300 mg of catalyst, 50 C, 11 h.
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Catalytic Results over TS-1. To get more information about catalytic performance of
TSꢀ1, effects of reaction conditions including amount of TSꢀ1 and molar ratio of H O to
2
2
ELA on the conversion of ELA to EP were investigated. Figure 5A shows the effect of
o
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
TSꢀ1 amount on the conversion of ELA to EP at 50 C. It can be seen that the reaction
rate of conversion of ELA to EP increased dramatically with the increase of TSꢀ1 amount.
1
00% ELA conversion can be obtained with the prolongation of reaction time. With the
increase of TSꢀ1 amount, the reaction time for 100% ELA conversion decreased. When
TSꢀ1 amount was 400 mg, the reaction time for complete conversion of ELA was only 7 h.
However, the EP yield decreased slightly when further prolonging the reaction time after
100% ELA conversion. For example, when TSꢀ1 amount was 400 mg, prolongation of
reaction time from 7 to 11 h, EP yield decreased slightly from 98.6% to 96.8%.
Effect of the amount of L acid sites of TSꢀ1 on the ELA conversion rate is shown in Figure 5B.
Concentration of L acid sites was calculated based on the amount of L acid sites on TSꢀ1
o
measured at 100 C (Table 2). Reaction rate was determined by the ELA conversion data at the
reaction time of 2 h shown in Figure 5A. The reaction rate is linear to the concentration of L acid
sites. This means that the ELA conversion rate is firstꢀorder dependence on the concentration of
L acid sites when the concentrations of H O and ELA were fixed. In this catalytic system, ELA
2
2
conversion reaction can be divided to two steps: (1) formation of active species on L acid sites;
(2) conversion of ELA to EP on active centers. It can be concluded that the formation of active
species on L acid sites is the rateꢀdetermining step.
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1
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1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
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5
5
5
5
5
5
5
6
0.7
1
00
(
A)
(B)
400 mg
9
8
7
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5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0.6
y=0.238x
3
00 mg
200 mg
2
0.5
R =0.9960
0.4
0.3
0.2
0.1
1
00 mg
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ELA conversion
EP yield
0.0
0
2
4
6
8
10
12
0
.0
0.5
1.0
1.5
2.0
2.5
3.0
3
-1
Reaction time (h)
Concentration of L acid sites × 10 (mol L )
Figure 5. (A) Effect of TSꢀ1 amount on conversion of ELA to EP. (B) Effect of the
concentration of L acid sites on ELA conversion rate at reaction time of 2 h. Reaction
conditions: 10 mL of ELA, 25 mL of 30% H O (molar ratio of H O to ELA = 2.80), 50
2
2
2
2
o
C.
280
260
100
(
e)
(B)
(A)
9
8
7
6
5
0
0
0
0
0
ELA conversion
EP yield
(d)
(c)
y=31.50x+38.27
2
R =0.9896
240
220
200
(
b)
40
30
180
(
a)
1
60
40
2
1
0
0
0
1
120
3
.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
0
2
4
6
8
10
12
-
1
Concentration of H O (mol L )
Reaction time (h)
2
2
Figure 6. (A) Effect of molar ratio of H O to ELA (a) 0.56, (b) 1.12, (c) 1.68, (d) 2.24
2
2
and (e) 2.80 on conversion of ELA to EP over TSꢀ1. (B) TOF values for conversion of
ELA over TSꢀ1 with different H O concentration at reaction time of 2 h. Reaction
2
2
o
conditions: 10 mL of ELA, 200 mg of TSꢀ1, 50 C.
Figure 6A shows the effect of molar ratio of H O /ELA on the conversion of ELA to
2
2
o
EP at 50 C. When the ratio of H O /ELA was 0.56, both ELA conversion and EP yield
2
2
increased slowly with prolongation of reaction time. When the molar ratio of H O /ELA
2
2
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was 1.12, ELA conversion and EP yield increased faster compared to the time course at
H O /ELA of 0.56. Further increase of the molar ratio of H O /ELA led to the increase of
2
2
2
2
ELA conversion and EP yield. When H O /ELA = 2.80, 96.4% ELA conversion, 92.8%
2
2
o
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
EP yield and 96.3% EP selectivity were given after reaction at 50 C for 11 h.
As described above, formation of active species on L acid sites is the rateꢀdetermining
step. Besides concentration of L acid sites, concentration of H O is the other key factor
2
2
for the formation of active species. The effect of concentration of H O on the reaction
2
2
rate is shown in Figure 6B. To eliminate the effect of concentration of L acid sites, TOF
value was used as the reaction rate, which was calculated according to the amount of L
acid sties on TSꢀ1 and the ELA conversion data at 2 h shown in Figure 6A. As shown in
Figure 6B, the conversion rate of ELA is also firstꢀorder dependence on the concentration
of H O . This further confirmed that formation of active species by reaction between
2
2
H O and L acid sites on TSꢀ1 is the rateꢀdetermining step.
2
2
Reaction Pathway for ELA Conversion over TS-1. Effect of reaction temperature on
conversion of ELA over TSꢀ1 is shown in Figure 7. TSꢀ1 shows high catalytic activity for
o
conversion of ELA. The reaction can proceed even at room temperature. At 25 C, 20.4% ELA
conversion and 19.0% EP yield were given after reaction for 11 h. Reaction temperature has
great effect on the catalytic performance of TSꢀ1 for conversion of ELA to EP. When the
o
temperature was elevated to 40 C, the reaction rate was enhanced dramatically, 68.5% ELA
conversion and 65.8% EP yield were reached after 11 h. Elevating the reaction temperature to 50
o
C, 100% ELA conversion and 97.8% EP yield were obtained after 9 h. Further increase of the
o
reaction time led to a slight decrease of EP yield. When the reaction temperature was 60 C, the
reaction rate increased further. 100% ELA conversion and 96.3% EP yield were obtained in 4 h.
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However, prolongation of reaction time led to the decrease of EP yield dramatically. 87.1% EP
yield was observed after 11 h. The decrease of EP yield is caused by the decomposition of EP.
To get more information about the side reaction of EP decomposition, the reaction was carried
o
o
0
1
2
3
4
5
6
7
8
9
0
1
2
3
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7
8
9
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5
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7
8
9
0
1
2
3
4
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8
9
0
out at 70 C, and the time course was recorded in Figure S3. At 70 C, 100% ELA conversion
and 97.9% EP yield were given after only 1.5 h. Dramatic decrease of EP yield occurred in the
residual reaction time. After 11 h, most of EP decomposed, and only 4.4% EP was left.
Furthermore, the decomposition rate of EP increased first, and then decreased. This is a dynamic
characteristic of selfꢀcatalyzed reaction. Otherwise, we had bubbled the gas in the reactor into
Ca(OH) aqueous solution. The clear Ca(OH) aqueous solution turn turbid at the reaction time
2
2
of 70 min. With prolongation of reaction time, precipitation of CaCO was obtained (Figure S4).
3
Thus, CO is one byꢀproduct of EP decomposition. By filtration and drying of CaCO , 7.60 g of
2
3
solid was collected. Theoretically, 8.35 g of CaCO can be obtained when 95.6% EP (as
3
o
mentioned above, after reaction at 70 C for 11 h, 4.4% EP was left) decomposed. Meanwhile, a
large amount of CH COOH formed after EP decomposition. Thus, the side reaction in this
3
catalytic system is mainly the decarboxylation of pyruvic acid. Pyruvic acid formed through the
hydrolysis of EP which is a selfꢀcatalyzed reaction. This is consistent with the dynamic
characteristic observed in time course of EP decomposition. EP was also applied as a reactant to
investigate the effect of temperature on the decomposition of EP over TSꢀ1 in detail (Figure S5).
o
When the temperature is 40 or 50 C, decomposition of EP is slow. Conversion of EP is ≤ 5%
o
after 9 h. However, the decomposition of EP at 60 C is accelerated dramatically. The conversion
of EP is about 13% after 9 h. These results are consistent with the results shown in Figure 7. At
such low reaction temperature, polymerization products were not detected in this catalytic
2
5
system, which were reported as the byꢀproducts in previous report.
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o
60 C
o
5
0 C
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8
9
0
ELA conversion
EP yield
o
40 C
o
25 C
0
2
4
6
8
10
12
Reaction time (h)
Figure 7. Effect of reaction temperature on conversion of ELA to EP over TSꢀ1. Reaction
conditions: 10 mL of ELA, 25 mL of 30% H O (molar ratio of H O to ELA = 2.80), 300
2
2
2
2
mg of TSꢀ1.
Main reaction
OH
O
TS-1,
H
2 2
O
O
O
O
O
Hydrolysis
Ethanol
Side reactions
O
O
Decarboxylation
OH
CO
2
+
+
OH
O
Scheme 1. Reaction pathway for ELA oxidation over TSꢀ1 with H O as oxidant.
2
2
Based on the results mentioned above, the reaction pathway for ELA oxidation over TSꢀ1 with
H O as oxidant is summarised in Scheme 1. At proper reaction temperature (for example 50 or
2
2
o
60 C), ELA can be completely oxidized to EP with ≥95% EP yield firstly. However, with
prolongation of reaction time, hydrolysis of EP would be inevitable due to the high concentration
of EP and the presence of H O /H O in the reaction system. Hydrolysis of EP is a selfꢀcatalyzed
2
2
2
reaction. So, further prolonging the reaction time, hydrolysis reaction rate was accelerated. By
hydrolysis of EP, pyruvic acid and ethanol were formed. As we know, keto acid is unstable in
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heated aqueous solution, and decarboxylation would occur. So, the formed pyruvic acid would
be converted into acetic acid and CO increasingly through decarboxylation.
2
Figure S6 shows the conversion of H O in the oxidation of ELA to EP over TSꢀ1 with
2
2
o
0
1
2
3
4
5
6
7
8
9
0
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1
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5
6
7
8
9
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1
2
3
4
5
6
7
8
9
0
nH2O2/nELA of 1.68. After reaction at 50 C for 13 h, 100% ELA conversion and 62.3% H O
2
2
conversion with 95.2% EP yield were given. Theoretically, when the conversion of ELA to EP is
00%, 59.5% of H O would be consumed for the oxidation. The actual H O conversion (62.3%)
1
2
2
2
2
is slightly higher than the theoretical value (59.5%) indicating that the decomposition of H O2
2
exists in this reaction although the amount of the invalid decomposition is low.
Catalytic Mechanism. As described in previous literature, oxidative dehydrogenation of ELA
o
25
to EP over TiO at 130 C with molecular O as oxidant follows a freeꢀradical mechanism.
2
2
However, epoxidation reactions over TSꢀ1 with H O as oxidant often follow a nonꢀradical
2
2
2
9
mechanism. To clarify the reaction mechanism in this work, confirmation of the freeꢀradical
mechanism or nonꢀradical mechanism was carried out firstly. Presence of hydroquinone, which
is a free radical scavenger, did not affect the catalytic performance of TSꢀ1 on conversion of
ELA to EP (Table S1 entries 1 and 2), implying that conversion of ELA to EP in our catalytic
system follows a nonꢀradical mechanism.
Formation of oxygen centred species is pivotal in zeolites or metal oxides with H O catalytic
2
2
system. To identify the active oxygen based species, UVꢀvis spectra of TiO , TSꢀ1, Ti/ZSMꢀ5,
2
TiHP and PꢀTSꢀ1 with aqueous H O solution were collected (Figure 8). For comparison, spectra
2
2
of these samples interacting with water were also provided. As described in previous literature,
4+
by contacting with H O aqueous solution, a new peak from the OꢀO moiety to the Ti center
2
2
3
4
would appear around 385 nm. For TiO , TSꢀ1, TiHP and PꢀTSꢀ1, additional and obvious
2
absorption profiles were observed in the range from 370 to 500 nm as compared to the UVꢀvis
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spectra of the samples that was treated by water, indicating the presence of OꢀO moiety to the
4
+
Ti center. Microenvironment of Ti species in anatase TiO is different from that in TSꢀ1
2
5
3,54
structure.
As described in previous report, the oxygen species on TiO ꢀtreated by H O is
2 2 2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
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5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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7
8
9
0
1
2
3
4
5
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7
8
9
0
1
2
3
4
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
mainly in the form of TiꢀOꢀOꢀTi, and an equilibrium exist in Ti(OOH) and Ti(OO) on TSꢀ1 after
34,37
contacting with H O .
This might be the reason for the different catalytic activity of TSꢀ1 and
2
2
TiO . The difference of catalytic performance of TSꢀ1 and TiO with H O as oxidant had been
2
2
2
2
5
5,56
also reported for the chlorohydrination of allyl chloride.
TiHP shows low activity for
oxidation of ELA to EP. This might be related to the low surface area of TiHP. Meanwhile, it can
be seen from the UV spectra in Figures 2 and 8, there are multifarious coordinated Ti species in
TiHP. The difference of microenvironment of Ti in TiHP and TSꢀ1 might also be a reason for the
low oxidation activity of TiHP. Physical properties including surface area, pore volume, and
morphology of PꢀTSꢀ1 are similar to that of TSꢀ1. However, the amount of L acid sites on PꢀTSꢀ
1 is lower than that of TSꢀ1. The introduced P species might interact with L acid sites on TSꢀ1
surface. Thus, the introduced P species and/or the presence of B acid sties might change the
microenvironment of Ti in TSꢀ1 and disrupt the catalytic performance of Ti(OOH). For Ti/ZSMꢀ
5
, nonꢀeffective catalyst for the conversion of ELA to EP (Figure 4), no obvious absorption
profiles can be observed in the range from 370 to 500 nm, implying the absence of Ti(OO)
and/or Ti(OOH) species. These results indicates that Ti(OO) and/or Ti(OOH) might be the active
oxygen based species for the conversion of ELA to EP.
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Contacted with H O
2
Contacted with H O2
2
P-TS-1
TiHP
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9
0
Ti/ZSM-5
TS-1
TiO2
2
00
300
400
500
600
Wavelength (nm)
Figure 8. UVꢀvis spectra of TiO , TSꢀ1, Ti/ZSMꢀ5, TiHP and PꢀTSꢀ1 interacted with
2
H O or aqueous H O solution.
2
2
2
As shown in Figure 8, OꢀO structure formed by H O on Ti(IV) centers in TSꢀ1.
2
2
However, it is hard to distinguish Ti(OOH) and Ti(OO) directly by UVꢀvis spectra. It had
been reported that Ti(OOH) and Ti(OO) formed simultaneously on TSꢀ1 after contacting
34
with H O , and an equilibrium existed in the two species. If TSꢀ1 was treated with
2
2
29
NaCO aqueous solution, the formation of Ti(OOH) would be suppressed. So, we
3
applied TSꢀ1 treated by Na CO to catalyse the conversion of ELA to EP in the presence
2
3
o
of H O at 50 C. After 11 h, only 13.9% ELA conversion and 11.5% EP yield were
2
2
obtained (Table S1 entry 4). This implies that Ti(OOH) is the active species in this
catalytic system. Furthermore, when oxidant of H O was substituted by tertꢀbutyl
2
2
hydroperoxide, 17.3% conversion of ELA was given and no EP was detected (Table S1
entry 3). As we know, under this conditions, formation of Ti(OOH) species is impossible
(
Figure S7). This further confirms that the active species in this catalytic system is
Ti(OOH). Additionally, the invalid performance of tertꢀbutyl hydroperoxide also
confirmed the nonꢀradical mechanism in this catalytic system as mentioned above.
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Based on the results mentioned above and previous literature, a mechanism for
oxidation of ELA to EP over TSꢀ1 in the presence of H O was proposed. As shown in
2
2
Scheme 2, active specie of Ti(OOH) formed by H O on Ti(OSi) in TSꢀ1. Then,
2
2
4
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
hydroxyl group of ELA reacted with Ti(OOH) leading to the dehydration. After that,
desorption of EP from TSꢀ1 occurred, and Ti(OH) species formed. Finally, further
dehydration of Ti(OH) and Si(OH) led to the formation of Ti(OSi)4.
H
Si
O
O
O
O
L
O
+H
2
O
2
Si
H
Si
Ti
Si
O
Ti
O
O
Si
O
O
Si
O
Si
Si
O
OH
ꢀ
H
2
O
ꢀH
O
2
O
O
O
O
O
OH
O
O
Si
H
Si
L
H
O
Ti
O
O
Ti
O
O
Si
Si
Si
O
O
Si
O
Si
Si
Scheme 2. Proposed mechanism for oxidation of ELA to EP on active sites of TSꢀ1 with
aqueous H O as oxidant.
2
2
Kinetic Analysis. Reaction kinetic analysis was conducted to understand the reaction
mechanism in detail. Initial reaction rate was measured based on the data of ELA
conversion. To avoid the mass transfer limitations and keep ELA conversion at a low
level, the time courses of the conversion of ELA were collected with a small amount of
o
TSꢀ1 (100 mg) at 40, 45, 50 and 55 C (Figure S8a). As shown in Figure S8a and S8b, the
effect of ELA concentration on the reaction rate is negligible. So, the reaction rate is zeroꢀ
order dependence on the concentration of ELA, indicating that the conversion of ELA to
EP step is the fast reaction step. This is accordant with the conclusion obtained above that
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2
2
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the formation of active species on L acid sites is the rateꢀdetermining step (Figures 5 and
6
). The formation of active species of Ti(OOH) is illustrated in equation (1) where the
4+
4+
Ti represented the framework Ti which caused the formation of L acid sites in TSꢀ1:
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
k'
Ti4+ + H
O
Ti(OOH)
(1)
2
2
Because the conversion of ELA is zeroꢀorder reaction to ELA concentration, the reaction
o
−5
−1 −1
rate (
S8b. Meanwhile,
described above. As shown in Figure 5B and Figure 6B,
r
) at 50 C is equal to the
is determined by the formation of active species of Ti(OOH) as
is proportional to the
concentration of L acid sites (framework Ti ) and the concentration of H O . So, it can
k value (4.3 × 10 mol L s ) which was shown in Figure
r
r
4+
2
2
4+
4+
be concluded that
r = k’[Ti ][H O ] where [Ti ] and [H O ] are the concentration of L
2 2 2 2
acid sites and H O respectively. According to the results shown in Figure S8, it can be
2
2
4+
−4
ꢀ1
−1
calculated that [Ti ] = 6.7 × 10 mol L and [H O ] = 7 mol L . Based on the values of
2
2
4+
r
, [Ti ] and [H O ], the rate constant of Ti(OOH) formation as shown in equation (1) at
2 2
o
−3
−1 −1
5
0 C can be calculated, k’ = 9.2 × 10 L mol s . By the same method, k’ values at 40
o
o
o
−3
−1 −1
−3
−1 −1
C, 45 C and 55 C are calculated, 2.3 × 10 L mol s , 4.9 × 10 L mol s and 1.4
−
2
−1 −1
×
10 L mol s are obtained respectively.
The Arrhenius plot for the oxidation of ELA over TSꢀ1 is shown in Figure S8c. Based
on a linear fitting method, the apparent activation energy (Ea) in this catalytic system was
−
1
obtained (103.4 kJ mol ). This value is quite close to the activation energies of
−1
−1
cyclohexanone ammoximation (93.2 kJ mol and 98.8 kJ mol ) over TSꢀ1 in the
57,58
presence of H O reported in literature.
According to the intercept of the line in Figure
2
2
12
−1 −1
S8c, preꢀexponential factor (A) was also calculated (2.1 × 10 mol L s ). Thus, the
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Arrhenius equation for ELA conversion in this catalytic system can be provided as
12
following: k = 2.1 × 10 exp(−12437/T).
Recyclability of TS-1. Recyclability is very important for heterogeneous catalysts. So, the
recyclability of TSꢀ1 catalyst was examined for the oxidation of ELA to EP. After each run, the
solid catalyst was separated from the reaction mixture by centrifugation. Without any treatment,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
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5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
the TSꢀ1 was used for the next run directly. Figure 9 shows the result of reuse test of TSꢀ1. After
o
1
0 runs, 100% ELA conversion and 96.6% EP yield were obtained at 60 C after 4 h. There were
almost no change in ELA conversion and EP yield throughout the reuse test. The Ti content in
the solution of the first run was tested by ICP, only 1.45 ppm of Ti (0.7 wt% titanium of total Ti
in TSꢀ1) was detected. This might be caused by the leaching of the unstable extraꢀframework Ti.
Furthermore, XRD, N physisorption and pyridineꢀFTIR were applied to test the structural
2
information of TSꢀ1 after reaction (10 runs). The results are shown in Figure S9, Figure S10, and
Table S2. Overall, the structure of TSꢀ1 is stable during the reaction. The structure stability of
TSꢀ1 might be related to the treatment of TSꢀ1 with dilute H SO and H O in the synthesis
2
4
2
2
procedure. By washing with dilute H SO and H O , the unstable component and impurity in TSꢀ
2
4
2
2
5
9
1
would be removed. High stability and recyclability of TSꢀ1 is promising for the
industrialization of this heterogeneous catalytic process.
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ELA conversion
EP yield
100
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Run
Figure 9. Reuse test of TSꢀ1 in the conversion of ELA to EP. Reaction conditions: 10 mL of
o
ELA, 25 mL of 30% H O (molar ratio of H O to ELA = 2.80), 300 mg of TSꢀ1, 60 C, 4 h.
2
2
2
2
CONCLUSIONS
TSꢀ1 was applied to catalyse the oxidation of ELA to EP in the presence of H O at low
2
2
o
reaction temperature. After reaction at 50 C for 9 h, 100% ELA conversion and 97.8% EP yield
were given. Conversion rate of ELA is affected by reaction temperature greatly. Higher reaction
o
temperature (70 C) promotes the conversion of ELA. However, decomposition of EP
(
hydrolysis and decarboxylation) was also accelerated, which caused the formation of byꢀ
products of acetic acid and CO . Additionally, active species of Ti(OOH) were confirmed and a
2
nonꢀradical mechanism was proposed. By kinetic analysis, the formation of Ti(OOH) is
−
1
confirmed as the rateꢀdetermining step. Apparent activation energy (103.4 kJ mol ) was also
obtained. Furthermore, TSꢀ1 showed high recyclability for conversion of ELA to EP with H O2
2
as oxidant.
ASSOCIATED CONTENT
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Additional XRD patterns, FTꢀIR spectra, photographs, kinetic plots, utilization of H O , and
2
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controlled reaction results were listed in the Supporting Information. This material is available
free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
*
Corresponding Author Tel.: +86 371 67781780; Eꢀmail addresses: zhoulipeng@zzu.edu.cn
ACKNOWLEDGEMENTS
We are grateful to the National Natural Science Foundation of China (21503192), China
Postdoctoral Science Foundation (2017M612418) and the Key Scientific Research Projects for
University in Henan Province (16A530009) for the financial supports.
REFERENCES
(1) Bozkurt, F.; Tornuk, F.; Toker, O. S.; Karasu, S.; Arici, M.; Durak, M. Z. LWT--Food Sci.
Technol. 2016, 65, 1044–1049.
(2) Wang, Y.; Lewis, J. D.; RománꢀLeshkov, Y. ACS Catal. 2016, 6, 2739–2744.
3) Zhou, J.; Chen, X.; Lu, L.; Govender, A.; Yang, H.; Shen, W. J. Mol. Catal. B: Enzym. 2016,
25, 42–48.
(
1
(4) Murlykina, M. V.; Sakhno, Y. I.; Desenko, S. M.; Shishkina, S. V.; Shishkin, O. V.; Sysoiev,
D. O.; Kornet, M. N.; Schols, D.; Goeman, J. L.; Van der Eycken, J.; Van der Eycken, E. V.;
Chebanov, V. A. Eur. J. Org. Chem. 2015, 4481–4492.
(5) Dennig, A.; Busto, E.; Kroutil, W.; Faber, K. ACS Catal. 2015, 5, 7503–7506.
(
6) Hernández, K.; Gómez, A.; Joglar, J.; Bujons, J.; Parella, T.; Clapes, P. Adv. Synth. Catal.
017, 359, 2090–2100.
2
(7) Sugiyama, S.; Fukunaga, S.; Ito, K.; Ohigashi, S.; Hayashi, H. J. Catal. 1991, 129, 12–18.
27
ACS Paragon Plus Environment

ACS Catalysis
Page 28 of 32
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
8) Causey, T. B.; Shanmugam, K. T.; Yomano, L. P.; Ingram, L. O. Proc. Natl. Acad. Sci. U. S.
A. 2004, 101, 2235–2240.
(9) Xu, P.; Qiu, J.; Gao, C.; Ma, C. J. Biosci. Bioeng. 2008, 105, 169–175.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(10) Zhang, B.; Zhu, Y.; Zhang, J.; Wang, D.; Sun L.; Hong, J. Bioresour. Technol. 2017, 224,
5
53–562.
(11) Holm, M. S.; Saravanamurugan, S.; Taarning, E. Science 2010, 328, 602–605.
(12) Oberhauser, W.; Evangelisti, C.; Caporali, S.; Santo, V. D.; Bossola, F.; Vizza, F. J. Catal.
2
017, 350, 133–140.
13) Yang, X.; Bian, J.; Huang, J.; Xin, W.; Lu, T.; Chen, C.; Su, Y.; Zhou, L.; Wang, F.; Xu, J.
Green Chem. 2017, 19, 692–701.
14) Lu, T.; Fu, X.; Zhou, L.; Su, Y.; Yang, X.; Han, L.; Wang, J.; Song, C. ACS Catal. 2017, 7,
274–7284.
(15) Sun, Z.; Liu, Y.; Chen, J.; Huang, C.; Tu, T. ACS Catal. 2015, 5, 6573–6578.
16) Wan, Y.; Zhuang, M.; Chen, S.; Hu, W.; Sun, J.; Lin, J.; Wan, S.; Wang, Y. ACS Catal.
017, 7, 6038–6047.
17) Coman, S. M.; Verziu, M.; Tirsoaga, A.; Jurca, B.; Teodorescu, C.; Kuncser, V.; Parvulescu,
V. I.; Scholz, G.; Kemnitz, E. ACS Catal. 2015, 5, 3013–3026.
18) Sugiyama, S.; Shigemoto, N.; Masaoka, N.; Sugetoh, S.; Kawami, H.; Miyaura, K.; Hayashi,
(
(
7
(
2
(
(
H. Bull. Chem. Soc. Jpn. 1993, 66, 1542–1547.
(19) Hayashi, H.; Sugiyama, S.; Kokawa, N.; Koto, K. Appl. Surf. Sci. 1997, 121–122, 378–381.
(20) Lomate, S.; Bonnotte, T.; Paul, S.; Dumeignil, F.; Katryniok, B. J. Mol. Catal. A: Chem.
2
013, 377, 123–128.
28
ACS Paragon Plus Environment

Page 29 of 32
ACS Catalysis
1
2
3
4
5
6
7
8
9
(
21) Zhao, X.; Zhang, C.; Xu, C.; Li, H.; Huang, H.; Song, L.; Li, X. Chem. Eng. J. 2016, 296,
2
17–224.
(22) Ai, M. Appl. Catal., A 2002, 232, 1–6.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
23) Liu, K.; Huang, X.; Pidko, E. A.; Hensen, E. J. M. Green Chem. 2017, 19, 3014–3022.
24) Hayashi, H.; Sugiyama, S.; Katayama, Y.; Sakai, K.; Sugino, M.; Shigemoto, N. J. Mol.
(
Catal. 1993, 83, 207–217.
25) RamosꢀFernandez, E. V.; Geels, N. J.; Shiju, N. R.; Rothenberg, G. Green Chem. 2014, 16,
358–3363.
26) Sugiyama, S.; Kikumoto, T.; Tanaka, H.; Nakagawa, K.; Sotowa, K.ꢀI.; Maehara, K.;
Himeno, Y.; Ninomiya, W. Catal. Lett. 2009, 131, 129–134.
(
3
(
(27) Zhang, C.; Wang, T.; Ding, Y. Appl. Catal., A 2017, 533, 59–65.
(28) Yasukawa, T.; Ninomiya, W.; Ooyachi, K.; Aoki, N.; Mae, K. Ind. Eng. Chem. Res. 2011,
50, 3858–3863.
(
(
(
(
(
(
29) Jiao, W.; He, Y.; Li, J.; Wang, J.; Tatsumi, T.; Fan, W. Appl. Catal., A 2015, 491, 78–85.
30) Wilde, N.; Pelz, M.; Gebhardt, S. G.; Gläser, R. Green Chem. 2015, 17, 3378–3389.
31) Lu, X.; Wu, H.; Jiang, J.; He, M.; Wu, P. J. Catal. 2016, 342, 173–183.
32) Simsek, E. B. Appl. Catal., B 2017, 200, 309–322.
33) Liao, J.; Li, H.; Zhang, X.; Xiao, D.; Qiang, N. Appl. Catal., A 2015, 491, 94−99.
34) Bonino, F.; Damin, A.; Ricchiardi, G.; Ricci, M.; Spano, G.; D'Aloisio, R.; Zecchina, A.;
Lamberti, C.; Prestipino, C.; Bordiga, S. J. Phys. Chem. B 2004, 108, 3573–3583.
(35) Chen, Z.; Yin, G. Chem. Soc. Rev. 2015, 44, 1083–1100.
(36) Wang, Y.; Shi, S.; Wang, H.; Zhu, D.; Yin, G. Chem. Commun. 2012, 48, 7832–7834.
29
ACS Paragon Plus Environment