Selective conversion of fructose into 5-ethoxymethylfurfural over green catalyst

Article abstract of DOI:10.1007/s11164-018-3640-5

Abstract: In this study, selective formation of 5-ethoxymethylfurfural (EMF) from one-pot conversion of fructose in a co-solvent of ethanol with tetrahydrofuran over green SO₃H-CD carbon was investigated for the first time using an ultrasonic system. The maximum EMF yield of 74% with 100% fructose conversion was achieved in mild conditions. Moreover, the better selectivity and the longer recyclability (eight cycles) for EMF production via particular reactions such as fructose dehydration and etherification were obviously found while the formation of 5-hydroxymethylfurfual, ethyl levulinate or humins was inhibited using SO₃H-CD carbon, comparing to commercial catalysts such as Amberlyst-35, SiO₂-Tosic acid and Al₂O₃. Graphical abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11164-018-3640-5

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-018-3640-5
Selective conversion of fructose
into 5‑ethoxymethylfurfural over green catalyst
Panya Maneechakr1 · Surachai Karnjanakom1
Received: 16 August 2018 / Accepted: 8 October 2018
© Springer Nature B.V. 2018
Abstract
In this study, selective formation of 5-ethoxymethylfurfural (EMF) from one-pot
conversion of fructose in a co-solvent of ethanol with tetrahydrofuran over green
SO3H-CD carbon was investigated for the frst time using an ultrasonic system.
The maximum EMF yield of 74% with 100% fructose conversion was achieved in
mild conditions. Moreover, the better selectivity and the longer recyclability (eight
cycles) for EMF production via particular reactions such as fructose dehydration and
etherifcation were obviously found while the formation of 5-hydroxymethylfurfual,
ethyl levulinate or humins was inhibited using SO3H-CD carbon, comparing to com-
mercial catalysts such as Amberlyst-35, SiO2-Tosic acid and Al2O3.
Extended author information available on the last page of the article
Vol.:(0123456789)
1 3

P. Maneechakr, S. Karnjanakom
Graphical abstract
Keywords Fructose · 5-ethoxymethylfurfural · SO3H-CD carbon · Selectivity ·
Recyclability
Introduction
In recent years, the conversion of carbohydrates into important chemical building
blocks or petroleum-based industrial organic chemistry such as 5-ethoxymethylfur-
fural (EMF), levulinic acid, 5-hydroxymethylfurfual (HMF), ethyl levulinate (EL)
and formic acid have attracted much attention since they can be easily found and
obtained from biomass [1, 2]. Among of them, EMF is a strong potential chem-
ical that can be applied as a blending/additive agent for diesel energy production
[3]. Fructose has been substantiated as an efective feedstock for EMF production
among all types of carbohydrates, which can be easily converted into HMF and
EMF by homogeneous and heterogeneous Brönsted acid catalysts [4–7]. Yang et al.
[8] reported that ~35% yield of EMF was obtained from fructose conversion using
a commercial H2SO4 catalyst. Kraus et al. [9] found that by-products such as EL
and humins were signifcantly suppressed while the yield of EMF was obviously
increased by using SO3H-functionalized ionic liquid. Moreover, some ionic liquids
and Lewis acids such as 1-butyl-3-methylimidazolium and AlCl3 are also identifed
as good catalysts for dehydration reaction [10, 11]. However, with their application
in industrial process, several problems such as high corrosion to equipment, high
1 3

Selective conversion of fructose into 5-ethoxymethylfurfural…
toxicity to environmental and recycling difculty always occur [12, 13]. From this
point of view, heterogeneous acid catalysts can be considered since they are envi-
ronmentally friendly [14]. To date, even many heterogeneous acid catalysts such as
HPW/MCM-41 [15], SO3H-polymeric material [16], and SO3H-SBA-15 [17] are
widely employed for EMF synthesis, but high production cost and long reaction
time (>10 h), as well as two-step synthesis are still required. Therefore, it is neces-
sary to develop the novel heterogeneous catalyst, which has lower cost, higher activ-
ity and better stability.
From this, we developed an SO3H-CD carbon catalyst prepared through hydro-
thermal synthesis (in situ carbonization and sulfonation). Here, cyclodextrin (CD)
consisting of an oligosaccharides structure (R-D-glucopyranose) was selected as
a carbon source since formation of more polycyclic carbon was found, leading to
the possibility of a high sulfonic amount functionalized on the carbon surface dur-
ing carbonization-sulfonation [18]. The physical and chemical properties of the as-
synthesized catalyst were investigated. Activity and selectivity of the catalyst were
investigated on ultrasonic-assisted conversion from fructose into EMF in the co-
existence of ethanol with tetrahydrofuran (THF) via various efects such as reaction
time, reaction temperature, THF amount and catalyst amount. Moreover, the reus-
ability of catalyst was also tested for eight cycles in optimum conditions, comparing
to various commercial catalysts such as Amberlyst-35, SiO2-Tosic acid and Al2O3.
To the best of our knowledge, this research has not yet been reported in elsewhere. It
is expected to provide highly efective catalyst and suitable system for EMF produc-
tion with high yield and high selectivity.
Experimental
Catalyst synthesis
In situ hydrothermal carbonization and sulfonation were applied for the synthesis
of SO3H-CD carbon. In brief, a certain amount CD was dissolved into 40 mL of
distilled water and vigorously stirred at 40 °C for 30 min. After homogeneous solu-
tion was obtained, 20 g of hydroxyethylsulfonic acid was then added and stirred for
1 h. Here, the weight ratio of hydroxyethylsulfonic acid to CD (4–1) was applied
in this synthesis, which was obtained from our preliminary study based on highest
acid amount on catalyst. The obtained solution was added into an autoclave (100 mL
volume size) and heated at 180 °C for 4 h. Thereafter, the SO3H-CD carbon (black
precipitate) was fltered, washed several times with distilled water and ethanol to
remove excess sulfate ions and fnally dried in vacuum oven at 105 °C for 12 h.
Catalyst characterization
The X-ray difraction (XRD) patterns were recorded on a Rigaku TTRAX III X-ray
difractometer using Cu Kα (λ=0.15418 nm) radiation at 40 kV and 20 mA with a
scanning range of 15°–75° at speed of 1°/min. N2 sorption isotherm was obtained at
1 3

P. Maneechakr, S. Karnjanakom
−196 °C using Quantachrome Autosorb 1. Total surface area and pore size of cata-
lyst were determined using the Brunauer–Emmett–Teller (BET) method and the Bar-
rett–Joyner–Hallenda (BJH) method, respectively. The distribution of SO3H group on
catalyst, as well as morphology of carbon sphere were observed by a scanning electron
microscope (SEM S-4800; Hitachi) equipped with a energy dispersive spectroscope
(EDS). Total acid amount on the catalyst was determined using titration. Typically,
0.2 g of catalyst with an aqueous solution of NaOH (30 mL, 0.1 M) were mixed and
stirred at ambient temperature for 1 h with a speed of 150 rpm. After centrifugal sepa-
ration, the supernatant solution was titrated by an aqueous solution of HCl (0.01 M)
using phenolphthalein as an indicator. Thermal decomposition of SO3H group on cata-
lyst was analyzed using a thermogravimetric analyzer (Mettler Toledo TGA/SDTA
851).
Catalytic testing
The catalytic conversion of fructose into EMF was performed in a three-neck round
bottom fask equipped with a refux condenser and an ultrasonic probe, as well as a
thermocouple thermometer. In each batch, the stirring speed and the frequency of the
ultrasonic probe were fxed at 700 rpm and 20 kHz, respectively. A 0.5-mmol sample
of fructose, 5 mL of ethanol, and required amount of THF and catalyst reactor was
loaded into reactor. Then, the reaction was conducted at diferent temperatures and
times in an oil bath. After fnishing the reaction, the mixture product was cooled in an
ice-bath, diluted and fltered with a 0.22 µm syringe flter. The separated spent cata-
lyst was washed several times with distilled water and ethanol to remove the adsorbed
by-products prior to reuse in the next run, and then dried at 105 °C for 12 h. The fruc-
tose and the formed products were analyzed by an Agilent 1200 HPLC chromatograph
equipped with an Aminex HPX-87H column and refractive index detector. A 0.5-mM
H2SO4 solution was used as the mobile phase at a fow rate of 0.6 mL/min and column
temperature of 60 °C. The fructose conversion and yield and selectivity of each product
were detemined based on external standard method and calculated using the following
equations:
Mole percentage of fructose reacted
Fructose conversion (%) =
Mole percentage of initial fructose
Mole percentage of product produced
Product yield (%) =
Mole percentage of initial fructose
Mole percentage of product produced
Product selectivity (%) =
Mole percentage of fructose reacted
1 3

Selective conversion of fructose into 5-ethoxymethylfurfural…
Fig. 1 Efect of reaction time
(1–8 h) on EMF produc-
tion derived from catalytic
conversion of fructose over
SO3H-CD-carbon. Reaction
conditions: 0.5 mmol of fruc-
tose, 24 mmol of THF, 5 mL of
ethanol, 50 mg of catalyst and
reaction temperature of 120 °C
Fig. 2 Efect of reaction tem-
perature (100–160 °C) on EMF
production derived from cata-
lytic conversion of fructose over
SO3H-CD-carbon. Reaction
conditions: 0.5 mmol of fruc-
tose, 24 mmol of THF, 5 mL of
ethanol, 50 mg of catalyst and
reaction time of 6 h
Results and discussion
Catalytic conversion of fructose into EMF over SO3H‑CD carbon
Figures 1 and 2 show the efect of reaction time and reaction temperature on conver-
sion of fructose in co-solvent using SO3H-CD-carbon. As shown in Fig. 1, fructose
conversion (100%) and EMF yield (63%) were achieved in 6 h via main consecu-
tive reactions including the dehydration of fructose into HMF and etherifcation of
HMF into EMF. However, yields of EMF were decreased to some extent with pro-
longation of reaction time beyond 6 h, suggesting that EMF was further converted
into other undesired by-products such as EL and humins via ethanolysis-rehydration
1 3

P. Maneechakr, S. Karnjanakom
and polymerization as observing the EL and other products (humins or soluble
polymers) selectivity increased [19, 20]. As indicated, these phenomena with simi-
lar trends were found with the result of reaction temperature (Fig. 2). Moreover, as
shown in Fig. 2, the fructose was completely converted while best EMF selectivity
was obtained at optimum reaction temperature of 120 °C. With the increase of reac-
tion temperature from 120 to 160 °C, the EMF yield was continuously decreased to
42% even though the fructose conversion kept stable at 100%, indicating that too
high of a temperature would cause the chain of side-reactions such as condensa-
tion, polymerization and decomposition, which could be clearly seen in the color
change of liquid product from brown to black. In addition, this phenomenon might
lead to the evaporation of ethanol from liquid phase, occurring the high viscosity
in system with hindering the mass transfer of mixture. It should be mentioned here
that SO3H-CD-carbon was stable at reaction temperature range used in this study,
which confrmed by TGA result in Fig. 3. As observed, the weight loss at tempera-
ture range of ~250 to ~500 °C was found, attributing to the decomposition of sul-
fonic group on catalyst [21]. The better selectivity for HMF production was found
at short reaction time (~1 h) and low reaction temperature (~100 °C). The reac-
tion route for synthesis of EMF and other products from fructose over acid catalyst
are summarized in Fig. 4. Firstly, fructose was activated by Brönsted acid site of
SO3H-CD-carbon to form HMF with water. During this step, ethyl fructose might
be possibly produced via ethanolysis and dehydration before HMF formation.Then,
HMF would be activated by Brönsted acid sites and followed by an ethanol molecule
to form EMF and water. Here, EL and humins always formed in several cases such
as too long reaction time, too high reaction temperature and overloading the catalyst
via several possible reaction pathways. For instance, epoxy groups of EMF were
protonated with acid sites to form cyclic oxonium of EMF and followed by later
encounters from the ring-opening reaction under a solution of ethanol and water to
form EL, as well as polymerization of HMF, EMF and EL to from humins [22]. It is
also possible that ultrasonic application may be related to the number of cavitation
Fig. 3 TG curve of
SO3H-CD-carbon
1 3

Selective conversion of fructose into 5-ethoxymethylfurfural…
Fig. 4 Possible reaction pathways including dehydration, etherifcation, ethanolysis-rehydration and
polymerization on conversion of carbohydrate into various products catalyzed by acid catalyst
bubbles formed in the medium, thus improving the EMF formation. Moreover, the
energy generated due to cavitation is transferred to the reaction system, which could
improve the process of interfacial area or mass transfer on the substrate towards a
fast reaction rate.
The efect of THF amount on the conversion of fructose into EMF at 120 °C for
6 h is shown in Fig. 5. Interestingly, the increase of THF amount from 0 to 36 mmol
resulted in promoting the formation of EMF while selectivity for EL and humins
production was remarkably suppressed. The THF molecules could preferentially
Fig. 5 Efect of THF amount
(0–42 mmol) on EMF produc-
tion derived from catalytic
conversion of fructose over
SO3H-CD-carbon. Reaction
conditions: 0.5 mmol of fruc-
tose, 5 mL of ethanol, 50 mg of
catalyst, reaction temperature of
120 °C and reaction time of 6 h
1 3

P. Maneechakr, S. Karnjanakom
arrange themselves in the immediate vicinity of hydrogen atoms of the hydroxyl
groups, enabling proton attack on fructose to initiate dehydration. The strong dehy-
dration ability of THF due to its anhydrous nature might also shift the equilibrium
to the product side and facilitate the water elimination from fructose. This might be
also attributed to reduction of interaction between hydrophilic surface catalyst and
EMF when more THF amount added in system, resulting in slowing the by-product
formation [8, 16]. In other words, it limited the rehydration of EMF into EL. How-
ever, increasing the THF amount from 36 to 42 mmol did not signifcantly improve
the EMF yield, indicating that optimum THF amount (36 mmol) and highest EMF
yield (74%) were obtained. Figure 6 shows the efect of catalyst amount on conver-
sion of fructose into EMF at 120 °C for 6 h. As expected, the EMF selectivity was
obviously increased with increasing of catalyst amount up to 50 mg. However, a
further increase in catalyst amount did not improve the EMF yield. This is attrib-
uted to the presence of an excessive amount of catalyst, which could lead to promot-
ing the unexpected side-reactions, especially for ethanolysis-rehydration with the
formation of other products as confrmed in EL and humins selectivity increase in
Fig. 6. In addition, it presented the uneconomic process as well. The comparisons of
one-pot synthesis of 5-ethoxymethylfurfural from fructose using SO3H-CD-carbon
with other literature are listed in Table 1. As expected and updated, the higher per-
formance of our catalyst and system were clearly found. Here, the physical efects
in terms of intense turbulence and microstreaming generated during the cavita-
tion could play a dominating role in fructose conversion, resulting in faster reac-
tion and higher EMF product when compared with the conventional system. This
could provide a facile way for further development. The physicochemical proper-
ties of SO3H-CD-carbon were also investigated since it exhibited high activity
for EMF production in our system. Figure 7 shows the XRD patterns of catalysts.
For pure CD-carbon and SO3H-CD-carbon, two difraction peaks at 15°–30° and
35°–50° appeared, corresponding to the presence of amorphous carbon composed
Fig. 6 Efect of catalyst amount
(10–90 mg) on EMF produc-
tion derived from catalytic
conversion of fructose over
SO3H-CD-carbon. Reaction
conditions: 0.5 mmol of fruc-
tose, 36 mmol of THF, 5 mL of
ethanol, reaction temperature of
120 °C and reaction time of 6 h
1 3

Selective conversion of fructose into 5-ethoxymethylfurfural…
Table 1 Comparison of maximum yield of EMF derived from fructose conversion using diferent cata-
lysts
Catalysts
Conditions
EMF yield (%)
55.0
References
[9]
Imidazolium propanesul- Refux system:
fonic acids
AlCl3
130 °C for 80 min
Refux system:
71.2
67.7
63.4
[11]
[16]
[17]
100 °C for 11 g
MIL-101-SO3H
Hydrothermal system:
130 °C for 15 h
Ar-SO3H-SBA-15
ACE pressure glass system:
116 °C for 4 h
OMC-SO3H
Fe3O4@C-SO3H
140 °C for 24 h
55.7
67.8
[26]
[27]
Hydrothermal system:
140 °C for 24 h
SO3H-CD-carbon
SO3H-CD-carbon
Ultrasonic system:
140 °C for 6 h
74.0
39.5
[This study]
[This study]
Refux system:
140 °C for 24 h
Fig. 7 XRD patterns of
SO3H-CD-carbon before and
after reactions
of randomly oriented aromatic carbon sheets [23]. Moreover, the lower intensity
of difraction peak and the slight shifting of peak to higher 2θ angle were clearly
found in SO3H-CD-carbon when compared pure CD-carbon, suggesting to the func-
tionalization of sulfonic groups on the sp2 carbon network [24]. Figure 8 shows N2
sorption isotherms of catalysts. All catalysts exhibited IUPAC type VI isotherms
with hysteresis loops, corresponding to mesoporous carbon material [25, 26]. The
SO3H-CD-carbon also exhibited lower surface area, pore volume and pore size than
CD-carbon, suggesting to the dispersion of sulfonic group on CD-carbon structure
(Table 2). The existence of sulfonic group with its well distribution on CD-carbon
1 3

P. Maneechakr, S. Karnjanakom
Fig. 8 N2-sorption isotherms
and pore-size distributions of
SO3H-CD-carbon before and
after reactions
Table 2 Physicochemical properties of various catalysts before and after reactions
Catalyst
Surface area
Pore volume
Pore size (nm)
Acid
(m2/g)
(cm3/g)
amount
(mmol/g)
CD-carbon
196
162
147
50
0.82
0.68
0.55
0.39
0.21
0.54
0.11
0.75
0.48
7.5
6.9
5.1
30.0
27.8
9.7
4.2
9.2
8.4
–
SO3H-CD-carbon
Spent SO3H-CD-carbona
Amberlyst-35
1.82
1.25
5.20
1.08
0.80
0.75
0.43
0.36
Spent Amberlyst-35a
SiO2-Tosic acid
Spent SiO2-Tosic acide
Al2O3
36
279
102
228
154
Spent Al2Oa3
aSpent catalyst obtained after recyclability test for eight cycles
Fig. 9 SEM-EDS of a CD-carbon and b SO3H-CD-carbon
1 3

Selective conversion of fructose into 5-ethoxymethylfurfural…
was clearly observed in SEM–EDS result (Fig. 9). Moreover, SO3H-CD-carbon and
pure CD-carbon also presented the same morphology of spherical shape.
Catalyst reusability and comparison between SO3H‑CD‑carbon and commercial
catalysts
The recycling of catalyst is an important parameter that can afect the overall EMF
production process. After the optimum conditions were obtained from out system,
the catalyst was reused for eight cycles on fructose conversion at 120 °C for 6 h. It
should be mentioned here that a blank reaction test was also performed in this con-
dition without using catalyst and the result found that no conversion of fructose into
any products were occurred, indicating that the existence of acid catalyst was still
necessary in this system. As shown in Fig. 10, no obvious reduction in catalytic per-
formance based on EMF yield (~74%) was found over frst to ffth reaction cycles.
However, the slight decrease in EMF yield was observed since recycling test was
carried out after ffth reaction cycle. This is attributed to leaching of the sulfonic
group from the catalyst and the adsorption of humins by-product on catalyst sur-
face which resulted in decrease of surface area and pore size of catalyst, as well as
mass transfer of intermediates to inner of catalyst structure [27], confrming by the
results of acid amount and textural properties of spent catalyst (Table 2). In other
words, the ethanolysis-rehydration were initially suppressed. These result indicates
that SO3H-CD-carbon possessed excellent reusability and stability for fve cycles.
Moreover, to evaluate the SO3H-CD-carbon as a promising catalyst for further
utilization in practical process, comparing its catalytic activity and reusability
with various commercial solid acid catalysts was also investigated (Fig. 10). It is
found that when Amberlyst-35, SiO2-Tosic acid were applied for catalytic conver-
sion of fructose, the highly obtained EMF yields were 69% and 66%, respectively.
However, even Amberlyst-35 had higher acid amount than SO3H-CD-carbon, but
lower EMF yield still obtained, resulting from its excessive acid amount, promot-
ing the formation of by-products. This is also believed that the interior layer of the
SO3H-CD-carbon sphere consisted of polyaromatic groups while the exterior layer
consisted of hydrophilic groups such –SO3H, phenolic –OH and –COOH groups,
which could contribute to the mass transfer, as well as the synergetic efect, lead-
ing to better activity and stability [28, 29]. Furthermore, EMF yield was decreased
to some extent after the frst reaction cycle, suggesting that facile leaching of the
sulfonic group in both catalysts, especially for Amberlyst-35, occurred while strong
adsorption of hydrophilic oligomeric by-products was found as well, especially for
SiO2-Tosic acid, and these phenomena could be verifed by physicochemical prop-
erties of fresh and spent commercial catalysts in Table 2. It should be mentioned
here that the rapid deactivation of these commercial catalyst may be resulted from
existence of highly hydrophilic properties, which favored to selectivity create an
appropriate environment for water adsorption, leading to poor reusability. Thus, the
regeneration process were further required for these spent commercial catalysts. In
the case of Al2O3, a lowest yield of EMF (12.6%) was obtained, which might be
explained by its low acid strength. However, better selectivity for HMF production
1 3

P. Maneechakr, S. Karnjanakom
Fig. 10 Reusability of a
SO3H-CD-carbon, b Amber-
lyst-35, c SiO2-Tosic acid and
d Al2O3 on EMF production
derived from catalytic conver-
sion of fructose. Reaction condi-
tions: 0.5 mmol of fructose,
36 mmol of THF, 5 mL of
ethanol, 50 mg of catalyst, reac-
tion temperature of 120 °C and
reaction time of 6 h
1 3

Selective conversion of fructose into 5-ethoxymethylfurfural…
was also found in Al2O3 when compared with other catalysts, probably due to only
selective promoting of fructose dehydration in frst step by Lewis acid site of Al2O3.
Based on these results, SO3H-CD-carbon could be considered as a promising cata-
lyst for EMF production from one-pot conversion of fructose in practical process.
Conclusions
In summary, the fructose conversion into EMF catalyzed by SO3H-CD-carbon was
studied using an ultrasonic system. The SO3H-CD-carbon also exhibited the reason-
able properties such acid site concentration, surface area and pore size for selective
production of EMF. The use of THF as co-solvent signifcantly resulted in suppress-
ing the formation of EL and humins via EMF ethanolysis-rehydration and polym-
erization. The optimum conditions such as 0.5 mmol of fructose, 36 mmol of THF,
5 mL of ethanol, 50 mg of catalyst, reaction temperature of 120 °C and reaction time
of 6 h were successfully achieved, providing a maximum EMF yield of 74%. The
SO3H-CD-carbon could be efectively reused for fve cycles without reduction of
EMF and regeneration.
Acknowledgements The authors wish to acknowledge Department of Chemistry, Faculty of Science,
Rangsit University for supporting all instruments and chemicals.
References
1. H. Wang, T. Deng, Y. Wang, Y. Qi, X. Hou, Y. Zhu, Bioresour. Technol. 136, 394 (2013)
2. L. Jiang, L. Zhou, J. Chao, H. Zhao, T. Lu, Y. Su, X. Yang, J. Xu, Appl. Catal. B 220, 589 (2018)
3. H. Li, S. Saravanamurugan, S. Yang, A. Riisager, Green Chem. 18, 726 (2016)
4. F.N.D.C. Gomes, F.M.T. Mendes, M.M.V.M. Souza, Catal. Today 279, 296 (2017)
5. P. Wataniyakul, P. Boonnoun, A.T. Quitain, M. Sasaki, T. Kida, N. Laosiripojana, A. Shotipruk,
Catal. Commun. 104, 41 (2018)
6. G. Sampath, S. Kannan, Catal. Commun. 37, 41 (2013)
7. M. Zuo, K. Le, Y. Feng, C. Xiong, Z. Li, X. Zeng, X. Tang, Y. Sun, L. Lin, Ind. Crops Prod. 112, 18
(2018)
8. Y. Yang, M.M. Abu-Omar, C. Hu, Appl. Energy 99, 80 (2012)
9. G.A. Kraus, T. Guney, Green Chem. 14, 1593 (2012)
10. H. Guo, X. Qi, Y. Hiraga, T.M. Aida, R.L.S. Jr, Chem. Eng. J. 314, 508 (2017)
11. B. Liu, Z. Zhang, K. Huang, Z. Fang, Fuel 113, 625 (2013)
12. X. Zhang, Y. Zhao, Q. Yang, J. Catal. 320, 180 (2014)
13. Y. Liu, H. Li, J. He, W. Zhao, T. Yang, S. Yang, Catal. Commun. 93, 20 (2017)
14. M. Shaikh, S.K. Singh, S. Khilari, M. Sahu, K.V.S. Ranganath, Catal. Commun. 106, 64 (2018)
15. A. Liu, Z. Zhang, Z. Fang, B. Liu, K. Huang, J. Ind. Eng. Chem. 20, 1977 (2014)
16. X. Liu, H. Li, H. Pan, H. Zhang, S. Huang, K. Yang, W. Xue, S. Yang, J. Energy Chem. 25, 523
(2016)
17. G. Morales, M. Paniagua, J.A. Melero, J. Iglesias, Catal. Today 279, 305 (2017)
18. R.S. Thombal, V.H. Jadhav, Appl. Catal. A 499, 213 (2015)
19. S.J. Dee, A.T. Bell, Chemsuschem 4, 1166 (2011)
20. J.A. Melero, G. Morales, J. Iglesias, M. Paniagua, B. Hernández, S. Penedo, Appl. Catal. A 466,
116 (2013)
21. L. Hu, X. Tang, Z. Wu, L. Lin, J. Xu, N. Xu, B. Dai, Chem. Eng. J. 263, 299 (2015)
22. D. Song, Y. Sun, Q. Zhang, P. Zhang, Y. Guo, J. Leng, Appl. Catal. A 546, 36 (2017)
1 3

P. Maneechakr, S. Karnjanakom
23. M. Hara, T. Yoshida, A. Takagaki, T. Takata, J.N. Kondo, S. Hayashi, K. Domen, Angew. Chem.
Int. Ed. 43, 2955 (2004)
24. H. Yu, S. Niu, C. Lu, J. Li, Y. Yang, Energy Convers. Manag. 126, 488 (2016)
25. R. Li, J. Zhao, D. Han, X. Li, Catal. Commun. 97, 116 (2017)
26. J. Wang, Z. Zhang, S. Jin, X. Shen, Fuel 192, 102 (2017)
27. Z. Yuan, Z. Zhang, J. Zheng, J. Lin, Fuel 150, 236 (2015)
28. J. Zhao, C. Zhou, C. He, Y. Dai, X. Jia, Y. Yang, Catal. Today 264, 123 (2016)
29. J. Wang, W. Xu, J. Ren, X. Liu, G. Lu, Y. Wang, Green Chem. 13, 2678 (2011)
Afliations
Panya Maneechakr1 · Surachai Karnjanakom1
*
Panya Maneechakr
panya.m@rsu.ac.th
Surachai Karnjanakom
surachai.ka@rsu.ac.th
1
Department of Chemistry, Faculty of Science, Rangsit University, Pathumthani 12000, Thailand
1 3