X. Li et al.
Keywords Ethyl levulinate · γ-valerolactone · Zr-GA · Catalytic transfer hydrogenation
ions [35]. Gallic acid is a kind of polyphenol compound,
in anti-oxidation and medicine [36]. In this work, we used
of Zr-GA-x catalysts with diferent molar ratios in N,N-
dimethylformamide and triethylamine. Using alcohol as a
solvent and H-donor, LA and its esters were converted to
GVL through CTH. It was found that the prepared Zr-GA-x
can catalyze the CTH reaction to provide a satisfactory yield
of GVL. As far as we know, this is the frst report about the
organic–inorganic hybrid catalyst Zr-GA-x has been used in
the CTH reaction of LA and its esters to produce GVL, and
the catalyst has the advantages of wide source of raw materi-
als, easily assemble synthesis and high stability.
1 Introduction
Due to the increasingly serious problems between the
exploitation and use of fossil fuels and the environment,
economy and politics, one of the most serious challenges
of the 21st century is to replace fossil fuels with more sus-
tainable alternatives [1, 2].As the world’s most important
sustainable renewable green resource, biomass accounts for
about 14% of the world total annual energy consumption. It
is the fourth largest energy source after oil, coal, and natural
gas, and becoming a kind of renewable substitutes that can
all countries [3, 4]. So far, various value-added chemicals
have been obtained from biomass, such as 5-hydroxymeth-
ylfurfural, lactic acid, furfural, furfuryl alcohol, levulinic
acid (LA), alkyl levulinate, and γ-valerolactone (GVL), etc.
[5–11]. Among them, GVL has the property of non-toxic
and biodegradable, which can be used as a green solvent
chemicals and high-performance liquid fuels [12–14].
catalytic transfer hydrogenation (CTH) reactions. In this
reaction, the alcohols used as a solvent and hydrogen source,
and fnally dehydrogenated to a ketone. CTH is a typical
Meerwein–Ponndorf–Verley reaction and it is widely used
in the reduction of carbonyl compounds. The use of a large
number of safe secondary alcohols instead of dangerous
gaseous hydrogen as H-donor makes it an ideal reduction
technology for carbonyl compounds [15–17]. The methods
of producing GVL mainly include direct hydrogenation
and transfer hydrogenation. Between them, direct hydro-
genation uses H2 as a hydrogen source, which is not only
costly, but has safety risks. At present, most of the research-
ers have solved the above-mentioned problems by means of
transfer hydrogenation, using LA and its esters to prepare
GVL through CTH. A large number of catalysts have been
reported for this reaction, such as Zr-containing zeolite,
ZrO2, MOFs, GO, zirconium phosphates, supported heter-
lysts, etc. [18–26]. Among them, zirconium-based materials
applications, in addition to being used for catalysis, they
can also be used for adsorption and separation [27, 28]. So
lysts have been developed for the CTH reaction of LA and
its esters, such as Zr-PhyA, Zr-HBA, Zr-CA, Zr-TMPA, Zr-
TPPA-3, Zr-HPAA, etc. [29–34].
2 Experimental Section
2.1 Chemicals
Methyl levulinate (ML), ethyl levulinate (EL), butyl levuli-
nate (BL), LA, ZrCl4, gallic acid (GA), GVL, N,N-dimeth-
ylformamide (DMF), triethylamine, methanol, ethanol,
n-propanol, isopropanol, 1-butanol, tert-butanol, 3-pentanol,
benzoic acid, 2,6-lutidine, pyridine and naphthalene are of
analytical grade and used without further treatment.
2.2 Catalyst Preparation
The preparation method of the as-prepared catalyst was
referred to the previous literature and was modifed [29]. In
a general procedure, 0.476 g (2 mmol) of ZrCl4 and 0.344 g
(1 mmol) of GA dissolve in DMF (20 mL) with the aid of
ultrasound, respectively. Then, the GA solution was added
dropwise to the ZrCl4 solution. After the mixture was clari-
fed, 3 mL of triethylamine was added dropwise, stirred vig-
orously at room temperature for 2 h and then aged at 80 °C
for 8 h. The mixed solution after aging was fltered, washed
with DMF and ethanol. The obtained solid was placed in a
vacuum drying oven at 80 °C for 14 h and then grounded to
obtain Zr-GA. For comparison, diferent Zr-GA-x catalysts
were synthesized by changing the raw material ratio, using
x mmol of ZrCl4 and 1 mmol of GA (x=1, 2, 3, 4), named
Zr-GA-1, Zr-GA-2/Zr-GA, Zr-GA-3, Zr-GA-4, respectively.
2.3 Catalyst Characterization
ral sources of chemical substances is becoming more and
more important in the feld of synthetic chemistry, especially
Fourier transform infrared (FT-IR) spectra were detected
with a Nicolet 360 FT-IR instrument (KBr pellet) in the
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