J. Lai et al.
both chemicals and fuels to the world [2, 3]. Therefore, great
attention has been paid to the development of the eꢀective
methods for the transformation of biomass into biofuels and
value-added chemicals, which has emerged as one of the
promising ways to alleviate the current reliance on fossil
fuel sources [4, 5].
Synthesis of GVL from levulinic acid and its ester via the
use of formic acid as the hydrogen donor was generally per-
formed over noble metal catalysts such as Au and Ru cata-
lysts [19]. Obviously, the use of noble metals and the cor-
rodibility of formic acid under harsh conditions have limited
the application of formic acid for the transfer hydrogenation
of levulinic acid and its ester. Compared with formic acid,
the use of alcohols as the hydrogen source for the transfer
hydrogenation of levulinic acid and its ester into GVL has
received much more attention in recent years. Up to now,
several catalytic systems have been developed for the trans-
fer hydrogenation reactions of levulinic acid and its esters to
GVL using various alcohols as the hydrogen source, includ-
Through careful design of catalytic systems, many kinds
of important chemicals as well as the liquid fuels have been
successfully derived from biomass resources [6]. Among
them, there has been a growing attention on the synthesis
of γ-valerolactone (GVL), owing to its versatile application
in many ꢁelds [7]. GVL has been identiꢁed as a green and
renewable solvent for chemicals reaction, and it was reported
that GVL sometimes could improve the performance of bio-
mass conversion and organic transformations in terms of
the catalytic eꢂciency as well as the product puriꢁcation
®
ing homogeneous Ru complexes, RANEY Ni, and Lewis
acids especially Zr based catalysts [20, 21]. However, some
drawbacks still need to overcome, such as harsh reaction
temperatures, long reaction time, low catalyst reactivity and
stability. Therefore, the development of new eꢂcient and
cost-eꢀective methods for the production of GVL is a highly
attractive task.
[
8, 9]. GVL can be used as an additive suitable for liquid
fuels, perfumes, and food [7]. More importantly, GVL can
serve as the intermediate for the production of gasoline and
diesel fuels (e.g., C8–C18 alkanes and 2-methyltetrahydro-
furan) and valuable chemicals, such as 1,4-pentanediol,
methyl pentenoate [10], and ionic liquids [11]. Owing to
the wide application of GVL, the synthesis of GVL from
renewable carbohydrates or the biomass-derived chemicals
have been extensively studied in recent years [12–14]. The
direct and simple way to produce GVL is the hydrogenation
of levulinic acid (LA) and its esters, which can be readily
synthesized from lignocellulosic biomass through multiple
catalytic steps in the presence of acid catalysts. However, the
hydrogenation step posed a challenge to researchers with the
combined eꢀect of the carbonyl and ester groups on selective
hydrogenation.
Herein we reported the synthesis and characterization of
a graphene oxide supported ZrO catalyst (ZrO /GO), con-
2
2
taining Lewis acidic zirconium sites and Bronsted acidic
carboxyl and hydroxyl groups, under hydrothermal method.
The as-synthesized ZrO /GO catalyst showed high catalytic
2
activity in the transfer hydrogenation of ethyl levulinate into
GVL. Obviously, our developed methods demonstrated some
advantages such as the use of easily preparative non-noble
metal catalyst with low cost, and did not use the explosive
hydrogen.
The catalytic reduction of levulinic acid and its esters
have been generally been performed in the presence of
metal catalysts, especially noble metal catalysts by the use
of hydrogen [15, 16]. Although hydrogen is a clean hydrogen
source, these catalytic systems demonstrated some draw-
backs such as the low solubility of molecular hydrogen in
most solvents, the need of high pressure, the use of expen-
sive noble metal catalyst, and the low stability of the metal
catalyst. For example, Yang et al. prepared porous carbon
nanoꢁbers encapsulated Ru nanoparticles for the transfer
hydrogenation of LA into GVL, which was performed at
2 Experimental Section
2.1 Materials and Methods
All other chemicals were purchased from Aladdin Chemicals
Co. Ltd. (Beijing, China). All solvents were purchased from
Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).
All of the chemicals and solvents were used directly without
puriꢁcation.
2.2 Catalyst Preparation
1
50 °C and 45 bar H pressure [17].
2
In recent years, catalytic reactions with other hydrogen
Graphene oxide (GO) was prepared by a modiꢁed Hummer’s
method [22]. Brieꢃy, graphite, NaNO and 98.0 wt% H SO
donors such as formic acid and alcohols instead of hydrogen
have received much interest [18]. This process can avoid
the use of explosive hydrogen; thus, it seems to be more
economical and much safer. In the process of the transfer
hydrogenation of levulinic acid and its esters into GVL, the
hydrogen donors were mainly used formic acid and alcohols.
It is highly attractive to perform the transfer hydrogenation
with formic acid, as it is also renewable from carbohydrates.
3
2
4
were ꢁrstly stirred at 0 °C for 30 min. Then KMnO was
4
added into the mixture slowly and the mixture was continu-
ously stirred at 0 °C for 2 h. After the addition of KMnO ,
4
the mixture was stirred for 2 h at 0 °C, subsequently at 25 °C
for 5 days. After that, 98 wt% H SO was added dropwise
2
4
and then stirred at 98 °C for 2 h. The temperature was then
reduced to 25 °C and the mixture was stirred for another
1
3