Production of cyclopentanone from furfural over Ru/C with Al11.6PO23.7 and application in the synthesis of diesel range alkanes

Article abstract of DOI:10.1039/c8ra08757a

The bio-based platform molecule furfural was converted to the high value chemical cyclopentanone over Ru/C (0.5?wt%) and Al_11.6PO_23.7 catalysts in good yield (84%) with water as the medium. After screening the reaction conditions, the selectivity for cyclopentanone and cyclopentanol could be controlled by adjusting the hydrogen pressure at the temperature of 433 K. Herein, we propose a new mechanism for the synergistic catalysis of a Bronsted acid and Lewis acid for the conversion of furfural to cyclopentanone through the cyclopentenone route, which is catalyzed by Ru/C and Al_11.6PO_23.7. In addition, based on cyclopentanone, higher octane number cyclic alkanes (>85% selectivity), which are used as hydrocarbon fuels, were synthesized via a C-C coupling reaction followed by hydrodeoxygenation.

Full text of DOI:10.1039/c8ra08757a

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PAPER
Production of cyclopentanone from furfural over
Ru/C with Al PO
and application in the
1
1.6
23.7
Cite this: RSC Adv., 2018, 8, 37993
synthesis of diesel range alkanes†
Tao Shen, Ruijia Hu, Chenjie Zhu, *abc Ming Li, Wei Zhuang,
ab
ab
ab
ab
ab
Chenglun Tang and Hanjie Ying *abc
The bio-based platform molecule furfural was converted to the high value chemical cyclopentanone over
Ru/C (0.5 wt%) and Al11.6PO23.7 catalysts in good yield (84%) with water as the medium. After screening the
reaction conditions, the selectivity for cyclopentanone and cyclopentanol could be controlled by adjusting
the hydrogen pressure at the temperature of 433 K. Herein, we propose a new mechanism for the
synergistic catalysis of a Bronsted acid and Lewis acid for the conversion of furfural to cyclopentanone
through the cyclopentenone route, which is catalyzed by Ru/C and Al11.6PO23.7. In addition, based on
cyclopentanone, higher octane number cyclic alkanes (>85% selectivity), which are used as hydrocarbon
fuels, were synthesized via a C–C coupling reaction followed by hydrodeoxygenation.
Received 23rd October 2018
Accepted 26th October 2018
DOI: 10.1039/c8ra08757a
rsc.li/rsc-advances
24–29
fuel energy and materials (Scheme 1).
Traditionally, CPO and
Introduction
CPL are synthesized via the ketonic decarboxylation of adipic
With the depletion of petroleum resources, the exploitation of acid or catalytic cyclization of 1, 6-hexanediol, followed by
1,2
30,31
renewable resources has drawn increasing attention. Biomass hydrogenation.
Recently, based on lignocellulose, a new route
is a renewable resource due to its abundant sources and short was proposed, in which furfural was converted to CPL with no
3,4
growth periods. Recently, accompanied by the successful petroleum compounds as the substrates.
synthesis of platform molecules from lignocellulose, the cata-
Inspired by the previous work of the Hronec group,
32–34
new
lytic conversion technology of transforming biomass into high- methods have been reported regarding furfural or furfuryl
value chemicals has shown great progress. Various furan-based alcohol aer hydrogenation and following rearrangement in
derivatives can be produced via the acid-catalyzed dehydration aqueous media to synthesize CPO. These studies showed that
5–9
of cellulose and hemicellulose. For example, furfural (FFA) hydrogenation metal catalysts (e.g., Pt/C, Pd–Cu/C and Ni-based
10
can be produced on an industrial scale from biomass. Based catalysts) have good selectivity for CPO. Besides, hydrogenation
on this, the catalytic hydrogenation and dehydration of furfural metal-based solid acid and solid base were also found to have
to a range of nonpetroleum-derived chemicals is signicant, good performance for the synthesis of CPO and CPL from
11
12
including 2-methyl furan (2-MF), furfural alcohol (FAL), tet- furfural, for example, Ru/MIL-101 (Materials of Institute Lav-
38
1
3
14
35
36
37
rahydrofurfuryl alcohol (THFA), tetrahydrofuran (THF), 2- oisier), Ru/carbon nanotubes (CNTs), Au/TiO
2
,
Ni/CNTs,
1
5
16
39
methyl tetrahydrofuran (MTHF), levulinic acid (LA), and and Ni/Cu–Mg–Al hydrotalcite. In addition, alloy catalysts
17,18
pentanediol.
the elds of materials, fuels and pharmaceuticals.
These chemical intermediates can be used in were also found to be efficient catalysts for the conversion of
19–23
Cyclopentanone (CPO) is another hydrogenation product of
furfural, and cyclopentanol (CPL) is the depth hydrogenation
product of CPO. CPO and CPL are versatile chemical intermedi-
ates that can be used to synthesize medicines, rubber chemicals
and fragrance chemicals, which are applied in pharmaceuticals,
a
College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University,
Nanjing, China. E-mail: zhucj@njtech.edu.cn; yinghanjie@njtech.edu.cn
b
National Engineering Technique Research Center for Biotechnology, Nanjing, China
c
Jiangsu National Synergetic Innovation Center for Advanced Bio-Manufacture,
Nanjing, China
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c8ra08757a
Scheme 1 Methods for the conversion of CPO and CPL from biomass
and their application.
1
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furfural converted CPO (e.g., Ni–Cu/SBA-15, Cu–Co alloy,
CuZnAl and CuNiAl hydrotalcite ). Considering the reported furfural. In this process (Scheme 2), furfural is rstly hydro-
catalysts, higher selectivity for CPL can be obtained while in genated to furfuryl alcohol. If furfuryl alcohol undergoes
catalytic systems consisting of hydrogenation catalyst and solid a Piancatelli rearrangement, the product will be 4-hydroxy-2-
Paper
40
41
hydrogenation and Piancatelli rearrangement product of
42,43
37
acid.
cyclopentenone (HCP), which will then undergo in-depth
Although some pioneering works have been performed in hydrogenation and dehydroxylation to produce CPO or CPL.
this area, this eld is still lacking regarding some detailed However, furfuryl alcohol in a Bronsted acid environment is
processes. For example, the understanding of the mechanism in dehydroxylated and undergoes a ring opening rearrangement
the cyclization process of the product is still in its infancy. reaction, and then, levulinic acid and in-depth hydrogenation
49
Herein, we report the design of a new catalyst, aluminium compounds are obtained as the products. Additionally, self-
phosphate (Al11.6PO23.7) and Ru/C, which is used in an aqueous condensation of CPO can occur while in an acidic environ-
environment to give a good yield of CPO and CPL. Additionally, ment. These are the major factors that limit the yield of CPO.
the selectivity of the targeted product could be controlled by The hydrogenation metal catalyst is another factor that limits
adjusting the hydrogen pressure. Al11.6PO23.7 is a bifunctional the yield of the product in this reaction. A higher hydrogenation
44
catalyst that has both an acid site and base site; thus, we could efficiency catalyst would convert furfural into THFA, which is
36
adjust the mole ratio of Al and P to control the amount of acid irreversibly transformed into CPO. To our delight, aer
and base, and also control the ratio of Lewis acid and Bronsted screening the hydrogenation metal and solid acid catalyst
acid. According to these properties, different mole ratios of Al (entries 1–10), we found that aluminium phosphate and Ru/C
and P catalysts were prepared to study the inuence factors and were favorable catalysts for this reaction.
cyclization mechanism during the hydrogenation of furfural in
According to the previous research, solid acid is an impor-
aqueous media. This is a novel and efficient catalytic system in tant factor that inuences the selectivity of LA and others.
this process, which, to the best of our knowledge, has not been Considering all of the factors in the rearrangement process, we
previously reported in this area.
CPO and 2-MF are novel products from the hydrogenation of Al and P aluminium phosphate solid acid catalysts as ring
furfural. Both are C5 feedstocks for the synthesis of long carbon opening and rearrangement catalysts. Among them, HfO has
2 2
screened HfO and TFA/SiO as well as different mole ratios of
2
cyclic alkanes. In our previous reports, carbonyl compounds a pure Lewis acid site, TFA/SiO is representative Bronsted acid
2
through the C–C coupling reaction consisting of aldol conden- catalyst, and aluminium phosphate has an adjustable ratio of L/
sation or HAA (hydroxyalkylation and alkylation) reaction with B acid sites. From the results presented in Table 1 (entries 1–7),
furan-based derivatives were prepared as fuel precursors, which we found that HfO
2 2
and TFA/SiO had poor selectivity for CPO
were applied to the synthesis of liquid hydrocarbon fuels and CPL. This phenomenon illustrated that the cyclization
45–47
through hydrodeoxygenation.
Here, we design a new route rearrangement is not a simple Lewis or Bronsted acid catalyzed
for the synthesis of cyclic alkanes for use in diesel range fuels rearrangement reaction. However, aer screening different
from the hydrogenation product of furfural.
mole ratios of Al- and P-type aluminium phosphate catalysts, we
found that aluminium phosphate well-catalyzed the rearrange-
ment. Additionally, the higher the molar ratio of the Al- and P-
type aluminium phosphate catalyst, the better the selectivity for
CPL and CPO. To determine the ultimate mole ratio of Al and P
Results and discussion
Hydrogenation of furfural to CPO or CPL
for this catalyst, we used 20 portions of Al(NO
3 3 2
) $9H O and 1
Building on the result of furfural aer hydrogenation, FAL and
THFA are the normal hydrogenation products.
and basic reaction conditions, dehydroxylation and ring
opening rearrangement products (e.g., FAL, THFA, MTHFA, LA,
portion of (NH HPO to prepare the aluminium phosphate
4
)
2
4
1
7,18
Under acidic
catalyst. Aer XPS analysis of these catalysts (Fig. S1†), the
maximum mole ratio of Al and P was determined to be 11.6 and
the atomic levels of O 1s, Al 2p and P 2p were 50.33%, 24.75%
and 2.12%, respectively (Fig. S1†).
1
6,19–23
and pentanediol) can be obtained, respectively.
CPO is the
Aluminium phosphate is a solid acid-base bifunctional
4
5
catalyst, as discussed in our previous reports. Aer NH
and CO -TPD tests (Fig. S2†), the amount of acidic and basic
Al11.6PO23.7 was found to be 1.211 mmol g and 0.705 mmol
3
-TPD
2
ꢀ1
ꢀ1
g
, respectively. Also, the ratio of Lewis/Bronsted acid can be
adjusted by changing the mole ratio of Al and P. Different mole
ratios of Al and P (e.g., 0.5, 1, 2, 5, and 20) aluminium phosphate
catalysts were prepared to test in this reaction. Aer XPS anal-
ysis of these catalysts, the molecular formula of the different
mole ratio Al and P aluminium phosphate catalysts were found
4
to be AlP1.2O , Al1.1PO4.2, Al2.1PO6.4, Al5.3PO12, Al11.6PO23.7. From
the results presented in Table 1 (entries 3–7), the maximum
mole ratio Al and P catalyst, Al11.6PO23.7, showed the best
selectivity for CPO and CPL. Considering the inuence of the
Scheme 2 Methods to obtain hydrogenation products from furfural.
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a
Table 1 Results of the hydrogenation of furfural catalyzed by different catalysts
Product (selectivity)
LA +
Entry
Catalyst
Solvent
Temp.
Con. (FFA)
FAL
CPO
CPL
THFA
others
1
2
3
4
5
6
7
8
Ru/C + TFA/SiO
2
H
H
H
H
H
H
H
H
H
H
H
H
H
2
2
2
2
2
2
2
2
2
2
2
2
2
O
O
O
O
O
O
O
O
O
O
O
O
O
433 K
433 K
433 K
433 K
433 K
433 K
433 K
433 K
433 K
433 K
433 K
433 K
433 K
433 K
433 K
413 K
393 K
453 K
100%
100%
100%
100%
100%
100%
100%
100%
100%
90%
100%
100%
96%
100%
100%
100%
100%
100%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
0%
5%
4%
3%
0%
0%
0%
0%
1%
90%
78%
3%
70%
0%
0%
3%
0%
0%
34%
46%
47%
64%
72%
74%
84%
56%
68%
0%
4%
74%
5%
0%
0%
27%
32%
13%
17%
11%
10%
6%
24%
24%
2%
7%
4%
4%
98%
96%
6%
76%
12%
39%
17%
36%
19%
17%
16%
10%
20%
17%
8%
Ru/C + HfO
Ru/C + AlP1.2
2
O
4
Ru/C + Al1.1PO4.2
Ru/C + Al2.1PO6.4
Ru/C + Al5.3PO12
Ru/C + Al11.6PO23.7
RANEY® Ni + Al11.6PO23.7
Pd/C + Al11.6PO23.7
Pt/C + Al11.6PO23.7
Ru/C + Al11.6PO23.7
Ru/C + Al11.6PO23.7
Ru/C + Al11.6PO23.7
Ru/C + Al11.6PO23.7
Ru/C + Al11.6PO23.7
Ru/C + Al11.6PO23.7
Ru/C + Al11.6PO23.7
Ru/C + Al11.6PO23.7
9
b
10
11
12
13
14
15
16
17
18
c
11%
19%
21%
2%
d
e
MeOH
THF
H
H
H
4%
b
b
2
2
2
O
O
O
78%
3%
72%
13%
21%
16%
a
Reaction conditions: Furfural (20 mmol), hydrogenation metal catalyst (0.5 wt%, 0.25 g) and solid acid (0.25 g), 4 MPa H
2
, reacted at the given
pressure.
b
c
temperature for 4 h. The products were analyzed and detected via HPLC. Reacted for 8 hours. Reacted at 2 MPa H
2
d
e
Hydrogenation metal catalyst respect to 0.25 wt%. Substrate furfural respect to 40 mmol.
ratio of Lewis/Bronsted acid and that Al11.6PO23.7 had the best controlled at 2 MPa, which indicates that the selectivity of CPL
catalytic properties, the pyridine-adsorbed infrared spectra were or CPO can be controlled by adjusting the hydrogen pressure.
analyzed to characterize the different molar ratio aluminium Also, we decreased the amount of hydrogenation metal catalyst
phosphate catalysts at temperatures of 313 K and 433 K (Fig. 1). to 0.25 wt% and increased the amount of substrate to 40 mmol,
From the results presented in Fig. 1 and Table S1,† we found as seen from Table 1, entries 12–13, and we found that a change
that Al11.6PO23.7 had the highest ratio of L/B at the reaction in the amount of hydrogenation metal catalyst has little inu-
temperature. This result showed that a high amount of Lewis ence on the yield of CPL. However, CPO was detected as the
acid with a small amount of Bronsted acid can promote the major product and furfural had poor conversion with an
cyclization rearrangement reaction. However, the pure Lewis
acid catalyst HfO
2
had the poor selectivity for CPO. This
phenomenon showed that the conversion of furfural to CPO
occurs via the synergistic catalysis of a Lewis acid and Bronsted
acid and that the catalyst must have a moderate ratio of L/B acid
at the reaction temperature.
Besides the inuence of the solid acid, the hydrogenation
metal is another factor that limits the yield of CPL. As observed
from Table 1 (entries 7–10), aer comparing different hydro-
genation metal catalysts, we found that Ru/C was the best
catalyst for this reaction. RANEY® Ni and Pd/C had high
hydrogenation activity, which was expressed as higher selec-
tivity for THFA as the ultimate product. Furthermore, Pt/C had
poor hydrogenation activity in this process since furfural was
not completely converted and no CPL product was detected
aer 8 hours. In addition, different reaction conditions were
tested for this reaction. From Table 1, Entry 11, we found CPO
as the major product when the hydrogen pressure was
Fig. 1 Pyridine adsorption FT-IR spectroscopy result of different mole
ratios of Al and P aluminium phosphate catalyst.
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increase in the amount of substrate under the same reaction
To research the in-depth process of the hydrogenation of
conditions. This phenomenon proved that hydrogen pressure is furfural to CPO or CPL, different reaction conditions and
a major factor in the yield of CPO. Additionally, it was clearly substrates were used to examine the mechanism of the cycli-
found that the cyclization rearrangement occurred in the zation process at different reaction times. As observed from
aqueous environment from the result in the Table 1, entries 8, Fig. 2(a), an interesting phenomenon was found that differed
14–15. Herein, MeOH and THF, as a proton organic solvent and from the previous report. In the previous work on the prepara-
non-protonic organic solvent, were tested in this reaction, tion of CPO and CPL, furfural was rst converted to furfuryl
respectively. From the results, we found that THFA was the alcohol, followed by Piancatelli rearrangement to HCP and
main product obtained in both solvents. Additionally, the converted to CPO via hydrogenation and dehydroxylation.
reaction temperature is another factor that inuenced the However, from the result shown in Fig. 2(a), no CPO or CPL was
major products. From the result in Table 1, entries 8, 16–18, we obtained with furfuryl alcohol as the substrate at 433 K with Ru/
found that the temperature determined the reaction speed and C and Al11.6PO23.7 as the catalyst. The hydrogenation of furfuryl
whether the reaction could be carried out or not. From Table 1, alcohol was very fast, and within 20 minutes all of the furfuryl
entries 16–17, we found that for the cyclization rearrangement alcohol was converted to levulinic acid (LA), tetrahydrofurfuryl
to occur, the reaction temperature had to be over 393 K, and we alcohol (THFA) and others. This result is contrary with the
also found that a higher temperature could increase the reac- previous mechanism of the hydrogenation of furfural to CPO. In
tion speed.
addition, different temperatures and hydrogen pressures were
Also, termination of this reaction did not occur during 4 hours tested using furfural as the substrate. From the results shown in
at a temperature of 413 K. In addition, the higher temperature Fig. 2(b), we found that at 393 K, furfural could not be converted
promoted the reaction process, but decreased the selectivity of to CPO. Also, we found that furfural was rstly completely
the target product. For example, compared with the lower reac- converted to furfuryl alcohol in this process, followed by the
tion temperature, more LA and other products were detected at conversion of furfuryl alcohol to THFA at a fast rate. Further-
the temperature of 453 K (Table 1, Entry 18). Hence, for the more, conversion of furfuryl alcohol to LA and others was not
efficient catalysts Ru/C and Al11.6PO23.7 with water as the medium restricted to these conditions, and the speed at which furfuryl
at the temperature of 433 K, CPL or CPO can be obtained as the alcohol was converted to LA and others was promoted by a high
main product. Furthermore, the catalysts can be recovered by temperature. Comparing Fig. 2(a) and (b), we can infer that FAL

ltration and washed with methanol aer the reaction. From the converted to THFA and others at a fast speed under the heating
results shown in Fig. S6,† it is observed that these catalysts can be reactor conditions, which is the reason why no targeted prod-
reused six times and maintain their catalytic efficiency. ucts were obtained using FAL as the substrate. In addition, from
Fig. 2 Conversion and selectivity of different reaction conditions at different times. (a) Furfuryl alcohol (FAL) as the substrate, reacted at the
temperature of 433 K, 4 MPa H ; (b) furfural as the substrate, reacted at the temperature of 393 K, 4 MPa H ; (c) furfural as the substrate, reacted at
the temperature of 433 K, 4 MPa H ; and (d) furfural as the substrate, reacted at the temperature of 433 K, 2 MPa H
2
2
2
2
.
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Fig. 3 Mechanism for the conversion of furfural to CPO.
the result shown in Fig. 2(c) and (d), within 10 minutes, the to form the furan methyl carbocation, which is catalyzed by the
slight conversion of furfural and higher selectivity for FAL were Bronsted acid site in Al11.6PO23.7. Aer that, intermediate a (4-
detected in this process. Furthermore, in the following few hydroxypenta-2,4-dienal) is formed through the carbocation
minutes, the selectivity of FAL decreased acutely, and the rearrangement, which is catalyzed by the Lewis acid site in
selectivity for CPO increased. This phenomenon demonstrated Al11.6PO23.7. In the following step, intermediate a is catalyzed by
that furfural was converted to FAL, and then FAL converted to Ru/C and converted to b (penta-2,4-diene-1,4-diol) in the
CPO immediately in this catalytic system. Additionally, the hydrogen environment. Finally, dehydroxylation occurs and the
selectivity for CPO and CPL can be controlled by adjusting the hydroxyl group in b is catalyzed by Al11.6PO23.7. Then the cyclo-
hydrogen pressure.
pentenone c intermediate is formed through the enol attack on
Encouraged by the previous report, we know that CPO is the the carbocation aer dehydroxylation, and CPO is obtained via
hydrogenation and Piancatelli rearrangement product of hydrogenation in this process at last. This mechanism is
furfural. During the rearrangement process, furfural is rst consistent with the result shown in Fig. 2. Additionally, the
hydrogenated to furfuryl alcohol. 4-Hydroxy-2-cyclopentenone cyclopentenone c was detected at the reaction time of 70 min,
is the intermediate product, which forms aer the Piancatelli and no HCP and FAL were detected at that time (see Fig. 4). This
rearrangement of furfural alcohol, and then following in-depth phenomenon is attributed to the Bronsted acid site in
hydrogenation and dehydroxylation, cyclopentanone or cyclo- Al11.6PO23.7, which promoted the formation of the furan methyl
50
pentanol is produced. From the previous report, there are two carbocation. Also, the in-depth hydrogenation product (1,4-
methods for the formation of 4-hydroxy-2-cyclopentenone
(HCP) (Fig. 3). One is the acid catalyzed enol attack of the
aldehyde carbocation, followed by cyclization to HCP, and the
other is via base-catalyzed aldol condensation. However, from
the result show in Fig. 2, there no HCP and a little FAL were
detected in this process. Hence, furfuryl alcohol conversion to
HCP during Piancatelli rearrangement may not be an exclusive
method to prepare CPO from furfural.
According to the results shown in Fig. 2 and the character-
ization of the Al11.6PO23.7 catalyst, we inferred the mechanism of
the hydrogenation of furfural to CPO as follows (Fig. 3). Initially,
furfural is converted to FAL, which is catalyzed by Ru/C in the
hydrogen environment, and then dehydroxylation of FAL occurs
Fig. 4 GC-MS result of furfural conversion to CPO.
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Scheme 3 Method for the synthesis of diesel range alkanes based on CPO from hemicellulose.
pentanediol) of intermediate b was detected by GC-MS (see out to synthesize another fuel precursor. Encouraged by the
56–59
Fig. S7.†) at a higher hydrogen pressure. This phenomenon previous result,
the hydroxyalkylation and alkylation reac-
demonstrated that intermediates b and c were formed during tions were sensitive to the acid strength of the catalyst. A strong
this process, and the process of rearrangement was not through acid was more active than weak acid for this reaction. Using
the HCP route. This result is consistent with the previous para-toluenesulfonic acid as a commercially available and effi-
34
report, where cyclopentenone c was a promising intermediate cient catalyst for this reaction, more than 90% yield of 1b was
in the conversion of furfural to CPO. In addition, based on obtained when 10% equivalent catalyst to cyclopentanone was
51–54
previous reports,
HCP would have been formed at a high used at 333 K for 6 hours (Table 2, Fig. S10†). Aer the reaction,
temperature with FAL as the substrate. However, as this process the catalyst and product were separated aer extraction with
was carried out at 433 K during, it is hard to prove that furfuryl water and ethyl acetate. Aer concentrating the ethyl acetate
alcohol as the substrate through HCP was converted to CPO. and water phases, the catalyst and product were obtained,
Hence, this cyclization reaction is a Bronsted acid and Lewis acid respectively.
synergistic catalytic process via dehydroxylation and
hydrogenation.
With the aim of synthesizing hydrocarbon fuels, hydro-
deoxygenation of C–C coupling products was performed in
a batch reactor. Hydrodeoxygenation is both hydrogenation and
deoxygenation. This process requires synergistic catalysis
between the hydrogenation catalyst and solid acid. Encouraged
Hydrodeoxygenation of C–C coupling reaction product
CPO and CPL are versatile chemical intermediates that are
45–47
by our previous work,
we found that the commercial catalyst
applied in various elds of daily life. Inspired by our previous
Pd/C added zeolite (H-beta) had the best selectivity for alkanes.
During this experiment, 5% equivalent Pd with 0.5 g H-beta (Si/
Al ¼ 40) to 5 mmol C–C coupling products was used as the
catalyst and reacted at 473 K, and water as the solvent and
45–47
work,
cyclopentanone can be used as a substrate to
synthesize diesel range fuels due to its carbonyl group. This
process consists of two steps. The rst step is a C–C coupling
reaction (e.g., hydroxyalkylation and alkylation or aldol
condensation) to increase the carbon number and octane value.
Then, hydrocarbon fuels were obtained aer the hydro-
deoxygenation of the C–C coupling products (Scheme 3).
According to the carbon numbers of the alkanes, we divided
these products into light alkanes (C1–C4), gasoline range
alkanes (C5–C8) and diesel range alkanes (C9–C16). Herein, we
chose furfural and 2-methyl furan as the substrates to couple
with CPO for the synthesis of diesel range hydrocarbon fuels,
3
MPa hydrogen pressure were required simultaneously. Aer
hydrodeoxygenation, the gas product was detected by GC with
a TCD detector and the liquid product was extracted with ethyl
acetate and detected with GC-MS (Fig. S8†). From the result in
Fig. 5 and 6, hydrodeoxygenation of the aldol condensation
product gives more than 50% yield of theoretical product, which
Table 2 Structures of the fuel precursors and their theoretical HDO
products
55
and all of the substrates came from hemicellulose.
Aldol condensation of bio-based carbonyl compounds and
47
furfural was carried out in our previous report. Aer Substrate
comparing mineral bases, organic bases and solid bases, we
found that organic amines were efficient catalysts to control the
single and double aldol condensation products. TBD (1,5,7-
triazabicyclo[4.4.0]dec-5-ene) was identied as an efficient and
reusable catalyst for this reaction. Herein, the experiments were
carried out in a methanol environment at room temperature,
and 10% equivalent catalyst to cyclopentanone was used to
catalyze the aldol condensation. To our surprise, a greater than
Fuel precursor
Theoretical alkane product
95% yield of 1a was obtained aer 10 minutes (Table 2,
Fig. S9†), and the product was isolated aer ltration with no
further purication. Furthermore, the catalyst in the solvent
could be reused for the next reaction. Hydroxyalkylation and
alkylation of cyclopentanone with 2-methylfuran were carried
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Experimental
Catalyst preparation
All reagents used in this work were of analytical regent grade,
commercially available and used without further purication.
Amorphous aluminium phosphate (AlPO) was prepared
48
according to the reported procedure. In a typical synthesis of
AlPO (Al/P ¼ 1), Al(NO ) $9H O and (NH ) HPO based on
3
3
2
4 2
4
a mole ratio of Al/P ¼ 1 were dissolved in water acidied with
nitric acid. Concentrated ammonia was added to this solution,
and a hydrogel was achieved at pH ¼ 8. The above hydrogel
solution was stirred for 1 h and then the solvent was ltered,
and the hydrogel was washed with distilled water twice. The
Fig. 5 Carbon yield of different alkanes from the HDO of different
precursors over the Pd/C + H-beta system. The diesel range alkanes,
ꢁ
ꢁ
hydrogel was dried at 120 C for 12 h and calcined at 550 C at
ꢁ
ꢀ1
gasoline range alkanes and light alkanes represent C
–C alkanes, respectively.
9
–C18, C
5
–C
8
and a heating rate of 5 C min in air for 30 min. The other AlPO
catalyst with different mole ratios of Al/P (e.g., Al PO, Al PO,
C
1
4
1
0
5
Al PO, AlP O) were prepared according to the abovementioned
2
2
method, but using different mole ratios of Al(NO ) $9H O and
3
3
2
(NH
4 2 4
) HPO .
Hafnium oxide was prepared via calcination of hafnium
hydroxide hydrate. Typically, the hydrogel was prepared via the
dropwise addition of a concentrated ammonia solution to an
4
aqueous solution of HfCl (10 mmol in 50 mL deionized water).
The mixture was stirred for 2 h at room temperature, aer which
ꢁ
a pH of 8–9 was reached, and then aged at 120 C for 6 h. The
ꢁ
catalyst was obtained through ltration and then dried at 50 C
overnight aer removing excess ions via thorough washing with
ꢁ
water. The samples were then calcined at 550 C for 4 h.
Triuoromethanesulfonic acid-based silicon dioxide (TFA/
SiO (30%)) was prepared using 7 g nano silica dispersed in
2
Fig. 6 Product distribution of alkanes from the HDO of the fuel 100 mL isobutanol and 3 g triuoromethanesulfonic acid dis-
precursors (left: 1a and right: 1b).
solved in 20 mL dichloromethane, which were added dropwise
to aqueous isobutanol aqueous with violent stirring at
a temperature of 353 K for 6 hours. Subsequently, the TFA/SiO2
is also accompanied by isomerization and decarbonylation. To
our delight, a small amount of C11 and C14 cyclic alkanes was
detected, which belong to the diesel range alkanes. However, it
is unfortunate that there was no theoretical product produced
aer hydrodeoxygenation of the hydroxyalkylation and alkyl-
ation product. This phenomenon is attributed to the stability of
the carbocation, where C–C cleavage of 2 at the carbon atom
adjacent to the furan ring generated a tertiary carbocation, and
the formation of the most stable tertiary carbocation led to the
C–C cleavage products during hydrodeoxygenation. From the
results shown in Fig. 5 and S12,† according to the different
cracking cleavage, more than 85% yield of C15 isomer alkanes
were obtained. To our delight, regarding the specicity of
cyclopentyl, hexatomic ring cyclic alkanes were obtained from
the cracking of cyclopentyl and subsequent rearrangement, and
the nal products C10 and C15 cyclic alkanes in the range of
diesel fuels. Hence, based on cyclopentanone, the C–C coupling
reaction followed by hydrodeoxygenation is an effective method
to prepared cyclic alkanes. Compared to straight chain alkanes,
cyclic alkanes have higher densities and volumetric heating
values due to the strong ring strain. Also, cyclic alkanes are the
second most abundant component in commercial and military
(30%) catalyst was obtained aer ltration and dried at 333 K
under vacuum.
Experimental
Hydrogenation of furfural to cyclopentanone or cyclo-
pentanol. Generally, furfural (20 mmol, 1.92 g) was added to
a solution of 50 mL deionized water and then transferred to
a 100 mL Parr pressure reactor. Then the hydrogenation metal
catalyst (0.25 g, 0.5% hydrogenation metal to furfural) and solid
acid catalyst (0.25 g) were added to the reactor. The reactor was
purged three times with nitrogen and charged with a given
pressure of H . Then, the reactor was heated to a given
2
temperature with vigorous stirring for 4 h. Aer completion, the
mixture was directly analyzed by HPLC. Finally, the mixture was

ltered. The catalysts were recovered by ltration and washed
with MeOH or EtOAc, and the ltrate was extracted with EtOAc.
Finally the obtained organic layer was evaporated to provide the
product.
Hydroxyalkylation and alkylation of cyclopentanone and 2-
0
methyl furan. 5,5 -(Cyclopentane-1,1-diyl)bis(2-methylfuran)
was prepared via a typical method. To a solution of 2-methyl-
furan (25 mmol, 2.05 g) and cyclopentanone (10 mmol, 0.84 g)
60–63
jet fuels, at a mass percent of 20–50 wt%.
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para-toluene sulfonic acid (1 mmol, 0.25 g) was added at 333 K
under solvent-free conditions for 6 h. Then, the mixture was
Conflicts of interest
diluted with water and extracted with EtOAc. The combined There are no conicts to declare.
organic extracts were concentrated under vacuum and puried
by column chromatography to provide the analytically pure
Acknowledgements
product 1a (2.116 g, 92%), which was isolated as a light brown
1
oil. H NMR (400 MHz, MeOD) d 5.85 (d, J ¼ 3.1 Hz, 2H), 5.83 (d,
This work was supported by the Program for the National
Natural Science Foundation of China (Grant No: 21776132); the
Young Elite Scientist Sponsorship Program by CAST; the
Changjiang Scholars and Innovative Research Team in Univer-
sity (Grant No: IRT_14R28); the Major Research Plan of the
National Natural Science Foundation of China (Grant No:
J ¼ 3.0 Hz, 2H), 2.20 (s, 6H), 2.16 (d, J ¼ 6.8 Hz, 4H), 1.73–1.67
1
3
(
m, 4H). C NMR (100 MHz, MeOD) d 158.32, 151.62, 106.70,
50.06, 37.81, 24.80, 13.47.
Aldol condensation of cyclopentanone and furfural. 2,5-
Bis(furan-2-ylmethylene)cyclopentan-1-one was prepared via
a typical method. Cyclopentanone (10 mmol, 0.84 g) and
furfural (20 mmol, 1.92 g) were diluted with MeOH to 10 mL
solution. The catalyst TBD (1 mmol, 0.139 g) was added to this
solution, and the reaction was carried out at room temperature
for 2 minutes. The product was separated from the solvent by
21390204); the Jiangsu National Synergetic Innovation Center
for Advanced Bio-Manufacture.
Notes and references

ltration and then desiccated to afford 2.394 g (96%) of product
1
2
1
3
1
a as a yellow solid; H NMR (400 MHz, CDCl ) d 7.59 (d, J ¼
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