One-pot catalytic selective synthesis of 1,4-butanediol from 1,4-anhydroerythritol and hydrogen

Article abstract of DOI:10.1039/c8gc00574e

A physical mixture of ReO_x-Au/CeO₂ and carbon-supported rhenium catalysts effectively converted 1,4-anhydroerythritol to 1,4-butanediol with H₂ as a reductant. The combination of these two catalysts in a one-pot reaction dramatically increased the selectivity of 1,4-butanediol as well as the conversion of 1,4-anhydroerythritol. The yield of 1,4-butanediol reached ～90%, which is the highest yield from erythritol and 1,4-anhydroerythritol so far, furthermore, at a relatively low reaction temperature of 413 K. This reaction involves the ReO_x-Au/CeO₂-catalyzed deoxydehydration of 1,4-anhydroerythritol to 2,5-dihydrofuran and ReO_x/C-catalyzed successive isomerization, hydration and reduction reactions of 2,5-dihydrofuran.

Full text of DOI:10.1039/c8gc00574e

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Page 1 of 35
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1
2
One-pot Catalytic Selective Synthesis of 1,4-Butanediol from
1,4-Anhydroerythritol and Hydrogen
3
4
a
a
a,b
*,a,b
Tianmiao Wang, Sibao Liu, Masazumi Tamura, Yoshinao Nakagawa,
Norihito
c
*,a,b
5
6
7
8
9
0
1
2
3
4
Hiyoshi, Keiichi Tomishige
a
Department of Applied Chemistry, School of Engineering, Tohoku University, 6ꢀ6ꢀ07 Aoba,
Aramaki, Aobaꢀku, Sendai, 980ꢀ8579, Japan
b
Research center for Rare Metal and Green Innovation, Tohoku University, 468ꢀ1 Aoba,
1
1
1
1
1
Aramaki, Aobaꢀku, Sendai, 980ꢀ0845, Japan
c
Research Institute for Chemical Process Technology, National Institute of Advanced
Industrial Science and Technology (AIST), 4ꢀ2ꢀ1 Nigatake, Miyaginoꢀku, Sendai, 983ꢀ8551,
Japan
* Corresponding Author: Yoshinao Nakagawa and Keiichi Tomishige
1
1
5
6
*Eꢀmail: tomi@erec.che.tohoku.ac.jp and yoshinao@erec.che.tohoku.ac.jp
1

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Abstract
The physical mixture of ReO
x
2
ꢀAu/CeO and carbonꢀsupported rhenium catalysts
3
4
5
6
7
8
9
0
effectively converted 1,4ꢀanhydroerythritol to 1,4ꢀbutanediol with H as a reductant. The
2
combination of these two catalysts in oneꢀpot reaction dramatically increased selectivity of
1,4ꢀbutanediol as well as conversion of 1,4ꢀanhydroerythritol. The yield of 1,4ꢀbutanediol
reached ~90%, which is the highest yield from erythritol and 1,4ꢀanhydroerythritol so far,
furthermore, at relatively low reaction temperature of 413 K. This reaction is composed of
ReO ꢀAu/CeO ꢀcatalyzed deoxydehydration of 1,4ꢀanhydroerythritol to 2,5ꢀdihydrofuran and
x
2
ReO /Cꢀcatalyzed successive isomerization, hydration and reduction reactions of
x
1
1
1
1
1
2,5ꢀdihydrofuran.
1
2
3
4
1
1
5
6
Keywords: Heterogenous catalysis, deoxydehydration, rhenium oxide, gold, oneꢀpot reaction
2

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Introduction
Renewable biomassꢀbased products as energy resources and feedstocks are in increasing
1
ꢀ5
demand as replacements of fossil resources. However, due to the high oxygen content of
biomassꢀderived platform compounds such as sugar alcohols, selective oxygen removal is
4
,5
one of the most important processes to produce biomassꢀbased chemicals. Among sugar
alcohols, glycerol and sorbitol have been frequently used as substrates of catalytic
1
ꢀ3
hydrodeoxygenation because of their large potential supply.
While selective oxygen
6
ꢀ7
removal of glycerol is possible to produce propanediols as main target chemicals, selective
oxygen removal of sorbitol is much more difficult, and the main products are deeply
deoxygenated ones such as hexane and smaller (≤ C3) compounds such as propylene
1
1
1
1
1
1
1
1
1
1
2
2
2
1,8ꢀ13
glycol.
Erythritol is a C4 sugar alcohol which is already produced as a sweetener in
1
4ꢀ17
industrial scale by fermentation.
Production of erythritol by fermentation of glycerol,
18
even nonꢀrefined one, is also possible. However, erythritol has been less investigated as a
substrate of deoxygenation than glycerol and sorbitol. This is because selective oxygen
removal of erythritol is more difficult than that of glycerol: the deeply deoxygenated products
such as butanols and nꢀbutane are coproduced, and high yield of the valueꢀadded target
19ꢀ21
products such as butanediols are not achieved.
Deoxydehydration (DODH) reaction is an attractive method to decrease the oxygen
content of biomassꢀderived molecules by simultaneously removing vicinal diols to C=C
22ꢀ24
bond.
Erythritol and its dehydrated product 1,4ꢀanhydroerythritol (1,4ꢀAHERY) are
frequently used as substrates for DODH, and their products are 1,3ꢀbutadiene and
2
5ꢀ29
2,5ꢀdihydrofuran (2,5ꢀDHF), respectively (eqn (1)ꢀ(2)).
Typical DODH systems use
3

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0
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2
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1
2
homogenous Re catalysts such as CH
3
ReO
alcohol, while development of heterogeneous DODH catalysts has also been carried out.
Recently, we reported ReO ꢀAu/CeO catalysts as effective H ꢀdriven heterogeneous DODH
It has been proposed that CeO support plays an important role in the
3 2
and nonꢀH reductants such as secondary
22
30,31
x
2
2
32,33
catalysts.
2
suppression of deep reduction of Re species to low valent Re species such as Re metal and
maintaining high valence (≥ +4) of the Re species, which can be an active Re species for the
DODH reaction, under the DODH reaction conditions. The studies on the effect of loading
2
amount of Re on CeO and the catalyst characterization suggest that monomeric Re species
attached on the surface of CeO support is a catalytically active species and polymeric Re
2
1
1
1
1
1
1
1
1
1
1
2
2
2
species is inactive species in the DODH reaction. Moreover, the DODH reaction is suggested
4
+
6+
to proceed by the redox mechanism between Re and Re . On the other hand, the Au
particles have a role on the activation of molecular hydrogen, and the activated hydrogen
2
species are supplied from Au surface to Re species via the CeO surface, to reduce the
6+
4+
oxidized Re species (Re ) to the reduced Re species (Re ). We prepared two types of
dp
ReO
x
ꢀAu/CeO
2
catalysts: Au loading by depositionꢀprecipitation (ReO
x
ꢀ Au/CeO
2
) and Au
imp
32,33
loading by impregnation (ReO
x
ꢀ Au/CeO
2
).
The former has smaller Au particles (3 nm)
and higher activity, and the latter has larger Au particles (12 nm) and lower activity. However,
imp
x 2
the ReO ꢀ Au/CeO is preferable for the polyol substrates such as glycerol and erythritol
(eqn (3) and (1)) due to the higher yield of DODH product (allyl alcohol and 1,3ꢀbutandiene,
imp
respectively), because the low H
2
activation ability of Au slows down the hydrogenation of
dp
alkenes. On the other hand, the ReO
x
ꢀ Au/CeO
2
is good for the DODH reaction of diol
dp
substrates such as 1,4ꢀAHERY (eqn (2)), because the selectivity of DHFs of ReO
x
ꢀ Au/CeO
2
4

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imp
1
2
3
4
5
6
7
x 2
(98%) is similar to that of ReO ꢀ Au/CeO (98%), while the reaction rate of
dp
imp
ReO
x
ꢀ Au/CeO
2
is 6 times higher than that ReO
ꢀPd/CeO
tetrahydrofuran (THF) via DODH and hydrogenation with high activity and selectivity
x
ꢀ Au/CeO
2
. We also reported a variant of
DODH using heterogeneous ReO
x
2
catalyst which converted 1,4ꢀAHERY to
34,35
(99%).
x 2
The structure of Re species is the same as that in ReO ꢀAu/CeO , the high activity
of ReO
x
ꢀPd/CeO
2
is derived from the high H
2
activation ability of Pd, and high dispersion of
Pd metal particles (<1 nm).
OH
ReO
x 2
-impAu/CeO
HO
+
2H
2
+ 4H
2
O
(1)
OH
OH
Erythritol
1
,3-Butadiene
8
9
O
ReOx-dpAu/CeO
O
2
+
2H
2
+ 2H
2
O
(2)
HO
OH
2
,5-DHF
1,4-AHERY
ReO
x
-impAu/CeO
2
OH
HO
OH
+
2H2
+ 2H
2
O
(3)
OH
Glycerol
Allyl alcohol
1
1
0
1
As well as 1,3ꢀbutadiene and THF, 1,4ꢀbutanediol (1,4ꢀBuD), used as an important
2
0
1
1
1
1
1
1
1
1
2
3
4
5
6
7
8
9
monomer and a solvent for synthesis in industry , can be a reduction product from erythritol
or 1,4ꢀAHERY. A number of studies about production of 1,4ꢀBuD by reduction of succinic
1
,36
acid (eqn (4)), which can be obtained by fermentation from glucose, has been reported.
1
,36,37
Over 80% yields of 1,4ꢀBuD from succinic acid have been reported.
1,4ꢀBuD from succinic acid requires 4 equiv. of H (eqn (4)). On the other hand, the
production of 1,4ꢀBuD from 1,4ꢀAHERY requires only 2 equiv. of H (eqn (5)), and this route
The production of
2
2
is more economical in terms of the reductant cost. However, the production system of
1,4ꢀBuD from erythritol are very limited.
O
OH
HO
+
4H2
+ 2H2O (4)
HO
OH
O
Succinic Acid
1,4-BuD
2
0
5

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O
HO
(5)
+
2H
2
2
+ H O
OH
HO
OH
1
2
1,4-AHERY
1,4-BuD
Rh or Ir catalysts modified with group 6ꢀ7 metal oxides are known to be active in CꢀO
1
9,21,37
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
hydrogenolysis of polyols,
however, it is difficult to remove secondary OH groups
consecutively without producing butanols over these catalysts. Only 25% yield of 1,4ꢀBuD is
19
obtained by erythritol hydrogenolysis over IrꢀReO
x 2
/SiO catalyst. Hydrogenolysis of
1,4ꢀAHERY over IrꢀReO /SiO and RhꢀMO /SiO (M = Mo, W, Re) does not produce
x
2
x
2
19,39
1,4ꢀBuD at all.
yield can also be produced by hydrationꢀreduction of 2,5ꢀDHF over ReO
catalysts (eqn (6)) with 1,4ꢀdioxaneꢀwater or THFꢀwater solvent and H
On the other hand, Pinkos et al. of BASF found that 1,4ꢀBuD with high
/TiO (Re = 6 wt%)
in a flow reactor.
x
2
40
2
1
1
1
1
1
1
1
1
1
1
2
2
2
The maximum yield of 1,4ꢀBuD was 85% at 427 K. As mentioned above, 2,5ꢀDHF is the
product in the Reꢀcatalyzed DODH reaction of 1,4ꢀAHERY (eqn (2)). Thus, 1,4ꢀAHERY may
be possible to be converted to 1,4ꢀBuD over Re catalysts. On the basis of the selective
conversion of 1,4ꢀAHERY to 2,5ꢀDHF catalyzed by ReO
process consisting of 1,4ꢀAHERY to 2,5ꢀDHF (413 K, H
to 1,4ꢀBuD catalyzed by ReO /TiO (427 K, H , 1,4ꢀdioxane + water solvent) in different
reactors can produce 1,4ꢀBuD from 1,4ꢀAHERY. Considering that two systems have common
reaction conditions such as reaction temperature, H reductant, and the main component of
solvent, the oneꢀpot conversion of 1,4ꢀAHERY to 1,4ꢀBuD is promising. Manzer of DuPont
reported in the patent that 30% yield of 1,4ꢀBuD is obtained from 1,4ꢀAHERY with ReO /C
at 473 K. The selectivity of 1,4ꢀBuD was as low as 41%, and
the main byꢀproducts were γꢀbutyrolactone (GBL) and THF. THF can be formed by
x
ꢀAu/CeO
2
, it seems that the tandem
2
, 1,4ꢀdioxane solvent) and 2,5ꢀDHF
x
2
2
2
x
41
(Re = 5 wt%) catalysts and H
2
41
hydrogenation of DHF or dehydration of 1,4ꢀBuD.
GBL may be formed by
6

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2
3
4
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0
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disproportionation of the precursor aldehyde of 1,4ꢀBuD (eqn (7)). The low selectivity might
be due to the high reaction temperature for ReO /Cꢀcatalyzed H ꢀdriven DODH with low
x
2
34
activity. Milder reaction conditions may be better for 1,4ꢀBuD production to suppress such
sideꢀreactions, and ReO ꢀAu/CeO with the DODH activity at low temperature (413 K) is
x
2
contributable to the oneꢀpot conversion of 1,4ꢀAHERY to 1,4ꢀBuD. In addition, the
1,4ꢀdioxaneꢀwater solvent was used for the conversion of 2,5ꢀDHF to 1,4ꢀBuD because H
is also a reactant as well as H (eqn (6)). On the other hand, water is not suitable solvent for
the DODH reaction catalyzed by ReO However, the conversion
2
O
2
3
2ꢀ35
x
ꢀM/CeO
2
(M = Au, Pd).
of 1,4ꢀAHERY to 2,5ꢀDHF gives water as a product (eqn (2)). Therefore, the addition of
water can be omitted in principle (eqn (5)) when the product water becomes a reactant in the
conversion of 2,5ꢀDHF regardless of low concentration of water.
1
1
O
HO
+
H
2
O + H
2
(6)
OH
2
,5-DHF
1,4-BuD
1
2
O
O
OH
HO
2
+ 2H
2
O
2
HO
O
2
O
4
-Hydroxybutanal
2
,5-DHF
2-HTHF
(
7)
2
+
2H
2
OH
(
main route)
1,4-BuD
O
HO
+
disproportionation
side route)
OH
(
GBL
1,4-BuD
1
1
3
4
This oneꢀpot system can decrease the requirement of reactors, separation of intermediates,
1
1
1
1
1
5
6
7
8
9
and solvent, maintaining high yield and productivity of the target product. In this study, we
combine the two catalyses within oneꢀpot reaction: the DODH of 1,4ꢀAHERY to 2,5ꢀDHF
x 2
over ReO ꢀAu/CeO and the conversion of 2,5ꢀDHF to 1,4ꢀBuD over another Re catalyst.
Over the combination of ReO ꢀAu/CeO and ReO /C catalysts, we obtained ~90% yield of
x
2
x
2
1,4ꢀBuD from 1,4ꢀAHERY and H at 413 K (eqn (5)). This yield is much higher than the
7

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literature ones of 1,4ꢀBuD from 1,4ꢀAHERY.
Results and Discussion
Production of 1,4ꢀbutanediol
Various supported Re catalysts were tested for the coꢀcatalysis with ReO
x
ꢀAu/CeO
2
dp
dp
(ReO
x
ꢀ Au/CeO
2
) in the reaction of 1,4ꢀAHERY (Table 1). We selected ReO
x
ꢀ Au/CeO
2
imp
32,33
because of the higher activity than ReO
carbonꢀsupported rhenium catalysts with ReO ꢀAu/CeO
of 1,4ꢀBuD. The ReO /CꢀBP (carbon black BP2000) performed higher conversion and better
x
ꢀ Au/CeO2.
The combination of
x
2
(entries 1ꢀ2) showed good selectivity
x
1
1
1
1
1
1
1
1
1
1
2
2
2
1,4ꢀBuD selectivity than ReO
x
/CꢀNR (activated carbon Norit RX3 extra). The combinations of
ReO /SiO , ReO /TiO , ReO /ZrO
x
2
x
2
x
2
, ReO /Al , and ReO /MgO with ReO ꢀAu/CeO (entries
x
2
O
3
x
x
2
3ꢀ7) showed very low yield of 1,4ꢀBuD. The main products of these Re catalysts were
2,5ꢀDHF and 2,3ꢀDHF, indicating that they have low activity in the conversion of DHFs.
32
Single ReO ꢀAu/CeO had high selectivity of 2,5ꢀDHF by DODH of 1,4ꢀAHERY (entry 8).
x
2
Single ReO
products include THF and 1,4ꢀBuD. This indicates that ReO
activity of DHFs ringꢀopening reaction to 1,4ꢀBuD. Adding ReO
ReO ꢀAu/CeO increased the selectivity of 1,4ꢀBuD and effectively decreased the selectivity
of other products such as DHFs which were rapidly converted to 1,4ꢀBuD over ReO /CꢀBP and
x
/CꢀBP showed very low activity in the reaction of 1,4ꢀAHERY (entry 9), and the
/CꢀBP and ReO /CꢀNR have high
/CꢀBP or ReO /CꢀNR to
x
x
x
x
x
2
x
ReO
conversion of 1,4ꢀAHERY probably due to the move of some Re species from carbon support
to the surface of CeO (entry 12), thereby increasing the number of active site of
x
/CꢀNR during the reaction (entries 1 and 2). Meanwhile, the addition also increased the
2
8

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9
0
1
2
3
4
5
6
7
8
9
0
1
2
ReO
x
ꢀAu/CeO
2
x
catalyst (discussed below). Because ReO /CꢀBP coꢀcatalyst showed the best
x 2
selectivity of 1,4ꢀBuD with ReO ꢀAu/CeO catalyst in the reaction of 1,4ꢀAHERY, it was used
in the following studies. The reaction over the catalyst mixture under Ar atmosphere (entry 10)
gave low conversion and many types of products, probably via dehydrogenation and reduction
with hydrogen produced by the dehydrogenation.
The optimizations of Re loading amount of ReO /CꢀBP (Fig. 1 (a)), weight ratio of
x
ReO /CꢀBP to ReO ꢀAu/CeO (Fig. 1 (b) and (c)), H pressure (Fig. 1 (d)), and reaction
x
x
2
2
temperature (Fig. 2) were carried out. The best result was obtained with the conditions in Table
1: 3 wt% Re for ReO /CꢀBP, 1:1 catalysts weight ratio, 8 MPa H , and 413 K. Addition of Re
x
2
1
1
1
1
1
1
1
1
1
1
2
2
2
on carbon dramatically increased the selectivity of 1,4ꢀBuD, as well as the conversion of
1,4ꢀAHERY. In the case of ReO ꢀPd/CeO catalyst for DODH + hydrogenation, the
x
2
weightꢀbased activity is increased until the Re loading of 2 wt%, and then it is decreased with
further Re loading, because the amount of monomeric Re species was maximized at 2 wt% of
3
5
32
Re. In our previous study on ReO ꢀAu/CeO , the leaching of Re and Au to the liquid phase
x
2
was negligible in glycerol DODH. On the other hand, metals on carbon support are easier to
4
2
escape including ReO
1 wt%, and thus the move of some Re species from CꢀBP to CeO
activity and that from CeO to CꢀBP can decrease the DODH activity. The stability of Re
species and the move between supports will be also discussed later. When the Re amount on
ReO /CꢀBP was higher than 3%, the THF selectivity slightly increased (Fig. 1 (a) and (b)).
Lower conversion of ReO ꢀAu/CeO + CꢀBP (Fig. 1 (a)) than that of ReO ꢀAu/CeO (Fig. 1 (b))
can be explained by the move of some Re species from CeO to CꢀBP. The amount of
x
/C, especially at high temperature. The Re loading in ReO
x 2
ꢀAu/CeO is
2
can increase the DODH
2
x
x
2
x
2
2
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2
3
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5
6
7
8
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0
1
2
ReO
x
ꢀAu/CeO
2
significantly affected the conversion of the reaction, while the selectivity was
ꢀAu/CeO
not so affected (Fig. 1 (c)), indicating that the rate of DODH catalyzed by ReO
x
2
controls the reaction rate of 1,4ꢀAHERY to 1,4ꢀBuD. In the DODH reaction of polyols over
single ReO ꢀAu/CeO , the formation of alkene from the diolate complex is the
x
2
3
3
rateꢀdetermining step. Therefore, this step is also the rateꢀdetermining step in the conversion
of 1,4ꢀAHERY to 1,4ꢀBuD.
At higher temperature of 443 K (Fig. 2), the selectivity of 1,4ꢀBuD decreased and that to
THF increased with the reaction time. The yield of 1,4ꢀBuD at 1 h was 43%, and the yield
decreased to be 37% after 4 h reaction time. This behavior suggested that 1,4ꢀBuD is
consecutively dehydrated to THF before total conversion of 1,4ꢀAHERY. Thus, lower
temperature of 413 K is more suitable for 1,4ꢀBuD formation. This reaction temperature is also
1
1
1
1
1
1
1
1
1
1
2
2
2
lower than those in the patent using ReO
x
/C catalyst (473 K), where THF formation decreased
41
the yield of 1,4ꢀBuD. The TOF based on the conversion and total Re amount of the mixture of
ꢀ1
ReO ꢀAu/CeO and ReO /CꢀBP at 413 K is calculated to be 5 h using the conversion increase
x
2
x
during 2 ꢀ 4 h reaction time (41% → 49%; Table S1, entries 2 and 3, ESI), which is comparable
ꢀ1
to that on ReO
x x 2
/C at 473 K (13 h ). High activity of ReO ꢀAu/CeO in DODH can decrease the
reaction temperature maintaining the productivity.
Fig. 3 and Table S1 (ESI) show the time course of the reaction of 1,4ꢀAHERY over the
mixture of ReO ꢀAu/CeO and ReO /CꢀBP. The selectivity of 1,4ꢀBuD increased until
x
2
x
1,4ꢀAHERY was totally converted. The selectivity of DHFs was kept low, indicating that
DHFs were rapidly converted. At short reaction time, the acetal from 4ꢀhydroxybutanal and
1,4ꢀAHERY (eqn (8)) (identified by GCꢀMS and NMR, ESI) was detected in significant
1
0

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selectivity. 4ꢀHydroxybutanal is thought to be in the equilibrium by the intramolecular
acetalization with 2ꢀhydroxytetrahydrofuran (2ꢀHTHF) (eqn (9)). 2ꢀHTHF can be formed by
the hydration reaction of 2,3ꢀDHF (eqn (7)). In fact, 4ꢀhydroxybutanal and 2ꢀHTHF were not
detected as products in the reaction of 1,4ꢀAHERY. On the other hand, the selectivity of the
acetal at low conversion of 1,4ꢀAHERY was rather high and 4ꢀhydroxybutanal is thought to
be trapped by acetalization and this decreases in the reactivity of formyl group. While the
formation of the acetal can be rather preferable in the reaction equilibrium, the hydrogenation
of 4ꢀhydroxybutanal to 1,4ꢀBuD gradually proceeds and the selectivity of the acetal decreases,
and finally the acetal was not detected at longer reaction time. The overreaction of 1,4ꢀBuD to
1ꢀbutanol or THF was slow under these reaction conditions. The yield of 1,4ꢀBuD reached 85%
at 24 h, and this yield value is much higher than the literature values of erythritol or
1
1
1
1
9,35
1,4ꢀAHERY conversions.
O
HO
+
O
HO
OH
4
-Hydroxybutanal
1,4-AHERY
(8)
O
O
+ H O
2
OH
O
Acetal
1
3
O
OH
HO
-Hydroxybutanal
(
9)
O
4
2-HTHF
1
1
4
5
It should be noted that the conversion of 1,4ꢀAHERY to 1,4ꢀBuD involves H
and consumption together with H consumption (eqn (2) and (6)). In the case of the
conversion of 2,5ꢀDHF to 1,4ꢀBuD using ReO /TiO , THFꢀwater or 1,4ꢀdioxaneꢀwater
2
O release
1
1
1
1
2
6
7
8
9
0
2
x
2
40
solvents were used, and the water was also a reactant as well as the solvent. In contrast,
water is not added at all in this work, and this means that the produced water can react
2
selectively even at the low concentration of H O during the reaction of 1,4ꢀAHERY.
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Therefore, we also tested the effect of water in the solvent in our system (Table 2). The
addition of water to solvent sharply decreased the conversion, indicating that the DODH
x 2
activity of ReO ꢀAu/CeO is suppressed by the presence of water. The conversion of
1,4ꢀAHERY was very low in water solvent (Table S2, entry 4, ESI), and similar behavior was
35
observed in the reaction of 1,4ꢀAHERY to THF over ReO
x
ꢀPd/CeO
2
.
The conversion of
1,4ꢀAHERY was very low in pure water solvent (Table S2, entry 4, ESI). The interpretation is
that higher concentration of water suppresses the formation of Re diolate which is the very
important surface intermediate species in DODH. The use of water solvent in DODH with
good yield has been only recently reported with the combination of KReO , Pd/C,
4
4
3
1
1
1
1
1
1
1
1
1
1
2
2
2
4ꢀ(dimethylamino)pyridine ligand and large amount of activated carbon. In addition, the
formation of acetal was suppressed by the presence of water (entries 3 and 4, and Fig. 3), and
the selectivity of 1,4ꢀBuD was slightly higher than the case in the absence of water. This
suggests that 4ꢀhydroxybutanal and 2ꢀHTHF intermediates were rapidly hydrogenated to
1,4ꢀBuD in the presence of water. The reaction can be conducted in THF solvent or even
without solvent (Table S2, entries 1 and 3, ESI). The selectivity of 1,4ꢀBuD was almost same
although the activity was slightly lower than that in the 1,4ꢀdioxane solvent.
Catalyst characterization
Because the catalysts were well mixed in the reaction, the characterization of used catalyst
was rather difficult. In our previous reports, the reduction of Re species on CeO
2
is
High valence Re
2 2
species on CeO can be easily reduced to Re with H in presence of promoters. In the
3
2ꢀ35
dramatically promoted by addition of promoters such as Au and Pd.
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x 2
DODH reaction of 1,4ꢀAHERY to 2,5ꢀDHF, Re species in ReO ꢀAu/CeO may have the redox
4
+
6+
6+
4+
32ꢀ35
pair of Re and Re , and Re reduced to Re with H
2
after the reaction.
The H ꢀTPR profiles of ReO /CꢀBP and CꢀBP support are shown in Fig. 4. The reduction
2
x
of CꢀBP started about 700 K, suggesting that CꢀBP support was not reduced in the reaction
conditions (413 K). The reduction of Re species started around 500 K. Although the
temperature was higher than reaction temperature, reduction of supported Re to the mixture
0
n+
37,44,45
of Re and Re can take place in the solvent at lower temperature than the TPR peak,
which can be explained by much higher H pressure under the reaction conditions than that
under TPR conditions. When ReO /CꢀBP was preꢀreduced at 673 K, the H consumption
2
x
2
ꢀ1
1
1
1
1
1
1
1
1
1
1
2
2
2
amount was decreased by 0.41 mmolꢁg , which corresponds to the reduction of Re from +7 to
average valence +2, suggesting that the part of Re species on CꢀBP is reduced to metallic state.
The formation of Re metal on ReO
has some activity in hydrogenation as discussed later.
The XRD patterns (Fig. S1, ESI) only showed CeO peaks in fresh or used catalyst
x x
/CꢀBP is also supported by the data that ReO /CꢀBP alone
2
mixture of ReO
x
ꢀAu/CeO
2
x
and ReO /CꢀBP. This indicates that Au and ReO
x
particles were
3
2ꢀ35
highly dispersed on both CeO
2
and/or carbon surfaces,
and suggesting that the
aggregation of particles is not so significant.
The TEM images of used catalyst mixture are shown in Fig. 5. CeO
located on the CꢀBP support as small aggregates composed of a few CeO crystallites. The
2
particles were
2
aggregate size (10ꢀ20 nm) was much smaller than that on the CeO
2
alone or ReO
x
ꢀAu/CeO
2
33
alone (0.2ꢀ1 ꢂm), while the primary crystallite size of CeO
2
(8 nm) is similar for CeO
2
33
33
x 2 x 2 x
alone, ReO ꢀAu/CeO alone, and ReO ꢀAu/CeO + ReO /CꢀBP. This suggests that the
1
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aggregates of CeO
2
are dispersed by the interaction between CeO
2
crystallite and the carbon
can be reduced by H
surface. In our recent paper, we found that the ReO
x
species on CeO
2
2
33
even when the promotor Au is absent on the same CeO
2
particle. The active hydrogen
species is supposed to move from particle to particle via proton and electron. As well as CeO2,
carbon can carry electrons, and thus the active hydrogen species can move from promotor
x 2 x
(Au) to Re in the mixture of ReO ꢀAu/CeO and ReO /CꢀBP. On the CꢀBP support (Fig. 5C),
Re species existed as highly dispersed state.
Reaction mechanism
1
1
1
1
1
1
1
1
1
1
2
2
2
To study the possible route of the reaction from 1,4ꢀAHERY to 1,4ꢀBuD and the role of
catalyst components, reactions of different substrates (or possible intermediates) were tested
over various related catalysts (Table 3). In this experiment, small amount of water was added
to the system (water: substrate = 1:1) because the DODH step of 1,4ꢀAHERY coꢀproduces
water, and formed water is used as a reactant for the subsequent steps. The substrate amount
(0.15 g) was set lower than the standard runs (0.5 g, Table 1) because the concentration of
possible intermediates was low in the standard runs for the reaction of 1,4ꢀAHERY over
ReO
ReO
x
x
ꢀAu/CeO
ꢀAu/CeO
2
2
+ ReO
x
/CꢀBP, for example Table 1, entry 1. The combination of
and ReO /CꢀBP (Table 3, entry 1) gave high yield of 1,4ꢀBuD (90%), which is
x
similar to the case of standard conditions (Table 1, entry 1). It should be noted that this yield
is clearly higher than the yield of 1,4ꢀBuD by the reaction of 2,5ꢀDHF over ReO /TiO
(Table 3,
entry 2) gave higher yield of THF and 2,3ꢀDHF than the result under the standard conditions in
x
2
40
x 2
(85%), indicating the superiority of the oneꢀpot system. Single ReO ꢀAu/CeO
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Table 1, entry 8, indicating that the successive reactions of 2,5ꢀDHF to THF by hydrogenation
and to 2,3ꢀDHF by isomerization are also catalyzed by ReO ꢀAu/CeO . In spite of this activity
of ReO ꢀAu/CeO in hydrogenation of 2,5ꢀDHF to THF, very high yield of 1,4ꢀBuD and very
low yield of THF over ReO ꢀAu/CeO + ReO /CꢀBP were observed, which suggests that the
x
2
x
2
x
2
x
activity of ReO
x
/CꢀBP in the successive reactions of 2,5ꢀDHF can be much higher than that
. Single ReO /CꢀBP (Table 3, entry 3) showed very low yield of 1,4ꢀBuD,
of ReO ꢀAu/CeO
x
2
x
THF and so on, while the conversion was significantly higher than the total yield of detected
products. This suggests that polymerized products are formed from 1,4ꢀAHERY or the
reduced compounds such as DHFs. The difference between the conversion and the sum of the
1
1
1
1
1
1
1
1
1
1
2
2
2
detected products’ yield was also observed over ReO
x
/CꢀBP in the reaction of 2,5ꢀDHF
/CꢀBP
(Table 3, entry 6). Medium yield of 1,4ꢀBuD was obtained, indicating that ReO
x
catalyzes the conversion of 2,5ꢀDHF to 1,4ꢀBuD, although high concentration of 2,5ꢀDHF
can promote the polymerization of 2,5ꢀDHF and hydrogenation to THF and can cause the
decrease in the yield of 1,4ꢀBuD. The combination of ReO /CꢀBP with ReO ꢀAu/CeO
2
x
x
enhanced the yield of 1,4ꢀBuD and suppressed the polymerization (Table 3, entry 4). The
activity of ReO ꢀAu/CeO was not so high in the reaction of 2,5ꢀDHF (Table 3, entry 5),
indicating that the reaction of 2,5ꢀDHF is mainly catalyzed by ReO /CꢀBP (Table 3, entry 6).
x
2
x
An important point is that single CꢀBP has almost no activity in the reaction of 2,5ꢀDHF
(Table 3, entry 7) and Re species supported on CꢀBP catalyzes the reaction of 2,5ꢀDHF.
Next, the reactions of 2,3ꢀDHF over various catalysts were also tested because 2,3ꢀDHF
is a possible intermediate for the formation of 1,4ꢀBuD. It should be noted that the difference
between the sum of the detected products’ yield and the conversion in the reaction of
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2,3ꢀDHF was commonly larger over all the catalysts, and this low carbon balance can be due
to the loss of 2,3ꢀDHF during the operation because of the low boiling point of 2,3ꢀDHF (327
K), which is lower than that of 2,5ꢀDHF (340 K). Therefore, the performance should be
compared on the basis of the yield of detected products. ReO ꢀAu/CeO + ReO /CꢀBP gave
x
2
x
relatively high yield of 1,4ꢀBuD in the reaction of 2,3ꢀDHF (Table 3, entry 8). Another
important product is 2ꢀHTHF formed by the hydration of 2,3ꢀDHF, and 2ꢀHTHFꢀderived
products were also detected such as 2,2’ꢀoxybis(tetrahydrofuran). The yield of 2ꢀHTHF and
its derivative was 41% on CꢀBP (Table 3, entry 11, the yield = (46/2+18)%), which was
higher than that on ReO ꢀAu/CeO (12%, Table 3, entry 9). This indicates that the hydration
x
2
1
1
1
1
1
1
1
1
1
1
2
2
2
of 2ꢀHTHF is mainly catalyzed by the surface of CꢀBP, probably the surface carboxylic or
phenolic groups formed on the surface of carbons. It should be noted that the formation of
x
1,4ꢀBuD in the reaction of 2,3ꢀDHF on ReO /CꢀBP (Table 3, entry 10) and no formation on
CꢀBP (Table 3, entry 11) indicates that Re species on ReO
hydrogenation of 2ꢀHTHF (or 4ꢀhydroxybutanal) to 1,4ꢀBuD.
x
/CꢀBP mainly catalyzes the
Scheme 1 summarizes the proposed reaction route from 1,4ꢀAHERY to 1,4ꢀBuD. In this
coꢀcatalyzed reaction, the ReO ꢀAu/CeO catalyst is in charge of the high conversion of
1,4ꢀAHERY to 2,5ꢀDHF (step Ⅰ). Meanwhile, the ReO /CꢀBP catalyst is responsible for the
x
2
x
isomerization of 2,5ꢀDHF to 2,3ꢀDHF (step Ⅱ), hydration of 2,3ꢀDHF to 4ꢀhydroxybutanal or
the hemiacetal/acetal (step Ⅲ), as well as the hydrogenation to 1,4ꢀBuD (step Ⅳ). Although
ReO
The rateꢀdetermining step is the reaction of 1,4ꢀAHERY over ReO
reaction was the hydrogenation of 2,5ꢀDHF to THF, which was suppressed by rapid
x
ꢀAu/CeO
2
has some activity in the ReO
x
/CꢀBPꢀcatalyzed steps, its role can be limited.
x
ꢀAu/CeO . The main side
2
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conversion of DHFs over ReO
and 2,3ꢀDHF to undetectable byꢀproducts; however, this activity is suppressed by addition of
ReO ꢀAu/CeO . Overall, the use of both ReO ꢀAu/CeO and ReO /CꢀBP at once in oneꢀpot
x x
/CꢀBP. ReO /CꢀBP has activity in the side reaction of 2,5ꢀDHF
x
2
x
2
x
system is effective in suppressing side reaction of reactive intermediates, leading to high yield
of 1,4ꢀBuD from 1,4ꢀAHERY. An important point is that the concentration of intermediate
with C=C such as 2,5ꢀ and 2,3ꢀDHF, which can be polymerized to give byꢀproducts and
decrease the carbon balance, was maintained to be very low, and this can be connected to high
yield of 1,4ꢀBuD.
1
1
1
1
1
1
1
1
1
1
2
2
2
Catalyst stability
x 2 x
The drawback of this coꢀcatalysis of ReO ꢀAu/CeO + ReO /CꢀBP is the decrease of
catalytic activity after usage (Table 4). The activity of the catalyst mixture dropped from 100%
nd
conversion (fresh) to 65% in the 2 run, and the selectivity of 1,4ꢀBuD also decreased. The
carbon balance was about 90%, suggesting that a small amount of products was adsorbed on
the catalysts. The carbonaceous deposits on catalyst surface might cover the active sites
leading the deactivation of catalysts. The leached amount of Re from the mixture of
x 2 x
ReO ꢀAu/CeO + ReO /CꢀBP in the absence of air was below 0.01% of total Re amount in the
catalysts by ICP analysis (filtration after cooling), indicating that Re in both catalysts was
almost not dissolved in the solution during the reaction. However, when the reaction solution
was collected in air, the Re leaching amount from the catalyst mixture increased to 0.25%.
This is probably due to oxidation of some of Re species and dissolution into the solution. The
x
move of Re species from ReO /CꢀBP in oxidized state was also suggested by the reaction
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tests with Au/CeO
2
+ ReO
x
x
/CꢀBP (Table 1, entry 12). When the ReO /CꢀBP was reduced
before mixing, the activity of the mixture was very low (Table 1, entry 13). This suggests that
the move of Re species is suppressed during the reaction, which agrees with that the leaching
of Re from the standard mixture was negligible. Anyway, the leached Re amount was too
small to be the reason for the deactivation of catalysts. On the other hand, the Re leaching
amount of single ReO
ReO /CꢀBP showing that the Re species on C is more labile than that on CeO
can to move from C surface to CeO surface, which might be a reason for the deactivation of
ReO /CꢀBP. In our previous paper, used ReO ꢀAu/CeO catalyst can perform almost the same
x
/CꢀBP (0.39%) was higher than that of the mixture of ReO
x 2
ꢀAu/CeO +
x
2
. The Re species
2
x
x
2
3
2
1
1
1
1
1
1
1
1
1
1
2
2
2
activity after regeneration by calcination after each usage. However, the combustibility of
carbon support makes such regeneration difficult. We tested heating the used catalyst mixture
at 573 K in air. At this temperature, the combustion of carbon support is minimal based on
TGꢀDTA profile (Fig. S2, ESI). Nevertheless, the activity was further decreased (44% conv.),
and the main product was 2,5ꢀDHF, indicating that both ReO /CꢀBP and ReO ꢀAu/CeO were
x
x
2
deactivated by air treatment. Then we tested the regeneration under N
2
or H . H
2 2
regeneration
had little effect on increasing the activity of used catalyst mixture (66% conv.). Regeneration
with N at 773 K for 1 h gave better result of 91% conversion and 83% 1,4ꢀBuD selectivity.
2
However, the activity was further decreased by further uses, and it dropped to 54%
th
conversion after 4 run. The decline of selectivity was lower than the decrease of activity,
indicating that ReO
x
ꢀAu/CeO
2
was more severely deactivated than ReO
x
/CꢀBP. The low
carbon balance of entries 9 and 10 might be due to the deactivation of ReO
x
/CꢀBP.
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Conclusions
The physical mixture of ReO
effectively converted 1,4ꢀAHERY to 1,4ꢀBuD with H
x
ꢀAu/CeO
2
and ReO
x
/CꢀBP (CꢀBP = carbon black 2000)
2
as reductant. The yield of 1,4ꢀBuD
reached ~90% at the reaction temperature of 413 K. This yield is higher than the reported
ones from erythritol or 1,4ꢀAHERY over other catalysts such as ReO /C single catalyst and
x
IrꢀReO
x
/SiO
2
as stepꢀbyꢀstep CꢀO hydrogenolysis catalyst. In this reaction, ReO
x 2
ꢀAu/CeO
catalyzed deoxydehydration (DODH) of 1,4ꢀAHERY to 2,5ꢀDHF, and ReO
x
/C catalyzed
successive isomerization, hydration and reduction reactions of 2,5ꢀDHF. The use of both
catalysts at once is effective in suppressing the formation of byꢀproducts derived from reactive
intermediates such as 2,3ꢀ and 2,5ꢀDHFs. Due to the deactivation of the catalyst mixture after
1
1
1
reaction, it is important to improve the reusability of ReO
regenerable catalyst system in the future study.
x
/CꢀBP catalyst and develop a
1
1
3
4
Experimental
1
1
1
1
1
2
2
2
2
2
2
5
6
7
8
9
0
1
2
3
4
5
The ReO
x
ꢀAu/CeO
2
(1 wt% Re, 0.3 wt% Au) catalyst was prepared by
depositionꢀprecipitation method for Au loading and subsequent impregnation for Re loading
3
2
according to our previous report. The activity test was conducted with autoclave reactor
equipped with an inner glass cylinder. After reaction, both gas and liquid phases were
analyzed by FIDꢀGC. The carbon balance (C.B.) of each analysis result was calculated using
eqn (10). The sum of the detected but unidentified products is denoted as “others” in results.
The FID sensitivity of “others” was assumed to be the same as that of 1,4ꢀbutanediol
(1,4ꢀBuD) unless denoted. When the C.B. is in the range of 100 ± 10% considering the
experimental error, the conversion and selectivity on the carbon basis are calculated by eqn
(11) and (12), respectively, and the data of C.B. are not shown in each result. In contrast,
when the C.B. is clearly lower than 100% (<90%), the conversion and selectivity on carbon
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basis are calculated by eqn (13) and (14) as below. The selectivity of “others” is the same as
the above case. The data of C.B. are shown in each result when clearly below 100%. We
think two reasons for low C.B. in the results. One is the use of substrate with low boiling
point, in particular, 2,3ꢀDHF. (b.p. 327 K). In the experiments of 2,3ꢀDHF substrate (Table 3,
entries 8ꢀ11), and in the results of significant yield of 2,3ꢀDHF product in the reaction of
1,4ꢀanhydroerythritol (Table 1, entries 3ꢀ5), it is thought that a part of 2,3ꢀDHF can be lost
2
during the purge of H before reaction and the filtration after reaction. The other reason is the
side reactions such as polymerization of unsaturated compounds like 2,5ꢀDHF or 2,3ꢀDHF
giving undetected products, and this phenomenon seems to be observed remarkably on
1
1
1
ReO /CꢀBP in Table 3, entries 1 and 4. The yield was calculated by eqn (15) for both cases.
x
The detailed experimental procedures are also described in electronic supplementary
information (ESI).
Amount of remaining substrateꢀꢁCꢀmolꢂ + Total amount of detected productsꢀꢁCꢀmolꢂ
C. B.ꢀꢁ%ꢂ=
×100
(10)
Amount of initial substrate (Cꢀmol)
1
1
1
1
1
3
4
5
6
7
Total amount of detected productsꢀꢁCꢀmolꢂ
Amount of remaining substrateꢀꢁCꢀmolꢂ + Total amount of detected productsꢀꢁCꢀmolꢂ
Conversionꢀꢁ%ꢂ=
×100
(11)
Amount of AꢀꢁCꢀmolꢂ
Total amount of detected productsꢀꢁCꢀmolꢂ
Selectivity of product Aꢀꢁ%ꢂ=
×100
×100
(12)
Amount of remaining substrateꢀꢁCꢀmolꢂ
Amount of initial substrate (Cꢀmol)
Conversionꢀꢁ%; low C. B.ꢂ=100ꢀ
(13)
Amount of A ꢁCꢀmolꢂ
Selectivity of product A ꢁ%; low C. B.ꢂ=
×100 (14)
Amount of initial substrate ꢁCꢀmolꢂꢀꢀ Amount of remaining substrate ꢁCꢀmolꢂ
Conversion (%) × Selectivity (%)
(15)
Yieldꢀꢁ%ꢂ=
100
2
0

Page 21 of 35
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Acknowledgments
This work is in part supported by “ALCA” program of Japan Science and Technology
Agency. We also thank Technical Division, School of Engineering, Tohoku University, for
NMR measurements.
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Page 25 of 35
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DOI: 10.1039/C8GC00574E
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2
a
Table 1 Reaction of 1,4ꢀAHERY over various supported Re catalysts combined with ReO ꢀAu/CeO2
x
Conv. /%
Product selectivity /%
Entry
Catalyst 1
Catalyst 2
(
C.B. /%) 1,4ꢀBuD THF 2,5ꢀDHF 2,3ꢀDHF GBL 1ꢀBuOH Acetal Others
1
2
3
4
5
6
7
8
ReO
ReO
ReO
ReO
ReO
ReO
ReO
ReO
x
x
x
x
x
x
x
x
–Au/CeO
–Au/CeO
–Au/CeO
–Au/CeO
–Au/CeO
–Au/CeO
–Au/CeO
–Au/CeO
—
2
2
2
2
2
2
2
2
ReO
x
/CꢀBP
/CꢀNR
/SiO
/TiO
/ZrO
/Al
/MgO
100
87
86
75
7
8
9
0
0
0
0
2
3
2
3
0
5
3
4
ReO
x
ReO
x
2
58 (86)
8
34
56
29
83
85
89
4
9
1
0
1
16
5
ReO
x
2
100 (86)
3
3
17
27
11
9
2
0
0
ReO
x
2
100 (82)
7
12
3
0
1
0
5
ReO
x
2
O
3
99
87
64
2
1
0
0
0
2
ReO
x
2
2
0
0
0
1
—
0
1
6
0
0
0
4
9
ReO
x
/CꢀBP
/CꢀBP
18
3
10
1
0
0
4
0
65
15
—
4
b
1
0
ReO
x
–Au/CeO
2
ReO
x
8
23
—
1
0
11
—
0
1
45
—
1
1
1
2
Au/CeO
Au/CeO
Au/CeO
2
2
2
—
< 1
80
3
—
90
12
—
4
—
1
—
0
1
ReO
x
/CꢀBP
/CꢀBP
c
1
3
ReO
x
2
0
2
0
0
0
82
a
3
4
1,4ꢀAHERY = 0.5 g, Wcat 1 = 0.15 g (Re = 1 wt%, Au = 0.3 wt%), Wcat 2 = 0.15 g (Re = 3 wt%), 1,4ꢀDioxane = 4
b
c
H x 2
g, P 2 = 8 MPa, T = 413 K, t = 24 h. PAr = 5 MPa. ReO /CꢀBP was reduced by H in 1,4ꢀdioxane at 413 K for 1
5
6
7
h before reaction. AHERY: anhydroerythritol, BuD: butanediol, THF: tetrahydrofuran, DHF: dihydrofuran, GBL:
γꢀbutyrolactone, BuOH: butanol, Acetal: 3,4ꢀ(4ꢀhydroxybutylidenedioxy)ꢀtetrahydrofuran. CꢀBP: carbon black
BP2000, CꢀNR: activated carbon Norit RX3 extra.
8
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2
Table 2 Effect of water addition to the1,4ꢀdioxane solvent in the reaction of 1,4ꢀAHERY over
a
3
ReO
x
ꢀAu/CeO
2
and ReO
x
/CꢀBP catalysts
Product selectivity /%
1,4ꢀBuD THF 2,5ꢀDHF 2,3ꢀDHF GBL 1ꢀBuOH Acetal Others
Water: 1,4ꢀAHERY
molar ratio
Entry
Conv. /%
1
2
3
4
0
0.25
1
100
86
86
90
92
91
8
5
3
2
0
0
0
0
0
0
0
0
2
1
1
1
2
1
1
1
0
0
0
0
3
2
2
5
77
4
35
a
4
5
6
1,4ꢀAHERY = 0.5 g, water = 0 to 0.3 g, Wcat (ReO ꢀAu/CeO , Re = 1 wt%, Au = 0.3 wt%) = 0.15 g, Wcat (ReO /CꢀBP, Re = 3 wt%) = 0.15
x 2 x
g, 1,4ꢀDioxane = 4 g, PH2 = 8 MPa, T = 413 K, t = 24 h. AHERY: anhydroerythritol, BuD: butanediol, THF:
tetrahydrofuran,
DHF:
dihydrofuran,
GBL:
γꢀbutyrolactone,
BuOH:
butanol,
Acetal:
7
8
9
3,4ꢀ(4ꢀhydroxybutylidenedioxy)ꢀtetrahydrofuran.
2
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Page 27 of 35
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DOI: 10.1039/C8GC00574E
a
1
Table 3 Reaction of 1,4ꢀAHERY and the intermediates over related catalysts
Catalyst
Conv. /%
(C.B. /%)
Entry
1
Substrate
Catalyst
Products (yield /%)
weight /g
O
O
O
ReO
x
ꢀAu/CeO
2
2
HO
0.15 + 0.15
OH (90),
(4),
(4),
100
+
ReO
x
/CꢀBP
others (2)
O
O
O
O
2
3
ReO
x
ꢀAu/CeO
0.15
0.15
100
(
32),
(27),
(25), others (6)
(0.3), others (1)
HO
OH
O
x
ReO /CꢀBP
HO
HO
33 (69)
OH (1),
O
O
O
ReO
x
ꢀAu/CeO
2
2
4
5
6
0.15 + 0.15
0.15
OH (80),
(13),
(4),
98
45
+
ReO /CꢀBP
x
others (3)
O
O
HO
ReO
x
ꢀAu/CeO
(23),
(13),
OH (2),
O
others (3)
O
O
O
HO
ReO /CꢀBP
0.15
OH (39),
(9),
(8),
94 (70)
x
others (9)
O
O
O
O
O
O
OH
7
8
9
CꢀBP
0.15
(3),
(1),
(1),
4
(
0.5), others (0.5)
O
ReO
x
ꢀAu/CeO
2
2
O
0.15 + 0.15 HO
100 (78)
+
ReO /CꢀBP
OH (60),
(12), others (6)
x
O
O
O
O
OH
HO
ReO
x
ꢀAu/CeO
0.15
0.15
(5),
OH (3),
49 (71)
(
2), others (10)
O
O
O
O
HO
1
0
1
ReO /CꢀBP
OH (24),
(6),
(2),
100 (38)
98 (80)
x
others (6)
O
O
O
O
O
OH
1
CꢀBP
0.15
(
46),
(18),
OH (8),
others (5)
a
2
3
Substrate = 0.15 g, water = 0.03ꢀ0.04 g (water : substrate molar ratio = 1 : 1), Wcat = 0.15 g for single, or 0.15 +
0.15 g for mixture (ReO
x
–Au/CeO
2
x
, Re = 1 wt%, Au = 0.3 wt%; or ReO /CꢀBP, Re = 3 wt%; or CꢀBP),
O
4
1,4ꢀDioxane = 4 g, PH2 = 8 MPa, T = 413 K, t = 4 h. HO
OH 1,4ꢀAHERY: 1,4ꢀanhydroerythritol;
2
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DOI: 10.1039/C8GC00574E
O
O
O
HO
1
OH 1,4ꢀBuD: 1,4ꢀbutanediol;
GBL: γꢀbutyrolactone;
THF: tetrahydrofuran;
O
O
O
OH
2
3
4
2,5ꢀDHF:
2,5ꢀdihydrofuran;
2,3ꢀDHF:
2,3ꢀdihydrofuran;
2ꢀHTHF:
2ꢀhydroxytetrahydrofuran.
2
8

Page 29 of 35
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a
Table 4 Reusability of the mixture of ReO ꢀAu/CeO and ReO /CꢀBP catalysts
x
2
x
Pretreatment
conditions
−
Usage Conv. /%
Product selectivity /%
Entry
time
1
(C.B. /%) 1,4ꢀBuD THF 2,5ꢀDHF 2,3ꢀDHF GBL 1ꢀBuOH Acetal Others
1
2
3
4
5
6
7
8
9
100
65
86
71
0
8
6
1
8
8
8
6
5
7
6
0
2
0
0
0
0
0
0
0
0
0
0
2
3
1
4
4
4
4
2
3
2
2
1
0
1
1
1
1
1
1
1
0
10
9
3
6
Nonꢀtreated
Air, 573 K, 4 h
2
2
44
80
0
9
H , 773 K, 3 h
2
2
66
70
68
79
83
82
58
54
8
9
N
N
2
2
, 773 K, 0.2 h
, 773 K, 0.5 h
2
69
0
9
11
5
2
79
0
2
N
2
2
, 773 K, 1 h
, 773 K, 3 h
2
91
0
1
4
N
2
65
0
4
6
N , 773 K, 1 h
2
3
76 (84)
61 (85)
0
1
9
1
0
N
2
, 773 K, 1 h
4
0
5
7
a
3
4
5
1,4ꢀAHERY = 0.5 to 0.3 g (based on the weight of catalysts), Wcat mixture = 0.3 to 0.18 g (ReO
x 2
–Au/CeO , Re = 1
x
wt%, Au = 0.3 wt%; ReO /CꢀBP, Re = 3 wt%), 1,4ꢀDioxane = 4 g, PH2 = 8 MPa, T = 413 K, t = 24 h. AHERY:
anhydroerythritol, BuD: butanediol, THF: tetrahydrofuran, DHF: dihydrofuran, GBL: γꢀbutyrolactone, BuOH:
6
7
butanol, Acetal: 3,4ꢀ(4ꢀhydroxybutylidenedioxy)ꢀtetrahydrofuran.
2
9