Stable vapor-phase conversion of tetrahydrofurfuryl alcohol into 3,4-2H-dihydropyran

Article abstract of DOI:10.1016/j.apcata.2012.12.017

Vapor-phase synthesis of 3,4-2H-dihydropyran (DHP) from tetrahydrofurfuryl alcohol (THFA) was investigated over acidic catalysts modified with transition metals. Catalytic activity of alumina was seriously deactivated in the reaction of THFA in nitrogen at 300 °C although the initial activity was high. Tetragonal ZrO₂ showed the catalytic activity to produce DHP at 350 °C. Alumina modified with Cu exhibits stable catalytic activity with high selectivity to DHP under hydrogen flow conditions, and the optimum activity was obtained at CuO contents of 5-10 wt.%: the selectivity to DHP was as high as 85%. Prior to the reaction, CuO was reduced to metallic Cu, which probably works as a product remover together with hydrogen to prevent coke formation. The reaction pathway from THFA to DHP was discussed: it is speculated that THFA is initially rearranged into 2-hydroxytetrahydropyran, which rapidly dehydrated to DHP.

Full text of DOI:10.1016/j.apcata.2012.12.017

Applied Catalysis A: General 453 (2013) 213–218
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Stable vapor-phase conversion of tetrahydrofurfuryl alcohol into
3,4-2H-dihydropyran
Satoshi Sato∗, Jun Igarashi, Yasuhiro Yamada
Graduate School of Engineering, Chiba University, Yayoi, Inage, Chiba 263-8522, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 October 2012
Received in revised form 1 December 2012
Accepted 8 December 2012
Available online 26 December 2012
Vapor-phase synthesis of 3,4-2H-dihydropyran (DHP) from tetrahydrofurfuryl alcohol (THFA) was inves-
tigated over acidic catalysts modified with transition metals. Catalytic activity of alumina was seriously
deactivated in the reaction of THFA in nitrogen at 300 ◦C although the initial activity was high. Tetragonal
ZrO2 showed the catalytic activity to produce DHP at 350 ◦C. Alumina modified with Cu exhibits stable
catalytic activity with high selectivity to DHP under hydrogen flow conditions, and the optimum activity
was obtained at CuO contents of 5–10 wt.%: the selectivity to DHP was as high as 85%. Prior to the reaction,
CuO was reduced to metallic Cu, which probably works as a product remover together with hydrogen
to prevent coke formation. The reaction pathway from THFA to DHP was discussed: it is speculated that
THFA is initially rearranged into 2-hydroxytetrahydropyran, which rapidly dehydrated to DHP.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Dehydration
Tetrahydrofurfuryl alcohol
3,4-2H-dihydropyran
Alumina catalyst
Copper
Rhodium
Inhibition of coke formation
1. Introduction
amine, furoic acid, 2-methylfuran, 2-methyltertahydrofuran, furan,
tetrahydrofuran [7–9], and cyclopentanone [10].
Biomass has the potential to serve as a sustainable chemi-
cal resource in the industrial society. In biorefinery development,
various biomass-based chemicals have been listed as potential can-
didates of biorefinery building blocks, and furfural is expected as
one of new candidates [1]. The new top 10 candidates are ethanol,
furans including furfural, glycerol, biohydrocarbons including iso-
prene, lactic acid, succinic acid, hydroxypropionic acid/aldehyde,
levulinic acid, sorbitol, and xylitol in this order. Furfural has been
widely investigated on the catalytic conversion into useful chem-
icals, whereas the reports of furfural are much less than those of
ethanol and glycerol.
Furfural with a low oxygen content is one of promising alterna-
tive chemical resources, and commercial production of furfural is
well established [1]. Furfural is prepared through the dehydration
of pentose polyols, such as xylose, or hemicelluloses catalyzed by
sulfuric acid [2–4] and solid acid [5,6]. Hemicellulose, a polymer
of glucose and xylose, is inedible biomass of some hardwoods and
agriculture residues such as corncob and sugar cane bagasse [2].
Furfural can be derived to useful chemicals, such as furfuryl alcohol,
tetrahydrofurfuryl alcohol (hereafter abbreviated as THFA), furfuryl
THFA can be obtained in the hydrogenation of furfural [8,11]
and is used as an industrial solvent [9]. Various useful chemicals,
such as ␦-valerolactone [12,13], tetrahydrofuran [13–16], 3,4-
2H-dihydropyran (abbreviated as DHP) [17–26], 1,5-pentanediol
[7,18,27–31], and 4-penten-1-ol [12,32–34], can be derived from
THFA. In industrial applications, DHP is a chemical intermediate: it
can be hydrated into 5-hydroxypentanal, which is further hydro-
genated into 1,5-pentandediol [18]. DHP is also well known as a
protection reagent of alcohol in organic synthesis [35].
It has been known that THFA is converted into DHP over alumina
catalyst since 1930s (Fig. 1) [18]. The alumina catalyst, however, is
readily deactivated in inert atmosphere such as N2 and He flow, so
that the yield of DHP is so high only in the initial period [17–19].
Several modifications of alumina with other metal oxides are found
in patent literatures: TiO2-rich TiO2-Al2O3 [20], V2O5/Al2O3 [22],
MoO3/Al2O3 [22], and alumina catalysts modified with various
metal oxides [23,24] work as a catalyst. It is reported that DHP yields
exceed 90% at 250–320 ◦C [20,26], while the deactivation behavior
is unclear. The catalyst needs regeneration process for the catalysts
used in the reaction [20].
There are several reports on the inhibition of deterioration of
acid-catalyzed reactions with the aid of supported noble metal in
hydrogen gas [36–38]. We have also found that alumina modified
by transition metals such as Co stabilizes the conversion of 3,3-
dimethyl-2-butanoneto produce 2,3-dimethyl-1,3-butadienein H2
∗
Corresponding author. Tel.: +81 43 290 3376; fax: +81 43 290 3401.
E-mail address: satoshi@faculty.chiba-u.jp (S. Sato).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.12.017

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S. Sato et al. / Applied Catalysis A: General 453 (2013) 213–218
Table 1
O
O
-
H2O
Physical and chemical properties of oxide catalysts.
OH
a
Catalyst
SA (m2g−1
)
NH3 desorption below 500 ◦Cb
Peak (◦C)
Amount (␮mol g−1
)
Fig. 1. Dehydration of THFA to DHP.
Al2O3
t-ZrO2
m-ZrO2
TiO2
200
179
39
260
262
217
246
147
108
2
flow [39], whereas the catalytic activity of alumina is seriously dete-
riorated irrespective of its high initial activity. Hydrogen with the
supported metal probably removes the product from the acid sites
prior to coke formation and plays an important role to stabilize the
catalytic activity of alumina.
42
97
t-ZrO2, tetragonal ZrO2; m-ZrO2, monoclinic ZrO2.
a
Specific surface area.
Calculated from TPD profiles in Fig. 2.
b
In this paper, we investigated effective systems for the con-
version of THFA into DHP to stabilize the catalytic activity and
discussed the reaction pathway from THFA to DHP together with
side reactions.
Temperature-programmed desorption (TPD) of NH3 adsorbed
at 100 ◦C was examined by neutralization titration using an elec-
tric conductivity cell immersed in aqueous H2SO4 solution, and the
detail procedure has been described elsewhere [41]. NH3 that des-
orbed with N2 carrier gas was bubbled into a dilute H2SO4 solution.
The amount of desorbed NH3 was monitored from the change in
conductivity of the solution. The sample was heated from 25 to
800 ◦C at a rate of 10 ◦C min−1 in N2 flow of 50 cm3 min−1. The
amount of acid sites is defined as the number of NH3 molecules
desorbed in the temperature range of 25–500 ◦C on the assump-
tion that one NH3 molecule adsorbs on one basic site of the catalyst
surface.
Temperature-programmed reduction (TPR) measurements
were performed from 25 to 900 ◦C at a heating rate of 5 K min−1 to
characterize the state of the supported metals. A mixture of H2/N2
(=1/9) was flowed at a rate of 10 cm3 min−1 and ambient pressure
over the catalyst filled in a quartz tube. The amount of H2 consumed
during the reduction was monitored with a thermal conductivity
detector.
2. Experimental
2.1. Catalyst samples
THFA and DHP were purchased from Tokyo Chemical Indus-
try Co, Ltd. 2-Hydroxyteterahydropyran was synthesized via the
hydration of DHP, according to a reference [40]. Metal nitrates such
as Co(NO3)2, Ni(NO3)2, and Cu(NO3)2 were purchased from Wako
Pure Chemical Industries Ltd. Alumina-supported noble metal cat-
alysts, such as M/Al2O3 (M = Rh, Pt, Pd; 0.5 wt.%), were supplied by
N.E. Chemcat Co. ␥-Al2O3 (DC-2382) and anatase TiO2 (DC-3124)
were supplied by Dia Catalyst. Tetragonal ZrO2 (abbreviated as
t-ZrO2) was supplied by Saint-Gobain K. K. and monoclinic ZrO2
(m-ZrO2) by Daiichi Kigenso Kagaku Kogyo Co. Yb2O3 and La2O3
were supplied by Kanto Kagagu Co., Ltd.
Supported base-metal catalysts were prepared by impregna-
tion using aqueous metal nitrate solution. The nitrate solution was
added to a support, and water was evaporated at ambient pressure
and 70 ◦C by being illuminated by 350-W electric light bulb. After
impregnation, the obtained solid was dried at 110 ◦C over 24 h and
then calcined at 500 ◦C for 3 h.
3. Results and discussion
3.1. Characterization of catalyst samples
Table 1 summarized specific surface area of oxide catalysts such
as Al2O3, t-ZrO2, m-ZrO2 and TiO2. Fig. 2 shows TPD profiles of
NH3 adsorbed on the samples. The samples have desorption peak
around 250 ◦C. The amount of desorbed NH3 as a function of acid
sites is also summarized in Table 1. Monoclinic ZrO2 was not acidic
because NH3 did not adsorb at 100 ◦C. It was proved that Al2O3,
t-ZrO2 and TiO2 were acidic, as it is well known.
2.2. Catalytic reaction
The reaction of THFA to DHP was performed in a fixed-bed
down-flow glass tube reactor with an inner diameter of 17 mm and
a length of 300 mm at 200–300 ◦C under atmospheric pressure at
N2- or H2-flow rate of 20 cm3 min−1. Prior to the reaction, the cat-
alyst was preheated in the carrier gas at 500 ◦C for 1 h. After the
preheating, the catalyst bed was cooled to the reaction temper-
ature, and the substrate was fed into the reactor at a liquid feed
rate of 1.5 cm3 h−1. Unless otherwise noted, a reaction was car-
ried out under the conditions using a catalyst of 0.5 g at 300 ◦C
and W/F = 0.32 g h cm−3, where W and F are catalyst weight and
reactant feed rate, respectively. The effluent was collected every
hours for 5 h at 0 ◦C and analyzed by FID-GC (GC-8A, Shimadzu Co.)
using a 60-m capillary column of TC-WAX (GL Science Inc.). A GC-
MS (QP5050A, Shimadzu Co.) was used to identify products in the
effluent.
4
Al2O3
3
t-ZrO2
2
m-ZrO2
1
2.3. Characterization of catalyst
TiO2
600
The specific surface area of the catalyst, SA, was calculated with
the BET method using N2 isotherm at −196 ◦C. Thermogravimetry-
differential thermal analysis (TG-DTA) was conducted in air
using Thermo plus TG8120 (Rigaku Co.). Transmission electron
microscopy (TEM) image was taken by a JEOL JEM-2100F micro-
scope operated at 120 kV.
0
0
200
400
Temperature / oC
Fig. 2. TPD profiles of NH3 adsorbed on oxide catalysts.

S. Sato et al. / Applied Catalysis A: General 453 (2013) 213–218
215
CuO
Co2O3
NiO
Rh
Pd
Pt
Fig. 4. TEM image of 10 wt% CuO/Al2O3 reduced at 500 ◦C.
0
200
400
600
800
Temperature / ºC
Al2O3, change in selectivity in H2 flow was similar to that in N2 flow
(Fig. 5A).
Fig. 3. TPR profiles of Al2O3-supported metal catalysts. Metal loading, 15 wt.% for
CuO, Co2O3, and NiO; 0.5 wt.% for Rh, Pd, and Pd.
3.3. Reaction of THFA over alumna catalysts modified with metals
Fig. 3 shows TPR profiles of alumina-supported metal oxides.
Co3O4/Al2O3 had reduction peaks at 339, 488, and 583 ◦C, and
NiO/Al2O3 had reduction peaks at 467 and 520 ◦C. CuO/Al2O3 had
reduction peaks at 221 and 246 ◦C. Rh/Al2O3 had a very small reduc-
tion peak at 231 ◦C, while Pt/and Pd/Al2O3 had no peaks. The TPR
results indicate that the supported metals of CuO/Al2O3, Pd/Al2O3,
Pt/Al2O3, and Rh/Al2O3 are in metallic state in the reaction of
THFA in H2 flow at 300 ◦C. Fig. 4 shows a TEM image of 15 wt%
CuO/Al2O3 reduced at 500 ◦C. Bright particles of alumina with the
size of 20–30 nm and dark copper particles with the same size as
alumina were observed in the sample.
Table 3 lists average catalytic activity of the samples in the initial
5 h. Commercial Rh/Al2O3 and Pd/Al2O3 used as a catalyst seemed
to have moderate activity in N2 flow at 300 ◦C. However, they were
deteriorated with time on stream, as shown in blue dotted lines
in Fig. 5B and C. The main product was DHP, and the by-products
were tetrahydropyran and ␦-valerolactone. In H2 flow, however,
Rh/Al2O3 showed stable conversion of THFA (Fig. 5B), while the
selectivity to DHP varied with time on stream. On the other hand,
Pt/Al2O3 and Pd/Al2O3 showed low selectivity to DHP in H2 flow
because hydrogenation to tetrahydropyran proceeded (Table 3),
and mass balance was low because of gasification.
Pt supported on acidic catalysts such as sulfated ZrO2 shows
a stable activity in the isomerization of alkane [36–38]. Unfor-
tunately, noble metals such as Pt, Rh, and Pd are insufficient for
keeping stable catalytic activity in H2 flow. The by-products were
tetrahydropyran, tetrahydrofuran, 1-pentanol, and 1-butanol in H2
flow over the catalysts. In addition, over Rh/Al2O3 and Pd/Al2O3,
␦-valerolactone was produced at 300 ◦C, and 1,5-pentandiol was
detected in H2 flow at a low temperature of 250 ◦C.
In contrast to the noble metals, CuO/Al2O3 showed stable con-
version and high selectivity to DHP in H2 flow, while it was
deteriorated in N2 flow (Fig. 5D). The by-products were tetrahy-
dropyran and ␦-valerolactone with a small amount produced even
in H2 flow. Mass balance in H2 flow over CuO/Al2O3 was as high
as that of Rh/Al2O3. Judging from the results of TPR (Fig. 3), it is
3.2. Reaction of THFA over several oxide catalysts
Table 2 summarizes the catalytic performance of several metal
oxide catalysts in the dehydration of THFA at 300 or 350 ◦C in N2
flow. DHP was produced over acid catalysts such as Al2O3, t-ZrO2,
and TiO2, whereas DHP could not be produced over m-ZrO2 and
rare earth oxides such as Yb2O3 and La2O3, which have only basic
sites [42]. Catalytic activity of acidic Al2O3 and t-ZrO2 was signif-
icantly decreased with time on stream, as shown in Fig. 5A. TiO2
also showed deterioration (figure not shown). In the acid catalysts,
Al2O3 and t-ZrO2 showed moderate activity to DHP because the
catalytic deactivation was occurred in 5 h. Thus, the results indi-
cate that dehydration of THFA needs acidic sites. In addition, over
Table 2
Dehydration of THFA over metal oxide catalysts in nitrogen flow.a
Catalyst
Temperature (◦C)
Conversion (%)
Selectivity (mol%)
DHP
THP
DVL
Others
Unrecovered
Al2O3
t-ZrO2
m-ZrO2
TiO2
Yb2O3
La2O3
300
350
350
350
300
300
85.2
85.9
17.4
47.5
16.6
7.2
71.8
71.0
7.9
27.7
0
0.3
0.3
0.2
0.2
0
0.3
0.6
1.9
0.4
0
4.5
5.1
31.2
7.6
7.4
78.7
23.1
23.1
58.7
64.1
92.6
21.3
0
0
0
THFA, tetrahydrofurfuryl alcohol; DHP, 3,4-2H-dihydropyran; THP, tetrahydropyran; DVL, ␦-valerolactone. Others contain several unidentified products. Unrecovered
products include gases and polymer products.
a
Reaction conditions were the same as those described in Section 2. Conversion and selectivity are the average of 1 h and 5 h.

216
S. Sato et al. / Applied Catalysis A: General 453 (2013) 213–218
100
80
60
40
20
100
80
60
Al2O3 in H2 at 300 oC
40
in H2
in N2
Al2O3 in N2 at 300 oC
ZrO2 in N2 at 350 oC
20
(A)
(B)
4
1
2
3
4
5
1
2
3
5
0
0
Time on stream / h
Time on stream / h
100
80
60
40
20
100
80
60
40
20
in H2
in N2
in H2
in N2
(C)
4
(D)
4
1
2
3
5
0
1
2
3
5
0
Time on stream / h
Time on stream / h
Fig. 5. Change in THFA conversion and DHP selectivity in different carrier gases with time on stream. (A) Al2O3 and ZrO2, (B) 0.5 wt.% Rh/Al2O3, (C) 0.5 wt.% Pd/Al2O3, and
(D) 15 wt.% CuO/Al2O3. Reaction was performed at 300 ◦C except for ZrO2 at 350 ◦C. Other conditions were the same as those described in Section 2.
obvious that Cu species are reduced to metallic state, which could
be maintained during the reaction in H2 flow.
Co3O4/Al2O3 had a similar catalytic behavior to those of Pt/Al2O3
and Pd/Al2O3: mass balance was low because of gasification. The
by-products were tetrahydropyran, tetrahydrofuran, 1-pentanol,
1-butanol, and ␦-valerolactone in H2 flow over NiO/Al2O3 catalyst,
while the by-products over Co3O4/Al2O3 catalyst were tetrahy-
dropyran, tetrahydrofuran, and ␦-valerolactone.
Table 4 shows the effect of CuO content of Al2O3-supported
catalysts on the reaction of THFA in H2 flow at 300 ◦C. The THFA con-
version was almost constant irrespective of CuO content or might
gradually increase with increasing CuO content. On the other hand,
the selectivity to DHP seems to be maximized at CuO content of
5–10 wt.%: mass balance in this CuO range was better than that at
high CuO contents as well as that at low contents.
3.4. Characterization of alumina used in the reaction
Fig. 6 depicts the change in catalytic activity of NiO/Al2O3 and
Co3O4/Al2O3 in H2 flow with time on stream, together with that of
CuO/Al2O3. Table 3 also lists their average activity. NiO/Al2O3 and
Fig. 7 shows TG-DTA profiles of pure Al2O3 and 5 wt.% CuO/Al2O3
catalysts used in the reaction in H2 flow at 300 ◦C for 5 h. A
large weight loss was observed at temperatures of 200–500 ◦C and
Table 3
Catalytic dehydration of THFA over alumna-supported catalysts in H2 at 300 ◦C.a
Metal or metal oxide
(content wt.%)
Conversion (%)
Selectivity (mol%)
DHP
THP
DVL
Others
Unrecovered
None
Rh
Rh
Pd
Pd
(0)
85.2
85.9
63.5 (in N2)
97.2
71.3 (in N2)
95.6
79.8
95.0
96.9
71.8
79.0
63.6
16.7
68.2
10.9
36.2
36.4
76.9
0.3
1.5
0.5
23.0
0.6
20.5
1.7
0.3
0.2
0.3
0
0.1
0
1.1
0.3
0.3
4.5
5.2
4.7
12.1
3.9
21.1
11.3
13.1
3.6
23.1
14.1
31.0
48.2
27.2
47.6
49.7
44.6
18.4
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(15)
(15)
(15)
Pt
Co3O4
NiO
CuO
5.6
0.8
Abbreviations are the same as those in Table 2. Others contain tetrahydrofuran, 1-butanol, 1-pentanol, 1,5-pentanediol and unidentified products. Unrecovered products
include gases and polymer products.
a
Reaction conditions were the same as those described in Section 2. Conversion and selectivity are the average of 1 h and 5 h.

S. Sato et al. / Applied Catalysis A: General 453 (2013) 213–218
217
Table 4
Catalytic dehydration of THFA over Al2O3-supported CuO catalysts in H2 flow at 300 ◦C.a
CuO loading (wt.%)
Conversion (%)
Selectivity (mol%)
DHP
THP
DVL
Others
Unrecovered
0
2
5
10
15
20
83.2
93.7
92.3
88.7
96.9
99.1
71.6
72.1
85.4
86.4
76.9
78.2
0.3
0.4
0.7
0.4
0.8
0.7
0.2
0.3
0.2
0.2
0.3
0.3
4.4
3.8
3.3
4.8
3.5
2.9
23.6
23.4
10.4
8.1
18.4
17.9
Abbreviations are the same as those in Table 2. Others contain unidentified products.
a
Reaction conditions were the same as those described in Section 2. Conversion and selectivity are the average of 1 h and 5 h.
100
+H2
-H2O
OH
O
O
O
OH
O
O
80
60
40
20
-H2
+H2
HO
CuO
Co2O3
NiO
O
O
-CH2O
+H2
HO
Fig. 8. Probable reaction routes in the reaction of THFA over alumina catalyst.
2-Hydroxytetrahydropyran was not detected in the THFA conversion at 300 ◦C.
exothermic peak at 300 ◦C, while the fresh CuO/Al2O3 had a weight
loss of dehydration with 4.1%. The weight loss in the removed
carbonaceous materials can be estimated by the difference of the
weight loss between fresh and used catalysts: the amounts of coke
deposited on pure Al2O3 and CuO/Al2O3 are 11.5 and 7.7%, respec-
tively. This indicates that the coke formation is inhibited in the
reaction over CuO/Al2O3 under H2 atmosphere conditions.
0
1
2
3
4
5
Time on stream / h
Fig. 6. Change in THFA conversion and DHP selectivity in H2 flow at 300 ◦C with
time on stream over 15 wt.% CuO/Al2O3 (circle), 15 wt.% Co2O3/Al2O3 (triangle) and
15 wt.% NiO/Al2O3 (squere) catalysts. Reaction conditions were the same as those of
described in Section 2.
3.5. Probable reaction route over alumina
180–450 ◦C in the samples of Al2O3 and CuO/Al2O3, respectively.
The alumina used in the reaction had a weight loss with 14.5% in
the TG profile at 500 ◦C, while the fresh alumina had a weight loss of
dehydration with 3.0%. The difference of the weight loss between
fresh and used catalysts would be regarded as carbon deposited
on the samples during the reaction. The carbon was exothermi-
cally removed in air at 330 and 440 ◦C (Fig. 7), and the color of the
used alumina turned white after TG analysis. The CuO/Al2O3 used
in the reaction, however, had a weight loss with 11.8% at 500 ◦C and
In
order
to
prove
an
intermediate
species,
2-
hydroxytetrahydropyran (2HTHP) was prepared as an intermediate
candidate. When 2HTHP, instead of THFA, was fed into the reactor
over Cu-alumina catalyst in H2 at 200 ◦C, 2HTHF was converted
to DHP and to ␦-valerolactone with the selectivity of 64 and
10%, respectively, at 100% conversion. The other products were
1-pentanol, pentanoic acid, and 1,5-pentanediol. Therefore, 2HTHP
can be readily dehydrated to DHP at a temperature lower than
300 ◦C which is the effective reaction temperature of THFA. It is
proposed that 2HTHP is probably an intermediate from THFA to
DHP.
Fig. 8 summarizes a probable reaction routes in the conver-
sion of THFA over modified alumina catalysts. At 300 ◦C, THFA
could be rearranged into 2HTHP. 2HTHP is immediately dehy-
drated to DHP, so that it could not be detected in the effluent
mixture. Thus, the rate determining step is probably the initial step,
which is the rearrangement of THFA into 2HTHP. The major by-
products such as tetrahydropyran and ␦-valerolactone are formed
through step-wise hydrogenation of DHP and dehydrogenation
of 2HTHP, respectively. Over the catalysts with high potential in
hydrogenation and hydrogenolysis, 1-pentanol, tetrahydrofuran,
and 1-butanol are formed via step-wise reactions, as shown in Fig. 8.
4. Conclusions
Fig. 7. TG-DTA profiles of Al2O3 and CuO/Al2O3 samples in air. (a) fresh Al2O3, (b)
fresh 5 wt.% CuO/Al2O3, (c) Al2O3 used in the reaction, and (d) 5 wt.% CuO/Al2O3
catalyst used in the reaction. The reaction of THFA was performed in H2 flow at
300 ◦C for 1 h.
Vapor-phase catalytic conversion of THFA to produce DHP was
investigated over acidic catalysts modified with transition metals.
Catalytic activity of alumina was seriously deactivated in N2 flow

218
S. Sato et al. / Applied Catalysis A: General 453 (2013) 213–218
at 300 ◦C, whereas the initial activity was high. Tetragonal ZrO2
also showed the same catalytic activity as alumina at 350 ◦C. The
catalytic activity of alumina modified with either Cu or Rh was
stabilized in the conversion of THFA into DHP under H2 flow con-
ditions. The optimum activity was obtained in the catalysts at
CuO contents of 5–10 wt.%: the selectivity to DHP exceeded 85%
and the best mass balance was achieved. CuO was reduced to
metallic Cu that was maintained during the reaction at 300 ◦C,
Cu metal probably works as a remover for deposited carbon and
prevents coke formation by the aid of hydrogen. In the conver-
sion of THFA to DHP, we propose that THFA is initially rearranged
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