9
0
S. Koso et al. / Journal of Catalysis 267 (2009) 89–92
Catalytic testing was performed in a 190-ml stainless steel
3. Results and discussion
autoclave with an inserted glass vessel. An aqueous tetra-
hydrofurfuryl alcohol solution of various concentrations was
placed into the autoclaves together with an appropriate amount
of catalysts (see Tables 1 and 2 for actual reaction conditions)
and stirring bar. After sealing the reactors, their air contents were
purged by flushing thrice with 1 MPa hydrogen (99.99%; Takachiho
Chemical Industrial Co. Ltd.). Autoclaves were then heated to the
required temperature and pressurized to 1 MPa for the reduction
The activity of Rh–MoO /SiO catalysts in the hydrogenolysis of
x
2
tetrahydrofurfuryl alcohol (THFA) is influenced by the amount of
Mo added to Rh, and the optimum was determined to be Mo/
Rh = 0.13 in terms of both the THFA conversion and turnover fre-
quency (TOF) of 1,5-PeD formation (Table 1, entries 1–5). Without
the addition of Mo, Rh/SiO2 showed much lower activity and the
main product was 1,2-PeD (Table 1, entry 6). As reported previ-
ously, Rh–ReO /SiO was effective in this reaction, and the opti-
2
pretreatment. After 1 h, the H pressure was increased to 8 MPa.
x
2
During the experiment, the stirring rate was fixed at 500 rpm. After
an appropriate reaction time, the reactors were cooled down, and
the gas-phase products were collected in a gas bag. The autoclave
contents were transferred to vials, and the catalysts were sepa-
rated by centrifugation and filtration.
mum amount of Re/Rh was 0.5 (Table 1, entries 7–9) [7]. At a
ratio of Re/Rh = 0.13, which is the same as the case of the optimum
Mo/Rh, the promoting effect of Re was not as pronounced as that of
Mo (Table 1, entries 3 and 7). According to the previous reports on
the hydrogenolysis of glycerol, the combination of H WO with Rh
2
4
In the hydrogenolysis of THFA, l,5-pentanediol (1,5-PeD), 1,2-
pentanediol (1,2-PeD), and 1-pentanol (1-PeOH) were produced.
The reaction scheme for the hydrogenolysis of THFA is shown in
Scheme 1. Additionally, 2-methyltetrahydrofuran, 2-pentanol
catalysts was effective [11,12]. Therefore, the additive effect of W
was also investigated, and it was found that the optimum amount
of W was W/Rh = 0.13 (Table 1, entry 10), although the details of
these results are not shown. The promoting effect of W also was
not as pronounced as that of Mo (Table 1, entries 3 and 10). In or-
der to maximize the yield of 1,5-PeD, the reaction temperature was
changed to 373 K and longer reaction times were applied. The
maximum 85% yield of 1,5-PeD on Rh–MoO /SiO (Mo/Rh = 0.13)
(
2-PeOH), and various products resulting from the cracking of
carbon-carbon bond in the molecule were also detected. A small
amount of methane was detected as a gaseous product. Conse-
quently, the sum of the cracking products, 2-methyltetrahydrofu-
ran, 2-pentanol, and gaseous product is integrated as ‘‘Others” in
the results. The analysis method for the products was described
in detail in the previous report [7].
Catalysts were characterized by measurement of CO adsorption
and by using transmission electron microscope (TEM, JEM 2010;
JEOL) operated at 200 kV. The methods were as detailed in the pre-
vious report [7]. Mo K-edge EXAFS spectra were measured at the
BL01B1 station at SPring-8 with the approval of the Japan Synchro-
tron Radiation Research Institute (JASRI; Proposal No. 2008B1235).
The storage ring was operated at 8.0 GeV. A Si (111) single crystal
was used to obtain a monochromatic X-ray beam. Measurements
were carried out in a way similar to that described in Ref. [9].
For the curve fitting analysis, the empirical phase shift and the
amplitude function for the Mo–O bond were extracted from the
x
2
was attained at 24 h reaction time (Table 1, entry 12). In contrast,
the maximum yield of 86% on Rh–ReO /SiO (Re/Rh = 0.5) was at-
x
2
tained at 36 h (Table 1, entry 16). While the activity of Rh–MoOx/
SiO2 was slightly lower than that of Rh–ReO /SiO when the con-
x
2
version level was not high (Table 1, entries 3 and 8), the reaction
time for the highest yield of 1,5-PeD was shorter on Rh–MoOx/
SiO . This can be explained by much higher activity of Rh–MoO /
2
x
SiO than that of Rh–ReO /SiO in very low concentration of THFA
2
x
2
(Table 1, entries 17 and 18). The catalyst also worked effectively in
higher concentration of THFA. The results of the activity test in
60 wt% THFA aqueous solution over Rh–MoO /SiO2 (Mo/
x
Rh = 0.13) and Rh–ReO /SiO (Re/Rh = 0.5) are listed out in Table
x
2
2. In addition, the catalysts were reused repeatedly in order to
evaluate the catalyst stability. The Rh–ReO /SiO gave higher activ-
x
2
data of Na
2 4
MoO . Theoretical functions for the Mo–Rh bond were
x 2
ity than Rh–MoO /SiO , but the stability was lower probably due to
calculated using the FEFF8.2 program [10]. Analyses of EXAFS data
were performed using a computer program (REX2000 Ver. 2.3.3;
Rigaku Corp.).
the leaching of Re [7].
In order to elucidate the promoting mechanism of the Mo addi-
tion, the interaction between Rh and Mo species in the catalyst
Table 1
Results of the hydrogenolysis of tetrahydrofurfuryl alcohol.
Entries
Catalyst
M/Rh
M = Mo, Re, W)
CO/
Rh
Catalyst
amount (g)
Temp.
(K)
Time
(h)
THFA
concentration
Conv.
(%)
Selectivity of products (%)
TOFa
(h 1)
ꢁ
(
1,5-
1,2-
PeD
1-
Others
(
wt%)
PeD
PeOH
1
2
3
4
5
6
7
8
9
Rh–MoO
x
/SiO
2
0.03
0.06
0.13
0.25
0.5
–
0.13
0.5
0.38
0.34
0.29
0.25
0.18
0.39
0.28
0.17
0.06
0.30
0.29
0.05
393
4
5
20.2
40.3
50.1
39.2
21.3
5.7
26.2
56.9
48.3
30.4
74.6
94.2
95.7
75.2
89.6
95.7
60.3
23.5
16.8
82.3
93.4
95.5
94.7
89.1
18.0
84.0
94.2
92.3
84.7
85.4
90.3
66.0
94.9
92.0
89.8
94.4
97.6
85.4
3.3
0.0
0.0
0.0
0.0
61.7
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.3
10.0
4.9
3.8
4.1
8.1
6.2
10.8
4.4
6.0
5.8
12.7
8.7
30.4
4.1
6.4
8.3
4.8
2.4
9.0
4.5
1.7
0.7
1.2
2.8
14.1
5.2
1.3
1.7
9.5
1.9
0.9
3.6
1.0
1.6
1.9
0.7
0.0
4.3
55
139
208
187
132
3
99
397
936
108
46
–
Rh/SiO
Rh–ReO
2
0.05
0.05
393
393
4
4
5
5
x
/SiO
2
1
0.13
0.13
10
11
12
13
14
15
16
17
18
19
x
Rh–WO /SiO
2
0.05
0.10
393
373
4
5
5
Rh–MoO
x
/SiO
2
12
24
36
12
24
36
4
–
88
–
Rh–ReO
x
/SiO
2
0.5
0.17
0.10
373
5
–
Rh–MoO
Rh–ReO
Rh=SiO
x
/SiO
2
0.13
0.5
0.13
0.29
0.17
–
0.10
0.10
0.05 + 0.05
373
373
393
1
1
5
25
17
–
x
/SiO
þ MoO
2
4
4
b
2
x
=SiO
2
Reaction conditions: 8.0 MPa initial H
2
pressure. 20 ml, aqueous solution of tetrahydrofurfuryl alcohol, PeD = pentanediol, PeOH = pentanol.
a
Turnover frequency (TOF) in hydrogenolysis is calculated on the basis of 1,5-pentanediol formation rate and the amount of CO adsorption at room temperature.
b
x 2 x 2
Loading amount of Mo on MoO /SiO is the same as that of Rh–MoO /SiO (Mo/Rh = 0.13).