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Chemistry Letters Vol.38, No.6 (2009)
Promoting Effect of Re Addition to Rh/SiO on Glycerol Hydrogenolysis
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ꢀ1;2
Akira Shimao, Shuichi Koso, Naoyuki Ueda, Yasunori Shinmi, Ippei Furikado, and Keiichi Tomishige
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Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573
2
International Center for Materials Nanoarchitectonics Satellite (MANA),
National Institute of Materials Science (NIMS) and University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573
(Received March 23, 2009; CL-090287; E-mail: tomi@tulip.sannet.ne.jp)
Modification of Rh/SiO2 with ReOx enhanced the activity
of glycerol hydrogenolysis remarkably and suppressed degrada-
tion reactions simultaneously. At the same time, the formation of
ature (Table 1, Entries 8 and 10). Another interesting point is that
the modification of Rh/SiO2 with ReOx enhanced the selectivity
of 1,3-propanediol formation. The selectivity of 1,3-propanediol
over conventional catalysts is usually very low. The conversion
order was found to be glycerol ꢂ 1,3-propanediol > 1,2-pro-
panediol (Table 1, Entries 5, 18, and 20). This result suggests
that 1,3-propanediol yield in the glycerol hydrogenolysis can
be decreased by the consecutive hydrogenolysis of 1,3-propane-
diol. On the other hand, the conversion order on Rh–ReOx/SiO2
was glycerol > 1,2-propandiol > 1,3-propanediol (Table 1,
Entries 2, 17, and 19). The low reactivity of 1,3-propanediol
on Rh–ReOx/SiO2 can enhance the yield of 1,3-propanediol in
the glycerol hydrogenolysis.
In addition, Rh–ReOx/SiO2 was also effective in the hydro-
genolysis of glycerol without any solvent (Table 1, Entry 15).
Compared to the case of the diluted glycerol, the selectivity of
1,3-propanediol was higher. The yield of 1,3-propanediol over
Rh–ReOx/SiO2 reached 12% (Table 1, Entry 16). It has been
reported that Rh(CO)2(acac) and H2WO4 in 1-methyl-2-pyrroli-
dinone gave 21% yield of 1,3-propanediol at a Rh-based turn-
1
,3-propanediol became more favorable on the Rh–ReOx/SiO2.
Glycerol is a major by-product in the production of biodiesel
by the transesterification of vegetable oils with methanol, and it
is also expected to be a building block in future biorefineries.
The potential conversion of renewable resources such as glycer-
ol into valuable commodity chemicals can facilitate the replace-
1
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ment of petroleum-based products. From this viewpoint, hy-
drogenolysis of glycerol to valuable propanediols becomes in-
creasingly important. It is reported here that the modification
of Rh/SiO2 with Re species enhanced the activity and the selec-
tivity in the glycerol hydrogenolysis.
The Rh–MOx/SiO2 (M ¼ Re, Mo, and W) catalysts were
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prepared by impregnation using RhCl3 3H2O, NH4ReO4,
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.
(
NH4)6Mo7O24 4H2O, (NH4)10W12O41 5H2O, and SiO2 (sur-
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face area 535 m g ) and calcined at 773 K. The amount of
Re, Mo, and W is represented in parenthesis as a molar ratio
to Rh, and it was optimized from activity tests. Rh loading
was 4 wt %. As a reference, commercially available Ru/C
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over frequency (TOF) of ca. 3 h
(TON) of 79 at 473 K and 32 MPa of synthesis gas (CO:H2 =
and turnover number
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1:2). In addition, it has recently been reported that Pt/WO3/
ZrO2 in 1,3-dimethyl-2-imidazolidinone gave 24% yield of 1,3-
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4
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3
(
5 wt %), Raney Ni, copper–chromite, and Amberlyst15 were
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used. Activity evaluation of the glycerol hydrogenolysis was car-
ried out in a 190-mL stainless autoclave and 20 mL of 20 wt %
aqueous glycerol solution. Procedures for the activity tests and
product analysis were carried out, and selectivity of products
was calculated in the same way as described in our previous
report.3
propanediol at Pt-based TOF of ca. 4 h and TON of 73 at
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443 K and 8 MPa H2. Although the present yield was smaller
than these reported results, advantages of Rh–ReOx/SiO2 are
that the glycerol hydrogenolysis proceeded without the use of or-
ganic solvent at a lower reaction temperature; moreover, a much
ꢁ1
higher TON (1320) and TOF (13.8 h ) were obtained (Table 1,
The modification of Rh/SiO2 with Re, Mo, and W species
enhanced the activity of the glycerol hydrogenolysis remarkably,
and the addition of Re is most effective (Table 1, Entries 1 and
Entry 16). In addition, in the case of the Rh–ReOx/SiO2, water
is much more suitable as a solvent than 1-methyl-2-pyrrolidi-
none and 1,3-dimethyl-2-imidazolidinone. In contrast, Rh/C +
H2WO4 was ineffective in the aqueous solution (Table 1,
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–5). They showed much higher activity than Raney Ni and cop-
per–chromite, which were used at higher reaction temperature
Table 1, Entries 13 and 14). It has been reported that the glyc-
8
Entry 12).
(
From the results of TEM observation, average metal particle
sizes of Rh/SiO2 and Rh–ReOx/SiO2 (Re/Rh = 1/2) were de-
termined to be 3:5 ꢃ 0:4 and 4:3 ꢃ 0:4 nm, respectively. On the
other hand, the amounts of CO adsorption (molar ratio: CO/Rh)
on Rh/SiO2 and Rh–ReOx/SiO2 were measured to be 0.39 and
erol hydrogenolysis proceeds by dehydration of glycerol to
acetol over Amberlyst and subsequent hydrogenation of acetol
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to 1,2-propanediol over Ru/C over Ru/C + Amberlyst. The
Rh–MOx/SiO2 showed higher activity than Ru/C and Ru/
C + Amberlyst (Table 1, Entries 6 and 7), and this suggests that
the hydrogenolysis over Rh–MOx/SiO2 can proceed in a direct
route. At the same time, modification of Rh/SiO2 suppressed
degradation reactions, which gave ethylene glycol, ethanol,
methane, and methanol by dissociation of carbon–carbon bonds
in the glycerol molecule. The selectivity of the degradation reac-
tion over Rh/SiO2 increased at lower H2 pressure or higher
reaction temperature (Table 1, Entries 9 and 11). On the other
hand, degradation selectivity on Rh–ReOx/SiO2 was maintained
to be low even at lower H2 pressure or higher reaction temper-
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0.17, respectively. From comparison of TEM and CO adsorp-
tion, Re modification can suppress CO adsorption by the direct
interaction between Re and Rh metal particles. Considering
the very low activity of ReOx/SiO2 the interaction between Rh
and ReOx might be related to the cooperative function as fol-
lows: the OH group in the reactants is adsorbed dissociatively
on ReOx species, and hydrogenolysis of the C–O bond catalyzed
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by neighboring Rh metal surface, although this mechanism is
not demonstrated at present. In addition, higher activity of Rh–
ReOx/SiO2 as compared with the reported catalyst system can
Copyright Ó 2009 The Chemical Society of Japan