GModel
MOLCAA-8869; No. of Pages11
ARTICLE IN PRESS
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M. Tamura et al. / Journal of Molecular Catalysis A: Chemical xxx (2013) xxx–xxx
OH
HO
OH
OH
HO
OH
1,3-Propanediol
1-Propanol
Glycerol
OH
OH
OH
1,2-Propanediol
2-Propanol
Propane
Scheme 1. Hydrogenolysis of glycerol.
density of the noble metal [52–55], cover of the unfavorable sites
on the noble metal [54–57], cooperation of additive metal species
with the noble metal [24,33,34,37–39,44,55,56], and control of
the noble metal structure [24,33,34,37–39,53–55,57]. Therefore,
it is important to investigate the further modification effect on
‘MOx-modified-Metal catalysts’ for the breakthrough in the het-
erogeneous catalyst design.
In this report, Ir-ReOx/SiO2 catalyst was modified with vari-
ous transition metals (Cu, Ni, Ag, Co, Zn, Ru, Rh and Pd), acidic
additives (S, P and B), and basic ion (Na). Among these catalysts,
Ru-added Ir-ReOx/SiO2 catalysts showed the highest activity for
the hydrogenolysis of glycerol. In addition, on the basis of TPR,
XRD, EXAFS and CO adsorption, the reaction mechanism over Ru-
modified Ir-ReOx/SiO2 catalyst and the catalyst structure will be
discussed.
2.1. Activity tests
Activity tests were performed in a 190-ml stainless steel auto-
clave with an inserted glass vessel. The catalyst was put into an
autoclave together with a spinner and an appropriate amount of
water and heated at 473 K with 8 MPa H2 for 1 h for the reduction
pretreatments. After the pretreatment, the autoclave was cooled
down, and hydrogen was removed. Glycerol (Wako Pure Chem-
ical Industries, Ltd., >99%) was put into the autoclave together
with sulfuric acid (Wako Pure Chemical Industries, Ltd.) diluted
with water. After sealing the reactor, the air content was purged
by flushing thrice with 1 MPa hydrogen (99.99%; Nippon Perox-
ide Co., Ltd.). The autoclave was then heated to 393 K, and the
temperature was monitored using a thermocouple inserted in the
autoclave. After the temperature reached 393 K, the H2 pressure
was increased to 8 MPa. During the experiment, the stirring rate
was fixed at 250 rpm (magnetic stirring). After an appropriate reac-
tion time, the reactor was cooled down and the gases were collected
in a gas bag. The autoclave contents were transferred to a vial,
and the catalyst was separated by centrifugation and filtration. The
standard conditions for the reaction were as follows: 393 K reac-
tion temperature, 8.0 MPa initial hydrogen pressure, 4 h reaction
time, 4 g glycerol, 2 g water, 1.5 mg H2SO4 (H+/Ir = 1) and 150 mg
supported metal catalyst. The parameters were changed appro-
priately in order to investigate the effect of reaction conditions.
Details of the reaction conditions are described in each result. The
products were analyzed using a gas chromatograph (Shimadzu GC-
2014 and GC-17A) equipped with FID. A TC-WAX capillary column
(diameter 0.25 mm i.d., 30 m) was used for the separation. Prod-
ucts were also identified using GC-MS (QP5050, Shimadzu). The
(2-PrOH) and propane. In addition, the degradation products such
as ethyleneglycol, ethanol, ethane and methane were detected. The
conversion and the selectivity were defined on the carbon basis in
the similar way as reported previously [19,20]. The mass balance
was also confirmed in each result and the difference in mass balance
was always in the range of the experimental error. The agreement
in terms of the mass balance indicated that polymeric by-products
were not formed ( 10%). The used catalyst was collected by cen-
trifugation. The collected catalyst was washed with excess water
and dried in air, and then calcined at 773 K at 3 h. A slight loss
(<10% in weight) was observed during the recovery process and
was compensated with fresh catalyst in each reuse experiment.
2. Experimental
The SiO2 (G-6, BET surface area 535 m2/g) supplied by Fuji
Silysia Chemical Ltd. was used as a support of the catalysts.
M/SiO2 (M = Rh, Ru, Pd, Ni, Co, Zn, Cu and Ag) catalysts and
Ir/SiO2 were prepared by impregnating SiO2 with H2IrCl6 (Furuya
Metals Co., Ltd.), RhCl3·3H2O (Soekawa Chemical Co., Ltd.),
RuCl3·nH2O (Kanto Chemical Co., Ltd.) and PdCl2 (Kanto Chemical
Co., Ltd.), Cu(NO3)2·3H2O (Fluka Chemical Co., Ltd.), Co(NO3)2·6H2O
(Wako Pure Chemical Industries, Ltd.), Zn(NO3)2·6H2O (Wako Pure
Chemical Industries, Ltd.), Ni(NO3)2·6H2O (Wako Pure Chemical
Industries, Ltd.) and AgNO3 (Wako Pure Chemical Industries, Ltd.).
After evaporating the solvent and drying at 383 K for 12 h, they
were calcined in air at 773 K for 3 h. M-Ir/SiO2 (M = Rh, Ru, Pd, Ni,
Co, Zn, Cu and Ag) were prepared by impregnating M/SiO2 after the
calcination procedure with H2IrCl6 (Furuya Metals Co., Ltd.), and
then the solvent was evaporated and dried at 383 K for 12 h. M-
Ir-ReOx/SiO2 (Rh, Ru, Pd, Ni, Co, Zn, Cu and Ag) were prepared by
impregnating M-Ir/SiO2 after the drying procedure with aqueous
solutions of NH4ReO4 (Soekawa Chemical Co., Ltd.). These catalysts
were calcined in air at 773 K for 3 h after drying at 383 K for 12 h.
This preparation method of catalysts is defined as method (A). The
loading amounts of Ir and Re were 4.0 and 7.7 wt%, respectively
(Re/Ir molar ratio = 2), and that of additive was represented by the
weight% of the additives to the total catalyst in parenthesis like
M(X)-Ir-ReOx/SiO2. M-Ir-ReOx/SiO2 (M = Na, P, B, S) were prepared
by impregnating Ir-ReOx/SiO2 prepared as above with (NH4)2SO4
(Wako Pure Chemical Industries, Ltd.), Na2CO3 (Wako Pure Chem-
ical Industries, Ltd.), (NH4)2HPO4 (Wako Pure Chemical Industries,
Ltd.) and (NH4)2B4O7 4H2O (Kanto Chemical Co., Ltd.). After evapo-
rating the solvent and drying at 383 K for 12 h, they were calcined in
air at 773 K for 3 h. This preparation method of catalysts is defined
as method (B). Ru(1)-Ir-ReOx/SiO2 and Ru(0.1)-Ir-ReOx/SiO2 were
also prepared by method (B). The catalysts prepared by the method
(B) were denoted as M-Ir-ReOx/SiO2 (B) (M = Rh, Ru, Pd, Ni, Co, Zn,
Cu, Ag, P, S, BandNa)andthecatalystswerepreparedbythemethod
(A) unless denoted.
2.2. Catalyst characterization
Temperature-programmed reduction (TPR) was carried out in
a fixed-bed reactor equipped with a thermal conductivity detector
using 5% H2 diluted with Ar (30 ml/min). The amount of catalyst
was 0.05 g, and temperature was increased from room tempera-
ture to 1123 K at a heating rate of 10 K/min. X-ray diffraction (XRD)
patterns were recorded by a diffractometer (Rigaku Ultima). Aver-
age metal particle size was estimated using the Scherrer equation