Ru/12SrO-7Al2O3 (S12A7) catalyst prepared by physical mixing with Ru (PPh3)3Cl2 for steam reforming of toluene

Article abstract of DOI:10.1016/j.catcom.2015.09.018

Steam reforming of toluene as a model of aromatics was performed over various Ru/12SrO-7Al₂O₃ (S12A7) catalysts, and the effects of Ru precursor, calcination and pre-treatment conditions on the catalytic activity and durability of Ru/S12A7catalysts were investigated. The catalytic activity of prepared Ru/S12A7 catalysts exhibited higher than that of a commercial Ru/Al₂O₃ (RA), despite low Ru loading. The catalysts prepared by the physical mixing of Ru (PPh₃)₃Cl₂ and S12A7 (PPH) had higher catalytic activities than the catalysts prepared by the impregnation with RuCl₃ nH₂O (CL). It is interesting that the N₂ pre-treated PPH and CL catalysts especially had higher catalytic activities than the H₂ pre-treated PPH and CL catalysts. In their catalysts, there was a linear relationship between the catalytic activity and the Ru dispersion estimated by CO chemisorption. The catalytic activity of the N₂ pre-treated PPH catalyst has little decreased with time on stream, whereas the catalytic activities of the N₂ pre-treated CL catalyst and H₂ pre-treated PPH catalyst gradually decreased with time on stream.

Full text of DOI:10.1016/j.catcom.2015.09.018

Catalysis Communications 72 (2015) 101–104
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Ru/12SrO–7Al2O3 (S12A7) catalyst prepared by physical mixing with
Ru (PPh3)3Cl2 for steam reforming of toluene
⁎
Hajime Iida , Kazuhide Noguchi, Takashi Numa, Akira Igarashi, Kazu Okumura
Department of Applied Chemistry, School of Advanced Engineering, Kogakuin University, 2665-1 Nakano-machi, Hachioji-shi, Tokyo 192-0015, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 July 2015
Received in revised form 12 September 2015
Accepted 21 September 2015
Available online 25 September 2015
Steam reforming of toluene as a model of aromatics was performed over various Ru/12SrO–7Al2O3 (S12A7)
catalysts, and the effects of Ru precursor, calcination and pre-treatment conditions on the catalytic activity and
durability of Ru/S12A7catalysts were investigated. The catalytic activity of prepared Ru/S12A7 catalysts exhibited
higher than that of a commercial Ru/Al2O3 (RA), despite low Ru loading. The catalysts prepared by the physical
mixing of Ru (PPh3)3Cl2 and S12A7 (PPH) had higher catalytic activities than the catalysts prepared by the
impregnation with RuCl3 nH2O (CL). It is interesting that the N2 pre-treated PPH and CL catalysts especially
had higher catalytic activities than the H2 pre-treated PPH and CL catalysts. In their catalysts, there was a linear
relationship between the catalytic activity and the Ru dispersion estimated by CO chemisorption. The catalytic
activity of the N2 pre-treated PPH catalyst has little decreased with time on stream, whereas the catalytic activ-
ities of the N2 pre-treated CL catalyst and H2 pre-treated PPH catalyst gradually decreased with time on stream.
© 2015 Elsevier B.V. All rights reserved.
Keywords:
Hydrogen production
Steam reforming
Ru/S12A7
Physical mixing
Ru (PPh3)3Cl2
1. Introduction
exhibited higher catalytic activity and lower coke formation rate in par-
tial oxidation of methane [6]. Li et al. have reported that Ni/C12A7
Catalytic steam reforming of hydrocarbons is an important route for
hydrogen production for fuel cell systems. Liquid fuels such as kerosene
are one of the promising hydrogen sources for fuel cell systems because
of its high energy density and low cost [1,2]. However, there is serious
catalyst deactivation due to the carbon deposition on the catalyst sur-
face because kerosene mainly contains alkanes with carbon number of
above 10, and aromatic hydrocarbons. In particular, typical nickel
based catalysts are well known to suffer from the carbon deposition
during the reaction [3]. Although an increase in the amount of steam
suppresses the coking, a high steam to carbon ratio (S/C ratio) causes
large energy consumption for vaporization of water. Therefore, the
developments of catalysts that have superior catalytic activity and dura-
bility for steam reforming of liquid fuels under low S/C conditions have
been demanded. In order to achieve the high catalytic activity and dura-
bility, how to activate the water over the catalyst surface to promote the
oxidation of hydrocarbon reactants and the deposited carbons is an im-
portant factor. Recently, Sekine et al. have focused on a redox property
of perovskite oxide supports to promote the oxidation of adsorbed
CHx species on the catalyst surface, and reported that Ni/LaAlO3 and
Ni/La0.9Sr0.2AlO3-δ catalysts showed excellent catalytic activity for
steam reforming of toluene [4,5]. On the other hand, 12CaO–7Al2O3
(C12A7) is known to have the nanocage that can incorporate active ox-
ygen ions (O−, O2−, and O22−). Yang et al. have reported that Ni/C12A7
showed excellent performance for steam reforming of biomass tar [7].
Recently, the authors have reported that the 12SrO–7Al2O3 (S12A7)
catalysts exhibited superior catalytic activities for steam reforming of
dodecane and toluene compared to a commercial Ru/Al2O3 catalyst be-
cause the active oxygen species in S12A7 contribute to the acceleration
of oxidation of CHx species on Ru metals [8]. However, the Ru/S12A7
catalyst suffered from gradual deactivation with time on stream.
In the present study, in order to improve the catalytic activity and
durability of Ru/S12A7 catalysts for steam reforming of toluene, the
effects of Ru precursor, the Ru-supporting method, and the calcina-
tion and pre-treatment conditions on the catalytic performances of
Ru/S12A7 catalysts were investigated.
2. Experimental
2.1. Catalyst preparation
S12A7 support materials were prepared as follows. Strontium
hydroxide (Kojundo Chemical Laboratory) was used as a strontium
precursor, aluminum hydroxide (Wako Pure Chemical Industries) or
γ-alumina (Strem Chemicals) was used as an aluminum precursor.
Both precursors were wet-blended with ethanol in a glove box under
nitrogen atmosphere. The Sr/Al (S/A) atomic ratio was 0.874 (slightly
Sr rich amount) [9]. After mixing until ethanol completely evaporated,
the mixture was calcined at various conditions. The calcination condi-
tions employed were as follows: calcination temperature: 873 K, ramping
rate of temperature: 200 K h−1, partial pressure for H2O of the stream
⁎
Corresponding author.
E-mail address: iida@cc.kogakuin.ac.jp (H. Iida).
http://dx.doi.org/10.1016/j.catcom.2015.09.018
1566-7367/© 2015 Elsevier B.V. All rights reserved.

102
H. Iida et al. / Catalysis Communications 72 (2015) 101–104
(pH2O): 1.9 kPa [9,10], cooling rate of temperature: 1500 K h−1 [9,10]. The
Sr/Al (S/A) atomic ratio was 0.874 (slightly Sr rich amount).
Ru/S12A7 catalysts were prepared by physical mixing with Ru
(PPh3)3Cl2 (PPH) and a conventional impregnation with RuCl3 nH2O
(CL). In the preparation of PPH catalysts, Ru (PPh3)3Cl2 (Wako Pure
Chemical Industries) and S12A7 powders were mixed by an agate
mortar for 0.5 h, the mixture then were calcined at 873 K for 1 h in a
stream of N2, then pelletized and crushed (0.5–1.0 mm φ). CL catalysts
were prepared as follows. An ethanol solution of ruthenium chloride
n-hydrate (Wako Pure Chemical Industries) was added to the S12A7
powder. The mixture was evaporated on a water bath at 373 K,
and the resultant material was dried for 15 h at 373 K, then finally
calcined in a stream of air at 873 K for 1 h, then pelletized and crushed
(0.5–1.0 mm φ) [8]. The loading of ruthenium was 1.0 wt.%. A commer-
cial Ru (2.0 wt.%)/Al2O3 (RA) catalyst was employed as a reference
catalyst.
2.2. Activity test
Steam reforming of toluene was performed at atmospheric pressure
using a conventional fixed bed flow reactor. The catalyst was placed in a
reaction tube (8 mm φ i.d.) made of quartz glass, and was then pre-
treated in an N2 or H2 stream (100 cm3-SATP min−1) at 873 K for 1 h.
H2O was supplied using a micro feeder and was then introduced via a
vaporizer to the reactor. Following the supply of steam, toluene was
supplied via a vaporizer to the reactor using a plunger pump. Nitrogen
was used as a carrier gas. Liquid products and unreacted liquid reactants
were trapped by an ice water bath located downstream of the reactor,
and the gas and liquid compositions were analyzed using gas chromato-
graphs with a thermal conductivity detector (TCD) and a flame ioniza-
tion detector (FID), respectively. The flow rate of gas products was
measured using a soap bubble flow meter or a wet gas meter. The reac-
tion conditions for steam reforming of toluene were a reaction temper-
Fig. 1. Relationship between catalytic acitivity and Ru dispersion of Ru/S12A7 catalysts; ○:
Ru(PPh3)3Cl2, N2 calcination, N2 pre-treatment; ●: Ru(PPh3)3Cl2, N2 calcination, H2 pre-
treatment; △: RuCl3 nH2O, N2 calcination, N2 pre-treatment; ▲: RuCl3 nH2O, N2 calcina-
tion, H2 pre-treatment; ◆: RuCl3 nH2O, Air calcination, H2 pre-treatment.
where VCO (m3
g
) is the amount of chemisorbed CO on the catalyst,
−1
-STP -cat
LCO (−) is the Ru content in the catalyst, fCO/Ru (= 0.5) is the stoichiomet-
ric factor for CO chemisorption on Ru, and MRu (= 101.07 g mol−1) is the
molar mass of Ru.
Turn over frequency (TOF) for steam reforming of toluene was de-
fined as follows:
F ꢀ X
TOF ¼
ð2Þ
ature 873 K, a S/C molar ratio of 2.0, a time factor (W/F) of 7 g hmol−1
.
VCO
ꢀ WCat
:
0:0224fCO=Ru
2.3. Catalyst characterization
where F (mol s−1) is the toluene molar flow rate, X (−) is the toluene
conversion at 0.5 h, and WCat. (g) is the catalyst weight.
X-ray diffraction (XRD; RINT2000, Rigaku) analysis of used catalysts
was carried out using Cu Kα radiation. The Brunauer–Emmett–Teller
(BET) surface area of the newly-prepared, pre-treated, and used cata-
lysts was determined by N2 adsorption at 77 K using a flow absorption
apparatus (Flow Sorb II 2300, Micromeritics). The composition of the
flow gas was N2:He = 30:70. The catalyst was degassed at 473 K for
15 min prior to the measurement.
3. Results and discussion
The catalytic activity, Ru dispersion, and TOFs of various Ru/S12A7
catalysts were listed in Table 1. The toluene conversion of Ru/S12A7
catalysts was higher than that of the RA catalyst, despite low Ru loading.
The amount of chemisorbed CO on the pre-treated catalysts was es-
timated by a pulse adsorption method. The ruthenium dispersion (DRu
)
of the catalysts was calculated from the amount of chemisorbed CO,
where DRu was defined as:
n
o
DRu
¼
VCO
f
CO=Ru=0:0224 =fLRu=MRug;
ð1Þ
Table 1
Catalytic properties and activity of Ru (1.0 wt.%)/S12A7 catalysts.
Ru precursor
Calcination
atmosphere atmosphere
Pre-treatment Ru
Toluene
TOF
b
dispersion conversion (s−1
)
(%)a
(%)b
Ru(PPh3)3Cl2 N2
N2
H2
N2
H2
H2
H2
5.7
4.0
1.4
0.3
0.5
2.0
80.1
61.9
42.1
21.3
15.2
11.8
5.7
6.3
12.2
28.8
12.3
1.2
RuCl3 nH2O
N2
Air
Commercial Ru
Fig. 2. Time dependency of catalytic activity of various Ru/S12A7 catalysts; ○: Ru(PPh3)3Cl2,
N2 calcination, N2 pre-treatment; ●: Ru(PPh3)3Cl2, N2 calcination, H2 pre-treatment;
△: RuCl3 nH2O, N2 calcination, N2 pre-treatment; ▲: RuCl3 nH2O, N2 calcination, H2 pre-
treatment; ◆: RuCl3 nH2O, Air calcination, H2 pre-treatment; ■: commercial Ru/Al2O3.
(2.0 wt.%)/Al2O3
a
After pre-treatment, CO/Ru = 0.5.
Time on stream: 0.5 h.
b

H. Iida et al. / Catalysis Communications 72 (2015) 101–104
103
Table 2
BET surface area of the Ru (1.0 wt.%)/S12A7 catalysts before and after the reaction.
Ru precursor
Calcination atmosphere
Pretreatment atmosphere
BET surface area (m2 g−1
)
Support
5.8
After calcination
5.4
After pretreatment
After reaction
Ru(PPh3)3Cl2
RuCl3 nH2O
N2
N2
Air
N2
H2
N2
H2
H2
H2
–
5.5
–
3.2
4.5
–
4.6
3.3
2.3
1.5
2.0
4.4
3.4
4.3
6.6
Commercial Ru (2.0 wt.%)/Al2O3
–
TOFs of Ru/S12A7 catalysts were higher than that of the RA catalyst
because the active oxygen species in S12A7 contribute to the accelera-
tion of oxidation of CHx species on Ru metals [8]. Fig. 1 shows the rela-
tionship between the catalytic activity and the Ru dispersion. A linear
relationship between the catalytic activity and the Ru dispersion esti-
mated by CO chemisorption was observed. The catalytic activity and
Ru dispersion of PPH catalysts were higher than those of the CL cata-
lysts. Ru (PPh3)3Cl2 fuses at relative lower temperature (432 K) before
the decomposition [11]. Therefore, it was inferred that the melted Ru
(PPh3)3Cl2 could be spontaneously spread over the surface of S12A7
support in the beginning of a calcination step, resulting in the increase
in the Ru dispersion. The CL catalyst calcined in the stream of N2 had
slightly higher catalytic activity than that calcined in the stream of air.
On the other hand, it is interesting that the N2 pre-treated PPH and CL
catalysts especially had higher catalytic activities and Ru dispersion
than the H2 pre-treated PPH and CL catalysts. Probably, the rapid reduc-
tion of Ru precursor in the stream of H2 promoted the sintering of Ru
complexes, resulting in the decrease in Ru dispersion. The mild reduc-
tion under inert atmosphere would prevent the sintering of Ru. The re-
sults indicate that the physical mixing of Ru (PPh3)3Cl2 and S12A7 and
the N2 pretreatment measured before the reaction are effective to
enhance the catalytic activity of the Ru/S12A7 catalyst by increasing
the Ru dispersion.
with time on stream. This fact revealed that the N2 pre-treated PPH
catalyst had superior durability for steam reforming of toluene.
Table 2 shows the BET surface area of the Ru/S12A7 catalysts before
and after the reaction. Fig. 1 and Table 2 indicate that the decrement of
BET surface area corresponds to the decrement of toluene conversion.
Fig. 3 shows the XRD profiles of Ru/S12A7 catalysts after the reac-
tion. In all of the catalysts, the diffraction peaks assigned to S12A7 of
used catalysts little changed compared to those of as-prepared catalysts,
unrelated to the deactivation behavior of the catalysts. Therefore, the
reason why the catalytic activity is decreased with time would be
explained by the decrease in the Ru dispersion due to the sintering of
catalysts. In addition, Kanda et al. reported that excess phosphorus spe-
cies over Ru-P/SiO2 catalyst acted as an anchor of Ru particles [12].
Therefore, it is inferred that the residual phosphorus species over the
PPH catalyst prevent the sintering of Ru particles.
The theoretical gas product composition for steam reforming of
toluene was obtained using a kinetic equilibrium calculation [13] of
the following reactions:
C6H5CH3 þ 7 H2O →7 CO þ 11 H2
CO þ 3H2 ⇄ CH4 þ H2O
ð1Þ
ð2Þ
ð3Þ
Fig. 2 shows the time dependency of catalytic activity of various
Ru/S12A7 catalysts. Little deactivation was observed in the N2 pre-
treated PPH catalyst, whereas the catalytic activities of the N2 pre-
treated CL catalyst and H2 pre-treated PPH catalyst gradually decreased
CO þ H2O ⇄ CO2 þ H2
Fig. 4 shows the comparison of the calculated and measured selec-
tivities for carbon contained products over Ru/S12A7 catalysts. The
good agreement shown between the calculated and measured CO2
and CO selectivities indicates that the water gas shift reaction over Ru/
S12A7 is close to those at a thermodynamic equilibrium state at 873 K.
The experimental CH4 selectivity for Ru/S12A7 was smaller than the
calculated values. This indicates that the methanation reaction was
Fig. 3. XRD profiles of Ru/S12A7 catalysts; a) Ru(PPh3)3Cl2, N2 calcination, N2 pre-
treatment; b) Ru(PPh3)3Cl2, N2 calcination, H2 pre-treatment; c) RuCl3 nH2O, N2 calcina-
tion, N2 pre-treatment; d) RuCl3 nH2O, N2 calcination, H2 pre-treatment; e) RuCl3 nH2O,
Air calcination, H2 pre-treatment.
Fig. 4. Comparison of the calculated and measured selectivities for carbon contained
products over Ru/S12A7; ○: CO2, ▲: CO, ■: CH4, ◇: C6H6.

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H. Iida et al. / Catalysis Communications 72 (2015) 101–104
suppressed over Ru/S12A7. The formation of benzene, which formed
by hydrogenating dealkylation (C6H5CH3 + H2 → C6H6 + CH4), over
Ru/S12A7 was a little.
PPH catalyst had superior catalytic activity and durability for steam
reforming of toluene.
References
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