Low-temperature catalytic steam reforming of toluene as a biomass tar model compound over three-dimensional ordered macroporous Ni-Pt/Ce1?xZrxO2 catalysts

Article abstract of DOI:10.1016/j.apcata.2020.117859

Ceria–zirconia solid solution (Ce_1?xZr_xO₂) is a fascinating catalyst support in steam reforming reaction. In order to further improve the performance of Ni-based catalyst with Ce_1?xZr_xO₂ as support for tar team reforming, three-dimensional ordered macroporous Ni-Pt/Ce_1?xZr_xO₂ (Ni-Pt/C_1?xZ_x-3DOM; x = 0.2, 0.3, 0.4) catalysts were prepared by a colloidal crystal template method and their catalytic performances for toluene steam reforming were investigated in low temperature range. The Ni-Pt/C_1?xZ_x-3DOM exhibited excellent catalytic performance, and toluene conversion of Ni-Pt/C_0.8Z_0.2-3DOM reached 90.4 % at 500 °C under 185 μmol/min toluene flowrate and 10,000 h^?1 GHSV. Besides, this catalyst showed good durability with 1.7 mg g_cat^?1 h^?1 carbon deposition rate during 30 h of operation at 600 °C. The characterization results demonstrated the Ni-Pt/C_1?xZ_x-3DOM exhibits desirable characteristics to promote the catalysis performance compared to non-porous Ni-Pt/C_1?xZ_x, including more oxygen vacancies on catalyst surface, higher specific surface areas, larger pore volumes, more meso-pores, smaller crystalline size of active component and support, and better reducibility.

Full text of DOI:10.1016/j.apcata.2020.117859

AppliedCatalysisA,General607(2020)117859
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Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Low-temperature catalytic steam reforming of toluene as a biomass tar
model compound over three-dimensional ordered macroporous Ni-Pt/
Ce1−xZrxO2 catalysts
Shuyu Zhoua, Zezhi Chena,*, Huijuan Gonga,b,*, Xiaoshu Wangb, Tingting Zhua, Yuchen Zhoua
a State Key Laboratory of Pollution Control and Resource Reuse, School of Environment, Nanjing University, Nanjing, 210023, PR China
b Center of Materials Analysis, Nanjing University, 210093, Nanjing, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Ceria–zirconia solid solution (Ce1−xZrxO2) is a fascinating catalyst support in steam reforming reaction. In order
to further improve the performance of Ni-based catalyst with Ce1−xZrxO2 as support for tar team reforming,
three-dimensional ordered macroporous Ni-Pt/Ce1−xZrxO2 (Ni-Pt/C1−xZx-3DOM; x = 0.2, 0.3, 0.4) catalysts
were prepared by a colloidal crystal template method and their catalytic performances for toluene steam re-
forming were investigated in low temperature range. The Ni-Pt/C1−xZx-3DOM exhibited excellent catalytic
performance, and toluene conversion of Ni-Pt/C0.8Z0.2-3DOM reached 90.4 % at 500 °C under 185 μmol/min
toluene flowrate and 10,000 h−1 GHSV. Besides, this catalyst showed good durability with 1.7 mg gcat−1 h−1
carbon deposition rate during 30 h of operation at 600 °C. The characterization results demonstrated the Ni-Pt/
Low temperature
Steam reforming catalyst
Three-dimensional ordered macroporous
structure
Ceria–zirconia solid solution
Biomass tar
C
1−xZx-3DOM exhibits desirable characteristics to promote the catalysis performance compared to non-porous
Ni-Pt/C1−xZx, including more oxygen vacancies on catalyst surface, higher specific surface areas, larger pore
volumes, more meso-pores, smaller crystalline size of active component and support, and better reducibility.
1. Introduction
tar content as well as increase the production of H2. Nickel (Ni)-based
catalysts are currently widely used in the steam reforming of tar due to
The use of biomass as a renewable energy has attracted increasing
interest since it could reduce the consumption of non-renewable energy
resources and alleviate the global warming and air pollution caused by
the emission of carbon dioxide (CO2), toxic gases and particles via the
combustion of fossil fuels. Among the various technologies of utilizing
biomass energy, gasification is one of the most promising methods
because the syngas produced can be used for power generation or as
feedstocks for the synthesis of liquid fuels and various chemicals.
However, one of the most critical problems in biomass gasification is
the tar issue. Tar is the condensable fraction of the biomass gasification
products, and mainly composed of single ring to 5-ring aromatic com-
pounds, which could deposit in the pipelines and equipment due to its
high freezing point, resulting in mechanical problems [1]. Moreover,
the presence of tar could reduce energy efficiency and lead to catalyst
deactivation in the subsequent syngas utilization [2]. Therefore, tar
removal is one of the main concerns of researchers involved in the
biomass gasification.
their high activity, low cost and easy regeneration. Metallic Ni can not
only effectively activate the CeH and CeC bonds in hydrocarbons, but
also activate the H2O and CO2 that participate in tar reforming and
water gas shift (WGS) reactions [3]. In particular, a Ni-based catalyst
doped with trace amount of some noble metal such as Pt, Pd, etc. can
not only promote the dispersion of Ni, but also produce a synergistic
effect between the doped noble metal and Ni [4]. Moreover, the noble
metals can promote the hydrogenation reaction of the coke precursors,
thus enhancing the activity and durability of the catalysts [5].
As the steam reforming of tar is endothermic, relatively high tem-
perature is favorable for the reaction. To provide high temperature
condition needed for the steam reforming, additional external heating
was generally input into the system, or a small amount of air or oxygen
was introduced to enable partial oxidation of the tar [6]. However, high
temperature means high energy consumption, and the introduction of
air or oxygen would reduce the calorific value of the product gas.
Moreover, high temperature is liable to Ni sintering, resulting in the
catalyst deactivation. Therefore, it is of great significance to operate the
steam forming of tar at around 400–600 °C, which would not only
Catalytic steam reforming has been extensively studied as one of the
major approaches to the elimination of tar, as it can effectively reduce
⁎ Corresponding authors at: State Key Laboratory of Pollution Control and Resource Reuse, School of Environment, Nanjing University, Nanjing, 210023, PR China.
E-mail addresses: chenzzg@nju.edu.cn (Z. Chen), gonghj@nju.edu.cn (H. Gong).
https://doi.org/10.1016/j.apcata.2020.117859
Received 10 August 2020; Received in revised form 18 September 2020; Accepted 21 September 2020
Availableonline25September2020
0926-860X/©2020ElsevierB.V.Allrightsreserved.

S. Zhou, et al.
AppliedCatalysisA,General607(2020)117859
enable sufficient utilization of the plant waste heat but also reduce
nickel sintering. To date, the improvement in the catalysis activity as
well as carbon deposition resistance for the nickel-based catalysts at
relatively low temperature (400–600 °C) is still a challenge.
on CeO2-3DOM. Isotopic exchange experiments showed that the CeO2-
3DOM catalyst produced more active oxygen than the counterpart CeO2
catalyst without holes, and this active oxygen is transferred more effi-
ciently to soot due to the macroporous structure. Li et al. [19] prepared
a series of Au/3DOM LaCoO3 catalysts for the oxidation of CO and
toluene. The results showed that the high adsorption oxygen con-
centration, good low-temperature reducibility, and strong interaction
between Au and 3DOM LaCoO3 are responsible for the excellent cata-
lytic performance.
It is well known that tar contains more than 100 hydrocarbon
compounds, including macromolecular aromatic compounds and
polycyclic aromatic hydrocarbons (PAHs) [7]. At low reforming tem-
perature, these aromatic hydrocarbons not only have high mass transfer
resistance but also tend to form carbon deposits which could cover the
active sites on the catalyst surface, resulting in the deactivation of the
catalyst. In order to enhance reforming performance and carbon de-
position resistance of the Ni-based catalysts, researchers have con-
ducted extensive researches on catalyst supports. Various materials
have been used as the Ni-based catalyst supports and promoters [3],
including alkali metal or rare earth metal doped Al2O3, alkaline-earth
metal oxides (MgO, CaO etc.), rare earth oxides (CeO2, La2O3 etc.),
zeolites (SBA-15, ZSM-5 etc.) and mineral-like supports (perovskite-,
spinel-, hydrotalcite-like compounds etc.). Park et al. [8] reported that
a 15 wt% Ni/CeO2(75 %)-ZrO2(25 %) catalyst exhibited a better cata-
lyst performance in terms of catalytic activity and stability compared
with commercial Ni catalysts for steam reforming of benzene. The su-
perior catalytic activity was attributed to its greater redox character-
istics and increased specific surface area. Sekine et al. [9] investigated
the effect of alkaline-earth metals (Sr, Ba and Ca) on the activity of a
Ni/LaAlO3 catalyst for steam reforming of toluene. They found that the
catalyst with 30 % La substituted by Sr showed the highest catalytic
performance, and they attributed the active oxygen species promoting
the reforming reaction to the lattice oxygen in the Ni/La0.7Sr0.3AlO3-δ.
Santamaria et al. [10,11] studied the effects of various supports and
promoters on the performance of Ni-based catalysts for tar steam re-
forming and found the significance of the deactivation are con-
sequences of supports properties such as metal-support interaction,
acidity and basicity. Moreover, the stability of catalysts can be greatly
improved by incorporating CeO2 as promoter, as its redox properties
enhanced the gasification of coke precursors.
Despite the great efforts made on the promotion effect of 3DOM
structure catalysts for gas-solid reactions, the research on the effect of
3DOM structure on biomass tar steam reforming have not yet been
reported. Furthermore, based on the excellent characteristics of the
Ce1−xZrxO2 for tar steam reforming described above, employing
Ce1−xZrxO2 with 3DOM structure as the support of steam reforming
catalyst might be an effective strategy to improve the activity and coke
resistance of catalyst at low temperature. In this work, the Ce1−xZrxO2
with 3DOM structure adopting three different Ce/Zr ratios (C1−xZx-
3DOM, x = 0.2, 0.3, 0.4) were prepared and used as the Ni-Pt bime-
tallic catalyst support. The prepared Ni-Pt/C1−xZx-3DOM were tested
catalytic performance in steam reforming of toluene, which was con-
sidered as a model compound of biomass gasification tar. In addition,
the conventional non-porous Ce1−xZrxO2 (C1−xZx-CP, x = 0.2, 0.3, 0.4)
were also prepared by the co-precipitation method and used as the Ni-
Pt bimetallic catalyst supports. The catalytic performances of the pre-
pared Ni-Pt/C1−xZx-CP were tested under the same conditions as that of
the Ni-Pt/C1−xZx-3DOM for comparison to study the influence of 3DOM
structure on the catalyst properties and toluene steam reforming per-
formance.
2. Experimental
2.1. Chemicals
The chemical reagents of methyl methacrylate (≥98.0 %), po-
tassium persulfate (K2S2O8, ≥99.5 %) Ce(NO3)3·6H2O (≥99.0 %),
ZrOCl2·8H2O (≥99.0 %), Ni(NO3)2·6H2O (≥98.0 %), ethyl alcohol
(≥99.7 %) and ammonium hydroxide (25.0 %−28 %) were all pur-
chased from Sinopharm Chemical Reagent Co., Ltd., China.
H2PtCl6·6H2O (Pt≥37.0 %) was purchased from Nanjing Chemical
Reagent Co., Ltd., China.
Among the various support materials being studied, cerium-zirco-
nium solid solution (Ce1−xZrxO2) materials have attracted extensive
attention due to their superior oxygen storage capacity and redox
property. According to the previous studies on steam reforming using
Ce1−xZrxO2 as the catalyst support, the Ce1−xZrxO2 could promote the
interaction between the active component and the support [12], and its
excellent redox performance can improve the reducibility of the sup-
ported metal [13], thereby enhancing the activity of the catalysts. In
addition, the lattice oxygen at the interface of the support and the ac-
tive metal is effective to dissociate the adsorbed water molecules,
producing more oxidizing species (eO and eOH groups). Therefore, the
carbonaceous components deposited on the surface of the catalyst
during the tar reforming process can be easily oxidized to CO and CO2,
ensuring good resistance to carbon deposition [14].
2.2. Catalyst preparation
2.2.1. Synthesis of polymethyl methacrylate (PMMA) colloidal crystal
template
Mono-disperse PMMA microspheres with an average diameter of ca.
310 nm, were synthesized following the procedures described in the
literature [23]. Specifically, 110 mL of methyl methacrylate was mixed
with 500 mL of deionized water in a 1000 mL three-necked round-
bottom flask under stirring at 300 rpm and degassing with flowing N2 at
70 °C. After stirring for 30 min, 15 mL of potassium persulfate solution
(dissolved 0.15 g K2S2O8) which had been preheated to 70 °C was
poured into the flask, followed by stirring for another 60 min, and then
the resulting emulsion was poured into 1000 mL of deionized water.
The produced colloidal suspension was transferred into a centrifuge
tube and centrifuged (TDZ5, Herexi Instrument & Equipment Co., Ltd.,
China) at 4000 rpm for 60 min. The precipitate was washed with
deionized water for three times to remove K2S2O8 completely. The
PMMA colloidal crystal template was obtained and dried in a drying
oven (YH-TS-9001, Yuheng Instrument & Equipment Co., Ltd., China) at
60 °C for 12 h.
In the last decade, three-dimensional ordered macroporous (3DOM)
materials have received extensive attention. 3DOM materials have
uniform large pore size (> 50 nm) and fixed periodic structure, which
enables them to provide more reactive sites, and promote mass transfer
of the reactants [15]. Therefore the catalyst support with 3DOM
structure is very suitable for the gas-solid reactions such as NOx selec-
tive reduction [16], soot and VOCs catalytic combustion [17–19], and
CH4 steam reforming [20]. In addition, many studies have found that
the 3DOM structure can also produce more oxygen vacancies and re-
active oxygen species, thus enhancing the mobility of reactive oxygen
species and the redox ability of catalysts [21,22], which play a critical
role in catalytic reaction. Wang et al. [17] studied soot combustion on
CuO-CeO2 catalysts, and found that the CuO-CeO2 with 3DOM structure
had higher catalytic activity and CO2 selectivity than the bulk CuO-
CeO2 catalyst prepared by sol-gel method. They attributed this result to
the improvement of mass transfer performance caused by the 3DOM
structure. Santiago et al. [18] studied the mechanism of soot oxidation
2.2.2. Synthesis of Ce1−xZrxO2-3DOM (x = 0.2, 0.3, 0.4)
The Ce1-xZrxO2 with 3DOM structure were prepared referring to the
literature approach [24]. Briefly, a certain amount of Ce(NO3)3·6H2O
2

S. Zhou, et al.
AppliedCatalysisA,General607(2020)117859
(99.9 %) and ZrOCl2·8H2O (99.9 %) were dissolved in an ethanol
aqueous solution (95 wt%). The mol ratio of Ce/Zr was controlled at 8/
2 (7/3, 6/4) and the total concentration of the metal ions in the solution
was set to 1 mol·L−1. After complete dissolution, the PMMA colloidal
crystal template was added into the solution to make its concentration
at 0.25 g·mL−1. The time for impregnation was 3 h. The excessive liquid
was removed through vacuum suction filtration with a Buchner funnel.
The obtained wet solid was dried in drying oven at 60 °C for 12 h, and
then calcined under air atmosphere with the temperature increasing to
300 °C and keeping 3 h, followed by increasing to 550 °C at a heating
rate of 1 °C min−1 and keeping 6 h. The formed products of Ce1−xZrxO2
(x = 0.2, 0.3, 0.4) were respectively labeled as C0.8Z0.2-3DOM (Ce/
of toluene occurred in a quartz tube reactor with 100 cm in length and
10 mm in inner diameter. In order to create a plug flow case and avoid
mass transfer limitations, catalyst bed height (L) and particle diameter
(d) were selected with respect to reactor inner diameter (D) so that D/d
≥ 10 and L/d ≥ 50 [27]. In the current work, 0.5 g of the catalyst
(particle size of 0.3–0.5 mm) was mixed with silica sand (inert material)
of the same average particle size to make the total height of catalyst bed
25 mm. The catalyst bed was fixed between two layers of quartz wool in
the middle of the quartz tube. Prior to the reforming experiment, the
catalyst was reduced by H2 (in H2/N2 (30/70, v/v) atmosphere at the
flowrate of 100 mL‧min−1) at 550 °C for 3 h. During the reforming re-
action, the toluene vapor was supplied by gas aeration via bubbling at
30 °C and 37 °C respectively with 100 mL‧min−1 of N2 controlled by a
mass flow controller, and under these conditions the flowrates of to-
luene were determined respectively as 185 and 270 μmol‧min−1 by an
on-line gas chromatography (GC, TRACE 1310 GC, ThermoFisher, USA)
via a flame ionization detector (FID). The GC equipped with a capillary
column (30 m ×0.53 mm × 3 μm, ON-5, Surwit Technology Inc.,
China), the inlet temperature was 200 °C and the oven temperature was
set at 120 °C. The steam was supplied by injecting water into an eva-
porator through a syringe pump. The water feed rate was adjusted to
controlled the ratio of steam to carbon (S/C) at 3. The toluene vapor
and steam were mixed evenly in the evaporator and then flowed into
the reactor. The gas guide line was kept at 150 °C to prevent con-
densation of the reactants. The gaseous products were cleaned after
passing through two gas cleaning cylinders respectively containing
isopropyl alcohol in ice-water bath and silica gel. The non-condensable
gas was collected in a gas sample bag. The gas hourly space velocity
(GHSV) of the reaction process was controlled at about 10,000 h−1. The
reforming experiments were conducted under different reaction tem-
peratures at 300, 350, 400, 450, 500, 550 and 600 °C, respectively.
Sampling did not start until the reaction had remained stable for one
hour. Gas products were analyzed by GC on a TRACE 1300 GC (Ther-
moFisher Scientific, USA) equipped with a valve housing (Aux Module).
Separation was carried out on two GC packed columns respectively
named Porapak Q (ThermoFisher Scientific, USA) and MolSieve 5A
(ThermoFisher Scientific, USA) which were installed in the Aux
Module. CO2 was separated from the other gas components by the
Porapak Q column, while all of the other gas component separation was
achieved by MolSieve 5A column. Argon was used as the carrier gas.
The temperature of the Aux Module was set at 70℃ during the mea-
surement. The content of each component in the product gas was de-
termined by the external standard method of GC. Each sample was
measured three times and the average value for each component was
Zr = 8/2), C0.7Z0.3-3DOM (Ce/Zr = 7/3) and C0.6 0.4
Z
-3DOM (Ce/
Zr = 6/4).
2.2.3. Synthesis of nonporous Ce1−xZrxO2 (x = 0.2, 0.3, 0.4)
The nonporous Ce1−xZrxO2 supports were prepared by a co-pre-
cipitation method referring to the literature [24]. The stoichiometric
amounts of precursors of Ce(NO3)3·6H2O and ZrOCl2·8H2O for pre-
paration of nonporous Ce1−xZrxO2 (x = 0.2, 0.3, 0.4) were dissolved
into deionized water under stirring. Ammonia solution (25 %, w/w)
was used as the precipitant to regulate pH of the solution at 8.0. The
obtained precipitates were washed using deionized water, followed by
dried in drying oven at 60 °C for 12 h. The dried precipitates were
calcined under the same conditions as that in the synthesis of 3DOM
samples. The formed products of Ce1−xZrxO2 (x = 0.2, 0.3 0.4) were
labeled as C0.8Z0.2-CP (in case of Ce/Zr = 8/2), C0.7Z0.3-CP (in case of
Ce/Zr = 7/3) and C0.6Z0.4-CP (in case of Ce/Zr = 6/4) respectively.
2.2.4. Synthesis of Ni-Pt/Ce1−xZrxO2 (x = 0.2, 0.3, 0.4) catalysts
Considering cost reduction and the synergistic effect of the active
metals, a common content of metal loading with 10 wt% of Ni and 1 wt
% of Pt [25,26] was adopted to prepare the Ni-Pt/Ce1−xZrxO2 catalysts
in this study. Ni-Pt/Ce1−xZrxO2-3DOM and Ni-Pt/Ce1−xZrxO2-CP cat-
alysts were prepared via an incipient wetness impregnation method
using Ni(NO3)2·6H2O and H2PtCl6·6H2O aqueous solution. After im-
pregnation, the catalysts were dried at 100 °C for 12 h and then calcined
at 550 °C for 4 h under air atmosphere. The obtained catalysts were
labeled as Ni-Pt/C1−xZx-3DOM and Ni-Pt/C1−xZx-CP, respectively.
2.3. Steam reforming of toluene experiment
The diagrammatic sketch of the setup to perform the steam re-
forming experiments is shown in Fig. 1. The catalytic steam reforming
Fig. 1. Experimental setup for the catalytic steam reforming of toluene.
3

S. Zhou, et al.
AppliedCatalysisA,General607(2020)117859
taken. The conversion of toluene was calculated using the following
185 μmol min−1, at the temperature of 500 °C and 600 °C, the corre-
sponding toluene conversions for all of the Ni-Pt/C1−xZx-3DOM ex-
ceeded 80 % and 93 %, respectively, while those for the Ni-Pt/C1−xZx-
CP were less than 50 % and 85 % respectively. Among them, Ni-Pt/
formula：
molesCO + molesCO2 + molesCH4
7 × molesC7H8
Toluene conversion (%) =
2.4. Catalyst characterization
×100
(1)
C
0.8Z0.2-3DOM achieved the highest toluene conversion, which reached
90.4 % at 500℃ and 95.6 % at 600℃. When the flowrate of toluene was
raised to 270 μmol min−1, a slight decrease in toluene conversion was
observed for either of the two groups of the catalysts. The toluene
conversion for Ni-Pt/C0.8Z0.2-3DOM at 500 °C and 600 °C dropped to
87.2 % and 90.1 %, respectively. Nevertheless, Ni-Pt/C1−xZx-3DOM
still showed higher toluene conversion than Ni-Pt/C1−xZx-CP.
Thermogravimetric analyses (TGA) was performed on an SDT 650
(Waters Corporation, USA) synchronous thermal analyzer. The tem-
perature programmed from ambient temperature to 700 °C at a heating
rate of 10 °C/min in the air stream at a flowrate of 50 mL‧min−1
.
It can be observed from Fig. 2 that in temperature range of
400–600℃, both of the Ni-Pt/C1−xZx-3DOM and Ni-Pt/C1−xZx-CP
presented the same trend of catalysis activity increasing with the in-
crease of Ce/Zr ratio in the supports, i.e. Ni-Pt/C0.8Z0.2 > Ni-Pt/
Scanning electron microscopy coupled with energy dispersive
spectroscopy was performed on a Quanta 250 FEG scanning electron
microscope (SEM, FEI, USA) with energy dispersive spectrometer (EDS,
Oxford Aztec X-MaxN 80, UK). Specimens were prepared by depositing
powder on double-sided carbon sticky tape affixed to an Al stub. All
SEM specimens except for EDS analysis were coated with 75 Å of Au
before the images were taken.
C
0.7Z0.3 > Ni-Pt/C0.6Z0.4, which indicates that Ce/Zr = 0.8/0.2 is the
preferable ratio of the prepared catalysts for catalyzing the steam re-
forming of toluene. The gas yields as well as the main gas products of
the reactions respectively catalyzed by Ni-Pt/C0.8Z0.2-3DOM and Ni-Pt/
C0.8Z0.2-CP under 185 μmol min−1 toluene flowrate at different tem-
peratures were compared and the results are displayed in Fig. 3.
It is known that besides the steam reforming reactions there were
several other reactions occurring simultaneously, such as water gas
shift reaction, hydrodealkylation and so on. The corresponding che-
mical equations of the main reactions are displayed as Eqs. (2)–(6) [28]:
X-ray fluorescence (XRF) spectrometry analysis was performed on
an ARL-9800 XRF (ARL, Switzerland) fluorescence spectrometer to
measure the relative content of metal elements in the catalysts.
X-ray diffraction (XRD) was recorded on an X’TRA diffractometer
(ARL, Switzerland) operated at 40 kV and 40 mA using Cu Kα radiation
source (k = 0.1540562 nm) and NaI (Tl) scintillation detector. The
catalysts were pre-treated with H2 at 550 °C for 1 h before the XRD
characterization. Scans were performed in a 2θ range from 10° to 90°
Steam reforming:C7H8+14H2 O 7CO2+18H2 H0298K=+581 kJ/mol
with the step of 0.02° and the scan rate of 8° min−1
.
(2)
X-ray photoelectron spectra (XPS) data were collected on a PHI
5000 VersaProbe XPS system (UIVAC-PHI, Japan) with a monochro-
matic Al Kα (hv = 1486.6 eV) X-ray source. The catalysts were pre-
treated with H2 at 550 °C for 1 h before the XPS characterization. The
charging effects were corrected by adjusting the binding energy of C1s
peak from adventitious carbon to 284.8 eV.
C7H8+7H2 O 7CO+11H2 H0298K=+869 kJ/mol
(3)
Water gas shift:CO+H2 O CO2 + H2 H0298K=-41 kJ/mol
(4)
Hydrodealkylation:C7H8 + H2
C6H6+CH4 H2098K=-42 kJ/mol
(5)
Surface areas, pore volumes and pore size distributions of the cat-
alyst samples were obtained through the measurements of N2 adsorp-
tion/desorption isotherms at −196 °C on a JW-BK122W static nitrogen
adsorption system (JWGB Science and Technology Company, China).
The surface areas and pore size distributions were calculated according
to the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda
(BJH) method, respectively.
Methane steam reforming
H2098K=+206 kJ/mol
:CH4 + H2 O CO+3H2
(6)
Therefore, the gas products included H2, CO2, CO, CH4, etc. It could
be observed in Fig. 3 that for both of the catalysts, gas yields increased
along with the increase of reaction temperature, and this result is in
agreement with that of toluene conversion. Besides, among all of the
gas products, H2 accounted for the largest proportion. According to
Fig. 3, it could be easily found that the catalysis activity of Ni-Pt/
H2 temperature-programmed reduction (H2-TPR) was performed
using an Auto Chem II 2920 chemisorption analyzer (Micromeritics,
USA). Around 100 mg of sample was pretreated under helium atmo-
sphere at 300 °C for 1 h and subsequently cooled to 40 °C, afterward, 10
% of H2/Ar flow (40 mL‧min−1) passed over the catalyst bed while and
the temperature ramped from 40 to 900 °C at a heating rate of
10 °C‧min−1. The hydrogen consumption signal was monitored by a
thermal conductivity detector (TCD).
C
0.8Z0.2-3DOM was much higher than that of Ni-Pt/C0.8Z0.2-CP, as the
yield of H2 with Ni-Pt/C0.8Z0.2-3DOM as the catalyst is even greater
than the total gas yield with Ni-Pt/C0.8Z0.2-CP as the catalyst under the
same conditions. When Ni-Pt/C0.8Z0.2-CP was used as the catalyst, CH4
was detected in temperature range from 400 to 600℃ and its yield
increased with the increase of reaction temperature. However, as to the
circumstance of Ni-Pt/C0.8Z0.2-3DOM, CH4 was not detected until the
temperature increased to above 550℃, moreover, CH4 yield is much
lower than that with Ni-Pt/C0.8Z0.2-CP as the catalyst. The less gen-
eration of CH4 also indicated that the catalyst Ni-Pt/C0.8Z0.2-3DOM has
a higher reforming activity than Ni-Pt/C0.8Z0.2-CP. It is worth pointing
out that CH4 is an undesirable by-product of the steam reforming, as
CH4 is an important precursor of carbon deposit, which is liable to
catalyst deactivation [29].
3. Results and discussion
3.1. Catalysis activity and composition of the gas products
Based on the theoretical calculation by the software NASA-CEA,
under the experimental conditions employed in this study, complete
conversion of toluene can be obtained in the temperature range of
300–600℃. Therefore, in order to investigate the activity of the pre-
pared catalysts at relatively low temperature, the toluene steam re-
forming experiments were carried out from 300 °C to 600 °C at two
toluene flowrates, and the conversion curves are shown in Fig. 2. For all
of the as-prepared catalysts, very little toluene was converted below
350 °C, while above 350 °C, toluene conversion increased with the in-
crease of temperature for both of the two types of catalysts. Compared
with the Ni-Pt/C1−xZx-CP, Ni-Pt/C1−xZx-3DOM exhibited significant
higher catalytic efficiency. When the flowrate of toluene was
The catalysis performance of the prepared Ni-Pt/C0.8Z0.2-3DOM
catalyst for the steam reforming of toluene was compared with other
Ni-based catalysts prepared by other research teams. The related data
are listed in Table 1. As shown in Table 1, for most of the Ni-based
catalysts, only when the temperatures are higher than 923 K can the
conversions of toluene reach a relatively high level (> 80 %). The to-
luene conversion attained 90.4 % at 773 K for the prepared Ni-Pt/
C
0.8Z0.2-3DOM, indicating that this catalyst has a higher low-tempera-
ture reactivity for toluene steam reforming compared to these catalysts.
4

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AppliedCatalysisA,General607(2020)117859
Fig. 2. Toluene conversion for the catalysts within toluene flowrate of (a) 185 μmol min−1 and (b) 270 μmol min−1 at different reaction temperatures.
evaporation. The weight increase between 250 and 450 °C could be
ascribed to the oxidation of Ni° and Pt° in the catalyst [39]. It is known
that different kinds of carbon deposit may be generated on the catalyst
surface including amorphous carbon and filamentous carbon [40]. In
the TGA profile, the weight loss peak at 500–700 °C could be attributed
to the filamentous carbon [40], while another kind of carbon deposit
named amorphous carbon which generally appears below 500 °C [40]
could not be observed. In the TGA profile of the catalyst, since the
weight loss of amorphous carbon occurs in the same temperature range
as the weight gain of the active metal (Ni and Pt) due to oxidation, the
weight loss peak of amorphous carbon might be covered by the weight
gain peak of the latter. Assuming that all the loaded Ni and Pt was
oxidized in the TGA process, the amount of amorphous carbon in the
catalyst could be calculated by subtracting the weight gain of the cat-
alyst in the TGA curve from the theoretical weight gain of Ni and Pt
after complete oxidation. Therefore, the amount of amorphous carbon
deposited was calculated as 21 mg gcat−1. The amount of filamentous
carbon deposit calculated by the TGA profile was 30 mg gcat−1. Based
on the above results, the total carbon deposition rate for Ni-Pt/C0.8Z0.2
-
Fig. 3. Gas yields and the main gas product compositions of the steam re-
forming of toluene catalyzed by Ni-Pt/C0.8Z0.2-3DOM and Ni-Pt/C0.8Z0.2-CP vs.
reaction temperature.
3DOM during the 30 h of operation was calculated as 1.7 mg gcat−1 h−1
,
which was much lower than those of the reforming catalysts reported in
other studies (as shown in Table 1). Besides, as reported by the previous
studies, the amorphous carbon is relatively easily removed by the oxi-
dants such as O2 and H2O [40]. In short, little carbon deposition sug-
gested that there are a great deal of active oxygen species on the cat-
alyst Ni-Pt/C0.8Z0.2-3DOM surface during the reaction process. The TGA
results demonstrated that this catalyst presented excellent resistance to
carbon deposition.
Furthermore, the steam reforming experiments in this work were car-
ried out under high toluene concentration (185 μmol min−1) and high
GSHV (10,000 h−1), which are relatively harsh conditions compared
with those of the other studies. Therefore, due to its excellent activity at
low temperature, the Ni-Pt/C1−xZx-3DOM could be a potential steam
reforming catalyst for tar removing.
3.3. Catalyst characterization
3.2. Catalyst stability
3.3.1. XRF
The stability of Ni-Pt/C0.8Z0.2-3DOM was tested for 30 h under the
condition of temperature at 600 °C, toluene flowrate of
185 μmol min−1, GHSV of 10,000 h−1 and S/C = 3. The results are
shown in Fig. 4. During the whole period, Ni-Pt/C0.8Z0.2-3DOM ex-
hibited excellent durability. The conversion of toluene maintained over
95 %, and the content of H2 in the produced gas maintained at a high
level around 70 %, while contents of other main gas products also kept
relatively stable.
The Ni and Pt content calculated by XRF analysis is shown in
Table 2. It could be observed that the measured values for each catalyst
are close to those of the nominal loadings (10 wt% and 1 wt%), which
indicated the wet impregnation method for catalyst preparation was
adequate.
3.3.2. SEM
Carbon deposition is one of the causes that result in catalyst deac-
tivation, therefore, carbon deposit characteristic of the catalyst Ni-Pt/
In this work, C1−xZx-3DOM were prepared using the templates of
the colloidal crystal arrays that were assembled by the closely packed
mono-disperse PMMA microspheres. The SEM images of PMMA,
C
0.8Z0.2-3DOM after 30 h of operation was investigated by TGA in the
air stream. The results are shown in Fig. 5. The weight loss in the
temperature range 30–200 °C could be attributed to moisture
C1−xZx-3DOM and Ni-Pt/C1−xZx-3DOM are shown in Fig. 6. As it is
observed in Fig. 6(a, b) that the PMMA colloidal spheres exhibit highly
5

S. Zhou, et al.
AppliedCatalysisA,General607(2020)117859
Fig. 4. Toluene conversion and gaseous components vs. operation time for Ni-
Pt/C0.8Z0.2-3DOM catalyst at the condition of T = 600 °C, toluene
flowrate = 185 μmol·min−1, GHSV = 10,000 h−1, and S/C = 3.
Fig. 5. The TG and DTG profiles of the Ni-Pt/C0.8Z0.2-3DOM catalyst after 30 h
of toluene steam reforming operation.
Table 2
Ni and Pt content of Ni-Pt/C1−xZx-3DOM and Ni-Pt/C1−xZx-CP catalysts.
Catalyst
Ni content (wt%)
Pt content (wt%)
CP
3DOM
CP
3DOM
Ni-Pt/C0.8Z0.2
Ni-Pt/C0.7Z0.3
Ni-Pt/C0.6Z0.4
9.86
9.25
9.53
9.31
9.92
9.69
0.92
0.97
0.91
0.98
0.93
0.96
uniform size (around 310 nm), and are closely packed into a highly
ordered three-dimensional arrangement. According to Fig. 6(c, e, g), it
could be found that despite the difference of Ce/Zr ratios in this study,
C
1−xZx-3DOM, have been produced with well-defined 3DOM structures
containing periodic voids interconnected by the open windows. The
PMMA windows are 210–228 nm in diameter, corresponding to a
shrinkage of about 30 % of the initial size of the PMMA microspheres.
After the impregnation and calcination process, the obtained Ni-Pt/
C
1−xZx catalysts (Fig. 6(d, f, h)) well retained the original 3DOM
structure.
In order to investigate the morphology changes of the used catalyst
Ni-Pt/C0.8Z0.2-3DOM after 30 h stability test, its SEM image was taken
and compared with that of the fresh Ni-Pt/C0.8Z0.2-3DOM. The SEM
images of both of them are shown in Fig. 7. The 3DOM structural fea-
ture was relatively completely preserved for the used Ni-Pt/C0.8Z0.2
-
6

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AppliedCatalysisA,General607(2020)117859
Fig. 6. SEM images of PMMA, C1−xZx-3DOM and Ni-Pt/C1−-xZx-3DOM. (a, b) PMMA; (c) C0.8Z0.2-3DOM; (d) Ni-Pt/C0.8Z0.2-3DOM; (e) C0.7Z0.3-3DOM; (f) Ni-Pt/
C0.7Z0.3-3DOM; (g) 3DOM C0.6Z0.4; (h) 3DOM Ni-Pt/C0.6Z0.4
.
3DOM, and no obvious morphology changes were observed in its SEM
image compared with the fresh catalyst sample, which illustrated that
the 3DOM structure could maintain relatively stable in the reforming
reaction. As shown in Fig. 7b, a small amount of moss-like carbon and
filamentous carbon could be observed in some microregions on the
surface of the used catalyst, which verified that carbon deposition
produced on the catalyst surface after long term steam reforming re-
action of toluene.
3.3.3. XRD
The diffraction patterns of the supports and catalysts are displayed
in Fig. 8I and 8II, respectively. As it is shown that all supports present
similar diffraction patterns of fluorite-type crystal structure (PDF ICDD
43-1002 for Ce0.8Zr0.2O2, PDF ICDD 28-0271 for Ce0.7Zr0.3O2 and PDF-
ICDD 38-1439 for Ce0.6Zr0.4O2). The diffraction patterns with 2θ at
28.7°, 33.2°, 47.7°, 56.6°, 59.3°, 69.7°, 76.9° and 79.3 are corresponding
to the (111), (200), (220), (311), (222), (400), (331) and (420) planes.
It could be observed from Fig. 8, with the increase of Zr content in the
7

S. Zhou, et al.
AppliedCatalysisA,General607(2020)117859
Fig. 7. SEM images of (a) the fresh Ni-Pt/C0.8Z0.2-3DOM and the used Ni-Pt/C0.8Z0.2-3DOM after the 30 h stability test.
Fig. 8. XRD patterns of the supports (I) and catalysts (II). I: (a) C0.8Z0.2-3DOM; (b) C0.7Z0.3-3DOM; (c) C0.6Z0.4-3DOM; (d) C0.8Z0.2-CP; (e) C0.7Z0.3-CP; (f) C0.6Z0.4-CP.
II: (a) Ni-Pt/C0.8Z0.2-3DOM; (b) Ni-Pt/C0.7Z0.3-3DOM; (c) Ni-Pt/C0.6Z0.4-3DOM; (d) Ni-Pt/C0.8Z0.2-CP; (e) Ni-Pt/C0.7Z0.3-CP; (f) Ni-Pt/C0.6Z0.4-CP.
support, the main diffraction peaks shift to higher values of 2θ and the
relative intensities of the peaks decrease and broaden, corresponding to
a decrease in the lattice parameter. This phenomenon might be due to
the replacement of the larger Ce4+ (0.97 Å) by the smaller Zr4+
(0.84 Å) [41]. In addition, no extra peaks ascribed to ZrO2 were ob-
served for the Ce1−xZrxO2 samples, which implied that ZrO2 was in-
corporated into the CeO2 lattice to form a solid solution while main-
taining the fluorite structure [42].
Table 3
The data of 2θ (111) and crystallite sizes of the supports and Ni0 particles of Ni-
Pt/C1−xZx-3DOM and Ni-Pt/C1−xZx-CP catalysts measured by XRD.
Catalyst
2θ/° (CeO2)
2θ/° (Ni0)
Ce1−xZrxO2
crystallite size
(nm)
Ni0 particle
size (nm)
CP
3DOM CP
3DOM CP
3DOM
CP
3DOM
All the catalysts present the same mainly diffraction patterns as the
supports except two diffraction peaks of Ni0 phase, indicating that the
introduction of Ni did not change the phase structure of Ce1−xZrxO2.
The diffraction patterns with 2θ at 44.4° and 51.8°on Ni-Pt/C1−xZx
samples could be assigned to the cubic Ni0 phase. The Ni0 peaks of the
Ni-Pt/C1−xZx-3DOM catalysts are broader than those of the corre-
sponding Ni-Pt/C1−xZx-CP catalysts, indicating that the average par-
ticle size of Ni in Ni-Pt/C1−xZx-3DOM is smaller. The average crystallite
size of each support and that of the corresponding Ni0 was respectively
calculated from the (111) diffraction of CeO2 (around 28.7°) and Ni
(around 44.4°) based on Scherrer equation [43], and the results are
shown in Table 3. Compared with the C1−xZx-CP, the C1−xZx-3DOM
showed smaller crystallite size with the same Ce/Zr ratio, which made
its adsorption energy for water molecules and the corresponding dis-
sociation barrier lower than the former due to its higher lattice strain
[44], and thus water molecules were dissociated and transformed into
active adsorbed oxygen species more efficiently on the C1−xZx-3DOM
supports. Furthermore, the smaller particle sizes of Ni on the C1−xZx-
3DOM means higher dispersion of Ni0, which allowed the catalyst Ni-
Pt/C1−xZx-3DOM to have more active sites as well as better steam re-
forming and anti-coking properties.
Ni-Pt/C0.8Z0.2 28.734 28.746 44.45 44.49
Ni-Pt/C0.7Z0.3 28.834 28.854 44.44 44.46
Ni-Pt/C0.6Z0.4 28.967 28.973 44.46 44.47
11.3
9.9
8.2
7.3
6.1
31.6 22.5
31.1 16.3
33.6 19.7
7.3
3.3.4. XPS
Chemical states of element Ce on the surfaces of the catalysts were
analyzed using XPS, and the narrow XPS spectra in Ce3d region are
shown in Fig. 9. In each XPS spectrum, the Ce3d profile could be se-
parated into ten peaks, among which the four peaks labeled “♦’’ with
the Ce3d5/2 binding energy (BE) peaks at 880.3
0.2 eV and
0.2 eV and
884.7
903.3
0.2 eV, and with the Ce3d3/2 BE peaks at 898.7
0.1 eV could be ascribed to the Ce3+ species. The other six
peaks labeled “*’’ with the Ce3d5/2 BE peaks at 882.2
0.2 eV,
888.9
900.9
0.2 eV and 898.1
0.2 eV, 907.8
0.2 eV, and with the Ce3d3/2 BE peaks at
0.2 eV and 916.6
0.1 eV could be as-
cribed to the of Ce4+ species. It is known that in the Ce1−xZrxO2, some
oxygen atom could move away from the lattice and leave behind two
electrons, which localize on two cerium atoms, thus an oxygen vacancy
is formed and Ce4+ is transformed into Ce3+ [45]. Therefore, the
content of oxygen vacancy is positively correlated with the content of
8

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AppliedCatalysisA,General607(2020)117859
Fig. 9. XPS spectra of the Ni-Pt/C1−xZx-3DOM and Ni-Pt/C1−xZx-CP catalysts in the Ce3d binding energy region.
loop in the relative pressure (P/P0) range of 0.8–1.0 could be observed
in 3DOM catalysts, demonstrating macropores existing in Ni-Pt/C1−xZx-
3DOM catalysts [23]. The related textural parameters of the C1−xZx
supports and the Ni-Pt/C1−xZx catalysts based on N2 adsorption iso-
therms are shown in Table 5. It can be observed that compared with the
support, the specific surface area and pore volume of the corresponding
catalyst decrease slightly, and the decrease extent for Ni-Pt/C1−xZx-
3DOM is higher than that for Ni-Pt/C1−xZx-CP. This might be due to
part of the channels in the supports were blocked by the loaded Ni and
Pt. As discussed above in XRD patterns, the particle size of Ni on the
3DOM catalyst is smaller than that on the CP catalyst. Under the same
load, more Ni particles on the 3DOM catalyst surface, resulting in more
channels in 3DOM samples blocked. Hence, the changes in the specific
surface area and pore volume for the Ni-Pt/C1−xZx-3DOM catalysts are
higher than Ni-Pt/C1−xZx-CP. It is obviously that the BET surface area
and pore volume of Ni-Pt/C1−xZx-3DOM are about twice that of Ni-Pt/
Table 4
Relative contents of Ce species on the surface of the catalysts.
Catalyst
Ce3+ (%)
Ce4+ (%)
Ce3+/Ce4+
CP
3DOM
CP
3DOM
CP
3DOM
Ni-Pt/C0.8Z0.2
Ni-Pt/C0.7Z0.3
Ni-Pt/C0.6Z0.4
21.19
19.58
18.32
26.94
25.25
22.17
78.81
80.42
81.68
73.06
74.75
77.83
0.27
0.24
0.22
0.37
0.34
0.28
Ce3+. According to the literature [46,47], in the reforming reaction,
toluene molecules firstly adsorbed on the metallic active site and de-
composed into active CHx and C2 species, and then the CHx and C2
species reacted with the adsorbed reactive oxygen species which was
formed by dissociation of H2O, producing H2, CO and CO2. During the
reaction process, the oxygen vacancies could act as a conductive
medium for oxygen ions, thereby enhancing surface reduction activity
of the catalyst [48]. Besides, at the oxygen vacancies, the adsorbed H2O
molecules on Ce3+ are easily dissociated into reactive oxygen species
(O*), which would react with the intermediate products to not only
promote the catalysis process [46] but also restrain the formation of
carbon deposits [49]. As shown in Table 4, based on the XPS spectra,
the ratios of the Ce3+/Ce4+ on the surfaces of Ni-Pt/C0.8Z0.2-3DOM, Ni-
Pt/C0.7Z0.3-3DOM and Ni-Pt/C0.6Z0.4-3DOM were calculated as 0.37,
0.34 and 0.28, respectively, while those on the surfaces of Ni-Pt/
C0.8Z0.2-CP, Ni-Pt/C0.7Z0.3-CP and Ni-Pt/C0.6Z0.4-CP were 0.27, 0.24
and 0.22, respectively. Therefore, one of the important reasons that the
Ni-Pt/C1−xZx-3DOM showed higher catalysis activity than the Ni-Pt/
C1−xZx-CP, suggesting that Ni-Pt/C1−xZx-3DOM could provide a larger
reaction area between the catalyst and the reactants. Furthermore, the
profiles of the catalyst pore-size distributions (Fig. 10b) indicated that
compared with Ni-Pt/C1−xZx-CP, there are more mesoporous in the Ni-
Pt/C1−xZx-3DOM, which is beneficial to the diffusion of reactant mo-
lecules [46].
3.3.6. H2-TPR
The catalyst reduction characteristic was determined by the H2-TPR
experiment, and the corresponding TPR curves are shown in Fig. 11.
For all of the catalysts, there is a major consumption of H2 at
200–300 °C, which could be attributed to the reduction peaks of NiO
and CeO2 on the catalyst surface [50]. The consumption of H2 at the
temperature of around 100–200 °C can be attributed to the reduction of
PtOx and surface CeO2 in strong interaction with Pt [51]. The peak at
the temperature of 600–800 °C is corresponding to the reduction of bulk
phase CeO2. It could be observed from Fig. 11 that, different from the
Ni-Pt/C1−xZx-CP catalyst, the H2 consumption peaks of PtO, NiO and
CeO2 of the Ni-Pt/C1−xZx-3DOM overlap, indicating relatively stronger
interactions between the reactive components of Ni and Pt and the
C
1−xZx-CP might be more Ce3+ species existing on the surface of the Ni-
Pt/C1−xZx-3DOM.
3.3.5. N2 adsorption/desorption
N2 adsorption-desorption isotherms of the catalysts are shown in
Fig. 10a. The isotherms of all the samples exhibit type IV characteristic
with H2-type hysteresis loop in the P/P0 range of 0.2–0.8, indicating
that textural mesopores exist in all the samples. A type H3 hysteresis
9

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AppliedCatalysisA,General607(2020)117859
Fig. 10. The nitrogen adsorption-desorption isotherms (a) and pore-size distribution plots (b) of Ni-Pt/C1−xZx-3DOM and Ni-Pt/C1−xZx-CP catalysts.
Table 5
Textural parameters of the supports and catalysts.
Table 6
H2 consumption (mmol H2‧g−1) of Ni-Pt/C1−xZx catalysts measured by H2-TPR.
Catalyst
BET surface area
Pore volume
Pore diameter
CP
(nm)
Sample
H2 consumption (mmol H2‧g−1
)
(m2‧g−1
CP
)
(cm3‧g−1
CP
)
CP
3DOM
3DOM
3DOM
3DOM
Ni-Pt/C0.8Z0.2
Ni-Pt/C0.7Z0.3
Ni-Pt/C0.6Z0.4
1.52
1.44
1.35
1.85
1.79
1.69
C
0.8Z0.2
24.89
29.43
28.46
20.21
24.43
20.21
51.05
53.85
52.56
39.18
43.65
38.56
0.22
0.15
0.18
0.15
0.12
0.16
0.51
0.55
0.49
0.40
0.41
0.39
7.5
7.2
7.6
9.7
8.9
9.2
8.4
8.6
8.2
9.1
9.7
9.3
C0.7Z0.3
C0.6Z0.4
Ni-Pt/C0.8Z0.2
Ni-Pt/C0.7Z0.3
Ni-Pt/C0.6Z0.4
supports of the Ni-Pt/C1−xZx-3DOM.
H2 consumption for each catalyst at low temperature (< 350℃)
were calculated through integrating the corresponding H2-TPR profile,
and the results are listed in Table 6. Ni-Pt/C1−xZx-3DOM catalysts
Fig. 11. H2-TPR profiles of Ni-Pt/C1−xZx-3DOM and Ni-Pt/C1−xZx-CP.
10

S. Zhou, et al.
AppliedCatalysisA,General607(2020)117859
showed a greater amount of low temperature hydrogen consumption
than the corresponding Ni-Pt/C1−xZx-CP. More H2 consumption means
more active phases in the catalysts. Therefore, more active phases as
well as the stronger interaction between the C1−xZx-3DOM support and
the active metal could be a factor that cause Ni-Pt/C1−xZx-3DOM cat-
alysts showing higher catalyst performance than Ni-Pt/C1−xZx-CP cat-
alysts in toluene steam reforming.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
The authors gratefully acknowledge the financial supports from the
National Natural Science Foundation of China (Nos. 22076077,
4. Conclusions
21577060),
Jiangsu
Science
and
Technology
Department
(BK20191256, BE2016172), Nanjing Municipal Committee of Science
and Technology (201722047) and Analysis & Test Fund of Nanjing
University.
Ni-Pt/C1−xZx-3DOM (x = 0.2, 0.3, 0.4) catalysts have been pre-
pared using a colloidal crystal template method, their catalytic per-
formances in steam reforming reaction were investigated in low tem-
perature range using toluene as a model compound of tar. As the
references, non-porous Ni-Pt/C1−xZx (Ni-Pt/C1−xZx-CP) were also
prepared and tested under the same conditions. The Ni-Pt/C1−xZx-
3DOM exhibited excellent catalytic performance, and toluene conver-
sion of Ni-Pt/C0.8Z0.2-3DOM reached 90.4 % under the conditions of
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1−xZx-CP, there are more Ce3+ species on the surface of Ni-Pt/C1−xZx-
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surface. Therefore, Ni-Pt/C1−xZx-3DOM show better oxidation-reduc-
tion activities due to producing more reactive oxygen species catalyzed
by Ce3+ species as well as faster transporting of these reactive oxygen
species by oxygen vacancies. The results of N2 adsorption/desorption
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