Biogas dry reforming for syngas production: Catalytic performance of nickel supported on waste-derived SiO2

Article abstract of DOI:10.1039/c4cy01126k

SiO₂ synthesized from photovoltaic waste by a vapor-phase hydrolysis method was applied as a support for a nickel catalyst in a biogas dry reforming process for the first time. The catalytic performance was compared with those of commercial precipitated SiO₂ and ordered mesoporous SiO₂. Nickel supported on waste-derived SiO₂ exhibited high CH₄ conversion (92.3%) and high CO₂ conversion (95.8%) at 800°C, and there was no deactivation after a 40 h-on-stream test. Catalyst characterization results revealed that the S_BET values and pore properties of catalysts affected the catalytic performance. A higher pore volume/S_BET ratio led to a smaller crystal metal size and higher metal dispersion, thus the catalyst was less prone to deactivation. This discovery will help improve catalyst design. The use of nickel supported on waste-derived SiO₂, which is competitive with commercial and mesoporous catalysts, shows the use of photovoltaic waste as a high value-added product; it can also deliver a cheap and environmentally benign support for catalysts in the biogas dry reforming process.

Full text of DOI:10.1039/c4cy01126k

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Biogas dry reforming for syngas production:
catalytic performance of nickel supported
Cite this: DOI: 10.1039/c4cy01126k
on waste-derived SiO †‡
2
a
abc
a
a
Xuejing Chen, Jianguo Jiang,*
Sicong Tian and Kaimin Li
SiO
for a nickel catalyst in a biogas dry reforming process for the first time. The catalytic performance was
compared with those of commercial precipitated SiO and ordered mesoporous SiO . Nickel supported on
waste-derived SiO exhibited high CH conversion (92.3%) and high CO conversion (95.8%) at 800 °C, and
there was no deactivation after a 40 h-on-stream test. Catalyst characterization results revealed that the
BET values and pore properties of catalysts affected the catalytic performance. A higher pore volume/SBET
2
synthesized from photovoltaic waste by a vapor-phase hydrolysis method was applied as a support
2
2
2
4
2
S
Received 30th August 2014,
Accepted 23rd September 2014
ratio led to a smaller crystal metal size and higher metal dispersion, thus the catalyst was less prone to
deactivation. This discovery will help improve catalyst design. The use of nickel supported on waste-derived
2
SiO , which is competitive with commercial and mesoporous catalysts, shows the use of photovoltaic waste
DOI: 10.1039/c4cy01126k
as a high value-added product; it can also deliver a cheap and environmentally benign support for catalysts
in the biogas dry reforming process.
www.rsc.org/catalysis
biogas dry reforming is a strongly endothermic process (see
eqn (1)), the high reaction temperature will achieve a relatively
1
. Introduction
7
,8
Biogas is a mixture of mainly methane and carbon dioxide,
which is produced by the anaerobic digestion of residual bio-
mass, such as landfill waste, municipal sludge, and food waste.
With the growing concern regarding global climate change
due to anthropogenic CO2 emission, biogas recycling for
high conversion of reactants. In addition, catalysts also play
a vital role in the catalytic dry reforming process, which
increases the cost substantially. Improving the stability and
choosing relatively cheap raw materials to prepare the catalyst,
without a loss of catalyst activity, are important.
1
energy-related applications has received much attention.
The main obstacle to improve stability is the deactivation
of catalysts, which is caused mainly by the deposition of
Therefore, biogas dry reforming for syngas production (eqn (1))
is a recycling option with several advantages: (i) biogas dry
reforming process can simultaneously consume the two main
9
,10
inactive carbon and the sintering of active metals.
To
improve catalyst stability, many studies have been conducted,
optimizing the active metals, catalyst supports, and catalyst
4 2 2
greenhouse gases (CH and CO ); (ii) the H /CO ratio is close to
3
,11–14
1
, which makes it suitable for further use in the carbonylation,
preparation methods.
During these processes, the low
hydroformylation, and Fischer–Tropsch synthesis of long-chain
cost and availability of the raw materials used for catalyst
preparation are important. Ni-based catalysts are commonly
used in the dry reforming process due to their reasonably good
activity and low cost compared to noble metals, although
they are more sensitive to coke formation than the noble
2
hydrocarbons; and (iii) the process avoids the separation of
3–5
CO , which is an energy intensive and costly process.
2
0
−1
CH
4
+ CO
2
↔ 2CO + 2H
2
, ΔH298K = 247 kJ mol
(1)
2
,10,13,15
12,16–18
19
metals.
MgO, TiO , CeO , Al O ,
Many dioxides including SiO ,
ZrO2,
2
2
0
8
11
3,21
15,22,23
The high cost and energy consumption of biogas dry
and their hybrids
have
2
2
2 3
6
reforming have restricted its industrial application. Because
been used as catalyst supports in the reforming process due to
their high specific surface areas and high thermal stability.
Among these, SiO and SiO -based catalyst supports are the
a
School of Environment, Tsinghua University, Beijing 100084, China.
2
2
E-mail: jianguoj@mail.tsinghua.edu.cn; Fax: +86 10 62783548;
Tel: +86 10 62783548
most widely used and the most promising for the industrial
application of the dry reforming process due to their availabil-
ity and various phase morphologies. Frontera et al. investi-
gated the activity and stability of several nickel catalysts
supported on different types of highly crystalline silica zeolites,
including Ni-ITQ-6, Ni-silicalite-1, and Ni-MCM-41, and found
b
Key Laboratory for Solid Waste Management and Environment Safety, Ministry
12
of Education of China, China
c
Collaborative Innovation Center for Regional Environmental Quality, China
†
‡
The authors declare no competing financial interest.
Electronic supplementary information (ESI) available. See DOI: 10.1039/c4cy01126k
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that the heterogeneity of the support surface strongly affected
The catalysts were dried at 60 °C for 6 h in a vacuum oven
and calcined at 800 °C for 4 h. Catalysts synthesized from
the SiO -H, SBA-15, and the SiO -P supports were designated
2 2
1
8
the catalyst performance. Ning Wang et al. also found that
the pore topology of different types of SiO affected the particle
2
dispersion, reducibility, and catalytic behavior of catalysts.
The synthesis of silica zeolites consumes large amounts
of organic template agents, and these zeolites are currently
not commercially available in large quantities. Therefore,
the development of new silica materials with a high specific
surface area, high thermal stability, and most importantly,
the potential for large-scale production is essential.
Ni/SiO -H, Ni/SBA-15, and Ni/SiO -P, respectively.
2
2
2.2 Catalyst characterization
2
4
XRD patterns were obtained with a D8 Advance X-ray
diffractometer (Siemens, Munich) using Cu Kα radiation
(
λ = 0.15406 nm), with a 2θ range of 0.3–80°. Scherrer's equa-
tion was used to estimate the mean Ni crystallite size based on
the diffraction peaks of the Ni (200) facet. Analysis of the Ni
loading of catalysts was undertaken using an XRF analyzer
In our previous study, polyporous nano-silica synthesized
from photovoltaic waste SiCl using a low-temperature vapor-
4
phase hydrolysis method (designated as SiO -H) was shown
2
(
XRF-1800, Shimadzu).
to have a relatively high specific surface area and high
Textual properties were measured by a surface area and
2
5
thermal stability. Considering the large-scale production
and poor treatment conditions of photovoltaic waste SiCl4,
porosity analyzer (ASAP 2020 HD88, Micromeritics) through
the nitrogen adsorption–desorption isotherms at 77 K.
The samples were degassed at 90 °C for 60 min and held at
the production of SiO -H as well as its further application as a
2
catalyst support for biogas dry reforming represents a useful
conversion of photovoltaic waste to a high value-added
product; it also provides a cheap and environmentally benign
support for catalysts in the biogas dry reforming process. Using
SiO -H as a waste-derived SiO support in biogas catalytic dry
160 °C for 120 min before analysis. A Brunauer–Emmett–Teller
(
BET) model was used to calculate the specific surface area and
a Barrett–Joyner–Halenda (BJH) model was used to calculate
the pore volume distribution.
2
2
Transmission electron microscopy (TEM) (JEM-2011,
JEOL Ltd.) was used to observe the morphology and distribu-
tion of metal sites. The samples were first dispersed in ethanol,
and then one drop of ethanol solution was placed on a copper
grid pre-coated with a formvar film and dried in air. SEM
reforming applications has not been reported previously.
A comprehensive evaluation of the catalytic performance
of nickel supported on waste-derived SiO2 in biogas dry
reforming was undertaken. SiO -H was used as a support for
2
a nickel catalyst in a biogas dry reforming process for the
(
S-5500, Hitachi) was also used to observe the morphology of
the samples.
2
The H temperature-programmed reduction (H -TPR) was
first time, and commercial precipitated SiO and mesoporous
2
2
SiO were also considered for comparison. Catalytic tests of
2
the three different nickel supported catalysts and the related
characterization of both fresh and spent catalysts were under-
taken systematically.
employed to analyze the reduction behavior of catalysts using
a chemisorption analyzer (AutoChemII 2920, Micromeritics).
Catalyst samples (50 mg, 20–40 mesh) were pretreated at
−1
4
00 °C for 1 h under flowing Ar (30 ml min ). Upon cooling to
2
. Materials & methods
5
0 °C, the sample was heated from room temperature (RT) to
−1
1000 °C with a temperature ramp of 10 °C min under a 5 vol%
2
.1 Support and catalyst preparation
−
1
H
2
/Ar stream (50 mL min ).
A low-temperature vapor-phase hydrolysis method was used
to synthesize SiO -H as previously reported. Silicon tetra-
chloride (99%, LDK Solar Ltd., Xinyu, China) was vaporized
and hydrolyzed with water vapor at a temperature of 200 °C, a
retention time of 5 s, and a H O/SiCl molar ratio of 2. Silica
powder was collected and dried at 105 °C for 2 h.
The TGA-MS method was applied to investigate the carbon
2
5
2
deposition with a TGA/DSC 1 STARe system (Mettler Toledo)
and a ThermoStar mass spectrometer (Pfeiffer). Samples were
treated at a rate of 10 °C min from RT to 900 °C under an oxy-
−1
2
4
−1
gen stream of 20 mL min with nitrogen as a protection gas.
Commercial precipitated SiO (designated as SiO -P) and
2
2
2.3 Catalytic tests
ordered mesoporous silica (SBA-15) were purchased (Sigma-
Aldrich, St. Louis, MO, USA). All three SiO supports were cal-
2
Catalytic tests for biogas dry reforming were conducted in a
fixed-bed reactor with a quartz glass tube (diameter = 6 mm)
under atmospheric pressure. 200 mg of the samples (20–40
mesh) were loaded in the center of the tube reactor. Before
the test, the catalysts were reduced at 800 °C in situ for 1 h
under a flow of 10 vol% H /N . A mixture gas (CH : CO : N =
0.4 : 0.4 : 0.2) with a flow rate of 50 mL min was used,
in which N2 was the reference gas for end gas analysis.
The products were analyzed using on-line GC apparatus
(GC-2014, Shimadzu) with a combined PC-1, MC-1, and MC-2
chromatographic column and a thermal conductivity detector.
Catalytic activity of all of the samples, including a blank
cined at 700 °C for 4 h to enhance their thermal stability and
remove surface moisture.
An ultrasonic-assisted wetness impregnation method was
used to prepare Ni/SiO catalysts with 10 wt% Ni. The metallic
2
precursor solution was obtained by dissolving NiIJNO ) ·6H O
3
2
2
2
2
4
1
2
2
−
(
2
99%, Sigma-Aldrich) in ethanol with a Ni/ethanol ratio of
g L . The three SiO supports were dispersed in ethanol
2
−
1
after ultrasonic oscillation to obtain a SiO colloidal solution.
2
The Ni precursor solution was then added dropwise to the
SiO2 colloidal solution under magnetic stirring. The solu-
tion was agitated at 70 °C for 12 h to remove the ethanol.
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sample (20–40 mesh SiO support without Ni), was tested at
2
temperatures from 600 to 900 °C after being in a steady state
for 1 h. Stability tests of Ni/SiO -H, Ni/SBA-15, and Ni/SiO -P
2 2
were conducted at 800 °C for 40 h on-stream, and the products
were analyzed every 30 min. The conversion (X) and the H /CO
2
ratio were calculated as follows:
[
[
CH ] [CH ]
4
in
4
out
XCH4 (%) 
XCO2 (%) 
100
100
[
CH4 ]in
CO ] [CO ]
2
in
2
out
[
CO2 ]in
H2
moles of H produced
2
ratio=
CO
moles of CO produced
3
Results and discussion
3
.1 Characterization of fresh catalysts
The XRD patterns of fresh catalysts are shown in Fig. 1.
Reflections of SiO and NiO were detected in the wide-angle
2
XRD patterns of all three fresh SiO
lysts (Fig. 1a). Three sharp peaks were clearly visible at 37.3°,
3.3° and 62.9°, which corresponded to the (111), (200), and
2
-supported nickel cata-
4
(
(
220) reflections of the crystal NiO structure, respectively
PDF#47-1049). Strong and broad diffractions with a wide 2θ
2
6
range at 15–30° were assigned to amorphous SiO2. Compared
to Ni/SiO -H and Ni/SiO -P, Ni/SBA-15 had a less erratic
2
2
Fig. 1 XRD patterns of fresh 10% Ni/SiO
2
catalysts (before reduction):
diffraction peak at 15–30°. This may be because SBA-15 has
a highly ordered mesoporous structure. This was confirmed
by the small-angle XRD patterns (Fig. 1b). Ni/SBA-15 had
remarkable peaks of ordered mesoporous silica (100), (110),
and (200) planes, indicating a high degree of hexagonal meso-
(a) wide-angle XRD patterns and (b) small-angle XRD patterns.
3
0
with the Ni dispersion order. Bappy Saha also proved that
a high pore volume/SBET ratio contributes to high catalytic
performance. The XRF results in Table 1 show that the Ni load-
ing was slightly higher than the set value of 10 wt%. This might
be caused by the weight loss during the pre-calcination of the
supports, resulting in a higher Ni content in the catalysts.
SEM images of the three supports are shown in Fig. S1.†
From the SEM images of the supports, we can see that both
2
7,28
scopic organization.
No peaks were found in the small-
angle XRD patterns of Ni/SiO -H and Ni/SiO -P, indicating
2
2
heterogeneous porosity.
The average crystallite size of NiO was determined by the
diffraction peak of the NiO (200) plane in the XRD patterns,
using Scherrer's equation (Table 1). The average crystal metal
size increased in the order Ni/SiO
2
2
-P < Ni/SiO -H < Ni/SBA-15,
2 2
SiO -H and SiO -P have a loose and porous structure with a
indicating a decreasing Ni dispersion order Ni/SiO -P >
non-uniform pore size, while SBA-15 has uniform cylindrical
pores. TEM images of fresh catalysts are shown in Fig. 2. The
translucent particles with an irregular shape are the supports
2
2
6,29
Ni/SiO -H > Ni/SBA-15.
The BET specific surface area (SBET)
2
value and pore properties of catalyst supports and freshly
prepared catalysts are shown in Table S1.† After impregnation,
the SBET value and pore volume decreased for the three
catalysts. This phenomenon might be caused by pore blocking
during the impregnation process. The SBET, pore volume,
average pore size, and average Ni loading of freshly prepared
catalysts are also presented in Table 1. The largest pore volume
2
5
of Ni/SiO -H and Ni/SiO -P catalysts (Fig. 2a and b); the
2
2
crystal NiO particles were uniformly supported on SiO
SiO -P. In contrast, Ni/SiO -P had a smaller NiO particle size
and greater homogeneity of metal dispersion. In Fig. 2c and d,
2
-H and
2
2
1
5,31
a two-dimensional hexagonal texture is observed in SBA-15.
The pores of Ni/SBA-15 exhibited a uniform size of ~5 nm
(Fig. S2†), which is also confirmed by the BET results in
Table 1. Some NiO particles were uniformly loaded on the
outside surface of SBA-15, which differed greatly from the
crystallite sites inside the porous structure. The regulated
growth of crystals inside the narrowly distributed channels
and largest average pore size were found in Ni/SiO -P, while
2
Ni/SBA-15 had the largest SBET value. There was no obvious
connection between the SBET value and the pore volume of the
catalysts, but the pore volume/SBET ratio decreased in the order
Ni/SiO -P > Ni/SiO -H > Ni/SBA-15, which was in accordance
2
2
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Table 1 Main textural properties of fresh catalysts
a
b
c
Ni loading
wt. (%)
Average crystal size
nm
8.38
10.23
6.25
S
BET
2
Pore volume
Average pore size
Å
Pore volume to SBET ratio
−1
3
−1
−9
Catalysts
Ni/SiO -H
m g
cm g
10
m
2
10.55
10.90
10.15
153
332
279
0.40
0.42
0.88
107
50
126
2.6
1.3
3.2
Ni/SBA-15
2
Ni/SiO -P
a
b
c
Determined by the XRF method. Determined using Scherrer's equation from the diffraction of the Ni (200) plane. Specific surface area
calculated by the BET method.
Fig.
3
H
2
-TPR profiles of Ni/SiO
2
catalysts (reduced under a
−
1
5
vol% H
2
/Ar stream at a temperature ramp of 10 °C min ).
in the TEM results. The H -TPR profiles also confirmed that
2
Fig. 2 TEM images of fresh catalysts (before reduction): (a) Ni/SiO
b) Ni/SiO -P, (c) and (d) Ni/SBA-15.
2
-H,
8
00 °C was the appropriate pre-reduction temperature for the
(
2
reduction of reducible catalysts.
3
.2 Catalytic performance in biogas reforming
might have been responsible for the difference in the NiO
particle size, resulting in less homogeneity of NiO particles
Effect of temperature. The dry reforming activity of
than those in Ni/SiO
supported NiO increased in the order Ni/SiO
2
-P and Ni/SiO
2
-H. The particle size of
-P < Ni/SiO -H <
catalysts is indicated by the conversion of CH and CO , and
4 2
the selectivity is expressed in terms of the H /CO ratio. Fig. 4
2
2
2
Ni/SBA-15, which was in agreement with the results from
shows the activity and selectivity results for all the three
Scherrer's equation.
types of SiO -supported nickel catalysts from 600 to 900 °C.
2
The reducibility and different Ni species in the SiO
2
-
4 2
Generally, the conversion of both CH and CO increased
supported nickel catalysts were investigated using H -TPR
as the temperature increased from 600 to 900 °C. This may
be because the dry reforming reaction of biogas is a strongly
endothermic reaction (eqn (1)), and a higher temperature
2
(
Fig. 3). All of the catalysts had a broad and overlapping
consumption peak from 300 to 800 °C, indicating the
presence of nickel oxides that had different interactions with
H
2
will increase the conversion rate, as observed in earlier
1
6,32
6,7,34
the supports.
of Ni/SiO -H, Ni/SBA-15, and Ni/SiO
and 750 °C, respectively, in the order Ni/SiO -H < Ni/SBA-15 <
The highest H
2
reduction temperature
studies.
Among the different catalysts, the CH4
2
2
-P was 680 °C, 700 °C,
conversion of Ni/SiO -H was the highest for the whole
2
temperature range, and when the temperature was higher
2
Ni/SiO
2
-P, suggesting an enhancement of NiO–SiO inter-
than 650 °C, the CH4 conversion of Ni/SiO -P was slightly
higher than that of Ni/SBA-15. As the temperature increased,
less difference was observed in the CO2 conversion of the
2
2
6,33
actions.
can be seen in the Ni/SBA-15 catalyst, i.e., the broad peak at
30 °C and the shoulder peak around 620 °C. These peaks
In addition, two separate reduction regions
4
different catalysts. Taking Ni/SiO -H as an example, the
2
might be related to the reduction of NiO particles supported
on the outside surface and those inside the porous structure
of SBA-15, respectively, which can also be clearly distinguished
4 2
CH conversion increased from 55% to 98% and the CO
conversion increased from 52% to 98% when the temperature
increased from 600 to 900 °C. When the temperature was
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The H /CO ratio of the different catalysts at various
2
temperatures is shown in Fig. 4c. When the temperature
was higher than 650 °C, the H
1. The reverse water-gas shift reaction (RWGS, eqn (2)) can
consume the additional H and produce CO, which lowers
2
/CO ratio of all samples was
<
2
9
the H
2
/CO ratio. When the temperature was <850 °C,
the H /CO ratio of Ni/SiO -H was slightly higher than those
2
2
of Ni/SBA-15 and Ni/SiO -P, indicating a smaller contribution
2
from the RWGS reaction.
0
−1
CO + H ↔ CO + H O, ΔH = 41 kJ mol
298K
(2)
(3)
2
2
2
0
−1
CH ↔ C + 2H , ΔH = 75 kJ mol
298K
4
2
Stability tests. Temperature tests indicated that at 800 °C,
both CH4 and CO2 conversions were high (>90%). Blank
tests showed that when the temperature was higher than
7
50 °C, H and CO were detected in the outlet gas (Fig. S3†),
2
which might be caused by RWGS reaction (eqn (2)) and
methane decomposition reaction (eqn (3)). Therefore, 800 °C
was chosen as the appropriate temperature to conduct
stability tests. Fig. 5 shows the 40 h on-stream catalyst test
results for all catalyst samples at 800 °C. All three of the
samples showed good stability during the 40 h on-stream,
and no decay of activity was found in all samples. The
conversion of CH
4
was slightly lower than the conversion of
CO and the H /CO ratio was <1.
2
2
The average CH
ratio are summarized in Table 2. The average CH
increased in the order Ni/SBA-15 < Ni/SiO -P < Ni/SiO -H,
4
conversion, CO
2
conversion, and H
2
/CO
4
conversion
2
2
and the average CO
Ni/SBA-15 < Ni/SiO
the RWGS reaction increased the conversion of CO2
and decreased the H /CO ratio. The higher the degree of
2
conversion increased in the order
2
-H < Ni/SiO -P. The contribution of
2
2
the reverse water-gas shift reaction process, the larger
the difference between CH4 and CO2 conversion and the
lower the H /CO ratio. These theoretical considerations are
2
confirmed by the actual test results shown in Table 2. The
highest average H /CO ratio of Ni/SiO -H indicated that the
2
2
secondary reaction was minimized to a greater extent than
in Ni/SBA-15 and Ni/SiO -P.
2
3.3 Post-reaction characterization
Fig. 6 shows the N2 adsorption–desorption isotherms and
BJH desorption pore size distribution analysis of fresh and
spent catalysts. The N
2
adsorption–desorption isotherms of
Fig. 4 The influence of temperature on the catalytic activity of Ni/SiO
2
both fresh and spent Ni/SiO -H (Fig. 6a) and Ni/SiO -P
2
2
catalysts: (a) CH
4
conversion, (b) CO
2
conversion, and (c) H
2
/CO ratio
(Fig. 6c) catalysts displayed an approximate type IV isotherm,
as defined by the International Union of Pure and Applied
Chemistry (IUPAC). The presence of a H3-type hysteresis loop
indicates the existence of mesopores, and the unlimited
−
1
−1
(
GHSV = 15 000 mL gcat
h , atmospheric pressure).
8
00 °C, both CH
4
and CO
2
conversions exceeded 90%. There
adsorption at high P/P
of plate-like particles give rise to slit-shaped pores.
0
values suggests that aggregates
2
4,35
is only a slight increase in CH4 and CO2 conversions at
temperatures >800 °C.
The results were also confirmed by Fig. 2a and b. The N2
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Table 2 Average catalytic activity of the three catalyst samples during
the 40 h on-stream test
Average CH
4
Average CO
2
Conversion
Average
/CO ratio
Catalysts conversion (%) conversion (%) difference (%) H
2
Ni/SiO
Ni/SBA-15 88.2
Ni/SiO -P 91.8
2
-H 92.3
95.8
93.9
96.5
3.5
5.7
4.7
0.946
0.924
0.937
2
2
7
with highly uniform cylindrical pores, which also supports
the XRD and TEM results. The fresh Ni/SiO -H and Ni/SiO -P
2
2
catalysts had a wide BJH desorption pore size distribution,
while fresh Ni/SBA-15 had a highly narrow size distribution
with a mean diameter of 5.0 nm, which was in accordance with
the HR-TEM results (Fig. S2†).
After the 40 h on-stream tests, there was a decrease in
the BET surface area and pore volume and an increase in
the average pore size of all the spent catalysts (see Table S1†).
This agreed with the BET analysis results for Ni/γ-Al O reported
2
3
3
6
by Srinivas Appari. The catalytic reaction process did not
change the shape of the N adsorption–desorption isotherms of
2
Ni/SiO -H and Ni/SBA-15, or their BJH desorption pore size dis-
2
tributions, and only a slight change in the average pore size was
observed due to a slight blocking phenomenon. There was a dif-
ference in the hysteresis loops of the fresh and spent Ni/SiO -P
2
catalysts. The shift in the relative pressure of the hysteresis loop
to a higher value was observed, leading to an obvious change in
the BJH desorption pore size distribution, with the average pore
2
7
size shifted greatly from 126 to 270 nm. According to Aziz,
the hysteresis loops at lower and higher relative pressures repre-
sent the intra- and interparticle porosity, respectively. There
might be a decrease in intraparticle porosity and an increase in
the interparticle porosity of Ni/SiO -P after a stability test, there-
2
fore the decrease in pore volume due to intraparticle porosity
may result in an increase of the average pore size.
Fig. 7 shows TEM images of spent catalysts. The original
structure of all catalysts was maintained after 40 h on-stream
2 2
tests. Spent Ni/SiO -H and Ni/SiO -P catalysts kept their
amorphous structures, and Ni/SBA-15 kept its two-dimensional
hexagonal texture. However, there was an obvious pore
size increase in the spent Ni/SiO -P catalyst (Fig. 7b),
2
which was supported by the BJH pore size distribution results
shown in Fig. 6c. A slight metal agglomeration phenomenon
was observed in spent Ni/SiO
2 2
-H and Ni/SiO -P catalysts
(
Fig. 7a and b). The two-dimensional hexagonal channel of
spent Ni/SBA-15 limited the agglomeration of active metals
inside the pore (Fig. 7c), while the active metals supported on
the outside surface experienced significant agglomeration, even
those detached from the SBA-15 support (Fig. 7d). Ilenia
Rossetti et al. also reported that large particles exposed a small
interface with the support surface, which led to a weaker inter-
action, thus easy detachment from the support. No carbon
was found in any of the three spent catalysts, indicating
negligible coke deposition.
Fig. 5 Stability tests of Ni/SiO
2
catalysts at 800 °C for 40 h: (a)
−1
−1
2
Ni/SiO -H, (b) Ni/SBA-15, and (c) Ni/SiO
2
-P (GHSV = 15 000 mL gcat
h ,
atmospheric pressure).
2
6
adsorption–desorption isotherms of both fresh and spent
Ni/SBA-15 (Fig. 6b) catalysts displayed a typical type IV
isotherm and a standard H1-type hysteresis loop, as defined by
the IUPAC, and were characteristic of mesoporous materials
The results of the TGA-MS analysis of the spent catalysts
are shown in Fig. 8. The thermograms can be divided into
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Fig. 6
N
2
adsorption–desorption isotherms and the BJH desorption pore size distributions of fresh and spent catalysts: (a) Ni/SiO
-P. The inset shows the pore size distribution.
2
-H,
(
b) Ni/SBA-15, and (c) Ni/SiO
2
Fig. 7 TEM images of spent catalysts: (a) Ni/SiO
c and d) Ni/SBA-15.
2 2
-H, (b) Ni/SiO -P, and
(
two different temperature regions (Fig. 8a). All of the spent
catalysts experienced an increase in weight at low tempera-
ture ranges and a decrease in weight at high temperature
ranges. The oxidation of nickel particles at temperatures
above 200 °C caused the weight increase, and the 3% weight
increase of the spent catalysts was inconsistent with the theo-
retical weight increase of 10% due to nickel particle oxidation,
1
7
which was also reported by Jianqiang Zhu. Weight loss at
Fig. 8 (a) TGA profiles of spent Ni/SiO
2
catalysts. (b) MS signals of CO
2
2
temperatures above 400 °C was ascribed to the oxidation of
−
1
−1
(
20 mL min
O
2
stream at a temperature ramp of 10 °C min with N
37
2
deposited carbon. CO MS signals from the TPO process of the
as a protection gas).
three spent catalysts are shown in Fig. 8b. Since O was used as
2
a reaction gas and N was used as a protection gas, the signal
2
for a molecular weight of 44 was only supposed to be CO
2
,
we can still distinguish that a higher amount of weight loss
from TGA resulted in a higher MS signal intensity. Thus, the
very weak CO signal intensity of spent Ni/SiO -P implied that
which was generated by the oxidation of deposited carbon. The
CO generation peak range of spent Ni/SiO -H, Ni/SBA-15, and
2
2
2
2
Ni/SiO
2
-P was 450–700 °C, 500–700 °C, and 580–700 °C, respec-
it has the lowest carbon deposit. The amount of coke deposited
on spent Ni/SiO -H, Ni/SBA-15, and Ni/SiO -P catalysts was
calculated to be 2.1, 2.7 , and 0.3 wt.%, respectively, which was
tively, corresponding to the weight loss temperature ranges of
the three catalysts. Although MS is a semi-quantitative method,
2
2
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in the low range of carbon deposited (0.89–6.56 wt.%) on
3 J. L. Ewbank, L. Kovarik, C. C. Kenvin and C. Sievers, Effect
of preparation methods on the performance of Co/Al O
3
1
7
Ni/SiO catalysts after a 30 h test, as reported by Zhu. In
2
2
conclusion, the results showed that little coke was deposited
on the catalysts, and the formation of coke was related to
the metal dispersion of the catalysts. The smaller crystal size
of metal catalysts will lead to a catalyst that is less prone to
deactivation.
catalysts for dry reforming of methane, Green Chem.,
2014, 16(2), 885.
4 M. Broda, V. Manovic, Q. Imtiaz, A. M. Kierzkowska,
E. J. Anthony and C. R. Muller, High-purity hydrogen via the
sorption-enhanced steam methane reforming reaction over a
synthetic CaO-based sorbent and a Ni catalyst, Environ. Sci.
Technol., 2013, 47(11), 6007–6014.
4
Conclusions
5
S. Chaemchuen, N. A. Kabir, K. Zhou and F. Verpoort, Metal-
2
In summary, waste-derived SiO obtained from photovoltaic
organic frameworks for upgrading biogas via CO adsorption
2
waste SiCl by a vapor-phase hydrolysis method was applied
4
to biogas green energy, Chem. Soc. Rev., 2013, 42(24),
as the support for a nickel catalyst in a biogas dry reforming
process for the first time. Catalytic test results showed that
the conversion of CH4 and CO2 increased as temperature
increased from 600 to 900 °C. When the temperature was
9
304–9332.
6
Y. Kathiraser, Z. Wang and S. Kawi, Oxidative CO reforming
2
of methane in La0.6Sr0.4Co0.8Ga0.2
fiber membrane reactor, Environ. Sci. Technol., 2013, 47(24),
4510–14517.
3
O -delta (LSCG) hollow
8
4
00 °C, it reached a high CH conversion (92.3%) and a high
1
CO2 conversion (95.8%), and there was no deactivation
after the 40 h on-stream test. Comparison with commercial
7
8
9
A. Serrano-Lotina and L. Daza, Influence of the operating
parameters over dry reforming of methane to syngas, Int. J.
Hydrogen Energy, 2014, 39(8), 4089–4094.
precipitated SiO
2 2
and ordered mesoporous SiO showed that
the catalytic activity of waste-derived SiO is equivalent to that
2
V. M. Shinde and G. Madras, Catalytic performance of highly
of commercial precipitated SiO
mesoporous SiO . The amount of coke deposited after stability
tests follows the order commercial precipitated SiO < waste-
2
and even superior to that of
dispersed Ni/TiO for dry and steam reforming of methane,
2
2
RSC Adv., 2014, 4(10), 4817.
2
A. Serrano-Lotina and L. Daza, Highly stable and active
catalyst for hydrogen production from biogas, J. Power
Sources, 2013, 238, 81–86.
2 2
derived SiO < mesoporous SiO . It is further demonstrated
that coke deposition in the biogas dry reforming process is related
to the textual properties of catalysts. A higher pore volume/SBET
ratio will lead to a smaller crystal metal size and higher metal
dispersion, thus the catalyst is less prone to deactivation.
This discovery will help improve catalyst design.
1
1
1
1
1
1
0 Y. H. Taufiq-Yap, Sudarno, U. Rashid and Z. Zainal,
CeO –SiO2 supported nickel catalysts for dry reforming of
2
methane toward syngas production, Appl. Catal., A, 2013,
4
68, 359–369.
2
In conclusion, waste-derived SiO used as a catalyst support
1 A. R. Derk, G. M. Moore, S. Sharma, E. W. McFarland and
H. Metiu, Catalytic Dry Reforming of Methane on
Ruthenium-Doped Ceria and Ruthenium Supported on
Ceria, Top. Catal., 2013, 57(1–4), 118–124.
2 P. Frontera, A. Macario, A. Aloise, P. L. Antonucci,
G. Giordano and J. B. Nagy, Effect of support surface on
methane dry-reforming catalyst preparation, Catal. Today,
in the biogas dry reforming process shows a high catalytic activity
and good stability, which is competitive with commercial and
mesoporous ones. Considering the large-scale production and
4
poor treatment conditions of photovoltaic waste SiCl , the pro-
duction of waste-derived SiO as well as its further applica-
2
tion as a catalyst support for biogas dry reforming represents a
useful conversion of photovoltaic waste to a high value-added
product; it also provides a cheap and environmentally benign
support for catalysts in the biogas dry reforming process.
2
013, 218–219, 18–29.
3 A. Luengnaruemitchai and A. Kaengsilalai, Activity of
different zeolite-supported Ni catalysts for methane
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Acknowledgements
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4 H. Y. Kim, J. N. Park, G. Henkelman and J. M. Kim, Design
of a highly nanodispersed Pd-MgO/SiO composite catalyst
with multifunctional activity for CH reforming, ChemSusChem,
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The authors gratefully acknowledge the Hi-Tech Research and
Development Program (863) of China for financial support
2
4
(grant no. 20121868156).
2
5 Z.-J. Zuo, C.-F. Shen, P.-J. Tan and W. Huang, Ni based on
dual-support Mg-Al mixed oxides and SBA-15 catalysts for
dry reforming of methane, Catal. Commun., 2013, 41,
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