A Ni-based catalyst with enhanced Ni-support interaction for highly efficient CO methanation

Article abstract of DOI:10.1039/c8cy00605a

Sophisticated manipulation of the metal-support interaction of catalysts is of great importance for achieving a higher catalytic efficiency, but remains as an open challenge. Herein, by using a simple metal-organic framework (MOF) based strategy, a Ni/NiAl₂O₄-M catalyst with an enhanced Ni-support interaction is successfully fabricated. The catalyst exhibits an enhanced low-temperature catalytic performance in CO methanation. CO conversion and CH₄ selectivity as high as 99.8% and 58.0%, respectively, are achieved on the Ni/NiAl₂O₄-M catalyst at 350 °C. The strong Ni-support interaction on the Ni/NiAl₂O₄-M catalyst results in more active H atoms, and promotes the formation of active CH? species which are the key intermediates for CO methanation. This not only enhances the conversion of CO into CH₄, but also suppresses the carbon deposition which has a negative effect on the catalytic reactions, thus improving the catalytic performance of Ni/NiAl₂O₄-M. Besides, the strong Ni-support interaction makes Ni/NiAl₂O₄-M highly resistant to sintering of the Ni nanoparticles during the catalytic reactions. The findings of the present work are helpful for fabricating catalysts with enhanced metal-support interaction for more efficient catalysis.

Full text of DOI:10.1039/c8cy00605a

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Bao, S. Li, D. Qi, Q. Wang, B. Zhao, T. Hu, L. Fan, B. Fan, R. Li, F. (. Tao and Y. Pan, Catal. Sci. Technol.,
2018, DOI: 10.1039/C8CY00605A.
Volume 6 Number 1 7 January 2016 Pages 1–308
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ISSN 2044-4753
PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
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DOI: 10.1039/C8CY00605A
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ARTICLE TYPE
Ni-based catalyst with enhanced Ni-support interaction for highly
efficient CO methanation
a
a
a
a
b
b
c
Xiaoliang Yan,* Chen Yuan, Jiehua Bao, Sha Li, Daizong Qi, Qianqian Wang, Binran Zhao, Tong
a
a
a
a
d
b
Hu, Liming Fan, Binbin Fan, Ruifeng Li,* Franklin (Feng) Tao, and Yun-Xiang Pan*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
Sophisticatedly manipulating the metalꢀsupport interaction of the catalysts is of great importance for achieving a higher catalytic
efficiency, but remains as an open challenge. Herein, by using a simple metalꢀorganic framework (MOF) based strategy, a Ni/NiAl O ꢀM
2
4
catalyst with an enhanced Niꢀsupport interaction is successfully fabricated. The catalyst exhibits an enhanced lowꢀtemperature catalytic
1
0
performance in CO methanation. The CO conversion and CH selectivity as high as 99.8% and 58.0%, respectively, are achieved on the
4
Ni/NiAl O ꢀM at 350 °C. The strong Niꢀsupport interaction on the Ni/NiAl O ꢀM results in more active H atoms, and promotes the
2
4
2
4
*
formation of the active CH species which is the key intermediates for the CO methanation. This not only enhances the conversion of CO
into CH , but also suppresses the carbon deposition which has a negative effect on the catalytic reactions, thus improving the catalytic
4
performance of Ni/NiAl O ꢀM. Besides, the strong Niꢀsupport interaction makes Ni/NiAl O ꢀM highly resistant to the sintering of the Ni
2
4
2
4
1
5
nanoparticles during the catalytic reactions. The findings of the present work are helpful for fabricating catalysts with enhanced metalꢀ
support interaction for more efficient catalysis.
based strategy to replace the thermal decomposition for preparing
20
Introduction
Niꢀbased catalysts. The Ni salts can be quickly decomposed by
the cold plasma at room temperature. This efficiently suppresses
the thermal diffusion and aggregation of the Ni atoms, thus
leading to a clean Niꢀsupport interface, a strong Niꢀsupport
interaction and Ni NPs with an optimal shape and a large surface
area. However, most of these strategies are complex multipleꢀstep
processes. Simpler strategies for sophisticatedly manipulating Niꢀ
support interface and interaction are highly desired. Furthermore,
fabricating Niꢀbased catalysts with targeted catalytic performance,
especially at low temperatures (≤ 400 ºC), still remains as an
open challenge, and needs a high degree of ingenuity and
creativity.
2
2
3
3
4
4
0
5
0
5
0
5
Heterogeneous catalysts with multiple components have
attract great attentions as results of the multifunctional properties
or/and synergistic performance due to the generation of the
5
5
6
6
7
0
5
0
5
0
1–10
interface.
The interface forms the basis for achieving
enhanced catalytic performances in reactions like coalꢀbased
methanation (CO+H ). Among the heterogeneous catalysts, Niꢀ
2
based catalysts are of particular interest for both lab research and
industrial applications, due to their catalytic performance
comparable to the nobleꢀmetalꢀbased catalysts as well as the low
1
1ꢀ13
price and abundance of Ni.
However, the poor activity and
selectivity at low temperatures (≤ 400 ºC) limit the applications
Metalꢀorganic framework (MOF) has been a hot topic in the
scientific community, due to its tunable topologies, pores and
1
4
of the Niꢀbased catalysts. The weak Niꢀsupport interface or
interaction has been shown to be the main origin for the poor
lowꢀtemperature performance. Sophisticatedly manipulating the
Niꢀsupport interaction is thereby a hot topic in chemistry.
functionalities. It has been widely used as catalysts directly or
23ꢀ30
catalyst supports.
Recently, it has been shown that MOF is
31ꢀ
also a promising template for forming catalysts via calcination.
The porous structures of the catalysts prepared by using MOF
Many strategies have been proposed for engineering the Niꢀ
35
15ꢀ22
support interface or interaction.
Wang et al. synthesized an
as the templates were demonstrated to be similar to those of the
ordered mesoporous Ni−Ce−Al catalyst with an evaporationꢀ
induced selfꢀassembly strategy in which the Ni precursor was
incorporated into the cores of the surfactant micelles, and thus,
the highly dispersed Ni nanoparticles (NPs) were stabilized in the
31ꢀ35
MOF templates.
This is benefit for achieving a high
dispersion of the metal nanoparticles, even at a high metal
31ꢀ35
content.
Herein, by using a simple MOFꢀbased strategy, a Ni/NiAl O ꢀ
2
4
1
9
mesoporous channels of the alumina matrix. A highly enhanced
activity and stability in the methane dry reforming was achieved
on the Ni−Ce−Al catalyst, and was attributed to the large surface
area of the catalyst, the strong Niꢀsupport interaction as well as
the high dispersion of the Ni NPs. Zou et al. used a coldꢀplasmaꢀ
M catalyst with a strong Niꢀsupport interaction is successfully
synthesized. The Ni/NiAl O ꢀM shows an enhanced ability in
2
4
catalyzing the CO methanation at low temperatures (≤ 400 ºC).
The strong Niꢀsupport interaction on Ni/NiAl O ꢀM results in
2
4
more active H atoms, and promotes the formation of the active
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 1

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Page 2 of 18
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DOI: 10.1039/C8CY00605A
CH* species which are the key intermediates of CO methanation.
This is the origin of the enhanced lowꢀtemperature catalytic
performance of Ni/NiAl O ꢀM in CO methanation.
Scherrer equation based on the Ni (111) peak on the XRD pattern.
adsorption−desorption isotherms were obtained at ꢀ196 °C in a
NOVA1200e analyzer (Quantachrome). Before the test, the
sample was degassed at 300 °C for 3 h under vacuum, removing
60 the impurities and moisture. The BrunauerꢀEmmettꢀTeller (BET)
surface areas were determined by analyzing the adsorption data in
N
2
2
4
5
Experimental
the relative pressure (p/p ) range of 0.02ꢀ0.15. Pore volume was
0
calculated from the amount of the N adsorbed at a p/p of 0.99.
2
0
Preparation of MIL-53 (Al). The Alꢀbased MOF, MILꢀ
3(Al), was synthesized via a hydrothermal process by using
Pore size distributions were obtained with the DFT method on the
adsorption branch using the cylindrical pore NLDFT model. Field
emission scanning electron microscopy (SEM) images were
obtained on a JSMꢀ7001F instrument. Transmission electron
microscopy (TEM) observations, including highꢀresolution TEM
5
6
7
7
8
8
9
9
5
0
5
0
5
0
5
Al(NO ) ·9H O (14.1 g, Tianjin Kermel Chemical Reagent Co.,
3
3
2
1
0
Ltd, AR, >99.0%), 1,4ꢀbenzenedicarboxylic acid (BDC, 47.9 mL,
Tianjin Guangfu Fine Chemical Research Institute, AR, >98.5%)
3
0
and deionized (DI) water (3.11 g). The hydrothermal process
was performed in a 100 mL Teflonꢀlined stainless steel at 220 °C
for 72 h. The precipitate from the hydrothermal process was
washed with DI water and dimethyl formamide (DMF, Tianjin
Kermel Chemical Reagent Co., Ltd, AR, >99.5%) for several
times to remove the BDC inside the cavities of MILꢀ53 (Al). And
then, the sample was further purified with ethanol and DI water to
remove the DMF. Finally, the sample was dried at 80 °C for 12 h,
leading to the formation of MILꢀ53(Al).
(
HRTEM) and elemental analyses, were performed on a FEI
2
Tecnai G F20 instrument. The samples were finely ground,
suspended in ethanol, and dispersed on a holey carbonꢀcoated Cu
grid.
1
5
The temperature programmed reduction by H (H ꢀTPR) and
2
2
CO pulse chemisorption experiments were measured on a
chemisorption apparatus (Micromeritics AutoChem II 2920). For
H ꢀTPR, 0.1 g of the sample was pretreated at 300 °C for 1 h in
2
2
2
3
3
4
4
5
5
0
5
0
5
0
5
0
5
ꢀ
1
He (30 mL min ). Afterwards, the system was cooled to 50 °C,
followed by heating to 1000 °C at a rate of 10 °C min in 10%
H /He (30 mL min ) and the signals of the thermal conductivity
2
Preparation of Ni/NiAl O -M and Ni/Al O -M by using
2
4
2
3
ꢀ1
the MOF-based strategy. Incipient wetness impregnation was
used to load the nickel precursor into MILꢀ53 (Al). 3.0 g of
Ni(NO ) ·6H O (Sinopharm chemical Reagent Co. Ltd.,
ꢀ
1
detector (TCD) was recorded. For H ꢀTPD, the sample was firstly
2
3
2
2
ꢀ1
reduced at 550 °C for 2 h in 10% H /He (30 mL min ), and then
2
AR, >98.0%) was dissolved in DMF solution. 10.6 g of MILꢀ53
Al) was impregnated with the nickelꢀnitrateꢀcontaining DMF
solution for 12 h. The product from the impregnation was dried at
20 °C for 12 h, followed by calcination at 900 °C for 3 h in air.
ꢀ
1
cooled down to 50 °C in He (30 mL min ) and saturated with
0% H /He (30 mL min ) for 1 h. After the physically adsorbed
2
(
ꢀ
1
1
H was purged by He for 2 h, the sample was heated to 900 °C at
2
1
−
1
ꢀ1
10 °C min in an He flow (30 mL min ). For CO pulse
chemisorption, the sample was firstly reduced at 550 °C for 2 h in
0% H /He (30 mL min ), and then cooled down to 35 °C in He
Reduction of the product by H2 produced the supported Ni
catalysts. For clarity, the calcined and reduced catalysts prepared
from the MOFꢀbased strategy were denoted by NiO/NiAl O ꢀM
ꢀ
1
1
(
2
2
4
ꢀ1
30 mL min ). After cooling, 5 mL of 5% CO/He was injected
and Ni/NiAl O ꢀM, respectively. For comparison, NiO/Al O ꢀM
2
4
2
3
into the system at 5 min intervals by the pulse method until a
saturation adsorption was observed. The thermogravimetric
analysis (TGA) curves were done on a Setaram SETSYS TGA
thermoanalyzer coupled with Hidden HPR20 QIC R&D mass
spectrometer (TGꢀMS). The carbon deposition on the used
was also prepared by using a strategy similar to that of
NiO/NiAl O ꢀM, except that the calcination was conducted at
2
4
600 °C. Reduction of NiO/Al O ꢀM by H led to the formation of
2
3
2
Ni/Al O ꢀM.
2
3
Preparation of Ni/Al O -C and Ni/NiAl O -C by using the
2
3
2
4
catalyst was characterized by the O temperature programmed
2
conventional strategy. We also prepared Ni/Al O via the
2
1
3
1ꢀ13
oxidation (O ꢀTPO) experiments with the same TGꢀMS system as
2
conventional strategy widely applied in literature.
4 g of
that of the TGA experiments.
Al O (Zibo Nuoda Chemical Co., Ltd.) was impregnated by an
2
3
Catalytic reactions. The hydrogenation of CO into methane
aqueous solution of Ni(NO ) ·6H O (4.95 g) for 12 h. The sample
3
2
2
(CO methanation) was studied at 1 MPa in a fixedꢀbed tubular
from the impregnation was dried at 120 °C for 12 h, followed by
calcination at 650 °C for 3 h in air, producing NiO/Al O .
reactor with an inner diameter of 10 mm. 0.2 g of the catalyst
00 (20ꢀ40 mesh) was diluted with 5.0 g of quartz sands in order to
avoid the hot spots in the catalyst bed during the reaction. Prior to
2
3
1
1
1
Reduction of NiO/Al O by H produced Ni/Al O . For clarity,
2
3
2
2
3
the Ni/Al O3 catalyst was denoted by Ni/Al O ꢀC. The
2
2
3
the reaction, the catalyst was firstly in situ reduced by H (20 mL
2
preparation of Ni/NiAl O ꢀC was similar to that of Ni/Al O ꢀC,
2
4
2
3
ꢀ1
min ) at 550 °C for 2 h, followed by cooling to 300 °C under Ar.
except that the calcination was conducted at 900 °C.
As soon as the temperature of the reactor reaching to 300 °C, a
Characterizations. The amount of the Ni on the catalysts
was determined by inductively coupledꢀplasma atomic emission
spectroscopy (ICPꢀAES) on a Thermo iCAP 6300 spectrometer.
UVꢀvisible diffuse reflectance spectra (UVꢀvisꢀDRS) were
recorded on a UVꢀvis spectrophotometer (Agilent Cary 100). Xꢀ
ray diffraction (XRD) measurements were carried out on a
Rigaku D/Maxꢀ2500 diffractometer with a scanning speed of 4 °
ꢀ
1
05 gas mixture of CO and H (50 mL min ) with a molar ratio of 1/2
2
was introduced into the reactor. The temperature of the reactor
−1
was next increased at a heating rate of 2.5 °C min . The outlet
gas was analyzed online by a gas chromatograph (GC) equipped
with a TCD detector and a 2ꢀm TDXꢀ01 packed column, using Ar
10 as the carrier gas. An ice trap was placed between the outlet of
the reactor and the GC to remove the moisture. Longꢀterm
stability of the catalysts in CO methanation was investigated at
ꢀ
1
min . The average size of the Ni NPs was calculated by using the
2
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

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DOI: 10.1039/C8CY00605A
ꢀ
1
ꢀ1
2+
4
00 °C, 1 MPa, and 15000 mL g h . CO conversion (XCO) and
NiO/NiAl O ꢀM samples obtained with calcined the Ni ꢀ
2 4
impregnated MILꢀ53 (Al) at 600 and 900 °C, respectively, for
further studies.
CH selectivity (
equations:
) were calculated by using the following
4
5
6
6
5
0
5
Figs. 1aꢀ1d and Fig. S5 in the ESI† illustrate the SEM and
TEM images of NiO/Al O ꢀM and NiO/NiAl O ꢀM. Both
2
3
2
4
5
(1)
2)
NiO/Al O ꢀM and NiO/NiAl O ꢀM are multilamellar, with the
2
3
2
4
spacing between the two layers being about 10ꢀ20 nm. Highly
dispersed NiO NPs confined in the space between two layers can
be clearly seen in the TEM images (Figs. 1b and 1d). The N2
adsorptionꢀdesorption curves of NiO/Al O ꢀM and NiO/NiAl O ꢀ
(
where, F , and F
are the volume flow rates of CO (or CH ) at
2
3
2
4
i in
i,out
4
M exhibit hysteresis loops in type H3 between adsorption and
the inlet and outlet, respectively. Turnover frequency (TOF) was
studied with 50 mg of the catalyst (20ꢀ40 mesh) at 400 °C with a
low CO conversion for the catalysts, and calculated by using
equation (3):
desorption at a p/p range of 0.6−1.0 (Fig. 1e), suggesting that the
0
1
0
two samples are both mesoporous. The pore diameter on
NiO/Al O ꢀM is about 10 nm, while that on NiO/NiAl O ꢀM is in
2
3
2
4
a range of 10ꢀ20 nm. The BET surface area of NiO/Al O ꢀM was
2
3
2
ꢀ1
calculated to be 206 m g , which is slightly larger than that of
(3)
2
ꢀ1
NiO/NiAl O ꢀM (185 m g ).
2
4
1
5
70
where XCO, FCO, in, W , M and DNi are the CO conversion, CO
(Fig. 1)
Ni
Ni
ꢀ
1
flow rate in mol s at inlet, weight of the catalyst in g, molar
ꢀ
1
mass of Ni in g mol and dispersion of the Ni NPs calculated by
CO pulse chemisorption, respectively.
Fig. 1f shows the results of the H
NiO/NiAl ꢀM. On the H ꢀTPR profile of NiO/Al
peaks, at 333 and 590 °C, respectively, are present, and attributed
2
ꢀTPR for NiO/Al
2
O
3
ꢀM and
O ꢀM, two
2 3
O
4
2
2
75
2
0
35,36
to the reduction of NiO.
On the H ꢀTPR profile of
2
NiO/NiAl O ꢀM, the peaks, due to the reduction of NiO, locate at
2
4
Results and discussion
3
51 and 463 °C, respectively, which are higher than those for
NiO/Al ꢀM. The broad peak at 795 °C on the H ꢀTPR profile
ꢀM indicates the presence of NiAl
higher reduction temperatures for NiO/NiAl ꢀM than those for
NiO/Al ꢀM indicate a stronger metalꢀsupport interaction on
NiO/NiAl
of NiAl
Fig. S2a in the ESI†) presents two weight loss locating in the 85 the metal NPs, and are like anchors fastening the metal NPs on
NiO/Al O -M and NiO/NiAl O -M. MILꢀ53 (Al) with
2
O
3
2
2
3
2
4
3
7
rhombicꢀshaped channels, consisting of AlO (OH) octahedra and 80 of NiO/NiAl
O
4
O
4
.
The
4
2
2
2
1
,4ꢀbenzenedicarboxylate organic framework, is one of the
O
2 4
3
0
2
3
3
4
4
5
5
0
5
0
5
0
widely used MOFs. The MILꢀ53 (Al) used herein shows a XRD
pattern and a morphology (Fig. S1 in the ESI†) identical to that
reported in literature. The TGA curve of the pure MILꢀ53 (Al)
O
2 3
2+
O
ꢀM. On NiO/NiAl
O could play as nuclei for the nucleation and growth of
2 4
O ꢀM, the Ni ions in the lattice
2
4
2 4
3
0
(
range of 350ꢀ450 °C and 550ꢀ650 °C, corresponding to the
the support. This could be responsible for the stronger metalꢀ
support interaction on NiO/NiAl ꢀM.
Ni/Al -M and Ni/NiAl -M. NiO/Al
NiO/NiAl ꢀM are next reduced by H at 550 °C to form
organic species, NO, due to the nitrate decomposition, was also 90 Ni/Al ꢀM and Ni/NiAl ꢀM. Peaks due to the faceꢀcentered
cubic Ni crystalline (PDF No. 04ꢀ0850) can be clearly seen on the
burning of the organic species with emission of CO , H O, and
2
O
4
2
2
2
+
small trace of C H . On the TGA curve of the Ni ꢀimpregnated
2
O
3
2
O
4
O ꢀM and
2 3
6
6
MILꢀ53 (Al), besides the peaks attributed to the burning of the
2
O
4
2
O
3
O
2 4
2
detected (Fig. S2b in the ESI†).
It has been reported that MILꢀ53 (Al) is decomposed into
amorphous Al O at 600 °C (Fig. S3 in the ESI), and the Al O is
XRD patterns of both Ni/Al
No peaks were observed for the amorphous Al
pattern of Ni/NiAl
2
O
3
ꢀM and Ni/NiAl
2
O
4
ꢀM (Fig. 2).
. On the XRD
3
O
2
3
2
3
2
2
+
31ꢀ33
converted into NiAl O in the presence of Ni ions at 900 °C.
2
O
4
ꢀM, besides the peaks of Ni, the peaks
are also present. By using the Scherrer
equation, the sizes of the Ni NPs were calculated to be 28 and 20
nm for Ni/Al ꢀM and Ni/NiAl ꢀM, respectively. ICPꢀAES
experiments demonstrate that the Ni amounts are 20.3 and 20.1
wt% on Ni/Al ꢀM and Ni/NiAl ꢀM, respectively. The BET
due to Al O is absence because of its amorphous form. NiAl O 100 surface area of Ni/Al ꢀM and Ni/NiAl ꢀM were measured to
be 149 and 144 m g , respectively. The pore diameters for
Ni/Al ꢀM and Ni/NiAl ꢀM are both in the range from 5 to 30
nm. Ni/NiAl ꢀM has a Ni NPs dispersion of 4.3% and a Ni NPs
surface area of 28.4 m gNi . These are both higher than those on
2
4
We next explored the influence of the calcination temperature on 95 assigned to NiAl O
2 4
2
+
the composition evolution of the Ni ꢀimpregnated MILꢀ53 (Al)
by using XRD and UVꢀvisꢀDRS (Fig. S4 in the ESI†). As
reflected by the XRD patterns (Fig. S4a), NiO appears with
O
3
O
2 4
2
2+
calcined the Ni ꢀimpregnated MILꢀ53 (Al) at 600 °C. The peak
2
O
3
O
2 4
O
O
2 4
2
3
2
4
2
2
3
ꢀ1
is present with the calcination temperature higher than 600 °C.
The sample after calcination at 900 °C is a composite containing
NiO and NiAl O . The UVꢀvisꢀDRS spectra (Fig. S4b) indicate a
O
3
O
2 4
2
O
4
2
4
2
2
ꢀ1
similar composition change with the calcination temperatures to
2+
2
ꢀ1
that reflected by the XRD patterns. Octahedrally coordinated Ni
in NiO appears with the calcination conducted at 600 °C, while
105 Ni/Al O ꢀM (3.1% and 20.3 m gNi ).
2 3
2
+
both octahedrally coordinated Ni in NiO and tetrahedrally
(Fig. 2)
2+
coordinated Ni in NiAl O are present with the calcination
2
4
3
4
conducted at 900 °C. We chose the NiO/Al O ꢀM and
2
3
This journal is © The Royal Society of Chemistry [year]
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DOI: 10.1039/C8CY00605A
Fig. 3 shows the TEM observation results for Ni/Al O ꢀM
CH4 selectivity on Ni/NiAl O ꢀC are 43.8% and 54.2%,
2 4
2
3
and Ni/NiAl O ꢀM, and the elemental mapping images of
respectively. As such, the CO conversion and CH selectivity on
4
2
4
Ni/Al O ꢀM and Ni/NiAl O ꢀM are plotted in Fig. 4. Both 60 Ni/NiAl O ꢀC are both lower than those on Ni/NiAl O ꢀM.
2
3
2
4
2
4
2
4
Ni/Al O ꢀM and Ni/NiAl O ꢀM exhibit
a
multilamellar
2
3
2
4
5
0
5
0
5
0
5
0
5
0
5
morphology. This is similar to those of the samples before
reduction (Fig. 1). As reflected by the HRTEM and elemental
mapping images, the Ni NPs are highly dispersed on the supports
on both Ni/Al O ꢀM and Ni/NiAl O ꢀM. By using the TEM
(Fig. 6)
(Table 1)
65
The TOF for the methanation was measured for further
comparing the catalytic activity of Ni/NiAl O ꢀM with that of
Ni/Al O ꢀM. The effects of external and internal diffusion were
2 3
2
3
2
4
observation results, the average size of the Ni NPs on Ni/Al O ꢀ
2
3
2
4
1
1
2
2
3
3
4
4
5
5
M was calculated to be 26 nm, which is slightly larger than that
on Ni/NiAl O ꢀM (18 nm) (Fig. S6 in the ESI†). The smaller Ni
ꢀ
1
2
4
excluded by using a reaction condition at 400 °C and 240 L g
cat
ꢀ
1
NPs on Ni/NiAl O ꢀM could be due to the stronger Niꢀsupport
h
(Fig. S7 in the ESI†). The external and internal diffusion was
interaction on Ni/NiAl O ꢀM, as compared to that on Ni/Al O ꢀM. 70 examined by changing the catalyst mass with a fixed weight
2
4
2
4
2
3
The lattice fringe with a distance of 0.203 nm observed on both
Ni/Al O ꢀM and Ni/NiAl O ꢀM is attributed to the Ni (111) plane.
hourly space velocity (WHSV) and by using the catalysts with
different diameters, respectively. The activity is almost
unchanged with changing the mass or diameter of the catalysts,
indicating that the reaction is in the kinetic region. The effect of
75 mass transport limitation and heat transfer are removed by
checking the WeiszꢀPrater criterion (Equation 4) and the Mears
criterion (Equation 5), respectively.
calculations are shown in the ESI†. The values of C
WP
Equation 4 are 1.7 × 10 and 2.7 × 10 for Ni/Al O ꢀM and
2 3
2
3
2
4
(
(
Fig. 3)
Fig. 4)
3
5
Fig. 5 shows the H ꢀTPD results for Ni/Al O ꢀM and
The details of the
2
2
3
Ni/NiAl O ꢀM. The peaks on the H ꢀTPD curve indicates the
in
2
4
2
ꢀ
3
ꢀ3
desorption temperature of the H formed from the combination of
2
the H atoms adsorbed on the catalyst surface. A lower desorption 80 Ni/NiAl O ꢀM, respectively, which are far less than 1, indicating
temperature suggests that the H atoms on the catalyst are more
active to participate in the catalytic reactions. As reflected in Fig.
2
4
that there are no internal diffusion limitations. The values of the
ꢀ
3
ꢀ3
Mears criterion in Equation 5 are 1.41 × 10 and 1.02 × 10 for
Ni/Al O ꢀM and Ni/NiAl O ꢀM, respectively, which are both less
5
, the H ꢀTPD curves of Ni/Al O ꢀM and Ni/NiAl O ꢀM have
2 2 3 2 4
2
3
2
4
two peaks, locating at temperatures lower than 400 °C and higher
than 600 °C, respectively. The lowꢀtemperature peak may be due 85 or mass transport limitations have been removed. The TOF of
than 3, suggesting that the interphase or intraparticle heat transfer
to the desorption of H formed from the H atoms adsorbed on the
Ni/Al O ꢀM and Ni/NiAl O ꢀM were calculated on the basis of
2 3 2 4
2
Ni NPs, and the highꢀtemperature peak may be related to the
the reaction rates and the surface Ni atoms numbers obtained
from the CO pulse adsorption, and plotted in Figs. 6c and 6d.
With increasing WHSV, the CO conversion decreases, whereas,
desorption of H formed from the H atoms adsorbed at the Niꢀ
2
3
8
support interfaces.
The H2 desorption temperatures on
Ni/NiAl O ꢀM is lower than those on Ni/Al O ꢀM, indicating that 90 the TOF increases firstly, and then reaches a steady value. TOF
2
4
2
3
the H atoms on Ni/NiAl O ꢀM could be more active than those on
of Ni/Al O ꢀM and Ni/NiAl O ꢀM are 1.43 and 1.64 mol
2
4
2
1
3
−1
2
4
CO
ꢀ1
−
ꢀ1
Ni/Al O ꢀM.
molNisurf
s
at 400 °C, with a WHSV of 240 L gcat h ,
2
3
respectively. The higher TOF further demonstrates the higher
activity of Ni/NiAl O ꢀM. The stabilities of Ni/Al O ꢀM and
Ni/NiAl O ꢀM were examined at 400 °C for 100 h (Fig. 7). Both
2 4
of the catalysts show an excellent stability, and there are no
decreases in CO conversion, CH selectivity and CH yield in 100
h.
(Fig. 5)
2
4
2
3
95
CO Methanation. The activities of Ni/Al O ꢀM and
2
3
Ni/NiAl O ꢀM towards the CO methanation are next explored.
2
4
4
4
During the reactions, CO and H with a ratio of 1:2, from the coal
2
gasification without further water gas shift reaction to increase
the amount of H , were used. For both Ni/Al O ꢀM and
2
−
r'A(obs) ρc R
2
2
3
CWP
=
<1
D C
e
As
Ni/NiAl O ꢀM, CO conversion, CH selectivity and CH yield
(4)
2
4
4
4
increase firstly, and then decrease slightly, with reaction
temperature increasing from 250 to 500 °C (Fig. 6a and 6b,
2
−
r'A R
1+0.33γχ
<
C De n−γbβb
(
1+0.33n
ω)
Ab
1
1
1
00
(5)
Table 1). The highest CO conversion and CH selectivity with
4
values of 99.8% and 58.0%, respectively, for Ni/NiAl O ꢀM are
2
4
(Fig. 7)
obtained at 350 °C, while those, with values of 99.6% and 60.0%,
respectively, for Ni/Al O ꢀM are present at 400 °C. As listed in
2
3
Discussion. As mentioned above, we prepared two catalysts,
05 i.e. Ni/NiAl O ꢀM and Ni/Al O ꢀM, by using the simple MOFꢀ
templated strategy, except that the calcination temperatures of the
two catalysts are different. In the CO methanation, the stability of
Table 1, the highest CO conversion and CH4 selectivity with
values of 96.3% and 54.5%, respectively, for Ni/Al O ꢀC are
2
4
2
3
2
3
obtained at 400 °C. The temperature for achieving the highest
activity on Ni/NiAl O ꢀM is lower by 50 °C than those on
2
4
Ni/NiAl O ꢀM is comparable to that of Ni/Al O ꢀM, but the lowꢀ
Ni/Al O ꢀM and Ni/Al O ꢀC. Thus, Ni/NiAl O ꢀM has a better
2
4
2
3
2
3
2
3
2
4
temperature activity of Ni/NiAl O ꢀM is higher than that of
catalytic performance at low temperature than the widely used
Ni/Al O catalyst. In addition, the highest CO conversion and
2
4
10 Ni/Al O ꢀM. The activity of Ni/NiAl O ꢀM is also higher than
2
3
2
4
2
3
4
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

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Catalysis Science & Technology
View Article Online
DOI: 10.1039/C8CY00605A
those of Ni/MILꢀ53 (Al), Ni/Al O ꢀC and Ni/NiAl O ꢀC. In
catalyst, and the lattice fringe with a distance of 0.203 nm, which
is attributed to the Ni (111) plane, can be clearly seen (Figs. 9c
2
3
2
4
addition, the stability of Ni/Al O ꢀC is much lower than that of
2
3
Ni/NiAl O ꢀM, with the CO conversion and CH selectivity 60 and 9d). This indicates that Ni/NiAl O ꢀM has a higher ability in
2
4
4
2
4
decreasing significantly within 40 h, from 97% and 55% to 62%
and 36%, respectively (Fig. S8 in the ESI†). As such,
Ni/NiAl O ꢀM is an excellent candidate catalyst for the CO
suppressing the aggregation of the Ni NPs. This could be another
reason for the enhanced catalytic performance of Ni/NiAl O ꢀM.
5
2
4
2
4
methanation.
We next demonstrate the ability of Ni/NiAl O ꢀM in
(Fig. 9)
65
2
4
suppressing the carbon deposition and sintering of the Ni
nanoparticles (NPs), by comparing Ni/NiAl O ꢀM with the
As demonstrated by the H ꢀTPR results (Fig. 1f), the Niꢀ
2
1
1
2
2
3
3
4
4
5
5
0
5
0
5
0
5
0
5
0
5
support interaction on Ni/NiAl O ꢀM is stronger. This could be
2
4
2
4
2+
widely used Ni/Al O ꢀC catalyst. It has been revealed that active
due to that, on Ni/NiAl O ꢀM, the Ni ions in the lattice of
2 4
2
3
39ꢀ44
carbon is the most crucial species in CO methanation.
On one
NiAl O could play as the nuclei for the nucleation and growth of
2 4
hand, the active carbon species is converted into graphitic carbon, 70 the Ni NPs, and are like anchors fastening the Ni NPs on the
which can lower the activity of the catalyst, via accumulation
NiAl O4 support. The stronger Niꢀsupport interaction can
2
*
or/and polymerization. On the other hand, CH species, which is
efficiently suppress the aggregation of the Ni NPs, and make the
Ni NP smaller. The smaller Ni NPs will result in more Niꢀsupport
interfaces. It has been reported that, on the Niꢀbased catalysts,
the key intermediate for CH4 production, is formed from the
reaction of the active carbon species with the adsorbed H
39,40
atoms.
Thus, the second fate is highly desired in CO 75 more Niꢀsupport interfaces and stronger Niꢀsupport interaction
methanation. We analyzed the carbon species formed during the
methanation on Ni/NiAl O ꢀM and Ni/Al O ꢀC by conducting
are benefit for the activation and dissociation of H2 on the
4
5ꢀ
catalysts, resulting in more active H atoms for further reactions.
2
4
2
3
50
O ꢀTPO experiments (Fig. 8a). Peaks at 103, 286, 448 and
As such, the more active H atoms on Ni/NiAl O ꢀM, as
2 4
2
6
1
70 °C appear on the O ꢀTPO curve of Ni/Al O ꢀC. The peak at
03 °C is due to the oxidation of the active carbon species, the 80 support interfaces and stronger Niꢀsupport interaction on
reflected by the H ꢀTPD results (Fig. 5), is due to the more Niꢀ
2
2
2
3
peaks at 286 and 448 °C are caused by the oxidation of the nickel
carbide, and the peak at 670 °C is assigned to the oxidation of the
graphitic carbon. The peaks due to the oxidation of the active
carbon species (103 °C) and nickel carbide (286 and 448 °C) also
Ni/NiAl O ꢀM. The more active H atoms can promote the
2 4
*
conversion of the active carbon species formed from CO into CH
species. This can, on one hand, enhance the conversion of CO
into CH (Fig. 6), on the other hand, suppress the formation of the
4
appear on the O ꢀTPO curve of Ni/NiAl O ꢀM (Fig. 8a). There is 85 graphitic carbon (Figs. 8 and 9), which has a negative effect on
2
2
4
no peak at the temperature higher than 600 °C on the O ꢀTPO
the activity of the catalysts. In addition, the stronger Niꢀsupport
interaction makes Ni/NiAl O ꢀM highly resistant to sintering
2
curve of Ni/NiAl O ꢀM. This indicates that the formation of the
2
4
2
4
graphitic carbon is efficiently suppressed on Ni/NiAl O ꢀM. In
(Figs. 8 and 9). These could be the reasons for the enhanced
catalytic performance of Ni/NiAl O ꢀM.
2
4
addition, the XRD pattern of the used Ni/NiAl O ꢀM is similar to
2
4
2
4
that of the fresh Ni/NiAl O ꢀM, while the coke is observed on the
90
2
4
XRD pattern of the used Ni/Al O ꢀC (Fig. 8b). This further
Conclusions
2
3
demonstrates the higher ability of Ni/NiAl O ꢀM in suppressing
In summary, a Ni/NiAl O ꢀM catalyst, with a strong Niꢀsupport
2
4
2 4
the coke deposition. Therefore, Ni/NiAl O ꢀM has a higher
interaction, was successfully fabricated by using a simple MOFꢀ
templated strategy. The strong Niꢀsupport interaction on
2
4
resistance to the formation or deposition of the graphitic carbon.
2+
This could be the one of the reasons for the enhanced catalytic 95 Ni/NiAl
performance of Ni/NiAl O ꢀM.
of NiAl
O
ꢀM is possibly due to that the Ni ions in the lattice
O which may play as the nuclei for the nucleation and
4
2
4
2
4
2
growth of the Ni NPs and be like anchors fastening the Ni NPs on
the NiAl O support. Ni/NiAl O ꢀM exhibits an enhanced lowꢀ
(Fig. 8)
2
4
2
4
temperature catalytic performance in CO methanation. The CO
00 conversion and CH4 selectivity as high as 99.8% and 58.0%,
respectively, are achieved on Ni/NiAl O ꢀM at 350 °C, which is
1
1
1
The sintering of the Ni NPs during the catalytic reactions is
also a key factor affecting the performance of the catalyst. As
reflected by the XRD pattern, the crystal structure of Ni/NiAl O ꢀ
2
4
lower by about 50 °C than the widely used Ni/Al O catalyst. The
2
3
2
4
strong Niꢀsupport interaction on Ni/NiAl O ꢀM results in more
2
4
M is maintained very well during the stability experiment of 100
active H atoms which can promote the formation of the active
h. Fig. 9 shows the TEM images of the Ni/NiAl O ꢀM and
2
4
*
05 CH species. This not only enhances the conversion of CO into
Ni/Al O ꢀC after the stability experiment of 100 h. The TEM
2
3
CH , but also suppresses the formation of the carbon deposition
4
observations indicate that the used Ni/Al O ꢀC has a Ni NPs size
2
3
which has a negative effect on the catalytic reactions, thus
enhancing the lowꢀtemperature catalytic performance of
Ni/NiAl O ꢀM. Besides, the strong Niꢀsupport interaction leads
of 150 nm, which is much larger than that of the fresh Ni/Al O ꢀ
2
3
C before the stability experiment (26 nm). As for Ni/NiAl O ꢀM,
2
4
2
4
after the stability experiment of 100 h, the size of the Ni NPs is
about 20 nm, which is almost the same as that of the fresh
Ni/NiAl O ꢀM before the stability experiment (18 nm). Carbon
10 Ni/NiAl O ꢀM to be highly resistant to the sintering of the Ni
2
4
NPs. This is also benefit for enhancing the lowꢀtemperature
catalytic performance of Ni/NiAl O ꢀM. These findings are
2
4
2
4
deposition can be clearly seen on the used Ni/Al O ꢀC (Figs. 9a
2
3
helpful for fabricating catalysts with strong metalꢀsupport
interactions for more efficient heterogeneous catalysis.
and 9b). However, on the used Ni/NiAl O ꢀM, the Ni NPs are
2
4
homogeneously dispersed in the multilamellar matrix of the
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 5

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Page 6 of 18
View Article Online
DOI: 10.1039/C8CY00605A
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Acknowledgments
This work was supported by the National Natural Science
Foundation of China (Nos. 21406153, 21503062 and U1662138),
Shanxi International Cooperation Project (Nos. 201703D421037
and 2015081048), Shanxi Provincial Key Innovative Research
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| Journal Name, [year], [vol], 00–00
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DOI: 10.1039/C8CY00605A
Table 1 CO conversion and CH selectivity of Ni/NiAl O ꢀM, Ni/Al O ꢀM, Ni/MILꢀ53 and Ni/Al O ꢀC at different temperatures
4
2
4
2
3
2
3
Temperature (℃ ) 250 275 300 325 350 375 400 425 450 475 500
Catalysts
Ni/NiAl O ꢀM
XCO (%)
14.2 30.1 50.3 75.7 100 100 99.8 99.4 98.6 97.2 94.9
0.2 35.5 53.5 58.3 53.8 55.3 56.7 55.3 53.7 57.1 44.7
13.7 16.7 28.8 45.8 68.3 92.4 99.6 99.2 98.2 95.6 92.4
0.7 24.6 38.9 57.5 60.1 55.7 54.7 53.8 50.9 50.3 50.2
2.7 6.6 9.9 19.5 32.4 49.0 75.9 96.4 97.2 96.8 95.3
0.3 25.8 47.7 52.8 60.8 63.2 54.9 50.1 53.6 52.7 48.6
11.5 14.7 26.9 40.5 63.8 89.7 96.3 96.1 96.0 94.2 91.3
2
4
2
(%)
Ni/Al O ꢀM
XCO (%)
2
3
1
(%)
Ni/MILꢀ53
XCO (%)
2
(%)
Ni/Al O ꢀC
XCO (%)
2
3
9
.6
25.8 37.9 56.9 56.0 55.2 54.5 53.0 50.5 49.2 46.1
(%)
5
1
0
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Fig. 1 (a) SEM and (b) TEM images of NiO/Al O ꢀM. (c) SEM and (d) TEM images of NiO/NiAl O ꢀM. (e) N adsorptionꢀdesorption
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Fig. 2 XRD patterns of Ni/Al O ꢀM and Ni/NiAl O ꢀM.
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Fig. 3 TEM images of Ni/Al O ꢀM (aꢀc) and Ni/NiAl O ꢀM (bꢀd).
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Fig. 4 Elemental mapping patterns of Ni/Al O ꢀM and Ni/NiAl O ꢀM.
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Fig. 5 H ꢀTPD curves of Ni/Al O ꢀM and Ni/NiAl O ꢀM.
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Fig. 6 (a) CO conversion and (b) CH selectivity on Ni/Al O ꢀM and Ni/NiAl O ꢀM at different reaction temperatures (0.1 MPa, 15000
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Fig. 7 Stability of (e) Ni/Al O ꢀM and (f) Ni/NiAl O ꢀM at 0.1 MPa, 400 °C and 15000 mL·g ·h .
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Fig. 8 TPO curves (a) and XRD patterns (b) of the Ni/NiAl O ꢀM and Ni/Al O ꢀC catalysts after the stability experiments of 100 h.
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Fig. 9 TEM images of the Ni/Al O ꢀC and Ni/NiAl O ꢀM catalysts after the stability experiment of 100 h.
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Table of Contents Entry for
Ni-based catalyst with enhanced Ni-support interaction for highly efficient CO
methanation
a
a
a
a
b
b
Xiaoliang Yan,* Chen Yuan, Jiehua Bao, Sha Li, Daizong Qi, Qianqian Wang,
c
a
a
a
a
Binran Zhao, Tong Hu, Liming Fan, Binbin Fan, Ruifeng Li,* Franklin (Feng)
d
b
Tao, and Yun-Xiang Pan*
a
College of Chemistry and Chemical Engineering, Taiyuan University of Technology,
Taiyuan, Shanxi 030024, P. R. China;
b
Department of Instrument Science and Engineering, School of Electronic
Information and Electrical Engineering, Shanghai Jiao Tong University, Shanghai
200240, P. R. China;
c
School of Chemical Engineering, Northwest University, Xi'an, Shaanxi 710069, P. R.
China;
d
Department of Chemical and Petroleum Engineering and Department of Chemistry,
University of Kansas, Lawrence, Kansas 66047, USA
Corresponding Authors:
yanxiaoliang@tyut.edu.cn (X. Yan); rfli@tyut.edu.cn (R. Li); yxpan81@sjtu.edu.cn
(Y. -X. Pan)
1

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A Ni/NiAl
2 4
O catalyst with an enhanced Ni-support interaction was successfully
fabricated for highly efficient CO methanation.
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