Monolithic Ni-MOx/Ni-foam (M = Al, Zr or Y) catalysts with enhanced heat/mass transfer for energy-efficient catalytic oxy-methane reforming

Article abstract of DOI:10.1016/j.catcom.2015.07.007

Abstract A series of monolithic nickel-foam-structured Ni-MO_x(M = Al, Zr or Y) binary catalysts to be used in the catalytic oxy-methane reforming have been developed, of which the Ni-MO_x catalysts are formed in-situ and embedded onto the Ni-foam struts by chemically etching Ni-foam using solution containing Al (or Zr, Y) nitrate. Among these catalysts, Ni-Al₂O₃/Ni-foam possesses the largest specific surface area and the highest amount of NiO species (i.e., Ni active site precursors), and as a result, exhibits the best catalytic performance with promising stability. Over this catalyst, CH₄ conversion of 86.4% can be obtained with H₂ selectivity of 96.6% and CO selectivity of 91.2% for a fed of CH₄/O₂ (2/1) at 700°C and a high gas hourly space velocity of 100 L g^{- 1} h^{- 1}. We anticipate our assay to be a new point which might stimulate commercial exploitation of the new-generation structured catalyst technology for the high-throughput catalytic oxy-methane reforming reaction.

Full text of DOI:10.1016/j.catcom.2015.07.007

Catalysis Communications 70 (2015) 1–5
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Monolithic Ni–MOx/Ni-foam (M = Al, Zr or Y) catalysts with enhanced
heat/mass transfer for energy-efficient catalytic oxy-methane reforming
⁎
⁎
Ruijuan Chai, Yakun Li, Qiaofei Zhang, Guofeng Zhao , Ye Liu, Yong Lu
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of monolithic nickel-foam-structured Ni–MOx(M = Al, Zr or Y) binary catalysts to be used in the catalytic
oxy-methane reforming have been developed, of which the Ni–MOx catalysts are formed in-situ and embedded
onto the Ni-foam struts by chemically etching Ni-foam using solution containing Al (or Zr, Y) nitrate. Among
these catalysts, Ni–Al2O3/Ni-foam possesses the largest specific surface area and the highest amount of NiO
species (i.e., Ni active site precursors), and as a result, exhibits the best catalytic performance with promising
stability. Over this catalyst, CH4 conversion of 86.4% can be obtained with H2 selectivity of 96.6% and CO selectiv-
ity of 91.2% for a fed of CH4/O2 (2/1) at 700 °C and a high gas hourly space velocity of 100 L g−1 h−1. We anticipate
our assay to be a new point which might stimulate commercial exploitation of the new-generation structured
catalyst technology for the high-throughput catalytic oxy-methane reforming reaction.
Received 10 June 2015
Received in revised form 3 July 2015
Accepted 8 July 2015
Available online 14 July 2015
Keywords:
Monolithic catalyst
Nickel catalyst
Foam
Catalytic oxy-methane reforming
Syngas
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
[4–7]. However, the Ni-based catalysts often suffer from sintering of the
Ni particles as well as the coke formation on Ni surface in this process.
With the continuous rise in energy demands and the ever-increasing
depletion of finite petroleum reserves, there is an urgent need to devel-
op economical and energy-efficient processes for the sustainable
production of fuels and chemicals. Natural gas consisting mainly of
methane, found in abundance compared to petroleum or coal, is consid-
ered as the future feedstock for the synthesis of value added products
[1]. Particularly, methane reforming has been gaining considerable
interests in the generation of syngas for subsequent production of
energy, chemicals, and fuels [2]. Steam reforming of methane is imple-
mented commercially for the production of syngas, but this process is
extremely endothermic and thus very energy- and capital-intensive.
Given the mild exothermicity and much higher efficiency, and especial-
ly the suitable H2/CO ratio which is beneficial for the downstream
synthesis (e.g., methanol synthesis and Fischer–Tropsch process), cata-
lytic oxy-methane reforming (COMR) is attracting more and more
attention as a compact and energy-efficient process [3].
Most efforts have been made on improvement of anti-sintering and
-coke Ni-based catalyst, for instance, by adding promoters (alkali, alkali
earth, and rare earth metal oxides) or/and utilizing different supports
(Al2O3, ZrO2, SiO2, La2O3 and Y2O3) [8–11]. The formation of ‘hot-
spots’ in the catalyst bed is considered as the one of the main causes
for the Ni-sintering and carbon deposition [12]. Thus, to develop a
novel catalyst system combining excellent catalytic performance with
enhanced heat transfer is a promising strategy to overcome these
major drawbacks.
Recently, monolithic foams have been attracting ever-growing inter-
ests in the catalysis application because of their distinguished features
(e.g., low pressure drop, high thermal conductivity and desired
mechanical robustness). Particularly, this new structure is opening an
opportunity on the development of novel monolithic catalyst with
significantly enhanced heat transfer that is desired for suppressing the
catalytic bed ‘hot- or cold-spots’ formation in the strongly exo- or
endo-thermic reaction processes. So far, some foam-structured catalysts
using SiC foam [13], compressed Ni–Al foam [14] and stainless steel
metal foam [15], have been reported for the methane reforming
processes. Such catalysts obtained via traditional wash-coating, dip-
coating or extrusion methods [16,17], however, suffer from the random
distribution of active components, detachment of coatings, binder
harmful contamination, and the blockage of channels [18]. Non-
coating method for effectively and efficiently embedding catalytic active
sites onto the foam struts is thus particularly desirable but is a signifi-
cantly challenging area.
Since the early 1990s, great efforts have been made on the develop-
ment of COMR process. Although the noble metal-based catalysts
(e.g., Pt and Rh) generally exhibit better performance and resistance
to carbon deposition, their wide-application is confined by the high
cost and limited availability. Ni-based catalysts are widely utilized for
COMR, mainly due to their moderate cost and satisfactory performance
⁎
Corresponding authors.
E-mail address: ylu@chem.ecnu.edu.cn (Y. Lu).
http://dx.doi.org/10.1016/j.catcom.2015.07.007
1566-7367/© 2015 Elsevier B.V. All rights reserved.

2
R. Chai et al. / Catalysis Communications 70 (2015) 1–5
-
Ni2+
NO3
Ni-foam
Mδ+
Ni
M
O
Etching and Calcining
Ni-foam
Catalyst
Scheme 1. The fabrication strategy of Ni–MOx/Ni-foam catalysts.
In this work, novel monolithic nickel-foam-structured binary catalysts
2. Experimental
engineered from the microscale to the macroscale were developed via
one-step wet chemical etching method (Scheme 1). This new approach
provided a combination of enhanced heat transfer [19], desired mechan-
ical robustness, and excellent catalytic performance for the COMR.
The nickel-foam-structured binary catalysts of Ni–MOx/Ni-foam
(M = Al, Zr or Y) were prepared by a facile wet chemical etching
method followed by thermal treatment activation, as described
B
A
D
C
E
F
Ni
NiO
Y2O3
Ni-Y2O3/Ni-foam
Ni-ZrO2/Ni-foam
Ni-Al O /Ni-foam
2
3
Ni foam
20 30
40
50
60
70
80
2-Theta (Degree)
Fig. 1. The photograph (A) and SEM image (B) of the untreated monolithic Ni-foam wafers. SEM images of fresh catalysts: Ni–Al2O3/Ni-foam (C), Ni–ZrO2/Ni-foam (D) and Ni–Y2O3/Ni-
foam (E). (F) XRD patterns of as-prepared Ni–MOx/Ni-foam catalysts.

R. Chai et al. / Catalysis Communications 70 (2015) 1–5
3
Table 1
summarizes their textural properties and NiO crystallite size as well as
MOx content. Fig. 1A,B shows the pristine Ni-foam chips with requested
circular shape and size according to the practical applications, and the
three-dimensional open cell structure with smooth strut surface. After
modified wet chemical etching and calcining, the Ni-foam strut surface
became coarse (Fig. 1C–E), in association with visible increase of the SSA
from ~1.0 m2 g−1 of the pristine Ni-foam to 24.6 m2 g−1 of the Ni–
Al2O3/Ni-foam, 4.6 m2 g−1 of the Ni–ZrO2/Ni-foam and 2.5 m2 g−1 of
the Ni–Y2O3/Ni-foam. According to the H2 consumption in H2-TPR
experiments, moreover, the NiO contents were estimated to be 9.6%,
7.5%, and 2.9% for the Ni–Al2O3/Ni-foam, Ni–ZrO2/Ni-foam, and Ni–
Y2O3/Ni-foam while the corresponding MOx contents were determined
by ICP–AES to be 4.6%, 0.3%, and 1.5% (Table 1). XRD patterns of the pris-
tine Ni-foam support and the fresh Ni–MOx/Ni-foam catalysts are
shown in Fig. 1F. The characteristic diffraction peaks of Ni (2θ = 44.5°;
51.8° and 76.4°) were observed in all the samples and the characteristic
diffraction peaks of NiO (2θ = 37.3°; 43.3°; 62.9°; 75.4° and 79.4°) could
be only observed in Ni–Al2O3/Ni-foam and Ni–ZrO2/Ni-foam. However,
crystalline phase of Y2O3 was observed while no detectable XRD peaks
corresponding to NiO could be identified in the Ni–Y2O3/Ni-foam
catalyst. The average size of the NiO particles was calculated using the
Scherrer's equation as 15–20 nm for the Ni–Al2O3/Ni-foam and Ni–
ZrO2/Ni-foam catalysts (Table 1). Clearly, much more NiO could be
induced on Ni–Al2O3/Ni-foam and Ni–ZrO2/Ni-foam than on the Ni–
Y2O3/Ni-foam (Table 1), which might be caused by the lower pH value
of Al(NO3)3 (pH of 2.9 to 3.5; start to end) and Zr(NO3)4 (1.1 to 3.9;
start to end) than of Y(NO3)3 (3.6 to 4.9; start to end) in the whole
etching process. Moreover, the quite different contents of Al2O3, ZrO2,
and Y2O3 might be caused by the different properties of nitrate salts.
Physicochemical characteristics of the monolithic Ni–MOx/Ni-foam catalysts.a
SSAb (m2
g−1
dNiO
NiO contentd
(%)
MOx contente
(%)
c
Catalyst
)
(nm)
Ni–Al2O3/Ni-foam
Ni–ZrO2/Ni-foam
Ni–Y2O3/Ni-foam
24.6
4.6
2.5
19.2
17.8
–
9.6
7.5
2.9
4.6
0.3
1.5
a
Textural features of Ni-foam substrate: 100 pores per inch (PPI), voidage of 95 vol.%,
and cell window size of 150–250 μm.
b
SSA values determined by N2-BET method.
NiO crystallite size (dNiO), deduced from XRD patterns using Scherrer equation.
NiO content was estimated (according to H2 + NiO = Ni + H2O) by H2-TPR.
MOx content of the whole catalyst was determined by ICP-AES.
c
d
e
elsewhere [20]. The catalysts were characterized by inductively coupled
plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction
(XRD), scanning electron microscopy (SEM), standard Brunauer–
Emmett–Teller (BET) theory based on N2 adsorption isotherm, H2-
temperature programmed reduction (H2-TPR), and thermogravimetric
analysis (TGA). The COMR was performed in a fixed-bed quartz tube
reactor (600 mm length by 6 mm inner diameter) at atmospheric
pressure. Details of catalyst preparation, catalyst characterization, and
catalyst evaluation are available in the Supporting material.
3. Results and discussion
3.1. Geometry, morphology, and structural features
Fig. 1 shows the geometry, morphology, and structural features of
our representative monolithic Ni–MOx/Ni-foam catalysts, and Table 1
A100
B100
80
80
CH4 conversion
60
CH4 conversion
H2 selectivity
60
40
20
0
H2 selectivity
CO selectivity
40
CO selectivity
CO2 selectivity
CO2 selectivity
20
0
500 550 600 650 700 750 800
500 550 600 650 700 750 800
Temperature ( )
oC
Temperature ( )
oC
C100
80
60
40
20
0
CH4 conversion
H2 selectivity
CO selectivity
CO2 selectivity
500 550 600 650 700 750 800
Temperature
oC
(
)
Fig. 2. CH4 conversion, syngas selectivity for temperature-dependent COMR over monolithic Ni–Al2O3/Ni-foam (A), Ni–ZrO2/Ni-foam (B) and Ni–Y2O3/Ni-foam (C). Reaction conditions:
0.200 g catalysts, 0.1 MPa, GHSV = 100 L g−1 h−1, CH4/O2 = 2/1.

4
R. Chai et al. / Catalysis Communications 70 (2015) 1–5
A100
B100
80
60
40
20
0
80
60
40
20
0
CH4 conversion
H2 selectivity
CH4 conversion
H2 selectivity
CO selectivity
CO2 selectivity
CO selectivity
CO2 selectivity
10 20 30 40 50 60 70 80
Time on stream (h)
1
2
3
4
5
6
7
8
9 10 11
Time on stream (h)
Fig. 3. CH4 conversion, syngas selectivity for the COMR vs time on stream using Ni–Al2O3/Ni-foam (A) and Ni–ZrO2/Ni-foam (B). Reaction condition: 0.200 g catalysts, 0.1 MPa, 700 °C,
GHSV = 100 L g−1 h−1, CH4/O2 = 2/1.
For example, serious self-hydrolysis of Zr(NO3)4 unavoidably made Zr
ions directly forming amorphous zirconium hydroxide (Fig. S1) precip-
itate [21] rather than depositing on Ni-foam struts during etching
process, leading to almost zero ZrO2 content on the Ni–ZrO2/Ni-foam.
Overall, high NiO and Al2O3 contents led to the highest SSA of the Ni–
Al2O3/Ni-foam while low SSA of the Ni–ZrO2/Ni-foam and Ni–Y2O3/Ni-
foam was due to their low MOx or NiO content (Table 1).
500.0 mmol L−1, however, yielded no better catalyst performance
than their corresponding representative catalysts (Table S1).
3.3. Stability
Besides activity/selectivity, stability is also a very important practical
consideration for a heterogeneous catalyst. Fig. 3 shows the CH4 conver-
sion and syngas selectivity for the COMR against the time on stream
using our Ni–Al2O3/Ni-foam and Ni–ZrO2/Ni-foam at 700 °C and a
GHSV of 100 L g−1 h−1. The Ni–Al2O3/Ni-foam exhibited an on-stream
time of 85 h till the reaction terminated at a CH4 conversion of ~70%,
almost 7 times longer than the Ni–ZrO2/Ni-foam (Fig. 3). In general,
carbon deposition and sintering of Ni–MOx catalysts are the main
cause for the catalyst deactivation. The amount of deposited carbon
3.2. Catalyst performance for COMR
Fig. 2 shows the temperature-dependent conversion and selectivity
for the COMR using our representative Ni–MOx/Ni-foam catalysts at a
high gas hourly space velocity (GHSV) of 100 L g−1 h−1. Clearly, the
three catalysts all showed increasing indicative of conversion/selectivity
along with the increase of reaction temperature from 500 to 800 °C. The
Ni–Al2O3/Ni-foam was the best catalyst, always delivering higher
conversion and syngas (CO + H2) selectivity than the other twos in
the whole reaction temperature studied. For instance, at a low reaction
temperature of 500 °C, the Ni–Al2O3/Ni-foam catalyst delivered a CH4
conversion of 69.1% and a satisfying syngas selectivity (H2, 89.0%; CO,
77.4%), slightly higher than either the Ni–ZrO2/Ni-foam (66.6% conver-
sion; 85.4%/79.2% selectivity to H2/CO) or the Ni–Y2O3/Ni-foam (66.1%
conversion; 82.1%/84.4% selectivity to H2/CO). At a high temperature
of 800 °C, a very high CH4 conversion of 93.6% could be achieved with
very high syngas selectivity (H2, 98.2%; CO, 96.7%) over the Ni–Al2O3/
Ni-foam catalyst; in contrast, a conversion of only 88.4% was obtained
with H2/CO selectivity of 96.3%/94.2% over the Ni–ZrO2/Ni-foam
and 86.6% conversion with 95.5%/93.6% selectivity to H2/CO over the
Ni–Y2O3/Ni-foam catalyst.
Not surprisingly, the Ni–Al2O3/Ni-foam catalyst possessed the
highest NiO content (9.6%) and the largest SSA (24.6 m2/g, Table 1),
and as a result, delivered the highest activity and selectivity for the
COMR. The catalytic performance of the Ni–Y2O3/Ni-foam and Ni–
ZrO2/Ni-foam seemed in good agreement with their low SSA values
(4.6 m2 g−1 for the Ni–ZrO2/Ni-foam and 2.5 m2 g−1 for the Ni–Y2O3/
Ni-foam, Table 1) rather than their NiO contents. The Ni–ZrO2/Ni-foam
had a high NiO content (7.5%) comparable to that (9.6%) for the Ni–
Al2O3/Ni-foam, but delivered a catalytic performance comparable to
the Ni–Y2O3/Ni-foam with a much less NiO content of only 2.9%. Clearly,
the COMR performance of our foam-structured Ni-based catalyst
system was sensitive to their chemical and textural features, being
closely related to the properties of the chemical etching solution.
Notably, our representative Ni–MOx/Ni-foam (M = Al, Zr or Y) cat-
alysts were obtained by using aqueous solutions of 125.0 mmol L−1
Al(NO3)3, 62.5 mmol L−1 Zr(NO3)4, and 125.0 mmol L−1 Y(NO3)3 as
chemical etching agents. Tuning the concentration of the Al-, Zr-, or Y-
containing chemical etching solutions in a wide range from 30.0 to
−1
−1
was measured by TGA to be 0.5 gcar
g
and 0.05 gcar
g
over the Ni–
cat
cat
Al2O3/Ni-foam and Ni–ZrO2/Ni-foam (Fig. S2), corresponding to the cok-
−3
−1
ing rates at 5.9 × 10
g
g−1 h−1 and 4.5 × 10−3 gcar
g
h−1. After the
car cat
cat
stability testing, moreover, the SSA was found to be reduced by 37%
from 24.6 m2 g−1 to 15.4 m2 g−1 for the Ni–Al2O3/Ni-foam while
by 70% from 4.6 m2 g−1 to 1.4 m2 g−1 for the Ni–ZrO2/Ni-foam. The
above results suggested that fast loss of the SSA was the main
cause for the quick deactivation rather than the carbon deposition.
Especially for the Ni–ZrO2/Ni-foam, serious insufficiency of ZrO2 in
the catalyst (Table 1) would result in poor textural stability thereby
leading to fast pore-structure collapse during reaction.
4. Conclusions
Our results tentatively establish a promising monolithic nickel-
foam-structured Ni-based catalyst for the high-throughput COMR
process, which can be obtained by a facile wet chemical etching method.
Promising CH4 conversion and remarkable syngas selectivity are achiev-
able over the Ni–Al2O3/Ni-foam at 700 °C with GHSV of 100 L h−1 g−1
.
Despite above advances, further improvement of the catalyst stability is
particularly desirable and remains challenging. To accomplish this goal,
chemical etching strategy should be modified to increase the textural
additive content in the Ni-foam-structured catalysts for pore-structure
robustness improvement, and the work along this line is in progress.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2015.07.007.
References
[1] P. Tang, Q.J. Zhu, Z.X. Wu, D. Ma, Energy Environ. Sci. 7 (2014) 2580–2591.

R. Chai et al. / Catalysis Communications 70 (2015) 1–5
5
[2] A. Caballero, P.J. Perez, Chem. Soc. Rev. 42 (2013) 8809–8820.
[3] T.V. Choudhary, V.R. Choudhary, Angew. Chem. Int. Ed. 47 (2008) 1828–1847.
[4] D.L. Li, Y. Nakagawa, K. Tomishige, Appl. Catal. A 408 (2011) 1–24.
[5] Y. Lu, Y. Liu, S.K. Shen, J. Catal. 177 (1998) 386–388.
[6] Y. Lu, J.Z. Xue, C.C. Yu, Y. Liu, S.K. Shen, Appl. Catal. A 174 (1998) 121–128.
[7] L. Chen, Y. Lu, Q. Hong, J. Lin, F.M. Dautzenberg, Appl. Catal. A 292 (2005) 295–304.
[8] J.J. Zhu, J.G. van Ommen, A. Knoester, L. Lefferts, J. Catal. 230 (2005) 291–300.
[9] H. Tanaka, R. Kaino, K. Okumura, T. Kizuka, K. Tomishige, J. Catal. 268 (2009) 1–8.
[10] L.L. Makarshin, V.A. Sadykov, D.V. Andreev, A.G. Gribovskii, V.V. Privezentsev, V.N.
Parmon, Fuel Process. Technol. 131 (2015) 21–28.
[15] L.X. Sang, B. Sun, H.Y. Tan, C.X. Du, Y.T. Wu, C.F. Ma, Int. J. Hydrog. Energy 37 (2012)
13037–13043.
[16] S.X. Cai, D.S. Zhang, L.Y. Shi, J. Xu, L. Zhang, L. Huang, H.R. Li, J.P. Zhang, Nanoscale 6
(2014) 7346–7353.
[17] Y.H. Li, Y.Q. Wang, Z.G. Zhang, X.B. Hong, Y. Liu, Catal. Commun. 9 (2008)
1040–1044.
[18] F. Basile, P. Benito, P. Del Gallo, G. Fornasari, D. Gary, V. Rosetti, E. Scavetta, D. Tonelli,
A. Vaccari, Chem. Commun. (2008) 2917–2919.
[19] Y.K. Li, Q.F. Zhang, R.J. Chai, G.F. Zhao, Y. Liu, Y. Lu, ChemCatChem 7 (2015)
1427–1431.
[11] L. Li, S.C. He, Y.Y. Song, J. Zhao, W.J. Ji, C.T. Au, J. Catal. 288 (2012) 54–64.
[12] H.M. Liu, D.H. He, Catal. Surv. Asia 16 (2012) 53–61.
[20] Y. Liu, H. Wang, J.F. Li, Y. Lu, H.H. Wu, Q.S. Xue, L. Chen, Appl. Catal. A 328 (2007)
77–82.
[13] H.T. Liu, S.Q. Li, S.B. Zhang, J.M. Wang, G.J. Zhou, L. Chen, X.L. Wang, Catal. Commun.
[21] P.D. Southon, J.R. Bartlett, J.L. Woolfrey, B. Ben-Nissan, Chem. Mater. 14 (2002)
9 (2008) 51–54.
4313–4319.
[14] V. Sadykov, V. Sobyanin, N. Mezentseva, G. Alikina, Z. Vostrikov, Y. Fedorova, V.
Pelipenko, V. Usoltsev, S. Tikhov, A. Salanov, L. Bobrova, S. Beloshapkin, J.R.H. Ross,
O. Smorygo, V. Ulyanitskii, V. Rudnev, Fuel 89 (2010) 1230–1240.