Open cell foam catalysts for CO2 methanation: Presentation of coating procedures and in situ exothermicity reaction study by infrared thermography

Article abstract of DOI:10.1016/j.cattod.2016.03.016

The carbon dioxide methanation reaction is highly exothermal (Δ_RH = ?165 kJ mol^?1). It is therefore essential to use processes able to control and efficiently evacuate the heat generated during the reaction. In this paper, a structur

Full text of DOI:10.1016/j.cattod.2016.03.016

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Open cell foam catalysts for CO2 methanation: Presentation of coating
procedures and in situ exothermicity reaction study by infrared
thermography
Myriam Freya, Thierry Romeroa, Anne-Cécile Rogera, David Edouardb,c,∗
a ICPEES, UMR 7515, UMR 7515, Group “Energy and Fuels for a Sustainable Development”, 25 rue Becquerel, 67087 Strasbourg, France
b USIAS (University of Strasbourg Institute for Advanced Study), Strasbourg, France
c LAGEP (Laboratoire d’Automatique et de Génie dEs Procédés), Université Claude Bernard Lyon 1, UMR CNRS 5007, 43 Bd du 11 Novembre 1918, 69622,
Villeurbanne, France
a r t i c l e i n f o
a b s t r a c t
The carbon dioxide methanation reaction is highly exothermal (ꢀRH = −165 kJ mol−1). It is therefore
essential to use processes able to control and efficiently evacuate the heat generated during the reaction.
In this paper, a structured bed filled with an open cell foam was chosen due to the many advantages
of this kind of reactor (high surface/volume ratio, low pressure drop, intensification of mass and heat
transfer. . .). Three kind of open cell foams, with different thermal properties, were studied: SiC, Alumina
and Aluminium. Coating procedures of a methanation catalyst (Ni/Ceria-Zirconia) developed in previous
work for SiC open cell foams were adapted to alumina and aluminium open cell foams. For the first
time, in situ infrared thermography was used to study the exothermicity of the reaction on the surface of
Article history:
Received 25 November 2015
Received in revised form 8 March 2016
Accepted 9 March 2016
Available online xxx
Keywords:
Coating
Platelet milli-reactors
Foam
CO2 methanation
Infrared imaging
Heat capacity
different foams.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
are usually far away from the energy consumption curves. The
energy produced needs to be stored. This storage can be of physical
Carbon dioxide is one of the gases responsible for the green-
house gas effect. There are natural sources responsible for its
presence (breathing, fermentation, fires, volcanoes, decomposition
of organic matter. . .), but also anthropogenic ones (combustion of
fossil resources and biomass, industries, agriculture. . .), the contri-
bution of the last ones being massively and constantly increasing
since the beginning of the industrial age. In order to reduce the
CO2 production or its emission into the atmosphere, many research
projects about capture and storage emerged [1]. Another pathway
to reduce these emissions is the valorisation of CO2 by transform-
ing it into valuable chemical compounds, like methane or longer
hydrocarbon species, methanol, esters, ether. . . [2].
In Europe, most of the scenarios forecasting the energy mix by
2050 report an increase in the share of renewable energies (RE)
at the cost of nuclear and fossil energies [3]. Solar and wind ener-
gies are intermittent and are hard to predict over the medium to
long term. Furthermore, the energy production curves from RE
or chemical nature. Therefore, the “Power-to-Gas” (PtG) concept
emerged as one of the chemical storage solutions. The aim of
PtG (Fig. 1) is to use the excess of RE to produce first hydrogen
through water electrolysis in order to inject the highest rate per-
mitted directly into the already existing natural gas pipelines. The
excess of hydrogen remaining and RE will then be converted into
methane through carbon dioxide hydrogenation. The total amount
of methane produced will also be injected into the natural gas
pipelines. The PtG concept is a suitable way to contribute to the
reduction or the stabilization of carbon dioxide in the atmosphere
and to help modulating energy distribution.
The
methanation
reaction
is
highly
exothermal
(ꢀRH = −165 kJ mol−1) and thermodynamically favored at low
temperatures. It is therefore essential to have a process capable to
efficiently evacuate the heat produced during the reaction in order
to keep a constant reaction temperature (e.g. thermodynamically
favorable). Moreover, an optimal temperature (i.e. without hot
spot in the catalytic bed) allows to keep a proper selectivity and
prevents a premature deactivation of the catalyst due to sintering.
Among the processes actually used for this reaction, two types of
reactors are used: fixed bed or fluidized bed. In the case of fixed
∗
Corresponding author.
E-mail address: david.edouard@univ-lyon1.fr (D. Edouard).
http://dx.doi.org/10.1016/j.cattod.2016.03.016
0920-5861/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Frey, et al., Open cell foam catalysts for CO2 methanation: Presentation of coating procedures and
in situ exothermicity reaction study by infrared thermography, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.03.016

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Fig. 1. Diagram illustrating the Power-to-Gas concept.
bed, the heat dissipation is poor and the only way to avoid thermal
runaway is to work under a diluted reactant flow (and thus to
limit the conversion rate). Fluidized bed allows efficient heat
dissipation due to a high solid-fluid heat transfer coefficient. The
counterpart of fluidized beds is that necessary to have continuous
feeding of catalyst due to the attrition of the catalyst (resulting
from as a result of continuous friction during fluidization). The
catalyst becomes smaller, is carried away by the fluid and leaves
the reactor, contaminating the downstream section of the process.
New processes combining the advantages of fixed and fluidized
beds have been developed over the past years: structured beds
(monoliths, static-mixer, fibrous networks, multi-channel beds. . .).
Among these structured beds, those formed of open cell foams
(OCF) coated with a catalyst offer many advantages: such as a high
surface/volume ratio, low pressure drop, a better control of the
reaction conditions, an intensification of mass and heat transfer
[4–6]. The last one is very interesting for the intensification of the
methanation reaction.
The objective of our work is to study the heat transfer of the
highly exothermal carbon dioxide methanation reaction. In this
study, a new platelet milli-reactor (PMR) is developed based on pre-
vious studies [7–11]. In order to study the heat transfer, an infrared
camera is used. Therefore, the main modifications (compared to
previous PMR [7–11], Fig. 2a) concern the heating system and the
metallic host structure (e.g. an infrared window (ZnSe) is inserted
in the upper part, Fig. 2b).
Most of the works published on heat study use thermocouples,
restricting temperature measurements to a few local points. IR
temperature measurement is commonly used for macro-scale heat
transfer studies [12,13]. Only few papers over the past decade have
been published for micro-scale heat studies; mainly single- and
two-phase flow heat transfer studies [14]. In best of our knowledge,
it is first time that a catalytic reaction in fixed bed is supervised,
in situ, by thermal infrared camera.
The IR window used only stands a maximal temperature of
250 ◦C. Therefore, in previous work [15], preliminary studies were
performed in order to choose a catalyst with enough catalytic activ-
ity (10–20% of CO2 conversion) at temperatures below 250 ◦C. The
catalyst chosen is composed of an active phase of nickel, often used
in literature for CO2 methanation [16–23], doped with ruthenium
(molar ratio of Ni/Ru of 1:100), in order to lower the reduction tem-
perature of the active phase [24,25], and a ceria-zirconia catalytic
support [26]. The presence of ceria-zirconia was shown to be essen-
tial to achieve higher conversion rates and methane selectivity near
98–100%, which is probably due to its participation in the reaction
mechanism as proposed by Ussa Aldana et al. [27].
In this paper, three OCF coated with a Ni-Ru/ceria-zirconia cat-
alyst: silicon carbide (SiC), aluminium (Al) and alumina (Al2O3);
with similar morphologies (i.e. approx. 30–40 PPI) but with differ-
ent thermal properties (intrinsic conductivity) are used in order
to show the effect of the heat transfer on the methanation reac-
tion. First, we present the coating procedure (developed in previous
Fig. 2. Differences between the “conventional” (a) and new PMR used in for this study (b).
Please cite this article in press as: M. Frey, et al., Open cell foam catalysts for CO2 methanation: Presentation of coating procedures and
in situ exothermicity reaction study by infrared thermography, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.03.016

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Fig. 3. Example of thermograph showing the position of uncoated OCF, coated OCF, thermocouple (TC) and hotspots (HS) at t = 0s (left) and t = 20s after the start of reaction
(right).
work for SiC OCF) adapted for the aluminium and the alumina
OCF. Then, for the first time, in situ infrared thermography is used
to monitor the heat generated on the catalyst surface during the
methanation reaction. The aim of this study is to observe the
hotspots formation for each OCF.
the sample is placed in an ultrasound (US) bath for 10 min in order
to remove the fraction of washcoat poorly anchored. An amount of
45 mg cm−3 of CZ was coated on each sample.
2.3. Foam impregnation of Ni-Ru
The samples were impregnated with nickel and ruthenium by
dipping into an ethanolic solution of nickel nitrate hexahydrate and
ruthenium acetylacetonate. The concentration of the solution is
adapted to the amount of active phase desired per impregnation
step. The foam is then dried at 100 ◦C for 2 h and calcined at 500 ◦C
for 6 h under air. The SiC, Al2O3 and Al foams coated with CZ and
impregnated Ni-Ru will be respectively named: SiCcat, Al2O3cat and
Alcat. A total amount of 19 mg cm−3 of active phase is impregnated
on each sample.
2. Material and methods
2.1. Preparation of the ceria-zirconia precursor solution
The ceria-zirconia precursor used was prepared by a « pseudo
sol-gel » method [28]. The starting salts, cerium acetate (III) and zir-
conium acetylacetonate(IV), were dissolved separately in propionic
acid (100 ◦C) in order to obtain a solution of 0.12 mol L−1 and gen-
erate the desired metallic propionates. Both solutions were then
mixed and heated under reflux for 2 h in order to give mixed pro-
pionates. A distillation under progressive vacuum is performed to
evaporate the solvent and leads, through oligomerization, to the
formation of a resin. The resin is then dissolved in a given quan-
tity of propionic acid to get the desired cationic concentration of
precursor.
2.4. XRD characterization
X-ray diffraction patterns (XRD) were recorded on a Brüker D8
Advance diffractometer with a LynxEye detector side and Ni filtered
Cu K␣ radiation (1.5418 Å) over a 2␪ range of 25–100 and a position
sensitive detector using a step size of 0.012 and a step time of 0.5 s.
2.2. Foam coating procedure with ceria-zirconia
2.5. Infrared camera temperature calibration
The foam is dipped for 10 min in the precursor solution. After
removing the excess of solution under a nitrogen flow (2 bar), the
foam is dried for 10 h and calcined under air at 500 ◦C for 6 h. Finally,
In order to calibrate the temperature measured by the infrared
camera (Optris PI 160: 160 × 120 Pixel and 120 Hz), an area above
Fig. 4. Impact of the dipping solution concentration on the coating and anchoring efficiency of the washcoat.
Please cite this article in press as: M. Frey, et al., Open cell foam catalysts for CO2 methanation: Presentation of coating procedures and
in situ exothermicity reaction study by infrared thermography, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.03.016

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Fig. 5. XRD diffractograms of SiC coated with CZ (samples A and B), CZ and ␤-SiC.
Fig. 8. Amount of washcoat deposited through eight coating steps after US.
Fig. 6. Mass increase and anchoring of the washcoat on Al2O3 compared to SiC.
2.6. Test procedure
The reaction was recorded by an infrared camera positioned
over the PMR through a ZnSe window. Two gas flows were used, 2
and 3 L h−1, and the mass of catalyst per volume of reaction cham-
ber was kept constant for the different foams studied. The reaction
chamber was filled with two OCF: an uncoated foam at the gas
inlet (OCFblank), as a blank sample, filling 1/3 of the reaction cham-
ber, followed by a foam coated with the catalyst (OCFcat) filling
the remaining 2/3 of the reaction chamber. The two foams where
placed with a 1 mm gap between them in order to avoid any direct
physical contact.
Fig. 7. Effect of the acidic treatment on the anchoring efficiency of the washcoat.
The catalyst was pre-reduced in an 80% H2/N2 stream
(46 mL min−1) in two steps. First in an external tubular reactor at
400 ◦C (heating rate: 2 ◦C min−1) for 6 h, then inside the PMR (i.e.
in situ) at 220 ◦C during 6 h to reduce the oxide layer that is formed
during the transfer between reactors. The chamber temperature is
increased (heating rate: 2 ◦C min−1) to 220 ◦C under a flow of H2/N2
with a molar composition of 36:10 with the same flow rate than
used for the reaction. The reactants are injected when the tem-
perature inside the reactor chamber reaches a steady state. The
reactant flow is composed of H2/CO2 (4:1), and N2 as an internal
standard. The molar ratio of H2/CO2/N2 was 36:9:10. The feed and
products were analyzed every 150 s using a programmable micro-
chromatograph (Agilent M200H, TCD detector, alumina poraplot
a thermocouple placed at the center of the reaction chamber was
used. The calibration was performed under a flow of H2/N2 (molar
ratio 36:10) with the same flow rate than used for the reaction.
The calibration is performed by adjusting the emissivity value in
order to have the same temperature value for this area and the
corresponding thermocouple (Fig. 3). The deviation between the
temperature measured with the thermocouple and the infrared
camera is of 0.5 ◦C. The emissivity values acquired are of 0.96 for
SiC (literature: 0.83–0.96), 0.87 for Al2O3 (literature: 0.8) and 0.90
for Al (literature: 0.83–0.94) [29].
Please cite this article in press as: M. Frey, et al., Open cell foam catalysts for CO2 methanation: Presentation of coating procedures and
in situ exothermicity reaction study by infrared thermography, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.03.016

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Table 1
Catalytic test results, specific surface and heat flow produced during the reaction near of steady state (t = 2000s) for different OCF
OCFcat
SiCcat
Flow rate (L h−1
)
XCO2 (%)
SCH4 (%)
SCO (%)
SC2H6 (%)
SBET (m2 g−1
33.8
)
Q (mW)
2
3
2
3
2
3
7.8
4.7
3.7
2.3
2.3
1.6
94.3
91.3
89.9
84.7
83.0
78.0
4.1
6.9
8.5
14.0
14.8
20.2
1.6
1.8
1.6
1.4
2.2
1.8
45
39
20
18
11
11
7.7
6.3
Al2O3cat
Alcat
washcoat amount deposited before and after ultrasounds (US) are
presented Fig. 4. After the first coating, no loss of washcoat has been
observed after US. The amount of washcoat remaining after US is
respectively of 31.5 and 19.8 mg cm−3 of foam for A and B. After one
coating step, the anchoring seems strong enough for both samples.
After several coating steps, sample A shows a relative loss of 9% after
each step, while the relative loss of sample B decreased from 5% to
1% over the coating steps. The anchoring is clearly stronger when
a less concentrated solution is used. The SEM images (Fig. 4) show
that the foam surface is completely covered regardless of the solu-
tion used. Sample A shows no cracking and a flat surface. Sample B
shows an irregular surface with superficial craking, both certainly
being responsible for the better anchoring of the washcoat.
XRD analysis were performed on the samples A and B (Fig. 5),
␤-SiC foam and CZ powder obtained by calcining a sample of the
dipping solution. The XRD patterns of CZ powder show the presence
of the fluorite cubic structure (Ce0.4Zr0.6O2, JCPD card No. 00-038-
1439), usually observed for ceria-zirconia mixed oxide with high
contents of ceria [30,31]. Reflections corresponding to (111), (200),
(220), (311), (222) and (400) planes are observed. The XRD patterns
of uncoated ␤-SiC foam also show the presence of a fluorite cubic
structure corresponding to ␤-SiC (␤-SiC, JCPD card No. 00-001-
1119). Reflections corresponding to (111), (200), (220), (311), (222)
and (400) planes are observed. The SiC diffraction peaks remain at
the same angle position after the coating of both samples compared
to the uncoated ␤-SiC foam. In the case of CZ, the diffraction peaks
belonging to the CZ crystallites of samples A and B show the pres-
ence of a shoulder at the left downside of the peaks at 2␪ angle of
29◦ and 48◦ and the peaks after 79◦, included, have disappeared or
are under detection limit. These observations are suggesting crys-
talline phase segregation, indicating a chemical anchoring of the CZ
washcoat on the foam.
and molecular sieve 5 Å columns). The CO2 conversion and CH4
selectivity were defined as follows:
ꢀ
ꢁ
ACO
2
XCO2 (%) = 1 −
× 10
ACO + ACH + ACO + 2AC
H
2 6
2
4
ꢀ
ꢁ
ACH
4
SCH4 (%) =
× 100
ACO + ACH + ACO + 2AC
H
2 6
2
4
X is the conversion, S the selectivity and A the surface areas of the
peaks obtained by chromatography and corrected by their corre-
sponding gas factors.
The theoretical heat flow (Q) generated during the reaction was
estimated, using the conversion and selectivities defined above, by
the following equation:
Q = FCH ꢁRHCH + FCOꢁRHCO
4
4
Qi is the heat produced by the generation of product i, Fi is the
molar flow rate of product i and ꢀRHi, is the enthalpy of reaction
of product i.
The temperature rise of each pixel (ꢀTpixel, measured by the
infrared camera) was calculated by the following relation:
ꢁTpixel(t) = Tpixel(t) − Tpixelatt<0
Tpixel(t) is the temperature measured by the infrared camera at
time t and Tpixelat t < 0 is the temperature measured by the infrared
camera before the injection of the reactants (t < 0).
3. Results and discussion
3.1. Development of coating procedures
3.1.1. SiC foam
The ␤-SiC foam provided by SICAT has a low specific surface area
(SBET ≈ 25 m2 g−1) that can be increased by calcination at 900 ◦C
for 2 h under air. This thermal treatment procedure generates a
natural SiO2-SiOxCy wash-coat layer allowing a better anchoring
of the active phase [15].
Two dipping solutions were prepared: a CZ precursor solution of
0.94 M in total cations (saturated solution) (sample A) and a 0.47 M
solution prepared from the 0.94 M solution by dilution (sample B).
The most concentrated solution will allow the lowest number of
dipping steps to achieve a desired washcoat amount. The 0.47 M
solution will allow us to study the impact of the dipping solu-
tion concentration on the anchoring strength of the washcoat. The
3.1.2. Alumina foam
Most of the alumina foams commercially available are ␣-
alumina (SBET ≈ 1 m2 g−1). The
␣ phase is the most stable
thermodynamically [32] among alumina phases, any thermal treat-
ment would therefore be useless. The same coating procedure than
for sample B was used on an alumina sample. The amount of wash-
coat deposited per coating step is presented Fig. 6. The amount of
washcoat deposited per coating step shows a linear trend. After
the first coating step, the amount of washcoat deposited was of
16.5 mg cm−3 with a relative loss of 0.8% under US. The amount of
CZ deposited is similar to the SiC foam, as well as the quality of
the anchoring. Therefore, despite the low surface area of the alu-
Table 2
CO2 conversion values (XCO2), ꢀTmean values, heat generated during the reaction (Q), sum of ꢀTpixel values and sum of ꢀTpixel values normalized by Q near of steady state
(t = 2000s) for different OCF under same flow rate (2 L h−1
)
ꢃ
107
227
169
n
n
ꢂ
ꢁT
i
Foam support
XCO2 (%)
ꢀTmean (K)
Q (mW)
ꢁTi (K)
(K mW−1
)
i=0
Q
i=0
SiCcat
Al2O3cat
Alcat
7.8
3.4
2.3
0.94
0.90
0.37
45.4
20.4
11.4
4841
4629
1927
Please cite this article in press as: M. Frey, et al., Open cell foam catalysts for CO2 methanation: Presentation of coating procedures and
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Fig. 9. ꢀTmean value of the foam samples over the time on stream under same flow rate (a: 2 L h−1 and b: 3 L h−1).
mina foam, the strong anchoring is also probably due to a chemical
uneven material surface and on the other hand to promote the
anchoring, not to a physical one.
development of a thicker alumina layer.
Fig. 7 displays the amount of washcoat deposited on the foam
samples with the different acidic treatments tested. Without treat-
ment 89% of the washcoat has been lost during the US. Short
treatment of 20 s in chloric acid followed by nitric acid has lead to
better anchoring with a relative loss of 32% after US and a washcoat
of 5.8 mg cm−3. An increase of the treatment time showed a neg-
ative effect on the anchoring with increasing relative losses after
US from 56 to 100 %. The treatment that showed the highest wash-
3.1.3. Aluminium foam
Aluminium
foams
have
insignificant
surface
areas
(SBET ≈ 0.01 m2 g−1). The coating procedures on metallic monolith
reported in literature use acidic treatment with nitric acid or
hydrochloric acid followed by nitric acid [33,34]. This kind of treat-
ment is used on the one hand to dissolve a fraction of the natural
alumina layer already coating the aluminium foam to create an
Fig. 10. ꢀT mapping at the reaction ignition (t < 22s) and near of steady state (t = 2000s) for different OCF under same flow (2l/h).
Please cite this article in press as: M. Frey, et al., Open cell foam catalysts for CO2 methanation: Presentation of coating procedures and
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coat deposition of 8.0 mg cm−3 and reasonable loss of 38% after US
was achieved by dipping the foam in nitric acid for 300 s. Therefore,
this chemical treatment procedure has been selected for aluminium
foam coating.
Fig. 8 displays the mass of washcoat deposited per coating step
depending on the chemical treatment chosen. The amount of coat-
ing per step increased linearly, achieving up to 45 mg cm−3 after 8
steps, unlike the untreated sample that showed an important loss
of the washcoat after US at step 7 and achieving only a deposition
of 19 mg cm−3 of washcoat after 8 steps.
of the OCFcat, then the temperature increased all over the OCFcat fol-
lowing the flow direction. The ignition time was of 4–5 s at 2 L h−1
Then, part of the heat generated by the reaction on the OCFcat
may be evacuated through the OCFblank. Although there is no direct
physical contact between OCFcat and OCFblank, they are indirectly
linked by the bottom and side walls of the reaction chamber, which
.
may explain the temperature increase on the OCFblank
.
Fig. 10 also displays a thermograph for each OCFcat when a
stationary state is reached (t = 2000s). SiCcat which showed the
highest catalytic activity also reveals the highest hotspots. Al2O3cat
that exhibited lower catalytic activity than SiCcat still shows some
hotspots. For the Alcat, it is difficult to confirm or refute clearly the
presence of hotspots because the low conversion rate reached with
Alcat didn’t produce enough heat.
In order to deposit the same amount of washcoat on the alu-
minium foam than the ceramic OCFs, twice the amount of coating
steps have been required due to the lower anchoring strength.
In order to overcome the influence of the heat variation
generated by the reaction (Q) for each OCF, we propose to nor-
malize the sum of ꢀTpixel values by the corresponding Q value.
The values displayed in Table 2 are respectively of 107, 227
and 169 K mW−1 for SiCcat, Al2O3cat and Alcat. SiC and Alu-
minium OCF show better results than alumina, which is coherent
with intrinsic ther−m1al conductivity values given in the literature
(SiC = 4–5 W m−1 K [36,37], Alumina = 1–2 W m−1 K−1 [35], Alu-
3.2. Catalytic tests: infrared recording
3.2.1. Catalytic test results and heat production estimation
The CO2 conversion values and selectivities of methane, car-
bon monoxide and ethane when the stationary state (t ≈ 2000s)
is reached during the catalytic tests are presented in Table 1. The
CO2 conversion rates of SiCcat, Al2O3cat and Alcat are respectively of
7.8, 3.7 and 2.3 for a flow rate of 2 L h−1 and 4.7, 2.3 and 1.6 for a
flow rate of 3 L h−1. The CO2 conversion rates vary for the different
OCFcats although the catalyst loading is the same for every sample.
These variations in terms of catalytic activity seem to be correlated
with the specific surfaces (SBET) of the OCF also given in Table 1. As
reported in previous work [35], a lower specific surface will lead to
a lower active phase particle dispersion and therefore to a smaller
number of active sites and weaker catalytic activity. Regarding the
selectivity values, it is important to remind that selectivities should
be compared at isoconversion.
minium = 218 W m−1 K−1 [38,39]). SiC has theoretically a lower
ꢃ
n
i=0
ꢁT
Q
i
thermal conductivity than aluminium, however, the
value
of SiCcat is lower than the one of Alcat. From this work, the better
performances are given by SiCcat > Alcat > Al2O3cat
.
Two assumptions can be suggested to explain this result. First,
because the conversion rates is low (in the case of Alcat), the direct
comparison is difficult.
Secondly, because the ceria-zirconia washcoat layer on the alu-
minium OCF is more important (compared to SiC), due to coating
procedure (see for instance 3.1.3), it may have significant effect on
the thermal conductivity properties of the Alcat. The presence of
this thicker oxide layer can locally decreases the thermal conduc-
tivity on the surface of the OCF. In addition, the chemical treatment
performed on the aluminium OCF may also be affected the intrinsic
thermal properties of the Alcat
A complementary studies with samples which present simi-
lar textural properties, allowing same active phase dispersion (i.e.
number of active sites), is essential to confirm or refute these
assumptions.
The results obtained for SiCcat with a flow rate of 3 L h−1 and
2 L h−1 for Al2O3cat display selectivities of respectively 91.3 and
89.9% for methane and 6.9 and 8.5% for CO. The differences between
these values are negligible regarding the difference in conversion
(4.7 and 3.7% respectively) and analytical measurement error. The
results at 3 L h−1 for Al2O3cat and 2 L h−1 for Alcat can be directly
compared, their conversion values are identical. Their selectivities
are respectively of 84.7 and 83.0% for methane and 14.0 and 14.8%
for CO.
4. Conclusion
3.2.2. Infrared camera temperature measurement during
catalytic tests
In this work, the coating of a ceria-zirconia catalyst was opti-
mized for three different open cell foams: silicon carbide, alumina
and aluminium. SiC was thermally treated to increase its anchor-
ing surface and a less concentrated dipping solution allowed better
anchoring strength. The washcoat of untreated alumina showed the
same anchoring strength than for SiC. Aluminium needed chemical
treatment, but even with the best anchoring efficiency achievable,
the washcoat showed a weaker anchoring than both ceramic open
cell foams.
A heat transfer study was performed on these three catalytic
foams. For the first time, the direct effect of the exothermal metha-
nation reaction on the foam’s surface temperature was recorded.
This study allows to observe in-situ the ignition reaction and to
show directly the formation of hotspots.
The ꢀTmean value (the mean value of the ꢀTpixel inside the cat-
alytic area), plotted versus the time for the different catalytic foams
is shown Fig. 9. For each type of foam, the heat generated during the
reaction, displayed in Table 1, is of the same order of magnitude for
both flow rates studied. For the Al2O3cat sample for example, the
heat generated are respectively of 20 and 18 under 2 and 3 L h−1
.
However, the ꢀTmean values are clearly lower under a flow rate of
3 L h−1. This result implies that the influence of the flow rate on
heat evacuation cannot be neglected. Consequently, the compari-
son of the different type of foams can only be carried out under the
same flow rate. Moreover, the differences between the different
ꢀTmean (i.e. for different OCFs) are not obvious at 3 L h−1. There-
fore, in this work, we will only focus on the results of the catalytic
tests performed under a flow rate of 2 L h−1, because at 3 L h−1, the
influence of the flow rate is more important on the temperature
profile at these conversion levels.
Thermographs representing the temperature rise for each pixel
(as ꢀTpixel values), at the beginning of the reaction are displayed
Fig. 10 for the different OCF studied. The OCFblank sample doesn’t
show any temperature rise, whereas the OCFcat clearly exhibits
increasing temperature values. The beginning of the reaction was
monitored and showed fast temperature increase, first at the entry
Further studies are necessary. It is important to increase the cat-
alytic activity on metallic foam at 220 ◦C in order to achieve direct
comparison of metallic and ceramic foams at isoconversion rates.
Acknowledgments
The authors would like to thank the ANR (project
ANR2010JCJC90401 SIMI9 ‘Millimatrix’), the Région Alsace and
Please cite this article in press as: M. Frey, et al., Open cell foam catalysts for CO2 methanation: Presentation of coating procedures and
in situ exothermicity reaction study by infrared thermography, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.03.016

G Model
CATTOD-10110; No. of Pages8
ARTICLE IN PRESS
8
M. Frey et al. / Catalysis Today xxx (2016) xxx–xxx
CNRS Emergence CO2 2014 (CAMICOM project) for their financial
support.
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Please cite this article in press as: M. Frey, et al., Open cell foam catalysts for CO2 methanation: Presentation of coating procedures and
in situ exothermicity reaction study by infrared thermography, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.03.016