Methane reforming process by means of a carbonated Na2ZrO3 catalyst

Article abstract of DOI:10.1246/cl.160136

Sodium zirconate (Na₂ZrO₃) was synthesized by a solid-state reaction and then it was tested in the methane reforming process. Na₂ZrO₃ was initially carbonated at different temperatures (550-700°C). Then, each ca

Full text of DOI:10.1246/cl.160136

Received: February 13, 2016 | Accepted: March 9, 2016 | Web Released: March 18, 2016
CL-160136
Methane Reforming Process by means of a Carbonated Na2ZrO3 Catalyst
J. Arturo Mendoza-Nieto, Elizabeth Vera, and Heriberto Pfeiffer*
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior s/n Cd. Universitaria,
Del. Coyoacán, CP 04510, Ciudad de México, Mexico
(E-mail: pfeiffer@iim.unam.mx)
Sodium zirconate (Na2ZrO3) was synthesized by a solid-
state reaction and then it was tested in the methane reforming
process. Na2ZrO3 was initially carbonated at different temper-
atures (550-700 °C). Then, each carbonated Na2ZrO3 sample
(composed by Na2CO3 and ZrO2) was used as a catalyst and
as a carbon dioxide supplier for syngas (H2 + CO) production
through the methane reforming reaction. Results clearly show
the formation of H2 and CO, evidencing a catalytic conversion.
Moreover, cyclic and structural analyses corroborated that
Na2ZrO3 could be used cyclically in the carbonation and
subsequent methane reforming processes, although the crystal-
line structure was not totally recovered.
ceramics. Thus, the aim of this work was to study, experimen-
tally, if Na2ZrO3 can be used for hydrogen production, acting
first as a CO2 captor and then as a catalytic material, during dry
methane reforming process.
Sodium zirconate was synthesized by a solid-state reac-
tion.16,19 Na2CO3 and ZrO2 were mechanically mixed and
calcined in air atmosphere at 900 °C for 12 h. A batch of
Na2ZrO3 was tested in dry reforming reaction in a Bel-Rea
catalytic reactor from Bel Japan, using 200 mg of sample.
Initially, samples were carbonated dynamically from 30 °C at
different temperatures (550, 600, 650, and 700 °C), using a gas
mixture of 60 vol % CO2 (Praxair, grade 3.0) and 40 vol % N2
(Praxair grade 4.8) with a total flow rate of 100 mL min¹1. Later,
samples were isothermally treated at the final carbonation
temperature for 0.5 h and then cooled down until 200 °C using
the same gas mixture. Finally, samples were dynamically heated
Keywords: H2 production
|
Sorption-enhanced methane reforming (SEMR)
Sodium zirconate
|
¹1
from 200 to 900 °C with a heating rate of 2 °C min using
¹1
The large increment in CO2 emissions from fossil fuels in
the last decades has become a threat to the environment.
Therefore, the search for alternative and cleaner energy sources
is an important scientific challenge. In this regard, H2 production
would be a viable solution for increasing energy demands.1
Among the H2 production processes, the most commonly used
methods are steam methane reforming (SMR), water-gas shift
reaction (WGSR), dry methane reforming, and ethanol-steam
reforming methods.2-7 All of them produce syngas, composed of
H2 and CO or CO2. Here, the removal of CO or CO2 is usually
a key step to purify H2, and different technologies have been
developed over the last years in order to accomplish it.8,9
Sorption-enhanced methane reforming (SEMR) can produce
highly pure H2 by using a mixture of a catalyst for the SMR
and a suitable CO2 captor.3,4,10 This process presents important
advantages over the SMR technology (which is industrially the
most used method for H2 production), such as lower temperature
operation, higher conversion yields, and the reduction of
subsequent purification requirements.4,11
CO2 sorbents must satisfy some properties for being used in
SEMR, for instance selective CO2 absorption in the presence of
steam, regeneration ability, good sorption-desorption kinetics,
and stability under temperature and steam.1,11 Recently, different
alkaline ceramics have been proposed as suitable CO2 captors
for the SEMR, such as CaO,1 Na2ZrO3,5 Li4SiO4,1,12 and
Li2ZrO3.3,11,12 Up to now, there are few reports in literature about
methane reforming using these materials.3,11,13-19 In all those
works, a reactor modeling of SEMR has been only theoretically
proposed, suggesting the use of alkaline ceramics for CO2
capture along with another material for methane reforming,
e.g. Ni/MgO catalyst.13 However, these proposals present the
disadvantage that H2 production requires the use of two different
materials. It must be pointed out that there is no experimental
evidence of syngas production using this kind of alkaline
100 mL min of a gas mixture composed of CH4 (5 vol %,
Praxair grade 5.0) complemented with N2. Reforming gas
products were analyzed each 15 °C until 900 °C, using a
Shimadzu GC 2014 gas chromatograph with a Carboxen-1000
column and an Alpha Platinum FTIR spectrometer from Bruker
connected to a ZnS gas flow cell. Cyclic experiments were
performed repeating the same experimental procedure described
above.
Pristine Na2ZrO3 and reforming products were characterized
by powder X-ray diffraction in the 10° ¯ 2ª ¯ 80° range, using
a goniometer speed of 1°(2ª) min¹1, with a diffractometer
Siemens D5000 coupled to a cobalt anode (- = 1.789 ¡) X-ray
tube.
Figure 1 shows the CH4 dynamic conversion to syngas
evaluated after a Na2ZrO3 carbonation process at 600 °C.
Between 200 and 750 °C, CO and H2 production was not
detected by FTIR and GC, respectively, indicating that the CH4
reforming process was not produced in that temperature range.
However, at temperatures higher than 750 °C, CO and H2
formation became evident, fitting with the CH4 reduction
content (Figure 1A). Additionally, CO evolution was followed
via FTIR analysis (Figure 1B). The CO vibration bands were
¹1
identified between the 2230 and 2030 cm range. Also, the
reactants presented vibration bands in the FTIR spectra. Methane
showed signals at 1390-1170 and 3200-2600 cm¹1, whereas
CO2 at 725-600, 2400-2235, and 3750-3560 cm¹1. Figure 1C
shows the hydrogen chromatograph peak, which increases
between 750 and 900 °C. The highest amount of hydrogen
(0.65 sccm) was obtained at 900 °C, during dry reforming
process. Conversely, CO2 was evidenced between 670 and
830 °C, which indicates that CO2 is being desorbed from
carbonated Na2ZrO3. The CO2 desorption is in good agreement
with the subsequent thermally CH4 reforming process. There-
fore, all these results confirm that CH4 reforming is taking place
Chem. Lett. 2016, 45, 685–687 | doi:10.1246/cl.160136
© 2016 The Chemical Society of Japan | 685

6.0
5.5
5.0
Reforming
temperature
/°C
0.6
0.5
0.4
0.3
0.2
0.1
0.0
CH4
900
885
600 °C carbonation
CO2
H2
1.0
0.5
0.0
865
850
800
(A)
CO
550
600
650
700
200 300 400 500 600 700 800 900
Temperature/°C
Carbonation temperature/°C
Figure 2. Thermal evolution of CH4 reforming from 800 to
900 °C using Na2ZrO3 samples carbonated dynamically at
different final temperatures (550, 600, 650, and 700 °C).
900 °C
875 °C
850 °C
1,75
Cycle 1
Cycle 2
Cycle 3
Cycle 4
825 °C
800 °C
1,50
750 °C
700 °C
650 °C
1,25
2240 2160 2080 2000
Wavenumber/cm−1
(B)
1,00
0,75
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber/cm−1
H2
CH4
0,50
900 °C
850 °C
825 °C
800 °C
750 °C
700 °C
650 °C
200 300 400 500 600 700 800 900
Temperature/°C
0,25
0,00
500
600
700
800
900
Temperature/°C
CO2
Figure 3. Dynamic evolution for hydrogen and carbon dioxide
(inset) gases during the methane reforming process, into cyclic
processes.
(C)
0
2
4
6
temperature was 600 °C. It may be related to the Na2CO3-ZrO2
external shell microstructural properties. It has been reported
that Na2ZrO3 carbonation produces different Na2CO3-ZrO2
external shell microstructures, depending on the temperature.16
At T ¯ 550 °C the external shell is composed by a mesoporous
shell, which improves different diffusion processes. It must be
pointed out that in the present work, the CO2 flow used for the
carbonation process was different (see the experimental section),
which must have modified the temperature limit for mesoporous
formation. Based on the results shown in Figure 2, it seems that
higher Na2ZrO3 carbonation temperatures may have densified
the Na2CO3-ZrO2 external shell, reducing CO2 desorption, and
consequently, the methane reforming process.
In order to analyze the possible cyclability of Na2ZrO3
in carbonation and subsequent CH4 dynamic conversion to
syngas, four cycles were performed into the same experimental
conditions described above using a new Na2ZrO3 batch.
Figure 3 shows the hydrogen and carbon dioxide gas chromato-
graph peaks’ evolution during the methane reforming process.
Retention time/min
Figure 1. (A) Dynamic evolution, (B) FTIR spectra, and (C)
chromatograms for methane reforming process, using Na2ZrO3
sample carbonated dynamically at 600 °C.
in the Na2ZrO3 previously carbonated particles, according to the
following reaction mechanism:
Na2ZrO3ðsÞ þ CO2ðgÞ ! Na2CO3ðsÞ þ ZrO2ðsÞ
ð1Þ
CH4ðgÞ þ CO2ðg, desorbed from reaction 1Þ
! 2H2ðgÞ þ 2COðgÞ
ð2Þ
A second set of experiments were performed varying the
Na2ZrO3 carbonation temperature. In all the cases, the reforming
process was produced. However, the maximum hydrogen
production varied as a function of carbonation and methane
reforming temperatures (Figure 2). Nevertheless, independently
of the methane reforming temperature, the best hydrogen
production was always obtained when the Na2ZrO3 carbonation
686 | Chem. Lett. 2016, 45, 685–687 | doi:10.1246/cl.160136
© 2016 The Chemical Society of Japan

Summarizing, the results confirmed that Na2ZrO3 is able to
capture CO2 (as it was already published16-18) and subsequently
perform the corresponding reforming process. The catalytic
process is produced in the presence of methane through a
simultaneous CO2 desorption. This process can be produced
cyclically, where the Na2ZrO3 structure is highly regenerated
after the double carbonation-catalytic process. Based on these
results, reaction 2 would be modified as follows:
(D)
(C)
(B)
CH4ðgÞ þ Na2CO3-ZrO2ðsÞ
! 2H2ðgÞ þ 2COðgÞ þ Na2ZrO3ðsÞ
This Na2CO3-ZrO2ðsÞ is produced after Na2ZrO3
carbonation; as shown in reaction 1:
ð3Þ
(A)
This work was financially supported by the projects
SENER-CONACYT and PAPIIT-UNAM. E. Vera and J. A.
Mendoza-Nieto thank to CONACYT and DGAPA-UNAM for
financial support, respectively. Finally, authors thank to A.
Tejeda for technical help.
10
20
30
40
50
60
70
80
2θ/°
Figure 4. XRD patterns of (A) original material, (B) dynam-
ically carbonated Na2ZrO3, (C) material obtained after CH4
reforming, and (D) material obtained after four CH4 reforming
processes. Crystalline phases of ( ) Na2ZrO3, ( ) Na2CO3,
( ) monoclinic ZrO2, and ( ) tetragonal ZrO2.
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Chem. Lett. 2016, 45, 685–687 | doi:10.1246/cl.160136
© 2016 The Chemical Society of Japan | 687