Manganese Based Perovskites in Ethanol Steam Reforming

Article abstract of DOI:10.1007/s10562-017-2207-1

Abstract: The reactivity of Bi_0.5Sr_0.5MnO₃, Bi_0.5Sr_0.5Mn_0.7Cu_0.3O₃, Bi_0.5Sr_0.5Mn_0.7Ni_0.3O₃, La_0.5Sr

Full text of DOI:10.1007/s10562-017-2207-1

Catal Lett
DOI 10.1007/s10562-017-2207-1
Manganese Based Perovskites in Ethanol Steam Reforming
1
2
3
2
1,3
G. Perin · M. Guiotto · M. M. Natile · P. Canu · A. Glisenti
Received: 29 May 2017 / Accepted: 3 October 2017
©
Springer Science+Business Media, LLC 2017
Abstract The reactivity of Bi0.5Sr0.5MnO ,
was also investigated. Ethanol conversion is highest in
La Sr Mn Ni O and significant selectivity toward
3
Bi Sr Mn0.7Cu0.3O , Bi Sr Mn Ni O ,
0
.5
0.5
3
0.5
0.5
0.7
0.3
3
0.5 0.5
0.7
0.3
3
La Sr Mn Cu O and La Sr Mn Ni O in etha-
hydrogen and CO is observed. The reduction pre-treatment
0
.5 0.5
0.7
0.3
3
0.5 0.5
0.7 0.3
3
2
nol steam reforming was studied. Different steam to carbon
ratios have been tested (therefore referred as S/C=1.5, and
S/C = 6). The effect of an ad hoc reduction pre-treatment
is more effective on nickel containing catalysts, enhancing
both ethanol conversion and H and CO selectivity.
2
2
*
G. Perin
giovanni.perin.1@studenti.unipd.it
1
2
3
Chemical Sciences Department, University of Padova, Via F.
Marzolo, 1, Padova 35131, Italy
Industrial Engineering Department, University of Padova,
Via F. Marzolo, 9, Padova 35131, Italy
CNR-ISTM, INSTM; Chemical Sciences Department,
University of Padova, Via F. Marzolo, 1, 35131 Padova, Italy
Vol.:(0
1
123456789)
3

G. Perin et al.
Graphical Abstract
Keywords Perovskites · Manganese · Steam reforming ·
also investigated [5] with the aim of improving the cata-
lytic performance, decreasing deactivation and avoiding Ni
sintering, moreover many perovskites display mixed ionic
and electronic conductivity, which makes them appealing
for a use in solid oxide fuel cells (SOFC). In this contribu-
tion several Mn-containing perovskite-based catalysts are
studied in ESR; manganese presence, in fact, was observed
to reduce carbon deposition and promote catalytic activ-
ity [6, 7], to the best of our knowledge this particular type
of perovskites have never been investigated before. The
reactivity obtained by doping manganites with Ni or Cu
was compared. Moreover, in order to test the possibility to
decrease the use of Lanthanum, a Critical Raw Material,
Bi based perovskites were studied. In all these catalysts
part of the A-site cation (La or Bi) is substituted by Sr. The
use of this element in the catalyst formulation is intended
to increase the activity in redox reactions (increasing the
oxygen mobility and the oxidation state of the cation in B)
and acting as alkaline promoter.
IT-SOFC · Ethanol
1
Introduction
Ethanol is an interesting hydrogen vector and thus an
energy vector when considering, as an example, a coupled
application in fuel cells. Hydrogen can derive from ethanol
steam reforming (ESR) [1, 2]; in this reaction the use of a
catalyst is fundamental because both selectivity and activ-
ity depend on catalyst composition. Several catalysts have
been investigated: oxide-based, metal and noble metal
based. Among these, Ni-containing catalysts revealed to
be interesting being active but less expensive than noble
metal based ones. Ni/Al O converted 100% ethanol at
2
3
4
00 °C with 91% selectivity for H [3]. The addition of
2
La O was suggested to decrease catalyst deactivation due
2
3
to carbon [4]. The use of La containing perovskites was
1
3

Manganese Based Perovskites in Ethanol Steam Reforming
2
Experimental
BET surface specific area was measured with a
Micromeritics AutoChem II 2920, after a degassing treat-
ment (2 h at 350 °C).
2
.1 Catalyst Preparation
Bi Sr MnO (BSM), Bi Sr Mn0.7Cu0.3O (BSMC),
2.3 Catalytic Tests
0
.5 0.5
3
0.5 0.5
3
Bi Sr Mn Ni O (BSMN), La Sr Mn Cu
O
3
0
.5 0.5
0.7
0.3
3
0.5 0.5
0.7
0.3
(
LSMC) and La Sr Mn Ni O (LSMN) powders were
Steam reforming of ethanol was conducted in a continu-
ous-flow fixed-bed quartz reactor at atmospheric pressure.
A water–ethanol solution (H O:C H OH ratios of 3:1 and
0
.5 0.5
0.7 0.3
3
synthetized by citrate route [8], starting from adequate
precursors: Bi(C H O ) (99.99% purity, Sigma-Aldrich),
6
5
7
2
2
5
Sr(NO ) (≥ 98%, Sigma-Aldrich), La O (99.9%,
12:1, having S/C=1.5 and S/C=6, respectively) was fed by
a syringe pump at 8.3 μl/min speed, and vaporized at 170 °C
on a SiC bed, using Ar as carrier gas, (flux controlled by
Brooks mass flow controller). Effluent gases were analysed
by Agilent 7820 gas-chromatograph, equipped with thermal
conductivity (TCD) and flame ionization (FID) detectors.
3
2
2
3
Aldrich), Mn(CH COO) ·4H O (≥99.0%, Sigma-Aldrich),
3
2
2
CuO (98%, Sigma-Aldrich), Ni(NO ) ·6H O (≥ 97%,
3
2
2
Sigma-Aldrich). After the dissolution of the precursors,
achieved with water in case of nitrates or with nitric acid
(
≥65% Sigma-Aldrich) for oxides and bismuth citrate, cit-
ric acid monohydrate (≥ 99.0%, Sigma-Aldrich) is added
in amount of 1.9:1 with respect of the total amount of cati-
ons. Ammonia (30–33% in water, Sigma-Aldrich) is added
while stirring, until pH 6.5 is reached. The solution is then
concentrated by evaporation at 90 °C until the formation of
a gel that is heated for 2 h at 400 °C. The ash-like, spongy
resulting material is ground into powder and then calcined
for 6 h at 1000 °C in air atmosphere.
Water, ethanol, acetaldehyde and CO were separated by the
2
PoraPak-Q column; for hydrogen, CO and methane analysis
a Molsieve ms5A column was used. The catalytic behaviour
was investigated with or without an activation treatment (in
5%H /Ar stream) specifically chosen on the basis of TPR
2
measurements.
3
Results and Discussion
2
.2 Catalyst Characterization
3.1 Characterization
X-ray diffraction patterns (XRD) were collected with a
Bruker D8 Advance automatic diffractometer, with Cu Kα
wavelength (λ = 0.154 nm) at a voltage of 40 kV and a
current of 40 mA.
As it is observed from XRD patterns (Fig. 1), the substitu-
tion of lanthanum with bismuth occurs without drawbacks
X-ray photoelectron spectroscopy (XPS) was recorded
by a Perkin Elmer PHI 5600ci Multi Technique System,
using AlKα radiation (1486.6 eV) working at 250 W.
The spectrometer was calibrated by assuming the bind-
ing energy (BE) of the Au 4f line to be 84.0 eV with
7
/2
respect to the Fermi level. Both extended spectra (sur-
vey—187.85 eV pass energy, 0.5, 0.05 s/step) and detailed
spectra (for Bi 4f, La 3d, Sr 3d, Mn 2p, Cu 2p, Ni 2p, O 1s
and C 1s—23.5 eV pass energy, 0.1, 0.1 s/step) were col-
lected. The standard deviation in the BE values of the XPS
line is 0.10 eV. The atomic percentage, after a Shirley-
type background subtraction [9] was evaluated by using
the PHI sensitivity factors [10, 11]. The peak positions
were corrected for the charging effects by considering the
C 1s peak at 285.0 eV and evaluating the BE differences.
Temperature-programmed reduction (TPR) measures
were collected with a Micromeritics AutoChem II 2920.
Experiments were performed in a downstream fixed bed
Fig. 1 XRD patterns of Bi Sr MnO (red), Bi0.5Sr0.5Mn0.7Cu
O
3
quartz tube reactor with a 5%H /Ar stream at 50 sccm/min,
0.5 0.5
3
0.3
2
(
yellow), Bi Sr Mn Ni O (green), La Sr Mn Cu O (blue)
0.5 0.5 0.7 0.3 3 0.5 0.5 0.7 0.3 3
raising temperature from RT to 900 °C at 10 °C/min speed;
and La Sr Mn Ni O (black) powders. Symbols stand for: aster-
0
.5 0.5
0.7 0.3
3
hydrogen consumption was monitored by a TCD detector.
isk (perovskite); filled rhombus (CuO); filled inverted triangle (NiO);
cross (Bi O ); filled square (Bi Mn O )
2
3
2
4
10
1
3

G. Perin et al.
in the crystalline structure of BSM. In the B-site doped
compounds, beside the major perovskitic crystalline
phase, traces of oxides segregation (CuO, NiO, Bi O , and
2
3
Bi Mn O ) can be seen. The calculated values for t-fac-
2
4
10
tor (BSM = 0.9838; BSMC = 0.9660; BSMN = 0.9719;
LSMC = 0.9742; LSMN = 0.9801) suggest the possibility
that B-doping can contribute to the instability of the crys-
talline structure.
The following surface area values were obtained for
2
2
Bi Sr MnO (13 m /g), Bi Sr Mn Cu O (10 m /g),
0
.5 0.5
3
0.5 0.5
0.7
0.3
3
2
Bi Sr Mn Ni O (10 m /g), La Sr Mn Cu
O
3
0
.5 0.5
0.7
0.3
3
0.5 0.5
0.7
0.3
2
2
(
10 m /g) and La Sr Mn Ni O (24 m /g).
0.5 0.5 0.7 0.3 3
O 1s XPS peaks (Fig. 2), show two contributions due
to perovskitic oxygen (529.5 eV), and to the presence of
carbonates and hydroxides (531.2–531.7 eV) [8, 12–15]. It
is worth to notice that nickel doping seems to induce lower
hydroxyls and carbonates formation with respect to cop-
per. The position of Sr 3d peaks (132.5 and 133.8 eV for
3
d , 3d ) is consistent with the presence of perovskite and
5/2 3/2
carbonate species. Mn2p and Mn2p binding energies
3
/2
1/2
(
642.1 and 653.5 eV, respectively), confirm the presence, in
all the samples, of both Mn(III) and Mn(IV), whose oxides
are reported in literature at 641.7 and 642.2 eV, respectively
[
12, 13].
Cu2p signal at 934.0 eV, marks the presence of hydrox-
3/2
ylated copper and shake-up peaks characteristic of Cu(II)
[
14, 15]. Ni2p peak (954.4 eV) is consistent with the
3
/2
presence of Ni(II) in the outmost layers, as confirmed by
the shake-up peaks (at 862.0 and 881.0 eV). The position
and shape of bismuth (159.0 eV), and lanthanum (834.2 eV)
are consistent with the presence of these elements in the
expected oxidation state [14].
XPS quantitative analysis (Table 1) shows a surface
segregation of bismuth for BSMC and BSMN, reducing
the surface amount of B-site dopants; BSM and BSMN
also suffer from Sr surface segregation. On the contrary,
lanthanum based materials seem not to be affect by segre-
gation phenomena in the same extent, displaying a nearly
stoichiometric composition of the surface. LSMC, in con-
trast with BSMC, presents a high surface content of cop-
per, with a B/A cations ratio of 0.99. A similar trend is
observable for nickel in LSMN, in which B/A is higher
than one.
Fig. 2 XPS spectra of O 1s and Mn2p peaks for Bi Sr MnO3
0
.5 0.5
(
red), Bi Sr Mn Cu O (yellow), Bi Sr Mn Ni O (green),
0.5 0.5 0.7 0.3 3 0.5 0.5 0.7 0.3 3
La Sr Mn Cu O (blue) and La Sr Mn Ni O (black)
0
.5 0.5
0.7
0.3
3
0.5 0.5
0.7 0.3
3
due to the severe surface segregation of Bi; the reduction
of Cu(II) is observed at 447 °C. The substitution with Ni
induces a shift of the Bi(III) and Mn (IV) peak to lower
temperature (497 °C). Nonetheless, it is possible to observe
that the substitution with copper or nickel in the B-site
shifts the onset of reduction to lower temperatures, as was
The TPR profile (Fig. 3) of BSM reveals a peak at
5
8
86 °C and weak contributions at about 400, 730, and
25 °C. The signal at 586 °C is attributed to the reduction
Bi(III) to Bi(0) and Mn(IV) to Mn(III) [16]. The weak sig-
nals at 400, 730 and 825 °C can be due to weakly adsorbed
oxygen and to the two step reduction of Mn(III) to Mn(II)
respectively, which was previously reported to proceed
by means of Mn O formation [17, 18]. The addition of
already observed on systems of the type LaB Mn O
0.2 0.8 3
[19]. In La containing perovskites, the temperature of the
reduction is lower, this is particularly evident in LSMN
sample, which shows two intense reduction peaks at 350
and 450 °C.
3
4
Cu causes a slight shift of the Bi(III) and Mn(IV) reduc-
tion peak toward higher temperature (679 °C), this may be
1
3

Manganese Based Perovskites in Ethanol Steam Reforming
Table 1 Surface composition of Bi0.5Sr0.5MnO3, Bi0.5Sr0.5Mn0.7Cu0.3O , Bi0.5Sr0.5Mn0.7Ni0.3O , La0.5Sr0.5Mn0.7Cu0.3O3 and
3
3
La Sr Mn Ni0.3O3
0
.5 0.5
0.7
Bi0.5Sr0.5MnO3
Bi
Sr
Mn
Experimental
Nominal
25.3
25
31.7
25
43.0
50
Bi0.5Sr0.5Mn0.7Cu0.3O3
Bi
Sr
Mn
Cu
Experimental
Nominal
49.6
25
21.7
25
24.3
35
4.4
15
Bi0.5Sr0.5Mn0.7Ni0.3O3
Bi
Sr
Mn
Ni
Experimental
Nominal
37.4
25
31.6
25
25.8
35
5.2
15
La0.5Sr0.5Mn0.7Cu0.3O3
La
Sr
Mn
Cu
Experimental
Nominal
17.7
25
33.5
25
29.0
35
19.8
15
La0.5Sr0.5Mn0.7Ni0.3O3
La
Sr
Mn
Ni
Experimental
Nominal
22.6
25
23.2
25
42.1
35
12.1
15
Nominal composition values are determined by the stoichiometric amounts
(
II) reduction may be more difficult in samples which have
a higher crystallinity degree [18].
3
.2 Catalytic Activity
ESR catalytic test results obtained at S/C = 1.5 (Fig. 4a),
indicate that ethanol conversion reaches 100% at 600 °C
(
80% at 470 °C) with La Sr Mn Ni O .
0.5 0.5 0.7 0.3 3
Lanthanum replacement with bismuth reduces ethanol
conversion from 90 to 43% (at 700 °C) in nickel doped sam-
ples, suggesting a cooperative effect between La and Ni;
this effect is less evident when doping with copper. Both
BSMC and LSMC reach about 30% ethanol conversion at
7
00 °C; BSM reaches 50% conversion at 700 °C. The XPS
compositions suggest that the presence on the surface of
significant amounts of Mn and Ni can be fundamental in
order to obtain high conversions (the atomic % of these ele-
ments is maximum in LSMN). As for the other B-site doped
materials, the surface segregation of Bi (in BSMC) and of
Sr (in LSMC) can significantly reduce the catalyst activity,
this effect pronounced even in the case of BSMN. A lower
amount of nickel (which is active in C–C cleavage) could
Fig. 3 TPR profiles of Bi Sr MnO (red), Bi Sr0.5Mn0.7Cu
O
3
0
.5 0.5
3
0.5
0.3
(
yellow), Bi Sr Mn Ni O (green), La Sr Mn Cu O (blue)
0.5 0.5 0.7 0.3 3 0.5 0.5 0.7 0.3 3
and La Sr Mn Ni O (black)
0.5 0.5
0.7 0.3
3
enhance the production C by-products (e.g. ethylene) and
2
thus of undesired carbon, leading to catalyst deactivation.
The main products detected are hydrogen and acetalde-
hyde (Table 2) in all cases but LSMN. For this catalyst the
main products are hydrogen, CO and CH ; acetaldehyde is
In all samples, the comparison between the estimated and
experimental H consumptions (Cu and Ni were considered
2
divalent) reveals the complete reduction of Bi(III) to Bi(0)
2
4
and of Mn(IV) to Mn(III), suggesting that Mn(III) to Mn
also observed, but only in the temperature range from 400 to
6
00 °C. Bismuth-based materials seem to favor dehydration
1
3

G. Perin et al.
Table 2 Ethanol conversion values, H , CO , and acetaldehyde
2
2
yields values obtained at 700 °C for the different catalysts in the etha-
nol steam reforming reaction; the conversions and yields obtained at
6
00 °C are also reported for La Sr Mn Ni O ; this, in fact, is the
0.5 0.5 0.7 0.3 3
temperature at which the catalyst performance are maxima
Catalyst
Χ EtOH
Y H2
Y CO2
Y CH CHO
3
BSM
S/C=1.5
S/C=6
Pretreated
BSMN
48
60
55
7
12
17
3
3
0
32
42
39
S/C=1.5
S/C=6
Pretreated
BSMC
43
54
79
9
12
28
3
0
12
27
32
57
S/C=1.5
S/C=6
Pretreated
LSMN
31
67
53
10
17
10
0
0
0
17
42
42
S/C=1.5
S/C=6
Pretreated
LSMC
95
100
96 (100)
61
62 (85)
66 (90)
32
45 (80)
10 (20)
9.5
10 (0)
31 (0)
S/C=1.5
S/C=6
Pretreated
25
36
39
3
5
8
0
0
0
18
22
33
and acetaldehyde for all catalysts but LSMN, for which H
2
and CO are the main products; CH and acetaldehyde are
2
4
observed only at temperatures higher than 600 °C.
A pre-treatment of reduction (5% H /Ar), chosen on
2
the basis of TPR measurement, was carried out in order to
investigate the effect of activation on activity and selectiv-
ity. The reduction was carried out with the aim of enhanc-
ing the surface content of active B-site reduced cations,
(
particularly in of BSMC and BSMN, whose content in
Fig. 4 Ethanol conversion (as function of temperature)
copper and nickel was very low) with a mild treatment, to
avoid the complete reduction of perovskite.
of
Bi Sr0.5MnO3
(red),
Bi0.5Sr Mn Cu
O
3
(yellow),
0
.5
0.5
0.5 0.5
0.7
0.7
0.3
Bi Sr Mn Ni0.3O (green), La Sr Mn Cu
O (blue) and
3
0
0
.5 0.5
.5 0.5
0.7
0.7 0.3
3
3
0.3
The reduction temperature was thus chosen ad hoc for
each catalyst, considering the first reduction process of
Bi(III) and Mn(IV) as the main criteria. The chosen val-
La Sr Mn Ni
O
(black) at different steam to carbon ratios:
S/C=1.5 (a) and S/C=6 (b)
ues are: Bi Sr MnO (560 °C), Bi Sr Mn Cu
O
3
0
.5 0.5
3
0.5 0.5
0.7
0.3
route instead of dehydrogenation, in particular in the case
of BSMC.
(525 °C), Bi0.5Sr Mn Ni0.3O
(470 °C),
0.5
0.7
3
La Sr Mn Cu O (450 °C) and La Sr Mn Ni
O
3
0
.5 0.5
0.7
0.3
3
0.5 0.5
0.7 0.3
Reactivity was further investigated with steam to carbon
ratio of 6 (Fig. 4b). The higher amount of water produces
higher conversions for ethanol: for LSMN almost complete
conversion is observed at 500 °C; for the other catalysts at
(400). XPS was performed soon after reduction, to evalu-
ate the presence of differences in surface composition with
fresh samples. The comparison between the atomic per-
centages before and after reduction revealed an enrichment
of B-site cations (reported to be responsible of catalytic
activity), this phenomenon is more relevant in the case of
BSMN (Table 3).
7
00 °C the ethanol conversion ranges from 35% (LSMC)
to 54% (BSMN), to 60% (BSM), to 65% (BSMC). As in
the former case, the main products detected are hydrogen
1
3

Manganese Based Perovskites in Ethanol Steam Reforming
Table 3 Surface composition of Bi0.5Sr0.5Mn0.7Cu0.3O and Bi0.5Sr0.5Mn0.7Ni0.3O after the reduction (5%H /Ar) treatment
3
3
2
BSMC
Bi
Sr
Mn
Cu
Reduced
Fresh
Nominal
44.7
49.6
25
20.0
21.7
25
23.3
24.3
35
12.0
4.4
15
BSMN
Bi
Sr
Mn
Ni
Reduced
Fresh
Nominal
23.3
37.4
25
28.6
31.6
25
42.7
25.8
35
5.3
5.2
15
Surface cation compositions of fresh catalysts and nominal values are reported for comparison
4
Conclusions
In this contribution several Mn based perovskites have
been developed and their properties and reactivity in ESR
have been tested; moreover the role of A-site cation was
investigated in order to understand if La replacement with
Bi represents a feasible possibility.
XRD and XPS measurements revealed the tendency to
segregation of bismuth, which is more evident in B-sub-
stituted samples. Lanthanum containing catalysts seem not
to be affected by segregation in the same extent; moreover,
La presence seems to favor the dehydrogenation reaction
path, yielding to higher H and CO production, especially
2
2
in the case of LSMN. These data suggest a strong correla-
tion between the chosen A-site cation and reaction path-
way, showing the relevant role played by lanthanum in
co-presence with nickel.
Beside the segregation effects, we have demonstrated
that a mild reduction pretreatment, accurately chosen
on the base of TPR results, could represent a solution to
enrich the surface content of B-site cations and enhance
the production of H and CO , as observed in particular
Fig. 5 Ethanol conversion (as function of temperature) of pre-
2
2
reduced Bi Sr MnO (red), Bi Sr Mn Cu
O
3
(yellow),
for BSMN. This suggests the possible use of bismuth for
a partial replacement of lanthanum, if paying attention
to surface segregation effects. LSMN promising catalytic
performances (allowing to reach 100% ethanol conversion
at 500 °C with high selectivity towards H and CO ) shed
0
.5 0.5
3
0.5 0.5
0.7
0.3
Bi Sr Mn Ni
O
(green), La Sr Mn Cu
O
(blue) and
0
0
.5 0.5
.5 0.5
0.7 0.3
0.7 0.3
3
3
0.5 0.5
0.7
0.3
3
La Sr Mn Ni O (black) tested under S/C=6. Ethanol conver-
sion of unreduced samples tested in same conditions is reported in
dashed lines for comparison
2
2
light onto the possibility of using Mn-based perovskites to
perform in-situ ethanol reforming in a SOFC anode. Fur-
ther measurements of stability and electrochemical activ-
ity have to be performed for a deeper characterization of
the material in a SOFC reaction environment.
Steam reforming tests were carried out on the activated
catalysts (Fig. 5) with steam to carbon ratio of 6, show-
ing that the reduction treatment was effective on BSMN
Acknowledgements We gratefully thank Cariparo, the European
(
conversion raises from 54 to 79% at 700 °C); the CH
4
Union’s 7th Framework Programme under Grant Agreement No.
and CO yields also increase, the main products detected
2
2
80890- NEXT-GEN-CAT and European Union’s Horizon 2020
are still acetaldehyde and hydrogen.
research and innovation programme under Grant Agreement No.
686086 PARTIAL-PGM for partial financing. The funding was pro-
vided by Fondazione Cassa di Risparmio di Padova e Rovigo.
These results allow thinking that an activation treat-
ment in hydrogen can enhance catalyst performances by
modifying the surface composition.
1
3

G. Perin et al.
1
1
1
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surface analysis. Wiley, New York
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