Steam reforming of glycerol over nano size Ni-Ce/LaAlO3 catalysts

Article abstract of DOI:10.1166/jnn.2015.8345

In this work, hydrogen production from glycerol by Steam Reforming (SR) was studied by Ni-Ce catalysts supported on LaAlO₃ perovskite in order to effect of the cerium loading amount and the reaction conditions. Nano size Ni-Ce/LaAlO₃

Full text of DOI:10.1166/jnn.2015.8345

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Nanoscience and Nanotechnology
Vol. 15, 522–526, 2015
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Steam Reforming of Glycerol Over Nano Size
Ni–Ce/LaAlO3 Catalysts
Seong-Hak Kim1, Yoo-Jin Go2, Nam-Cook Park3ꢀ∗, Jong-Ho Kim3,
Young-Chul Kim3, and Dong-Ju Moon4ꢀ∗
1Department of Advanced Chemicals and Engineering, Chonnam National University, 77 Yongbong-ro,
Buk-gu Gwangju 500-757, Republic of Korea
2Department of Chemicals Engineering, Chonnam National University, 77 Yongbong-ro,
Buk-gu Gwangju 500-757, Republic of Korea
3Faculty of Applied Chemical Engineering and the Research Institute for Catalysis, Chonnam National University,
77 Yongbong-ro, Buk-gu Gwangju 500-757, Republic of Korea
4Korea Institute Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu Seoul 136-791, Republic of Korea
In this work, hydrogen production from glycerol by Steam Reforming (SR) was studied by Ni–Ce
catalysts supported on LaAlO3 perovskite in order to effect of the cerium loading amount and the
reaction conditions. Nano size Ni–Ce/LaAlO3 catalysts were prepared by precipitation method.
The structure of the catalysts was characterized by XRD analysis. The morphology, dispersion and
the reduction properties of catalysts was examined by SEM, TEM, H -chemisorption and TPR,
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2
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respectively. It was found that 15 wt% Ni-5 wt% Ce/LaAlO3 catalyst showed the highest glycerol
Copyright: American Scientific Publishers
conversion and hydrogen selectivity. In addition, the catalyst also showed the high carbon diox-
ide selectivity and the lowest methane selectivity. The results indicate that the catalyst promotes
methane reforming reaction. The highest activity in the 15 wt% Ni–5 wt% Ce/LaAlO3 was attributed
to the proper cerium loading amount. Moreover, the lowest metal crystal size and rise in active site
were found to have an effect on catalytic activity and hydrogen selectivity. The 15 wt% Ni–5 wt%
Ce/LaAlO3 catalyst exhibited excellent performance with respect to hydrogen production at reaction
ꢀ
temperature of 450 C, at atmospheric pressure, 20 wt% glycerol solution and GHSV = 6,000 mL/
g-cat·hr.
Keywords: Glycerol, Hydrogen Production, Nickel, Cerium, Steam Reforming.
1. INTRODUCTION
vector, thus gaining more importance with the subsequent
development of fuel cells and the rising energy demands.2
Steam reforming of glycerol theoretically generates
only carbon dioxide and hydrogen, according to reaction
Eq. (1).
Recently, extensive use of fossil fuels has led to emer-
gence problems: like depletion of petroleum reserves,
global warming, acid rain, etc. Consequently, the renew-
able and environmental resource, Bio-diesel has attracted
considerable interest worldwide.1 Bio-diesel can be pro-
duced by the trans-esterification reaction of triglyceride
with methanol; by-product 10 wt% glycerol. It is pro-
posed that an increase in the production of Bio-diesel from
renewable raw materials will result in an overabundance
of glycerol in the market, which can possibly be supplied
at low cost. Many investigators have focused on steam
reforming of glycerol as a hydrogen production process.
The hydrogen is considered as the future clean energy
C3H8O3 +3H2O ↔ 3CO2 +7H2
(1)
Reaction in Eq. (1) may be viewed as the combination
of the glycerol decomposition (Eq. (2)) and water-gas-shift
reaction (Eq. (3)).
C3H8O3 ↔ 3CO+4H2
CO+H2O ↔ CO2 +H2
(2)
(3)
The noble metals (Rh, Pt) were found to have promising
catalytic performance in terms of conversion and selectiv-
ity for steam reforming of glycerol.3 However, high cost
∗Authors to whom correspondence should be addressed.
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doi:10.1166/jnn.2015.8345

Kim et al.
Steam Reforming of Glycerol Over Nano Size Ni–Ce/LaAlO3 Catalysts
and low availability of these metals have led to a search
for alternative metals, which are cheaper and more readily
available. For that reason, nickel based catalysts are widely
used due to their high activity at much lower cost.
However, the main problem encountered was the forma-
tion of carbon deposits and deactivation by of the catalyst
due to Ni sintering. It is hence highly desirable to develop
catalyst that is inexpensive, active and stable during the
glycerol reforming reaction. According to the literature,
Ce and La have been described to inhibit the growth of
metal particles and favor the removal of carbon deposits
from metal surface.4
The aim of the present work was to investigate the
hydrogen production in steam reforming of glycerol over
Ni based catalysts. The Ni–Ce and Ni–La catalysts sup-
ported on LaAlO3 perovskite employed Ce and La loading
amount 5 wt%, respectively. Catalyst of Ni supported on
LaAlO3 perovskite was also prepared for a comparative
analysis. The physicochemical properties of both the cata-
lysts were characterized and correlated with their catalytic
performance.
located inside an electric oven of low thermal inertia. The
temperature inside the reactor is measured by means of a
thermocouple, located inside the catalytic bed. Typically,
1 g of catalyst was loaded in the reactor and an aque-
ous solution containing glycerol was fed into the reactor
by an HPLC (high-pressure liquid chromatography) pump.
The product stream was separated into a liquid phase and
a gas phase in a condenser connected to the reactor out-
let. The gaseous products were analyzed on-line by gas
chromatography using a Shimatzu-14B model chromato-
graph equipped with a TCD (thermal conductivity detec-
tor). Finally H2, CH4, CO and CO2 were separated in a
Hayesep D column (ꢁ1/8ꢁꢁ × 7 m, 100/120 mesh) using
Ar as the carrier gas.
3. RESULTS AND DISCUSSION
3.1. Characterization of Catalysts
The XRD measurements of prepared LaAlO3 supported Ni
catalyst and Cerium, Lanthanum promoted Ni/LaAlO3 cat-
alysts are shown in Figures 1(A) and (B), respectively. All
the catalysts exhibit strong diffraction peaks that appear
around 2ꢂꢀ = 33ꢀ, corresponding to perovskite structures.
For the calcined catalysts (Fig. 1(A)), the diffraction
lines of nickel phases were presented at 2ꢂꢀ = 37ꢃ2ꢀ, 43.4ꢀ
and 63ꢀ for NiO in all catalysts.6 Figure 1(B) shows the
2. EXPERIMENTAL DETAILS
2.1. Catalyst Preparation
The used perovskite was in the form of ABO3, with La in
the A sites and Al in the B sites. This LaAlO3 perovskite
ꢀ
550 C for 2 hours. The diffraction lines show that NiO
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was prepared by means of the citric acid-method, in which
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citric acid was added to the sol–gel method.5 The mix-
Copyright: Amerꢀican Scientific Publishers
ture was obtained in the form of a gel, dꢀried at 110 C
overnight in an oven and calcined at 400 C for 2 h and
ꢀ
850 C for 11 h in air.
The catalysts of 15Ni/LaAlO3, 15Ni–5Ce/La–AlO3 and
15Ni–5La/LaAlO3 were prepared by means of a precip-
itation method using Na2CO3, in which the Ni loading
amount was 15 wt% and the Ce, La loading amounts were
5 wt%, respectively.
The precipitate was stirred at 80 ꢀC for 1 h, then repeat-
edly washed and filtereꢀd with distilled water and finally
dried overnight at 110 C in oven. Subsequently, all the
ꢀ
synthesized catalysts were calcined at 500 C for 5 h.
2.2. Catalysts Characterization and Reaction Test
Catalysts were characterized by X-ray diffraction (XRD)
instrument (Rigaku, Japan, DMAX100, Cu-Kꢀ, Ni filter),
Scanning electron microscope (SEM) instrument (JEOL,
JSM-5400A), Transmission electron microscope (TEM)
instrument (JEOL, JEN-2000FXII), H2-chemisorption and
Temperature-programmed reduction (TPR) instrument
(Chemisorption Analyzer, BEL-CAT, BEL, Japan).
The steam reforming of glycerol was carried out under
atmospheric pressure in a fixed-bed reactor. Prior to the
reaction, the catalyst was reduced in situ at 550 ꢀC for 2 h
in a mixture of H2 (3 ml/min) and Ar (27 ml/min). The
reactor consisted of a stainless steel (i.d. = 16 mm), (L =
400 mm) tubular reactor to hold the catalyst and it was
Figure 1. XRD patterns of calcined catalysts (A) and reduced catalysts
(B): (a) Ni/LaAlO3, (b) Ni–Ce/LaAlO3, (c) Ni–La/LaAlO3.
J. Nanosci. Nanotechnol. 15, 522–526, 2015
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Steam Reforming of Glycerol Over Nano Size Ni–Ce/LaAlO3 Catalysts
Kim et al.
Table I. Physicochemical properties of different catalysts.
hindering the access of the reacting gasses to the active
surface.8
Catalyst
Ni size (nm)a
Metal dispersion (%)
The TPR profiles of catalysts are shown in Figure 4
the Ni/LaAlO3 catalyst presented a reduction peak at low
temperature (345 ꢀC), which can be attributed to the reduc-
tion of NiO species on the surface of the support. The
reduction peaks of Ni–Ce/LaAlO3 and Ni–La/LaAlO3 cat-
alysts are evident at 360 and 385 ꢀC,9ꢄ10 respectively.
An evident shift in the reduction peaks of Ni species to
high temperature can be seen in the profile, suggesting
that the introduction of Ce can improve the interaction
between Ni species and catalyst environment.7 The cata-
lysts promoted with Ceri um exhibited less reducible activ-
ity than the Ni/LaAlO3 catalyst attributable to the increase
in the metal-support interaction and better nickel disper-
sion. Consequently, it can be concluded that Ce species
obviously reduces the size of Ni particles and improves
the interaction between the Ni species and environment.
Ni/LaAlO3
Ni–Ce/LaAlO3
Ni–La/LaAlO3
33
26
31
2.3
3.2
1.3
Notes: aSized of Ni particles on catalysts determined by Scherrer equation.
was completely reduced to Ni, at 2ꢂꢀ = 44ꢃ5ꢀ and 51.8ꢀ.
The crystallite sizes of Ni in the catalysts were determined
using Scherrer equation. It was evident that the Ni/LaAlO3
catalyst has relatively large Ni crystallites (33 nm), while
they were significantly smaller in modified catalysts.
Table I shows the physicochemical properties of Ni
catalysts. Ni Size of Ni/LaAlO3, Ni–Ce/LaAlO3 and Ni–
La/LaAlO3 was measured as 33, 26 and 31 nm, respec-
tively. The Ni–Ce/LaAlO3 catalyst exhibited smallest Ni
size; this result was in agreement with the conclusion
revealed by SEM micrograph (Fig. 2).7 Also, Table I
shows the metal dispersion of catalysts measured using
H2-chemisorption. Metal dispersion was found to be 2.3,
3.2 and 1.3% for Ni/LaAlO3, Ni–Ce/LaAlO3 and Ni–
La/LaAlO3, respectively. Therefore, we concluded that
more active sites were present on the Ni-Ce/LaAlO3 cat-
alyst surface than on the other catalysts. Figure 2 shows
the SEM images of the calcined and used catalysts. In
all the SEM images of catalysts, the metal was observed
to be supported on the perovskite support and the metal
particles were dispersed into sized particles. Figure 3
shows the TEM images of the calcined and used cat-
alysts. After reaction, Ni/LaAlO3 catalyst exhibited two
kinds of carbon deposits whisker-type and encapsulating
carbon. However, Ni–Ce/LaAlO3 catalysts had deposits of
whisker-type carbons. According to the literature, whisker-
like carbon possess essentially no or little toxicity, but
encapsulating carbon deposits have high toxicity, which
could progressively encapsulate the Ni particles, thus
3.2. Catalytic Activity
Table II summarizes the extent of glycerol conversion
and product selectivity of glycerol steam reforming on
Ni/LaAlO3, Ni–Ce/LaAlO3 and Ni–LaAlO3 catalysts at
ꢀ
conditions of 20 wt% glycerol solution, 450 C reaction
temperature and GHSV = 6,000 mL/g-cat·ht. When com-
pared to the Ni/LaAlO3 catalyst, both La and Ce modified
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Ni/LaAlO3 catalysts achieved higher glycerol conversion.
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Regarding gas products distribution, lower methane selec-
Copyright: American Scientific Publishers
tivity was observed for La, Ce modified Ni/LaAlO3 cat-
alysts. This observation is indicative of higher activity in
the methane steam reforming.
The Ni–Ce/LaAlO3 catalyst demonstrated the highest
conversion of glycerol and H2 selectivity than other cat-
alysts. Furthermore, because of smaller Ni particle size,
the catalyst exhibited good catalytic performance. It is
also indicative from the study that Ni particle size and
Figure 2. SEM images of Ni/LaAlO3, Ni–Ce/LaAlO3 and Ni–La/LaAlO3 catalysts. (1) Ni/LaAlO3 (a) before and (aꢁ) after reaction, (2) Ni–Ce/LaAlO3
(b) before and (bꢁ) after reaction, (3) Ni–La/LaAlO3 (c) before and (cꢁ) after reaction.
524
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Kim et al.
Steam Reforming of Glycerol Over Nano Size Ni–Ce/LaAlO3 Catalysts
Figure 3. TEM images of Ni/LaAlO3, Ni–Ce/LaAlO3 and Ni–La/LaAlO3 catalysts. (1) Ni/LaAlO3 (a) before and (aꢁ) after reaction, (2) Ni–Ce/LaAlO3
(b) before and (bꢁ) after reaction, (3) Ni–La/LaAlO3 (c) before and (cꢁ) after reaction.
4. CONCLUSION
The performance of Ni/LaAlO3 catalysts promoted with
Ce, La for glycerol steam reforming was investigated.
The Ce modified nickel perovskite catalyzed the forma-
tion of small Ni particle size as confirmed by XRD and
SEM analyses. The Ni–Ce/LaAlO3 catalyst for the glyc-
erol steam reforming at 450 ꢀC exhibited the best result. In
addition, the Ni–Ce/LaAlO3 catalyst led to higher water–
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gas shift reaction (CO + H O ↔ CO + H ) and methane
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2
2
2
Copyright: American Scientific Publishers
steam reforming reaction (CH4 +H2O ↔ CO+3H2). Fur-
thermore, the consequence of interaction between the Ni
particles and support might well-explain the beneficial
influence of the catalytic activity for glycerol reforming
reactions. Thus, it is concluded that Ni particle size and
the metal dispersion served as important factors in deter-
mining the catalytic activity for hydrogen production by
steam reforming of glycerol.
Figure 4. TPR analysis of catalysts : (a) Ni/LaAlO3, (b)Ni-Ce/LaAlO3,
(c) Ni–La/LaAlO3 catalysts.
Acknowledgment: This work was supported by the
Priority Research Centers Program through the National
Research Foundation of Korea (NRF) funded by the
Ministry of Educations, Science and Technology (2009-
0094055), BK21 program from the Ministry of Education,
Science and Technology resources Development, Republic
of Korea and supported partly by the Ministry of Knowl-
edge Economy of Korea and the Korea Institute of Science
and Technology (KIST).
Metal dispersion had an effect on the catalytic per-
formance of the catalyst. The Ni–Ce/LaAlO3 catalyst
exhibited high carbon dioxide selectivity and lower car-
bon monoxide and methane selectivity. This indicates
that the catalyst favored water–gas shift reaction (CO +
H2O ↔ CO2 +H2) and methane steam reforming reaction
(CH4 +H2O ↔ CO+3H2).
Table II. Glycerol conversion and gas product selectivity in the
presence of different catalysts (20 wt% glycerol, 450 ꢀC, GHSV =
6,000 mL/g-cat·hr).
References and Notes
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C1 compound
selectivity (%)
Conversion
(%)
H2 Selectivity
(%)
Catalysts
CO
CH4
CO2
Ni/LaAlO3
Ni–Ce/LaAlO3
Ni–La/LaAlO3
87ꢃ8
94ꢃ6
89ꢃ2
60ꢃ8
63ꢃ4
61ꢃ1
0ꢃ2
0ꢃ5
0ꢃ4
7ꢃ4
2ꢃ9
2ꢃ2
92ꢃ4
96ꢃ6
97ꢃ4
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525

Steam Reforming of Glycerol Over Nano Size Ni–Ce/LaAlO3 Catalysts
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Received: 18 March 2013. Accepted: 18 April 2013.
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