Effect of CaO Addition on Nickel Catalysts Supported on Alumina for Glycerol Steam Reforming

Article abstract of DOI:10.1007/s10562-019-02792-w

Abstract: Hydrogen production by glycerol steam reforming is an attractive alternative, as it represents the conversion of a waste in a high-added value product. In this work, three catalysts were synthesized by wet impregnation of nickel precursor in different supports: γ-Al₂O₃ prepared by boehmite calcination, α-Al₂O₃ and 15 wt% CaO-γ-Al₂O₃ prepared by wet impregnation of calcium oxide precursor in γ-Al₂O₃. A commercial catalyst for methane steam reforming was also evaluated. Catalytic tests were performed at 500?°C, glycerol feed of 20% v/v and GHSV of 200,000?h^?1. The calcium oxide incorporation reduced the formation of nickel aluminate phase (NiAl₂O₄) and the amount and strength of catalyst acidity, while increasing the amount and strength of basic sites. Furthermore, it was the only catalyst that has not presented deactivation in 30?h of reaction, showing the highest glycerol conversion and hydrogen yield after 24?h of reaction. Ni/γ-Al₂O₃ and Ni/α-Al₂O₃ presented a severe deactivation, which was associated with coke formation. The synthesized catalysts presented better catalytic performance for glycerol steam reforming in comparison with commercial catalyst, in terms of higher glycerol conversion, glycerol conversion to gas and hydrogen yield. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-019-02792-w

Catalysis Letters
https://doi.org/10.1007/s10562-019-02792-w
Efect of CaO Addition on Nickel Catalysts Supported on Alumina
for Glycerol Steam Reforming
João Paulo da S. Q. Menezes1 · Flávia C. Jácome1 · Robinson L. Manfro1 · Mariana M. V. M. Souza1
Received: 4 February 2019 / Accepted: 18 April 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Hydrogen production by glycerol steam reforming is an attractive alternative, as it represents the conversion of a waste in a
high-added value product. In this work, three catalysts were synthesized by wet impregnation of nickel precursor in diferent
supports: γ-Al2O3 prepared by boehmite calcination, α-Al2O3 and 15 wt% CaO-γ-Al2O3 prepared by wet impregnation of
calcium oxide precursor in γ-Al2O3. A commercial catalyst for methane steam reforming was also evaluated. Catalytic tests
were performed at 500 °C, glycerol feed of 20% v/v and GHSV of 200,000 h−1. The calcium oxide incorporation reduced the
formation of nickel aluminate phase (NiAl2O4) and the amount and strength of catalyst acidity, while increasing the amount
and strength of basic sites. Furthermore, it was the only catalyst that has not presented deactivation in 30 h of reaction,
showing the highest glycerol conversion and hydrogen yield after 24 h of reaction. Ni/γ-Al2O3 and Ni/α-Al2O3 presented a
severe deactivation, which was associated with coke formation. The synthesized catalysts presented better catalytic perfor-
mance for glycerol steam reforming in comparison with commercial catalyst, in terms of higher glycerol conversion, glycerol
conversion to gas and hydrogen yield.
* Mariana M. V. M. Souza
mmattos@eq.ufrj.br
1
Centro de Tecnologia, Escola de Química- Universidade
Federal do Rio de Janeiro (UFRJ), Bloco E, sala 206,
Rio de Janeiro, RJ CEP 21941-909, Brazil
Vol.:(0123456789)
1 3

J. P. S. Q. Menezes et al.
Graphical Abstract
Keywords Glycerol · Reforming · Hydrogen · Nickel · Alumina · Calcium oxide
glycerol has lots of impurities like the catalyst, alcohols,
fatty acids, salts and water, thus its direct use in usual appli-
cations, as pharmaceutical, cleaning and food industries,
which require a high level of purity, is impracticable. There-
fore, developing a new route for glycerol conversion into
high-added value products would not only solve the problem
of glycerol disposal, but would also contribute for turning
biodiesel production more competitive towards diesel pro-
duction. In this context, the hydrogen production by glycerol
steam reforming must be highlighted.
1 Introduction
Although fossil fuels played an essential role in developing
many sectors of economy, these resources are non-renewable
and its extensive use is related to pollutant gases emission,
especially gases associated with global warming. Thus, con-
sidering the increasing concern about environmental issues,
there is an urgent demand in gradually incorporate biofuels,
as biodiesel and ethanol, in current energy supply matrix [1].
Biodiesel is mostly produced by oil/fat transesterifcation
and Brazil is one of the pioneers in its production and use.
Currently, ANP (Brazilian Agency for Petroleum, Natural
Gas and Biofuels) stipulates the addition of 9% biodiesel in
diesel, which has grown biodiesel production in the country.
However, biodiesel production by transesterifcation gener-
ates glycerol as a byproduct, as 100 kg of glycerol is pro-
duced for each ton of biodiesel produced [2]. This produced
Hydrogen is the most abundant element in the world and
its use in chemical industries is indispensable. For instance,
hydrogen is employed for ammonia and methanol produc-
tion, for oil refning in hydrotreatment and hydrocracking
processes, and for Fischer–Tropsch synthesis. Furthermore,
hydrogen is considered a clean fuel, as its application in
fuel cells does not release signifcant amount of pollutant
1 3

Efect of CaO Addition on Nickel Catalysts Supported on Alumina for Glycerol Steam Reforming
gases. However, most of hydrogen production currently is
through natural gas (48%), heavy oils (30%) and coal (17%).
Only a small part of the production is provided by water
electrolysis (4%) or by biomass derivatives (1%) [3]. The
study of glycerol conversion into hydrogen also intends to
increase the participation of green resources in the hydrogen
production matrix.
reported that addition of CaO–MgO to alumina not only
decreased coke formation but also modifed the nature of
carbon deposits. Furthermore, the addition of basic promot-
ers as Cs, Ca, Mg, Sr and Ba would enhance shift reaction,
because CO adsorption and H2O dissociation are promoted
by weak basic centers, and would suppress methane forma-
tion, as alkali promoters block and modify step and defect
sites that are responsible for methane formation [15].
In this work, nickel catalysts with diferent alumina sup-
ports were evaluated in glycerol steam reforming. The nov-
elty of the paper lies on the modifcation of nickel supported
on alumina with calcium oxide, in order to reduce catalyst
acidity and coke formation.
In glycerol steam reforming, synthesis gas (hydrogen
and carbon monoxide) is produced by reaction of glycerol
with steam, at atmospheric pressure and temperatures above
500 °C. CO is converted by shift reaction (Eq. 1) produc-
ing more hydrogen and CO2. The global reforming reaction
(Eq. 2) is endothermic [4].
CO + H2O ↔ CO2 + H2
(1)
2 Experimental
C3H8O3 + 3H2O ↔ 7H2 + 3CO2
(2)
Hydrogen yield for glycerol steam reforming is higher
than for methane steam reforming; for one mole of glycerol
feed, seven hydrogen moles can be produced, while only
three moles of hydrogen by one mole feed of methane. Fur-
thermore, methane reforming represents a fuel consump-
tion for producing hydrogen, which is not true for glycerol
reforming [5]. Beyond that, methane reforming takes place
at 700–1000 °C, while glycerol steam reforming takes place
at lower temperatures.
2.1 Catalyst Preparation
Three catalysts were synthesized by wet impregnation of
20 wt% nickel precursor [Ni(NO3)2·6H2O - Vetec] on dif-
ferent supports: γ-Al2O3 synthesized by boehmite (Sasol)
calcination at 500 °C in air fow (60 mL min−1), commer-
cial α-Al2O3 and 15 wt% CaO–Al2O3 synthesized by wet
impregnation of calcium oxide precursor [Ca(NO3)2·4H2O]
on γ-Al2O3 support followed by calcination at 500 °C with
air (60 mL min−1). The catalysts were dried at 100 °C over-
night and calcined at 500 °C with air (60 mL min−1) for
converting nickel nitrate into nickel oxide. The catalysts will
be referred to as Ni–γAl, Ni–αAl and NiCaAl, respectively.
A commercial catalyst used for methane steam reforming
was also evaluated for comparison and will be referred to as
NiCaAlcom.
Developing an adequate catalyst for glycerol steam
reforming with good properties as high dispersion of active
phase, stability, low coke and byproduct formation and high
hydrogen yield, is a subject that needs investigation and fur-
ther improvements. A good catalyst for glycerol reforming
has to be active for the cleavage of C–C bonds and water gas
shift reaction, while inhibiting the cleavage of C–O bonds
and methanation reaction [6–9]. Noble metal catalysts are
more active for reforming reaction and resistant to deactiva-
tion by coke deposition. However, considering the high costs
of these catalysts, it is more economical the development
of catalysts based on non-noble metals, as nickel or cobalt,
which are also active for C–C bond cleavage [8].
2.2 Catalyst Characterization
The chemical composition of the catalysts was veri-
fed by X-ray fuorescence (XRF) with a Rigaku Primini
spectrometer.
γ-Alumina is the most employed support in steam reform-
ing catalysts, because of its high surface area that leads to a
good dispersion of the active phase. However, many authors
have reported high coke formation on γ-alumina catalysts
that causes catalyst deactivation. Silva et al. [5] suggested
that coke formation occurs in γ-alumina acid sites due to
dehydration, cracking and polymerization reactions. CaO
has been employed as a promoter for Ni/Al2O3 catalysts used
in reforming of methane, increasing conversion [10] and
decreasing coke deposition [11, 12]. However, the role of
CaO during glycerol steam reforming is not yet well studied;
Huang et al. [13] verifed that simultaneous modifcation of
Ni/Al2O3 with Mo, La, Ca and Mg improved the catalytic
stability for this reaction, while Charisiou et al. [14] recently
N2 adsorption–desorption experiment was carried out at
− 196 °C using a Micromeritics TriStar 3000 equipment.
Specifc area of the catalysts was calculated by BET method
and specifc pore volume was determined by BJH method.
The samples were outgassed and dried under vacuum for
24 h at 300 °C before the analysis.
X-ray powder difraction (XRD) was used for determining
crystalline structures of the catalysts and for nickel aver-
age crystallite size calculation before and after reaction by
Scherrer equation, using the peak at 44.5º, the most intense
Ni peak. The equipment used was a Rigaku Minifex II
X-ray difractometer coupled with a graphite monochroma-
tor using CuKα radiation (30 kV and 15 mA). The analysis
were conducted with a step of 0.05°, counting time of 1 s
1 3

J. P. S. Q. Menezes et al.
for step and over a 2θ range of 5–90°. The reduced catalysts
were analyzed after ex-situ reduction at the same conditions
used in catalytic tests and spent catalysts were analyzed after
reaction. Ni dispersion (D) of the catalysts was calculated
according to Anderson [16] (Eq. 3).
Temperature-programmed desorption of ammonia (TPD-
NH3) was used for catalyst acidity determination. Firstly,
the reduction of the catalysts was performed at 800 °C for
30 min with a heating rate of 10 °C min−1 and a fow rate of
30 mL min−1 of a 1.8% H2/Ar mixture. After reduction, the
adsorption of ammonia was done at 70 °C for 30 min using
a mixture of 4% NH3/He, and the removal of physisorbed
ammonia was performed with He fow of 30 mL min−1.
The ammonia desorption was conducted with a rate of
20 °C min−1 up to 800 °C for 30 min. Ammonia consump-
tion (ratio m/z=15) was registered by a Pfeifer QMG-220
mass spectrometer.
6.Vm
D =
(3)
d.Am
where Vm is the Ni atomic volume (0.0109 nm3), d is the
crystallite size (nm) and Am is the surface area of a single
nickel atom (0.0649 nm2).
Ni dispersion was also calculated by H2 chemisorp-
tion, using frontal method. The analysis was conducted in
an apparatus equipped with TCD for monitoring hydro-
gen adsorption. Prior to analysis, the catalyst (50 mg)
was reduced at 800 °C with 30 mL min−1 of H2 and 60
mL min−1 of N2 fow, the same reduction condition used
in catalytic test. The catalyst was heated up to 800 °C with
30mL min−1 of a mixture 1.8% H2/Ar, then a fast cooling
was conducted up to 200 °C, by opening the oven, in order
to detect a peak of hydrogen consumption for chemisorption
on TCD signal. At 200 °C, 30mL min−1 of argon fow was
passed through the reactor for 30 min, then a fast heating
rate of 120 °C min−1 was performed up to 800 °C, in order
to observe the desorption of chemisorbed hydrogen. Des-
orption peak was used for dispersion calculation and it was
assumed that reduction degree of the catalysts prior to analy-
sis was 100%, as they were reduced in a condition richer
in hydrogen than TPR condition. Hydrogen physisorption
was not considered, as temperature employed on analysis
was high enough to guarantee only hydrogen chemisorption.
Dispersion (DC) was calculated according to Bartholomew
et al. [17] (Eq. 4).
Temperature-programmed desorption of CO2 (TPD-CO2)
was performed for calculating basicity of the catalysts. Prior
to analysis, 150 mg of the samples were treated at 150 °C
with 30 mL min−1 of Argon. After that, the adsorption of
CO2 was realized at 25 °C using a mixture 10% CO2/He,
and the removal of physisorbed CO2 was conducted with He
fow of 30 mL min−1 for 1 h. CO2 desorption was conducted
with a rate of 20 °C min−1 up to 1000 °C and the signal was
registered with a TCD.
For quantifying coke deposition in spent catalysts, ther-
mogravimetric analysis (TGA) and differential thermal
analysis (DTA) with a TA SDT Q600 equipment were per-
formed. For analysis, masses between 3 and 10 mg were
weighted on the equipment itself and the analysis was car-
ried out up to 1000 °C with a rate of 10 °C min−1 under a
synthetic air fow of 50 mL min−1.
2.3 Catalytic Tests
Before the reaction beginning, 150 mg of catalysts were
mixed with 750 mg of silicon carbide, which corresponds
to a proportion of 1:5 (catalyst/silicon carbide). The catalysts
were reduced in situ under 30% H2/N2 fow (90 mL min−1)
up to 800 °C at a heating rate of 10 °C min−1 and remaining
at this temperature for 30 min.
1.17X
DC(%) =
(4)
W.f
where X is the H2 uptake in µmoles per gram of the cata-
lyst, W is the weight percentage of nickel and f is the frac-
tion of nickel reduced to the metal, considered 100% as no
nickel oxide species were observed in XRD analysis after
reduction.
The reactions were conducted in a fxed bed quartz reac-
tor, at 500 °C, atmospheric pressure and gas hourly space
velocity (GHSV) of 200,000 h−1. The feed consists of an
aqueous solution of glycerol (20% v/v), which represents a
water:glycerol molar ratio of 16.2, and was injected to the
reactor by a pump (Eldex 1SAM), with fow rate of 0.106
mL min−1. The vaporization of the solution was carried out
in a vaporizer at 225 °C under He fow as a diluent; the He
fow was calculated for being 20% v/v of the total gas fow
(250 mL min−1); line and valves were also kept at 225 °C
for avoiding glycerol condensation.
Temperature-programmed reduction (TPR) was used for
determination of reduction profle and reducibility degree
of the catalysts. The analysis was performed in a conven-
tional apparatus equipped with a thermal conductivity
detector (TCD). Prior to analysis, approximately 50 mg of
the samples were treated at 150 °C under 30 mL min−1 of
argon. After the pretreatment, the reduction was conducted
up to 1000 °C with a heating rate of 10 °C min−1 under 30
mL min−1 of a mixture 1.8% H2/Ar. Reduction degree was
calculated as the ratio between hydrogen consumption meas-
ured by area under TPR profle and theoretical hydrogen
consumption assuming that all nickel species were reduced.
The separation of liquid and gas phases of the product
was conducted in a heat exchanger at 10 °C. The gas phase
was analyzed online by a gas chromatograph (GC) Shi-
madzu GC-2014 equipped with two columns (RT-QPLOT
and Carboxen 1010) and thermal conductivity (TCD) and
1 3

Efect of CaO Addition on Nickel Catalysts Supported on Alumina for Glycerol Steam Reforming
fame ionization (FID) detectors. The liquid phase was ana-
lyzed by high-performance liquid chromatography (HPLC)
Shimadzu Prominence with a Bio-Rad Aminex HPX-87H
column, utilizing 0.01 M H2SO4 as eluent at 0.6 mL min−1,
and with UV and refractive index detectors.
The catalyst performance was evaluated according to the
equations described in Menezes et al. [18].
3 Results
3.1 Catalyst Characterization
The compositions of the calcined catalysts and of the com-
mercial catalyst are presented in Table 1. The measured
composition is similar to the desired nominal composition.
The commercial catalyst also presents small amounts of
magnesium and potassium oxides.
BET surface areas and pore volumes are also presented in
Table 1. Ni–αAl catalyst presented the lowest BET surface
area, which is in accordance with literature. Pompeo et al.
[19] obtained a surface area of 10 m2 g−1 for a nickel cata-
lyst supported on α-alumina. Ni–γAl presented the highest
BET surface area and the incorporation of calcium oxide
reduced BET surface area, as also observed by Dias and
Assaf [10]. Adsorption–desorption isotherms of nitrogen
for Ni–αAl exhibited the type II pattern, which is typical
for non-porous material; on the other hand, all the other
catalysts exhibited the type IV pattern, which are typical for
mesoporous materials [20].
The XRD patterns of the support, calcined, reduced and
spent catalysts are presented in Fig. 1. In calcined catalysts,
peaks related to NiO at 2θ equal to 37.3º, 43.6º and 63.3º
(JCPDS 47-1049) are observed and in reduced catalysts,
peaks at 44.6º, 51.8º and 76.4º (JCPDS 04-0850) related to
Ni are noticed, which proves that the reduction is efcient
in converting NiO into Ni species.
A broad peak at 26°, which is related to coke deposits
over catalysts throughout reaction, was observed mainly on
Ni–αAl and Ni–γAl catalysts. Silicon carbide peaks were
observed because its difculty of separation from spent cata-
lysts. Furthermore, the peaks related to nickel oxide are not
observed on the spent catalysts, which indicates that reduced
Ni phase is stable under reaction conditions, suggesting a
good interaction between nickel phase and the supports.
Sharp peaks at 25.6º, 35.2º, 43.3º, 37.9º, 55.6º, 57.3º,
61.4º and 66.4º (JCPDS 10-173) correspond to α-alumina
and are observed in all XRD profles of Ni–αAl catalyst,
presented in Fig. 1a. In Ni–γAl profles, presented in Fig. 1b,
broad peaks related to γ-alumina are observed; furthermore
peaks related to spinel phase (NiAl2O4) at 37.0o, 45.0o and
65.6o (JCPDS 10-339) are also observed, and its formation
is related to the strong interaction between nickel oxide and
1 3

J. P. S. Q. Menezes et al.
(b)
(a)
(d)
(c)
Fig. 1 XRD patterns of Ni–αAl a, Ni–γAl b, NiCaAl c and NiCaAlcom d catalysts
alumina. Spinel phase was not observed on NiCaAl catalyst
profles, showing that calcium oxide incorporation prevents
the interaction between nickel and alumina, as observed by
Wang and Lu [21] for Ni/CeO2/Al2O3 catalysts.
XRD profles of the reduced and spent catalysts and are
shown in Table 1, which also shows the nickel dispersion
determined by Anderson correlation. Ni–αAl presented
the biggest nickel crystallite size (22.9 nm) and the lowest
dispersion (4.4%) among the catalysts, which is in accord-
ance with its lowest BET surface area (Table 1). More-
over, the addition of calcium oxide on alumina support
increased the nickel crystallite size and decreased notice-
ably the dispersion in comparison with the catalyst without
calcium oxide. This result agrees with the decreasing on
BET surface area from 145 to 65 m2 g−1 with calcium
oxide incorporation, which may cover and block alumina
pores. Nickel dispersion is higher for NiCaAl than for
NiCaAlcom.
Peaks related to calcium oxide at 2θ equal to 32.0, 37.4
and 53.9o (JCPDS 48-1467) are shown on XRD of NiCaAl
and NiCaAlcom catalysts, presented in Fig. 1c, d respec-
tively; however, their intensities are higher on NiCaAlcom,
which indicates that calcium oxide is less dispersed on this
catalyst in comparison with NiCaAl. Furthermore, peaks
related to a mixed oxide (CaO)x(Al2O3)11 at 2θ equal to 7.8º,
15.8º, 30.3º and 66.8º (JCPDS 41-0358) are observed on
NiCaAlcom catalyst. It is possible to observe that CaO peaks
disappear after reaction, which may be related to its conver-
sion to Ca(OH)2 and/or CaCO3, which may be well dispersed
on alumina surface, as observed by other authors [22, 23].
The mean nickel crystallite sizes were determined
before and after reaction using nickel peak at 44.5º on
Considering the analysis error, it was not possible to
observe signifcant diference between nickel crystallite sizes
before and after reaction, which suggests that sintering pro-
cess is not signifcant for these catalysts. NiCaAl catalyst
1 3

Efect of CaO Addition on Nickel Catalysts Supported on Alumina for Glycerol Steam Reforming
presented the highest increase in crystallite size, from 15.3
to 16.8 nm, which is irrelevant.
reduction peaks between 400 and 690 °C, and NiO incorpo-
rated on alumina for aluminate spinel phase formation, with
reduction peak above 700 °C. Thus, it is possible to infer the
existence of NiAl2O4 species on Ni–γAl catalyst, which is in
agreement with XRD analysis.
Ni dispersion was also measured by hydrogen chemisorp-
tion and the results are presented in Table 1. Comparing with
the results obtained from XRD, it is possible to observe that
the values are much lower, which it is expected as XRD
is a bulk technique and H2 chemisorption quantifes only
surface nickel species. However, both results followed the
same tendency, as Ni–αAl has presented the lowest disper-
sion (0.6%) and Ni–γAl has presented the highest dispersion
(1.3%). These results are in accordance with other authors
in the literature. Cheng et al. [24] obtained a dispersion of
0.74% for 5 wt% Co–10 wt% Ni/Al2O3 by hydrogen chem-
isorption and this low metal dispersion was attributed to
the high metal loading (15 wt%) employed. Jing et al. [25]
reported values of 0.84–1.07% for Ni dispersion on 15%Ni/
CaO–Al2O3 catalysts prepared by coprecipitation, with dif-
ferent Ca/Al ratios.
Reduction profile of NiCaAl presented one peak at
335 °C, related to bulk NiO, four peaks between 400 and
800 °C, which are associated with NiO interacting with
Al2O3 and CaO in diferent levels of interaction, and one
peak located at 895 °C, related to nickel aluminate reduc-
tion. Comparing NiCaAl and Ni–γAl TPR profles, it is pos-
sible to observe a decrease of nickel aluminate formation,
because the peak located above 700 °C has a higher area
for Ni–γAl catalyst. This result corroborates the decrease
of nickel dispersion by calcium oxide incorporation, caused
by reduction of interaction between nickel species and the
support. The formation of nickel species with low interac-
tion with alumina when calcium is added to the support was
also observed by Dias and Assaf [10] and Ashok et al. [22].
Reduction profile of NiCaAlcom catalyst presented
three overlapping peaks in the range of 500–950 °C, the
frst located at 600 °C, the second at 678 °C and the last
at 788 °C. There is also a small peak located at 386 °C,
however the major reduction of NiO species occurs in tem-
peratures above 400 °C, which indicates a stronger interac-
tion between nickel oxide and the support for NiCaAlcom
catalyst.
Figure 2 shows the TPR analysis of the catalysts. Ni–γAl
and Ni–αAl catalysts presented only one reduction peak cen-
tered at 800 °C and 440 °C, respectively. Rynkowski et al.
[26] reported the existence of three diferent nickel species
in a catalyst supported on alumina: bulk NiO, with reduc-
tion peak below 400 °C, NiO interacting with alumina, with
440°C
The reduction degrees of the catalysts are shown in
Table 2. The lowest reduction degree (54%) was observed
for Ni–αAl catalyst, which is associated with its biggest
Ni crystallite size, because inner nickel oxide particles are
more inaccessible for hydrogen molecules, so the reduction
is limited.
590°C
Ni-αAl
800°C
Ni-γAl
685°C
765°C
788°C
436°C
640°C
678°C
600°C
335°C
895°C
NiCaAl
TPD-NH3 profles of the catalysts are shown in Fig. 3
and calculated acidity is presented in Table 2. The litera-
ture classifes peaks below 400 °C as weak acid sites, while
above this temperature the sites are classifed as strong acid
sites [27]. Thus, all the catalysts have presented mainly weak
acid sites. Ni–αAl catalyst showed no NH3 desorption peaks,
therefore its acidity is zero, which was expected because
of its low BET area. Ni–γAl and NiCaAl presented similar
profles, with peaks centered at 186 °C and 163 °C, respec-
tively. However, the acidity per area is higher for Ni–γAl
386°C
NiCaAl com
100 200 300 400 500 600 700 800 900 1000
Temperature (°C)
Fig. 2 TPR profles of the calcined catalysts
Table 2 Hydrogen uptake and reduction degree (RD) of NiO calculated from TPR results, amount of desorbed NH3 per mass and per BET area
calculated from TPD-NH3 results and amount of desorbed CO2 from TPD-CO2
Catalyst
µmol H2 gcat−1
RD (%)
μmol NH3 gcat−1
μmol NH3 m−2
μmol CO2 m−2
Ni–αAl
Ni–γAl
NiCaAl
NiCaAlcom
1964.8
2526.0
3243.5
1993.1
54
90
97
100
0.0
0.0
3.1
1.6
0.3
2.7
6.2
14.9
3.3
458.9
105.4
24.1
1 3

J. P. S. Q. Menezes et al.
most intense CO2 desorption peak at 740 °C. Ashok et al.
[29] also observed two regions of CO2 desorption for Ni–Fe
catalysts supported on calcium oxide and alumina. The frst
region from 100 to 350 °C was assigned to low-strength
basic sites, such as bicarbonates that result from the interac-
tions between CO2 and weak basic surface hydroxyl groups,
while the second region from 400 to 600 °C was associated
with high-strength basic sites, such as unidentate carbonates,
formed in the presence of over-saturated CaO species. In this
work, the peak observed at high temperature (740 °C) on
both NiCaAl and NiCaAlcom catalysts were more intense
than peaks observed at low temperatures, indicating the pres-
ence of high amount of over-saturated CaO species. Ni–αAl
catalyst presented only a small peak located at 325 °C, which
was expected because of its low BET surface area.
Isothermal
Ni- Al
186 ºC
163 ºC
Ni- Al
NiCaAl
224 ºC
NiCaAl com
0
100 200 300 400 500 600 700 800
Temperature (ºC)
The results of basicity presented in Table 2 show an
increase in the amount of basic sites by CaO incorporation,
as NiCaAl presented the highest basicity (14.9 µmol CO2
m−2) and Ni–γAl presented basicity of 6.2 µmol CO2 m−2.
These results of basicity are in agreement with the values
obtained by Ashok et al. [29] for Ni–Fe catalysts supported
on alumina promoted with various amounts of calcium oxide
(0.5–2 wt%); they found basicity values from 16.4 µmol
CO2 m−2 for the catalyst promoted with 0.5 wt% of CaO to
24.7 µmol CO2 m−2 for the catalyst promoted with 2 wt%.
Fig. 3 TPD-NH3 profles of the reduced catalysts
325 °C
Ni- Al
Ni- Al
365 °C
270°C
650 °C
135 °C
740 °C
3.2 Catalytic Tests
290 °C
490 °C
136 °C
NiCaAl
Glycerol conversion and glycerol conversion to gas are
presented in Fig. 5a, b, respectively. Ni–αAl and Ni–γAl
obtained the highest glycerol conversion in the frst 8 h of
reaction, with glycerol conversion in the range of 85–100%.
However, they sufered a severe deactivation after 24 h of
reaction. Ni–γAl conversion decayed to 67% in 24 h of reac-
tion and was kept constant between 67 and 77%; on the other
hand, Ni–αAl conversion was reduced to 61% and was kept
constant between 61 and 67%. Thus, the deactivation of
Ni–αAl catalyst was more severe, which can be explained
by the lowest reduction degree, lowest nickel dispersion and
highest coke formation, as will be seen later. The deacti-
vation of nickel catalysts supported on alumina has been
widely reported in the literature. Sánchez et al. [30] observed
deactivation of Ni catalysts supported on γ-alumina after 8 h
of reaction at 600 °C and 650 °C.
740 °C
688 °C
427 °C
NiCaAlcom
800 900 1000
100
200
300
400
500
600
700
Temperature (ºC)
Fig. 4 TPD-CO2 profles of the catalysts
catalyst, as also the strength of acid sites, because of the
higher temperature of desorption. Thus, the addition of a
basic promoter, as calcium oxide, reduced the acidity, which
was also observed by Sánchez-Sánchez et al. [28]. NiCaAl-
com catalyst presented lower acidity than NiCaAl, which
can be explained by the presence of small amounts of other
promoters, as MgO and K2O, or by the diferent synthesis
method.
NiCaAlcom presented the lowest glycerol conversion
and glycerol conversion to gas during all reaction time
and also presented deactivation as glycerol conversion was
reduced from 68% in the frst hour to 40% in 24 h of reac-
tion. This worst catalytic performance may be explained
by the lower Ni dispersion in comparison with NiCaAl and
Ni–γAl; furthermore, it presented lower nickel content, thus
the availability of nickel species is lower for this catalyst.
In contrast, NiCaAl catalyst was the only catalyst without
TPD-CO2 profles of the catalysts are presented in Fig. 4
and the values of basicity normalized by BET surface area
are shown in Table 2. First, it is observed that calcium oxide
addition shifted CO2 desorption peaks for higher tempera-
tures, indicating stronger basic sites. Ni–γAl presented three
broad desorption peaks in the region of 100–500 °C and only
a small peak at 650 °C, while NiCaAl catalyst presented the
1 3

Efect of CaO Addition on Nickel Catalysts Supported on Alumina for Glycerol Steam Reforming
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
Ni- Al
Ni- Al
NiCaAl
NiCaAl com
Ni-
Ni-
NiCaAl
NiCaAlcom
1
2
3
4
5
6
7
8
24 25 26 27 28 29 30
1
2
3
4
5
6
7
8
24 25 26 27 28 29 30
Time (h)
(b)
(a)
Time (h)
100
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
Ni-
Ni-
NiCaAl
NiCaAlcom
90
80
70
60
50
40
30
20
10
0
Ni-
Ni-
NiCaAl
NiCaAlcom
1
2
3
4
5
6
7
8
24 25 26 27 28 29 30
1
2
3
4
5
6
7
8
24 25 26 27 28 29 30
(d)
Time (h)
(c)
Time (h)
Fig. 5 Glycerol conversion (a), glycerol conversion into gas (b), H2 yield (c), and hydrogen production rate (d) for the catalysts during glycerol
steam reforming. Reaction conditions: 500 °C, GHSV of 200,000 h−1 and 20% v/v glycerol solution
any deactivation during reaction time: glycerol conversion
was kept between 70 and 80% during all reaction time and
was higher than glycerol conversion of Ni–γAl after 24 h
of reaction.
Figure 5c, d shows hydrogen yield and hydrogen production
rate during reaction time. It is possible to observe that Ni–αAl,
Ni–γAl and NiCaAl showed a similar behavior, with mean
H2 yields of 37, 33 and 35%, respectively. Hydrogen mean
production rate was 4900, 4400 and 3900 μmol H2g−1 min−1,
respectively. On the other hand, NiCaAlcom presented the
lowest mean hydrogen yield (13%) and lowest hydrogen pro-
duction rate, around 1600 μmol H2g−1 min−1. This result is
associated with the lowest glycerol conversion to gas and indi-
cates a low activity for glycerol reforming and shift reactions.
Figure 6 shows selectivities for reforming gases: H2, CO,
CO2 and CH4. It is observed that Ni–αAl presented the lowest
hydrogen selectivity which suggests that hydrogen generated
in reforming is being consumed for coke formation by CO and
CO2 hydrogenation (Eq. 5 and 6), or by methane formation by
methanation reactions (Eq. 7 and 8).
The diference between glycerol conversion and glycerol
conversion to gas for all the catalysts, except for Ni–αAl,
may be explained by liquid byproduct formation (acrolein,
acetol and propanoic acid). Ni–αAl was the only catalyst in
which the glycerol conversion and glycerol conversion to gas
are almost the same during reaction time, which indicates
low byproduct formation. Ni–γAl presented the highest dif-
ference in the frst hour of reaction, as glycerol conversion
was 98% and glycerol conversion to gas was around 50%;
this behavior suggests not only liquid byproduct formation
but also high coke formation in the frst hour of reaction,
which explains the fast deactivation. NiCaAl and NiCaAl-
com presented similar behavior of glycerol conversion and
glycerol conversion to gas, with a diference around 20%
between both parameters, suggesting that coke formation
was better distributed in reaction time, so deactivation was
less severe for these catalysts in comparison with Ni–γAl
catalyst.
CO + H2 ↔ C + H2O
(5)
CO2 + 2H2 ↔ 2H2O + C
(6)
CO + 3H2 ↔ CH4 + H2O
(7)
1 3

J. P. S. Q. Menezes et al.
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
Ni- Al
Ni- Al
NiCaAl
NiCaAl com
Ni- Al
Ni- Al
NiCaAl
NiCaAl com
1
2
3
4
5
6
7
8
24 25 26 27 28 29 30
1
2
3
4
5
6
7
8
24 25 26 27 28 29 30
(b)
(a)
Time (h)
Time (h)
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
Ni- Al
Ni-
Al
NiCaAl
NiCaAl com
Ni- Al
Ni-
Al
NiCaAl
NiCaAl com
1
2
3
4
5
6
7
8
24 25 26 27 28 29 30
1
2
3
4
5
6
7
8
24 25 26 27 28 29 30
(c)
(d)
Time (h)
Time (h)
Fig. 6 Selectivities to H2 (a), CO (b), CO2 (c) and CH4 (d) for the catalysts. Reaction conditions: 500 °C, GHSV of 200,000 h−1 and 20% v/v
glycerol solution
with the other catalysts is associated with the highest
CO2 + 4H2 ↔ CH4 + 2H2O
(8)
activity to methanation reactions, as already mentioned
Analyzing the frst 8 h of reaction, Ni–αAl presented
superior selectivity to CO and lower selectivity to CO2
than NiCaAl and Ni–γAl, which suggests a low activity for
shift reaction for Ni–αAl catalyst. Moreover, it was noticed
that CO2 selectivity increases and CO selectivity decreases
throughout reaction time, which suggests that CO is being
consumed for coke formation by CO disproportionation
reaction as presented in Eq. 9.
before, corroborating the lowest hydrogen selectivity for
this catalyst.
Table 3 shows liquid byproducts yields: acrolein, acetol
and propanoic acid. Acrolein and acetol are produced by
glycerol dehydration (Eqs. 10 and 11), and acrolein forma-
tion takes place mainly in Bronsted acid sites of the sup-
port, as it was observed by several authors [31–33]. Propa-
noic acid is produced by acetol isomerization (Eq. 12) as
observed by Corma et al. [34].
2CO ↔ CO2 + C
(9)
- 2H O
A high activity for shift reaction was observed for NiCaAl
and Ni–γAl catalysts, expressed by the lowest CO and high-
est CO2 selectivities, which enhances hydrogen production.
NiCaAlcom is not very active for shift reaction, as can be
observed by high CO and low CO2 selectivities. NiCaAlcom
presented the highest CO mean selectivity (25%). For this
catalyst, CO selectivity decreases from 32% in the frst hour
to 7% after 24 h of reaction.
2
HO
OH
O
OH
(10)
acrolein
glycerol
- H O
2
OH
HO
OH
(11)
O
OH
Acetol
glycerol
Ni–αAl catalyst showed the highest mean methane
selectivity (12%). This high selectivity in comparison
1 3

Efect of CaO Addition on Nickel Catalysts Supported on Alumina for Glycerol Steam Reforming
Table 3 Acrolein (Yacr), acetol
Catalyst
Yacr (1–8 h) Yacr (24–30 h) Yace (1–8 h) Yace (24–30 h
)
Yacp (1–8 h) Yacp (24–30 h
)
Coke (%)
(Yace) and propanoic acid
(Yacp) average yields and coke
formation measured by TGA
analysis
Ni–αAl
Ni–γAl
NiCaAl
0.1
7.6
5.9
0.1
1.0
6.0
3.6
2.2
6.7
28.4
12.4
2.6
2.3
26.2
13.2
0.4
2.7
0.6
0.7
8.8
3.9
59.1
31.9
32.9
22.5
11.6
4.3
NiCaAlcom 3.5
of reaction, which is associated with coke formation that
may cover alumina acid sites.
OH
O
The catalysts with basic promoters, NiCaAl and NiCa-
Alcom, presented the highest acetol and propanoic acid
yields during all reaction time. Mean propanoic acid yields
were 10.3% for NiCaAl and 4.1% for NiCaAlcom; and mean
acetol yields were 27.4% for NiCaAl and 12.8% for NiCa-
Alcom. Stošić et al. [35] studied the efect of acid-basic
catalytic properties on glycerol dehydration and reported
that, diferently from acrolein formation that is favored on
Bronsted acid sites, acetol yield increases with reduction in
amount and strength of acid sites.
(12)
Acetol
Ni–αAl catalyst showed the lowest byproduct yields,
which corroborates the low diference between glycerol
conversion and conversion to gas. This may be explained by
its low surface area and no availability of support acid sites
for byproduct formation. The mean byproduct yields for this
catalyst were 0.1% for acrolein, 2.4% for acetol and 0.5% for
propanoic acid. On the other hand, Ni–γAl catalyst presented
the highest acrolein yield in the frst 8 h of reaction, which is
associated with its highest acidity. The mean acrolein yield
in the frst 8 h was 8.6% and decreased for 1% in the last 7 h
TGA and DTA analysis are presented in Fig. 7 and the
amount of coke is shown in Table 3. The deactivation
noticed for the catalysts are related with coke formation. The
highest coke formation (59.1%) was observed for Ni–αAl
catalyst, which corroborates its severe deactivation. A big
100
100
6
8
6
4
2
0
-2
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
607 ºC
Ni- Al
Ni- Al
4
474 ºC
400ºC
2
590 ºC
0
-2
100 200 300 400 500 600 700 800 900 1000
100 200 300 400 500 600 700 800 900 1000
100
90
80
70
60
50
40
30
20
10
0
6
100
90
80
70
60
50
40
30
20
10
4
NiCaAl com
NiCaAl
430ºC
4
2
0
540 ºC
432ºC
2
380 ºC
540ºC
0
-2
0
-2
100 200 300 400 500 600 700 800 900 1000
100 200 300 400 500 600 700 800 900 1000
Temperature (ºC)
Temperature (ºC)
Fig. 7 TGA and DTA of the spent catalysts
1 3

J. P. S. Q. Menezes et al.
nickel crystallite size, observed for Ni–αAl catalyst, may
have contributed for its deactivation, because coke is formed
preferentially in the presence of big crystallite sizes, as
reported by Lisboa et al. [36].
shown by TG analysis. The consumption of hydrogen for
coke and methane formation explained the lowest hydrogen
selectivity for this catalyst. NiCaAlcom catalyst presented
the worst catalytic performance in terms of glycerol conver-
sion, conversion to gas and hydrogen production, with low
activity for shift reaction.
Acid sites presented on Ni–γAl, NiCaAl and NiCaAlcom
catalysts may be associated with coke formation, as reported
by Atia et al. [31]. According to the literature, amorphous
coke presents a lower oxidation temperature in comparison
with flamentous coke [37]. Thus, it is observed that Ni–αAl
presented higher amount of flamentous coke and the cata-
lysts modifed with calcium oxide, NiCaAl and NiCaAl-
com, presented higher amount of amorphous coke, as cal-
cium oxide addition in NiCaAl catalyst shifted DTA peaks
for lower temperatures; the main DTA peak for Ni–γAl is
located at 474 °C and for NiCaAl is located at 430 °C. The
tendency of CaO–MgO modifed catalyst to form lower
amount of coke, and with lower oxidation temperature, as
compared to Ni/Al2O3, was also observed by Charisiou
et al. [14]. Ashok et al. [37] attributed the lower oxidation
temperature of coke formed on Ni/CaO–Al2O3–CeO2 to the
superior and stable catalytic performance of this catalyst
in comparison with the catalyst with no ceria doping for
toluene steam reforming, relating the lower temperature of
oxidation with a more easily gasifcation of surface carbon.
This is in agreement with our results, as NiCaAl catalyst
presented a coke with lower oxidation temperature than
Ni–γAl catalyst, which contributed for its higher stability
during reaction time.
In terms of liquid byproduct formation, calcium oxide
addition reduced acrolein formation but increased acetol and
propanoic formation in comparison with Ni–γAl catalyst.
On the other hand, Ni–αAl catalyst presented insignifcant
liquid byproduct formation, explained by its lowest BET area
and acidity.
Acknowledgements The authors thank FAPERJ, CNPq, and CAPES
for fnancial support granted to carry out this work, and Greentec/EQ/
UFRJ for N2 adsorption analyses.
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1 3