Production of Hydrogen by Steam Reforming of Ethanol over Pd-Promoted Ni/SiO2 Catalyst

Article abstract of DOI:10.1007/s10562-020-03257-1

Abstract: This study investigated the influence of palladium on the catalytic performance of Ni/SiO₂ obtained by incipient wetness impregnation method. Ni/SiO₂ and Pd–Ni/SiO₂ catalysts were tested in the steam reforming of

Full text of DOI:10.1007/s10562-020-03257-1

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Catalysis Letters
https://doi.org/10.1007/s10562-020-03257-1
Production of Hydrogen by Steam Reforming of Ethanol
over Pd‑Promoted Ni/SiO2 Catalyst
Carlos Alberto Chagas1 · Robinson Luciano Manfro1 · Fabio Souza Toniolo2
Received: 9 March 2020 / Accepted: 7 May 2020
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
This study investigated the infuence of palladium on the catalytic performance of Ni/SiO2 obtained by incipient wetness
impregnation method. Ni/SiO2 and Pd–Ni/SiO2 catalysts were tested in the steam reforming of ethanol for hydrogen pro-
duction. X-ray difraction, X-ray fuorescence spectroscopy, N2 adsorption–desorption, temperature programmed reduction
with hydrogen (H2-TPR) and X-ray photoelectron spectroscopy were used to characterize the catalysts in detail. The incor-
poration of small amount of palladium into Ni/SiO2 catalyst shifts the reduction of Ni species towards lower temperatures.
All catalysts displayed total ethanol conversion and high H2 selectivity (~60%) above 500 °C. Compared to other Ni-based
catalysts reported in the recent literature, the catalysts here investigated show promising potential for further application
in the hydrogen production by ethanol steam reforming, but CO selectivity should be decreased for fuel cell applications.
Graphic Abstract
Production of hydrogen by steam reforming of ethanol over Pd-promoted Ni/SiO2 catalyst
H2
H2O
EtOH
Catalytic Ethanol
Steam Reforming
Ni
Ni
Pd
SiO2
Keywords Nickel · Palladium · Promoters · Hydrogen · Ethanol
1 Introduction
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-020-03257-1) contains
supplementary material, which is available to authorized users.
Ethanol steam refor ming (ESR) reaction
(C2H5OH+3H2O→6H2 +2CO2) using an appropriate cata-
lyst is an efcient route for renewable hydrogen production
and has been highlighted in the literature [1–6]. In addition,
ethanol is atmospheric carbon neutral since the amount of
CO2 produced by steam reforming is consumed by the bio-
mass growth, and this ofers a nearly closed carbon loop not
contributing to the greenhouse gas emissions [7, 8]. The
selection and development of a suitable catalyst for ESR is a
* Fabio Souza Toniolo
toniolo@peq.coppe.ufrj.br
1
School of Chemistry—Federal University of Rio de Janeiro,
P.O. BOX 68542, Rio de Janeiro 21941-909, Brazil
2
Chemical Engineering Program of COPPE—Federal
University of Rio de Janeiro, P.O. BOX 68502,
Rio de Janeiro 21941-914, Brazil
Vol.:(0123456789)
1 3

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C. A. Chagas et al.
key aspect, once the catalyst must be stable, active, selective,
and maximize hydrogen production while simultaneously
avoiding the formation of byproducts (CO and CH4). Coke
formation is a major issue in the ESR, which may lead to a
decrease in catalytic activity and selectivity towards hydro-
gen, as well as to catalyst deactivation, limiting the industrial
application [9, 10]. Carbon formation on the catalyst surface
may take place via several reactions, such as ethanol dehy-
dration to ethylene, followed by polymerization to coke; the
“Boudouard” reaction; and decomposition of hydrocarbons
(methane and ethylene) [11, 12]. The extent of each reaction
depends on both chosen catalyst and reaction conditions.
Noble metal catalysts, such as Rh, Ru, Pd and Pt, can
efectively break C–C and C–H bonds with a relatively good
stability, but the fuctuating price and high cost limit their
large-scale application [13, 14]. On the other hand, cata-
lysts containing transition metals, mainly Ni [15–17] and Co
[18–20], have been largely investigated as active catalysts
for ESR reaction and exhibited catalytic activities compara-
ble to those based on noble metals. Ni-based catalysts have
been widely employed on commercial scale in reforming
processes for more than 40 years [1], especially due to the
excellent capability for C–C and C–H bond cleavage and
low cost compared to expensive noble metals [21, 22]. How-
ever, Ni-based catalysts deactivate by carbon deposition and
aggregation of active Ni particles more severely than noble
metal catalysts, shortening their lifetime in the ESR reac-
tions [1, 23]. Preventing the deactivation of Ni catalysts still
remains a major challenge.
and characterized systematically by diferent techniques
(XRD, XRF, N2 adsorption–desorption, H2-TPR and XPS)
in order to understand the structure–activity relationship.
2 Experimental
2.1 Catalysts Preparation
Ni/SiO2 and Pd–Ni/SiO2 catalysts were synthesized by
incipient wetness impregnation method [31]. The nominal
loading amount of Ni and Pd were 10 and 1 wt.%, respec-
tively. Commercial SiO2 gel powder (Sigma-Aldrich,
60–200 mesh) used as support was previously calcined at
650 °C for 6 h under heating rate of 5 °C/min in a mufe
furnace. Nickel was impregnated on the silica support (1.001
cm3/g pore volume, obtained by N2 adsorption/desorption
experiments) with an aqueous solution of nickel precursor
salt Ni(NO3)2.6H2O Sigma-Aldrich. After impregnation,
the sample was dried in mufe furnace at 110 °C overnight
followed by calcinations in 2 steps: frstly at 350 °C for 3 h
(heating rate of 2 °C/min) and then at 650 °C for 5 h (5 °C/
min) under static atmosphere. 1%Pd-10%Ni/SiO2 catalyst
was prepared by sequential impregnation of palladium over
Ni/SiO2 catalyst using a palladium nitrate aqueous solution
(Pd(NO3)2, 10 wt.% in 10 wt.% nitric acid, Sigma-Aldrich).
Subsequently, the sample was dried and calcined similarly.
This frst calcination step was carried out in order to prevent
nickel to redissolve in the palladium solution during the sec-
ond impregnation step. All catalysts were crushed and sieved
to obtain the fraction between 0.18 and 0.12 mm, and from
now on 10%Ni/SiO2 and 1%Pd-10%Ni/SiO2 catalysts are
denominated as NiSiO and PdNiSiO, respectively.
To minimize coke deposition and metal sintering, sev-
eral alternatives have been suggested such as the addition
of small amount of noble metals [7, 24]. Generally, it is
possible to enhance the resistance to coke deposition and
to prevent nickel sintering by adding small amount of noble
metal promoters [25, 26]. Palma et al. [27] concluded that
addition of small amount of Pt and Rh improves the catalytic
performance and coke resistance in the ethanol reforming.
Pereira et al. [28] studied the efect of introducing small
loading of Rh and Ru into Co/SiO2 catalysts for the auto-
thermal reforming of ethanol, aiming a synergistic efect
between Co and Rh or Ru. Authors concluded that the noble
metal facilitates the reduction of cobalt under experimental
conditions of oxidative steam reforming of ethanol due to
the intimate contact between Co and the noble metal (Ru or
Rh) phases in the silica-supported bimetallic systems. Dop-
ing supported transition metal catalysts with palladium has
been presented as promising to enhance the reduction of Ni
under mild conditions and to improve the air-resistibility of
Ni originated from the stabilization efect of Pd [29, 30].
Here we studied the infuence of palladium on the cata-
lytic performance of Ni/SiO2 in the ethanol steam reforming
for hydrogen production. Ni/SiO2 and Pd–Ni/SiO2 catalysts
were prepared by incipient wetness impregnation method
2.2 Catalysts Characterization
Chemical composition analysis was performed by X-ray
fuorescence spectroscopy (XRF) using a Rigaku spectrom-
eter RIX 3100 model apparatus equipped with a rhodium
standard tube as source of radiation. Around 300 mg of each
sample was pelletized and analyzed quantitatively.
Textural properties were determined by nitrogen adsorp-
tion/desorption experiments at liquid nitrogen temperature
using a Micromeritics ASAP2010 gas adsorption instru-
ment. All samples were degassed under vacuum at 300 °C
for 24 h prior to the measurements. The specifc surface area
was calculated using the Brunauer–Emmett–Teller (BET)
method in a relative pressure range of 0.05–0.3. The pore
size distribution was determined from desorption branches
by the Barrett–Joyner–Halenda (BJH) method.
X-ray powder diffraction (XRD) measurements were
performed in a Minifex Rigaku difractometer. The XRD
patterns were collected using CuKα radiation (λ = 1.5406
1 3

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Production of Hydrogen by Steam Reforming of Ethanol over Pd-Promoted Ni/SiO2 Catalyst
Å) operated at 30 kV and 15 mA in the range from 10 to 80°
with a step size of 0.05° and counting time of 1 s per step.
Crystalline phases were identifed by using JCPDS (Joint
Committee on Powder Difraction Standards) database. The
mean crystallite size was calculated using Scherrer equation.
XRD patterns of the catalysts reduced ex-situ at the same
conditions employed prior to the catalytic tests (i.e., 600 °C
for 2 h under 50 mL/min of H2) were also obtained in order
to analyze crystallographic features of the materials resulting
from the activation pretreatment.
min). This reduction conditions was established based on
H2-TPR analysis. Reactant mixture with H2O/ethanol molar
ratio=3/1 was injected with a syringe pump (0.05 mL/min)
into a vaporizer at 200 °C and mixed with a nitrogen fow
(50 mL/min) before entering the reactor. The gas hourly
space velocity (GHSV) of ethanol and water was 48,500 h−1.
Gaseous products were analyzed on line by gas chromatog-
raphy (Shimadzu, model GC-2014) containing two columns
(RT-QPLOT and Carboxen 1010) and equipped with a TCD
using He as a carrier gas. The liquid phase was collected in
the condensers and subsequently analyzed by a Shimadzu
Prominence high-performance liquid chromatography
(HPLC) equipped with a Bio-Rad Aminex HPX-87H col-
umn, using 0.01 M H2SO4 as eluent at 0.6 mL/min, and with
UV and refractive index detectors. Time-on-stream stability
tests were carried out at 500 °C in order to estimate deac-
tivation of the catalysts. Ethanol conversion and selectivity
to diferent gaseous products were calculated according to
the equation used by Mondal et al. [7]. All the catalytic tests
were carried out in duplicates and the values obtained for
ethanol conversion showed a standard deviation below 3.0%.
Ethanol equilibrium conversion as a function of tem-
perature was calculated taking into account the law of mass
action described by Soave–Redlich–Kwong equation of
state, and the equilibrium constant derived from the stand-
ard Gibbs free energy for the ESR reaction. According to
thermodynamics analysis, ethanol equilibrium conversion is
approximately total over the entire temperature range tested
in this work (see Figure S1 in supplementary information,
SI).
Temperature-programmed reduction with hydrogen
(H2-TPR) experiments were performed on a system equipped
with a TCD detector employing a mixture of 1.53 vol.%
H2/Ar (30 mL/min) fowing through the sample. Prior to
H2-TPR analysis, the samples were pretreated at 150 °C for
30 min under argon fow of 30 mL/min and then cooled
down to room temperature in argon gas fow before reduc-
tion. The temperature was linearly raised up to 1000 °C at
10 °C/min, and hydrogen consumption was continuously
monitored by thermal conductivity detector (TCD). A trap
of molecular sieve ensured the water retention prior to the
detector, so that only hydrogen consumption was measured.
X-ray photoelectron spectroscopy (XPS) was performed
to determine the chemical state and the surface composi-
tion of the calcined catalysts. XPS analysis was carried out
using an ESCALAB 250 spectrometer (Thermo Scientifc),
employing monochromatic Al Kα (1486.6 eV) as X-ray
source. The C 1 s signal at 284.6 eV was binding energy
reference. Spectra were analyzed using a Gaussian-Loren-
zian peak shape obtained from CasaXPS® software version
2.3.15.
Coke deposition on spent catalysts was determined by
thermogravimetric analysis (TGA). Each sample was heated
from room temperature (10 °C/min) up to 1000 °C under
fow of air (60 mL/min). Quantifcation of coke was calcu-
lated according to the equation:
3 Results and Discussion
Table 1 shows results of textural and physicochemical prop-
erties of the catalysts and SiO2 support. The chemical com-
positions measured by XRF revealed that Ni and Pd contents
are in good agreement with nominal composition, indicating
that the synthesis method was appropriate to incorporate the
metal loading.
mcoke
C =
musedcatalyst x t
In which mcoke is the mass of coke on the catalyst calcu-
lated from TGA profle; musedcatalyst is the mass of catalyst
remaining after TGA analysis, and t is the time-on-stream.
The nitrogen adsorption/desorption measurements and
the Barrett Joyner Halenda (BJH) pore size distributions are
shown in Fig. 1. All isotherms are similar to type IV accord-
ing to the IUPAC classifcation, indicating the mesoporous
nature of the materials [32]. In all the cases it was found a
narrow pore size range with mean diameter about 100 Å, as
evidenced in the BJH pore size distribution profles (Fig. 1).
Textural properties (surface area, pore volume, mean pore
diameter) of the SiO2 support and catalysts obtained from
the adsorption–desorption isotherms of nitrogen are also
summarized in Table 1. BET surface area and pore volume
of SiO2 support decreased after incorporation of the metals
(Ni and Pd), which can be attributed to the partial plugging
2.3 Catalytic Performance Test
The reforming reaction at stoichiometric conditions was
conducted in a continuous fixed-bed quartz reactor at
atmospheric pressure, and temperature from 200 up to 600
°C in steps of 100 °C. Initially, 200 mg of catalyst diluted
with 400 mg of carborundum (SiC) was reduced in situ
at 600 °C for 2 h fowing pure H2 (50 mL/min) and then
cooled down to room temperature under He fow (50 mL/
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C. A. Chagas et al.
Table 1 Physicochemical
*
Catalyst
Chemical composition SBET (m2/g)
Vpore (cm3/g)
DBJH (Å)
Lc (Å)
and textural properties of the
(wt.%)
Pd
catalysts and SiO2 support
Ni
SiO2
PdO
NiO
SiO2 (support)
NiSiO
PdNiSiO
–
–
1.1
–
9.3
9.5
100
90.7
89.4
284
258
200
1.001
0.863
0.773
110
110
103
–
–
80
–
140
145
SBET specifc surface area obtained from BET method; Vpore Derived from single point measured at P/
P0 =0.98; DBJH desorption mean pore diameter
*Mean crystallite size calculated by Scherrer equation
600
0.4
0.3
Adsorption
Desorption
500
400
300
200
100
600
0.2
BJH desorption
0.1
PdNiSiO
PdNiSiO
0.0
0.4
0.3
Adsorption
Desorption
500
400
300
200
100
0.2
BJH desorption
0.1
NiSiO
NiSiO
0.0
0
600
0.4
0.3
Adsorption
Dersoption
500
400
300
200
100
0
0.2
BJH desorption
0.1
SiO2 (support)
SiO2 (support)
0.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0
100
200
300
400
500
600
Relative Pressure (P/Po)
Mean pore diameter (Å)
Fig. 1 N2 adsorption–desorption isotherms and pore size distribution of the catalysts and SiO2 support
of SiO2 mesopores by NiO and PdO crystals limiting the
accessibility of N2 molecules.
did not modify the nature of the nickel phase. Importantly, a
small peak located at 2θ=34.2° in the XRD pattern of PdNi-
SiO catalyst corresponding to (101) difraction plane can be
attributed to PdO phase (JCPDS no. 41-1107). The mean
crystallite sizes for PdO and NiO were estimated by using
the Scherrer equation and the values are given in Table 1.
Therefore, the second calcination after addition of palladium
did not afect the dimension of NiO crystallites. The cata-
lysts were reduced ex-situ at the same conditions employed
prior to the catalytic tests and were immediately analyzed by
XRD. Difractograms are displayed in Fig. S2 (SI) and we
verifed absence of difraction peaks for metallic palladium
The successful syntheses of the catalysts were also con-
frmed by X-ray difraction (XRD) patterns in Fig. 2. All
XRD patterns presented a difuse peak around 2θ=23°, cor-
responding to (101) difraction plane, which agrees with that
expected for α-cristobalite silica (JCPDS no. 39–1425). The
XRD patterns of NiSiO and PdNiSiO catalysts exhibited the
difraction peak relative to silica, and additional peaks at
2θ=37, 43 and 62°. These peaks correspond to (111), (200)
and (220) difraction planes related to NiO phase (JCPDS
no. 41-1107). This result also suggests that the Pd addition
1 3