Catalytic reforming of tar model compound over La1-xSrx-Co0.5Ti0.5O3-δ dual perovskite catalysts: Resistance to sulfide and chloride compounds

Article abstract of DOI:10.1016/j.apcata.2021.118013

Sr-containing La_1.0-Co_0.5Ti_0.5O₃ as dual perovskite materials were investigated for the steam reforming of the toluene (SRT) reaction. The impact of Sr-doping on tolerance towards tar contaminants (chloride & H<

Full text of DOI:10.1016/j.apcata.2021.118013

Applied Catalysis A, General 613 (2021) 118013
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Applied Catalysis A, General
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Catalytic reforming of tar model compound over La1-xSrx-Co0.5Ti0.5O3-δ
dual perovskite catalysts: Resistance to sulfide and chloride compounds
Ashok Jangam, Sonali Das, Subhasis Pati, Sibudjing Kawi*
Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore, 119260, Republic of Singapore
A R T I C L E I N F O
A B S T R A C T
Keywords:
Sr-containing La1.0-Co0.5Ti0.5O3 as dual perovskite materials were investigated for the steam reforming of the
toluene (SRT) reaction. The impact of Sr-doping on tolerance towards tar contaminants (chloride & H2S) for the
SRT reaction was also studied. Overall, an optimum catalyst composition of La0.8Sr0.2-Co0.5Ti0.5O3 gave superior
reforming activity than others. At 700 ◦C (S/C = 2), La0.8Sr0.2-Co0.5Ti0.5O3 exhibited ~ 90 % of toluene con-
version and stable for 21 h. La0.8Sr0.2-Co0.5Ti0.5O3 also displayed 80 % and 65 % of toluene conversion in the
presence of 0.1 % and 1% of trichloroethylene (TCE) at 700 ◦C. XRD analysis revealed the formation of dual
perovskite structures for calcined Sr doped La1.0-Co0.5Ti0.5O3 materials and negligible Co agglomeration during
SRT reaction. TGA analysis revealed that the formation of carbon was insignificant during the SRT reaction at
700 ◦C. Finally, the superior catalytic performance of La0.8Sr0.2-Co0.5Ti0.5O3 catalyst over others is attributed to
the availability of surface Co species (H2 chemisorption), mobile O2 species, and an optimum basic character.
Biomass tar model reforming
Chloride tolerance
Reversible H2S poisoning
Dual perovskites
H2-rich syngas
1. Introduction
conversion, H2 yields, and stability. Several types of catalysts such as
natural minerals [10–13], bio-char [14,15], supported metal oxides
Tar is a complex mixture of largely aromatic hydrocarbons (like
benzene, toluene, phenols, naphthalene, etc.), which is generated from
thermal reaction of organic compounds with steam or limited supply of
oxygen causing sequential pyrolysis and partial oxidation of organic
compounds [1–4]. Biomass and, recently, refuse-derived fuel from
municipal solid waste are some of the most commonly available
renewable organic compounds. Converting these organic compounds to
energy via gasification processes is a promising waste-to-energy tech-
nology in recent times [5]. However, the main concern for the potential
commercialization of this technology is the complete conversion or
removal of tar generated during the gasification process. Though tar is
rich in hydrocarbon energy, it often causes major operational challenges
due to fouling and blocking at a colder section of the gasifier, and
interfering with downstream catalytic processes. Thus, efficient con-
version of tar not only solves the above operational problems but also
significantly improves the quality of synthesis gas generated. Moreover,
catalytic conversion via steam reforming is one of the striking ap-
proaches for complete tar conversion in the gasification process, as it
generates more valuable H2 rich syngas [6–9].
[16–22], promoted metal catalysts [23–27], zeolites [28], structured
catalysts (hydrotalcite, perovskites, and phyllosilicates) have been re-
ported for steam reforming of tar reaction [29–35]. Among all, nickel
and cobalt-based catalysts are the choices of priority due to their
promising steam reforming activity and availability. These metal cata-
lysts have been in monometallic forms [36,37], alloyed with other
transition metals [38–40], and promoted with base metal oxides [20,33,
41,42]. Among them, Ni-based catalysts were extensively explored for
steam reforming of tar reaction, especially in the absence of poisoning
compounds such as sulfur. Whereas, cobalt-based catalysts have been
investigated for various reforming reactions in the presence of
sulfur-like compounds. Due to high oxophillic and redox nature,
Co-based systems showed enhanced catalytic performance for resistance
towards coke deposition, sulfur and NOx like compounds compared to
Ni-based catalysts [43,44].
In order to adopt these catalyst systems for the gasification process of
biomass and municipal solid waste (MSW) feedstocks, the catalysts must
be active and resistant to natural inorganic trace compounds such as S,
Cl, and N-compounds present in biomass and MSW feedstocks [45–47].
During steam reforming of tar reaction, catalysts tend to lose their ac-
tivity due to the poisoning effect of coke deposition, sulfide, and chloride
In the steam reforming of tar reaction, the role of the catalyst is
pivotal. The catalyst has to exhibit high catalytic activity concerning tar
* Corresponding author.
E-mail address: chekawis@nus.edu.sg (S. Kawi).
https://doi.org/10.1016/j.apcata.2021.118013
Received 23 August 2020; Received in revised form 10 January 2021; Accepted 12 January 2021
Available online 18 January 2021
0926-860X/© 2021 Published by Elsevier B.V.

A. Jangam et al.
Applied Catalysis A, General 613 (2021) 118013
species, resulting in a slow decline of tar reforming efficiency. The
content of Clꢀ and sulfur compounds is highly dependent on the nature
of the feedstock. Sulfur compounds are the major poisonous compounds
present in biomass feedstocks. For MSW, it is possible to have a high
quantity of chloride compounds both in inorganic (NaCl) and organic
(PVC) form [48–50]. The sulfur poisoning of metal catalysts is caused by
the formation of stable and inactive metal sulfide compounds, making
metal species unavailable for reforming reaction. Similarly, poisoning
due to chloride compounds is due to the formation of metal chlorides,
which can potentially leach to downstream, depleting the metal from the
catalyst. Compared to other poisonous compounds, deactivation of the
catalyst due to sulfur and chloride compounds is serious, and few in-
stances of it are irreversible. Therefore, it is required to develop efficient
tar reforming catalysts which can resist deactivation by sulfur and Clꢀ
like poisonous compounds.
measure H2 temperature-programmed reduction (H2–TPR), H2 pulse
chemisorption, and O2/CO2 temperature-programmed desorption (O2/
CO2–TPD) experiments for all the materials. X-ray photoelectron spectra
(XPS) of the reduced and spent La1-xSrx-Co0.5Ti0.5O3 materials were
measured using a Kratos AXIS spectrometer with a spatial resolution of
30
μ
m equipped with an Al K
α
(h
υ
= 1486.6 eV; 1 eV = 1.6302 × 10ꢀ 19
J) X-ray source. The amount and nature of coke deposited during the
SRT reaction are measured using the Shimadzu DTG-60 analyzer (TG/
DT analysis). The detailed description for the above characterization
techniques was provided in supplementary material and also reported
elsewhere [31].
2.3. Steam reforming activity over La1-xSrx-Co0.5Ti0.5O3 materials in H2S
and TCE compounds
Our previous report, CeO2 promoted Co-based perovskites were
investigated for steam reforming of toluene (SRT) reaction and its sta-
bility against coke deposition, H2S, and NO poisoning [51]. Various
types of Ni-based mono and bi-metallic perovskite materials were also
reported for the steam reforming of the toluene reaction. In all the cases,
the unique properties of perovskite materials such as high oxygen
mobility, basicity, and redox property play a crucial role in promoting
tar conversion activity and suppressing coke deposition during tar
reforming reaction [16,36,52–56]. In a work, well-dispersed Rh sites on
the LaCoO3 perovskite layer showed improved H2S tolerance during
reforming reaction [57]. Given the above works, herein, we have re-
ported LaxSr1-xCo0.5Ti0.5O3 materials for SRT application, where toluene
was used as a model for the biomass-derived tar compound. The role of
Sr-doping to Lax-Co0.5Ti0.5O3 perovskite materials characteristics and
their influence towards toluene reforming activity was investigated with
and without S and Clꢀ compounds. A mixture gas of 50 ppm H2S balance
He gas is used for sulfur tolerant experiments, and trichloroethylene
(TCE) is used as a model compound for Clꢀ tolerant studies. TCE is a
nonflammable liquid; upon decomposition at high temperature, 1 mol of
TCE releases 03 mol of Clꢀ ions. Finally, a structure-activity relation was
elucidated using various characterization of reduced and spent catalysts.
Steam reforming of toluene activity over La1-xSrx-Co0.5Ti0.5O3 ma-
terials with and without H2S and TCE compounds was carried out in a
fixed-bed reactor (Fig. S1) [31,51]. The testing conditions for SRT re-
action in the absence of any poisonous compounds were catalyst weight
= 0.1 g, toluene flow rate = 188 μmol/min, steam–to–carbon (S/C) ratio
= 2, reaction temperature = 700 ◦C and reduction temperature = 750
◦C/1 h. In addition to above-operating conditions, for chloride tolerance
tests, TCE concentration of 0.1 and 1% was fed with toluene. For sulfur
compounds, tolerance tests, reaction temperature of 800 ◦C, and H2S
concentration of ~ 50 ppm was used. The 50 ppm of H2S concentration
was achieved by co-feeding 10 sccm of 500 ppm of H2S/He and 90 sccm
of pure He gas. Before the SRT reaction, all the catalysts were reduced in
30 sccm flow of H2 gas at 750 ◦C/1 h. After reduction, the temperature
was to the desired reaction temperature in He gas (100 sccm). Water and
toluene were preheated at 250 ◦C, mixed with He gas and fed onto the
catalyst. The unconverted reactants and liquid products were removed
while the product mixture is passing through a ice cold trap from the
reforming reaction. The gaseous product was analyzed using a GC with a
TCD detector. Using a calibration curve and considering the total flow
rate, the molar flow of each gas will be calculated. The % toluene con-
version was calculated using Eq (1):
2. Experimental
XT (%) = (nCH4 + nCO + nCO2) * 100 / (7*nr in
)
(1)
where X is toluene conversion percentage, and n is the molar flow rate of
2.1. La1-xSrx-Co0.5Ti0.5O3 perovskites synthesis
CH4, CO, and CO2 gases.
A series of LaxSr1ꢀ xCo0.5Ti0.5O3 perovskite materials were synthe-
sized using ethylene glycol (EG) assisted sol gel method as reported
elsewhere. In this synthesis method, the metal nitrate precursors of La,
Sr and Co elements, and Ti(OC3H7)4 of the required quantity were first
dissolved in 10 mL of solvent mixture (DI water = 5 mL, EG = 2 mL and
ethanol = 3 mL). At 60 ◦C, the solution was then stirred to get a gel-like
mixture. The gel solution was then dried at 100 ◦C in an oven for 24 h.
The oven-dried sample was air calcined in a box furnace at 400 ◦C/1 h,
followed by 800 ◦C/3 h. The obtained powdered sample was ground into
3. Results and discussion
3.1. Characteristics of fresh and reduced La1-xSrx-Co0.5Ti0.5O3 perovskite
materials
The powdered XRD patterns for calcined and reduced La1-xSrx-
Co0.5Ti0.5O3 materials are displayed in Fig. 1(A) and (B), respectively.
XRD pattern for La1.0- Co0.5Ti0.5O3 material, as in Fig. 1(A) has dif-
fractions corresponding to cubic perovskite structure (2θ = 32.4◦, 39.9◦,
46.4◦, and 57.6◦). Upon replacing La with Sr in La1-xSrx- Co0.5Ti0.5O3
material, new diffractions are observed in addition to the cubic struc-
ture, which corresponds to the presence of tetragonal perovskite struc-
ture. This phase is more evident in high Sr-containing materials. Similar
dual perovskite structures are also reported in high Sr containing
Sr2TiO4 materials [58]. Additionally, the impurity phase of SrCO3 is
barely observed for the Sr1.0-Co0.5Ti0.5O3 catalyst. The absence of dif-
fractions corresponding to cobalt oxide species suggests that cobalt
species are either well mixed within the catalyst material or in the
perovskite structure. Furthermore, the diffractions corresponding to
various perovskite phases remain intact even after treating the
La1-xSrx-Co0.5Ti0.5O3 materials in H2 gas (Fig. 1(B)). However, there is a
change in the intensity of the diffractions between different catalysts.
The persistence of perovskite structures in the reduced form of La1-xSrx-
Co0.5Ti0.5O3 is due to the dominance of species such as La, Sr, and Ti
a fine powder with a particle size of < 125 μm. The synthesized samples
were labeled as La1-xSrx-Co0.5Ti0.5O3 perovskites, where x represents the
strontium (Sr) molar ratio. About 06 materials were prepared with
changing nominal contents of La and Sr compositions to understand the
influence of Sr doping in La1.0-Co0.5Ti0.5O3 materials for steam reform-
ing performance.
2.2. Characterization techniques for La1-xSrx-Co0.5Ti0.5O3 materials
The surface area of the freshly calcined La1-xSrx-Co0.5Ti0.5O3 mate-
rials were measured using Micromeritics ASAP 2020 analyzer by
adopting the Brunauer-Emmett-Teller (BET) method. Powdered X-ray
diffraction (XRD) patterns for La1-xSrx-Co0.5Ti0.5O3 materials were ob-
tained using Shimadzu XRD-6000 X-ray diffractometer. The samples
were scanned between 20◦ and 80◦ with a scan rate of 2◦/min. Thermo
Scientific TPDRO 1100 series system (with TCD detector) was used to
2

A. Jangam et al.
Applied Catalysis A, General 613 (2021) 118013
Fig. 2. H2-TPR profiles of calcined (a) La1.0-Co0.5Ti0.5O3, (b) La0.8Sr0.2
-
Co0.5Ti0.5O3, (c) La0.6Sr0.4-Co0.5Ti0.5O3, (d) La0.4Sr0.6-Co0.5Ti0.5O3, (e)
La0.2Sr0.8-Co0.5Ti0.5O3 and (f) Sr1.0-Co0.5Ti0.5O3 perovskite materials.
Table 1
BET surface area, H2 uptakes, O2 desorption, CO2 desorption and surface Co
content for La1-xSrx-Co0.5Ti0.5O3 catalysts.
Catalyst
BET-
SA
aH2
Total O2
desorbed
Total CO2
desorbed
bSurface
uptakes
Co content
(m2/
g)
(μ
mol/
(μ
mol/g)
(μ
mol/g)
(μmol/g)
g)
La1.0
Co0.5Ti0.5O3
La0.8Sr0.2
Co0.5Ti0.5O3
La0.6Sr0.4
Co0.5Ti0.5O3
La0.4Sr0.6
Co0.5Ti0.5O3
La0.2Sr0.8
-
15.8
16.1
6.8
1473.5
2248.0
2475.9
2233.9
2560.4
2736.9
9.9
16.8
42.7
26.9
46.3
76.5
73.9
41.2
82.3
80.4
54.8
42.5
31.8
-
54.5
39.2
39.0
44.5
47.1
-
-
3.4
Fig. 1. XRD patterns of (A) air calcined at 800 ◦C and (B) H2 reduced at 750 ◦
C
for (a) La1.0-Co0.5Ti0.5O3, (b) La0.8Sr0.2-Co0.5Ti0.5O3, (c) La0.6Sr0.4-Co0.5Ti0.5O3,
(d) La0.4Sr0.6-Co0.5Ti0.5O3, (e) La0.2Sr0.8-Co0.5Ti0.5O3 and (f) Sr1.0-Co0.5Ti0.5O3
perovskite materials.
-
1.8
Co0.5Ti0.5O3
Sr1.0
-
1.0
Co0.5Ti0.5O3
a
b
Calculated from H2-TPR results.
Measured from H2 chemisorption experiments at 35 ◦C.
oxides, these are known to be barely reducible or un- reducible oxides.
Though Co oxides can be reduced to form metallic Co species, the dif-
fractions corresponding to metallic Co species are scarecely observed in
Fig. 1(B). Overall, from XRD analysis, it can be inferred that cubic
perovskite structure is the dominant phase for La1.0-Co0.5Ti0.5O3 and low
Sr containing catalysts. In contrast, both tetragonal and cubic perovskite
structures exist in high Sr containing La1-xSrx-Co0.5Ti0.5O3 materials, and
these perovskite structures are stable in reducing environment.
samples, it can be inferred that the persistent nature of perovskite
structures in La1-xSrx-Co0.5Ti0.5O3 catalysts is due to the
high-temperature reducibility behavior. The La1-xSrx-Co0.5Ti0.5O3 ma-
terials required about 850 ◦C for complete reduction of reducible spe-
cies. The total reducible species measured for La1.0-Co0.5Ti0.5O3,
La0.8Sr0.2-Co0.5Ti0.5O3, La0.6Sr0.4-Co0.5Ti0.5O3, La0.4Sr0.6-Co0.5Ti0.5O3,
La0.2Sr0.8-Co0.5Ti0.5O3 and Sr1.0-Co0.5Ti0.5O3 materials are 1473.52,
H2-TPR analysis was adopted to check the reducibility of La1-xSrx-
Co0.5Ti0.5O3 perovskite materials up to 950 ◦C. The obtained H2 con-
sumption profiles were depicted in Fig. 2, and the total H2 uptakes were
provided in Table 1. From Fig. 2, it is clear that all the catalysts have
multiple reduction centers between 250 ◦C and 900 ◦C; however, the H2
consumption varies between the materials. As per previous reports, the
H2 consumption in La1-xSrx-Co0.5Ti0.5O3 perovskite materials is from a
multi-stage reduction of Co oxides (Co3O4 → CoO → Co◦) and mobile
oxides (ABO3 → ABO3-δ) available in the perovskite structure. Other
oxides present in La1-xSrx-Co0.5Ti0.5O3 perovskites such as La, Sr, and Ti
2248.04, 2475.92, 2233.88, 2560.42 and 2736.93
μ
mol.gꢀ 1, respec-
tively. Furthermore, the Co-based reducibility at 750 ◦C for
La1.0-Co0.5Ti0.5O3,
La0.8Sr0.2-Co0.5Ti0.5O3,
La0.6Sr0.4-Co0.5Ti0.5O3,
La0.4Sr0.6-Co0.5Ti0.5O3, La0.2Sr0.8-Co0.5Ti0.5O3 and Sr1.0-Co0.5Ti0.5O3
materials are 71.2 %, 92.5 %, 109.3 %, 104.4 %, 94.1 % and 78.8 %,
respectively. From TPR results, it can be inferred that at 750 ◦C, the
majority of the Co oxide species in La1-xSrx-Co0.5Ti0.5O3 can be reduced
to catalytically active lower oxidation states.
The CO2-TPD experiments were conducted to monitor the change in
the basicity of La1-Co0.5Ti0.5O3 material by replacing La with Sr oxides.
The obtained CO2 curves with desorption temperature were displayed in
Fig. 3. Overall, three types of CO2 desorption centers were observed for
La1-xSrx-CTO materials. The first desorption peak is observed between
100 ◦C and 200 ◦C, which is mainly allocated to either basic sites with
low-strength or physisorbed sites [60,61]. This type of CO2 desorption
oxides are known to be un-reducible [51,59]. In Fig. 2, for La1-Co0.5
-
Ti0.5O3 material, a broad dual-stage H2 consumption behavior has
appeared between 250 and 850 ◦C. The H2 consumption in La1.0-Co0.5
-
Ti0.5O3 material is mainly attributed to the multi-stage reduction of Co
and mobile oxygen species available in the material. Similar reduction
behavior is also observed for Sr-containing La1-xSrx-Co0.5Ti0.5O3 perov-
skite materials. By correlating this result with XRD patterns of reduced
3

A. Jangam et al.
Applied Catalysis A, General 613 (2021) 118013
Fig. 3. CO2-TPD profiles for reduced (a) La1.0-Co0.5Ti0.5O3, (b) La0.8Sr0.2
-
Fig. 4. O2-TPD profiles for reduced (a) La1.0-Co0.5Ti0.5O3, (b) La0.8Sr0.2
-
Co0.5Ti0.5O3, (c) La0.6Sr0.4-Co0.5Ti0.5O3, (d) La0.4Sr0.6-Co0.5Ti0.5O3, (e)
La0.2Sr0.8-Co0.5Ti0.5O3 and (f) Sr1.0-Co0.5Ti0.5O3 perovskite materials.
Co0.5Ti0.5O3, (c) La0.6Sr0.4-Co0.5Ti0.5O3, (d) La0.4Sr0.6-Co0.5Ti0.5O3, (e)
La0.2Sr0.8-Co0.5Ti0.5O3 and (f) Sr1.0-Co0.5Ti0.5O3 perovskite materials.
SA for La1.0-Co0.5Ti0.5O3 material is 15.8 m2/g. Upon replacing La with
0.2Sr species, the SA was slightly increased to reach 16.1 m2/g, and a
further increase in doping of Sr in La1.0-Co0.5Ti0.5O3 led to a drastic
reduction in SA. By considering XRD patterns (as in Fig. 1) of calcined
materials, it can be inferred that the SA reduction for high Sr-containing
materials is possibly due to the presence of a new perovskite phase,
which might be deposited in the pores of parent cubic perovskite phase.
peak is dominating in both La1.0-Co0.5Ti0.5O3 and La0.8Sr0.2-Co0.5Ti0.5O3
and is almost negligible in high Sr-containing materials. The second
peak is between 350 ◦C and 600 ◦C, which is assigned to basic sites with
moderate strength. The intensity of this CO2 desorption peak seems to be
increased with the Sr oxide content in the material. The third CO2
desorption peak is observed at above 850 ◦C and is obvious in
Sr-containing catalysts only. This peak corresponds to the decomposi-
tion of stable carbonates, possibly SrCO3 species. In general, the strength
of the basic centers is correlated with the temperature at which CO2 is
desorbed, and the number of basic centers is measured as the area under
the desorption peak. Furthermore, the basicity of La1-xSrx-Co0.5Ti0.5O3
perovskite determined by considering the CO2 desorbed peak area up to
700 ◦C, as in Fig. 3. The basicity was measured to be 16.42, 26.63,
3.2. Steam reforming of biomass tar model
Fig. 5 depicted the SRT activity for La1-xSrx-Co0.5Ti0.5O3 materials
without poisonous compounds. The SRT performances were performed
at a reaction temperature of 700 ◦C and at a relatively lower steam-to-
carbon of 2. The time-dependent toluene conversion and product for-
mation rate for La1-xSrx-Co0.5Ti0.5O3 materials were displayed in Figs. 5
and S1, respectively. In this study, H2, CO, CO2, and trace amounts of
CH4 (<1%) the main gaseous product were detected, which is consistent
with the previous report [51]. In Fig. 5, La1.0-Co0.5Ti0.5O3 gave a toluene
15.748, 36.61, 67.91 and 68.40
μ
mol.gꢀ 1 for La1.0-Co0.5Ti0.5O3,
La0.8Sr0.2-Co0.5Ti0.5O3, La0.6Sr0.4-Co0.5Ti0.5O3, La0.4Sr0.6-Co0.5Ti0.5O3,
La0.2Sr0.8-Co0.5Ti0.5O3 and Sr1.0-Co0.5Ti0.5O3 materials, respectively.
This result shows, except La0.6Sr0.4-Co0.5Ti0.5O3 material, the amount of
CO2 desorbed was seemed to be increasing trend with higher Sr-amount
in the material. Moreover, it can be established that the basicity strength
of the La1.0-Co0.5Ti0.5O3 material is significantly improved by adding Sr
oxide species, which helps the Sr-containing material to activate the
steam easier and enhance the reaction between steam and carbon, which
ultimately results in an enhancement in toluene conversion and sup-
pression of coking during SRT reaction.
Next, O2-TPD experiments were conducted to know the availability
of mobile oxygen species in La1-xSrx-Co0.5Ti0.5O3 materials reduced at
750 ◦C. And the obtained O2-desorption profiles were displayed in
Fig. 4. From the figure, it can be observed that there are two O2-
desorption peaks for high Sr-containing materials i.e., Sr1.0-Co0.5Ti0.5O3
and La0.2Sr0.8-Co0.5Ti0.5O3 catalysts - a minor low-temperature desorp-
tion peak below 400 ◦C and a major high-temperature desorption peak
above 750 ◦C. The amount of O2 desorbed is measured to be 9.85
μmol/
g, 54.52
mol/g for La1.0-Co0.5Ti0.5O3, La0.8Sr0.2-Co0.5Ti0.5O3, La0.6Sr0.4
Co0.5Ti0.5O3, La0.4Sr0.6-Co0.5Ti0.5O3, La0.2Sr0.8-Co0.5Ti0.5O3 and Sr1.0
μ
mol/g, 39.23
μ
mol/g, 38.98
μ
mol/g, 44.48
μ
mol/g and 47.11
μ
-
-
Co0.5Ti0.5O3 materials, respectively. From this result, it can be
concluded that the amount of mobile O species is higher for La0.8Sr0.2
-
Co0.5Ti0.5O3 material than others. For the steam reforming reaction, the
crucial role of mobile oxygen species is either to enhance the reaction
between carbon and oxygen species or reaction of steam to generate
active hydroxyl groups. In either case, it ultimately promotes the toluene
reforming activity with reduced carbon deposition.
Fig. 5. SRT activity over reduced (a) La1.0-Co0.5Ti0.5O3, (b) La0.8Sr0.2
-
Co0.5Ti0.5O3, (c) La0.6Sr0.4-Co0.5Ti0.5O3, (d) La0.4Sr0.6-Co0.5Ti0.5O3, (e)
La0.2Sr0.8-Co0.5Ti0.5O3 and (f) Sr1.0-Co0.5Ti0.5O3 perovskite materials. Condi-
tion: W =100 mg; toluene flow rate =188 μmol/min; H2O flow rate = 2632
mol/min, S/C = 2; reduction temperature =750 ◦C/1 h and reaction tem-
The BET surface area (SA) for the calcined La1-xSrx-Co0.5Ti0.5O3
materials were presented in Table 1. From Table, it is observed that the
μ
perature =700 ◦C.
4

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Applied Catalysis A, General 613 (2021) 118013
conversion between 75 % and 85 % within the testing period of 21 h.
Upon replacing 0.2La with Sr in La0.8Sr0.2-Co0.5Ti0.5O3, the toluene
conversion reached a maximum of 90 % and gave nearly stable con-
version throughout the testing period. With the further replacement of
La with Sr, the toluene conversion was reduced. Overall, the catalytic
increased Co particle size. It is reported that the surface Co sites in lower
–
–
oxidation state are responsible for activating C C and C H bonds
present in the toluene molecule. And the toluene conversion is further
enhanced by other characteristics of the material such as basicity and O
mobility, which promotes the reaction between steam and carbon of
toluene. This result indicates the highest toluene conversion for
La0.8Sr0.2-Co0.5Ti0.5O3 material is possibly due to Co sites available on
the catalyst surface. Furthermore, by considering other characteristics, it
can also be inferred that the stable catalytic performances of these cat-
alysts are due to the structural stability of the La1-xSrx-Co0.5Ti0.5O3
perovskite materials and enhanced basicity nature obtained by doping
with Sr oxides.
performance are in the decreasing order of La0.8Sr0.2-Co0.5Ti0.5O3
>
>
La1.0-Co0.5Ti0.5O3 > La0.6Sr0.4-Co0.5Ti0.5O3 > La0.4Sr0.6-Co0.5Ti0.5O3
La0.2Sr0.8-Co0.5Ti0.5O3 > Sr1.0-Co0.5Ti0.5O3 catalyst. It can also be
observed from Figures that the decrease in the toluene conversion is
minimal at these experimental conditions. In general, the initial steam
reforming activity greatly influenced by the availability of surface Co
sites, and the long term stability of the material was determined by
oxygen mobility, basicity, and structural stability of the material during
SRT reaction. Moreover, the deactivation of Co-based catalysts is caused
by the accumulation of carbon, active metal sintering, and oxidation of
active metal centers in the steam environment.
As highlighted before, for the catalysts to be applied for steam
reforming of tar derived from MSW, it should be resistant to the
poisonous compounds such as chlorides and sulfides. Here, we have
chosen two best compositions of La0.8Sr0.2-Co0.5Ti0.5O3 and La0.6Sr0.4
-
In this study, the amount of surface Co sites was measured using H2
pulse chemisorption at 35 ◦C for all the reduced LaxSr1.0-x-Co0.5Ti0.5O3
materials. The amount of surface Co sites are calculated to be 41.2, 82.3,
Co0.5Ti0.5O3 materials for further evaluating their catalytic performance
in the presence of poisonous compounds. Tetrachloroethylene (TCE) is
used as a model for chloride compound, and 50 ppm of H2S is used as a
sulfur compound. Fig. 6 depicted the steam reforming of toluene for
La0.8Sr0.2-Co0.5Ti0.5O3 and La0.6Sr0.4-Co0.5Ti0.5O3 materials at 700 ◦C in
the presence of 1000 ppm and 1% of TCE. By comparing the activity
profiles in Fig. 5 with Fig. 6, it is observed that for La0.8Sr0.2-Co0.5Ti0.5O3
material, the initial toluene conversion was 85 % in the absence of TCE,
whereas it is decreased to ~ 70 % in the presence of 1000 ppm of TCE
and is further reduced to below 60 % with 1% TCE. On the other hand,
the La0.6Sr0.4-Co0.5Ti0.5O3 catalyst showed continuous deactivation
behavior and reached below 20 % of toluene conversion from 80 %
within 12 h of the testing period. The deactivation behavior is more
severe in the presence of 1% TCE.
80.4, 54.8, 42.5 and 31.8
μ
mol/g-cat correspondingly for La1.0
-
Co0.5Ti0.5O3, La0.8Sr0.2-Co0.5Ti0.5O3, La0.6Sr0.4-Co0.5Ti0.5O3, La0.4Sr0.6
-
Co0.5Ti0.5O3, La0.2Sr0.8-Co0.5Ti0.5O3 and Sr1.0-Co0.5Ti0.5O3 materials.
The Co particle size was also calculated using H2 chemisorption values.
It is calculated to be 35.3, 18.0, 18.5, 27.2, 34.9, and 46.7 nm, respec-
tively for La1.0-Co0.5Ti0.5O3, La0.8Sr0.2-Co0.5Ti0.5O3, La0.6Sr0.4
-
-
Co0.5Ti0.5O3, La0.4Sr0.6-Co0.5Ti0.5O3, La0.2Sr0.8-Co0.5Ti0.5O3, and Sr1.0
Co0.5Ti0.5O3 materials reduced at 750 ◦C. The result shows that the
surface Co content is significantly increased with replacing 0.2Sr with La
species in La1.0-Co0.5Ti0.5O3 catalyst. However, a further increase in Sr
content caused a decrease in surface Co species’ availability and
Fig. 6. SRT activity over (A) La0.8Sr0.2-Co0.5Ti0.5O3 and (B) La0.6Sr0.4-Co0.5Ti0.5O3 catalysts in the presence of 0.1 % of TCE, and (C) La0.8Sr0.2-Co0.5Ti0.5O3 and (D)
La0.6Sr0.4-Co0.5Ti0.5O3 catalysts in the presence of 1% of TCE. Condition: W =100 mg; toluene flow rate =188
μmol/min; H2O flow rate = 2632 μmol/min, TCE
concentration = 0.1 and 1.0 %; reduction temperature =750 ◦C/1 h and reaction temperature =700 ◦C.
5

A. Jangam et al.
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These catalysts are further tested for sulfur tolerance ability during
effect due to sulfur compound exposure in lower Sr-containing materials
is temporary. Finally, the better performance for La0.8Sr0.2-Co0.5Ti0.5O3
material is due to its enhanced O lability and basicity nature. These
properties promote the conversion of cobalt sulfides to SOx and Co oxide
species in the presence of H2, H2O, and COx at the post H2S exposure
region.
SRT reaction at 800 ◦C. The change in the catalytic performance as
product distribution upon exposure of 50 ppm of H2S is presented in
Fig. 7. In Fig. 7, the SRT performance for the initial 3 h time is before H2S
exposure, and the performance between the dotted lines is in the pres-
ence of 50 ppm of H2S. In both tests, H2S was introduced for about 6 h.
The change in the toluene conversion after stopping H2S was monitored
for both the catalysts. It was reported that the deactivation behavior of
Co-based catalysts for sulfur-containing hydrocarbon reforming reaction
is because of the formation of cobalt sulfide compounds (Co◦ + H2S →
CoS + H2). The formed sulfide compounds are inert and catalytically
inactive for hydrocarbon reforming reactions. However, the catalytic
activity can be regenerated by making these sulfide compounds to
decompose or oxidize to generate Co sites and SOx compounds. Thus, the
activity of Co-based materials is highly influenced by the stability of the
sulfide compounds in the reaction environment.
3.3. XRD analysis of spent materials
The stability of the perovskite structural phase before and after the
SRT reaction for La1-xSrx-Co0.5Ti0.5O3 catalysts was analyzed using XRD
analysis. The XRD patterns for La1-xSrx-Co0.5Ti0.5O3 catalysts after the
reforming activities, as in Fig. 5 was provided in Fig. 8. In the figure, all
the catalysts have diffractions at 2θ = 32.4◦, 39.9◦, 46.4◦, and 57.6◦,
which correspond to the availability of cubic perovskite structure. This
phase is also observed in reduced La1-xSrx-Co0.5Ti0.5O3 catalysts (Fig. 1
(B)), indicating the stability of the perovskite phase during SRT reaction
at 700 ◦C. A stark difference in Fig. 8 compared to Fig. 1(B) is the
absence of diffractions corresponding to the tetragonal perovskite
structure. This could be due to either conversion of the tetragonal
perovskite to cubic structure or its decomposition to form corresponding
metallic and metal oxide phases. Furthermore, all the spent La1-xSrx-
Co0.5Ti0.5O3 materials have diffraction at 2θ ~ 44.5◦, corresponds to the
availability of the Co◦ phase. Moreover, the intensity of this peak is
much stronger for high Sr containing La1-xSrx-Co0.5Ti0.5O3 materials,
indicating the possibility of agglomeration of Co species during
reforming reaction. The presence of the cubic perovskite structure and
metallic Co phase is also observed for La1-xSrx-Co0.5Ti0.5O3 materials
tested in the presence of H2S and TCE compounds (Fig. S3). Overall,
from XRD analysis, it can be concluded that the cubic perovskite
structure of La1-xSrx-Co0.5Ti0.5O3 materials is quite stable in the highly
reductive environment of toluene reforming, and crystallite size of
metallic Co is smaller for low Sr-containing catalysts. This could be one
of the reasons for the better SRT activity of La0.8Sr0.2-Co0.5Ti0.5O3 than
other catalysts.
In Fig. 7(A), La0.8Sr0.2-Co0.5Ti0.5O3 gave toluene conversion of above
90 % before H2S exposure, and while upon exposure to H2S, it decreased
to nearly 20 %. The activity was recovered to the original level of
toluene conversion in the post-H2S exposure region. On the other hand,
for the La0.6Sr0.4-Co0.5Ti0.5O3 catalyst, though the initial toluene con-
version is the same as La0.8Sr0.2-Co0.5Ti0.5O3 material, in the presence of
H2S the toluene conversion decreased to ~15 % and the catalytic per-
formance could not come back to the original level in the post-H2S
exposure zone. From this result, it can be deduced that the poisoning
3.4. FE-SEM images of reduced and spent catalysts
Fig. 9 presents the FE-SEM images of La1.0-Co0.5Ti0.5O3, La0.8Sr0.2
-
Co0.5Ti0.5O3 and Sr1.0-Co0.5Ti0.5O3 catalyst obtained after reduced at
750 ◦C for 1 h and after SRT reaction at 700 ◦C.
The micrograph of La1.0-Co0.5Ti0.5O3 as in Fig. 9(a) shows the
irregular sized gains fused together with clear boundary. The mean grain
Fig. 7. SRT activity over (A) La0.8Sr0.2-Co0.5Ti0.5O3 and (B) La0.6Sr0.4
-
Co0.5Ti0.5O3 perovskite materials in the presence 50 ppm of H2S. Condition: W
Fig. 8. XRD patterns of (a) La1.0-Co0.5Ti0.5O3, (b) La0.8Sr0.2-Co0.5Ti0.5O3, (c)
La0.6Sr0.4-Co0.5Ti0.5O3, (d) La0.4Sr0.6-Co0.5Ti0.5O3, (e) La0.2Sr0.8-Co0.5Ti0.5O3
and (f) Sr1.0-Co0.5Ti0.5O3 catalysts after steam reforming of toluene activity at
700 ◦C as in Fig. 5.
=100 mg; toluene flow rate =188 μmol/min; H2O flow rate = 2632 μmol/min,
H2S =50 ppm for 5 h; reduction temperature =750 ◦C/1 h and reaction tem-
perature =800 ◦C.
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A. Jangam et al.
Applied Catalysis A, General 613 (2021) 118013
Fig. 9. FE-SEM images of (a) La1.0-Co0.5Ti0.5O3, (b) La0.8Sr0.2-Co0.5Ti0.5O3, (c) Sr1.0-Co0.5Ti0.5O3 catalysts reduced at 750 ◦C, and (d) La1.0-Co0.5Ti0.5O3, (e) La0.8Sr0.2
-
Co0.5Ti0.5O3, (f) Sr1.0-Co0.5Ti0.5O3 catalysts after steam reforming of toluene activity at 700 ◦C.
size is in nanoscale range, approximately 80 nm for the sample reduced
at 750 ◦C for 1 h. Moreover, a bright spot on each grain could be
attributed to the metallic Co or partially reduced Co species, which are
still in present in the perovskite structure. Comparatively, the image
after SRT reaction at 700 ◦C shows the agglomeration of the particles
and highly irregular sizes. Also, filament like structures are observed in
the images, indicates the formation of filamentous carbon during SRT
reaction at 700 C. Similar grain size and bright spots for each grains for
reduced La0.8Sr0.2-Co0.5Ti0.5O3 catalyst is observed (in Fig. 9(b)). There
is slight agglomeration is observed for the catalyst after SRT reaction at
700 ◦C. For Sr1.0-Co0.5Ti0.5O3 catalyst, irregularly shaped particles are
separated among each other is observed. And, upon SRT reaction, much
sever agglomeration of particles observed for this catalyst.
the amount of OL/OAds in La1-xSrx-Co0.5Ti0.5O3 materials can also be
related to their steam reforming performance. This result indicates that
the mobility of O species (OL) in La1-xSrx-Co0.5Ti0.5O3 is enhanced with
the replacement of La with 0.2Sr species in the catalysts, supporting the
observations made in O2-TPD results (Fig. 4). Next, Fig. 10(B) has O 1s
BEs of La1-xSrx-Co0.5Ti0.5O3 materials after the SRT reaction at 700 ◦C. In
Fig. 10(B), in addition to above O species observed for reduced mate-
rials, they have BE at 533.9 ± 0.5 eV, which is attributed to O species
from adsorbed OH groups. This kind of O species can be expected in the
spent catalysts because the catalysts are exposed to the steam environ-
ment during SRT reaction. Finally, this result indicates the role of Sr
doping in enhancing O species mobility of La1-xSrx-Co0.5Ti0.5O3 material
and its involvement in the SRT reaction at 700 ◦C. By combining this
result with the H2 chemisorption result, it can be concluded that the
better reforming activity of La0.8Sr0.2-Co0.5Ti0.5O3 is possibly due to the
presence of high surface Co species and enhanced O2 mobility during
SRT reaction.
3.5. XPS analysis of reduced and spent catalysts
The nature of surface elements presents in freshly reduced and spent
La1-xSrx-Co0.5Ti0.5O3 materials were analyzed using the XPS study. The
binding energy (BE) profiles for O 1s and Co 2p species before and after
SRT reaction at 700 ºC of La1-xSrx-Co0.5Ti0.5O3 materials are depicted in
Figs. 10 and 11, respectively. The Sr 2p BE profiles before and after SRT
reaction were provided in Fig S4. In Fig. 10(A), the reduced La1-xSrx-
Co0.5Ti0.5O3 materials have O 1s BEs corresponding to lattice oxygen
(OL) at 529.4 ± 0.3 eV and adsorbed oxygen species (OAds) at 531.2 ±
Next, Fig. 11 shows the Co 2p binding energy profiles for reduced
and spent La1-xSrx-Co0.5Ti0.5O3 perovskite materials. In Fig. 11A, the Co
2p3/2 BEs are at ~781.9 eV and ~ 780.2 eV, which are assigned to Co2+
and Co3+ species [62,63]. The BE peak at around 786 eV is assigned to
oxidized species. It is also observed that comparatively, the Co 2p BEs of
spent catalyst were shifted slightly to higher values than reduced ma-
terials. This shift to higher BE values in spent catalyst indicates that the
interactions between Co species and support species were significantly
enhanced during the reforming reaction. Furthermore, The peak at ~
786 eV, corresponding to oxidized species, seems to be significantly
enhanced for all the spent catalysts except for the La08Sr0.2-Co0.5Ti0.5O3
catalyst. This result indicates a certain degree of Co oxidation during
steam reforming of toluene reaction at 700 ◦C; as a result, there could be
0.3 eV. In the figure, moving from Sr1.0-Co0.5Ti0.5O3 to La1.0
-
Co0.5Ti0.5O3 materials, it was observed that the surface OL/OAds species
were increased with the decrease in Sr content in the material. And
La0.8Sr0.2-CTO has higher OL/OAds species than La1.0-Co0.5Ti0.5O3. The
higher OAds species for higher Sr containing La1-xSrx-Co0.5Ti0.5O3 ma-
terials is attributed to the presence of surface carbonates. Furthermore,
7

A. Jangam et al.
Applied Catalysis A, General 613 (2021) 118013
Fig. 10. O 1s binding energies of (A) reduced at 750 ºC and (B) spent at 700 ºC
(a) La1.0-Co0.5Ti0.5O3, (b) La0.8Sr0.2-Co0.5Ti0.5O3, (c) La0.6Sr0.4-Co0.5Ti0.5O3, (d)
La0.4Sr0.6-Co0.5Ti0.5O3,
Co0.5Ti0.5O3 catalysts.
(e)
La0.2Sr0.8-Co0.5Ti0.5O3
and
(f)
Sr1.0-
Fig. 11. Co 2p binding energies of (A) reduced at 750 ◦C and (B) spent at 700
◦C (a) La1.0-Co0.5Ti0.5O3, (b) La0.8Sr0.2-Co0.5Ti0.5O3, (c) La0.6Sr0.4-Co0.5Ti0.5O3,
(d) La0.4Sr0.6-Co0.5Ti0.5O3, (e) La0.2Sr0.8-Co0.5Ti0.5O3 and (f) Sr1.0
-
a decrease in the surface Co active species during reforming reaction.
However, this oxidation is almost negligible for La08Sr0.2-Co0.5Ti0.5O3
catalyst. It could be one of the reasons for the stable performance of the
La08Sr0.2-Co0.5Ti0.5O3 catalyst over others. The absence of BE corre-
sponding to Co◦ species in both reduced and spent catalysts is possibly
due to the existence of strong Co metal to SrOx/LaOx support interaction
in the perovskite structure.
Co0.5Ti0.5O3 catalysts.
the formation of stable sulfide species is also verified using XPS analysis
over perovskite materials after the SRT reaction, as in Fig. 7. The S 2p
binding energy profiles as in Fig. S6 shows that the presence of stable
surface sulfide species is almost negligible. The absence of surface sul-
fide species could be the reason for the recovery of the perovskite ma-
terials to it’s original level of toluene reforming activity.
Furthermore, the Sr 3d BE profiles for reduced and spent La1-xSrx-
Co0.5Ti0.5O3 are deconvoluted to two types of species (Fig. S4). The BE at
~ 132.3 eV is assigned to SrO species, and BE at ~ 133.1 eV is assigned
to SrCO3 or SrTiO3 species. It is also observed that comparatively, the BE
for spent catalysts are slightly shifted to higher values than reduced
catalysts, indicates the possibility of conversion of SrO into SrCO3 like
species during SRT reaction. Besides, the presence of stable chloride
species after SRT reaction in the presence of 1% TCE is verified using
XPS analysis. Fig. S5 has Cl 2p3/2 BE at around 781.3 is corresponding to
the presence of inorganic chloride species. When considering the ele-
ments present in the perovskite materials, these chlorides be the for-
mation of SrCl2 species. According to the previous report, Sr species in
the perovskite structure promoted steam activation during the SRT re-
action. As a result, it enhanced toluene reforming activity and suppress
carbon formation during SRT reaction. By considering the above results,
the slight decrease in the performance of perovskite materials in TCE
presence could be formation of inert inorganic chloride species. This
could be one of the possible reasons for the enhanced coke deposition
during SRT reaction in the presence of TCE compounds. Furthermore,
3.6. Carbon analysis
The nature and amount of coke deposited during SRT reaction over
La1-xSrx-Co0.5Ti0.5O3 materials were determined using TGA/DTA ana-
lyses. The TGA and DTA profiles of La1-xSrx-Co0.5Ti0.5O3 after SRT re-
action at 700 ◦C (as in Fig. 5) are presented in Fig. S7. The result shows
that carbon formation during pure SRT reaction at 700 ◦C is almost
negligible, supporting these catalysts’ stable SRT performances. Also, it
indicates the crucial role of Sr species in La1-xSrx-Co0.5Ti0.5O3 catalyst in
activating steam to promote the reaction between carbon and steam
during SRT reaction at 700 ◦C. Furthermore, the TGA and DTA profiles
of La0.8Sr0.2-Co0.5Ti0.5O3 and La0.6Sr0.4-Co0.5Ti0.5O3 catalysts after SRT
reaction in the presence of TCE and H2S are presented in Fig. 10. The
TG/DT profiles in Fig. 10(A) shows an intense weight loss associated
with an exothermic differential thermal peak between 400 ◦C and 600
◦C. This weight loss is due to the oxidation of carbon species deposited
8

A. Jangam et al.
Applied Catalysis A, General 613 (2021) 118013
during the SRT reaction. The amount of carbon deposited is highly
dependent on the concentration of TCE present during the SRT reaction.
The weight loss for La0.8Sr0.2-Co0.5Ti0.5O3 and La0.6Sr0.4-Co0.5Ti0.5O3 is
1.95 % and 6.87 % for 0.1 % TCE and 11.56 % and 18.6 % for 1% TCE,
respectively. By combining this result with XPS results as in Fig. S5, it
can be concluded that the poisoning effect of Clꢀ species is suppressing
the reaction between steam and carbon during SRT reaction. Similar
kinds of carbon species were also deposited over La0.8Sr0.2-Co0.5Ti0.5O3,
and La0.6Sr0.4-Co0.5Ti0.5O3 tested in the presence of H2S at 800 ◦C.
Overall, it is observed that the amount of carbon deposited over
La0.8Sr0.2-Co0.5Ti0.5O3 is significantly lower than La0.6Sr0.4-Co0.5Ti0.5O3
at all SRT conditions.
3.7. Poisonous effect of H2S and TCE compounds
Ni and Co-based catalysts are the most commonly explored non-
noble metal-based catalysts for various hydrocarbon reforming re-
–
actions by virtue of their ability to activate C C and C–H bonds of
hydrocarbons [64]. Among them, mono-metallic Co and its combination
with other oxides (Mo, Fe, and etc.) are much applied for reforming of
hydrocarbons in the presence of sulfur-like poisonous compounds, due
to its redox nature and ability to form reactive metal sulfide species. In
this study, the role of introducing base metal oxide on the toluene
reforming reaction is studied, and it was observed that an optimum
perovskite catalyst composition of La0.8Sr0.2 Co0.5Ti0.5O3 achieved the
best steam reforming performance compared to other catalysts. Gener-
ally, the catalyst’s performance was expressed with respect to the
toluene conversion and long term catalytic stability. The initial toluene
conversion is mainly influenced by the number of surface-active metal
species and the rate of reaction between the reactants on metal sites. The
catalytic deactivation is caused by metal sintering, metal species con-
version to oxides, or other inactive states and carbon encapsulation
during reforming reaction. In this study, steam reforming of toluene
activity as in Fig. 5 shows stable toluene conversion over perovskite
materials, however different catalysts have different toluene conver-
sions throughout the testing period. It is also observed that replacement
of about 0.2La with Sr in La1-xSrx-Co0.5Ti0.5O3 enhanced the surface Co
species availability (it is confirmed by H2 chemisorption analysis) and
basicity (CO2-TPD, Fig. 3). The basic sites the material helps to enhance
the activation of steam and reaction with toluene and also neutralize the
acidic sites of the material, which are responsible for hydrocarbon
cracking reaction. As a result, a reduction in the carbon deposition rate is
observed. It is confirmed from the carbon analysis of spent La1-xSrx--
Co0.5Ti0.5O3 materials (Fig. S7).
Fig. 12. DT/TGA profiles (A) after SRT at 700 ◦C in the presence of TCE
compound over (a) La0.6Sr0.4-Co0.5Ti0.5O3 (1%), (b) La0.8Sr0.2-Co0.5Ti0.5O3
(1%), (c) La0.6Sr0.4-Co0.5Ti0.5O3 (0.1 %) and (d) La0.8Sr0.2-Co0.5Ti0.5O3 (0.1 %),
and (B) at 800 ◦C in the presence of 50 ppm of H2S over (a) La0.8Sr0.8
Co0.5Ti0.5O3 and (b) La0.6Sr0.4-Co0.5Ti0.5O3 catalysts.
-
According to a well-accepted toluene reforming mechanism, toluene
is first decomposed on the active metal species to generate hydrogen and
carbon. The deposited carbon reacts with the reforming agent, i.e.,
steam to generate CO, CO2, and more H2. The competition between
these two reactions causes either encapsulation or suppression of carbon
formation around the active centers during reforming reaction [6].
Compared to the activities in Fig. 5, it is clearly observed that there is a
lower catalytic performance in the presence of various concentrations of
Cl- compounds (TCE) (Fig. 6). For La0.8Sr0.2-Co0.5Ti0.5O3 material, the
initial toluene conversion was decreased with an increase in TCE con-
centration in the reactant mixture. This decrease in the activity is
possibly caused by the accumulation of carbon during the reforming
reaction, which is confirmed by DT/TGA analysis (Fig. 12A). The
deposition of carbon for La0.6Sr0.4-Co0.5Ti0.5O3 is much higher than
other catalysts, which could be a possible reason for continuous deac-
tivation behavior, although the reaction period. Furthermore, upon
exposure to 50 ppm of H2S at 800 ◦C, both perovskite catalysts showed a
sudden decrease in the catalytic performance (Fig. 7). It could be due to
the conversion of metallic Co to considerable stable cobalt sulfide
compounds [65]. At the same reaction temperature, the catalytic per-
formance is recovered back to nearly 95 % of initial performance in the
absence of H2S. The decomposition of cobalt sulfide to generate metallic
cobalt species results in catalytic recovery at the same reaction tem-
perature. The slight decrease in the activity compared to initial perfor-
mance in the post H2S exposure region is possible because of the
accumulation of carbon during reforming reaction, confirmed by DT/TG
analysis (Fig. 12B).
In essence, the promotional effect of introducing Sr in La1-xSrx-
Co0.5Ti0.5O3 perovskite materials is primarily credited to its ability to
enrich the surface metal sites and suppress the coking rate by promoting
the reaction between steam and carbon precursors deposited on cobalt
surface during SRT process.
4. Conclusions
Overall, an optimum La0.8Sr0.2-Co0.5Ti0.5O3 perovskite material
composition of showed superior steam reforming of toluene perfor-
mance of all La1-xSrx-Co0.5Ti0.5O3 perovskite materials. The tests for H2S
and chloride compounds tolerance shown that La0.8Sr0.2-Co0.5Ti0.5O3
catalyst possesses resistance towards 0.1–1% of the TCE compound.
Moreover, upon introducing 50 ppm of H2S at 800 ◦C, the toluene
conversion on La0.8Sr0.2-Co0.5Ti0.5O3 material is dropped to 20 %, and
9

A. Jangam et al.
Applied Catalysis A, General 613 (2021) 118013
[14] S. Wang, R. Shan, T. Lu, Y. Zhang, H. Yuan, Y. Chen, Appl. Energy 263 (2020),
114565.
that was maintained for 5 h of H2S exposure. Subsequently, after stop-
ping H2S in feed, this catalyst was able to regenerate about 95 % of
initial activity at the same reaction temperature. This result indicates
that the poisoning effect of sulfur compounds for La0.8Sr0.2-Co0.5Ti0.5O3
material is temporary during the SRT reaction at 800 ◦C. Furthermore,
O2-TPD and XPS results revealed that the oxygen mobility of La1-
xSrxCo0.5Ti0.5O3 material could be significantly enhanced by replacing a
small amount of La with Sr species. From XRD analysis, the stability of
cubic perovskite structures during the reductive and reaction environ-
ment, and insignificant Co agglomeration was perceived. From CO2-TPD
studies, lower strength basic sites are higher for the best catalyst, i.e.,
La0.8Sr0.2-Co0.5Ti0.5O3 is observed. TGA has shown the negligible coke
formation during SRT reaction at 700 ◦C, and that the addition of TCE
and H2S in feed led to enhanced carbon formation during SRT reaction at
700 ◦C and 800 ◦C, respectively. Finally, these kinds of perovskite
structured La1-xSrxCo0.5Ti0.5O3 materials have good potential for appli-
cation in high-temperature biomass/MSW derived tar reforming pro-
cesses, where tolerance towards inorganic sulfur and chloride
compounds is a necessity.
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Ashok Jangam: Conceptualization, Methodology, Investigation,
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Declaration of Competing Interest
[35] U. Oemar, Y. Kathiraser, M.L. Ang, K. Hidajat, S. Kawi, ChemCatChem 7 (2015)
3376–3385.
The authors report no declarations of interest.
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The authors gratefully acknowledge the financial support from Na-
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Minister’s Office, Singapore and the National Environment Agency
under the Waste-to-Energy Competitive Research Program (WTE CRP
1501 103), Agency for Science, Technology and Research (AME-IRG
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