https://doi.org/10.1177/0734242X221080084
Waste Management & Research
2022, Vol. 40(9) 1433 –1439
© The Author(s) 2022
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DOI: 10.1177/0734242X221080084
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Introduction
Thermal and thermo-catalytic degradation of waste polymers
into valuable hydrocarbons, like fuel oil, is an area of great inter-
est due to depletion of natural resources (Gaca et al., 2008).
Thermal degradation requires a very high temperature (500°C to
900°C). It produces liquid products that mainly contain heavier
hydrocarbons (C6–C25; Akpanudoh et al., 2005; Lin et al., 2004).
The use of catalyst not only decreases the degradation tempera-
ture but also maximises the yield of lower hydrocarbons (Bobek-
Nagy et al., 2020; Chai et al., 2020; Shah et al., 2021). Various
catalysts including silica, alumina, zeolites, mesoporous materi-
als and heteropolyacids have been tested for polymer degradation
to get valuable hydrocarbons (Aguado et al., 2007; Mastral et al.,
2006; Serrano et al., 2000; Shah et al., 2021; Wang et al., 2021).
Heteropolyacids, also known as polyoxometalates (POMs), have
been reported for catalytic cracking of plastic. POMs are molecu-
lar metal oxide clusters that possess larger number of Brönsted
acid sites that accelerate the cracking process (Shah et al., 2021).
Natural clays have acidic sites which made them suitable for
catalytic applications. Various types of clays, such as bentonite,
smectite, montmorillonite and kaolin have been used as a cata-
lyst/support due to their porosity, active surface elements. They
have good thermal stability which ensures their use in applica-
tions at high temperature. Kaolin and Fire clay had been reported
for catalytic cracking of polyethylene (PE) with liquid yield of
73% and 43%, respectively (Attique et al., 2018; Patil et al.,
2018). Wei Luo et al. (2021) reported kaolin clay for pyrolysis of
PE at 600°C to get liquid and oil products. Clays impregnated
with POMs had been reported to enhance oil yield up to 81%
(Attique et al., 2018, 2020). Thus, POM increases the polymer
Fe-POM/attapulgite composite materials:
Efficient catalysts for plastic pyrolysis
Saira Attique1, Madeeha Batool1, Oliver Goerke2, Ghayoor Abbas3,
Faraz Ahmad Saeed4, Muhammad Imran Din1, Irfan Jalees5,
Ahmad Irfan6, Duncan H Gregory7 and Asma Tufail Shah2,8
Abstract
This article describes the catalytic cracking of low-density polyethylene over attapulgite clay and iron substituted tungstophosphate/
attapulgite clay (Fe-POM/attapulgite) composite materials to evaluate their suitability and performance for recycling of plastic waste
into liquid fuel. The prepared catalysts enhanced the yield of liquid fuel (hydrocarbons) produced in cracking process. A maximum
yield of 82% liquid oil fraction with a negligible amount of coke was obtained for 50% Fe-POM/attapulgite composite. Whereas,
only 68% liquid oil fractions with a large amount of solid black residue was produced in case of non-catalytic pyrolysis. Moreover,
Fe-POM/attapulgite clay composites showed higher selectivity towards lower hydrocarbons (C5–C12) with aliphatic hydrocarbons as
major fractions. These synthesised composite catalysts significantly lowered the pyrolysis temperature from 375°C to 310°C. Hence,
recovery of valuable fuel oil from polyethylene using these synthesised catalysts suggested their applicability for energy production
from plastic waste at industrial level as well as for effective environment pollution control.
Keywords
Waste recycling, pyrolysis, tungstophosphate, liquid hydrocarbon, polyethylene, GC-MS
Received 18th September 2021, accepted 22nd January 2022 by Associate Editor Mario Grosso.
1 Institute of Chemistry, University of the Punjab, New Campus,
Lahore, Pakistan
2
Faculty III Process Sciences, Institute of Materials Science and
Technology, Fachgebiet Keramische Werkstoffe, Technische Universität
Berlin / Chair of Advanced Ceramic Materials, Berlin, Germany
3 Faculty of Pharmacy and Alternative Medicine, Islamia University
Bahawalpur, Bahawalpur, Pakistan
4 Ahmad Saeed & Co Pvt. Ltd. 473 G3, Lahore, Pakistan
5 Institute of Environmental Engineering and Research, University of
Engineering and Technology, Lahore, Pakistan
6 Department of Chemistry, College of Science, King Khalid
University, Abha, Saudi Arabia
7
WestCHEM, School of Chemistry, University of Glasgow, Glasgow, UK
8 Interdisciplinary Research Centre in Biomedical Materials (IRCBM),
COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan
Corresponding authors:
Asma Tufail Shah, Interdisciplinary Research Centre in Biomedical
Materials (IRCBM), COMSATS University Islamabad, Lahore Campus,
Raiwind Road, Lahore 54000, Pakistan.
Email: [email protected]
Madeeha Batool, Institute of Chemistry, University of the Punjab,
New Campus, Lahore 54590, Pakistan.
Email: [email protected]
1080084WMR0010.1177/0734242X221080084Waste Management & ResearchAttique et al.
research-article2022
Original Article
1434 Waste Management & Research 40(9)
conversion that in turn enhances the liquid oil formation, which
is a more useful fuel.
In the present study, attapulgite clay has been impregnated
with Cs salt of iron substituted POM (tungstophosphate) to
develop highly efficient acidic cracking catalyst. Attapulgite is a
hydrated magnesium–aluminium silicate material that consists of
tetrahedrally arranged double chains of silica interconnected by
octahedral oxygen and hydroxyl groups enclosing aluminium
and magnesium ions in a chain-like structure (Araújo et al.,
2002). This tetrahedral arrangement extends throughout the chain
and forms channels through the structure (Murray, 1999). Due to
its exceptional structural properties, attapulgite has been selected
as a support which has been loaded with the Cs salt of iron sub-
stituted tungstophosphate. The resultant hybrid material shows
excellent results for plastic degradation reactions and produces a
high amount of liquid fuel. Moreover, the synthesised catalysts
distinctly affect the pyrolysis temperature and thus cracking pro-
cess starts at 310°C that is significantly lower than non-catalytic
cracking at 375°C. Therefore, the prepared hybrid materials are
remarkably effective for conversion of waste plastic materials
into value added chemicals.
Materials and methods
Materials
Sodium tungstate dihydrate (98%), disodium hydrogen phos-
phate (98%), iron nitrate nonahydrate (99%), cesium chloride
(99%) and acetic acid (99.5%) were supplied by Sigma Aldrich.
All chemicals were used as received without further purification
unless otherwise stated. Attapulgite clay was obtained from
Ahmad Saeed & Co Pvt Ltd. Low-density PE pellets (irregular
shape with 20 µm thickness) were purchased from the local
market.
Method
Synthesis of Cs salt of iron substituted tungstophosphate (Fe-
POM). Iron substituted Keggin tungstophosphate was synthe-
sised by a simple method as reported in the literature (Simões
et al., 1999). Briefly, 15.156 mmol (5 g) of sodium tungstate
(Na2WO2·2H2O) and 1.38 mmol (0.246 g) of disodium hydrogen
phosphate (Na2HPO4·12H2O) were dissolved in 31 mL of
deionised water. Then, 1.82 mmol (0.735 g) of ferric nitrate
(Fe(NO3)3·9H2O) was added to the above mixture, and pH was
adjusted to 4.8 with glacial acetic acid. The resultant mixture was
heated to 80°C–85°C, filtered if needed and then 6.82 mmol of
cesium chloride (CsCl) dissolved in 5 mL of deionised water was
added to this mixture dropwise. The solution was cooled to room
temperature and 150 mL of ethanol was added as an antisolvent.
The resultant solid was separated and dissolved in 60 mL of water
at 60°C and recrystallised using ethanol – filtered, washed many
times with ethanol – and dried at 100°C for 10 hours. The product
(Cs6[FePW11O39]·12H2O) was abbreviated as Fe-POM.
Synthesis of Fe-POM/attapulgite clay. A series of catalysts
were prepared by impregnating with different concentrations
(10%, 30% and 50% weight relative to attapulgite) of Fe-POM
as follows: aqueous suspension of attapulgite clay (1 g) was
prepared in 50 mL of water. Then, an aqueous solution of the
calculated amount of Cs6[FePW11O39]·12 H2O was added into
it under constant stirring followed by heating till complete
evaporation of water. Finally, the composites were dried in an
oven at 110°C (overnight). The synthesised composites were
symbolised as Fe-POM-10, Fe-POM-30 and Fe-POM-50 cor-
responding to attapulgite impregnated with 10%, 30% and
50% of Cs6[FePW11O39]·12 H2O.
Cracking experiment. PE cracking experiment was performed
by batch operation using a pyrex glass reactor (280 mm × 50 mm)
as shown in Figure 1. PE pellets were mixed with the catalyst in a
weight ratio 20:1 and placed in the reactor for catalytic cracking.
Heating of reactor was done in two steps: In the former step, it
was heated at 2°C min–1 to 120ºC under the flow of nitrogen (30
mL min–1) to remove any adsorbed water molecules; however, in
the latter, N2 supply was disconnected and the temperature was
increased to cracking temperature (heating rate 5°C min–1). The
experiment was carried out up to 3 hours. Liquid products and
solid residue were weighed directly; however, the amount of gas-
eous products was determined indirectly by measuring the differ-
ence in weight of both liquid products and solid residues from the
total weight of PE feed. Total polymer conversion was estimated
by the ratio of polymer converted to liquid fuel and the amount of
sample fed initially. Liquid hydrocarbons were analysed by a Gas
Chromatograph-Mass Spectrometer (GC-MS QP2010S) using the
ZB-5 MS column with dimensions of 30 m × 0.32 mm × 0.25 µm.
Characterisation techniques. Characterisation of synthesised
catalysts was accomplished by various analytical techniques like
Fourier Transform Infrared (FTIR) spectroscopy, Powder X-ray
Diffraction (PXRD), Scanning Electron Microscopy and Energy-
dispersive X-ray spectroscopy (SEM-EDX) and Thermogravi-
metric analysis (TGA). FTIR spectroscopy was used to identify
functional groups with the help of an FTIR Spectrometer (model
41630; Agilent technology) operating in the Attenuated Total
Reflection (ATR) mode. Spectra were recorded at room tempera-
ture (4 cm–1 resolution, 256 scans/sample). TGA was performed
on Netzsch STA 409 instrument; approximately, 20 mg sample
was placed in alumina crucibles, and the temperature programme
was set to rise at a rate of 10°C min–1 up to 1000°C in the argon
environment (flow rate: 60 mL min–1). The surface morphology
of prepared composites was examined by an Philips XL30 ESEM
instrument. Gold targets were used for the pre-coating of samples
by a Polaron SC7640 sputter coater. The elemental composition
of the samples was obtained with the help of INCA X-Act EDX
detector. The crystalline structure of prepared composites was
evaluated by PXRD performed on a PANalytical XPERT-PRO
system working at 40 kV and 40 mA utilising Cu Kα radiation.
Attique et al. 1435
Figure 1. Schematic diagram for set up used for polyethylene cracking experiments.
Figure 2. FT-IR spectra of (a) attapulgite, (b) Fe-POM-50, (c)
Fe-POM-30, (d) Fe-POM-10 and (e) Fe-POM samples.
The scanning step size was 0.02 degrees, and scanning rate 0.5 s/
step, and scan range 5°–85°. Liquid products were analysed by a
Gas chromatography–mass spectrometry (GC-MS)-QP2010S
instrument using the ZB-5 MS column (30 m × 0.32 mm ×
0.25 µm) under flow of He gas. GC and MS conditions were as
follows: Initial GC oven temperature was kept at 40°C for 1 min-
ute, then heated to 310°C at a heating rate of 3°C min–1 and held
constant for 30 minutes. The temperature of the injector was
maintained at 280°C while the detector was held at 310°C. Elec-
tron Impact (EI) ionisation mode was used to record mass m/z
from 30 to 500. Ion source and interface temperatures were kept
at 180°C and 250°C, respectively. All compounds were identified
from NIST/EPA/NIH MS Library.
Results and discussion
Characterisation of catalysts
FTIR. FTIR spectrum (Figure 2) of attapulgite clay exhibited
characteristic asymmetric vibrations at 920 cm–1 and 800 cm–1
corresponding to Si–O–H and Al–O–Si bonds, respectively. A
shoulder peak at 1193 cm–1 is ascribed to Si–O–Si bond in clay
(Araújo et al., 2002; Mendelovici, 1973). The vibrational band at
1600 cm–1 is attributed to coordinated water molecules (Figure 2).
Fe-POM/attapulgite clay samples exhibit only a few characteristic
vibration bands of POM. FTIR spectrum of bulk Fe-POM shows
typical asymmetric vibrations for P–Oa–W, W=Od, W–Ob–W
bridges between corner-sharing WO6 octahedra, and W–Oc–W
bridges between edge-sharing WO6 octahedra at 1084 cm–1,
982 cm–1, 895 cm–1 and 789 cm–1, respectively (Rocchiccioli-Del-
tcheff et al., 1983; Shah et al., 2012). The W–O–Fe vibrations are
located at 666 cm–1 (Gamelas et al., 2003). In case of 50% POM/
attapulgite, only P–Oa–W and W–Oc–W stretching vibrations can
be seen at 1080 cm–1 and 789 cm–1, which are characteristic of
Fe-POM Keggin structure. However, W=Od and W–Ob–W vibra-
tions of Fe-POM structure located at 982 cm–1 and 895 cm–1 are
not obvious due to overlapping with the strong bands of silica
present in clay’s structure.
XRD. Attapulgite clay exhibited a high degree of crystallinity as
shown in Figure 3. The diffraction peak observed at 2θ values of
8.5°, 20.2° and 35.0° are ascribed to basal space of attapulgite
framework (PDF No. 02–0018). The peaks located at 2θ values of
13°, 16.4°, 20.8° and 50.1° correspond to silica layers of the clay.
The most intense peak corresponding to quartz impurities (PDF No.
33–1161) is located at 2θ = 26.8° (Araújo et al., 2002; Christ et al.,
1969; Suki et al., 2013). XRD patterns of Fe-POM exhibits a cubic
crystalline phase that is characteristic of Keggin tungstophosphate
(Dias et al., 2004; Zhang et al., 2013). Diffraction patterns of
1436 Waste Management & Research 40(9)
Fe-POM/attapulgite clay composites present all the characteristic
peaks of attapulgite but only a few diffraction peaks of Fe-POM
Keggin structure. Attapulgite impregnated with 50% Fe-POM
exhibit characteristic peak of Fe-POM at 2θ value of 8.3°, but in
10% and 30% Fe-POM/clay samples, this peak is masked by
intense diffraction peaks of silica present in clay structure.
Thermogravimetric analysis. TGA of Fe-POM, attapulgite and
Fe-POM impregnated attapulgite composites is shown in Figure
4. TGA data collected for attapulgite exhibited weight loss in four
distinct steps. The first two steps are attributed to dehydration and
the next two steps correspond to dehydroxylation. During the first
step, which starts at ~50°C, physiosorbed water molecules are
removed (4 wt.%). The second step (located at 245°C) corre-
sponds to the loss of hydrated water molecules (~2%). The last
two steps are complex comprising overlying weight loss steps.
The third step is related to two concurring reactions occurring at
450°C and 495°C (comprising weight loss of ~4%). The last step
occurs around 650°C and is also completed at 786°C and 820°C
(weight loss ~3%). Vágvölgyi et al. have also proposed that the
dehydration and dehydroxylation of attapulgite take place in a
series of steps (Vágvölgyi et al., 2008). These steps are ascribed to
the loss of (1) adsorbed water molecules, (2) water molecules of
hydration, (3) coordinated water molecules, and (4) the loss of
water molecules through dehydroxylation.
Fe-POM showed a weight loss of 6% up to 250°C that was
ascribed to water molecules of crystallisation, and no further
noticeable weight loss was observed up to 1000°C. Fe-POM/atta-
pulgite composites also exhibited thermal behaviour analogous to
attapulgite clay, and the weight loss observed during thermal anal-
ysis could be ascribed to the loss of coordinated H2O molecules
and dehydroxylation of silica containing layers in attapulgite.
However, compared to attapulgite, attapulgite impregnated with
Fe-POM exhibited reduced weight loss in the dehydroxylation
phase, and this weight loss kept on reducing by increasing the
amount of Fe-POM. Attapulgite impregnated with 50% Fe-POM
showed least weight loss during this dehydroxylation step due to
reduced percentage of attapulgite clay (from 100% to 50%) and
increased percentage of Fe-POM (from 0% to 50%) compared to
bare attapulgite, and Fe-POM did not lose any water in this region.
SEM-EDX analysis. SEM analysis was conducted to investigate
the morphology of prepared catalysts. Attapulgite clay showed
crystalline morphology as can be seen in Figure 5. Fe-POM
exhibited a cubic crystalline structure as reported for cesium and
silver salts of Keggin tungstophosphate (Dias et al., 2004; Zhu
et al., 2013). However, SEM images of Fe-POM/attapulgite com-
posites did not show this crystalline morphology, indicating the
uniform distribution of Fe-POM on the attapulgite surface due to
the interaction of Fe-POM particles with the clay. Another distinct
change in the morphology of Fe-POM/attapulgite composites was
the change in the lustre of pure attapulgite and Fe-POM loaded
attapulgite. Fe-POM impregnated attapulgite samples were more
lustrous compared to pure attapulgite. Furthermore, EDX analysis
was performed to determine the elemental composition of these
composite materials. EDX analysis of attapulgite shows that the
major components of attapulgite are MgAl silicate, while iron and
titanium are present in trace amounts (Araújo et al., 2002). EDX
spectrum of Fe-POM/attapulgite composites revealed that in addi-
tion to MgAl silicate, tungsten and cesium were also present, con-
firming the successful loading of Fe-POM on the attapulgite
substrate. Moreover, the weight percentage of W and Cs increased
by increasing the percentage of Fe-POM. The highest percentage
Figure 3. Powder XRD patterns of (a) Fe-POM, (b) Fe-
POM-50, (c) Fe-POM-30, (d) Fe-POM-10 and (e) attapulgite.
Figure 4. Thermal gravimetric analysis of Fe-POM/
attapulgite composites.
Attique et al. 1437
of W and Cs were observed for the 50% Fe-POM loaded attapulg-
ite composite. Atomic and weight percentages of elements found
in all composites are shown in Table S1.
Thermal catalytic cracking of PE
The results of PE cracking in the absence and presence of cata-
lysts are summarised in Table 1. Thermal cracking took place at
a very high temperature (375°C), while in presence of catalysts
the cracking temperature was dropped to a great extent. However,
various catalysts showed different behaviour for the cracking of
PE. Fe-POM exhibited low yield of liquid oil products, and
the cracking started at a higher temperature, that is, 350°C.
Impregnation of Fe-POM on attapulgite clay decreased the
cracking temperature to 310°C and enhanced the liquid yield by
large amounts. At the same time, the amount of residue
was lowered considerably. The liquid yield was enhanced by
increasing the amount of Fe-POM loading. Attapulgite impreg-
nated with 50% Fe-POM produced 82% liquid hydrocarbons,
Figure 5. SEM images of (a) Fe-POM-50, (b) Fe-POM-30, (c) Fe-POM-10 and (d) attapulgite clay and (e) Fe-POM samples.
Table 1. Percentage yield of degradation products over
various catalysts.
Catalyst Cracking
temperature
(°C)
Liquid
oil (%)
Gas
(%)
Residue
(%)
No catalyst 375 68 10 22
Fe-POM 350 74.67 15.83 9.5
Attapulgite 310 72.7 17.3 10
Fe-POM-10 310 78.4 16.5 5.1
Fe-POM-30 310 80.1 16.7 3.2
Fe-POM-50 310 82.0 15.9 2.1
Recycled Fe-POM-50 310 81.8 15.8 2.4
1438 Waste Management & Research 40(9)
while solid residue was reduced to ⩽2%. On the contrary, pure
attapulgite produced 72% liquid oil that was far less than the
Fe-POM/clay composite samples. POM impregnated on atta-
pulgite creates extra Brönsted acid sites that synergistically
enhance catalyst activity for cracking of PE. The enhancement
in catalyst acidity would have reduced the cracking temperature
and degraded heavier hydrocarbons into smaller ones. PE crack-
ing reactions proceed over the Brönsted acidic sites as described
earlier, and therefore, with increasing acidic sites the tempera-
ture required for cracking decreases (Aydemir and Sezgi, 2013).
Moreover, recycled 50% Fe-POM/attapulgite sample exhibited
negligible activity loss when applied for low-density PE crack-
ing that proved it to be a truly heterogeneous catalyst.
Composition of liquid products. The oil fraction obtained by
PE cracking was analysed by GC-MS. Every single peak in
the chromatogram corresponded to a specific compound. The
molecular weight and structure of these compounds were identi-
fied by mass spectrometer. It was found that the oil acquired
over all prepared catalysts contained hydrocarbons distribution
between C5 and C21 (Figure 6). Nearly 60% hydrocarbons com-
prised of petroleum fractions (C5–C12), while ⩾35% fractions
were Kerosene-like hydrocarbons (C13–C18). High molecular
weight hydrocarbons (C19–C21) were ⩽5%. All the tested cata-
lysts shifted the product distribution towards lower hydrocar-
bons, and the effect was most profound in oil obtained using
50% Fe-POM/attapulgite sample. Although C5–C8 are produced
in enormous amounts in oil obtained using 50% POM loaded
sample, the maximum is observed for C9–C10 hydrocarbon frac-
tion. On the contrary, Fe-POM gave maximum distribution of
C10–C13 fractions, while oil obtained by thermal cracking
showed the maximum at C12–C14 fractions (Figure 6).
Detailed GC-MS analysis revealed that oil produced by cata-
lytic cracking contained mainly aliphatic hydrocarbons (paraffins
and olefins). The relative abundance of paraffins and olefins
produced by different catalysts are given in Table S2 (Supplemental
material). Among the lower hydrocarbons (C5–C12), olefins were
more abundant, while in case of heavier hydrocarbons, paraffins
were prominent. Non-catalytic oil produced a higher percentage
of paraffinic hydrocarbons (Table 2), as non-catalytic degradation
occurred at a higher temperature, which favours paraffin forma-
tion (Rahimi and Karimzadeh, 2011). The formation of olefins
during non-catalytic and catalytic cracking is also explained by
Haag-Dessau mechanism (Kotrel et al. 2000). For catalytic crack-
ing, Si: Al ratio also affects the olefin and paraffin distribution
(Han et al., 2004; Wei et al., 2005; Yoshimura et al., 2001). The
maximum percentage of olefin was achieved over 50% Fe-POM/
attapulgite catalyst that could be attributed to the creation of pro-
tonic acidified sites (from Fe-POM) and incorporation of Si and
Al (from attapulgite) in catalyst. However, no aromatic com-
pounds could be detected in oil samples, and the exclusion of aro-
matics is of great importance from environmental point of view
(Artetxe et al., 2012). Thus, the prepared catalyst Fe-POM/atta-
pulgite could be regarded as an efficient and cost-effective cata-
lyst for degradation of waste polymeric materials.
Conclusion
This research reports the synthesis and characterisation of iron
substituted tungstophosphate (Fe-POM) impregnated attapulgite
clay using various concentrations of Fe-POM (10%, 30% and
50%). The synthesised materials have been successfully charac-
terised by FTIR, XRD and SEM-EDX analysis. TGA explains
the thermal stability of these composite materials. Fe-POM
impregnated attapulgite composites have been used as catalysts
for PE cracking. The synthesised composite materials exhibit
extraordinary performance for the conversion of PE to lower
hydrocarbons; hence, the yield of fuel oil was enhanced to a con-
siderable extent. By increasing the amount of Fe-POM loading,
oil yield enhances, and therefore maximum oil yield is exhibited
by 50% Fe-POM/attapulgite sample. Furthermore, these com-
posites also lower the pyrolysis temperature and hence make the
cracking process economical. Moreover, valuable hydrocarbons
Figure 6. Comparison of distribution of carbon number for
various oil samples obtained by thermal, Fe-POM, attapulgite
and 50% Fe-POM/attapulgite catalysts.
Table 2. Product distribution in oil obtained by different
catalysts.
Catalyst Carbon number Weight (%)
Alkanes Alkenes
No catalyst C5–C12
C13–C18
>C18
19.1
21.35
14.67
16.62
21.20
–
Fe-POM C5–C12
C13–C18
>C18
24.85
25.04
6.80
26.18
16.09
–
Fe-POM-50 C5–C12
C13–C18
>C18
27.03
23.83
4.05
28.79
14.79
–
Attapulgite C5–C12
C13–C18
>C18
25.77
27.37
5.44
28.38
12.47
–
Attique et al. 1439
have been recovered from waste polymeric materials by prepared
catalysts for transportation fuels, suggesting the applicability of
these catalysts for energy recovery from plastic waste along with
effective pollution control of the environment.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to
the research, authorship, and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the
research, authorship, and/or publication of this article: Higher Education
Commission of Pakistan is greatly acknowledged for the grant of
Indigenous PhD Scholarship (PIN No. 213-66412-2PS2-074). The
authors are also thankful to Higher Education Commission for NRPU
project grant (6776/NRPU/R&D/HEC) to complete this research work.
ORCID iD
Asma Tufail Shah https://orcid.org/0000-0001-9624-1842
Supplemental material
Supplemental material for this article is available online.
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