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\DOI{10.5802/crchim.343}
\datereceived{2024-03-04}
\daterevised{2024-06-06}
\datererevised{2024-07-17}
\dateaccepted{2024-09-17}
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Blank run & \parbox[t]{1cm}{\centering Relative area} & 3\% FeO/Al & \parbox[t]{1cm}{\centering Relative area} & 5\% FeO/Al & \parbox[t]{1cm}{\centering Relative area}\vspace*{2pt}  \\ 
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%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{Materials and Energy Valorization of Biomass and Waste : The Path for Sustainability and Circular Economy Promotion}
%\def\cdr@specialtitle@french{Valorisation \'energ\'etique et mati\`ere de la biomasse et des d\'echets : la voie de la durabilit\'e et de la promotion de l'\'economie circulaire}
%\makeatother

\title{FeO--alumina catalyst for reforming waste polyethylene
terephthalate (PET) pyrolyzed products: synthesis, characterization, and
performance evaluation\vspace*{-3pt}}

\alttitle{Catalyseur FeO--alumine pour le reformage des d\'{e}chets de
produits pyrolys\'{e}s en poly\'{e}thyl\`{e}ne t\'{e}r\'{e}phtalate
(PET) : synth\`{e}se, caract\'{e}risation et \'{e}valuation des
performances}

\author{\firstname{Ephraim Akuaden} \lastname{Audu}\CDRorcid{0000-0002-0520-5166}\IsCorresp}
\address{National Research Institute for Chemical Technology, Basawa,
Zaria, Kaduna State, Nigeria}
\email{akuadenaudu@gmail.com}
\email[E. A. Audu]{ephraim.audu@narict.gov.ng}

\author{\firstname{Adebola Femi} \lastname{Ade-Ajayi}\CDRorcid{0000-0002-5725-4656}}
\addressSameAs{1}{National Research Institute for Chemical Technology,
Basawa, Zaria, Kaduna State, Nigeria}

\author{\firstname{Aisha Ayoola} \lastname{Osigbesan}\CDRorcid{0009-0003-4612-9512}}
\addressSameAs{1}{National Research Institute for Chemical Technology,
Basawa, Zaria, Kaduna State, Nigeria}

\author{\firstname{Zaharaddeen Sani} \lastname{Gano}\CDRorcid{0000-0002-7334-5531}}
\addressSameAs{1}{National Research Institute for Chemical Technology,
Basawa, Zaria, Kaduna State, Nigeria}

\author{\firstname{Jeffrey Tsware} \lastname{Barminas}\CDRorcid{0000-0002-3897-1043}}
\addressSameAs{1}{National Research Institute for Chemical Technology,
Basawa, Zaria, Kaduna State, Nigeria}

\shortrunauthors

\thanks{National Research Institute for Chemical Technology (NARICT)
under project number FGN/AB2021/ERGP30122610}

\keywords{\kwd{Catalyst}
\kwd{FeO}
\kwd{Polyethylene terephthalate}
\kwd{Pyrolysis}
\kwd{Reforming}
\kwd{Plastic waste}}

\altkeywords{\kwd{Catalyseur}
\kwd{FeO}
\kwd{Poly\'{e}thyl\`{e}ne t\'{e}r\'{e}phtalate}
\kwd{Pyrolyse}
\kwd{R\'{e}former}
\kwd{D\'{e}chets plastiques}}

\begin{abstract}
The growing rate of plastic pollution in Nigeria and across the globe,
coupled with the need to harness such waste for useful purposes, is a
pressing global concern. In this study, a new type of catalyst was
synthesized by incorporating mesoporous FeO onto  aluminium oxide
trihydrate (alumina) and applied in
reforming polyethylene terephthalate (PET) pyrolyzed gas into valuable
fuels.  The pyrolysis process was carried out at 500 \textdegree C
while vapor reforming was carried out using 0.5 g of catalyst loading
in a fixed bed reactor at 450 \textdegree C for 90 min. Scanning
electron microscopy analysis of catalysts revealed particle sizes of
1.42--7.63, 1.37--10.75, and 2.66--6.34 \tralicstex{μ}{$\upmu$}m for alumina, 3\%
FeO/Al, and 5\% FeO/Al, respectively. The percentage compositions of Fe
in the synthesized catalyst from the X-ray fluorescence results were
found to be 4.7\% and 3.62\% for 5\% FeO/Al and 3\% FeO/Al,
respectively. XRD analysis revealed that the synthesized catalysts were
non-crystalline. Catalyst performance evaluation from the gaseous
product revealed a decrease in oxygen from 23.3\% in the blank run to
5.33\% in 5\% FeO/Al. The H\textsubscript{2} content was found to be highest in
5\% FeO/Al with a value of 17.14\% while the CH\textsubscript{4} content was found
highest in 3\% FeO/Al (16.22\%). Fourier transform infrared analysis of
the liquid products inferred peaks corresponding to aromatic and
saturated hydrocarbons, which was confirmed by gas chromatography mass
spectrometry analysis. Findings from this research demonstrated that
the synthesized catalyst was able to reform waste PET pyrolyzed gas
into valuable products, addressing environmental challenges and
providing alternative energy sources.
\vspace*{-3pt}
\end{abstract}

\begin{altabstract}
Le taux croissant de pollution plastique au Nigeria et dans le monde,
associ\'{e} \`{a} la n\'{e}cessit\'{e} de valoriser ces d\'{e}chets
\`{a} des fins utiles, constitue une pr\'{e}occupation mondiale
pressante. Dans cette \'{e}tude, un nouveau type de catalyseur a
\'{e}t\'{e} synth\'{e}tis\'{e} en incorporant du FeO m\'{e}soporeux sur
de l'alumine et appliqu\'{e} au reformage du gaz pyrolys\'{e} du PET en
carburants pr\'{e}cieux. Le processus de pyrolyse a \'{e}t\'{e}
r\'{e}alis\'{e} \`{a} 500 \textdegree C tandis que le reformage de la
vapeur a \'{e}t\'{e} effectu\'{e} en utilisant 0,5 g de catalyseur
charg\'{e} dans un r\'{e}acteur \`{a} lit fixe \`{a} 450 \textdegree C
pendant 90 min. L'analyse SEM des catalyseurs a r\'{e}v\'{e}l\'{e} des
tailles de particules de 1,42 \`{a} 7,63, 1,37 \`{a} 10,75 et 2,66
\`{a} 6,34 \tralicstex{μ}{$\upmu$}m pour l'alumine, 3 \% FeO/Al et 5 \% FeO/Al
respectivement. La composition en pourcentage de Fe dans le catalyseur
synth\'{e}tis\'{e} \`{a} partir des r\'{e}sultats XRF s'est
av\'{e}r\'{e}e \^{e}tre de 4,7 \% et 3,62 \% pour 5 \% FeO/Al et 3 \%
FeO/Al respectivement. L'analyse XRD a r\'{e}v\'{e}l\'{e} que les
catalyseurs synth\'{e}tis\'{e}s sont non cristallins. L'\'{e}valuation
des performances du catalyseur \`{a} partir du produit gazeux a
r\'{e}v\'{e}l\'{e} une diminution de l'oxyg\`{e}ne de 23,3 \% dans
l'essai \`{a} blanc \`{a} 5,33 \% dans 5 \% FeO/Al, la teneur en H2
s'est av\'{e}r\'{e}e la plus \'{e}lev\'{e}e dans 5 \% FeO/Al avec une
valeur de 17,14 \% tandis que CH4 la teneur la plus \'{e}lev\'{e}e a
\'{e}t\'{e} trouv\'{e}e dans 3 \% FeO/Al (16,22 \%). L'analyse FTIR des
produits liquides a induit des pics correspondant aux hydrocarbures
aromatiques et satur\'{e}s, ce qui a \'{e}t\'{e} confirm\'{e} par
l'analyse GCMS. Les r\'{e}sultats de cette recherche ont
d\'{e}montr\'{e} que le catalyseur synth\'{e}tis\'{e} \'{e}tait capable
de reformer les d\'{e}chets de gaz pyrolys\'{e}s du PET en produits
pr\'{e}cieux, r\'{e}pondant ainsi aux d\'{e}fis environnementaux et
fournissant des sources d'\'{e}nergie alternatives.
\end{altabstract}
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\section{Introduction}\label{sec1}
\vspace*{-5pt}

The increasing global production and use of plastics, such as
polyethylene terephthalate (PET), \mbox{polyethylene} (PE), polystyrene (PS),
and others, have led to growing concern about environmental pollution
and waste management. Nigeria is the most populous country in Africa,
located at the west African subregion. It holds a land area of 
932,768~km$^{2}$ with an estimated population of 211.4
million~\cite{1}. According to Sogbanmu~\cite{2}, Nigeria ranks
ninth globally among countries with the highest contributions to
plastic pollution, producing 2.5 million tons of plastic waste
annually~\cite{3}. Furthermore, over 88\% of the plastic waste
generated is not recycled, suggesting that such waste is not properly
managed. Currently, most plastic waste in the country is dumped at
sites and landfills or incinerated. Improper disposal of plastic waste
can lead to the leaching of toxic additives into water bodies, blocking
of drainages, generation of microplastics, air pollution, and the
release of greenhouse gases~\cite{4,5}. To achieve the United Nations
Sustainable Development Goals (UN SDGs) by 2030, it is crucial to
evaluate policy actions and programs at state, national, and regional
levels to address plastic pollution~\cite{6}. 

PET has been used in many applications such as in bottles for beverages
and water and  packaging materials for foods and textiles~\cite{4,7,8}.
However, the use of PET poses significant challenges due to its
non-biodegradability, thereby leading to the generation of accumulated
plastic waste. Consequently, finding sustainable and environmentally
friendly methods for proper management of such waste is\break \mbox{imperative.}

Several conventional methods for plastic waste management have been
considered; however, most of these methods have limitations. For
instance, recycling plastic waste, which involves melting
thermoplastics and remolding it to other products, is not sustainable
due to the low-quality products produced~\cite{9}. Burning plastics in
incinerators is another method of plastic waste management.
Nevertheless, this method suffers several limitations, including
generating greenhouse gases (CO$_{2}$, CH$_{4}$), air pollution, soil
contamination, and even posing a threat to human health. Pyrolysis, as
a plastic waste management method, offers promising solutions to
address the limitations faced by other conventional methods~\cite{10,11}. 
Pyrolysis of plastic waste aligns with SDG 12, which aims to
ensure sustainable consumption and production patterns by turning
plastic waste into valuable resources. It offers the advantage of
converting waste to valuable products such as fuels and other chemical
feedstock, minimal environmental impact, job creation, renewable energy
production, carbon sequestration, and promoting a circular
economy~\cite{12,13}.\looseness=-1 

Pyrolysis is a process of breaking down long-chain hydrocarbons into
smaller chains with the \mbox{application} of heat and pressure in the absence
of oxygen, leading to the formation of valuable products like gases,
pyrolysis oils, and char~\cite{14}. The liquid oil can be further
upgraded to produce fuels (gasoline, C5--C12 and diesel,
C13--C20), lubricants, and other valuable
chemicals~\cite{15}. Typically, pyrolysis involves heating the
feedstock to a high temperature range between 400 and 800~\textdegree C,
resulting in the rupturing of chemical bonds in the feedstock and
formation of smaller molecules~\cite{16, 17}. Pyrolysis is categorized
into slow, fast, and flash pyrolysis based on the residence times and
heating rates resulting in different product yields and
compositions~\cite{18,19}. 

Several studies have been conducted on the pyrolysis of PET, which have
shown that it contains saturates and aromatic compounds similar to
those found in crude oil. For example, Xue et~al.~\cite{20} carried out pyrolysis of plastics including PET using
zeolite catalyst and found that aromatic hydrocarbons were the major
products (52.71\%) with lower yields of saturates (alkanes and
alkenes). In another study, Du et~al.~\cite{21} showed that
aromatic hydrocarbons (mostly benzene) were obtained during the
pyrolysis of PET carpet waste with ZSM-5 and CaO catalysts to enhance
deoxygenation of the products. Suriapparao et~al.~\cite{22} investigated the co-pyrolysis of PET with rice husk
and found that it promoted the formation of aromatic oxygenates and
biphenyl hydrocarbons. However, the major components obtained in
microwave pyrolysis of PET were aromatics. The study also revealed that
PET pyrolysis oil contains impurities, tars, a wide distribution of
hydrocarbons, and oxygenated compounds, necessitating the need for
upgrading such oils using suitable catalysts.

It has been reported that the use of acidic catalysts can aid in
cracking and aromatization reactions during the pyrolysis of
plastics~\cite{23,24}. Additionally, the use of catalysts can decrease
the reaction temperature, shorten the reaction time, and reduce the
formation of unwanted byproducts~\cite{25,26}. Supported iron
catalysts have emerged as a promising option for PET pyrolysis, as
literature has reported their enhanced efficiency, low cost, and
selectivity during the pyrolysis process~\cite{27,28}.

Although prior works have reported the synthesis of iron--alumina based
catalysts~\cite{29,30,31,32}, none have reported the synthesis of
iron--alumina based \mbox{catalysts} from mesoporous FeO derived from natural
magnetic sand available locally in Nigeria. Moreover, no work has
reported the use of such a catalyst for reforming PET pyrolysis
vapor. In this study, a new type of catalyst was developed based on the
combination of a novel mesoporous iron oxide synthesized from natural
magnetic sand with alumina. The synthesized catalyst was then used to
upgrade PET pyrolysis gas into valuable fuels. This study aims to
answer the following research questions: first, how does the synthesized
catalysts affect the distribution of pyrolysis products of PET after
reforming; second, the effect of 3\% and 5\% FeO catalyst loading
on selectivity. The findings of this study will contribute to the
development of innovative catalysts and environmentally friendly
approaches for PET pyrolysis into valuable fuels.

\section{Materials and methods}\label{sec2}

\subsection{Material and equipment}\label{sec21} 

PET was obtained from used drinking water
bottles within Zaria, Kaduna State. Prior to the experiment, PET bottle
samples were cut into smaller pieces (average size
within 2~cm ${\times}$ 2~cm) and allowed to dry in the laboratory. Aluminum
oxide trihydrate (alumina) was purchased from Suffolk, England. Iron
oxide (prepared from magnetic sand), weighing balance (Kern-EW6000,
with an accuracy of 0.001~g), digital hotplate with a magnetic stirrer
(Stuart CD162), muffle furnace (SXL-1008 Gallenkamp, England), vacuum
pump, hot air oven (Genlab, UK), gas mask, Whatman No. 1 filter paper,
distilled water (Water Still Aquatron [A8000] Distiller), and Infrared
Syngas Analyzer
Gasboard-3100P (Hubei Cubic-Ruiyi Instrument) were utilized. All
reagents were used as supplied.\looseness=-1

\subsection{Catalyst preparation}\label{sec22} 

Mesoporous FeO was incorporated into alumina through the incipient
wetness impregnation technique to synthesize 3\% and 5\% FeO loaded on
alumina (3\% and 5\% FeO/Al). The mesoporous FeO synthesized from
magnetic sand according to the method of Gano et~al.~\cite{33} was
used to prepare 3\% and 5\% FeO precursor solution. The predetermined
volume of precursor solutions, which is equivalent to the pore volume
of the alumina, was then carefully added to the support. The mixture
was continuously mixed until a homogeneous reddish-brown paste was
obtained. The paste was oven-dried at 105~\textdegree C overnight,
after which it was calcined in a muffle furnace for 3~h at
500~\textdegree C.

\subsection{Pyrolysis process}\label{sec23} 

PET pyrolysis was conducted using a multifunctional pyrolysis reactor
system (PRS) at the National Research Institute for Chemical Technology
(NARICT), Zaria (Figure~\ref{fig1}). The PRS consisted of a pyrolyzer and 
fixed bed reactor (FBR; stainless steel tube, 40 cm length, 1 cm internal
diameter; Figure~\ref{fig2}). Initially, 200 g of PET was charged into the
pyrolyzer followed by the passage of nitrogen gas at 0.5 bar for 1 h to
create an inert environment. Pyrolysis was then carried out at
350~\textdegree C until the pressure in the pyrolyzer reached 10~bar.

\begin{figure}
\includegraphics{fig01}
\caption{\label{fig1}Multifunctional pyrolysis and fixed bed reactor
system at NARICT, Zaria.}
\end{figure}

\begin{figure*}
{\vspace*{-3pt}}
\includegraphics{fig02}
{\vspace*{-3pt}}
\caption{\label{fig2}Process flow diagram for the pyrolysis
process.}
{\vspace*{-4pt}}
\end{figure*}

While the pyrolyzer pressure was building up, 0.5~g of the catalyst was
loaded in between glass wool plug beds inside the FBR. Prior to the
start of the catalytic reforming process, N$_{2}$ gas was allowed to
flow through the reactor at 0.5 bar for 15 min. Subsequently, the
catalyst was reduced under H$_{2}$ flow at 0.5 bar and 450~\textdegree
C for 90 min. When the pressure in the pyrolyzer is 10 bar, the bypass
valves are opened to allow the pyrolysis vapor to contact the catalyst
at 450~\textdegree C. At the end of the catalytic reforming process,
the product was passed through a condenser into a liquid gas separator
tank, where the condensable product is collected while the
non-condensable product is directed to an online syngas analyzer (Hubei
Cubic-Ruiyi Instrument) for \mbox{analysis.} The experiment was also conducted
using the same condition but without catalyst for comparison. 
\looseness=-1

{\vspace*{-1pt}}

\subsection{Catalyst characterization}\label{sec24}

{\vspace*{-1pt}}

Morphology of the samples was performed using a Phenom World 
scanning electron microscopy (SEM)
analyzer (Thermo Fisher, Waltham, US). Infrared data was collected
using a Shimadzu-8400S Fourier Transform Infrared Spectrometer (Kyoto,
Japan) over the range of 4000--400~cm$^{-1}$. X-ray diffraction (XRD)
measurements were conducted to determine the crystallinity of the
sample using a Rigaku MiniFlex X-ray Diffractometer (Texas, USA) with
$2{\theta}$ between 2\textdegree~and 80\textdegree~while elemental composition was
determined using a Genius IF Xenemetrix X-ray fluorescence
(XRF) analyzer (Jordan Valley).

{\vspace*{-1pt}}

\subsection{Product characterization}\label{sec25} 

The composition of non-condensable products (gas) was measured
using an online syngas analyzer (Hubei Cubic-Ruiyi Instrument). The
functional groups in liquid products were determined using an 
attenuated total reflectance (ATR) mode
of Shimadzu-8400S Fourier Transform Infrared Spectrometer (Kyoto,
Japan) within the scan range of 600--4000~cm$^{-1}$. The composition of
hydrocarbons in the liquid sample was determined using Agilent
19091S-433UI GCMS. Data was acquired using a 
$30~\mathrm{m}\times250~\upmu\mathrm{m}\times0.25~\upmu\mathrm{m}$
capillary column flow rate of carrier gas (helium) set to 1.169
mL/min at a flow velocity of 39.404 cm/s. The initial column
temperature was set to 50~\textdegree C and held for 5 min, and then ramped
to 300~\textdegree C at 10~\textdegree C/min for 20 min. A sample
volume of 1 ${\upmu}$L was injected using the splitless injection mode
at a temperature of 300~\textdegree C. The peaks of the resulting
chromatographs were identified using the National Institute of
Standards and Technology standard reference database.

\begin{figure*}
{\vspace*{-3pt}}
\includegraphics{fig03}
{\vspace*{-4pt}}
\caption{\label{fig3}SEM micrograph at ${\times}$2000 of (a) alumina, (b) 3\%
FeO/Al, and (c) 5\% FeO/Al.}
\vspace*{-4pt}
\end{figure*}

{\vspace*{-1pt}}
\section{Results and discussion}\label{sec3} 

{\vspace*{-1pt}}
\subsection{Catalyst characterization}\label{sec31} 

{\vspace*{-1pt}}
\subsubsection{SEM analysis}\label{sec311} 

The size and morphology of the catalyst samples were analyzed using SEM
analysis, and the results are shown in Figure~\ref{fig3}. Alumina
particles (Figure~\ref{fig3}a)
were irregular polyhedrons with angular shapes, which
may improve permeability after sintering; see Kim et~al.~\cite{34}.
Both 3\% FeO/Al and 5\% FeO/Al catalysts exhibited a rough, flaky
surface with irregularly shaped particles (Figures~\ref{fig3}b,c),
which were identified as mesoporous FeO deposited on the support
after impregnation. The lighter regions in the images are composed
primarily of the support while the darker regions are iron
particles~\cite{29,35}.  \mbox{Additionally}, the SEM images revealed many
smaller \mbox{particles} dispersed on the surface of the support in 5\%
FeO/Al, indicating successful dispersion of the mesoporous FeO on the
support. These observations confirm the successful synthesis of the
catalyst as supported by similar finding in the literature~\cite{36}.

The particle size analysis (Figure~\ref{fig4}) revealed the presence of
individual grains detectable at higher magnification (${\times}$2000) to be
predominantly in the range of 1.42--7.63, 1.37--10.75, and
2.66--6.34~$\upmu$m for alumina, 3\% FeO/Al, and 5\% FeO/Al, respectively.
The average particle diameters were 4.45, 4.74, and
3.85~$\upmu$m for alumina, 3\% FeO/Al, and 5\% FeO/Al, respectively. The
smallest particle size was found in 5\% FeO/Al. This suggests that
impregnation with mesoporous FeO increased the surface area and
therefore, could enhance the catalytic activity due to availability of
more active sites for reaction.


\begin{figure*}
\includegraphics{fig04}
\vspace*{-5pt}
\caption{\label{fig4}Histogram showing particle size distribution of
(a) alumina, (b) 3\% FeO/Al, and (c) 5\% FeO/Al.}
\vspace*{-5pt}
\end{figure*}


\subsubsection{XRF analysis}\label{sec312} 

The metal compositions determined by XRF analysis of all the
synthesized catalysts and supports are presented in Table~\ref{tab1}. As shown in
the table, the mesoporous FeO has been successfully incorporated onto
the support, with the percentage compositions of Fe detected to be
3.43\% and 4.74\% for 3\% and 5\% FeO/Al catalysts, respectively, while
Fe detected in alumina was just 0.11\%. These compositions are
comparable to the metal loadings in the calculation, suggesting that
the synthesis process was effective. Moreover, the Al compositions were
found to be 45.50\%, 47.11\%, and 47.90\% for 5\% FeO/Al, 3\% FeO/Al,
and alumina (the support), respectively, implying successful
impregnation. Other elements were detected in negligible
concentrations, signifying fewer impurities in the 
\mbox{synthesized}\unskip\break
catalyst. These findings are consistent with the work by Tanarungsun
et~al.~\cite{37}, where Fe and other metals were impregnated onto
TiO$_{2}$ support.


\begin{table}
\caption{\label{tab1}Elemental compositions of 3\% FeO/Al, 5\% FeO/Al,
and alumina}
\tabcolsep=2pt
\begin{tabular}{cccc}
\thead
{Elements} & \parbox[t]{2cm}{\centering 3\% FeO/Al (\%)} & 
\parbox[t]{2cm}{\centering 5\% FeO/Al (\%)} & 
\parbox[t]{1.5cm}{\centering Alumina (\%)}\vspace*{2pt} \\
\endthead
Si & \01.36 & \01.52 & \01.35 \\ 
AI & 47.11 & 45.50 & 47.96 \\ 
Fe & \03.43 & \04.74 & \00.11 \\ 
Ti & \00.00 & \00.01 & \00.03 \\ 
Ca & \00.38 & \00.16 & \00.17 \\ 
P & \00.01 & \00.00 & \00.01 \\ 
K & \00.00 & \00.00 & \00.00 \\ 
Mn & \00.01 & \00.01 & \00.01 \\ 
Mg & \00.21 & \00.75 & \02.14 \\ 
Zn & \00.04 & \00.07 & \00.04 
\botline 
\end{tabular}
\vspace*{-5pt}
\end{table}

\subsubsection{XRD analysis}\label{sec313} 

The XRD patterns obtained for alumina (a), 3\% FeO/Al (b), and 5\%
FeO/Al (c) are presented in Figure~\ref{fig5}. It was observed that the
pure alumina was the only crystalline phase identified by the 
International Centre for Diffraction Data (ICDD). 
However, the crystallinity of the synthesized catalyst
samples was not detected, indicating that the catalyst is amorphous in
nature. Amorphous catalysts have been shown to have higher surface
areas, more active sites, and enhanced reactivity~\cite{38}. Several
studies have reported similar results when iron oxide is doped on
alumina. For instance, Ramdhani et~al.~\cite{30}, Zhong 
et~al.~\cite{39}, and Kamboj et~al.~\cite{40}
\mbox{reported} the absence of crystalline peaks after impregnation of alumina
with iron oxide, suggesting the formation of an amorphous phase. The
formation of a non-crystalline phase when FeO is impregnated on alumina
could be because of high dispersion of Fe on the surface of the
catalyst as reported in a previous study~\cite{30}. Another factor
that could affect the crystallinity of the synthesized catalyst is the
calcination temperature (450~\textdegree C). Several researchers have
reported higher crystallinity for iron oxide doped on alumina at higher
temperatures in the range of 500--1000~\textdegree C~\cite{39,41}.

\begin{figure}
{\vspace*{3pt}}
\includegraphics{fig05}
{\vspace*{3pt}}
\caption{\label{fig5}XRD pattern for (a) 3\% FeO/Al, (b) 5\% FeO/Al, and
(c) alumina.}
{\vspace*{3pt}}
\end{figure}

\subsection{Product analysis}\label{sec32} 

\subsubsection{Analysis of gaseous products}\label{sec321} 

Gaseous products were analyzed using an online gas analyzer after
exposure to different catalysts. The obtained results are presented in
Figures~\ref{fig6}--\ref{fig8} for 3\% FeO/Al, 5\% FeO/Al, and blank run, respectively.
The compositions of the components were reported when the readings from
the analyzer stabilized, with values expressed as molar fractions in
percentage (\%). Oxygen content decreased from 23.3\% in the blank run
to 10.96\% and 5.33\% in 3\% FeO/Al and 5\% FeO/Al, respectively,
indicating a decrease in oxygenated compounds when the synthesized
catalyst was used. The H$_{2}$ content was highest in 5\% FeO/Al, with
a value of 17.14\%. Conversely, the CH$_{4}$ content was highest in 3\%
FeO/Al (16.22\%) and lowest in 5\% FeO/Al (12.11\%). The CO value decreased
from 14.02\% in the blank run to 12.51\% and 12.64\% in 3\% FeO/Al and
5\% FeO/Al, respectively, indicating an improvement in the synthesized
catalyst. The CO$_{2}$ value was found to be 20.96\%, 30.03\%, and 36.86\% for
the blank run, 5\% FeO/Al, and 3\% FeO/Al, respectively. Furthermore,
the low heating value was found to be 6.41, 7.72, and 7.84 MJ/m$^3$
for the blank run, 3\% FeO/Al, and 5\% FeO/Al, respectively. Similar
findings was reported by Dhahak et~al.~\cite{42} and Li et~al.~\cite{43}. 
It is evident that the presence of the catalyst has improved the
overall quality of the gas by reducing the O$_{2}$ content, and increasing
the  syngas (H$_{2}$/CO) and methane contents. These results
demonstrated the effectiveness of the synthesized catalyst in reforming
the pyrolysis gas. 

\begin{figure}
\includegraphics{fig06}
\caption{\label{fig6}Gas analysis of reformed PET pyrolysis vapor using
3\% Fe/Al catalyst.}
\end{figure}

\begin{figure}
\includegraphics{fig07}
\caption{\label{fig7}Gas analysis of reformed PET pyrolysis vapor
using 5\% Fe/Al catalyst.}
\end{figure}

\begin{figure}
\includegraphics{fig08}
\caption{\label{fig8}Gas analysis of pyrolysis vapor in blank run.}
\end{figure}

\subsubsection{Analysis of liquid products}\label{sec322} 

Fourier transform infrared-ATR (FTIR-ATR) spectroscopy and 
gas chromatography mass spectrometry (GCMS) techniques were used to study the
functional groups and hydrocarbon composition of the liquid products
obtained before and after reforming using 3\% and 5\% FeO/Al catalysts.
The FTIR spectra of the liquid product are shown in Figure~\ref{fig9}
while the major functional groups are presented in Table~\ref{tab2} with their
corresponding assignments. The results showed that the catalysts were
able to reform PET vapor into aliphatic alkanes as can be seen by the
presence of peaks at 2988 and 2899~cm$^{-1}$, which were
absent in the blank run. Additionally, the peaks at 929, 1290, 1420,
and 1689~cm$^{-1}$ appeared to be more prominent in the
reformed product using 5\% FeO/Al catalyst, suggesting an increase in
the quantity of aromatics. This underscores the excellent performance
of the synthesized catalyst. A similar result has been reported in a
previous study by Nasution et~al.~\cite{44}.

\begin{table*}
\caption{\label{tab2}FTIR assignments for liquid products obtained for
blank run and after catalytic reforming of pyrolysis vapor}
\tabcolsep=3pt\fontsize{9.5}{12}\selectfont
\begin{tabular}{cccccc}
\thead
Peaks (cm$^{-1}$) & Blank run & 3\% FeO/Al & 5\% FeO/Al & 
Type of vibration & Nature of functional group \\ 
\endthead
3050 & $\checkmark$ & $\checkmark$ & $\checkmark$ & C--H stretching  & Unsaturated aromatic \\ 
2924  & $\times$ & $\checkmark$ & $\checkmark$ & C--H stretching & Aliphatic alkanes \\ 
2854 & $\times$ & $\checkmark$ & $\checkmark$ & O--H stretching  & Alcohols \\ 
1689 & $\checkmark$ & $\checkmark$ & $\checkmark$ & C=O stretching & Alkenes \\ 
1420 & $\checkmark$ & $\checkmark$ & $\checkmark$ & C--H stretching  & Aromatic ring \\ 
1292 & $\checkmark$ & $\checkmark$ & $\checkmark$ & C--H scissoring and bending & Alkene \\ 
1180 & $\checkmark$ & $\checkmark$ & $\checkmark$ & C--O stretching  & Alcohols, esters, carboxylic acids \\ 
923 & $\checkmark$ & $\checkmark$ & $\checkmark$ & C--H bending & Alkene \\ 
713 & $\checkmark$ & $\times$ & $\checkmark$ & C--H bending  & Alkene, phenyl ring substitution \\ 
713 & $\checkmark$ & $\checkmark$ & $\checkmark$ & C--H bending  & Alkene, phenyl ring substitution 
\botline 
\end{tabular}
\tabnote{Key: $\checkmark  = \mathrm{present}$, $\times = \mathrm{absent}$.}
\end{table*}

\begin{figure}
\vspace*{2pt}
\includegraphics{fig09}
\caption{\label{fig9}FTIR spectra of liquid product for blank run and
after catalytic reforming of pyrolysis vapor.}
\end{figure}

The analysis of liquid products by GCMS provided insight into the
composition of hydrocarbons present with and without the catalyst. The
composition of hydrocarbons present in the samples is \mbox{summarized} in
Table~\ref{tab3} while the GCMS chromatogram is presented in Figure~\ref{fig10}.
The results showed a significant change in hydrocarbon composition
between the blank run and the reformed products. All the samples contained
mixtures of aliphatic and aromatic hydrocarbons. However, increasing
the percentage of mesoporous FeO impregnated in the catalyst (from 3\% to
5\% FeO) facilitated a selective catalytic reforming process as seen
in the significant reduction of peaks from the blank run to that in the 5\%
FeO/Al sample. This led to a reduction in the formation of undesirable
byproducts such as ketones, alcohols, esters, and acidic compounds,
which were found in \mbox{significant} amounts in the blank run. These findings
are in agreement with the work of Aisein et~al.~\cite{45},
Nasution et~al.~\cite{44}, and ROTTA et~al.~\cite{46}.
Moreover, the data obtained substantiates the presence of aromatics and
aliphatic hydrocarbons as inferred by the FTIR results. The findings
indicated that the synthesized catalyst could transform complex
pyrolysis vapor containing a wide range of products into a more
streamlined composition of hydrocarbons. Similar results have been
reported by\break Malik et~al.~\cite{47}.

\begin{figure*}
\includegraphics{fig10}
\caption{\label{fig10}GCMS analysis of liquid products from catalytic
reforming process (a) blank run, (b) 3\% FeO/Al and (c) 5\% FeO/Al.}
\end{figure*}

\begin{table*}
\caption{\label{tab3}Composition of liquid product obtained for blank
run and after catalytic reforming of pyrolysis vapor}
\tabcolsep=2pt\fontsize{9.5}{12}\selectfont
\begin{tabular}{lclclc}
\thead
Blank run & \parbox[t]{1.5cm}{\centering Relative area} & 3\% FeO/Al &
\parbox[t]{1.5cm}{\centering Relative area} & 5\% FeO/Al &
\parbox[t]{1.5cm}{\centering Relative area}\vspace*{2pt} \\ 
\endthead
Cyclohexane, methylene- & 0.1244 & Cycloeicosane & 1.1838 & Norbornane & 0.5448 \\ 
1,1'-Bicyclohexyl & 0.1193 & 1-Chloroeicosane & 2.1595 & Benzene, chloro- & 0.1316 \\ 
Biphenyl & 1.2557 & \parbox[t]{3cm}{\raggedright Octadecane, 1-(ethenyloxy)-} & 11.0148 & Cyclohexanol & 0.1455 \\ 
1,1'-Biphenyl, 3-methyl- & 0.1059 & \parbox[t]{3cm}{\raggedright Eicosane, 9-cyclohexyl-} & 1.2875 & 1,1'-Bicyclohexyl & 1.2929 \\ 
1,1'-Biphenyl, 4-methyl- & 0.1236 & \parbox[t]{3cm}{\raggedright Bis(2-ethylhexyl) phthalate} & 8.3623 & Biphenyl & 1.6627 \\ 
Fluorene & 0.2151 & Octacosanal & 0.9057 & Fluorene, 2,4a-dihydro- & 0.153 \\ 
(E)-Stilbene & 0.1875 & \parbox[t]{3cm}{\raggedright Methoxyacetic acid, heptadecyl ester} & 1.7296 & 1,1'-Biphenyl, 4-methyl- & 0.2786 \\ 
9-Hexadecenoic acid & 0.1144 & \parbox[t]{3cm}{\raggedright 9,12-Octadecadienoyl chloride, (Z,Z)-} & 15.3116 & Fluorene & 0.1634 \\ 
\parbox[t]{3cm}{\raggedright Phenanthrene, tetradecahydro-} & 0.1218 & \parbox[t]{3cm}{\raggedright Methoxyacetic acid, heptadecyl ester} & 4.1935 & Diisooctyl phthalate & 33.7527 \\ 
Phenanthrene & 1.4882 & 6-Nitroundec-5-ene & 10.4797 & \parbox[t]{3cm}{\raggedright Carbonic acid, octadecyl prop-1-en-2-yl ester} & 0.2488 \\ 
\parbox[t]{3cm}{\raggedright 2-Methyl-Z,Z-3,13-octadecadienol}\vspace*{2pt} & 0.1339 & \parbox[t]{3cm}{\raggedright 10-Methyl-E-11-tridece-1-ol 
{{acetate}}}
& 6.2048 & Octacosane & 21.1329 \\ 
\parbox[t]{3cm}{\raggedright 9,12-Octadecadienoic acid (Z,Z)-} & 0.2398 & 9-Octadecynenitrile & 12.0354 & Erucic acid & 1.0636 \\ 
Naphthalene, 1-phenyl- & 0.8766 & 7,11-Hexadecadienal & 4.9289 & \parbox[t]{3cm}{\raggedright 9,12-Octadecadienoyl chloride, (Z,Z)-} & 21.1182 \\ 
Anthracene, 1-methyl- & 0.2604 & 9-Octadecenal & 11.8024 & 9-Octadecenal & 18.0856 \\ 
o-Terphenyl & 1.9577 & \parbox[t]{3cm}{\raggedright 9,12-Octadecadienoyl chloride, (Z,Z)-} & 5.6292 & \multicolumn{1}{c}{--} & -- \\ 
Phenanthrene, 4-methyl- & 1.4162 & \multicolumn{1}{c}{--} & -- & \multicolumn{1}{c}{--} & -- \\ 
Heptadecane & 2.1588 & \multicolumn{1}{c}{--} & -- & \multicolumn{1}{c}{--} & -- \\ 
Naphthalene, 2-phenyl- & 1.1002 & \multicolumn{1}{c}{--} & -- & \multicolumn{1}{c}{--} & -- \\ 
Heneicosane & 0.1318 & \multicolumn{1}{c}{--} & -- & \multicolumn{1}{c}{--} & -- \\ 
m-Terphenyl & 0.4636 & \multicolumn{1}{c}{--} & -- & \multicolumn{1}{c}{--} & -- \\ 
p-Terphenyl & 0.2767 & \multicolumn{1}{c}{--} & -- & \multicolumn{1}{c}{--} & -- \\
1-Chloroeicosane & 0.1083 & \multicolumn{1}{c}{--} & -- & \multicolumn{1}{c}{--} & -- \\\tabularBreak{1}    

\parbox[t]{4.5cm}{\raggedright 2-Propenoic acid, 2-cyano-3-(4-dimethylaminophenyl)-, ethyl ester} & 0.1069 & \multicolumn{1}{c}{--} & -- & \multicolumn{1}{c}{--}& -- \\
\parbox[t]{4.5cm}{\raggedright Spiro[2.3]hexan-4-one, 5,5-diethyl-} & 0.1214 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\
9,12-Octadecadienal & 0.2133 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
1-Chloroeicosane & 0.8156 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
Eicosane & 3.0545 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
Diisooctyl phthalate & 13.8353 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--} & -- \\ 
Eicosane & 0.2271 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--} & -- \\ 
\parbox[t]{4.5cm}{\raggedright 9-Methyl-10,12-hexadecadien-1-ol acetate}\vspace*{2pt} & 0.7105 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
\parbox[t]{4.5cm}{\raggedright Carbonic acid, eicosyl vinyl ester} & 0.31 & \multicolumn{1}{c}{--} & --& \multicolumn{1}{c}{--} & -- \\ 
\parbox[t]{4.5cm}{\raggedright Hexadecane, 1-(ethenyloxy)-} & 0.331 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
\parbox[t]{4.5cm}{\raggedright Hexadecane, 1-(ethenyloxy)-} & 0.5 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
\parbox[t]{4.5cm}{\raggedright Phthalic acid, isohexyl neopentyl ester} & 13.803 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
\parbox[t]{4.5cm}{\raggedright Bis-(3,5,5-trimethylhexyl) phthalate} & 0.4155 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
\parbox[t]{4.5cm}{\raggedright 1,2-Benzenedicarboxylic acid, monobutyl ester} & 0.3703 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
Erucic acid & 0.3204 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
Eicosane & 0.5716 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
6-Nitroundec-5-ene & 0.8206 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
Cycloeicosane & 10.9885 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
Cycloeicosane & 0.2487 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
9-Octadecenal & 13.0695 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
9,12-Octadecadienal & 10.4876 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& -- \\ 
\parbox[t]{4.5cm}{\raggedright (Z)-1,3-Dimethoxypropan-2-yl docos-13-enoate} & 15.4166 & \multicolumn{1}{c}{--}& -- & \multicolumn{1}{c}{--}& --\vspace*{2pt} 
\botline 
\end{tabular}
\end{table*}


\section{Conclusion}\label{sec4}

This study investigated the pyrolysis of PET into fuel using
synthesized mesoporous FeO-based catalysts (3\% FeO/Al and 5\% FeO/Al).
Analyses using SEM, XRF, and XRD revealed the catalyst's well-defined
morphological, structural, and compositional properties. Reforming
using catalysts reduced oxygen content whereas CH$_{4}$ and H$_{2}$
contents were improved in the gaseous products. FTIR and GCMS analyses
of liquid products demonstrated the catalyst's ability to reform
pyrolysis vapor into valuable products.

These findings highlight the potential of mesoporous FeO-based
catalysts in converting PET waste into valuable fuel products. This
research contributes to the management of plastic waste by providing an
alternative pathway for its conversion into useful products.


\section*{Declaration of interests} 
The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\section*{Funding}

The authors appreciate the 
NARICT for the financial and technical support rendered in
carrying out this research under project number FGN/AB2021/{\ubreak}ERGP30122610.

\CDRGrant[NARICT]{FGN/AB2021/ERGP30122610}

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