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Rajak, et al.

Impregnation is one approach that is frequently used to create biodiesel, which also shows how these metal
to enhance the performance of mixed metal oxides. oxides interact with various feedstocks and reaction
Comparing impregnation to monometallic oxides, as conditions. According to Table 3, these modified
was covered in Section 5, the catalyst’s stability, surface catalysts produce normalized time results ranging from
area, and acid or basic strength are all improved. For 79% to 98%, showing that they are quite reactive. In
instance, at a low temperature of 60°C, doping MgO with some circumstances, catalysts treated with sulfonic acid
9% lithium results in a FAME production of 93.9% and can accomplish 100% FAME conversion. However,
an oil-to-methanol ratio of 12:1. The amount of water their catalytic activity may be reduced by high methanol
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in crude oil and FFAs is also well tolerated by catalysts concentrations. Widely utilized in metal oxide
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made of mixed metal oxides during transesterification. catalytic processes, mesoporous SBA-15 is prized
Calcium-containing perovskites (calcium titanate, for its exceptional qualities, including big, consistent
calcium manganate, calcium ferrite, calcium zirconate, pore size, large contact area, corrosion resistance, and
and CaO-cerium dioxide) are among the metal oxides recycling. 344
that are known for their great stability and capacity to
generate high FAME yields. 336 6. The efficiency of heterogeneous catalysts in
biomass-derived biodiesel production
5.6. Mixed-metal oxide derivatives for biodiesel
production While some studies have examined biodiesel quality,
When producing biodiesel, mixed-metal catalysts a comprehensive analysis is beyond the scope of this
have shown strong catalytic activity, especially when article. The feedstock’s fatty acid composition affects
increasing the effectiveness of active catalytic sites. various quality characteristics, including density,
By using this method, less catalyst is required to retain viscosity, and cetane number. These elements determine
good catalytic performance and get high conversion the total quality of the fuel and how well the biodiesel
rates. When paired with sulfate metal oxides, mixed- separation and purification procedures work. These
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metal catalysts show better structural and physical refinement stages and the FAME profile have an
characteristics than their monometallic counterparts. impact on parameters, such as the pour point and flash
The different sulfated oxides and mixed-metal catalysts point. Heterogeneous catalyst efficacy is primarily
utilized in the transesterification reaction, together with assessed by biodiesel production and conversion
information on their feedstocks and references, are conditions, which are impacted by energy efficiency
described. With normalized time yields continuously variables, such as reaction time and temperature. In
over 90%, Table 3 highlights the efficiency of catalysts every case, extra methanol and the catalysts should be
made of mixed metals doped using sulfated oxides. The collected and re-utilized. In the process, heterogeneous
CaO-MgO combination stands out among the several catalysts usually exist as solid phases, in contrast
oxides of mixed metals due to its great efficacy. 338 to homogeneous catalysts, which are liquid-based.
Several studies have shown that adding MgO, CaO, or A major limitation of heterogeneous catalysts is the post-
zinc to catalysts increases the incidence of saponification separation procedures, notwithstanding their benefits,
in addition to catalytic activity. Sulfate ions, which which include reduced methanol use. The increased
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may be added to transition metals, increase the acidity cost of these catalysts is still a drawback, albeit it can
of the catalyst and produce both acidic and superacidic be decreased by employing pre-cursors produced from
sites. As sulfonation increases the number of sites biomass.
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for Lewis and Brønsted acids, it increases the surface Heterogeneous catalysts have an adjustable surface
acidity and produces electrophiles. Sulfonation is area, porosity, basicity, and acidity, which increase
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also the recommended method for controlling metal the variety of feedstocks that may be utilized for
oxide hydrophobicity, which is a crucial component in esterification and transesterification. In addition, these
maximizing catalyst performance. catalysts remove the need for extra pre-treatment to
The benefits of doping solid acid heterogeneous lower the FFA concentration, which makes them very
catalysts with sulfated oxides have been emphasized helpful for processing oils with high acidity.
in a number of investigations. Typical solid super acids The biodiesel yields that range from 89% to
include sulfate, zirconium dioxide, sulfate-titanium 99% may be obtained using biomass-based CaO
(IV) oxide, sulfate-tantalum oxide, and sulfate/niobium catalysts. However, when catalyst loadings were
oxide. An overview of sulfated metal oxides is added large (25%), Pawar et al. found reduced conversion
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Volume 22 Issue 5 (2025) 24 doi: 10.36922/AJWEP025130095