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Rajak, et al.

The impregnation process is also known as capillary to create a sol and a gel. Due to its great versatility, the
and dry impregnation. The solution is absorbed into approach may work with a wide range of pre-cursors,
the supporting material and then dried to remove the most frequently alkoxides (M(OR)n)‐. 269
solvent from its substrate. A solid-particle-based colloidal solution called the
The two main categories of this technique are wet sol and a continuous liquid phase called the gelation
impregnation and dry impregnation. The size of the phase are the two main stages of the sol-gel process. 273,274
solution and the method of solid-solution interaction Numerous benefits, including excellent yields, low
are the primary distinctions between the two. Wet temperatures of operation, and cost-effectiveness, are
impregnation uses an excess solution that is then dried provided by the sol-gel technique. This method has
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after a pre-determined amount of time. In dry starting been used effectively in many research studies, such
wetness impregnation, the quantity of solution utilized as those by Sharm et al., Ciesielczyk et al., Danks
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is at least as large as the amount of pore space of the et al., Navas et al., and Rahman et al., Based on
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active phase or sustaining solid. 263,264 A number of the following equations, the sol-gel process usually
variables, such as temperature and the starting solution’s involves three primary routes: hydrolysis (Equation I),
concentration, might impact the effectiveness of the condensation (Equation II), and mixed condensation
impregnation methods. 265,266 Wetting time, solution (Equation III).
viscosity, and pre-cursor solubility are all impacted by –MOR+H O→–MOH+ROH (I)
temperature. 267,268 Studies have successfully used the 2
impregnation approach, such as the creation of potassium –MOH+ROM–→–MOM+ROH (II)
fluoride/CaO nano-catalysts. 269,270 For instance, to –MOH+HOM–→MOM+H O (III)
transesterify soybean oil, a lithium/zinc oxide catalyst 2
was made through impregnation and calcination.
Catalytic activity and catalyst characteristics were 4.6. Co-solvent preparation method
shown to be correlated in the study, which also noted A co-solvent system consists of water mixed with a
that the calcination temperature and lithium loading miscible or partially miscible organic solvent, creating
affected lithium/zinc oxide performance. a modified aqueous medium. This phenomenon,
Benefits of the impregnation process include reduced termed cosolvency, relies on the solvent’s dual
expenses, quicker preparation, and improved control characteristics: hydrogen-bonding capacity (either as
over the end-product catalyst properties. However, donor or acceptor) and the presence of hydrophobic
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achieving a homogeneous catalytic component domains. These properties enable co-solvents to modify
dispersion on the support surface is a difficult task. solution thermodynamics and enhance the solubility
of diverse compounds. To increase catalytic activity
4.5. The sol-gel process and accelerate the catalyzed processes, the co-solvent
The sol-gel method serves as a versatile approach for approach is a catalyst preparation methodology that
both catalyst synthesis and feedstock preparation. overcomes limitations in mass transfer between oil and
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This wet-chemical technique involves the transition methanol. In several transesterification processes,
of a colloidal suspension (sol) into a continuous three- tetrahydrofuran is frequently employed as a co-solvent
dimensional network (gel), enabling the production of in co-solvent catalyst systems. The effectiveness of this
homogeneous, high-purity materials with controlled strategy has been shown in a number of investigations,
porosity. The process begins with nanoparticle with the co-solvent technique producing FAME yields
dispersion in the liquid phase, followed by controlled that range from 90% to 98.5% conversion. 282,283
agglomeration and gelation, making it particularly
valuable for creating tailored catalytic materials and pre- 5. The impact of heterogeneous catalysts’
cursor formulations. A popular technique for catalytic chemical and physical characteristics on
feedstocks having colloidal characteristics, such as biodiesel production
silicon dioxide, the sol-gel method is comparable to the
precipitation process. The sol-gel procedure ensures The functionality of catalysts that are uniform, which
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a consistent distribution of components and allows usually appear in the liquid state, differs from that of
for the fabrication of porous materials, in contrast to catalysts that are heterogeneous and have a solid shape.
conventional catalyst preparation methods. Usually, Although homogeneous catalysts are readily accessible,
inorganic pre-cursors or colloidal dispersions are used reasonably priced, have quick processing times, and

Volume 22 Issue 5 (2025) 20 doi: 10.36922/AJWEP025130095