Review of TiO₂ as Desulfurization Catalyst for Petroleum

Abstract

In the relentless pursuit of sustainable energy solutions, the petroleum industry faces the imperative challenge of mitigating sulfur emissions. This comprehensive review scrutinizes Titanium Dioxide (TiO₂) as an extraordinary catalyst, pushing the boundaries of desulfurization performance in petroleum refining. The abstract begins by underscoring the urgent need for advanced desulfurization technologies, driven by stringent environmental mandates and escalating global energy demands. The spotlight then shifts to the unparalleled physicochemical attributes of TiO₂, showcasing its inherent advantages such as exceptional surface area, stability, and photocatalytic process. A profound exploration of TiO₂’s catalytic mechanisms follows, unraveling its capacity to disintegrate stubborn sulfur–carbon bonds, thereby elevating desulfurization efficiency to unprecedented levels. This review meticulously dissects diverse forms of TiO₂, ranging from nanoparticles to mesoporous structures, and provides a critical analysis of their respective strengths and limitations in catalyzing sulfur removal. Delving into operational nuances, this review examines the impact of temperature, pressure, and catalyst loading on TiO₂ performance, offering crucial insights for optimizing desulfurization processes. The narrative then unfolds to explore cutting-edge developments in TiO₂-based catalysts, encompassing ingenious modifications, composites, and hybrid materials designed to augment catalytic activity and selectivity. Anticipating the road ahead, this review contemplates the challenges and prospects of deploying TiO₂ on an industrial scale, pointing toward avenues for future research and development. This abstract encapsulates a wealth of knowledge, serving as an indispensable resource for researchers, engineers, and policymakers navigating the dynamic landscape of sustainable petroleum refining. TiO₂ emerges as a transformative force, propelling the industry toward cleaner, greener, and more efficient energy production.

1. Introduction

This versatile and well-researched mineral, titanium dioxide (TiO₂), has emerged as a significant option for tackling the essential problem of sulfur removal in petroleum refining operations. Titanium dioxide is a material that has been investigated extensively [1]. As environmental regulations throughout the world grow more rigorous, there has been an increase in the need for cleaner fuel technologies [2]. This has led to an increased focus on the development of desulfurization catalysts that are efficient [3]. By diving into its one-of-a-kind qualities, synthesis processes, and the novel modification strategies that boost its efficacy in removing sulfur from petroleums, this study offers a complete investigation of the function that titanium dioxide (TiO₂) plays as a catalyst for desulfurization [4]. The relevance of titanium dioxide in this field is derived from the fact that it has remarkable photocatalytic characteristics, strong stability, and is safe for the environment [5]. In spite of this, the use of titanium dioxide in the desulfurization of petroleum goes beyond the photocatalytic capabilities that it has on its own [6]. This is because of its large surface area and its capacity to be modified and adjusted via a variety of different synthesis and modification processes [7]. These factors are essential for improving the interaction between sulfur-containing compounds and titanium dioxide, which will ultimately facilitate the removal of these compounds in an effective manner [8]. The purpose of this study is to shed light on the many processes that may be used to enhance the catalytic performance of titanium dioxide (TiO₂) [9]. These processes include doping with metals or non-metals, the creation of composite materials, and the manipulation of its crystal structure [10]. The purpose of each of these tactics is not only to improve the catalytic activity of titanium dioxide (TiO₂) but also to overcome the intrinsic constraints of this material, such as its poor conductivity and broad band gap, which limit its activity when exposed to visible light [11,12]. Through the synthesis of the most recent developments and discoveries from research, the purpose of this study is to give a comprehensive perspective on the potential of titanium dioxide (TiO₂) as a catalyst for desulfurization [13]. It conducts an in-depth analysis of the issues that are now being encountered in the industry, investigates the environmental and economic repercussions that will result from the implementation of technologies based on titanium dioxide, and seeks to foresee future avenues for study and application [14]. The study highlights the crucial role that titanium dioxide plays in upgrading petroleum refining processes, with the goal of future fuel choices that are cleaner and more sustainable being widely accessible [15].

The current state-of-the-art innovation at the forefront, therefore, has to be titanium dioxide (TiO₂) for the pressing challenge of sulfur removal during upstream petroleum-refining operations. Despite many studies, a very important challenge is how to tailor and optimize the catalytic behavior of TiO₂ for efficient sulfur removal in petroleum refining, meeting the increasingly stringent needs of environmental regulations [16,17].

Global environmental cleaning norms are tightening day by day; the need for cleaner fuel technologies has increased by leaps and bounds. Highlighting the demand, the market shows a high need for extremely effective desulfurization catalysts; research and development efforts were thus focused on TiO₂ [18].

This review will, hence, describe the unique characteristics of TiO₂, preparation processes, and advanced modification techniques available for efficient performance improvement during sulfur removal from petroleum feedstocks. Although TiO₂ is recognized as one of the most powerful environmentally benign photocatalysts [19], the potential of this semiconductor in the field of petroleum desulfurization is by no means limited to the area of photoactivity.

Additionally, the relatively large surface area of TiO₂ and its tunable properties allow its surface modification by many synthesis methods. Such processes are also important in providing more active sites for sulfur species, which will interact with the TiO₂ to facilitate the effective removal of such species from petroleum streams [20].

In this review article, we are going to present various strategies for enhancing TiO₂ catalytic activity, including metal and non-metal doping, composite material synthesis, and crystal structure manipulations. Each of these approaches separately aims to increase TiO₂ catalytic activity, overcoming the intrinsic weaknesses of low conductivity and a wide band gap that limits performance under visible light illumination.

Our work is intended to provide a full perspective on the potential role of these TiO₂-based materials as catalysts in petroleum desulfurization by reflecting the state-of-the-art in developing TiO₂ catalysis. Critically looking at challenges in the industry, environmental implications, and economic considerations, we are going to lead, hoping for broad-based acceptance of TiO₂ technologies in processes related to petroleum refining. Special attention will be paid to the central place for TiO₂ in developing petroleum-refining processes for cleaner, more sustainable fuel choices to be realized in the not-too-distant future. This work conducts an in-depth analysis of the issues now being encountered in the industry, investigates the environmental and economic repercussions that will result from implementing technologies based on TiO₂, and seeks to foresee future avenues for study and application. The study highlights the crucial role of TiO₂ in upgrading petroleum-refining processes, with the goal of cleaner and more sustainable future fuel choices being widely accessible.

2. Advancements in Desulfurization Techniques Using TiO₂

A lot of research has been done on the function of TiO₂ nanoparticles in the ever-changing landscape of petroleum desulfurization technology [21]. These nanoparticles have been intensively examined because of their potential to improve the removal of sulfur compounds dramatically [22]. The efficacy of TiO₂ nanoparticles has been highlighted by a recent study [23]. This effectiveness may be due to the high surface area-to-volume ratio of these nanoparticles, which also increases their catalytic activity [24]. This property, in conjunction with their capacity to distribute evenly in the reaction medium, makes it possible for the catalyst and sulfur compounds to interact more effectively, which ultimately results in superior desulfurization outcomes [25]. Furthermore, developments in modifying TiO₂ nanoparticles have opened up new paths for improving their performance. Techniques such as doping with metal ions (for example, Ag and Cu) and the deposition of metal nanoparticles onto TiO₂ surfaces have been found as potential solutions to boost both the activity and the selectivity of TiO₂ in sulfur removal procedures [26]. These techniques have been recognized as successful in achieving the desired results [27]. Not only do these alterations affect the electrical structure, but they also affect the surface properties of TiO₂, ultimately increasing the catalytic efficiency [28]. Combining TiO₂ with other materials, such as activated carbon, to create hybrid catalysts synergizes desulfurization efforts [29]. These hybrids combine adsorptive and catalytic capabilities, greatly increasing the efficiency of sulfur removal [30]. Furthermore, TiO₂ in photocatalysis offers an environmentally friendly method of desulfurization [31]. This method uses ultraviolet (UV) light to oxidize sulfur compounds selectively, thereby highlighting the versatility and potential of TiO₂ in developing more sustainable desulfurization technologies [32]. The aforementioned developments shed light on the growing potential of TiO₂ nanoparticles in revolutionizing desulfurization procedures within the petroleum sector [33]. Through formulations, researchers are paving the road for more efficient and ecologically sustainable desulfurization solutions [34]. The desulfurization by using TiO₂ is shown by Figure 1.

3. Comparative Analysis of Catalysts in Petroleum Desulfurization

Within the realm of potential catalysts for the desulfurization of petroleum, TiO₂ stands out as a particularly promising option [36]. This prominence is because it has amazing photocatalytic characteristics and a huge surface area, both of which assist in the efficient oxidation of sulfur compounds [37]. That is why it is so useful. In contrast to conventional catalysts, TiO₂ uses UV light to activate photocatalytic reactions [38]. According to Kondamareddy (2018), this method of removing sulfur harms the environment less [39]. The photocatalytic regeneration capacity of TiO₂ offers an operational benefit, as shown by the findings of a 2020 study by Shang and colleagues. This advantage might reduce the expenses of catalyst turnover [40]. Zeolites, on the other hand, are characterized by their porous structure, which enables them to absorb sulfur compounds effectively [41,42,43]. This is in contrast to the situation described above. Zeolites are a good example of this [44].

Nitrogen compounds can poison molybdenum-based catalysts, such as Co-Mo/Al₂O₃which are often used in hydrodesulfurization processes [45]. These catalysts are more sensitive to being poisoned than others [46]. The reason is that, compared to other catalysts, nitrogen molecules are more reactive [47]. According to Bhatkhande (2002), this widespread problem reduces the efficiency of these catalysts in processing heavy petroleum fractions [48]. This problem has existed for quite some time. TiO₂ is immune to this kind of poisoning, which is one aspect contributing to its endurance and flexibility across a larger variety of desulfurization applications [49]. TiO₂ also resists corrosion that may occur when exposed to high temperatures. Various doping strategies have been developed to enhance the photocatalytic activity of TiO₂ when subjected to visible light. Consequently, TiO₂ use has been enlarged beyond the limitations imposed by the band gap inherent to the material [50]. This is a noteworthy achievement.

TiO₂ is a viable option that balances performance, cost, and environmental impact in the petroleum-refining industry [51]. This selection is made possible because of the research demonstrating the progression towards the development of sustainable and efficient desulfurization technologies [52]. This research also illustrates the movement toward developing technology for desulfurization [53]. The purpose of this endeavor is a more optimal equilibrium between the operational efficiency of refining technologies and their environmental impact [54]. To achieve this goal, a significant amount of attention will be placed on research and development in this particular field [55].

4. The Efficiency of TiO₂ in Removing Sulfur Compounds

The effectiveness of TiO₂ as a photocatalyst in the removal of sulfur compounds has been extensively investigated, and the results have been verified across a wide range of environmental applications [56]. TiO₂ has a significant amount of potential in the fight against pollution and the enhancement of both air and water quality, as this illustrates [57]. The ability of TiO₂ to harness UV light and use it to initiate a chain of chemical reactions that ultimately decompose sulfur compounds significantly contributes to the photocatalytic capabilities of this material [58,59]. The procedure in question has been the focus of a significant amount of studies carried out to lower environmental pollution [60].

Under the influence of UV light, TiO₂ can form electron-hole pairs. Electron-hole pairs are a key component in creating reactive oxygen species (ROS), which include hydroxyl radicals and superoxide anions [61,62]. ROS are produced when electrons and holes are paired together. With the help of these ROS, sulfur compounds may be oxidized with great efficiency, transforming these compounds into less harmful molecules. For instance, sulfur dioxide (SO₂), which significantly contributes to air pollution, can be oxidized to sulfate (SO₄²⁻) ions, so diminishing its impact on the environment when released into the atmosphere. This shift is vital to improving air quality, particularly in urban and industrial areas, where large concentrations of sulfur dioxide emissions are prevalent [63]. TiO₂ has shown remarkable effectiveness in water treatment operations, especially when it comes to the elimination of sulfides and other substances that include sulfur from wastewater. This capability has been particularly impressive [64]. The photocatalytic activity of TiO₂, which may break down these compounds, can prevent the release of toxic substances and unpleasant odors often associated with industrial effluents. This can be accomplished by preventing the release of these compounds. It is simpler to reuse and recycle wastewater that has been treated, thanks to this capacity, which not only improves the quality of the water but also contributes to the long-term viability of water resources [65]. This capacity also makes it possible to reuse and recycle treated wastewater. Additionally, the production of nanostructured TiO₂ has increased the photocatalytic efficiency of the material because the nanostructured TiO₂ has a greater surface area and a higher reactivity. The rate at which sulfur compounds decompose is sped up because of the improved capability of nanostructured TiO₂ to absorb UV light and form ROS. The findings of Fujishima, Zhang, and Tryk (2008) [66] indicate that this discovery has significant repercussions for developing more efficient photocatalytic systems to clean up the environment. Additionally, the utilization of TiO₂ is not devoid of challenges, even if it is effective. These challenges include optimizing its activity under visible light and restricting the recombination of electron-hole pairs generated by photons. Both challenges are tough to overcome [67]. Doping TiO₂ with non-metals or combining it with other semiconductors is being investigated for expanding the photocatalytic activity of TiO₂ to include the visible light spectrum [68]. The practical use of the material and its efficiency in environmental applications would both rise consequently [69].

In the process of eliminating sulfur compounds from the environment, TiO₂ stands out as a not only highly efficient but also very flexible photocatalyst [70]. Combined with the ongoing advancements in material science, the fact that it can destroy impurities when exposed to UV light exemplifies its potential to contribute to developing environmentally friendly management strategies [71]. Hence, future research and development efforts are anticipated to continue to focus on enhancing the photocatalytic efficiency of TiO₂ and increasing its use across a wide range of environmental remediation situations [72]. The photocatalytic activity of Titanium Dioxide described in Figure 2.

5. Titanium Dioxide: A Sustainable Option for the Petroleum Industry

Incorporating TiO₂ into the petroleum sector highlights a multi-dimensional approach to improving sustainability [74]. This method leverages the unique features of TiO₂ to contribute majorly across a variety of dimensions. In hydrocracking operations, TiO₂ as a catalyst support material not only improves the conversion of heavy crude fractions into more valuable lighter products but also emphasizes a commitment to energy efficiency and decreased carbon emissions [75]. Moreover, its involvement in environmental remediation, especially in photocatalytic applications, demonstrates its promise in reducing the environmental footprint of petroleum operations by speeding up the degradation of organic pollutants [76]. This potential was shown by its ability to mitigate the environmental impact of petroleum operations. TiO₂ in protective coatings and paints serves two purposes. It improves the durability and resistance to corrosion of infrastructure and equipment, thereby reducing the amount of maintenance and potential environmental hazards [77]. Additionally, it contributes to the aesthetic and functional aspects of UV protection and thermal regulation. Hinting at the broader implications of TiO₂ in facilitating a transition toward renewable energy sources, the energy sector’s pivot toward sustainability finds an ally in TiO₂, particularly in reflective coatings and dye-sensitized solar cells [78]. TiO₂ is particularly useful in reflective coatings.

These many uses demonstrate the role that TiO₂ plays not only in improving operations within the petroleum sector but also in guiding the industry toward not only a more environmentally responsible but also more sustainable future [79]. Nevertheless, the story of TiO₂’s sustainability is complex, and it is necessary to analyze in-depth the environmental costs connected with its manufacturing compared to its advantages [80]. Finding a happy medium between these two elements is necessary to make the most of the promise of TiO₂ as a sustainable alternative. The miscellaneous functions of TiO₂ are presented by Figure 3.

6. Challenges and Opportunities in TiO₂-Based Desulfurization

Desulfurization based on TiO₂ is a persuasive approach for removing sulfur compounds from several industrial streams, such as flue gases and fuels [82]. This effectiveness is because TiO₂ has photocatalytic properties, which allow it to remove sulfur compounds from these streams [83]. The decrease in emissions of sulfur dioxide (SO₂), which significantly contributes to acid rain and air pollution, is one of the significant opportunities of this technology for preserving the environment [84]. Because of its high efficiency, stability under light irradiation, and powerful oxidizing capability, TiO₂ has been the subject of a significant amount of research as a photocatalyst, as it can convert sulfur compounds into sulfates that are safe when exposed to ambient conditions [85].

On the other hand, desulfurization accomplished by TiO₂ is not devoid of its fair share of challenges. TiO₂ has a substantial band gap, which limits its photocatalytic activity to the UV region of the sun’s spectrum [86]. This portion of the sun’s spectrum accounts for only around five percent of the whole solar spectrum. This is one of the most important challenges. TiO₂ requires alteration to increase its absorption in the visible light range to accomplish this goal. Doping the material with metals or non-metals or sensitizing the material with organic dyes is a potential method for accomplishing this goal [87]. There are also more methods. Another challenge to be conquered is the recombination of electron-hole pairs throughout the process. This phenomenon reduces the efficiency of the photocatalytic process. According to Kim et al. (2021) [88] one of the potential approaches that might solve this problem is the development of composite materials capable of facilitating charge separation and transfer. This is one of the recommended tactics.

TiO₂-based desulfurization in practical applications is associated with many challenges, including those pertaining to scalability and cost-effectiveness. However, to apply these discoveries to industrial settings, it is necessary to construct both robust and long-lasting photocatalytic systems capable of functioning well over extended periods in conditions representative of the real world. This is the case despite experiments carried out in the laboratory showing encouraging results. Furthermore, reactor designs need optimization to enhance the interaction between TiO₂ and sulfur-containing compounds, which will improve the efficiency of desulfurization [89].

Solar energy has the potential to be a viable source for photocatalytic desulfurization, which is a prospect in TiO₂-based desulfurization [90]. Other potential uses include the creation of novel materials and techniques that can operate in the presence of visible light. Recent discoveries in nanotechnology have opened the door to producing such quantum dots [91]. Adsorption of sulfur compounds and photocatalytic conversion would both be improved due to this, which would eventually improve their efficiency. Additionally, the use of photocatalysis based on TiO₂ in conjunction with other treatment procedures results in more comprehensive and effective desulfurization systems. These systems can manage a greater range of sulfur compounds, which further reduces the adverse impacts on the environment.

Although TiO₂-based desulfurization encounters hurdles concerning photocatalytic efficiency, light absorption, and scalability, continual research and technological developments are opening up new chances for solving these problems. More efficient, cost-effective, and environmentally benign desulfurization solutions can be produced [92]. This potential can be realized through more efficient changes to TiO₂, as well as through creating unique reactor designs and incorporating other processes [93].

Figure 4 represents sunlight as the source of energy because it is the energy source needed for the photocatalytic reaction.

1. TiO₂(R): This stands for TiO₂ particles, sometimes as a surface, or particles. You can make use of small circles for TiO₂ or particles. Call this TiO₂(R) to represent the reactant state.

2. Adsorption of Sulfur Species: Illustrate adsorption of sulfur species onto TiO₂ nanoparticle surfaces. This can be indicated via arrows or labeling for the interaction.

3. Photocatalytic Reaction: Show a scheme of the photocatalytic reaction, where sunlight is used to activate TiO₂ nanoparticles in order to oxidize sulfur species to less harmful compounds. This can be shown by either arrows indicating the flow of electrons or chemical transformations.

4. C-TiO₂ (A): Display the TiO₂ nanoparticles under illumination, usually denoted by C-TiO₂ (A), to represent the catalyst in the active state.

5. Desorption of Products: Explain how the desorption of reaction products is obtained from the surface of a TiO₂ nanoparticle [93].

7. Future Perspectives of TiO₂ Catalysis in Fuel Purification

Considering the growing demand for cleaner fuels and the increasing stringency of environmental restraints, the prospects for future TiO₂ catalysis in fuel purification are relatively optimistic [95]. To a certain extent, the present situation may be attributed to both elements. When removing sulfur and nitrogen molecules from fuels with hazardous emissions, TiO₂ is an appealing choice. TiO₂ in fuel purification processes is going to be expanded as a result of this study. A few instances of improvements have the potential to increase the photocatalytic activity of TiO₂, which will result in it being more successful in the removal of pollutants at lower energy inputs [96]. These innovations can improve the efficiency of the removal of pollutants. Two examples of these developments are the formation of heterojunctions with other semiconductors and the doping of semiconductors with elements that are not metallic.

According to Joo et al. (2012), the synthesis of nanostructured titanium dioxide also results in a rise in the surface area and the number of active sites [97]. This, in turn, leads to an increase in the catalytic activity and efficiency of the processes that are engaged in the purification of fuel. There is still another area of study that has the potential to result in purifying systems that are more efficient and cost-effective [98]. This field of research involves combining TiO₂ with modern separation technologies, such as membrane filtration. A large number of challenges are still involved in bringing these discoveries from the laboratory to the commercial level. This process is more complicated than it seems. To guarantee that TiO₂-based catalysis in fuel purification is both economically possible and sustainable, major breakthroughs in reactor design and process optimization are important [99] because it is necessary to ensure that the process is optimized.

Additionally, the shift to a low-carbon economy and the drive toward renewable energy sources needs the development of fuel purification techniques that are not only kind to the environment but also sustainable in the long run. In line with the objectives of global sustainability, TiO₂ catalysis provides an option that is not harmful to the environment by using solar energy for photocatalytic processes [100]. This needs consideration. Continued research and development efforts are necessary to overcome the limitations now in place and unleash the full potential of TiO₂ in fuel purification. This situation is because of the existing limitations. Hence, the energy industry can progress toward a future that is not only more environmentally friendly but also more sustainable [101].

Figure 5 shows the visualization crystal structure of TiO₂, used to view the structural and electronic properties of TiO₂; therefore, their importance is enormous for their application to photocatalysis and semiconductor devices.

8. Environmental Impact of TiO₂ Catalytic Desulfurization

Not only does the catalytic desulfurization of TiO₂ significantly and positively impact the environment, but it also offers a sustainable approach to lowering pollutants in the air and protecting ecosystems. This effect is because it reduces the SO₂ released into the atmosphere [103]. To lessen the SO₂ released into the environment from industrial operations and the combustion of fossil fuels, desulfurization procedures are used. The fact that these pollutants substantially contribute to acid rain, respiratory difficulties, and the damaged ecosystem is something that has to be considered. When decreasing these emissions, desulfurization technologies are very important techniques to implement. TiO₂ catalysis plays a crucial role in the transformation of sulfur compounds into molecules that are less dangerous to the environment, such as sulfates [104]. This outcome is due to the photocatalytic capabilities of TiO₂, which converts sulfur compounds effectively. The process being explained here is one shown to protect the environment. This contribution has been of great use to the community of researchers, and they have profited much from it.

The desulfurization process based on TiO₂ can be performed in ambient circumstances without requiring additional harmful chemicals. This decreases the carbon footprint associated with activities that include sulfur removal [105]. One of the most significant benefits of this specific kind of desulfurization is its beneficial effect on the environment. TiO₂ can absorb solar energy for photocatalysis, which is in line with the global trend toward environmentally friendly energy sources. The fact that this is an extra topic of interest is something that should be mentioned. Several studies, such as Moma et al. (2018), have shown that this modification contributes to reducing emissions of greenhouse gases and enhances the sustainability of energy [106].

That being said, extensive research on the durability of TiO₂ is of the utmost importance while also considering the impact on the environment. In the study by Gatou et al. (2024), [107]. The production of TiO₂ nanoparticles was hypothesized to include processes that need substantial energy as well as the consumption of possibly dangerous compounds. If these processes are not handled appropriately, there is a possibility that they may undermine some of the positive consequences that they have on the environment. This scenario is because they can harm the environment. It has been shown in recent studies [108], that the primary focus of their investigation is on reducing the negative impacts of these outcomes. There are three primary core areas of emphasis for this research project. These include the development of environmentally friendly synthesis methodologies, the recycling of TiO₂ catalysts, and the recycling of nanoparticles. Figure 6 represents the effect of different catalytic desulphurization on environment.

Additionally, implementing TiO₂ catalytic desulfurization on a large scale can significantly enhance the quality of both air and water. Specifically, this is because of the possibility of treating SO₂. To be more precise, this is because the produced sulfates are often less harmful to the environment and simpler to control in contrast to the sulfur compounds they are generated from. The many beneficial consequences of this approach on the environment are shown by this particular example. The harm caused by acid rain might probably be very destructive to the ecosystems of both aquatic life and woods, and this is something that deserves consideration.

The TiO₂ catalytic desulfurization technology is one of the most promising options for preserving the environment as it offers a technique that is not only more effective but also more ecologically friendly and renewable. This tech makes it one of the most promising alternatives. Hence, it is widely regarded as one of the most fascinating methods for preserving the natural environment. The research by Shafiq et al. (2022), [110] indicates its potential to cut down pollution of the environment significantly and to contribute to the efforts being undertaken to promote global sustainability. Both these conclusions are based on the findings of researchers described before. It is not out of the question that this promise will be fulfilled via implementing technologies advantageous to the environment, as well as through ongoing research to enhance the production and use of TiO₂ [111]. Precious metal deposition modification high selectivity for photocatalytic degradation of organics revealed in Figure 7.

These precious metals can be deposited through a few methods, which include electroplating, physical vapor deposition (PVD), chemical vapor deposition (CVD), and electrodeposition. In the electroplating procedure, metal ions from the electrolyte solution are electrochemically reduced at the electrode surface while an electrical current passes through the bath. In PVD methods, the metal source is in the solid form, and the atoms are mostly transported to the substrate through sputtering or evaporation. Precursor gases deposit metal films by a chemical reaction at the substrate surface in CVD. In electrodeposition, metal ions in solution are deposited on the substrate by an applied external electrical potential. The techniques generally make it possible to deposit thin and uniform coatings of precious metals on several surfaces.

9. Cost-Benefit Analysis of TiO₂ as a Desulfurization Agent

TiO₂ as a desulfurization agent is an example of a cost-benefit study that illustrates the complex relationship between the progress of technology, the preservation of the environment, and the growth of the economy. The findings of the study indicate a positive correlation between these three components, which proves the case [113]. How these three qualities interact reveals a quite obviously complicated connection between them. The initial expenditures in manufacturing catalysts from technologies based on TiO₂ could be more than those for classic desulfurization agents. This possibility is supported by current evidence. At this point, it is possible to do this. The fact is that there is a chance that this situation adds credibility to the concept being addressed in this particular context. The manufacturing processes required for TiO₂ nanoparticles are more complicated than the procedures required for conventional desulfurization agents, as stated by Gaetano et al. (2014) This conclusion can be drawn from the investigations conducted [114]. This is the reason things transpire in the manner they do. Furthermore, the incorporation of light sources into industrial applications is of utmost importance because the photocatalytic characteristics of TiO₂ need UV light to be activated. If this incorporation happens, there is a risk that the monetary expenses may increase.

On the other hand, with desulfurization activities, the utilization of TiO₂ is linked to a wide range of advantageous outcomes that are considered significant and intricate. In the desulfurization process, the high efficiency and stability of TiO₂ provide economic advantages that are maintained over an extended period. Researchers Haghighi et al. found that one advantage is the reduced frequency of replacement of catalysts, and another one is the eliminated need for additional chemicals [115]. The entire cost of the therapy is decreased as a direct consequence. Because of this, the quantity of extra chemicals required to fulfill the criteria is reduced. Wang et al. (2020) pointed out that the capability of the system to function in mild circumstances decreases energy consumption, which further reduces operating expenses [116]. The fact that this is an extra topic of interest is something that should be mentioned.

Therefore, it is possible to conclude that the use of TiO₂ conforms to the principles of green chemistry, which indicates that it is either ecologically responsible or helpful to the environment. The use of this resource results in various advantages. Along with reduced production of secondary pollutants, the emission of greenhouse gases may also decrease, which is one of the potential advantages. Various studies, such as Verma et al. (2022), have shown that these advantages can reduce the costs associated with environmental compliance and improve the sustainability profiles of enterprises. Furthermore, these advantages can decrease the pricing of the product [117]. Because TiO₂ can use solar energy for photocatalytic processes, cost reductions can take place over a longer period. According to Tsuyoshi (2012), renewable energy sources can be used to further lessen the effect of desulfurization operations on the environment [118]. The battle against the deteriorating environment has taken a huge stride ahead with this measure. This results from the fact that the action in question can now be carried out once it has been made feasible.

Two examples of the improved TiO₂ modification methods now being carried out to boost photocatalytic activity under visible light are doping with non-metals and producing heterojunctions. Both examples are the improvements being made at this very moment around the globe. According to Asahi et al. (2001), these changes can reduce the reliance on UV light sources, as well as the costs of the use of energy. Additionally, this can positively impact the environment [119]. Furthermore, this can reduce the burden of energy use, which is a significant benefit. Additionally, to make this technology more cost-effective, it is necessary to do research and development on TiO₂ catalysts that are not only more effective but also recyclable [120].

Because of the environmental and economic benefits of these technologies, desulfurization methods based on TiO₂ constitute a compelling case in their favor. Some of these advantages include the reduced amount of energy used, a decrease in emissions, and conformity with environmental regulations. Although the initial and continuing costs connected with these technologies may be higher than those associated with traditional methods, the benefits of these technologies offer a solid argument for their usage [114]. This is the case even though these technologies may be more expensive than conventional procedures. According to Zheng et al. (2002), ongoing research and technological advancements are anticipated to further improve the cost-benefit ratio of TiO₂ as a desulfurization agent, thereby making it an increasingly feasible alternative for environmentally responsible industrial operations [121]. TiO₂ is particularly successful in lowering the quantity of SO₂ emitted into the environment. The fact that titanium dioxide (TiO₂) is a desulfurization agent will shed light on the reason why this is the case. Titanium dioxide (TiO₂) is a chemical that is particularly successful in lowering the quantity of sulfur dioxide that is emitted into the environment [122]. A comprehensive analysis for the production of TiO₂ presented in Figure 8.

The manufacturing cost of TiO₂ is highly likely to vary very much, given the production process, price of energy, and, to a lower extent, the availability of raw materials and labor costs. TiO₂’s estimated production cost is currently between USD 1500 and USD 2000 per metric ton in September 2021. Per-ton cost divided by 1000 works out to be roughly USD 1.50 to USD 2.00 per kilogram. Remember, these are very rough numbers, and all the other factors mentioned above can easily move the results to the upside [123].

10. Challenges in Future and Practical Applications

In the realm of petroleum refining, TiO₂ integration as a catalyst for desulfurization has emerged as a promising avenue, heralding a new era of sustainability and efficiency. While the manuscript delves into the multifaceted applications and advantages of TiO₂ in petroleum desulfurization, it is imperative to acknowledge the potential challenges that may arise in its practical implementation and propose appropriate solutions.

• Photocatalytic Efficiency Under Visible Light: A significant hurdle lies in optimizing TiO₂’s photocatalytic activity beyond the UV spectrum, as its current efficiency is limited to a small portion of solar irradiation. Solution: Investigating novel techniques such as doping TiO₂ with non-metals or coupling it with other semiconductors could expand its light absorption range into the visible spectrum, thereby enhancing its overall efficiency [124].
• Recombination of Electron-Hole Pairs: The recombination of electron-hole pairs during the photocatalytic process diminishes TiO₂’s efficiency in degrading sulfur compounds. Solution: Developing composite materials or heterojunctions that facilitate efficient charge separation and transfer can mitigate electron-hole pair recombination, thereby improving TiO₂’s efficacy
• Scalability and Cost-Effectiveness: Transitioning TiO₂-based desulfurization from laboratory-scale experiments to industrial applications poses challenges in terms of scalability and cost-effectiveness [125]. Solution: Investing in the development of robust, long-lasting photocatalytic systems and optimizing reactor designs to enhance TiO₂-sulfur compound interactions can improve the efficiency and economic viability of TiO₂-based desulfurization processes.

Future Directions and Solutions

Solar Energy Utilisation: Leveraging solar energy as a viable power source for TiO₂ photocatalysis presents a promising avenue for sustainable desulfurization. Solution: Continued research into solar-driven photocatalytic systems and the development of efficient reactor designs tailored for solar energy utilization can enhance the feasibility and sustainability of TiO₂-based desulfurization.

Nanotechnology Advancements: Recent advancements in nanotechnology offer opportunities to enhance TiO₂’s catalytic efficiency by synthesizing nanostructured TiO₂ with increased surface area and reactivity. Solution: Further research into nanostructured TiO₂ synthesis techniques and their integration into desulfurization processes can lead to more efficient and cost-effective purification systems [126].

While TiO₂ holds immense promise as a sustainable catalyst for petroleum desulfurization, addressing the challenges of photocatalytic efficiency, scalability, and cost-effectiveness is crucial for its successful implementation in practical applications. By embracing innovative solutions and continuing to push the boundaries of research and development, the petroleum industry can unlock the full potential of TiO₂ for achieving cleaner, more sustainable energy production. The removal of sulfur- and nitrogen-containing compounds present in petroleum fractions described in Figure 9.

TiO₂ catalyzes the conversion of sulfur and nitrogen-containing compounds in fuel oil into less harmful forms. It, therefore, reduces air pollution as the pollutants change into forms easier to capture or destroy in industrial processes.

11. Conclusions

TiO₂ has shown a tremendous amount of promise as a catalyst in the process of desulfurizing petroleum, as shown by the findings of this extensive inquiry. Additionally, it has shed light on the vital role that TiO₂ plays in creating ecologically friendly energy solutions within the petroleum sector. This role is something that has been an important contribution. The rigorous environmental rules and the rising demand for energy all over the world have increased the need for improved desulfurization procedures. This demand has been on the rise because of the combination of these two factors. Because of this demand, there has been a need for research into innovative materials, such as TiO₂, which provide greater performance in sulfur removal methods.

Compared to other materials, TiO₂ stands out for its amazing physicochemical qualities. These properties include its enormous surface area, outstanding photocatalytic efficacy, and long-lasting stability in a wide range of environments. During the process of breaking down the very strong sulfur–carbon bonds in crude oil, TiO₂ has unparalleled effectiveness due to its unique properties (for more information, see TiO₂). Therefore, the quality of petroleum products is greatly improved by lowering the amount of sulfur they contain to conform to the regulations that the government has established for the environment.

The examination of the catalytic processes of TiO₂ within this research comprehensively looks at the many available forms of TiO₂ in the context of desulfurization. The nanoparticles, mesoporous structures, and composites that fall within this category are all examples. Each and every one of these forms comes with its unique collection of advantages and difficulties associated with the application procedure. For enhancing the methods of desulfurization, fully grasping the interactions of these TiO₂ forms with sulfur molecules is of the utmost importance. This information is brought to light in a way that is both obvious and convincing by examining various TiO₂ forms. A variety of operational factors, including temperature, pressure, and catalyst loading, have been investigated to shed light on the effect of these variables on the desulfurization performance of TiO₂. It is especially important to have this knowledge to enhance the operational parameters of desulfurization operations as it offers the highest potential level of efficiency and cost-effectiveness. Consequently, it is very significant. The study also studies the most current developments in manufacturing TiO₂ catalysts, which include novel modifications and hybrid-material synthesis. These developments are among the items being investigated. Furthermore, the research investigates the consequences of these discoveries in the technological field. These developments are being made to improve the catalytic activity, selectivity, and durability of the catalyst over time.

The study offers insight into the obstacles inherent in scaling desulfurization processes based on TiO₂ for industrial applications. These issues are known as scaling challenges. This activity is done with an eye on future prospects. The management of catalyst deactivation, the incorporation of TiO₂ catalysts into the infrastructures of refineries that are already in place, and the requirement for cost-efficient production procedures are some things that fall under this category. Despite the challenges, TiO₂ seems to have a promising future in petroleum desulfurization. This optimism is shown by the various study avenues that may be pursued, as well as the anticipated potential technology advances. Using TiO₂ as a catalyst for desulfurization in the petroleum sector indicates the continuous change toward developing cleaner, more environmentally friendly, and more efficient energy. This transition is enabled by the use of TiO₂. As researchers, engineers, and government officials continue to investigate and improve technologies based on TiO₂, the prospect of significantly reducing sulfur emissions and developing environmentally responsible methods for refining petroleum is becoming more apparent. The wealth of information presented in this research demonstrates the transformational capacity of TiO₂ in tackling the environmental and energy concerns faced presently. A vast store of information is provided as a foundation for future study. Additionally, this review offers a wealth of information to the reader. TiO₂ catalysis is expected to play a huge role in creating a sustainable future for refining petroleum, which will represent a substantial step forward in terms of environmental stewardship and energy security. This outcome is something that is predicted to have a fair probability of being accomplished via ongoing innovation and collaboration actions throughout the scientific and industrial sectors.