Advances in Catalysts Research

The discovery of new technologies to potentially improve catalyst efficiency is seen as an emerging approach. The current chapter deals with the barriers that are being faced during advancing of different catalysts. Various strategies have been developed over the past few decades to overcome shortcomings such as cost inefficacy, instability due to moisture, salty environment and reduced work efficiency in heterogeneous condition. Extensive research is being carried out to find cheap and environmentally friendly renewable resources for the development of catalysts for different reactions. This chapter focuses on photocatalysis, electrocatalysis, and recent advances in biocatalysis. These techniques are employed due to their cost effectiveness and efficiency. So, we have detailed here working condition and mechanism of these techniques. Biocatalysis is described here in detail due to its green nature as emerging science is stressing upon green synthesis and catalysts.

Heterogeneous catalysis has become pivotal to the world chemical and petrochemical industry as nearly 90% of all chemical products are produced in the processes in which at least one stage involves the use of catalysts. In this chapter fundamental information on heterogeneous catalysis with its advantages and disadvantages is provided together with its use in different catalytic reactions.

Heterogeneous catalysis, using ferrites nanoparticles (NPs), graphene oxide (GO), and their nanocomposites, has garnered immense interest due to their distinct merits such as non-toxicity, facile synthesis, cost-effectiveness, and ease of recovery. Two important aspects covered under heterogeneous catalysis are enzyme mimic activity and photocatalytic degradation of organic pollutants. Ferrite NPs and GO-based composites have tunable properties as compared to pristine ferrite NPs and GO. The presence of GO in the nanocomposite endows it with numerous surface functional groups for interaction with different species which provide binding sites for metal ions and organic contaminants as well as enhance their enzyme mimic potential. On the other hand, the presence of ferrite NPs in the composites imparts magnetic properties to them. These enzyme mimics can be used in the biomedical application in enzymeless sensors, which are otherwise costly and require sophisticated storage conditions. Graphene-ferrite composites have greater surface area and lower band gap owing to which they have potential application as photocatalysts. The magnetic-GO NC can substitute commercially used TiO₂ which absorbs only ultraviolet radiations due to wide band gap (3.2 eV) for degradation of organic contaminants in the wastewater treatment. This chapter provides an overview of the recent strategies for the synthesis/properties of ferrites NPs/GO and their nanocomposites followed by their applications in the field of photocatalysis and enzyme mimics.

Artificial enzymes have received immense interest due to their exceptional properties such as high stability and low cost. Polyphenol oxidase enzyme is well known for its contribution in the field of food industry, biosensors, medicine, and water remediation. Thus, polyphenol oxidase mimics are now envisioned as a relevant alternative with a wide range of implementations in the field of biosensing. Till date, various nanomaterials along with metal complexes and metal–organic frameworks have been explored to mimic polyphenol oxidase activity. This chapter summarizes the latest progress in the field of polyphenol oxidase mimics, and highlights the factors affecting the polyphenol oxidase mimic activity. The kinetic studies and mechanism of polyphenol oxidase as well as its mimic has been compared. The biosensing techniques to evaluate the polyphenol oxidase and mimic activity of synthesized materials have also been reported. The future research challenges and opportunities to enhance the polyphenol oxidase mimic activity are summarized.

Recently, visible light-activated semiconductor photocatalyts have attracted the scientific community due to their immense success in wastewater treatment as well as decomposition of hazardous organic pollutants. In this work, sphalerite ZnS nanoparticles (NPs) with various ruthenium (Ru) concentrations have been synthesized via solvothermal method. The feasible doping of Ru into the ZnS matrix has been confirmed by structural characterizations. The electronic and optical properties have been investigated both experimentally as well as theoretically. Ru plays a vital role in the reduction of the optical band gap and simultaneous enhancement of the absorptivity towards the visible region of the solar spectrum. The photocatalytic degradation efficiency of Ru-doped ZnS has been tested for the degradation of methylene blue (MB) under visible irradiation of a light-emitting diode (LED). Photoluminescence quenching as well as Bader charge analysis have shown Ru acting as a charge centre, and plays a key role in the transfer mechanism. Moreover, due to incorporation of Ru, nonmagnetic ZnS becomes magnetic. The optical properties of the system significantly enhanced due to Ru. Thus proposed Ru-doped ZnS system can be a cost-effective superior photocatalyst as well as a good potential candidate for optoelectronic applications.

Ensuring the cleanliness and non-toxicity of water resources is crucial as they are the most valuable assets for human beings. Water pollution has emerged as a significant worldwide concern in recent times, particularly due to the contamination of diverse organic substances such as pharmaceuticals and personal care products (PPCPs), persistent organic pollutants (POPs), and organic dyes. Recently, the use of reactive oxidative radicals or species in photocatalysis, which is an advanced oxidation process, has garnered significant interest for the remediation of organic pollution. The utilization of photocatalysis in solar-powered reactions holds great potential in tackling energy and environmental issues. Effective light absorption, enhanced charge separation and mobility, and expedited surface reactions are crucial factors that greatly impact the effectiveness of photocatalysis, and these can be achieved through the thoughtful design of photocatalysts. Numerous global endeavors have been undertaken thus far to create and pursue high-performance materials, encompassing techniques like doping, amalgamating with quantum dots, regulating heterojunctions, optimizing exposed facets. The promising candidates consist of inorganic metal alloy/metal oxide/metal sulfide, organic–inorganic hybrid materials such as metal–organic frameworks (MOFs), and organic semiconductors like covalent organic frameworks (COFs). In the final part of the analysis, there are also discussions about the main obstacles and viewpoints regarding photocatalysts, aiming to contribute to the advancement of this vibrant area of research.

Trace N₂O emissions in ammonia burner during the nitric acid production process have received special attention as N₂O is recognized as a potent greenhouse gas that actively participates in global warming. The abatement of N₂O complies to international commitments aiming to reduce the greenhouse gas emissions through the installation of appropriate technologies. Different strategies have been categorized, the most efficient one involving the implementation of heterogeneous catalytic reactor in various positions of nitric acid plant. The catalyst composition strongly depends on the running temperature privileging mixed-metal oxides for N₂O decomposition at medium and high-temperature whereas Platinum Group Metal-supported catalysts can be preferred for end-of-pipe technologies running at low temperature with the help of reducing agent. This present chapter focusses on medium and high-temperature (350–900 °C) application. Different theoretical and experimental approaches will be discussed in order to get more insights into the design of active sites, especially under more realistic running conditions to improve the understanding of kinetics and get more relevant reaction mechanisms that could further provide guidelines for the preparation of more stable and selective catalysts.

The concentration of nitrogen oxyanions in natural waters has steadily increased in recent decades, as a result of the intensification of agriculture and population growth. Reverse osmosis, ion exchange, adsorption and electrodialysis are currently used as separation technologies for water denitrification. Also, nitrite reduction technologies such as biological treatment and catalytic reduction, are able to convert nitrite into inert nitrogen gas. Several studies have proposed the catalytic reduction of nitrite to nitrogen in water over Pd supported on different materials as a promising alternative for water treatment. In this chapter, an overview of the current state of the art of catalytic nitrite reduction is presented. The use of catalysts supported on CeO₂, Nb₂O₅, ZrO₂, TiO₂, γ-Al₂O₃, SiO_2, and ZSM-5 for the removal of high concentrations of nitrite in water is reported in this chapter. All synthesized materials were evaluated and they showed catalytic activity in the reduction of nitrites in the water. The total conversion was achieved by catalysts supported in γAl₂O₃, ZSM-5 (Si: Al = 30), SiO_2, and TiO₂. Among this group, the most nitrogen-selective under the evaluated conditions were supported on ZSM-5 (Si: Al = 30) and TiO₂. These findings contribute to the existing data, providing insights into previously untested materials as supports for water removal nitrite catalysts.

The ever-growing energy crisis and environmental pollution motivated scientific researchers to develop a green energy economy. Hydrogen generation through electrochemical water splitting has shown immense potentiality to be an important energy conversion technology towards the said goal. The electrochemical water splitting consists of two half-cell reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The overall water splitting is sluggish as both of these half-cell reactions involve multiple proton and electron transfer steps. Theoretical as well as experimental results have revealed that the noble-metal-based electrocatalysts (such as Pt and RuO₂) possess superior electrocatalytic activity toward water splitting. However, these materials lack commercial-scale applicability due to their high price and lower abundance. Recently, numerous investigations have been conducted to develop cheap and efficient noble-metal-free electrocatalysts. Pure water is a poor conductor of electricity and thus an electrolyte is added to facilitate the overall water-splitting process. The efficiency and cost-effectiveness of water electrolysis are higher in an alkaline medium if all the technical aspects related to it are considered together. An electrocatalyst with sufficient bifunctional activity towards both HER and OER in the same operational condition simplifies the electrolyzer optimization process and consequently, higher efficiency in full water splitting is achieved. So, a cheap and efficient bifunctional noble-metal-free electrocatalyst for water splitting in an alkaline medium is highly desirable. Borides, carbides, pnictides, and chalcogenides of transition metals like Fe, Co, Ni, etc. show significant promise in that context. Few transition metal-based heterostructures and engineered electrocatalysts also exhibit desirable bifunctional activity towards overall water splitting. This chapter provides a brief idea about electrocatalytic water splitting and also summarizes some recent advancements in noble-metal-free bifunctional electrocatalyst development. Finally, the future prospects in the development of efficient and cheap bifunctional electrocatalysts for water splitting have been discussed.

This chapter presents aspects related to the electrochemical approach to hydrogen technologies, considering key concepts that drive both the thermodynamic and kinetic phenomena of the redox processes involved. Strategies to improve surface processes on various electrode materials are considered. The fundamental approach to the development of applied technologies illustrates the impact on the environment and energy, as well as the role of related physicochemical processes.

The SO₄/TiO₂ acid and CaO/TiO₂ base catalysts have been successfully prepared for the conversion of waste frying oil into biodiesel. The acid catalyst was prepared through direct sulfation of TiO₂ with H₂SO₄, and the base catalyst was prepared through a thermal method between TiO₂ and CaO in an autoclave reactor. This process has been carried out with variations in the concentration and temperature of calcination. The purpose of this study is to obtain catalysts with the highest acidity and basicity values ​​and then apply them to the esterification and transesterification processes of waste frying oil into biodiesel. The results show that the SO₄/TiO₂-1.5–600 (where 1.5 is the concentration of H₂SO₄, and 600 is the calcination temperature in °C) was the catalyst with the highest acidity (2.49 mmol NH₃/g). Application of this catalyst in the esterification of waste frying oil was successfully achieved, with the highest reduction in free fatty acid (FFA) content of 66.21%. The transesterification reaction of the esterified oil was carried out using a catalyst with the highest basicity, CaO/TiO₂-20–700 (8.13 mmol HCl/g), (where 20 is the concentration of CaO, and 700 is the calcination temperature in °C). This catalyst succeeded in converting waste frying oil into biodiesel of 58.13% with the main composition of methyl ester being methyl oleate.