Exclusive Review Papers in Catalytic Materials

Catalytic materials exist in several forms and can be prepared using different methodologies and protocols. They can also be applied in many fields, such as environmental and sustainable catalysis, renewable fuels production, synthetic chemistry, gas storage/capture, biocatalysis, catalysis, photocatalysis, chemical sensing, and so on.

This Special Issue includes outstanding reviews on catalytic materials for different applications. In this regard, biocatalysis received special attention in searching for new biotechnological advances. Contribution 1 reviewed a series of key parameters governing the enzyme–nanoparticle immobilization phenomena, from a thermodynamic and kinetic point of view. Special attention was focused on magnetite nanoparticles anchored to enzymes, leading to hybrid catalysts with an enhanced application as biocatalysts with special emphasis on cancer therapy. Enzymes have attracted great attention among researchers because of their ability to mimic relevant biological reactions carried out by their natural counterparts but with the capability to overcome natural enzymes’ drawbacks, such as low thermostability or narrow substrate scope. The promising enzyme-like properties of these systems make enzymes excellent candidates for innovative solutions in different scientific fields such as analytical chemistry, catalysis or medicine. Thus, contribution 2 explored the catalytic activity of gold enzymes and hybrid gold enzyme systems that combine gold with different nano or biomaterials to improve their performance. This review carried out a deep insight into gold-based enzymes, covering the enzymatic reactions and the structural features of these hybrid gold-based systems. The hybrid materials highlighted inorganic hybrids with carbon, MOFs and metal-based supports, and organic and biohybrids. This review provided a representative picture of the potential of these structures to solve future technological challenges in sensing, catalysis and biomedicine.

Thermocatalytic reactions, such as hydrogenation and dehydrogenation, are also under study where single-atom catalysts (SACs) are a trend in modern catalysis. Contribution 3 covered the relevance of nickel single-atom catalysts in hydrogenation and dehydrogenation reactions. It is currently used in industrial processes as a homogenous and heterogeneous catalyst. This review discusses recent advances in the synthesis, structure, and application of nickel SACs, mainly in catalytic hydrogenation/dehydrogenation reactions and in the dry reforming of methane. The information herein discussed can be useful for developing novel nickel SACs for various processes. The design of catalysts for hydrogenation reactions was also covered in contribution 4. This review focused on the application of heterogeneous catalysts for oxime hydrogenation to amines and hydroxylamines concerning the methods applied for pharmaceutical synthesis. The common way of amine synthesis implies the reduction of nitro compounds, nitriles, and imines, but with many restrictions and difficulties. Thus, heterogeneous catalytic hydrogenation of oximes appeared to be the simplest way to obtain amines or hydroxylamines. This review discussed the catalytic performance of different catalysts, mainly noble (Pt, Pd) and non-noble metals (Ni, Co) that can be used in industrial applications.

Environmental catalysis also received special attention, both for water and air purification. The presence of emerging contaminants in water sources has raised concerns worldwide due to low mineralization rates, and zero levels of degradation in some cases. For these reasons, researchers in the field are focused on advanced oxidation processes (AOPs) as a powerful tool for the degradation of persistent pollutants. These AOPs are based mainly on the in situ production of hydroxyl radicals (OH^•) generated from an oxidizing agent (H₂O₂ or O₂) in the presence of a catalyst. Contribution 5 paid special attention to the Fenton reaction, which stands out due to its operational simplicity and good levels of degradation for a wide range of emerging contaminants. However, it has some limitations, such as the storage and handling of H₂O₂. In this regard, this review focused attention on using the electro-Fenton (EF) process in which H₂O₂ is generated by the action of the oxygen reduction reaction (ORR). Different catalysts for both Fenton and ORR reactions were covered, including a detailed discussion of the most important factors controlling the catalytic performance. Contribution 6 complemented the relevance of AOP technologies for water treatment. In this case, the authors detailed the use of perovskite oxides as promising catalysts for different AOPs. The physical and chemical catalytic properties of perovskite were largely related to oxygen vacancies (OVs). In this review, the recent advances in the regulation of OVs in perovskite for enhancing the functionality of the catalyst were reviewed. An insight was provided into the OVs of perovskite and reduction mechanism in AOPs in this review, which is helpful for readers to better understand the methods of regulation and detection of OVs in various AOPs. Among the environmental issues under control nowadays, nitrogen oxide (NOx) removal also requires great attention due to legislative changes in environmental policies. In this regard, diesel engines work in most commercial vehicles to carry items from various firms; nevertheless, diesel engines emit massive amounts of NOx harmful to human health. Contribution 7 reviewed the selective catalytic reduction (SCR) technology as the main approach for reducing NOx emissions from diesel engines. After a detailed revision of the regulations, different diesel engines were considered, from personal vehicles to marine engines, providing a suitable starting point for future research into reducing NOx emissions from diesel engines, particularly for engines with comparable specifications.