In this chapter, we have briefly studied electrocatalysis. Electrocatalysis plays an important role in many synthetic procedures, such as biodiesel production, CO2 reduction, O2 evolution reaction, etc. Numerous electrocatalytic kinetic characteristics are discussed to fairly assess the efficiency of electrocatalysts, including overpotential (η), exchange current density (i0 ) and Tafel slope (b). These variables are essential and provide valuable insight into the electrochemical reaction's process. Due to this, herein, we give a brief overview of these kinetic characteristics along with a review of different electrocatalysts for various reactions. 

Self-aggregates microenvironment affords a robust platform for synthesizing conventional and novel materials in aqueous media. Consequential enhanced the rate of reaction and reduced the barrier for organic solvents. A solvent is frequently asked to perform multiple tasks at once, such as ensuring contacts between substrates with different polarities, controlling heat transmission, and promoting the interaction that results in the ultimate transformation. Nature has chosen water as a solvent to carry out all types of chemical transformations, regardless of whether the substrates are soluble or not. Of course, surfactants resolve the various problems that arise from the interaction of insoluble substrates and reagents. The use of surfactants under micellar conditions represents one of the largest methods to achieve catalysis in water. To date, micellar systems are present in many areas, e.g., medical science, nanoscience, organochemistry and industries of their vast application. We explained the role of micelles and vesicles on the reactivity of nucleophiles towards the cleavage of the organophosphorus compounds. Recent developments includeapplication of micellar catalysis to complex single-phase and multiphase systems in which the surfactant plays multiple roles and interphase transport effects are often important. The distribution of the reagents between the aqueous phase and the micellar phase was described in terms of a simple pseudo-phase model (PPM). These quantitative treatments for the catalytic action of anionic reactants and the cationic micelles for cleaving the phosphate and thiophosphate ester improved an understanding of competitive counterion binding, the effects of reactive and inert solubilizates, functionalized surfactants, and the use of surfactant aggregates as reaction templates. 

 In recent years, attempts to follow green protocol in organic synthesis have emerged along with the use of green solvent, solvent-free reaction conditions, the concept of multicomponent reactions and use of green catalysts. Fe3O4 is an oxide of iron called magnetite mineral; it is a ferromagnetic and strongly magnetic mineral on earth. It was the first mineral structure that was applied in X-ray. It is found that the nanomagnetic oxide shows an inverse spinel structure. Its unique properties, such as high Curie temperature, high spin polarization, and verwey transition, gains attention towards it. Nano-magnetic oxide is employed as a green catalyst. It can be synthesized by physical methods, microbial methods and wet chemical preparation methods. It demonstrates excellent catalysis in organic synthesis that gives a good yield; it enjoys an advantage over other catalysts as it is easily separable from the reaction mixtures using a bar magnet, and it is green & eco-friendly. It also shows wide applications in various fields, such as water treatment, biodiesel production, lithium-ion battery, and the biomedical field.

Nanocatalysts revolutionize organic chemistry for the conversion of various organic reactions to obtain a high yield, low hazard and stability. It plays an important role in the transformation of organic reactions due to its high surface area, small size, and low reaction time. Therefore, green methodology, both in the synthesis of nanocatalysts and organic transformation reactions, is an advanced technology, and findings promise results. Many scientists all over the world synthesised nanoparticles and used them as catalysts in Knoevenagel condensation. In this book chapter, we documented the synthesis and characterisation techniques of the homo/hetero metallic nanocatalyst and applied it in the Knoevenagel condensation reaction for its reusability and easy separation after a chemical reaction because, in organic chemistry, separation is a tedious job for finding pure compounds.

Noble metals like platinum, gold, silver, rhodium, palladium and copper were used as catalysts and promoters in oligomerization hydrogenation, dehydrogenation, and oxidation reaction to get valuable chemicals, and green fuel without any harmful effect on the environment. Platinum, rhodium, palladium, copper, monometallic and bimetallic with reducible and non-reducible supported material zeolites, Si/Al, MCM-41 and Al2O3 show excellent activity toward conversion of reactants. Among noble metals, gold has shown low activity and high deactivation. The C4 hydrocarbon formation was faster than C6 during the oligomerization reaction over the metal catalyst at mild reaction conditions. 

Photocatalysis is gaining momentum for the degradation of persistent pollutants apart from other applications, including wide-scale industrial use. Non-Hazardous, efficient, greener approach and reusable properties make photocatalyst potential molecules for field application. Heterogenous make available solid surface, absorb photoenergy and initiate redox process for target molecules. Modification of heterogenous catalysis and improvement of the process is continuously accessed for better performance. The current chapter deals with some important practical aspects and challenges with some important heterogeneous catalysts like TiO2 , ZnO, CdS,etc.