The last decade has seen an increasing number of reports on the use of NHC–metal complexes for catalysis in water, therefore this review is aimed to introduce the whole research on this area, in which the use of water or aqueous/organic media is to be applied. Since the first discovery of the NHC carbenes by Arduengo, work on the synthesis of NHC–metal organometallic compounds has revolutionized the field of catalysis, gradually displacing the typical phosphine and amine-type ligands in view of their higher stability and reactivity. Aqueous catalysis has become a hot topic in Green Chemistry due to the positive implications for the use of water as reaction media.

A series of novel bis(NHC) Cu( i ) catalysts enables the production of triazoles with different substitution patterns and bioconjugation via “click” chemistry under homogeneous and/or heterogeneous catalytic conditions in aqueous media.

The growing demand for clean and efficient fuels in the world reflects the rapid growth in automotive vehicles and more stringent environmental regulations. Hence, the refining industry must employ diverse strategies to obtain a gasoline pool made up of streams from different processes focused on improving the fuel quality and the octane ratings suitable for the current demanding automotive performance. The composition of gasoline varies mainly from each country’s policies, climate, environmental regulations, financial capacity, and local producer’s oil refining infrastructure. However, a generally accepted composition by source of the gasoline pool is: FCC naphtha and reformate, making up about 60%, light straight-run naphtha and alkylate gasoline, around 30%, isomerate, close to 5%, and variable proportions of butane, oxygenating agents, such as methyl-ter-butyl ether (MTBE), ter-amyl-methyl ether (TAME) and/or ethanol and additives for the remaining 5%. This review is focused on the recent research in the advancement and development of catalysts for the different processes used by the oil refining industry to improve the composition and properties of gasoline fuels. A detailed section on the Fischer-Tropsch process, where liquid hydrocarbons are potentially employed to further produce clean gasoline, is also discussed. A section devoted to research on biogasoline as a potential renewable fuel is also addressed. Finally, a discussion of the physicochemical properties of the gasoline blending components is also provided. GRAPHICAL ABSTRACT

In the Oil Industry, part of the extracted crude oil is commonly found in form of emulsions, mainly as water-in-oil (W/O) and oil-in water (O/W), emulsions, and more complex emulsions are less frequent but can also be found, such as water-in-oil-in-water (W/O/W) and oil-in-water-in-oil (O/W/O). These emulsions must be broken before the starting of the oil refining process because water generates operational problems like increasing crude viscosity, corrosion of equipment, piping and clogging of pumps and equipment, causing unscheduled production stoppages. O/W emulsions, can also be intentionally generated as a strategy to reduce the viscosity of very heavy crudes and facilitate their transport to the storage, and processing center. However, in any case, these emulsions must be broken before the crude is processed. Different technologies employing chemicals, electric fields, membranes, biological techniques, ultrasound and microwaves have been studied to favor the breaking of O/W emulsions. Microwaves have proven to be an excellent alternative to break emulsions quickly, efficiently, and with minimal energy losses. This paper review accounts for the research studies on the microwave-assisted breaking of W/O and O/W emulsions for oilfield applications with and without the simultaneous application of demulsifying chemicals. The possible mechanisms by which microwaves accelerate emulsion breakage, and their advantages for a more sustainable industry are also discussed. Graphical Abstract