Pickering emulsion-derived nano/microreactors for unconventional interfacial catalysis: state-of-the-art advances and perspectives in green reactions

Pickering emulsions (PEs) are an emerging class of surfactant-free dispersions, which are stabilized by solid particles such as nanoparticles, covalent-organic frameworks (COFs), metal-organic frameworks (MOFs), polymers, and proteins. They are very promising for green interfacial catalytic reactions. Many research groups around the globe are focusing on the design and development of innovative PE based nano/microreactor systems for interfacial catalysis owing to their multiple and unique features, such as environmental compatibility, remarkable stability, high selectivity, ease of preparation, high interfacial area, high conversions, and distinct stimulus responsiveness. Since their groundbreaking discovery in 2010, PE-based systems have been specifically identified and developed as efficient candidates for catalytic applications. In this review, we comprehensively described recent advancements in the design and preparation of PEs and systematically highlighted their applications in green catalysis using as-fabricated nano/microreactors, with a special emphasis on environmental safety. The most common mechanistic approaches used during the development of PEs are also discussed. Current research progress in the arena of unconventional catalytic reactions using PE based nano/microreactors is described with a focus on diverse catalytic reactions including Pickering interfacial catalysis (PIC), thermo-responsive MOF-based PE catalytic systems, and cascade reactions. Finally, the current challenges and future development of PEs for catalysis are discussed.