Recent Progress in Selective Oxidations with Hydrogen Peroxide Catalyzed by Polyoxometalates

Abstract

In this chapter, we summarize recent progress achieved in the liquid-phase selective oxidation of organic compounds using hydrogen peroxide as the green oxidant and anionic transition-metal oxide nano-sized clusters or polyoxometalates (POMs) as catalysts. POMs possess a unique combination of properties, including inorganic nature, metal oxide-like structure, thermal stability, thermodynamic stability to oxidation and hydrolysis over a wide pH range, tunable solubility, acid, and redox properties. In recent years, POMs have received significant attention as homogeneous molecular catalysts and building blocks for the construction of heterogeneous catalysts for green selective oxidations. Therefore, both homogeneous and heterogeneous POM-based catalyst systems will be covered in their relevance to the environmentally benign production of vital oxygen-containing compounds and oxidative decontamination of toxic compounds. The chapter starts with a description of some novel highly selective POM catalysts capable of heterolytic activation of H2O2. Then new approaches to biphasic catalysis with POMs are discussed in terms of their compliance with the principles of green chemistry. Finally, recent achievements in POM immobilization techniques, such as irreversible adsorption on carbon nanomaterials, encapsulation within supramolecular complexes covalently anchored to silica, and incorporation within metal–organic frameworks, are surveyed with special attention given to catalyst stability and reusability.