Mo-V-Phosphoric Heteropoly Acids and Their Salts: Aqueous Solution Preparation - Challenges and Perspectives

Vanadium‐containing heteropoly acids (HPAs) are effective acidic and oxidizing catalysts in various reactions. The existing wide application of such catalysts requires their safe, waste‐free, and easy preparation on a large scale. Unfortunately, the so‐called ether method, first suggested more than 100 years ago, is still mainly used for the purpose, producing a lot of harmful waste material. Nowadays environmental safety requirements necessitate revision of such preparation processes and searching for alternative methods of synthesis. At present, there exist a range of new methods for preparing HPAs, with a so‐called peroxide method seeming to be the most generally applicable one. For this reason, the aim of this review is to discuss some recent progress in obtaining aqueous solutions of Keggin and Wells–Dawson Mo‐V‐P HPAs and their salts. These solutions can be used as individual homogeneous oxidation catalysts, bifunctional catalysts for one‐pot acidic and oxidizing transformations, or precursors for preparing their heterogeneous analogues. Preliminary V2O5 activation by addition of hydrogen peroxide H2O2 allows one to obtain vanadium‐containing heteropoly acid (HPA) solutions directly from V2O5, MoO3, and H3PO4 without extraneous components. Such a synthetic pathway, named a peroxide route, offers a promising ecological method for preparing valuable Mo‐V‐P HPAs in short reaction times on a large scale.