Applications of transition metallates in catalysis

Transition metallates have attracted much attention as one important kind of transition metal containing catalysts with the advantages of low cost, commercial availability, less toxicity, and good stability. Metallate is the name given to any complex anion containing a metal ligated to several atoms or small groups. Typically, the metal will be one of the transition elements and the ligand will be oxygen (oxometallate: WO₄^2-, PMo₁₂O₄₀^3-, etc.), other chalcogenide (thiometallate: MoS₄^2-, etc.), or halogen (halometallate: PtCl₆^2-, TiF₆^2-, etc.). The properties of metallates can be controlled by transition metal substitution and the counter-cations alteration at molecular levels. However, most of the research on applications of metallates in catalysis is focused on oxometallates. In this review, besides oxometallates, the other kinds of transition metallates such as thiometallates, cyanometallates, and halometallates as the efficient catalysts in catalytic reactions are also summarized. Furthermore, the use of metallates in combination with ionic liquids is emphasized herein, which is regarded as a promising method to guarantee the recyclability of metallate catalysts.