Abstract: Molybdophosphoric acid with Keggin structure is an effective catalyst for oxidation reactions.As the central atom, coordinated atom and equilibrium atom in the molydophosphoric acid are displaced in a suitable manner, it exhibits increasing catalytic properties although the structure of the anion keeps unchanging, In this paper a series of Keggin molybdophosphoric acids containing different equilibrium cations were synthesized by a coprecipitation method.The prepared samples were characterized by means of FTIR, XRDand other techniques.Particularly the thermal stability of Li(Na,K, Cs)equilibrium molybdophosphoric salts were investigated.The catalytic acitivity over this series of samplers for one-step oxidation of isobutyraldehyde to produce methacrolic acid was measured as well.The experimental results indicate that Cs⁺ equilibrium molybdophosphoric salts is the best catalyst for the mentioned reaction.

Key words: Molybdophosphoric salt with Keggin structure, Equilibrium cation, Stability, Catalytic oxidation, Isobutyraldehyde