KINETICS AND MECHANISM OF A SELF- OSCILATION REACTION OF KEPLERATE-TYPE POLYOXOMOLIBDATE DEGRADATION IN AN AQUEOUS SOLUTION

Abstract

Mechanism of the $\{\text{M}{{\text{o}}_{\text{132}}}\}~=~{{(\text{N}{{\text{H}}_{\text{4}}})}_{\text{42}}}[\text{Mo}_{72}^{\text{VI}}\text{Mo}_{60}^{\text{V}}{{\text{O}}_{\text{372}}}{{(\text{C}{{\text{H}}_{\text{3}}}\text{COO})}_{\text{3}0}}{{({{\text{H}}_{\text{2}}}\text{O})}_{\text{72}}}]$(~300H₂O)·(~10CH₃ COONH₄) polyoxomolybdate degradation in an aqueous solution is proposed and substantiated for the time using kinetic modeling. The mechanism includes four stages: I) non-catalytic cleavage of the Mo–O bond between the polyoxomolybdate fragments; II) recovery of the bonds between the polyoxomolybdate fragments; III) catalytic cleavage of the Mo–O bond between the polyoxomolybdate fragments; IV) increase of O₂ concentration due to the decay of the conjugate pair $\text{O}_{2}^{\bullet -}/\text{HO}{{\text{O}}^{\bullet }}$ releasing the oxygen molecule and due to O₂ diffusion from the gas phase into the polyoxomolybdate aqueous solution. A kinetic model of the considered process is proposed. It is shown that bond recovery prevails over bond cleavage in the polyoxomolybdate due to low residual O₂ concentration in the solution. At the same time, increasing the O₂ concentration in the solution up to some “critical” value restarts the avalanche-like autocatalytic process of Mo–O bond cleavage in the polyoxomolybdate.