It is shown that a series of one- and two-electron-reduced heteropolya
nions of the Keggin- and Dawson-types convert quantitatively NO into N
2O in acidic aqueous media. The corresponding oxidized forms of the he
teropolyanions are fully regenerated. Unsubstituted and lacunary heter
opolyanions, as well as the substituted heteropolyanions of these two
groups, prove active in this context.