Electron spin resonance studies of free and supported 12-heteropoly acids. Part 4.—The reduction of H3+n(PVnMo12–nO40)·xH2O and the influence of supports on their properties

Abstract

The reduction of PV_nMo_12–n heteropoly acids (HPA) with n= 1–3 has been studied, and a sequence of V⁴⁺ e.s.r. signals obtained is described. The main signal is a single symmetric line of 150–300 G width originating from interacting metal atoms. Although the vanadium ion is much more easily reduced, at high reduction temperatures an Mo⁵⁺ signal originating from the destroyed Keggin anion is additionally observed. The destruction of the Keggin anion structure is increased when loading the HPA on a support, which simultaneously improves the conditions for the formation of O^–₂ oxygen radicals. On alumina the typical properties of HPA were shown to change, as observed by e.s.r. spectroscopy.