Electron spin resonance studies of formation of SO –2 radicals on calcium oxide

Abstract

The formation of SO^–₂ radicals on CaO has been studied by e.s.r. spectroscopy. CaO, prepared by evacuating CaCO₃ at 1173 K was exposed to sulphur dioxide at 473 K. Under these conditions, SO^–₂ radicals were observed at concentrations of ≈ 3 × 10¹⁷ spins g^–1. The effect of the heat-treatment temperature of the starting CaCO₃ and of the adsorption temperature have been examined. The SO^–₂ radicals are stable up to 473 K, but decay with second order kinetics above 498 K. The radicals react with oxygen to form SO^–₄ radicals at 77 K and SO^–₃ radicals at room temperature.