Characterization of clinoptilolite by interaction of H₂S, CO, and SO₂ by the e.s.r. technique

A study was made of the interaction of H₂S, CO, and SO₂ over activated clinoptilolite at 400°C using the electron spin resonance (e.s.r.) technique. It was observed that the CO- paramagnetic ions are formed over fresh activated clinoptilolite when treated with CO at ∼ 400°C. It was also observed that two types of SO₂^- ions, i.e., A-type SO₂^- with hyperfine structure (h.f.s.) and B-type SO₂^- without h.f.s. are formed over clinoptilolite depending on the experimental conditions. The B-type SO₂^- ion takes part in the reduction of SO₂ by CO or H₂S. The presence of CO over fresh activated clinoptilolite poisons the sites that are responsible for the formation of B-type SO₂^- ions. At room temperature, adsorbed H₂S on the fresh activated clinoptilolite is responsible for the formation of paramagnetic Al³⁺ ions in the structure of clinoptilolite. Clinoptilolite has both electron-accepting and -donating sites. A plausible mechanism for the interaction of H₂S, CO, and SO₂ over activated clinoptilolite is discussed.