Interaction of SO 2 with iron deposited on CaO(100)

Abstract

The interaction of SO 2 with iron-covered CaO(100) at 373, 473, and 673 K was studied using X-ray photoelectron spectroscopy (XPS). Iron was deposited onto a CaO(100) surface in the metallic form; however, at lower iron coverages, other forms of iron relative to the metallic form were present. Scanning auger mapping analysis showed a random distribution of iron on CaO at both low iron coverage and high iron coverage. The adsorbed sulfur at 373 K on pure CaO and at low iron coverages was identified as sulfite. At high iron coverages, both sulfide and sulfite were identified. The sulfite formation was higher at low iron coverage than on pure CaO, but it decreased with increasing iron coverage. It was found that the iron sites at high iron coverage were blocking the active sites on the CaO surface; the reactivity at high coverage was similar to that of pure metallic iron. Sulfide formation increased with increasing iron coverage. Similar observations were made at 473 K, but the reactivity on iron at high coverage was considerably lower than that at 373 K. The total sulfur adsorbed was observed to be higher for all iron coverages at 373 K than for pure CaO. At 673 K, the reactivity on iron-covered surfaces was lower than that at either 373 or 473 K. However, the reactivity of iron-covered CaO was more than pure CaO at 673 K.