Interactions of NO and SO 2 with iron deposited on silica

Abstract

The interactions of NO and SO 2 with both clean and iron-deposited, single-crystal surfaces of SiO 2 at temperatures of 298, 473, and 673°K were studied using X-ray photoelectron spectroscopy. Neither NO nor SO 2 showed any reaction with clean SiO 2 at the three temperatures studied. The iron that was deposited onto the SiO 2 surface remained in the metallic state. Both NO and SO 2 interacted with this iron-covered silica (Fe/SiO 2). The total amount of adsorbed gas increased with increased iron coverage. Two forms of nitrogen, nitride and molecularly adsorbed NO, were observed when an Fe/SiO 2 surface at 298°K was exposed to NO. When the reaction was carried out at 473°K, the amount of nitride increased, but molecularly adsorbed NO was no longer observed. AT 673°K, neither form of nitrogen was observed. An adsorbed oxygen peak appeared at all three temperatures. The presence of both the nitride and the oxygen peaks indicated that dissociation of NO occurred on the Fe/SiO 2 surface. When the Fe/SiO 2 system at 298°K was exposed to SO 2, two forms of sulfur, sulfate and sulfide, were observed. At 473°K the amount of sulfide increased slightly while the amount of sulfate decreased slightly. Neither form of sulfur was observed at 673°K.