Heterogeneous interaction of Br2, Cl2 and Cl2O with solid KBr and NaCl substrates: The role of adsorbed H2O and halogens

Abstract

The interaction of Br₂, Cl₂ and Cl₂O with different solid alkali halides, namely KBr and NaCl substrates, has been investigated in a low-pressure flow reactor. The observed main gaseous reaction products of the reactions of Cl₂ and Cl₂O with solid KBr substrates are Br₂ and BrCl. The reaction of Cl₂O with solid NaCl substrates leads to formation of Cl₂ and small amounts of HOCl. The role of surface-adsorbed H₂O (SAW) and the influence of adsorbed halogens have been investigated. Evidence for the formation of adsorbed Br₂ owing to mechanical stress has been found for solid KBr. Dehydration of the substrate under vacuum leads to a better ordered, more crystalline and hence less-reactive surface and decreases the number of reactive surface sites. Adsorption of halogen compounds such as BrCl, Cl₂ and Br₂ leads to effective dehydration of the KBr or NaCl substrate by competing for limited amounts of SAW. In this way, the reduced degree of hydration of the substrate alkali ions leads to activation of the halogen exchange reactions or catalytic activity.