The kinetics of the heterogeneous reaction of BrONO2 with solid alkali halides at ambient temperature. A comparison with the interaction of ClONO2 on NaCl and KBr

Abstract

The heterogeneous reactions of BrONO₂ and ClONO₂ with solid alkali halides have been investigated in a Teflon-coated Knudsen flow reactor at ambient temperature. The initial uptake coefficients γ₀ of BrONO₂ on NaCl and KBr substrates are γ₀=0.31±0.12 and γ₀=0.33±0.12, respectively. For NaCl substrates BrCl, Br₂ and HCl and for KBr both Br₂ and HBr are observed as products. HCl and HBr result from the interaction of NaCl and KBr, respectively, with HNO₃ generated in the hydrolysis of BrONO₂. Using NaCl we observed Br₂ which is formed from heterogeneous BrONO₂ decomposition which also occurs on solid KBr samples. Halogen exchange reactions are competing with hydrolysis and decomposition which also take place on non-reactive salts such as NaNO₃ and Na₂SO₄. A high rate of initial uptake (0.2⩽γ₀⩽0.4) and a Br₂-yield of the order of 50% are observed on non-reactive salts with a closed mass balance for Br₂. The ClONO₂–salt system has been reinvestigated. Experiments on NaCl, KBr (reactive salts) and on NaNO₃, Na₂SO₄ (non-reactive salts) have been performed. The hydrolysis of ClONO₂ was not observable in contrast to heterogeneous decomposition which occurred on non-reactive salts with a Cl₂-yield of (25±5)%. We fitted our uptake experiments using a simple Langmuir–Hinshelwood model with satisfactory results.