Mechanistic study of the heterogeneous conversion of NO2 into HONO and N2O on acid surfaces

Abstract

The heterogeneous conversion of NO₂ into HONO and N₂O on acid surfaces has been investigated in an 11 l Pyrex glass reactor under simulated atmospheric conditions and in a 64 l quartz glass reactor at reduced pressure. NO₂, N₂O and HONO were monitored with time by long-path tunable IR diode laser absorption spectroscopy using single vibrational rotational lines at 1641.0, 1254.47 and 1254.46 cm^–1, respectively.

The experimental results show that NO₂ is heterogeneously converted on acid surfaces into HONO and then into N₂O. HONO formation in the reaction system has been found to occur by the heterogeneous reaction of NO₂ with adsorbed water on the surface and does not require NO. The experimental findings indicate that the nitrosyl ion probably plays an important role in converting HONO into N₂O and HNO₃. A mechanism is proposed which can explain the experimental findings.