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.