A SPECTROSCOPIC AND GRAVIMETRIC STUDY OF THE SOOT-NO2/N2O4 REACTION AT VARIOUS TEMPERATURES

A study of the hexane soot- NO2 N2O4 reaction, with and without water vapor, over a range of concentrations and temperatures has been conducted. Two types of reaction are evident: activated chemisorption and redox. In the case of activated chemisorption, nitrogen-containing species are formed on the soot resulting in an increase in its mass. The other reaction in which 82-95% of the soot is converted into CO2 and CO is the major redox reaction, during which NO and N2O also are formed. This redox reaction commences at temperatures near 60°C. The major redox and activated chemisorption reactions are competitive in the sense that, if activated chemisorption is initiated, it precludes the major redox reaction. The presence of water vapor and dilution of NO2 N2O4 by N2or air inhibit the major redox reaction and the irreversible activated chemisorption reaction dominates. In addition, a third reaction termed the minor redox reaction occurs under all conditions with the evolution of CO and CO2. The quantities of effluent gases from this reaction are significantly lower than those evolved during the major redox reaction. The rate equations for the formation of CO2from the major redox reaction, and CO2 and CO from the minor redox reaction, have been determined. A mechanism for the major redox reaction is presented. A determining role of NO2 monomer in redox reactions of soot and NO2 N2O4 is indicated. © 1990.