MODELING THE THERMAL DENOX PROCESS IN FLOW REACTORS - SURFACE EFFECTSAND NITROUS-OXIDE FORMATION

We have investigated the impact of surface reactions such as NH3 decom position and radical adsorption on quartz flow reactor data for Therma l DeNO(x) using a model that accounts for surface chemistry as well as molecular transport. Our calculations support experimental observatio ns that surface effects are not important for experiments carried out in low surface to volume quartz reactors. The reaction mechanism for T hermal DeNO(x) has been revised in order to reflect recent experimenta l results. Among the important changes are a smaller chain branching r atio for the NH2 + NO reaction and a shorter NNH lifetime than previou sly used in modeling. The revised mechanism has been tested against a range of experimental flow reactor data for Thermal DeNO(x) with reaso nable results. The formation of N2O in Thermal DeNO(x) has been modell ed and calculations show good agreement with experimental data. The im portant reactions in formation and destruction of N2O have been identi fied. Our calculations indicate that N2O is formed primarily from the reaction between NH and NO, even though the NH2 + NO2 reaction possibl y contributes at lower temperatures. At higher temperatures N2O concen trations are limited by thermal dissociation of N2O and by reaction wi th radicals, primarily OH. (C) 1994 John Wiley & Sons, Inc.