Limitations on the rapid reduction of nitrogen oxides in exhaust gas streams

Abstract

ALL commercially important combustion systems produce exhaust gases containing substantial amounts of nitrogen oxides and molecular oxygen. Because of the part played by nitrogen oxides in smog formation and acid-rain production, methods of reducing NO_x emissions have been subject to intense research. In 1986, Perry and Siebers¹ proposed a new chemical method for removing NO_x from diesel exhaust gas by adding cyanuric acid (HNCO)₃, and suggested that this new process, called RAPRENOx (rapid reduction of NO_x) could control the emission of NO_x from most combustion devices. Here we show that surface chemistry is responsible for the effective reduction of NO_x, confirming recent results². In stainless steel, in the absence of oxygen, NO is effectively reduced by cyanuric acid at 700 °C. When oxygen is present, however, NO is produced by the reaction with cyanuric acid at 700 °C. Under conditions where surface effects are important (such as in the first demonstration experiments reported on RAPRENOx) the reduction of NO by cyanuric acid is adversely affected by oxygen.