STUDY OF THE REDUCTION AND REOXIDATION OF A CAO SURFACE

The reduction of NO with CO and H-2 is shown to comprise two basic rea ctions: a surface oxygen abstraction by the reducing agent and a reoxi dation of the surface by NO. The former reaction step has been demonst rated by transient CO2 formation during CO exposure of oxidized CaO su rfaces, while the latter was demonstrated by N-2 and/or N2O transient formation during NO exposure of a prereduced CaO surface. It was shown that at low temperatures (between room temperature and 500 degrees C) both N-2 and N2O were formed, but at temperatures above 500 degrees C only N-2 was observed. The activation energies of the respective step s have been determined using temperature-programmed reaction experimen ts. The activation energy of the surface oxygen abstraction was determ ined to be 25 kcal/mol and is similar to the apparent activation energ y of the overall reaction; The activation energy of the NO bond breaka ge was determined to be maximum 10 kcal/mol as measured by N2O formati on. The importance of an N2O2- or N2O22- intermediate in the formation of N2O will be discussed, and the importance of N2O decomposition in forming N-2 at temperatures above 500 degrees C will be compared with a N surface diffusion mechanism.