NO reduction by activated carbons. 7. Some mechanistic aspects of uncatalyzed and catalyzed reaction

In this last paper of a series devoted to uncatalyzed and catalyzed reduction of NO by carbon, we discuss some mechanistic aspects of this reaction, which is thought to be a viable alternative to selective catalytic reduction by ammonia or hydrocarbons. We present a summary of the results of isothermal and temperature-programmed reduction studies on a metal-free activated carbon and carbon loaded with K, Ca, Fe, Cu, Cr, Co, and Ni catalysts. All the results obtained on catalyzed NO reduction are consistent with a simple oxidation - reduction (redox) mechanism involving the following kinetically significant steps: (1) chemisorption of NO on the catalyst surface; (2) transfer of oxygen from the catalytically active sites to the carbon reactive sites; and (3) desorption of oxygen from the carbon surface. A comparison with the proposed mechanisms for selective catalytic reduction is offered, as well as a mechanistic interpretation of the NO reduction enhancement in the presence of O₂.