Suppression of nitrogen oxides emission by carbonaceous reductants

The present status of NOx emission from power stations and automobiles is first summarized, and the controlling regulations in respective areas are reviewed. In spite of much progress, we have to further reduce the NOx emission in all the areas. In order to develop more effective technology, the fundamental understanding of the relevant reactions is essential. The heterogeneous reactions, like NOx and N2O formation from coal char, NOx and N2O reduction with carbon, and NOx reduction with hydrocarbon gases over heterogeneous catalysts are not well understood yet. This paper briefly summarizes our recent studies on the heterogeneous reactions of NOx formation and destruction. The importance of surface nitrogen species is emphasized in all the reaction systems. The presence of such surface species plays a very important role, not only in NOx destruction on carbon surfaces, but also in the NOx release during coal char combustion. Finally, future research areas are identified, where we need to understand what actually happens under high-temperature reaction conditions.