Catalysts for Direct Decomposition of NOx in Exhausts

Abstract : Eltron Research, Inc., is pursuing the rational development of catalysts for direct (reagentless) decomposition of NOx. This is the most economical imaginable approach for post-combustion removal of nitrogen oxides because costs for reagent and reagent delivery (i.e., ducting, etc.) are eliminated, and catalysts demonstrating activity to the present time are inexpensive ($1-$4/lb). The decomposition of nitrogen oxides in simulated exhaust streams over new brownmillerite catalysts has been examined in a range of temperatures and residence times. Results are indicative of the occurrence of reagentless activity in gas streams containing up to 16 percent oxygen. Performance was nonmonotonic in temperature, with an activity maximum occurring between 550 and 600 deg C. For example, up to 90% conversion of NOx at 250 deg C and 130,000/h has been attained. Using CO as a reductant at 800,000/h and 1000 deg C , one catalyst removed 16 percent of 477 ppm NO in a stream also containing 16 percent oxygen. These results suggest the potential efficacy of the catalysts for the direct decomposition of nitrogen oxides in high-temperature (400-1000 deg C) exhaust gases in, e.g., gas turbine and diesel engines. In addition, the catalysts were found to be effective at oxidizing CO. The enhancement of activity obtained using carbon monoxide is particularly relevant in such applications.