2026 Volume 69 Issue 2 Pages 76-90
We developed NOx-To-Ammonia (NTA) technology, which aims to create an efficient reaction system that can convert NO into NH3 by supplying exhaust gases containing interfering gases, such as excess oxygen and water vapor, directly onto a catalyst. The process can be used without pretreatment, including oxygen removal, NO concentration, or water vapor separation. The present NTA reaction used C3H6 as a hydrogen source. Of the various combinations of active metals and carrier oxides tested, Ag and TiO2 (rutile) exhibited the highest activity in the C3H6-NTA reaction. Since high catalytic activity was obtained at low Ag loading, we developed an ET method in which Ag is reduced while supported in ethanol. This ET catalyst exhibited very high initial activity, but it deteriorated over time due to silver aggregation. Thus, we investigated a method of first supporting Nd on the TiO2 support, followed by supporting Ag. Supporting Nd generated new pores with a diameter of approximately 14 nm, stabilizing the catalytic activity of the Ag catalyst. The maximum NH3 yield was 88 %. It was clarified that NH3 is selectively generated as the reduction product under strong oxidizing conditions with 10 % oxygen because the combustion temperature of NH3 is remarkably higher than the generation temperature of NH3. Diffuse reflectance FTIR revealed that NO3– adsorbed on the support reacts with C3H6 to produce NH3. This study enables the generated NH3 to be used not only as a reductant for subsequent NH3-SCR, but also as an alternative to the Haber–Bosch process for NH3 synthesis. It has been demonstrated that NO can be converted from a harmful waste product into a raw material for NH3 production.
