Progress in catalytic strategies for mitigating NOx/N2O emissions: from mechanisms to applications

Abstract

In the context of global warming, the emission of the greenhouse gas nitrous oxide (N₂O) is an important factor limiting the application of ammonia fuels in marine and offshore power. The effective control of N₂O emissions by suppressing N₂O generation at the source and after-treatment of exhaust gases has a highly urgent practical significance. The primary source of N₂O in ammonia-fueled engines is the side reaction in aftertreatment process of nitrogen oxides (NO_x)—selective catalytic reduction (SCR). SCR is also an up-and-coming N₂O aftertreatment technology, so developing highly efficient N₂O-inhibiting NO_x-SCR catalysts and N₂O-SCR catalysts is the key to emission control. This article innovatively provides a detailed review of the principles and influencing factors of these two types of catalysts, respectively. Firstly, the generation mechanism of N₂O in the NO_x-SCR process with several common reducing agents is reviewed, and then the influencing factors of the catalyst performance are classified, the development and optimization of N₂O-SCR catalysts in recent years are reviewed, such as improving the structure of the catalyst. Then, the mechanism of N₂O-SCR with different reducing agents is reviewed, and the influencing factors and optimization methods of N₂O-SCR catalysts are classified and reviewed, such as adjusting the catalyst preparation conditions, changing the active component loading to increase the acidic center. Finally, some suggestions and outlooks for future research directions are presented. It is hoped that this paper can provide a theoretical basis for developing efficient catalysts adapted to industrial applications and contribute to the control of N₂O emissions.