Research progress of simultaneous removal of NOx and N2O from the tail gas of nitric acid production

Harmful gases such as NOx (NO and NO2) and N2O are emitted during the production of dilute nitric acid by ammonia oxidation, which can lead to environmental problems such as photochemical smog (NOx), ozone layer depletion (NOx and N2O), and global warming (N2O). It is imperative to remove NOx and N2O from the tail gas of nitric acid production. After introducing the generation pathways and control measures of NOx and N2O during nitric acid production, we summarized the main technological routes for simultaneous removal of NOx and N2O from the tail gas according to the research, development and application situations, including one-stage processes such as simultaneous SCR of NOx and N2O, SCR of NOx and decomposition of N2O over a composite catalyst, and two-stage processes such as catalytic N2O decomposition followed by SCR of NOx, SCR of NOx followed by SCR of N2O, and SCR of NOx followed by catalytic N2O decomposition. The principles and characteristics of different technological routes were analyzed. It was pointed out that the one-stage processes face challenges of improving the purification performance toward N2O. The two-stage process of SCR of NOx followed by catalytic N2O decomposition, has advantages of low consumption of reducing agent and high purification efficiency of N2O. Further research should focus on lowering the temperatures of both SCR of NOx and catalytic N2O decomposition and improving the tolerance of catalysts to co-existing gases (O2, H2O, etc.). © 2023 Chemical Industry Press. All rights reserved.