Nitrous oxide as a green oxidant: a holistic evaluation based on economic, environmental, and safety metrics

Abstract

Sustainable chemical synthesis requires atom-efficient and highly selective oxidation processes. Nitrous oxide, N₂O, exhibits unique reactivity in oxidation catalysis due to its ability to deliver selective mono-oxygen species, thereby minimising overoxidation. Industrially, the majority of N₂O is produced via the five-step thermal decomposition of ammonium nitrate, a process limited by safety, environmental, and economic concerns. Recent advances in catalyst design offer the one-step direct catalytic oxidation of ammonia (NH₃), potentially streamlining production while reducing costs. However, the performance of different N₂O production routes across process-based metrics remains poorly understood, making the benefits of the one-step route hypothetical. Furthermore, the majority of existing frameworks for evaluating emerging technologies fail to integrate the three fundamental pillars of sustainability: economic viability, environmental performance, and societal safety. Here, we present an integrated framework encompassing all three pillars of sustainability by combining techno-economic analysis, life cycle assessment, and quantitative safety indicators such as Dow's fire & explosion index and TNT equivalency. Specifically, for N₂O, we compare the one-step direct NH₃ oxidation process with the conventional five-step route and find that the former, which employs fossil-derived or electrolytic hydrogen-based green NH₃, reduces both production costs and carbon footprint by over 20% while significantly lowering safety hazards. In addition, we benchmark N₂O against hydrogen peroxide (H₂O₂), a well-established oxidant, and demonstrate that N₂O produced from a fossil/green NH₃ blend can match the carbon footprint of H₂O₂ while offering ca. 40% cost savings and lower safety risks. Given the benefits of one-step N₂O, we also demonstrate its potential in a key application: phenol synthesis via direct oxidation of benzene, compared with the conventional cumene route and the H₂O₂-based direct oxidation. Overall, our findings highlight N₂O's potential in oxidation chemistry and underscore the value of our integrated sustainability framework for assessing new technologies.