Origins of N2O Selectivity Limits in Catalyzed Ammonia Oxidation
Ivan Surin, Evgenii V. Kondratenko, Javier Pérez-Ramírez
TL;DR
This paper explains why ammonia oxidation to nitrous oxide (N2O) has a selectivity limit and shows how adjusting reaction conditions can improve N2O production.
Contribution
The study identifies direct NH3-to-N2 conversion as the main cause of N2O selectivity loss and proposes strategies to enhance selectivity.
Findings
Direct oxidation of NH3 to N2 is the main reason for incomplete N2O selectivity.
Water cofeeding and adjusting reactant partial pressures increased N2O selectivity from 81% to 90%.
Reduction of in situ-formed NO by NH3 is a significant route to secondary N2O.
Abstract
Ammonia (NH3) oxidation to nitrous oxide (N2O) is a promising route to obtain this selective oxidant, but controlling product distribution is inherently challenging because N2O occupies an intermediate nitrogen oxidation state between N2 and NO. Despite recent advances, leading CeO2-based catalytic systems have consistently encountered a selectivity limit in the range of 80–85%. Herein, CeO2-supported Mn single atoms are employed as a stable, selective benchmark to investigate the origins of the N2O selectivity losses. Thorough kinetic analysis revealed that direct oxidation of NH3 to N2 is the main reason for incomplete N2O selectivity. This reaction dominates in a thin upstream catalyst bed layer, driven by its strong dependence on the NH3 partial pressure that ensures dense surface coverage by N-containing intermediates and promotes their irreversible coupling to N2. However, due to…
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Taxonomy
TopicsAmmonia Synthesis and Nitrogen Reduction · Catalytic Processes in Materials Science · Advanced oxidation water treatment