Oxide catalysts for ammonia oxidation in nitric acid production: properties and perspectives (original) (raw)

Selective catalytic oxidation of ammonia by nitrogen oxides in a model synthesis gas

Fuel, 2013

Synthesis gas generated by the gasification of nitrogen-containing hydrocarbons will contain ammonia. This is a catalyst poison and elevated levels of nitrogen oxides (NO X) will be produced if the synthesis gas is combusted. This paper presents a study of the selective oxidation of ammonia in reducing environments. The concept is the same as in traditional selective catalytic reduction, where NO X are removed from flue gas by reaction with injected ammonia over a catalyst. Here, a new concept for the removal of ammonia is demonstrated by reaction with injected NO X over a catalyst. The experiments were carried out in a model synthesis gas consisting of CO, CO 2 , H 2 , N 2 and NH 3 /NO X. The performance of two catalysts, V 2 O 5 /WO 3 /TiO 2 and H-mordenite, were evaluated. On-site generation of NO X by nitric acid decomposition was also investigated and tested. The results show good conversion of ammonia under the conditions studied for both catalysts, and with on-site generated NO X .

Selective catalytic oxidation of ammonia to nitric oxide via chemical looping

Nature Communications, 2022

Selective oxidation of ammonia to nitric oxide over platinum-group metal alloy gauzes is the crucial step for nitric acid production, a century-old yet greenhouse gas and capital intensive process. Therefore, developing alternative ammonia oxidation technologies with low environmental impacts and reduced catalyst cost are of significant importance. Herein, we propose and demonstrate a chemical looping ammonia oxidation catalyst and process to replace the costly noble metal catalysts and to reduce greenhouse gas emission. The proposed process exhibit near complete NH 3 conversion and exceptional NO selectivity with negligible N 2 O production, using nonprecious V 2 O 5 redox catalyst at 650 o C. Operando spectroscopy techniques and density functional theory calculations point towards a modified, temporally separated Mars-van Krevelen mechanism featuring a reversible V 5+ /V 4+ redox cycle. The V = O sites are suggested to be the catalytically active center leading to the formation of the oxidation products. Meanwhile, both V = O and doubly coordinated oxygen participate in the hydrogen transfer process. The outstanding performance originates from the low activation energies for the successive hydrogen abstraction, facile NO formation as well as the easy regeneration of V = O species. Our results highlight a transformational process in extending the chemical looping strategy to producing base chemicals in a sustainable and cost-effective manner.