Ammonia oxidation in a microreactor

What is ammonia oxidation?

When ammonia reacts with oxygen in the presence of a rhodium-platinum wire gauze catalyst, the primary product is nitric oxide:

4NH₃ (ammonia) + 5O₂ (oxygen) -> 4NO (nitric oxide) + 6H₂O (water)

The reaction is usually done in the gas phase, at fairly high temperature (750 to 920 degrees C) and moderate pressure (atmospheric to 100 psi). Higher pressure allows for smaller and less expensive reactors. The contact time needed is 0.0003 seconds. Care must be taken to keep the inlet ammonia concentration low enough to avoid explosive mixture. The reaction is quite exothermic.

(Please note: there are some side reactions that are important when modeling this process.)

Nitric oxide is a gas that decomposes in air, so it's typically made only when needed immediately.

For more information on ammonia oxidation, please consult these references.