F. S. Boericke has written:

'Equilibrium in the reduction of ferrous chromite by hydrogen and energy requirements in the selective reduction of iron in chromite' -- subject(s): Chromite

It's a method for converting NOx gases to N2 and H2O with the help of a catalyst and using usually ammonia as a reducing agent.

Depends on what emissions standards it's compliant with. If you have an EPA2010 or Euro6 compliant engine, water is just a byproduct of the Selective Catalytic Reduction system.

DEF (diesel exhaust fluid) is used as a consumable in SCR (selective catalytic reduction) in order to lower NOx concentration in the diesel exhaust emissions from diesel engines.

Selective breeding.