NOx Selective Catalytic Reduction (NO_x‑SCR) by Urea: Evidence of the Reactivity of HNCO, Including a Specific Reaction Pathway for NOx Reduction Involving NO + NO₂

To treat the NOx emissions from diesel vehicles, NOx selective catalytic reduction (SCR) process by NH₃ requires the use of a precursor: an urea aqueous solution. Using an innovative experimental synthetic gas bench adjusted to powdered catalysts and allowing the use of urea or ammonia, the competitive reactivity of the HNCO intermediate species was evidenced. This intermediate species was found to be highly reactive toward NO₂, without NOx reduction. During the SCR process, a mix of both NO and NO₂ was evidenced to react with HNCO and contribute to the NOx reduction efficiency, resulting in an original pathway.