Autocatalytic synergism observed during lean-NOx reduction with a bifunctional reductant over Ag/Al2O3 catalyst

Autocatalytic kinetic synergism between the conventional selective catalytic reduction of NOx by hydrocarbon (HC-SCR) and ammonia (NH3-SCR) has been observed during lean-NOx reduction with a bifunctional reductant (an amino alcohol) over a Ag/Al2O3 catalyst, resulting in significant enhancement of the deNOx activity. Monoethanolamine (MEA) employed as the bifunctional reductant produces effective reductants such as H2, NH3, and isocyanate species, thereby transforming the single-functional Ag/Al2O3 catalyst for HC-SCR into a dual-functional catalyst for both HC-SCR and NH3-SCR. The production of those highly reactive intermediate reductants by MEA initiates the autocatalytic deNOx process, while the kinetic synergy in the deNOx catalysis can be attributed to the formation of (OH⋯N) hydrogen bonds in and among MEA molecules. Based on steady-state kinetic data, reaction pathways have been proposed for MEA-SCR over Ag/Al2O3, and a method for further improvement in deNOx activity has been demonstrated in a dual-bed reactor system.