title: Determining the storage, availability and reactivity of NH3 within Cu-Chabazite-based Ammonia Selective Catalytic Reduction systems.
abstract: Three different types of NH3 species can be simultaneously present on Cu(2+)-exchanged CHA-type zeolites, commonly used in Ammonia Selective Catalytic Reduction (NH3-SCR) systems. These include ammonium ions (NH4(+)), formed on the Brønsted acid sites, [Cu(NH3)4](2+) complexes, resulting from NH3 coordination with the Cu(2+) Lewis sites, and NH3 adsorbed on extra-framework Al (EFAl) species, in contrast to the only two reacting NH3 species recently reported on Cu-SSZ-13 zeolite. The NH4(+) ions react very slowly in comparison to NH3 coordinated to Cu(2+) ions and are likely to contribute little to the standard NH3-SCR process, with the Brønsted groups acting primarily as NH3 storage sites. The availability/reactivity of NH4(+) ions can be however, notably improved by submitting the zeolite to repeated exchanges with Cu(2+), accompanied by a remarkable enhancement in the low temperature activity. Moreover, the presence of EFAl species could also have a positive influence on the reaction rate of the available NH4(+) ions. These results have important implications for NH3 storage and availability in Cu-Chabazite-based NH3-SCR systems.
authors: Materials innovation institute (M2i), Mekelweg 2, 2628 CD Delft, The Netherlands.
authors: I
authors: I
authors: Lezcano-Gonzalez
authors: U
authors: U
authors: Deka
authors: B
authors: B
authors: Arstad
authors: A
authors: A
authors: Van Yperen-De Deyne
authors: K
authors: K
authors: Hemelsoet
authors: M
authors: M
authors: Waroquier
authors: V
authors: V
authors: Van Speybroeck
authors: B M
authors: BM
authors: Weckhuysen
authors: A M
authors: AM
authors: Beale
mesh_terms: D000641:Ammonia / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D013499:Surface Properties; D013696:Temperature; D017641:Zeolites / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; C554923:chabazite; D017641:Zeolites; D000641:Ammonia; D003300:Copper