Determining the storage, availability and reactivity of NH3 within Cu-Chabazite-based Ammonia Selective Catalytic Reduction systems

作者：Lezcano Gonzalez I; Deka U; Arstad B; Van Yperen De Deyne A; Hemelsoet K; Waroquier M; Van Speybroeck V; Weckhuysen B M^*; Beale A M

来源：Physical Chemistry Chemical Physics, 2014, 16(4): 1639-1650.

DOI：10.1039/c3cp54132k

Three different types of NH3 species can be simultaneously present on Cu2+-exchanged CHA-type zeolites, commonly used in Ammonia Selective Catalytic Reduction (NH3-SCR) systems. These include ammonium ions (NH4+), formed on the Bronsted acid sites, [Cu(NH3)(4)](2+) complexes, resulting from NH3 coordination with the Cu2+ 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 Cu2+ ions and are likely to contribute little to the standard NH3-SCR process, with the Bronsted 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 Cu2+, 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.

• 出版日期2014