Water: A promoter of ammonia selective catalytic reduction over copper-exchanged LTA zeolites

Abstract

Negative effects of water on the hydrothermal stability of ammonia (NH3) selective catalytic reduction (SCR) catalysts are well known. Thus, developing water-resistant, zeolite-based transition metal catalysts like copper (Cu) for mitigating nitrogen oxides from mobile sources is very challenging. Here we show that water markedly facilitates the migration of copper ions from sterically inaccessible sod cage to the readily accessible lta one through six-membered rings within a copper-exchanged high-silica Cu-LTA zeolite. We also show that this ubiquitous molecule promotes the low-temperature SCR activity of the Cu-LTA catalyst with a plausible reaction [H2O-Cu-NH3]+ intermediate. We anticipate that water might play a beneficial role in nitrogen oxides removal over metal-containing zeolites for cleaner air via tuning the active sites and reaction pathways.