The Origin of an Unexpected Increase in NH3–SCR Activity of Aged Cu-LTA Catalysts

We have recently reported an increase in low-temperature NH3–SCR activity of the copper-exchanged (Cu/Al = 0.50), high-silica (Si/Al = 23) LTA catalyst when it is hydrothermally aged at 1023–1173 K. Here we demonstrate that this unexpected phenomenon originates from the migration of Cu+ ions present inside the sod cages of Cu-LTA to the vacant single 6-rings which accompanies their oxidation to Cu2+ ions during (hydro)­thermal aging. Hence, the sod cages, which are inaccessible to almost all reactant species so as to be regarded as useless for zeolite catalysis, were found to serve as a “catalyst reservoir” during the course of nitrogen oxides (NO x ) reduction with NH3.