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

Abstract

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 (NOx) reduction with NH3.