Solid-State Ion-Exchange of Copper into Zeolites Facilitated by Ammonia at Low Temperature

The effect of the gas phase during solid-state ion-exchange of copper into zeolites was studied by exposing physical mixtures of copper oxides ((Cu2O)-O-I and (CuO)-O-II) and zeolites (MFI, *BEA, and CHA) to various combinations of NO, NH3, O-2, and H2O. It is shown that heating these mixtures to 250 degrees C results in active catalysts for the selective catalytic reduction of NO with NH3 (NH3-SCR), indicating that the Cu has become mobile at that temperature. Such treatment allows for a fast (<5-10 h) preparation of copper-exchanged zeolites. Scanning transmission electron microscopy analysis of Cu-CHA prepared using this method shows homogeneous distribution of the Cu in the primary particles of the zeolite. In situ XRD reveals that the Cu ion-exchange is related to the formation of (Cu2O)-O-I. When the zeolite is mixed with (CuO)-O-II, addition of NO to the NH3-containing gas phase enhances the formation of (Cu2O)-O-I and the Cu ion-exchange. The mobility of Cu at low temperatures is proposed to be related to the formation of [Cu-I(NH3)(x)](+) (x >= 2) complexes.