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

Abstract

The effect of the gas phase during solid-state ion-exchange of copper into zeolites was studied by exposing physical mixtures of copper oxides (Cu I 2 O and Cu II O) and zeolites (MFI, *BEA, and CHA) to various combinations of NO, NH 3, O 2, and H 2 O. It is shown that heating these mixtures to 250 °C results in active catalysts for the selective catalytic reduction of NO with NH 3 (NH 3 -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 Cu I 2 O. When the zeolite is mixed with Cu II O, addition of NO to the NH 3 -containing gas phase enhances the formation of Cu I 2 O and the Cu ion-exchange. The mobility of Cu at low temperatures is proposed to be related to the formation of [Cu I (NH 3 ) x ] + ( x ≥ 2) complexes.