Solid-State Ion-Exchange of Copper into Zeolites Facilitated by Ammonia at Low Temperature
Artikel i vetenskaplig tidskrift, 2015
The effect of the gas phase during solid-state ion-exchange of copper into zeolites was studied by exposing physical mixtures of copper oxides (CuI2O and CuIIO) and zeolites (MFI, *BEA and CHA) to various combinations of NO, NH3, O2 and H2O. It is shown that heating these mixtures to 250°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 homogenous 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 CuI2O. When the zeolite is mixed with CuIIO, addition of NO to the NH3-containing gas phase enhances the formation of CuI2O, and the Cu ion-exchange. The mobility of Cu at low temperatures is proposed to be related to the formation of [CuI(NH3)x]+ (x≥2) complexes.