CROWN-ETHER MEDIATED SYNTHESIS OF FAU-TYPE AND EMT-TYPE ZEOLITES IN THE PRESENCE OF PHOSPHATE ANIONS - STUDY OF THE INCORPORATION OF GALLIUM

Syntheses were performed in the system )O(3):(1-y)Ga2O3:zP(2)O(5):(2.4 -4.1)Na2O:0.4(18C-6 or 15C-5):(140-180)H2O. For the Si-Al system, the presence of P2O5 allows the crystallization of EMT at high alkalinity, due to the complexation of AI(OH)(4)(-) by phosphate anions. Remarkab ly, this complexation is less efficient when 18C-6 is replaced by 15C- 5, giving FAU phases with low Si/Al ratio. The addition of small amoun ts of Ga (y=0.05-0.1) leads to intergrowth formation of EMT and FAU. T his is ascribed to the preferential location of Ga in the double six-r ings which connect the successive FAU sheets. In the absence of P2O5, Ga is less reactive than Al and will be more homogeneously distributed over the framework. Under these conditions, up to 25% of Al can be su bstituted by Ga in the EMT structure. (C) 1997 Elsevier Science B.V.