Crown-ether mediated synthesis of FAU- and EMT-type zeolites in the presence of phosphate anions: study of the incorporation of gallium

Abstract

Syntheses were performed in the system 10SiO 2: yAl 2O 3:(1− y)Ga 2O 3: zP 2O 5:(2.4−4.1)Na 2O:0.4(18C-6 or 15C-5):(140−180)H 2O. For the Si-Al system, the presence of P 2O 5 allows the crystallization of EMT at high alkalinity, due to the complexation of Al(OH)4/− by phosphate anions. Remarkably, 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 amounts of Ga ( y=0.05–0.1) leads to intergrowth formation of EMT and FAU. This is ascribed to the preferential location of Ga in the double six-rings which connect the successive FAU sheets. In the absence of P 2O 5, 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 substituted by Ga in the EMT structure.