Synthesis of Gallosilicate UZM-12 and Offretite Zeolites via a Charge Density Mismatch Approach and Their Characterization

Abstract

The synthesis of gallosilicate zeolites are carried out based on the charge density mismatch (CDM) approach and the characterizations of the representative products (i.e., UZM-12 and offretite) are described. The phase selectivity of the crystallization was found to differ according to the synthesis temperature, as well as to the type of inorganic cations. It is also shown that the structure-directing ability of Ga is considerably different from that of Al in intermediate-silica synthesis conditions (5≤Si/Me≤16, Me = Al or Ga). The presence of Ga in the tetrahedral framework positions of UZM-12 and offretite gallosilicates is evidenced by a combination of powder XRD, IR, and 71Ga and 29Si MAS NMR. In particular, the 29Si MAS NMR results clearly show the existence of two distinct tetrahedral sites in both gallosilicate zeolites. The methanol-to-olefin (MTO) performance of a series of UZM-12 zeolites with alumino-, galloalumino-, and gallosilicate compositions is also presented.