ITQ-7: A New Pure Silica Polymorph with a Three-Dimensional System of Large Pore Channels

Abstract

A novel topology, consisting of a three‐dimensional system of large pore channels, is found for the zeolite ITQ‐7 (see picture). This material has been synthesized by combining the structure‐directing effects of fluoride ions and a new organic cation purposefully designed to promote the crystallization of a low‐density silica phase. ITQ‐7 is the least dense crystalline silica phase known so far.

The chemistry of phase selectivity in the synthesis of high-silica zeolites

“…This allows the smaller T -O -T bond angles in the D4R units that otherwise would incur an energetic penalty to the structure. All-silica syntheses with fluoride have yielded the novel zeolites ITQ-7 [53], ITQ-12 [54,55], and ITQ-13 [56]; each of these zeolites possesses D4R units.…”

Synthesis of ITQ-7 with a new template molecule and its crystal structure analysis in the as synthesized form

“…In contrast to beta, however, this material can be obtained with a highly ordered silicate framework structure. It is typically synthesized with a specific structure directing agent (SDA), 1,3,3-trimethylspiro[6-azoniabicyclo [3.2.1]]octane-6,1′-pyrrolidine (TAD), in a narrow synthesis field using the fluoride route [2]. The crystal structure of the calcined material (zeolite framework type ISV [3]) has been reported recently by Villaescusa et al [2].…”

“…It is typically synthesized with a specific structure directing agent (SDA), 1,3,3-trimethylspiro[6-azoniabicyclo [3.2.1]]octane-6,1′-pyrrolidine (TAD), in a narrow synthesis field using the fluoride route [2]. The crystal structure of the calcined material (zeolite framework type ISV [3]) has been reported recently by Villaescusa et al [2]. In successive papers very interesting catalytic properties have been reported [4][5][6].…”

Structural Chemistry of Zeolites

“…They are the most complex structures yet observed and are discussed further in Section 7.3.4, along with the 2D 10-ring zeolite IM-5 [40]. In addition, new 3D-connected 12-ring silicates ITQ-17 [25] and germanosilicates ITQ-17 [41], ITQ-21 [42], and ITQ-26 [43] add to the previously known structures with this connectivity, the faujasite and Beta structures (see, for example, Figure 7.15). ITQ-17 is related to the disordered Beta structures originally prepared, having the same framework layers, but these are stacked differently, in an ordered tetragonal arrangement and including D4Rs.…”

“…The work of Camblor at the ITQ on the introduction of fluoride ions into low water content synthesis gels gave many new porous silica polymorphs of zeolites with large pore volumes, where the fluoride ions have a dual role of assisting silicate condensation and crystallization and balancing the positive charge on the framework [24]. Early examples of the success of this model for new structures include the highly porous small-pore zeolite ITQ-3 (with 2D 8-ring pore system), the large-pore 1D channel structure ITQ-4 (there are now many 1D 12-ring channel structures known), and the 3D 12-ring ITQ-7 [25]. This approach has subsequently been used very productively by many researchers in the field.…”