Extra-large pore zeolite (ITQ-40) with the lowest framework density containing double four- and double three-rings

Abstract

The first zeolite structure (ITQ-40) that contains double four (D4) and double three (D3) member ring secondary building units has been synthesized by introducing Ge and NH 4 F and working in concentrated synthesis gels. It is the first time that D3-Rs have been observed in a zeolite structure. As was previously analyzed [Brunner GO, Meier, WM (1989) Nature 337:146-147], such a structure has a very low framework density (10.1 T∕1,000 Å 3 ). Indeed, ITQ-40 has the lowest framework density ever achieved in oxygen-containing zeolites. Furthermore, it contains large pore openings, i.e., 15-member rings parallel to the [001] hexagonal axis and 16-member ring channels perpendicular to this axis. The results presented here push ahead the possibilities of zeolites for uses in electronics, control delivery of drugs and chemicals, as well as for catalysis.double three-rings in zeolites | low framework density zeolites | germanosilicate zeolites T here is an increasing interest in the synthesis of zeolites with low framework density and extra-large pores (>12 tetrahedral atoms). The preparation of such materials will increase the use of zeolites in catalysis (1, 2) while further expanding their possibilities in microelectronics by preparing materials with low values of the high-frequency dielectric constant, or for uses related with controlled delivery of chemicals and diagnostic treatment (3, 4).In 1989, Brunner and Meier performed a topological analysis on synthesized zeolites and aluminophosphates with four-connected frameworks (5). They found that when the frameworks were grouped as a function of the smallest ring present in the structure, the minimum framework density calculated for each of the groups decreases with the smallest ring size. These results suggested that one way of preparing low framework density zeolites could be to build structures with four-and three-rings. Following this suggestion and the recognition that several beryllium-containing natural zeolites, such as lovdarite and nabesite, have three-rings in their structures, Cheetham et al. (6) prepared a large pore (14 × 8 × 8) zeolite with Be that contains three-rings. Previously, Davis et al. considered using zinc as a framework cation to promote the formation of three-rings, and while three zincosilicates containing three-rings were subsequently synthesized, none of them contain extra-large pores (7-9). Later, we have shown by theoretical and experimental work, that Ge has a directing effect toward the formation of double four-rings (D4Rs) (10, 11), and the presence of these secondary building units (SBUs) has allowed the synthesis of several large and extra-large pore zeolites (12-15). Among those, Instituto de Tecnologia Química number 33 (ITQ-33) contains D4Rs and three-ring units in the structure and has a low framework density (12.3 T∕1;000 Å 3 ). Very recently, an interrupted zeolite with a three-dimensional mesoporous channel system (ITQ-37) has been presented (16), which contains D4Rs and has the lowest framework density reported (10.3 T∕1000...

Layered zeolitic materials: an approach to designing versatile functional solids

“…184,185,186 Moreover, it was demonstrated that germanium very preferentially occupies D4R positions. 187,188,189,190 One of these structures was ITQ-15, 191 which structure was shown to be formed by 14x12 ring pores and was denominated UTL, following the IZA code (see Figure 28a).…”

Why Zeolites Have So Few Seven-Membered Rings

“…While several intriguing zeolites with densities in this range have recently been synthesized, 15,16 …”

Synthesis of an extra-large molecular sieve using proton sponges as organic structure-directing agents

“…In fact, zeolites with 16-ring pores are very rare; the only example is the germanosilicate ITQ-40 (22). ITQ-51 is one of the very few extra-large-pore zeolites with ≥16-ring channels that are stable in air after calcination.…”

“…Although Curtis and Deem (19) predicted that these zeolitic structures are thermodynamically feasible, only three microporous materials with 16-rings have been reported. Of these three materials, two are oxyfluorinated gallium phosphates, ULM-5 (20) and , with gallium in diverse atomic coordination (tetrahedral and octahedral); the other is the germanium-rich ITQ-40 containing 16 × 16 × 15-rings and structural defects (22). More specifically, in the AlPO family, it is possible to find structures with 12-, 14-, and 18-rings, but AlPO structures with 16-rings have not been reported up to now, as far as we know.…”