Design of zeolite by inverse sigma transformation

Abstract

Although the search for new zeolites has traditionally been based on trial and error, more rational methods are now available. The theoretical concept of inverse σ transformation of a zeolite framework to generate a new structure by removal of a layer of framework atoms and contraction has for the first time been achieved experimentally. The reactivity of framework germanium atoms in strong mineral acid was exploited to selectively remove germanium-containing four-ring units from an UTL type germanosilicate zeolite. Annealing of the leached framework through calcination led to the new all-silica COK-14 zeolite with intersecting 12- and 10-membered ring channel systems. An intermediate stage of this inverse σ transformation with dislodged germanate four-rings still residing in the pores could be demonstrated. Inverse σ transformation involving elimination of germanium-containing structural units opens perspectives for the synthesis of many more zeolites.

Zeolites with Continuously Tuneable Porosity

“…All these reactions used Ge-UTL with a Si/Ge ratio of 6.0:1. Above an [H + ] of approximately 8 m and under the same conditions described in reference [21], all samples produced the COK-14 variant of the OKO topology. Under neutral and 0.01m conditions, IPC-4 was formed, but at [H + ] between 0.5 m and 6 m, the 200 reflection, which is indicative of the interlayer spacing in the materials, shows a steady shift to a decreasing scattering angle (i.e.…”

“…[13] Zeolites with the OKO topology can be prepared by two methods, either directly through hydrolysis at very high acidity (e.g. 12 m HCl), the so-called inverse sigma transformation route, to give a material called COK-14, [21] or by the intercalation of silica species into IPC-1P, prepared by hydrolysis at low acidity, to give IPC-2. [13,16] IPC-2 and COK-14 differ in their structural details (e.g.…”

The importance of T⋯T⋯T angles in the feasibility of zeolites

“…In addition to the classic solvothermal approach, where new gel compositions and new families of templates have contributed, among other, to the rising number of zeolites, novel methods such as 'inverse sigma' and 'ADOR (assembly, disassembly, organisation, reassembly)' approaches have been recently presented [13,14]. They start from existing zeolites containing individual layers interconnected by D4Rs (double four rings) where a high concentration of Ge favours delamination by selective removal of the D4Rs, and where subsequent condensation may lead to one or several new fully condensed phases.…”

“…It may be thought that the latter is a small number, but this depends T angles in the feasibility of zeolites on the efforts dedicated to try to synthesise new zeolites. The narrow differences in their relative free energies [15] is a factor against increasing their number, although some new synthesis methods allow to overcome certain energetic barriers by following a less straight synthesis path [13,14]. Assessing zeolite feasibility is a challenging issue and several attempts have been made [16][17][18].…”

Expansion of the ADOR Strategy for the Synthesis of Zeolites: The Synthesis of IPC‐12 from Zeolite UOV

“…In the UTL ADOR process at low acidity the disassembly process dominates, but at very low pH (high acidity) the disassembly also happens quickly but is followed by a subsequent rearrangement process, with extra silicon‐containing bridges forming between the layers, resulting, after calcination, in a different zeolite IPC‐2 15, 16, 17. This rearrangement process does not occur in UOV , instead the higher acidity promotes reconnection of the layers without the intercalation of any extra silicon.…”