Critical Role of Dynamic Flexibility in Ge‐Containing Zeolites: Impact on Diffusion

Abstract

Incorporation of germaniumi nz eolites is well known to confer staticf lexibility to their framework, by stabilizing the formationo fs mall rings. In this work, we show that the flexibility associated to Ge atoms in zeolitesg oes beyond this static effect, manifesting also ac lear dynamic nature,i nt he sense that it leads to enhanced molecular diffusion.O ur study combines experimental and theoretical methods providinge videncef or this effect, which has not been described previously,a sw ell as ar ationalizationf or it, based on atomistic grounds.W eh ave used both pure-silica and silico-germanate ITQ-29 (LTA topology) zeolites as ac ase study.B ased on our simulations, we identify the flexibility associated to the pore breathing-like behaviori nduced by the Ge atoms, as the key factor leading to the enhanced diffusion observed experimentally in Ge-containingz eolites.

Fabrication and molecular transport studies of highly c-Oriented AFI membranes

“…It is noted that mesitylene (7.5 Å) is slightly larger than the channel size (7.3 Å), yet it can pass through the AFI channels quickly. Similar observations have also reported in many other zeolite systems that the effective pore size of zeolites is often found larger than the crystallographic pore size and the deviation sometimes can be up to 0.5 Å [36][37][38][39].…”

A procedure for identifying possible products in the assembly–disassembly–organization–reassembly (ADOR) synthesis of zeolites

“…Research so far has concentrated on parents that have silica-rich layers linked by germanium-rich cubic units, termed double four rings (d4rs). [12][13][14][15][16] Generally, to be successful in the ADOR process, these d4r units must contain enough Ge to break the connections between the layers as the Ge is hydrolysed, allowing the parent zeolite to be disassembled. 17,18 The specific location of the Ge within the d4r units is often difficult to determine without highly specialised diffraction experiments.…”

Influence of Flexibility on the Separation of Chiral Isomers in STW‐Type Zeolite

“…Some of them exhibit flexible phenomena [25] such as breathing, [26] swelling, [27] linker reorientation, [28] negative/positive thermale xpansion [29] and subnetwork displacement, [30] which are generally triggered by external stimuli such as temperature, pressure or guest adsorption. [32] Moreover, changes in the chemical compositionc an also alter the flexibility pattern of af ramework, since the presence of germanium in zeolites confers static and dynamic flexibility [33] to an otherwise rigid framework. [32] Moreover, changes in the chemical compositionc an also alter the flexibility pattern of af ramework, since the presence of germanium in zeolites confers static and dynamic flexibility [33] to an otherwise rigid framework.…”

“…[9c] However,f or most frameworks, this intrinsic flexibility [31] involves just lattice vibrations and does not affect strongly adsorptionp roperties or the crystalline regularity.T hese frameworks are commonly treated as rigid, and zeolites are typically assigned to this category.H owever,t he intrinsic flexibility of a zeolite may also induce changes in the pore opening that can disrupt the structurals electivity of this material. [32] Moreover, changes in the chemical compositionc an also alter the flexibility pattern of af ramework, since the presence of germanium in zeolites confers static and dynamic flexibility [33] to an otherwise rigid framework. Thus,t he interplay between flexibility .…”