Pair distribution function analysis of pressure treated zeolite Na-A

Abstract

Pair distribution function studies using X-ray scattering data from zeolite Na-A samples treated at pressure up to 8 GPa indicate a pressure-induced amorphisation mechanism involving loss of crystallographic order of the aluminosilicate framework but retention of the local sodium to oxygen bonding.

Confined H2O molecules as local probes of pressure-induced amorphisation in faujasite

“…The observed structural changes upon amorphisation in faujasite are consistent with a recent study on zeolite NaA; PDF analysis 38 showed that amorphisation was related to distortion in that case of the D4R's linking the sodalite cages and the simultaneous loss in regularity of the latter. In a recent study of a pressure-amorphized, sodalite-type metal organic framework containing I 2 molecules, 39 PDF results indicate that the sodalite topology is retained, but that the 6-membered rings are distorted.…”

In Situ Flow MAS NMR Spectroscopy and Synchrotron PDF Analyses of the Local Response of the Brønsted Acidic Site in SAPO‐34 during Hydration at Elevated Temperatures

“…First, it should be noted that the PDF peaks contain the contributions of more interatomic distances than earlier PDF studies on zeolite beta and siliceous chabazite, both of which contain only one type of T atom (Si). After a termination ripple at r =1.2 Å, the first main feature is a broad peak with a maximum at r =1.54 Å (P−O bond), and upon increasing the temperature a shoulder appears at r =1.78 Å (Al−O bond).…”

Synthesis of a Novel Zeolite through a Pressure‐Induced Reconstructive Phase Transition Process

“…In this order-to-disorder transition, the T-O-T angles change, whilst O-T-O angles and T-O distances remain unmodified. [10][11][12][13][14] Further compression leads to a high density amorphous (HDA) phase that does not revert back to the original zeolite. In this transition from LDA to HDA (called polyamorphism) some T À O bonds are broken, while new T À O linkages are formed.…”

“…In this transition from LDA to HDA (called polyamorphism) some T À O bonds are broken, while new T À O linkages are formed. [10,11] Also, the presence of water associated to cations [15] and the nature of these cations has been found to be important in the response of zeolites to high pressures. [10, 15a, 16] Previous high-pressure studies of zeolite A (LTA), with a Si/Al ratio close to one, have shown that its compressibility strongly depends on the ability of the pressure-transmitting medium (PTM) to penetrate into the zeolite pores.…”

“…[17] Using non-penetrating fluids as PTM, Al-containing LTA follows the typical zeolite behavior with an LDA phase at relatively low pressures, while further pressure increase gives rise to the formation of an HDA phase. [10][11][12] Notably, a theoretical study predicted a reversible PIA in Al-rich LTA, with two amorphous phases, and also three PIA steps in pure-silica LTA, with only the first being reversible. [18] Despite many high-pressure experiments performed on porous solids, it has not led to a new ordered zeolitic material.…”