Atomic Resolution Analysis of Silver Ion‐Exchanged Zeolite A

Abstract

The three‐dimensional structure of Ag ion‐exchanged zeolite A was studied by XRD and scanning transmission electron microscopy. Despite the difficulties in the microscopic investigation of zeolites with high Al content, the arrangement of isolated Ag ions and Ag clusters of six atoms was visualized (see picture).

Atomic resolution analysis of porous solids: A detailed study of silver ion-exchanged zeolite A

“…5a shows the atomic distribution with, in the majority of cases, nine Ag atoms contained in each sodalite cage. Four cations [14] form a square (if we consider a 2-dimensional object, but representing a cube formed by eight atoms for the real cage) separated from each other by 4.72 Å (Fig. 5b) and situated in the 6-rings which form the sodalite cages; this fits perfectly with the model obtained by Rietveld refinement of the powder X-ray diffraction data (Fig.…”

“…The formation of octahedral clusters is also in agreement with a complete ion exchange as linear clusters which could be formed Intensity profiles performed on the atoms marked as 1, 2, and 3 in (b) and 4, 5, and 6 with the interatomic distance between these atoms being 2.70 Å. (e) Sodalite cage slightly tilted to observe the complete distribution of silver [14].…”

“…To image the zeolite, the materials were carefully dispersed onto carbon tabs and coated with a fine layer of gold. Computer simulations were carried out with the purpose of corroborating and facilitating the interpretation of the images (see Mayoral et al [14]). …”

“…When Na + was exchanged with UO 2þ 2 , the sensitivity was believed to decrease [12]; a similar example was found when Cd 2+ cations were introduced into the cages of zeolite A (LTA type) [13]. With the development of transmission electron microscopes, a promising route has been opened for the observation of these solids using spherical aberration correctors (C s ) applied to the scanning transmission electron microscopy mode (STEM) [14]. In this mode the beam is converged into a very fine spot which is scanned over the sample; however, the number of electrons concentrated in such a small area, below 1 Å for a C s -corrected machine, could end up in drilling a hole above some certain beam density [15].…”

Synthesis of 4A Zeolite and Characterization of Calcium- and Silver-Exchanged Forms

“…Silver ions migrate and undergo auto-reduction upon vacuum dehydration to form Ag 0 that interacts with silver ions to form clusters. The reduction process in anhydrous conditions can be written as [25]:…”