Cation-exchange in synthetic zeolite L: The exchange of hydronium and ammonium ions by alkali metal and alkaline earth cations

A Single‐Site Platinum CO Oxidation Catalyst in Zeolite KLTL: Microscopic and Spectroscopic Determination of the Locations of the Platinum Atoms

“…The result confirms previous reports that platinum complexes located in the D sites readily migrate to the E sites upon oxidation. [12,13] The EXAFS data show that the surroundings of the Pt atoms, on average, also changed as a result of the oxidation, in agreement with the STEM images. Because the average Pt À O coordination number at the bonding distance of nearly 2.0 increased from 2 to nearly 3 (Table 1), we postulate that the oxidation led to the formation of platinum oxo species, [20] with approximately one oxo O atom per Pt atom, corresponding to the increase in the PtÀO coordination number.…”

“…After oxidation, the band at 3743 cm À1 , assigned to zeolite silanol groups, [11] was the only n OH band remaining, consistent with the expectation that the platinum complexes had preferentially undergone ion exchange with K + ions located near zeolite Al atoms rather than Si atoms. [12,13] Pt L III edge EXAFS spectra of this catalyst (Table 1; for fitting details, see the Supporting Information) are in accord with the IR data, indicating a Pt À N shell with a coordination number of nearly 4. The Pt À O support coordination number of nearly 2 indicates that each Pt atom was bonded, on average, to two zeolite surface oxygen atoms.…”

“…The 5 unique bonding locations (A-E) of the Pt atoms are described elsewhere. [12,13] PtÀO bond distances determined by EXAFS spectroscopy were used with STEM images to determine the Pt atom locations. O red, T-site Si/Al purple, Pt green, N blue; H not shown for clarity.…”

Hydrothermal modification of natural zeolites to improve uptake of ammonium ions

“…This comparison indicates that the treated zeolites composed of mainly phillipsite have similar but slightly higher exchange capacities than reported previously for other zeolites. 15,17,21,22 3.3 Ion-exchange mechanism of ammonium ions Phillipsite modified from MOR3 at 100 • C in 3 M NaOH solution, with the highest ion-exchange capacity for ammonium ions, was used to investigate the uptake mechanism of ammonium ions. Figure 4 shows the relationship between the uptake of ammonium ions by phillipsite and the amounts of Na and Mg 2+ were not detected.…”

Pressure-induced hydration and cation migration in a Cs+ exchanged gallosilicate zeolite LTL: Synchrotron X-ray powder diffraction study at ambient and high pressures

“…The chemistry of these confined species, coupled with the confinement geometry, play an important role in determining catalytic, ion exchange and molecular sieving properties [1]. To alter the chemistry and geometry of a given framework, cation substitution and temperature effect have been applied extensively [2][3][4][5], while pressure effect has been limited to measuring compressibilities and investigating structural amorphizations [6,7]. Recently, however, interests in exploring the high pressure chemistry of zeolites have expanded in both experimental and theoretical studies and demonstrated how a zeolitic framework responds to applied hydrostatic pressure and how this can regulate the zeolitic water content, cation distribution, and selectivity toward foreign species [8][9][10][11].…”