Effects of Adsorbate Molecules on the Quadrupolar Interaction of Framework Aluminum Atoms in Dehydrated Zeolite H,Na-Y

Abstract

The effect of adsorbate molecules on the quadrupolar interaction of framework aluminum atoms with the electric field gradient in dehydrated zeolite H,Na-Y has been studied by (27)Al MAS NMR and (27)Al MQMAS NMR spectroscopy at magnetic fields of 9.4 and 17.6 T. Upon adsorption of molecules interacting with bridging OH groups by hydrogen bonds (acetonitrile and acetone), the quadrupole coupling constant of framework aluminum atoms was found to decrease from 16.0 MHz (unloaded zeolite) to 9.4 MHz. Adsorption of molecules, which cause a proton transfer from the zeolite framework to the adsorbates (ammonia and pyridine), reduces the quadrupole coupling constant to 3.8 MHz for coverages of 0.5-2 molecules per bridging OH group. The experiments indicate that the quadrupole coupling constant of framework aluminum atoms in dehydrated zeolite H,Na-Y reflects the chemical state of adsorbate complexes formed at bridging OH groups. In agreement with earlier investigations it was found that a proton affinity of the adsorbate molecules of PA = 812-854 kJ/mol is necessary to induce a proton transfer from the zeolite framework to the adsorbed compounds. This proton transfer is accompanied by a strong improvement of the tetrahedral symmetry of zeolitic framework AlO(4) tetrahedra and a decrease of the electric field gradient.

Structure and Catalytic Characterization of a Second Framework Al(IV) Site in Zeolite Catalysts Revealed by NMR at 35.2 T

“…Figure 3 reveals two Al sites in the tetrahedaral region of the spectrum, whose isotropic chemical shifts δ 1 and δ 2 obtained after applying known methods for shearing and fitting of the second-order quadrupolar induced shifts δ qis are 55 ppm and 59 ppm for the Al(IV)-1 and Al(IV)-2 sites, respectively. 37,38 Due to the distribution of both the isotropic chemical shift values and of δ qis values, the absolute values of the isotropic chemical shifts δ 1 and δ 2 are less critical than the fact that both shifts are in the known tetrahedral region. However, unlike the ultra-high field HMQC data in Figure 2, the data in Figure 3 cannot reveal if an Al atom in the catalyst generates a hydroxyl proton site.…”

“…44,45 NMR spectroscopy has played a key role in trying to understand structure and reactivity relationships in the context of catalyst synthesis and post-synthetic treatments, with the observation of Al (IV) signals in the known tetrahedral 50-65 ppm region vs. Al(VI) signals near 0 ppm as the most commonly employed marker of BAS framework Al and EFAl in HZSM-5 catalysts, respectively. 38,46,47 The limitations of detecting signals from quadrupolar Al atoms in non-spherical bonding environments are well known, which is why the majority of data in the literature centers on hydrated HZSM-5 catalysts. Similarly, signals at 4.0-4.5 and 2.5-2.9 ppm in 1 H solid-state NMR spectra of dehydrated HZSM-5 have been used as indicators of hydroxyl groups on BAS and EFAl species, respectively.…”

Retracted: Studies on the luminescence properties of cerium co‐doping on Ca2MgSi2O7:Eu2+ phosphor by solid‐state reaction method

“…[27] Various important physical and chemical properties of materials can be studied by using photons to induce excited electronic states in the material system and analyzing the optical emission as these states relax. [28,29] 3.5.1 | Ca 2 MgSi 2 O 7 :Ce 3+ phosphor…”

Photoluminescence properties of novel Ba2Lu5B5O17:Eu3+ red emitting phosphors with high color purity for near-UV excited white light emitting diodes

“…13,[15][16][17] The efficiency of commercial green (ZnS:Cu + ,Al 3+ ) and blue (BaMgAl 10 O 17 :Eu 2+ ) phosphors is much higher than that of commercial red (CaS:Eu 2+ , Y 2 O 2 S:Eu 3+ and Y 2 O 3 :Eu 3+ ) phosphors. 15,18,19 However, the sulde and oxysulde based red phosphors have poor chemical stability and high toxicity, and decompose at high temperature. 18,20 The other commercial red phosphors like Eu 2+ activated nitride compounds (CaAlSiN 3 and Sr 2 Si 5 N 8 ) have several drawbacks such as complex preparations and high cost.…”