Synthesis of an unexpected [Zn₂]²⁺ species utilizing an MFI-type zeolite as a nano-reaction pot and its manipulation with light and heat

Abstract

Compared with mercury, the existence of [Zn2](2+) species is rare. We succeeded in preparing a stable [Zn2](2+) species by utilizing an MFI-type zeolite as a nano-reaction pot, which was confirmed using XAFS spectroscopy: the bands at R = 2.35 Å due to the Zn(+)-Zn(+) scattering and at 9660.7 eV due to the 1s-σ* (the anti-bonding orbital comprised of the 4s-4s orbital) transition of the [Zn2](2+) species. This species also gives the characteristic band around 42 000 cm(-1) due to its σ-σ* transition. Furthermore, UV-irradiation corresponding to the σ-σ* transition causes the bond dissociation, forming two unprecedented Zn(+) ions, and detached Zn(+) ions were recombined through heat-treatment at 573 K: [Zn(+)-Zn(+)] ⇄ 2Zn(+). These processes were reproduced by applying the DFT calculation method to the assumed triplet, σ(α)-σ*(α), structure formed on the M7-S2 site with the specific Al array in the MFI-type zeolite. Research into the specific field using zeolites to synthesize "ultra-state ions" is very promising.

High Zn/Al ratios enhance dehydrogenation vs hydrogen transfer reactions of Zn-ZSM-5 catalytic systems in methanol conversion to aromatics

“…edge peaks at ca. 9664.1 eV (feature B) and 9669.8 eV (feature C) and no trace of the characteristic ZnO resonance at 9679.7 eV.The characteristic XANES features of the activated material are in line with previous reports on Zn-zeolites[31,65,66] and Zn-enzymes[67][68][69]. The average coordination geometry for Zn-sites in activated Zn-ZSM-5 is hence expected to be still pseudotetrahedral, but significantly distorted.…”

“…As discussed in more details in the Supporting Information, (Fig. S4) feature X can be tentatively connected with the formation of atomic-like Zn 0 species [70] or Zn + -Zn + dimers [65] in very low abundance (<10% total Zn), although further studies are required to clarify its origin. Fig.…”

Recent Advances in the Synthesis, Characterization and Application of Zn+‐containing Heterogeneous Catalysts

“…Post-synthetic modifi cation of MFI-type zeolites can also be used to synthesize [Zn 2 ] 2+ and Zn + species, using HMFI and Zn vapor as reactants. [ 37 ] Zn 0 vapor reacts with HMFI zeolite leading to the initial formation of Zn 2+ -ion-exchanged MFI. With increasing exposure to Zn 0 vapor, [Zn 2 ] 2+ was formed through a spontaneous reverse disproportionation reaction between the Zn 2+ ions and Zn 0 vapor.…”

Evolution of Zn Species on Zn/HZSM‐5 Catalyst under H2 Pretreated and its Effect on Ethylene Aromatization

“…Meanwhile, a new band at 320 nm appeared at the reduction temperatures of >300 °C, suggesting the formation of Zn + species in the zeolite. It has been proved that UV irradiation can transform [Zn + −Zn + ] to two Zn + ions, and detached Zn + ions can be recombined through heat treatment at 300 °C . Chen et al .…”

“…It has been proved that UV irradiation can transform [Zn + À Zn + ] to two Zn + ions, and detached Zn + ions can be recombined through heat treatment at 300°C. [23] Chen et al [24] also noticed the presence of extra electrons in the framework of the as-prepared Zn 2 + -ZSM-5 zeolite and proposed that the transition of these extra electrons to the 4 s orbitals of Zn 2 + cations and the formation of Zn + ions are responsible for the optical absorption in the range of 278-390 nm. Therefore, the appearance of the band at 320 nm supports the presence of Zn + ions.…”