Success in Making Zn⁺ from Atomic Zn⁰ Encapsulated in an MFI-Type Zeolite with UV Light Irradiation

Abstract

For the first time, the paramagnetic Zn(+) species was prepared successfully by the excitation with ultraviolet light in the region ascribed to the absorption band resulting from the 4s-4p transition of an atomic Zn(0) species encapsulated in an MFI-type zeolite. The formed species gives a specific electron spin resonance band at g = 1.998 and also peculiar absorption bands around 38,000 and 32,500 cm(-1) which originate from 4s-4p transitions due to the Zn(+) species with paramagnetic nature that is formed in MFI. The transformation process (Zn(0) → Zn(+)) was explained by considering the mechanism via the excited triplet state ((3)P) caused by the intersystem crossing from the excited singlet state ((1)P) produced through the excitation of the 4s-4p transition of an atomic Zn(0) species grafted in MFI by UV light. The transformation process was well reproduced with the aid of a density functional theory calculation. The thus-formed Zn(+) species which has the doublet spin state exhibits characteristic reaction nature at room temperature for an O2 molecule having a triplet spin state in the ground state, forming an η(1) type of Zn(2+)-O2(-) species. These features clearly indicate the peculiar reactivity of Zn(+) in MFI, whereas Zn(0)-(H(+))2MFI hardly reacts with O2 at room temperature. The bonding nature of [Zn(2+)-O2(-)] species was also evidenced by ESR measurements and was also discussed on the basis of the results obtained through DFT calculations.

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

“…In addition, a distinct isotropic ESR signal appeared at g = 1.9980, ascribed to the paramagnetic Zn + species. 14 It follows from what has been said that this change initiated by irradiation with light in the wavenumber region 50 000 to 35 000 cm −1 corresponds to the σ → σ* excitation energy of the [Zn 2 ] 2+ species (Fig. S7 †).…”

“…[12][13][14] The final number shown in the sample notation indicates the ion exchange capacity that was evaluated by assuming one Zn 2+ -ion exchange per two protons in MFI.…”

“…Previously, our studies confirmed that this B3LYP-optimized MFI zeolite model comprised of 10-MR in cavities reproduced well the experimentally observed data. [12][13][14]22,[24][25][26][27][28][29][30][31] Taking our previous studies into consideration, we used the M7 site for the Al substitution position; 32 and we defined the Al configuration as the [M7-S2] arrangement. [12][13][14]30 To optimize fully the larger MFI geometry with a 10-MR cavity, we used the 6-311G(d) basis set for the zinc atom and the 6-31G (d) basis set for the Al atom, as well as four O atoms that were connected to the substituted Al atom.…”

“…[12][13][14]22,30 The reason why we chose this model is because it had been confirmed previously that the calculation using this model provides a complete description of the electronic states of a monomeric Zn 2+ ion embedded in MFI in the activation processes of H 2 or CH 4 activation at temperatures around 300 K, as well as the formation of Zn + ions. [12][13][14]30 The resulting structural parameters of the optimized [Zn 2 ] 2+ -(M7-S2) model were found to be 1.92 and 2.32 Å for the Zn-O and Zn-Zn distances, respectively, which are well consistent with the structural data obtained from our EXAFS analysis (Table 1). In addition, the UV-vis spectrum reproduced by the time-dependent density functional theory (TD-DFT) calculation using the [Zn 2 ] 2+ -(M7-S2) model showed qualitative agreement with the experimental spectrum (Fig.…”

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

“…Based on this report, an approach for the synthesis of Zn + species with a paramagnetic nature was developed, involving UV irradiation of Zn encapsulated in the MFI‐type zeolite ( Figure 5 ). 36 A transformation mechanism was proposed based on UV–vis DR spectra and DFT calculations (see the Characterization section for details), as described in Equation (3). …”