Adsorption of NO in Li-exchanged zeolite A. A density functional theory study

Danilczuk, Marek; Lund, Anders

doi:10.1016/j.cplett.2010.03.055

Cited by 8 publications

(4 citation statements)

References 32 publications

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“…zeolites, alumina, aluminosilicalites or higher-order oxides are attractive materials in numerous applications in catalysis. Previous research has shown that those materials play a significant role in the separation and stabilization of various reactive intermediates as atoms, radicals, radical ions, and clusters [1][2][3][4][5][6][7]. Studies of such intermediates are very important for a better understanding of the mechanisms of chemical reactions in polymerization, heterogeneous catalysis, photochemistry, and radiation chemistry and biology.…”

Section: Introductionmentioning

confidence: 99%

Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state

Lund

Danilczuk

2012

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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Electron paramagnetic resonance (EPR) spectroscopy was applied to study the paramagnetic species formed from styrene, 1,1-diphenylethylene, α-methylstyrene, β-methylstyrene and methylmethacrylate adsorbed on amorphous silica gel after -irradiation at 77 K. Radicals formed by the hydrogen atom addition at the vinyl group of the monomers were observed in all samples. The hydrogen atoms were shown to originate to a large extent from the adsorbent by using silica gel with deuterated silanol groups. An EPR spectrum assigned to a propagating radical was observed at increased temperature for samples containing methylmethacrylate (MMA). The structures of the adsorption complexes, the respective hyperfine coupling constants and the adsorption energies were calculated by applying DFT quantum chemical methods. The reaction between an MMA molecule and the MMA radical and the structure of the propagating radical was modeled. The calculated hyperfine coupling constants for all radicals confirmed the assignment of the experimental spectra.3

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Section: Introductionmentioning

confidence: 99%

Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state

Lund

Danilczuk

2012

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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“…Their positions were frozen during optimalization procedure in contrast to the positions of other atoms, which were fully relaxed. It allowed one to take into account the local flexibility of the zeolite framework . The computational model shown in Figure presents the structure of one from the centers stabilizing •+ CO radical cation.…”

Section: Methodsmentioning

confidence: 99%

“…It allowed one to take into account the local flexibility of the zeolite framework. 15 The computational model shown in Figure 1 presents the structure of one from the centers stabilizing •+ CO radical cation. In a similar way, the structure of two other centers was defined.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

C-Centered Radicals in γ-Irradiated H-ZSM-5 Exposed to CO

et al. 2012

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The radical reactive intermediates play an important role in many catalytic and radiation reactions. To study their geometry and electronic structure, time-resolved methods or stabilization at low temperature in inert matrixes is requisite. In this Article, we present the EPR study on carbon-centered radicals formed in γ-irradiated H-ZSM-5 zeolite exposed to 13CO. Two EPR doublets with different 13C hyperfine splittings were assigned to two carbon centered radicals stabilized in different sites. According to DFT calculations, the anisotropic doublet A with A x = 30.2 mT, A y = 27.4 mT, and A z = 26.0 mT represents the centers in which •+CO radical cation interacts with lattice oxygen placed between Al and Si atoms or between two Si atoms. The second doublet B with A iso = 21.4 mT was assigned to •CO radical attached to the oxygen of terminal silanol group. The analysis of radical electronic structure proved the sp2 hybridization of 13C atoms in all observed centers. These centers react with oxygen even at 77 K forming coadsorption complexes characterized by EPR anisotropic singlet of the peroxide radical. The concentration of B centers distinctly decreases with dehydration temperature of zeolite. This effect was explained by the gradual loss of hydroxyl groups bonded to the terminal Si atoms in the temperature range 400–700 °C.

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“…14,15 Several studies have calculated EPR properties of transition metal substituted zeolites. [16][17][18] This spectroscopic technique is very sensitive to the transition metal environment and can be very successfully used to characterise transition metal centers. However all of the ab-initio studies on EPR properties for these systems have used a cluster-in-vacuo gas-phase approach to calculate the g-tensor.…”

Section: Introductionmentioning

confidence: 99%

Accurate spin–orbit and spin–other-orbit contributions to the g-tensor for transition metal containing systems

Deyne

Pauwels

Speybroeck

et al. 2012

Phys. Chem. Chem. Phys.

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In this paper an overview is presented of several approximations within Density Functional Theory (DFT) to calculate g-tensors in transition metal containing systems and a new accurate description of the spin-other-orbit contribution for high spin systems is suggested. Various implementations in a broad variety of software packages (ORCA, ADF, Gaussian, CP2K, GIPAW and BAND) are critically assessed on various aspects including (i) non-relativistic versus relativistic Hamiltonians, (ii) spin-orbit coupling contributions and (iii) the gauge. Particular attention is given to the level of accuracy that can be achieved for codes that allow g-tensor calculations under periodic boundary conditions, as these are ideally suited to efficiently describe extended condensed-phase systems containing transition metals. In periodic codes like CP2K and GIPAW, the g-tensor calculation schemes currently suffer from an incorrect treatment of the exchange spin-orbit interaction and a deficient description of the spin-other-orbit term. In this paper a protocol is proposed, making the predictions of the exchange part to the g-tensor shift more plausible. Focus is also put on the influence of the spin-other-orbit interaction which becomes of higher importance for high-spin systems. In a revisited derivation of the various terms arising from the two-electron spin-orbit and spin-other-orbit interaction (SOO), new insight has been obtained revealing amongst other issues new terms for the SOO contribution. The periodic CP2K code has been adapted in view of this new development. One of the objectives of this study is indeed a serious enhancement of the performance of periodic codes in predicting g-tensors in transition metal containing systems at the same level of accuracy as the most advanced but time consuming spin-orbit mean-field approach. The methods are first applied on rhodium carbide but afterwards extended to a broad test set of molecules containing transition metals from the fourth, fifth and sixth row of the periodic table. The set contains doublets as well as high-spin molecules.

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Adsorption of NO in Li-exchanged zeolite A. A density functional theory study

Cited by 8 publications

References 32 publications

Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state

Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state

C-Centered Radicals in γ-Irradiated H-ZSM-5 Exposed to CO

Accurate spin–orbit and spin–other-orbit contributions to the g-tensor for transition metal containing systems

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