Study of the state of nickel in ion-exchanged NiNaY zeolite by IR spectroscopy using molecular hydrogen adsorbed at low temperatures

The state of nickel cations in NiNaY zeolite subjected to thermal vacuum and oxidative-reductive treatment was analyzed using diffuse reflectance IR spectra of molecular hydrogen, CO, and hydroxy groups. In a sample dehydrated at 570 K, nickel forms oxide particles, which are presumably located in big cavities of a zeolite. Heating of the sample at 670 K results in decomposition of the oxide with the participation of hydroxy groups followed by the formation of stabilized Ni²⁺ cations in large cavities of the zeolite. Calcination of NiNaY zeolite in a hydrogen atmosphere at 730 K leads to Ni²⁺ cation reduction to the metal state and to the formation of acidic hydroxy groups. Nevertheless, Ni²⁺ cations can be regenerated by reoxidation of the reduced sample with oxygen at 670 K and further evacuation at 870 K. Thermal destruction of NiO in the reoxidized sample also proceeds on acidic hydroxy groups, but the temperature of this process is higher than the temperature of oxide decomposition in the initial NiNaY zeolite. The IR spectra of molecular hydrogen complexes with Ni²⁺ cations were observed for the first time. A considerable decrease in the H-H stretching vibration frequency for the coordinated molecules (up to 210 cm’1) can be explained by electron density redistribution between a hydrogen molecule and the cation in the complex     

IR spectra of aqueous disperse systems adsorbed atmospheric gases: 1. Nitrogen

Spectral characteristics of (H₂O) _i , N₂(H₂O) _i , and (N₂)₂(H₂O) _i cluster systems, where 10≤i≤50, are studied in the 0 ≤ ε ≤ 3500 cm^?1 frequency range with the molecular dynamics method on the basis of a flexible molecule model. After nitrogen is captured by an aqueous disperse system, the absorption of the IR radiation by this system increases owing to the enhancement of intramolecular vibrations. In general, the reflection of the outer IR radiation by nitrated aqueous disperse systems is attenuated; however, when the nitrogen concentration increases twofold, there is a tendency toward an increase in the fraction of reflected radiation. As the nitrogen concentration in a system of water clusters rises, the power of radiation emitted by the system increases significantly and the number of electrons interacting with the outer IR radiation decreases.     

Heats of immersion of some ion-exchanged A and X zeolites of divalent cations

Heats of immersion in water (integral heats of hydration) of anhydrous zeolites NaA, CdA, ZnA, CoA, NaX, CdX, ZnX, CoX and NiX have been determined calorimetrically at 25°C. Sodium in NaA and NaX has been replaced by divalent cations to the extent of 70–100% . The data are correlated to the size of the cations and to the standard enthalpy changes of the corresponding ion-exchanged equilibria. The latter values are analysed in terms of three processes: hydration of ions in solution, hydration of zeolites, and electrostatic binding energy of cations to the zeolite framework.     

Effect of the state of vanadium cations on the IR spectra of adsorbed carbon monoxide

ESR and IR-spectrosocpic studies of the effect of the state of vanadium ions on the IR-spectra of adsorbed CO have revealed complex formation of CO with V⁴⁺ (vCO at 2192 and 2205 cm^–1) and V³⁺ (vCO at 2178 and 2185 cm^–1) ions.

---

-- - CO. CO V⁴⁺ (vCO 2192, 2205 cm^–1) V³⁺ (vCO 2178, 2185 cm^–1).

     

Carbamic acid: molecular structure and IR spectra.

Infrared absorption spectra of mixed H2O, NH3 and 12CO2/13CO2 ices subjected to 1 MeV proton irradiation were investigated. The results of analyses of the spectra suggest formation of carbamic acid at low temperatures. The stability of this compound in the solid phase is attributed to intermolecular hydrogen bonding of the zwitter-ion (NH3+ COO-) structure.     

IR spectra of CO and NO adsorbed on CuO

The original heterogeneity of CuO surface is suggested to account for the presence of two states of surface copper cations with different effective charges.

---

CuO, . , .

     

Influence of molecular electronic properties on the IR spectra of dimeric hydrogen bond systems: polarized spectra of 2-hydroxybenzothiazole and 2-mercaptobenzothiazole crystals

We have studied the polarized IR spectra of the hydrogen-bonded molecular crystals of 2-hydroxybenzothiazole (HBT) and 2-mercaptobenzothiazole (MBT). The crystal structure of 2-hydroxybenzothiazole was determined by X-ray diffraction. The polarized spectra of the crystals were measured, in the frequency ranges of the ν_N-H and ν_N-D bands, at room temperature, and at 77 K. In both systems an extremely strong H/D isotopic effect in the spectra was observed, involving reduction of the well-developed ν_N-H band fine structure to a single prominent ν_N-D line only. The two ν_N-H bands were also shown to exhibit almost identical properties, band shapes, temperature and dichroic properties included. The spectra were quantitatively reconstituted, along with the strong isotopic effect, when calculated using the ‘strong-coupling’ theory, assuming the centrosymmetric dimers of HBT or MBT to be the structural units responsible for the crystalline spectral properties. The similarity of the spectra of the two crystalline systems was considered to be a result of longer-distance couplings between the proton vibrations in the dimers, via the aromatic ring electrons. When investigating the ‘residual’ ν_N-H band shapes for crystals isotopically diluted by deuterium, we observed some ‘self-organization’ effects in the spectra, indicating the energetically favored presence of two identical hydrogen isotopes in each hydrogen bond dimer.     

Information from IR fundamental and overtone spetra of diatomics adsorbed in zeolites NaCaA

From fundamental and overtone spectra of CO, NO and D₂ adsorbed in zeolites NaCaA the constants of the internuclear potential can be derived for the adsorbed state. As the interactions with the zeolite surface are dominated by van der Waals forces, they remain less affected by adsorption. In contrast to diatomics adsorbed on transition metal surfaces, no considerable alteration of bond energy can be observed. The frequency shift is essentially due to the change of the harmonic force constant and indicates the interaction potential depending almost linearly on the vibrational state. The heterogeneity of the cation distribution inside the zeolites is reflected in the broadening of the adsorbate bands.     

Quantum chemical predictions of IR spectra and thermodynamic properties of tetrazole derivates

We have predicted the optimized geometries, infrared spectrum, and thermodynamic properties for six tetrazole derivates at density functional theory and second-order Møller–Plesset perturbation theory (MP2) level with the 6-31G** basis set. Their heats of formation were calculated accurately using the designed isodesmic and isogyric reactions. The computed total energies, heat of formation, and enthalpy of combustion consistently indicate the stability: 5-(2,4,6-trinitrophenyl)-2H-tetrazole > 5-(2,4,6-trinitrophenyl)-1H-tetrazole > 5-(2,4,6-trinitrophenyl)-5H-tetrazole The similar result for the isomers of 5-(2,4,6-trinitrobenzyl)-tetrazole: 5-(2,4,6-trinitrophenyl)-2H-tetrazole > 5-(2,4,6-trinitrophenyl)-1H-tetrazole > 5-(2,4,6-trinitrophenyl)-5H-tetrazole.     

Intensities of C-H IR stretching bands of ethane and propane adsorbed by zeolites as a new spectral criterion of their chemical activation via polarization resulting from stretching of chemical bonds

Polarization of ethane and propane resulting from adsorption of these hydrocarbons by protons and different cations in mordenite, ZSM-5, and Y zeolites was studied by diffuse reflection Fourier transform IR spectroscopy (DRIFTS). Perturbation of adsorbed molecules by protons and sodium cations is weak, while positions of absorption bands for both these zeolites are very close to each other. In contrast, distributions of C-H IR stretching bands in intensities are somewhat different. This effect is pronounced much stronger for adsorption of light paraffins by bivalent alkaline earth and zinc cationic forms of these zeolites. Distribution of relative intensities of absorption bands strongly depends in this case both on the nature of cations and on the zeolites, while the most strongly perturbed vibrations are the initially fully symmetric C-H stretching vibrations. The corresponding low-frequency shifts and relative intensities of IR bands are increasing for different cations and zeolites in the following sequences: Na < Ca < Mg < Zn and Y < Mor approximately ZSM-5, while the difference in distribution of relative intensities of C-H stretching bands is pronounced much stronger than for the low-frequency shifts of these bands. Therefore, the relative intensities of IR C-H stretching bands are much better criterion of perturbation of light paraffins upon adsorption than the frequencies of these bands, which are traditionally used for this purpose. In addition, distribution of C-H IR stretching bands in intensity also provides unique information on anisotropy of polarizability of different C-H bonds created by their vibrations. For the acid and acid-base catalysis, where the main source of chemical activation arises from polarization of adsorbed molecules, such information is most important, while the anisotropy of polarizability provides a unique information on selective activation of different chemical bonds resulting from their stretching. The obtained results also demonstrate the possibility to use for testifying of the strength of Lewis acid sites instead of adsorption of the model molecular probes adsorption of the paraffins themselves.