Quantum chemical calculation of infrared spectra of acidic groups in chabazite in the presence of water

Abstract

The changes in the spectra of the acidic group in chabazite are studied by quantum chemical calculations. The zeolite is modeled by two clusters consisting of eight tetrahedral atoms arranged in a ring and seven tetrahedral atoms coordinated around the zeolite OH group. The potential energy and dipole surfaces were constructed from the zeolite OH stretch, in-plane and out-of-plane bending coordinates, and the intermolecular stretch coordinate that corresponds to a movement of the water molecule as a whole. Both the anharmonicities of the potential energy and dipole were taken into account by calculation of the frequencies and intensities. The matrix elements of the vibrational Hamiltonian were calculated within the discrete variable representation basis set. We have assigned the experimentally observed frequencies at ϳ2900, ϳ2400, and ϳ1700 cm Ϫ1 to the strongly perturbed zeolite OH vibrations caused by the hydrogen bonding with the water molecule. The ABC triplet is a Fermi resonance of the zeolite OH stretch mode with the overtone of the in-plane bending ͑the A band͒ and the overtone of the out-of-plane bending ͑the C band͒. In the B band the stretch is also coupled with the second overtone of the out-of-plane bending. The frequencies at ϳ3700 and ϳ3550 cm Ϫ1 we have assigned to the OH stretch frequencies of a slightly perturbed water molecule.

Proton Transfer in Zeolites

“…Due to hydrogen bonding with the adsorbed H 2 O molecule the zeolitic OH stretching is strongly red-shifted, and resonance with the overtone of the in-plane SiOH bending creates a window at the overtone position (see Ref. [36] for a recent model calculation). Figure 22.4 shows the observed spectrum [37] and the assignment based on MP2 frequency calculations [34].…”

Heterogeneous and multiphase chemistry of trace atmospheric gases with mineral dust and other metal containing particles

“…66 They can be attributed to the formation of strongly hydrogen bonded H + (H 2 O) n species or complexes of water with newly formed Brønsted acidic hydroxyl groups upon nitric acid adsorption. [72][73][74] The signature for hydrogen bonding is evidenced by the two broad absorption bands at ~ 2900 and ~ 2450 cm -1 . [72][73][74] A third broad absorption band at ~ 1700 cm -1 is more difficult to see in Figure 3.1 because of other absorption bands in this region.…”

“…[72][73][74] The signature for hydrogen bonding is evidenced by the two broad absorption bands at ~ 2900 and ~ 2450 cm -1 . [72][73][74] A third broad absorption band at ~ 1700 cm -1 is more difficult to see in Figure 3.1 because of other absorption bands in this region. [72][73][74] These three broad absorption bands have been proposed to be characteristic of hydrogen bonded hydroxyls arise due to a Fermi resonance of zeolite OH stretch mode with the overtone of bending vibrations.…”

“…[72][73][74] A third broad absorption band at ~ 1700 cm -1 is more difficult to see in Figure 3.1 because of other absorption bands in this region. [72][73][74] These three broad absorption bands have been proposed to be characteristic of hydrogen bonded hydroxyls arise due to a Fermi resonance of zeolite OH stretch mode with the overtone of bending vibrations. 74 Zeo − O − … Na + + HNO 3 ↔ Zeo − O − … H + + Na + NO 3 − (3.1)…”

“…[72][73][74] These three broad absorption bands have been proposed to be characteristic of hydrogen bonded hydroxyls arise due to a Fermi resonance of zeolite OH stretch mode with the overtone of bending vibrations. 74 Zeo − O − … Na + + HNO 3 ↔ Zeo − O − … H + + Na + NO 3 − (3.1)…”