Fourier Transform Infrared Study on the Encapsulation of CO in Zeolite Y under the Moderate Temperature and Pressure Conditions

Abstract

were observed during the room-temperature adsorption of CO over NaY zeolite. This was accompanied by the appearance of a prominent band at 2356 cm -1 along with the sidebands at 2336, 2342-2348, and 2364-2370 cm -1 in the ν 3 region of CO 2 vibrations. The intensity and the frequency of these bands showed monotonic changes on evacuation, temperature rise, and exchange of Na + ions with a proton or a group IIA cation and also on using the isotopically labeled CO. For instance, the adsorption of isotopic 13 C 16 O and 12 C 18 O gases gave rise to a uniform red shift in all the major ν(CO) bands, corresponding to a frequency ratio of ν( 13 CO)/ν( 12 CO) ≈ 0.978 and ν(C 18 O)/ν(C 16 O) ≈ 0.976. Similarly, all the asymmetric stretching bands of CO 2 showed a uniform isotopic shift corresponding to ν( 13 C)/ν( 12 C) ≈ 0.971. Furthermore, the intensity of most of the above-mentioned bands in ν(CO) and ν 3 (CO 2 ) regions exhibited an exponential type growth behavior with increasing adsorbate pressure, though the extent of this growth was different for individual vibrations. No significant change was, however, observed in the frequency and the intensity of the hydroxyl region bands on adsorption of CO under experimental conditions of this study. Arguments are presented to show that the observations of this study are not in harmony with the reported modes of direct CO adsorption at the specific zeolitic sites such as the charge-balancing cations, Al 3+ sites, or the Bronsted acid sites. Instead, the formation of the weakly held (CO) n and (CO 2 ) n molecular clusters occluded in the zeolitic cavities and stabilized under the cation field is in conformity with the data of this study.

Fourier Transform Infrared and Quasi-Elastic Neutron Scattering Investigations on the Binding States and the Dynamics of Benzene Molecules in the Pores of MCM-41 Molecular Sieves

“…13,14 A Mattson model Cygnus-100 FTIR spectrophotometer equipped with a DTGS detector was used in transmission mode, and 300 scans were co-added at a resolution of 4 cm -1 for plotting of each spectrum. The sample wafer (2.5 cm diameter, ∼70 mg) was subjected to a pretreatment at 350°C (24 h, 1.3 × 10 -3 mbar), cooled to ambient temperature, and then exposed to a desired amount of benzene (1-11 mmol g -1 ).…”

“…8,9 At the same time, the interaction of small adsorbate molecules with the framework sites, hydroxy groups, charge balancing cations, and the extraframework aluminum sites, etc., has been demonstrated in a number of publications. [10][11][12] In the previous studies reported from this laboratory, [13][14][15][16][17][18][19] we employed FTIR spectroscopy and quasielastic neutron scattering (QENS) methods with the objective of monitoring the state of guest molecules occluded in zeolitic cavities at temperatures of ambient and above, and also under the varying conditions of pressure. In these studies we demonstrated that small molecules such as CO, CO 2 , benzene, and cyclohexane existed in a clustered state when occluded at room temperature in microporous zeolites of X-, Y-and ZSM-5 type.…”

FT-IR study of the adsorption of carbon monoxide and of some nitriles on Na-faujasites: Additional insight on the formation of complex interactions

“…Low temperature [30][31][32][33][34][35] and room temperature [36] IR studies of CO adsorption on alkali-metal faujasites have been published. In this paper we report on our re-examination of the CO-NaFAU system and on a new study on the adsorption of hindered nitriles on NaX and NaY samples, in order to check if interactions similar to those observed on NaMOR are detectable on these systems.…”

Determination of Acid/Base Properties by Temperature Programmed Desorption (TPD) and Adsorption Calorimetry

“…The use of substituted pyridines, such as 2,6-dimethylpyridine (lutidine), has also been considered in order to probe specifically the Brönsted sites, because of their basic character and the steric effect of the methyl groups [121]. Carbon monoxide meets many criteria that have promoted its extensive use as a surface probe for the study of Lewis as well as Brönsted sites particularly by IR and NMR spectroscopy [7,119,122]. The CO molecule has an asymmetric charge and is easily polarized.…”