Faujasite infrared studies

Relatively few studies have focused on influence of the acid/base properties of the support on the chemisorption of reactants on supported metal clusters. A NMR study by Tong et al.23 showed that the stretching frequency of CO chemisorbed on zeolite supported Pt particles correlates with the surface local density of states (LDOS) of the Pt. The LDOS also showed a correlation with the faujasite framework acidity, but an explanation of this correlation is lacking. Several infrared studies on similar supported Pt catalysts show that the mode of CO... 

An IR spectrum of zeolite L (LTL) was pubUshed as early as 1971 by Ward in his review article on infrared studies with zeoHtes [383] which dealt predominantly with faujasite-type materials (vide supra). He observed in deammoniated samples of NH4-L sharp bands at 3740 and 3630 cm and a broad band centered around 3200 cm. After evacuation at 813 K, only the 3740 cm" band remained. Similarly, Weeks and Bolton [467] foimd on deammoniation of NH4,K-L, besides the absorbance at 3740 cm, a single weak band at 3630 cm". Major changes occurred in the framework region. 

The infrared study of the benzene adsorption in faujasites at room temperature showed that the two different shifts of bands of CH out of plane vibrations could be related to... 

McNicol et al. (49) used luminescence and Raman spectroscopy to study structural and chemical aspects of gel growth of A and faujasite-type crystals. Their results are consistent with a solid-phase transformation of the solid amorphous network into zeolite crystals. Beard (50) used infrared spectroscopy to determine the size and structure of silicate species in solution in relationship to zeolite crystallization. 

Infrared Spectroscopic Study of the Isotopic Exchange of Lattice Hydroxyls in Synthetic Faujasites... 

Infrared spectral studies of pyridine adsorbed on alkali metal ion-exchanged faujasites have demonstrated the absence of Brpnsted acidity, as reported by Eberly (151), Ignat eva et al. (208), and Ward (156, 209-211). Pyridine is adsorbed weakly by coordination to the alkali metal ions (151, 156). Addition of small amounts of water does not result in formation of Br0nsted acid sites, indicating that the coordinate bound pyridine is not associated with Lewis acid sites in the zeolite framework (210). 

Infrared spectral studies of rare earth (RE) ion-exchanged faujasites have been reported by Rabo et al. (214), Christner et al. (217), Ward (211, 212), and Bolton (218). Distinct hydroxyl absorption bands are observed at 3740, 3640, and 3522 cm-1 after calcination at temperatures in the range of 340° to 450°C. As previously discussed, the hydroxyl groups at 3740 cm-1 are attributed to silanol groups either located at lattice termination sites or arising from amorphous silica associated with the structure. The hydroxyl groups that form the 3522 cm-1 band are nonacidic to pyridine or piperidine and are thought to be associated with the rare earth cations. 

The decomposition of Co2(CO)8 in faujasites has been studied in some detail. Low-temperature spin-echo ferromagnetic nuclear resonance spectroscopy shows that very small Co particles are formed in supercages of zeolite NaX by microwave plasma activation at low temperatures (86). In situ far-infrared spectroscopy revealed that adsorbed Co2(CO)s interacts with accessible supercage cations in NaY and CoY (239). Carbonyl complexes of different Co nuclearity, such as Co4(CO)i2 and Co(CO)4, are also formed (227,228). In HY the Co atoms are oxidized to Co ions by the zeolite protons. 

Infrared Spectroscopy and Cumene Cracking Studies on Single Component Rare Earth Forms of Synthetic Faujasite... 

Oare earth forms of zeolites X and Y type faujasites possess superior catalytic properties for various reactions such as alkylation, isomerization, and cracking (9, 12, 18). Structural studies involving x-ray diffraction and CO chemisorption have been made to locate the positions of the rare earth (11, 14, 16). Hydroxyl groups and their relationship to surface acidity have been studied by infrared spectroscopy, utilizing the adsorption of pyridine and other basic molecules (2, 6, 21, 22, 23). Since much of the previous research has involved measurements on mixed rare earth faujasites, a need existed for a more systematic study of the individual rare earth zeolites, in regard to both structural and catalytic properties. The present investigation deals with the Y, La, Ce, Pr, Sm,... 

K. S. Smirnov and D. Bougeard,/. Raman Spectrosc., 24, 255 (1993). Raman and Infrared Spectra of Siliceous Faujasite. A Molecular Dynamics Study. 

Field strength-dependent infrared shifts, similar to those observed with CO adsorbed on various zeolites (85), have also been observed for CO2 adsorbed on alkaline earth cation-exchanged faujasites (90,91). In the study of Carter et al. (86), the heats of adsorption of the ethylene (18.1-8.3 kcal/mole) were related to changes in frequency of the double bond vibration of the adsorbed molecules. 

I.A. Beta, H. Jobic, E. Geidel, H. Bohlig B. Hunger (2001). Spectrochim. Acta A, 57, 1393-1403. Inelastic neutron scattering and infrared spectroscopic study of furan adsorption on alkali-metal cation-exchanged faujasites. 

E. Geidel, H. Jobic S.F. Parker (1999). Proceedings of the 72 International Zeolite Conference, (Ed). M.M.J. Treacy, B.K. Marcus, M.E. Bisher J.B. Higgins), Materials Research Society, Pittsburgh, pp.2609-2614. Vibrational spectroscopic investigations of pyrrole adsorption in faujasites studies by infrared, Raman and neutron spectroscopy. 

Although the basic model looks very good, the actual situation must be more complex since faujasite and Y zeolites cannot have full long-range order. The actual positions of the H atoms must vary somewhat from 1 unit cell to another, and such variations may lead to particularly active catalytic sites in just a few of the unit cells. Hopefully, singlecrystal infrared absorption studies, similar to those carried out for many silicates, will yield data on the orientation of the OH groups, thereby testing the Olson-Dempsey model. 

Following the above studies, Bennett and Smith (9, 11) showed that stricter dehydration caused La atoms in La-exchanged faujasite to move into I. Furthermore, the same dehydrated crystal of La-faujasite had essentially equal occupancy factors at 25° and 420°C, thereby ruling out any control of cation distribution from a pure temperature variation. Although not strictly proven from x-ray data, correlation of the above results with those obtained by many authors—see particularly Rabo et al. (53)—from infrared methods shows beyond reasonable doubt that the positions of cations depend strongly on even small quantities of residual molecules. It is possible that 1 water molecule is sufficient to bridge between 2 or more La atoms in I. Hence, for 19 La atoms per unit cell of fully-exchanged Y-zeolite, only about 10 water molecules are needed, compared with 260 in the hydrated specimen. 

The adsorption of furan, 2,5-dihydrofuran and tetrahydrofuran on sodium-ion exchanged faujasites with different Si/Al ratios was studied by combining temperature-programmed desorption (TPD), inelastic neutron scattering (INS), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), quantum mechanical computations and Monte-Carlo simulations. 

---