Ferrierite and SUZ-4 Zeolite:  Characterization of Acid Sites

Abstract

A detailed FTIR characterization of acid sites in two structurally related zeolites, ferrierite and SUZ-4, is carried out. Assignment of OH groups observed in the spectra is addressed taking into account zeolite structure and composition. In ferrierite, at least four types of bridging OH groups vibrating in 10-, 8-, and 6-membered rings are identified using a combination of experimental and computational techniques. Our results suggest that framework aluminum in ferrierite is preferentially sited in extended rings at the intersections of 8-and 6-ring channels resulting in a high concentration of OH groups in the large cages in 8-ring channels. The IR band corresponding to these hydroxyls, 3601 cm -1 , is not significantly shifted to low frequencies because the OH groups are vibrating in extended rings. At the same time, access to these hydroxyls is restricted by 8-membered rings. The band at 3565 cm -1 assigned to the bridging OH-groups in 6-membered rings is responsible for the strongly asymmetric shape of the experimental spectrum. For SUZ-4 zeolite, deconstruction of the spectrum, supported by H-D exchange and accessibility studies, results in three IR bands at 3560, 3592, and 3610 cm -1 corresponding to OH groups in 6-, 8-and 10-membered rings. The intensity of the first band is considerably lower than that in ferrierite, indicating that the residual potassium cations are located in small cages or in double 6-rings. The low-intensity band at 3560 cm -1 and the similar intensities of the bands at 3592 and 3610 cm -1 lead to a near-symmetrical experimental spectrum.

Methane Combustion over Pd Catalysts Loaded on Medium and Large Pore Zeolites

“…However, our previous NH 3 TPD experiments have revealed no significant differences in the distribution of acid strengths between H-TNU-10 and H-ferrierite [14]. According to the IR investigations reported so far, in addition, the acidity associated with framework Al atoms is stronger in ZSM-5 than in ferrierite or its high-silica analog, i.e., ZSM-35 [26][27][28], suggesting that the formation of well-dispersed PdO particles within TNU-10 and ferrierite cannot be correlated solely to the zeolite acidity. Further study is necessary to better elucidate the role of zeolite pore structure in the stabilization of intracrystalline PdO particles.…”

Probing the Accessible Sites for n-Butene Skeletal Isomerization over Aged and Selective H-Ferrierite with d3-Acetonitrile

“…1). Since it is known that the OH groups in the 8-MR pores absorb at lower wavenumbers than those in the 10-MR channels (30,31), the observed shift implies that upon CD 3 CN adsorption Brønsted sites remain vacant in the cages of the 8-MR pores. This indicates that with the formation of carbonaceous deposits at least part of the entrances of the 8-MR pores is blocked so that sites in these cages become inaccessible for both CD 3 CN and butenes.…”

“…Figure 1 shows the IR spectra of fresh H-FER, of H-FER with adsorbed CD 3 CN, and the difference of these two spectra. The fresh H-FER spectrum displays a peak at 3742 cm the H-FER structure (30,31). A band around 3700 cm −1 (32) indicates the presence of nonframework aluminum species.…”

Influence of Al Distribution and Defects Concentration of Ferrierite Catalysts Synthesized From Na-Free Gels in the Skeletal Isomerization of n-Butene

“…Samples synthesized in fluoride medium from gels containing pyrrolidine are much less active, and, although the highly deactivated samples present a good selectivity to Table 4 Catalytic activity in the n-butene isomerization for the low-defect samples Samples FER1 FER-bmp-TMA-20d FER-bmp-TMA-83d FER-bmprol-TMA-20d FER-pyrr-10d FER-pyrr-TMA-10d Time (min) 5 720 5 720 5 720 5 720 5 720 5 720 Conversion (% molar) 40. 15 isobutene, this decreases very rapidly with the conversion (Fig. 4), and therefore a very low isobutene yield is obtained at high t.o.s.…”

“…A substantial number of contributions focuses on mechanistic aspects of this reaction, for unimolecular and bimolecular mechanism have been proposed to take place inside the zeolite channels and to yield different products, in particular isobutene [4][5][6][7][8][9], on the deactivation mechanism of the reaction, as the selectivity to the targeted isobutene strongly enhances with time-onstream and hence with catalyst deactivation [10][11][12], and on the contribution of the number, type and location of acid sites. Indeed, acid sites can be located in different positions in the framework, either in the 10-MR channel or in the ferrierite cage accessible through 8-MR windows [13][14][15][16] and, moreover, the contribution of extra-framework Lewis acid sites has also been studied [17][18][19].…”