Uses of i.r. spectroscopy in identifying ZSM zeolite structure

Effect of Sublimation Treatment on the Catalytic Performance of MFI Catalysts in Pyridine and 3‐Picoline Synthesis

“…The absorption bands at 1225, 1150-1050, 800, and 450 cm -1 are typical of highly siliceous materials. These absorptions bands have been assigned to the external asymmetric stretching, internal asymmetric stretching, external symmetric stretching and the bending modes of the Si(Al)O 4 tetrahedra, respectively [16]. A characteristic band at 550 cm -1 due to the asymmetric stretching mode in double-ring blocks is observed in each of the samples [17,18], which confirms that all the samples have the MFI structure.…”

Indirect Observation of Structured Incipient Zeolite Nanoparticles in Clear Precursor Solutions

“…[19] On the other hand, crystalline Si-O networks, both dense and porous silica structures, are unambiguously distinguishable from amorphous silica by the presence of an IR peak near 1230 cm À1 . [5,7,14,20,21] This peak is indicative of the presence of translational symmetry in the silicon-oxygen network and therefore may serve as an even better indicator for the existence of zeolite subnanoparticles when other crystalline dense silica phases are not present. This is especially important for analyzing zeolite films.…”

“…Analysis of the range 400-650 cm À1 clearly shows the presence of the peak near 550 cm À1 which is the commonly used indicator for the silicalite-1 structure. [14] So far, the small peak near 625 cm À1 in the spectra of the as-made samples has not been discussed in detail in the literature, because in transmittance IR spectra it overlaps with the much stronger peak at 550 cm À1 and appears only as a shoulder. The peak broadening observed for the spin-coated films can be due to several factors: 1) phonon confinement effects; the small size of the particles suggests a strong impact of particle-particle interaction on the bulk phonons due to the close particle packing in the formed film; 2) possible partial damage of the zeolite subnanoparticles during the coating procedure; and 3) deposition of subnanoparticles with both well-developed and poor MFI structures from the clear TEOS-CTAB solution.…”

“…The peak near 550 cm À1 is well pronounced and the ratio of the IR absorption near 550-650 cm À1 to that near 440-480 cm À1 is even higher than the value of 0.72 considered as indicative of fully crystalline MFI zeolites. [14] Note that the intensity ratios measured in IR transmittance on KBr pellets cannot be compared straightforwardly to those measured by RAIR spectroscopy, because the latter technique is selective for vibrational modes with induced dipole moments having a nonzero component perpendicular to the surface.…”

“…[1b, 5,7,12,13] Based on the presence of a band near 550 cm À1 , which is widely accepted to be characteristic of the MFI structure, [14] either crystalline [1b, 12] or amorphous character of the precursor particles has been suggested. [5,7,13] These IR studies were performed on freeze-dried samples, [12,13] extracted precursor particles, [1b, 5] and original sols.…”