Crystal structure of different dealuminated Y-type zeolites determination of framework vacancies and non-framework species

Abstract

Powder X-ray diffraction has been used to investigate the crystal structure of various dealuminated Y-type zeolites in order to study framework vacancies and non-framework species, in relation to the dealurnination process. The number of framework vacancies has been determined for different dealumination modes, degrees of dealumination and acid or basic treatments. Information has been provided on the nature of extraframework species. Their number and position have also been specified. It has been shown that for all investigated samples, these species are found in sodalite cages [sites S(1') and S(II')], and also in supercages [S(II)] for the least dealuminated sample. Aluminium and silicon framework populations have been calculated from X-ray diffraction combined with magic-angle spinning n.m.r. data so as to understand the dealumination mechanism.

Six Single-Crystal Structures Showing the Dehydration, Deamination, Dealumination, and Decomposition of NH4+-Exchanged Zeolite Y (FAU) with Increasing Evacuation Temperature. Identification of a Lewis Acid Site

“…The coefficients indicate the number of unit cells. They decrease because we have assumed that the vacancies have been filled by Si 4+ ions from adjacent unit cells (reconstruction) . The experimental conditions have been such that any water that formed should have left the zeolite crystal relatively quickly.…”

“…In later work on non-hydrated samples of a very similar material, a signal at 60−70 ppm is attributed to framework aluminum and to “tetrahedrally coordinated aluminum atoms in neutral extraframework aluminum oxide clusters” . Earlier crystallographic work had found Al 3+ ions at three sites, I‘, II‘, and II, all too far from oxygens of the zeolite framework to coordinate to them, so those Al 3+ ions must be fully coordinated by non-framework oxygens. A very recent report using 27 Al MAS NMR and X-ray diffraction from powders finds non-framework Al 3+ at sites I‘ and II‘…”

“…In this report, the crystals studied have not been steamed. The extraframework Al 3+ is not at any of the positions described above, , but rather they coordinate to framework oxygens; they are at a site that does not have a designation, within the D6R between sites I and I‘. There are no reports of high-resolution NMR work on such a material.…”

Changing the characteristics and properties of zeolite Y and nano-anatase in the formation of a nano-anatase/Y composite with improved photocatalytic and adsorption properties

“…The increase in B iso (T) indicates a decrease in the total occupation of this position, which is due to a decrease in the Si/Al modulus, which is indeed smaller (Si/Al = 2.3) than in the initial structure (Si/Al = 5) (Jeanjean et al 1989). The refinement of the mixed occupation of Si/Al turned out to be uninformative due to the proximity of atomic numbers, and as a consequence, the atomic scattering curves.…”

“…The crystal structure refinement of zeolite Y [the initial atomic coordinates of the zeolite framework with Si/ Al = 5.2 ± 0.5 and a = 24.49 Å were taken from the (Baerlocher et al 2007) 1 3 study (Jeanjean et al 1989)] (Table 1) was performed by varying, apart from the peak profile parameters and background, the parameter a of the cubic unit cell, the displacement parameter B iso for the Si atom in the only independent T position (T = Si, Al) with the coordinates − 0.0548 0.1261 0.0360, and one overall parameter B iso for four independent oxygen atoms (O1, − 0.1077 0.0000 0.1077; O2, − 0.0009 − 0.0009 0.1391; O3, − 0.0345 0.0749 0.0749; O4, 0.0687 0.0687 0.3264).…”