Fractal Extra-Framework Species in De-aluminated LaY Zeolites and Their Catalytic Activity

Abstract

Lanthanum-containing Y (LaY) zeolites were prepared by ionic exchange from NaY parent zeolite. The LaY zeolites were de-aluminated by steaming. De-aluminated zeolites presented different Si/Al ratio. The physicochemical properties of these catalysts were characterized by X-ray diffraction, pyridine and xenon adsorption, infrared spectroscopy and 29 Si, 27 Al, 129 Xe, 139 La solid-state nuclear magnetic resonance spectroscopy. Furthermore, a fractal geometry approach was adopted to describe the evolution in the texture as a consequence of de-alumination. The catalytic properties of materials were evaluated in the n-hexane cracking reaction. The catalyst with the highest catalytic activity was the zeolite highest de-aluminated (Si/Al ratio of 3.7). Such performance was attributed on the one hand, to active extra-framework aluminum species hosted in the large cavities of zeolites and, on the other hand to redistribution of lanthanum species into the zeolite as a consequence of de-alumination.

On Three-Fold Coordinated Si Sites in Mesoporous MCM-41 Catalysts

“…Silica surface fractal dimension is smaller than 2, then, the surface has to be constituted by chains. This proposition has been already discussed in previous works [19][20][21].…”

“…To understand the coordination of the Si sites, the NMR results incorporate the study of a zeolite Faujasite Y for comparison purposes. Indeed, zeolites are built by Si(4Al), Si(3Al), Si(2Al), Si(1Al) and Si(0Al) units, whose NMR signals are at -86, -92, -97, -102 and -108 ppm, respectively [21]. Si(nAl) units build the zeolite framework, where n is the number of aluminums bonded to tetrahedral silicon.…”

Solid-state nuclear magnetic resonance investigations of the nature, property, and activity of acid sites on solid catalysts

“…Experimental approaches of solid-state NMR spectroscopy on activated solid catalysts Solid-state NMR spectroscopy allows the determination of the type, strength, accessibility, and concentration of surface sites [11][12][13][14][15][16]. Via one-and two-dimensional solid-state NMR techniques, parameters of the local structure of the catalyst framework and their surface sites are available [8][9][10][17][18][19][20][21][22][23][24]. Hydroxyl protons acting as catalytically active Brønsted acid sites can be investigated in a direct manner by 1 H MAS NMR spectroscopy [12][13][14][15].…”

Impact of cationic lanthanum species on zeolite Y: an infrared, excess infrared and Raman spectroscopic study

“…In the research eld of zeolites, the characteristic vibrational modes of aluminosilicate frameworks, such as the TO 4 (T ¼ Si, Al) stretching and the bending modes of the rings, were frequently used to estimate the structure of zeolites and monitor the nucleation/ crystal growth of zeolites. [1][2][3] Moreover, the characteristic bands of guest species, [4][5][6] probe molecules [7][8][9] and OH stretches in Si(OH)Al groups 10,11 were oen used to explore the host-guest interactions, the location of extra-framework cations, the acidity of zeolites, etc.…”