Preparation and characterization of hierarchical USY by post-treatment

Abstract

Two modifying agents, citric acid and EDTA2Na, were used to modify USY zeolite to obtain the hierarchical USY with high crystallinity. XRD, N 2 isothermal sorption, 27 Al and 29 Si NMR, and TEM were adopted to characterize the dealumination process in the post-treatment of USY. The results showed that all modified USY have increased surface areas and pore volume due to the removal of non-framework Al species. Besides, framework dealumination occurred in the modification process. USY-EC, which was modified by the combined effects of citric acid and EDTA-2Na, has the highest SiO 2 /Al 2 O 3 ratio of 19.40 and relatively high crystallinity.

An anion-promoted increase of the SiO2/Al2O3 ratio of zeolites

“…The increase of the SiO 2 /Al 2 O 3 ratio of zeolites can, to a certain degree, enhance the intensity of acidity and the thermal/hydrothermal stability, which are crucial for improving the conversion and/or selectivity of acid-catalyzed chemical reactions and possibly for prolonging the durability of catalysts. 13–18 Considerable efforts have been made to increase the SiO 2 /Al 2 O 3 ratio of zeolites and several strategies have been developed so far involving: (1) control of the SiO 2 /Al 2 O 3 ratio in the reaction mixture; 19–21 (2) dealumination of zeolites via post-treatment, including hydrothermal steaming and chemical leaching such as acids, salts, chelating agents, SiCl 4 or other halides and the combination of both the methods; 22–29 (3) use of organic structure-directing agents, especially those with a high C/N ratio or low charge density 16,17,30–34 and (4) introduction of hydroxyl radicals (·OH) or metal ions. 35,36 For example, an ultrastable Y zeolite (USY) widely used as a fluid catalytic cracking catalyst is usually prepared via the high-temperature hydrothermal steaming of NH 4 Y with a low SiO 2 /Al 2 O 3 ratio.…”

Hydroisomerization Principles of Acenaphthene to Alkyladamantanes over Modified USY-Supported Pt Catalysts

“…Al NMR spectroscopy was used to analyze the coordination modes of the framework Al atoms, as shown in Figure c. A range of USY zeolites demonstrated an impressive resonance of 60 ppm, indicating tetrahedrally coordinated framework Al (FAl) sites, as well as a broad peak approximately 0 ppm, which was attributable to extra-framework Al (EFAl) sites in octahedral coordination . Notably, the steaming treatment of USY-S and USY-AS showed more pronounced deconvoluted peaks between 20 and 40 ppm, representing the more disordered Al­(V) present at the edges of the framework .…”

“…A range of USY zeolites demonstrated an impressive resonance of 60 ppm, indicating tetrahedrally coordinated framework Al (FAl) sites, as well as a broad peak approximately 0 ppm, which was attributable to extra-framework Al (EFAl) sites in octahedral coordination. 39 Notably, the steaming treatment of USY-S and USY-AS showed more pronounced deconvoluted peaks between 20 and 40 ppm, representing the more disordered Al(V) present at the edges of the framework. 40 This was due to the fact that the steaming treatment partially broke the Al−O bond but did not remove the Al atoms.…”