Dealuminierte Molekularsiebe vom Typ Y Zur Porosität dealuminierter Molekularsiebe

Abstract

Die Porenvolumina und Porenradienverteilungen von drei dealuminierten Zeolithen werden durch Adsorptions‐ und Quecksilber‐porosimetrische Messungen bestimmt. Die Entstehung der Sekundärporen wird diskutiert.

Formation of Mesopores in USY Zeolites: A Case Revisited

“…Dealumination itself cannot be responsible for this effect because silicate ions migrate quickly into the newly created Al vacancies inside the USY framework [21,22]. Some observations in the present work and in previous studies by means of 29 Si MAS NMR, XRD and IR spectroscopy [10] as well as energy-dispersive X-ray diffraction (EDXRD) measurements [23] give evidence to a partial amorphization of the zeolite Y crystals under action of steam.…”

Reaction of the hydroxy groups of zeolites with phosphorylating agents

“…Al(OH) 6 specimen of zeolite Y studied here gave signals at d ‫ם‬ 59 for framework Al, and at d ‫מ‬ 2 for the nonfra- Table 2.…”

“…They constitute a bridge between silicon and aluminum in the aluminosilicate framework, where they occur in the strongly acidic structural unit Si-O(H)-Al [5]. They are present as terminal silanol groups (Si-OH) at sites where dealumination has occurred in the process of preparing the zeolite, as well as by migration of silicon atoms at the surface of mesopores [6]. They are also found on extraframework alumina [7], which in part may be in the form Al(OH) 3 or Al(OH) ‫ם2‬ .…”

Phase Transformations in Alkaline and Acid Leached Y Zeolites Dealuminated by Steaming

“…These should be transformed into aluminate ions in presence of alkaline solutions. Because of a low concentration of free lattice vacancies in the steamed DAY framework [5] a surface alumination seems to be preferred compared with the possibility of the aluminate ions to enter framework sites. Such an enrichment of Al-containing precipitates onto the crystal surfaces is already known from silicalite [20] and highly-siliceous faujasite [21] treated in solutions of sodium aluminate.…”

“…The created non-framework aluminium is enriched in modified species on the crystal surface and the surface of mesopores [3,4]. The mesopores result from an annealing of the framework [5] by migration of ortho-silicic acid formed under the action of the steam [6].…”