(Al)MCM-41 Molecular Sieves. Aluminium Distribution, Uniformity and Structure of Inner Surface

Autor:	Naděžda Žilková, Jiří Čejka, Jiří Dědeček, Josef Kotrla
Rok vydání:	2003
Předmět:	Inorganic chemistry Cationic polymerization chemistry.chemical_element General Chemistry Heterogeneous catalysis Molecular sieve Ion chemistry.chemical_compound Crystallography Adsorption chemistry Aluminium Pyridine Spectroscopy
Zdroj:	Collection of Czechoslovak Chemical Communications. 68:1998-2018
ISSN:	1212-6950 0010-0765
DOI:	10.1135/cccc20031998
Popis:	The effect of the framework Al content and synthesis procedure on the number of framework Al atoms located on the surface of (Al)MCM-41 channels and the distribution of the Al atoms between single Al atoms and various Al-O-(SiO)1,2-Al species was investigated. The total number of accessible framework Al atoms on the channel surface was obtained from the ion exchange capacity for Na+ ions and pyridine adsorption. The number of Al pairs on the surface and their distribution between different local arrangements of the channel surface was estimated using VIS spectroscopy of Co2+ ions. At low framework Al contents, Al atoms occupy only accessible T sites on the surface of the channel walls. In aluminium-rich (Al)MCM-41, a significant part of Al atoms is incorporated inside the channel walls and these Al atoms do not form cationic sites. Al atoms on the wall surface preferentially form Al-O-(SiO)1,2-Al sequences, enabling siting of divalent cations. Different synthesis procedures resulted in differences in Al distribution. The channel surface of the (Al)MCM-41 is formed by two regular local structures containing two types of deformed six-membered rings with Al-O-(SiO)1,2-Al sequences forming cationic sites.
Databáze:	OpenAIRE
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