Al-rich beta zeolites. Distribution of Al atoms in the framework 4 and related protonic and metal-ion species

0451427 - ÚFCH JH 2017 RIV US eng J - Journal Article
Sazama, Petr - Tabor, Edyta - Klein, Petr - Wichterlová, Blanka - Sklenák, Štěpán - Mokrzycki, Lukasz - Pashkova, Veronika - Ogura, M. - Dědeček, Jiří
Al-rich beta zeolites. Distribution of Al atoms in the framework 4 and related protonic and metal-ion species.
Journal of Catalysis. Roč. 333, JAN 2016 (2016), s. 102-114. ISSN 0021-9517. E-ISSN 1090-2694
R&D Projects: GA ČR GA15-12113S; GA ČR GA15-13876S; GA ČR(CZ) GA15-14007S
Institutional support: RVO:61388955
Keywords : Template-free BEA* * Framework Al * Lewis and Bronsted acidity
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 6.844, year: 2016

Al-rich BEA ⁄ zeolites with Si/Al 4.5 and 5.1, prepared by a template-free synthesis, were compared to a 34 conventional (Si-rich) BEA ⁄ (Si/Al 11.3) regarding (i) the distribution of Al atoms in the framework, (ii) 35 the behavior of the H-BEA ⁄ samples at high temperature, and (iii) the nature of charge balancing counter 36 metal-ion species. 27 Al and 29 Si (CP) MAS NMR, and FTIR of adsorbed d 3 -acetonitrile and UV–Vis spec- 37 troscopy of Co(II) ions as probes of close Al atoms were used and the study was further supported by 38 DFT molecular dynamic calculations of Co(II) sites in the BEA ⁄ zeolites. In contrast to the Si-rich BEA ⁄ , 39 the Al atoms in the Al-rich BEA ⁄ are mostly arranged in AlSiAl sequences with their Al atoms facing 40 two different channels, which thus cannot bind bare divalent ions. Conversely, two Al atoms from two 41 different AlSiAl sequences can face the same channel and they represent close unpaired Al atoms located 42 in two different rings. They can be compensated by [Co(II)(H 2 O) 6 ] 2+ , and in dehydrated zeolites by pro- 43 tons, monovalent metal-ions, and metal-oxo structures such as formally monovalent [Co(III)O] + . Only Al 44 atoms in AlSiSiAl sequences in one ring and a minor fraction of AlSiAl sequences face the same channel 45 and thus they can be balanced by bare divalent cations. Therefore, the Al-rich and conventional Si-rich 46 BEA ⁄ differ substantially in the population of AlSiAl sequences, but not in the Si A Al arrangement in 47 the inner surface of zeolite channels which is relevant for binding counter-ion species. The concentration 48 of acid and redox sites in Al-rich BEA ⁄ is proportional to the increased Al content in the framework, but 49 without marked change of their structure.
Permanent Link: http://hdl.handle.net/11104/0252626