Effect of Ge/Si substitutions on the local geometry of Si framework sites in zeolites: A combined high resolution²⁹Si MAS NMR and DFT/MM study on zeolite Beta polymorph C (BEC)

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F61388955%3A_____%2F18%3A00488843" target="_blank" >RIV/61388955:_____/18:00488843 - isvavai.cz</a>

Result on the web

<a href="http://dx.doi.org/10.1016/j.micromeso.2018.03.021" target="_blank" >http://dx.doi.org/10.1016/j.micromeso.2018.03.021</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1016/j.micromeso.2018.03.021" target="_blank" >10.1016/j.micromeso.2018.03.021</a>

Result language

angličtina

Original language name

Effect of Ge/Si substitutions on the local geometry of Si framework sites in zeolites: A combined high resolution²⁹Si MAS NMR and DFT/MM study on zeolite Beta polymorph C (BEC)

Original language description

We employed density functional theory/molecular mechanics (DFT/MM) calculations and 29 Si magic-angle spinning (MAS) NMR spectroscopy to investigate the effect of single and multiple Ge/Si substitutions on the 29 Si NMR parameters as well as the local geometry of SiO 4 tetrahedra of the nearest (Ge-O-Si) and next-nearest (Ge-O-Si-O-Si) neighboring Si atoms. The influences of the Ge/Si substitutions are compared with the effects of the corresponding Al/Si substitutions (i.e., Al-O-Si and Al-O-Si-O-Si, respectively). Zeolite Beta polymorph C (BEC), containing double four-membered rings (D4Rs) and exhibiting three distinguishable T sites in the framework, was chosen for this study as a model of germanium containing zeolites. Our computations give a systematic downshift of the 29 Si chemical shift of Si by 1–6 ppm for Ge-O-Si sequences. Furthermore, the contributions of two, three, and four Ge atom s as the nearest neighbors to the downshift of Si are not additive and the calculated downshifts lie in the intervals from 2 to 6 ppm, from 1 to 9 ppm, and from 5 to 11 ppm, respectively. Conversely, the contributions of two, three, and four Al atoms as the nearest neighbors are approximately additive. The downshifts caused by Ge nearest neighbors are less than half compared with the corresponding downshifts caused by Al. Moreover, our calculations show that there are no systematic contributions of Ge and Al as next-nearest neighbors (i.e., Ge-O-Si-O-Si and Al-O-Si-O-Si, respectively) to the 29 Si chemical shift of Si, and not even the direction (sign) can be predicted without calculating the corresponding sequence.

Czech name

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Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

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OECD FORD branch

10403 - Physical chemistry

Project

<a href="/en/project/GA15-14007S" target="_blank" >GA15-14007S: Active sites in zeolite catalysts. DFT and multi-spectroscopic analysis</a><br>

Continuities

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Publication year

2018

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

Microporous and Mesoporous Materials

ISSN

1387-1811

e-ISSN

—

Volume of the periodical

267

Issue of the periodical within the volume

SEP 2018

Country of publishing house

NL - THE KINGDOM OF THE NETHERLANDS

Number of pages

10

Pages from-to

124-133

UT code for WoS article

000435060700015

EID of the result in the Scopus database

2-s2.0-85044509771