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)

Kód výsledku v IS VaVaI

RIV/61388955:_____/18:00488843 - isvavai.cz

Výsledek na webu

http://dx.doi.org/10.1016/j.micromeso.2018.03.021

DOI - Digital Object Identifier

10.1016/j.micromeso.2018.03.021

Jazyk výsledku

angličtina

Název v původním jazyce

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)

Popis výsledku v původním jazyce

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.

Název v anglickém jazyce

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)

Popis výsledku anglicky

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.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10403 - Physical chemistry

Projekt

GA15-14007S: Aktivní místa v zeolitických katalyzátorech. DFT a multispektroskopická analýza

Návaznosti

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

Rok uplatnění

2018

Kód důvěrnosti údajů

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

Název periodika

Microporous and Mesoporous Materials

ISSN

1387-1811

e-ISSN

—

Svazek periodika

267

Číslo periodika v rámci svazku

SEP 2018

Stát vydavatele periodika

NL - Nizozemsko

Počet stran výsledku

10

Strana od-do

124-133

Kód UT WoS článku

000435060700015

EID výsledku v databázi Scopus

2-s2.0-85044509771