Carbon-13 nmr investigations of structure and mobility of adsorbed hydrocarbons

Propane Aromatization on Zn-Modified Zeolite BEA Studied by Solid-State NMR in Situ

“…The essential downfield shift of the signal from the CH− group as compared with gaseous propene by 30 ppm may arise from the strong interaction of a propene double bond with Zn sites. The shift of the signals at a double bond does not exceed 10 ppm at the weak interaction of an olefin double bond with Brønsted acid sites , or Na + cations . Similar signals for the products of propane conversion on zinc-loaded zeolite MFI were identified by Ivanova et al They assigned these signals to the asymmetric π complex of propene with zinc cations.…”

“…The shift of the signals at a double bond does not exceed 10 ppm at the weak interaction of an olefin double bond with Brønsted acid sites 22,34 or Na + cations. 35 Similar signals for the products of propane conversion on zinc-loaded zeolite MFI were identified by Ivanova et al 36 They assigned these signals to the asymmetric π complex of propene with zinc cations.…”

Density Functional Calculations of the 29Si and 27Al MAS NMR Spectra of the Zeolite Mazzite: Analysis of Geometrical and Electronic Effects

“…The results summarized in Table 1 show that, even for a small model such as Si 2 O 7 H 6 , some qualitative characteristics of the 29 Si NMR spectrum of mazzite are already reproduced. The different geometrical environment of the two sites leads to two different calculated σ and δ values, following the same order as those known experimentally for mazzite, [15][16][17] i.e., Si I at a more negative δ than Si II .…”

“…In our calculations, we considered the experimental structure reported by Galli, 14 which corresponds to a solid with a Si/Al ratio of 2.7. In this context, we have chosen to compare the calculated 29 Si chemical shifts with the experimental spectra of mazzite samples with similar Si/Al ratios (Si/Al ) 3.1; 15 Si/Al ) 4.2 16,17 ) rather than to the values obtained for a fully siliceous mazzite. These spectra correspond to silicon sites surrounded by a first shell of silicon neighbors.…”

Carbon-13 nuclear magnetic resonance of simple molecules adsorbed on catalytic surfaces

“…Similar balancing of changes in chemical shift on adsorption can be discerned in the data of Michel and co-workers on butenes, hexene-1, and toluene. 39 This would indicate that, for molecules of greater complexity than ethylene, the surface polarizes the molecule, redistributing the electron cloud thereby making the molecule more susceptible to specific attack by protons or other charged species.…”