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Sites in decationized zeolites

The infrared stretching frequency of the hydroxyl associated with the Bronsted sites in decationized zeolites, fails in the range 3600 to 3660 cm. As the Si/Al ratio in the framework increases, this frequency tends to decrease. What does this suggest about the acidity of the highly siliceous zeolites ... [Pg.340]

To study the interaction of adsorbed molecules with active sites in decationized zeolites we used optical electronic spectroscopy, which was successful (17-19) with silica-alumina catalysts. The results (17-19) were then extrapolated to zeolites 20-21). [Pg.243]

The object of this work was to study the influence of pretreated, decationized NH4-zeolites on adsorbed A,iV-dimethylaniline molecules. Such influence is caused by, proton-donating and electron-deficient active sites in decationized zeolites. Interaction of an aromatic amine molecule (M) with the proton-donating site leads to the formation of the MH+ molecule ion interaction with the electron-deficient site results in the M+ cation radical. Stabilization of these states by adsorption leads to the... [Pg.243]

Bosa5ek et al. (168) used wide-line 27A1 NMR measurements of stationary samples to measure the EFG at the nuclear site in decationated zeolites. In zeolite Na-Y they measured a line half-width of Sv1/2 = 61 kHz (for vL = 16 MHz) which led, via theoretical considerations (173) to vD = 840 kHz the calculated field gradient was 2.9 V/A2. In hydrated samples this gradient was partially averaged by random reorientation of water molecules, giving <5v,/2 = 5.7 kHz and vQ = 256 kHz. [Pg.269]

Characterisation of acid sites in decationated zeolites Study of NH3 sorption by frequency-response technique and FTIR spectroscopy... [Pg.116]

Schemes I—III do not differ significantly from those reported in the literature (8,12). First, the electron-deficient centers in the zeolites must arise at the expense of proton-donating sites. Secondly, the nonproton centers formed in decationized zeolites are essentially different from each other. Both facts are confirmed by the results of our investigations on the electronic spectra of decationized zeolites. Schemes I—III do not differ significantly from those reported in the literature (8,12). First, the electron-deficient centers in the zeolites must arise at the expense of proton-donating sites. Secondly, the nonproton centers formed in decationized zeolites are essentially different from each other. Both facts are confirmed by the results of our investigations on the electronic spectra of decationized zeolites.
The source of Lewis acidity in decationated zeolites (H-forms) was assigned on the basis of infrared structures [25], to the generation of tricoordinated (=A1 and i ) sites within the zeolite framework (scheme 2). [Pg.312]

Hyperfine interaction has also been used to study adsorption sites on several catalysts. One paramagnetic probe is the same superoxide ion formed from oxygen-16, which has no nuclear magnetic moment. Examination of the spectrum shown in Fig. 5 shows that the adsorbed molecule ion reacts rather strongly with one aluminum atom in a decationated zeolite (S3). The spectrum can be resolved into three sets of six hyperfine lines. Each set of lines represents the hyperfine interaction with WA1 (I = f) along one of the three principal axes. The fairly uniform splitting in the three directions indicates that the impaired electron is mixing with an... [Pg.275]

The main problem now is to justify the process.schematically depicted by Reactions 11 and 12. From pulse NMR experiments, Mestdagh, Stone, and Fripiat (12) have measured the lifetime (r) of a proton on a surface oxygen site in a decationated Y zeolite... [Pg.524]

G. V. Tsitsishvili (Academy of Sciences of the Georgian SSR, Tbilisi, USSR) The nev method of description of the adsorption isotherms allows one, on the basis of the theory of volume filling of micropores, to characterize adsorption on the microporous adsorbent containing adsorption sites of different nature. For zeolites, there are approximately two adsorption sites cations and framework. The existence of cations in different positions must be taken into account. It is important to use the Dubinin approach to desorption-adsorption equilibrium on decationized and other forms of zeolites. We have already obtained some good results in this direction. [Pg.85]


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See also in sourсe #XX -- [ Pg.241 ]




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Decationation

Decationized zeolites

Zeolites decationated

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