Bronsted acid sites and surface structure in zeolites: High resolution {sup 29}Si NMR REDOR study
- Univ. of Wisconsin, Milwaukee, WI (United States)
There are Lewis sites in nanoparticles of nonframework alumina (NFAl) created by the thermal treatment. The Bronsted sites are OH groups bridging framework silicon and aluminum. First, it is demonstrated that it is possible to estimate semiquantitatively heteronuclear second moments M{sub 2}{sup Si-H} in acid zeolite s having chemisorbed ammonia using an adapted {sup 29}Si CP REDOR (cross-polarization rotational echo double resonance) technique. Then we show that, on this basis and with comparison with simple models, two kinds of bridging OH groups are distinguishable: (i) one donating its proton to NH{sub 3}, forming NH{sub 4}{sup +} reorienting isotropically rapidly, and (ii) one operating as a proton donor to a strongly hydrogen-bonded ammonia. It is suggested that a noticeable fraction of the acidic OHs react with, and therefore are neutralized by, nonframework alumina. Moreover, preliminary information on an exchange process involving NH{sub 4}{sup +} is presented. 45 refs., 10 figs., 5 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 137378
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 41 Vol. 99; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
Similar Records
Modeling Lewis acidity of transition aluminas by numerical simulations
Fluorination of USY and modification of its catalytic properties