. (1993). Interaction of ammonia with Broensted acid sites in different cages of zeolite Y as studied by proton MAS NMR. Journal of Physical Chemistry, 97(40), 10394-10402. DOI: 10.1021/j100142a022General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ?
Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Ammonia adsorption onto acidic Y zeolites is studied with 'H MAS N M R (at 295-320 K). The influence of the amount of adsorbed ammonia is investigated in the presence of sodium or cesium as exchangeable cations and for different framework compositions (Si/Al= 2.4-12). The B r~n s t e d sites in unloaded or partially loaded zeolites are observed near 6 = 3.9 for protons in supercages and near 6 = 4.6 for protons in sodalite cages.Ammonium ions under condition of no proton-exchange resonate at 6 = 8.1. These species are detected as such only in the sodalite cages. In the supercages, a signal at 6 = 6.9 is observed, which is ascribed to an exchange involving NH4+ (6 = 8,1), H + (6 = 3.9), and NH3 (6 = 0.8). Furthermore, in the sodalite cages, a signal at 6 = 6.5 is observed, which is ascribed to an exchange involving NH4+ (6 = 8.1), H+ (6 = 4.6), and NHs (6 = 0.8), but with different relative residence times. Additionally, ammonium-ammonia signals are found at 6 = 5.3-5.9 and at a position determined by the NH3/NH4+ ratio in the zeolite (6 = 7-1). For the ammoniumammonia species proton-exchange between ammonium and ammonia is fast compared to the time scale of the N M R experiment. For at least two ammonium species proton-exchange with the Br~nsted protons is fast, and consequently the lines are shifted to 6 = 6.9 and 6.5. This implies that ammonium ions observed at 6 = 8.1 have the lowest basicity and the ammonium ions at 6 = 6.5 have the highest basicity. However, for the temperature range used, ammonia reacts statistically with the Bransted sites of different acid strength.
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