Interaction of ammonia with Broensted acid sites in different cages of zeolite Y as studied by proton MAS NMR

Abstract

. (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.

Enhancement of Nafion based membranes for direct methanol fuel cell applications through the inclusion of ammonium-X zeolite fillers

“…The methanol permeability shown by 5 wt.% submicron NH 4 -X zeolites composite membranes is 2.28 Â 10 À7 cm 2 s À1 which is lower than 3.00 Â 10 À7 cm 2 s À1 measured for the membrane with 5 wt.% submicron Na-X zeolites (Supplementary Table S1). This can be explained by the complex dynamic interactions which take place within the NH 4 -X filler, for example the exchange: NH 4 þ , NH 3 and H þ that occurs in both the supercages and sodalite cages of FAU zeolites [29] and the formation of NH 3 and protons through the reaction:…”

Comparison of a combined quantum mechanics/interatomic potential function approach with its periodic quantum-mechanical limit: Proton siting and ammonia adsorption in zeolite chabazite

“…[15][16][17][18] Hence, the energy of adsorption of NH 3 depends not only on the energy of deprotonation of the zeolite ͑DP͒, but also on the proton affinity of NH 3 ͑PA͒ and the binding energy of the ammonium ion onto the negatively charged surface ͑ion pair binding energy IP͒, as shown in the thermodynamic cycle below.…”

“…[15][16][17][18] Detailed comparison of the QM-Pot chemisorption energy with microcalorimetric data was already made in Ref. 9.…”

13C and 23Na Solid-State NMR Study on Zeolite Y Loaded with Mo(CO)6

“…The shift to higher field of the proton NMR signal for the NH 4 + cations as described above is consistent with a counter migration of ammonium cations into the sodalite cages, at least to some extent. 27 Note that the samples whose MAS NMR spectra are shown in Figures 7b,d and 8b,d have been annealed at 373 K for 10 h which may have facilitated cation migration. This Na + migration is at a striking difference to the behavior of dehydrated NaY which shows no or only minor Na + cation migrations from the sodalite cages into the supercages upon loading.…”