Thermal stability of tetrapropylammonium (TPA) and tetra methylammonium (TMA) cations occluded in SAPO-37 molecular sieves
1993; Elsevier BV; Volume: 13; Issue: 3 Linguagem: Inglês
10.1016/s0144-2449(05)80278-7
ISSN1873-3115
AutoresMarguerite Briend, A. Lamy, M.J. Peltre, Pascal P. Man, D. Barthomeuf,
Tópico(s)Metal-Organic Frameworks: Synthesis and Applications
ResumoThe oxidative thermal decomposition of TMA and TPA hydroxides in SAPO-37 and the correlativestructural changes were followed, as a function of temperature, by infrared absorption spectroscopy, thermoprogrammed oxidation associated with gas chromatography and mass spectrometry, and 27Al MAS n.m.r. TPA, located in the supercages, is first decomposed in the 473–623 K range via a series of β-eliminations with the evolution of propene. The degradation of TMA starts above 523 K up to 823 K with the major release of acetonitrile, via a mechanism involving the intermediate occurrence of trimethylammonium methyl ylide, its decomposition to trimethylamine followed by further pyrolysis. The TPA and TMA decomposition occurs with the appearance of acidic OH groups associated with bands at 3637 and 3575 cm−1 respectively, in the infrared absorption spectra. In spite of the oxidative conditions, coke is formed and remains in the SAPO-37 cavities if the calcination temperature is lower than 823 K. 27Al MAS n.m.r. spectra suggest that TPA is interacting with the framework AIO4 tetrahedra. The loss of crystallinity of SAPO-37 with regard to water at room temperature is greatly decreased if TMA is kept trapped in the socialite cages.
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