ALPO-34 and SAPO-34 synthesized by using morpholine as templating agent. FTIR and FT-Raman studies of the host–guest and guest–guest interactions within the zeolitic framework

Abstract

IR and Raman spectra of morpholine, a structure-directing agent, entrapped within the chabasite-related structures of both ALPO-34 and SAPO-34, are discussed. It is revealed that some vibrational features of the morpholine, which is present in the protonic form, are very sensitive to both host–guest (framework–morpholine) and guest–guest (morpholine–morpholine and morpholine–water) interactions occurring within the zeolites. FTIR spectroscopy shows that: (a) the NH 2 group of the protonated morpholine is H-bonded to the zeolitic frameworks (more strongly in SAPO-34); (b) the CH 2 vibrations in the 1500–1300 cm −1 region are sensitive to the surrounding being different for the ALPO-34 compared with the SAPO-34. Raman spectroscopy reveals that the ring-breathing mode of the morpholine has a small red-shift (from 822 cm −1 for the protonated molecule in solution, to 815 cm −1 in SAPO-34), and is deeply decreased in intensity when the molecule is in the constrained space of the zeolitic cages. In this case, two new modes at 472 and 245 cm −1, tentatively assigned to morpholine–framework motions, are also present. IR and Raman bands are better resolved in the case of morpholine in ALPO-34 where the template–framework interactions are weaker.