ALPO-34 and SAPO-34 Synthesised by Using Morpholine as Templating Agent. FTIR and FT-Raman Studies of the Host-Guest and Guest-Guest Interactions Within the Zeolitic Framework

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 NH₂ group of the protonated morpholine is H-bonded to the zeolitic frameworks (more strongly in SAPO-34); (b) the CH₂ vibrations in the 1500-1300cm^-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 822cm^-1 for the protonated molecule in solution, to 815cm^-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 245cm^-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.