Microporous Aluminophosphate ULM-6: Synthesis, NMR Assignment, and Its Transformation to AlPO4-14 Molecular Sieve
文摘
A pure fluorinated aluminophosphate [Al8P8O32F4·(C3H12N2)2(H2O)2] (ULM-6) has been synthesized via an aminothermal strategy, in which triisopropanolamine (TIPA) is used as the solvent together with the addition of propyleneurea and HF. The 13C NMR spectrum demonstrates that 1,3-diaminopropane, the in situ decomposer of propyleneurea, is the real structure-directing agent (SDA) for ULM-6 crystals. The local Al, P, and F environments of the dehydrated ULM-6 are investigated by 1D and 2D solid-state NMR spectroscopy. The spatial proximities are extracted from 19F{27Al}, 19F{31P}, 27Al{19F}, and 31P{19F} rotational-echo double resonance (REDOR) NMR experiments as well as 19F → 31P heteronuclear correlation (HETCOR) NMR and {31P}27Al HMQC NMR experiments, allowing a full assignment of all the 19F, 27Al, and 31P resonances to the corresponding crystallographic sites. Moreover, it is found that the structure of ULM-6 is closely related to that of AlPO4-14. A combination of high-temperature powder XRD, thermal analysis, and 19F NMR reveals that the removal of fluorine atoms at higher temperature is crucial to the phase transformation of ULM-6 to AlPO4-14. The calcined product shows high CO2/CH4 and CO2/N2 selectivity with ratios of 15.5 and 29.1 (101 kPa, 25 °C), respectively.
