EVALUATION OF MN(II) FRAMEWORK SUBSTITUTION IN MNAPO-11 AND MN-IMPREGNATED ALPO4-11 MOLECULAR-SIEVES BY ELECTRON-SPIN-RESONANCE AND ELECTRON-SPIN ECHO MODULATION SPECTROSCOPY

MnAPO-11 and Mn-impregnated AlPO4-11 (Mn-AlPO4-11) samples were prepared with various manganese contents and studied by electron spin resonance (ESR) and electron spin-echo modulation (ESEM). At high manganese content (4.25 mol %), the spin-spin interaction broadens the ESR spectra of MnAPO-11 and Mn-AlPO4-11 so that they show only a broad line at g = 2.01. At low manganese content (0.1 mol %), the ESR spectra of MnAPO-11 and Mn-AlPO4-11 exhibit the same parameters (g = 2.01 and A almost-equal-to 93.5 G), but the spectra obtained from MnAPO-11 samples are better resolved. Two-pulse ESEM of MnAPO-11 and Mn-AlPO4-11 with adsorbed deuterium oxide shows that the local environments of manganese in the hydrated samples are different. This indicates that the manganese species environments in MnAPO-11 and Mn-AlPO4-11 are different, suggesting that Mn(II) is framework substituted in MnAPO-11 since it obviously occupies an extra-framework position in Mn-AlPO4-11. The framework incorporation in MnAPO-11 is confirmed by a three-pulse ESEM study of deuterium modulation resulting from interactions of deuterated adsorbates with manganese which indicate that the manganese occupies a negatively charged site in MnAPO-11.