Titanium-substituted zeolites and molecular sieves investigated by NMR

Si-29 MAS NMR spectra for TS-1, TiMCM-41, and Ti-beta, and P-31 MAS NMR spe ctrum for TiAlPO4-11 have been obtained before and after CO treatment that reduces Ti4+ to Ti3+. We have used the large paramagnetic influence of Ti3 on the NMR spectrum to obtain information about the location of titanium i n metal-substituted molecular sieves. The unpaired electrons were found to cause a large reduction in the intensity of the NMR signal of the paramagne tic samples when compared to their diamagnetic counterparts. The intensity loss seems to be proportional to the number of paramagnetic titanium ions p resent in the sample. The data suggest that the Fermi contact interaction i s the main mechanism responsible for the large reduction of the NMR signal, whereas dipolar interactions were found to be negligible. Our results stro ngly indicate that most of the titanium atoms are sitting at a framework si te for the materials investigated in the present contribution.