The identity of titanium centres in microporous aluminophosphates compared with Ti-MCM-41 mesoporous catalyst and titanosilsesquioxane dimer molecular complex: A spectroscopy study

Titanium-aluminophosphate and silico-aluminophosphate with chabasite-like structures (TAPO-34 and TAPSO-34) have been hydrothermally synthesised using morpholine as structure-directing agent. The local environment of Ti(IV) sites in these materials was studied using diffuse-reflectance UV-Vis, photoluminescence and Raman spectroscopies. This study, combined with the study of Ti-grafted MCM-41 mesoporous catalyst and a titanosilsesquioxane dimer molecular complex with a well-defined co-ordination of the Ti(IV) centers, revealed that a fraction of Ti(IV) ions are present in tetrahedral co-ordination, consistent with some Ti(IV) ions being incorporated into the aluminophosphate frameworks. However, Raman spectroscopy showed that around 20% of the total amount of the titanium used in the gel synthesis is present in a TiO₂-like extra-phase.