Isomorphous Substitution of Framework Atoms by Titanium in VPI-5 Aluminophosphate Molecular Sieve

Extra-large pore aluminophosphate molecular sieve TiVPI-5 was synthesised hydrothermally in the presence of di-n-butylamine and transformed by the calcination process at 500 °C to a large pore TAPO-8. Incorporation of titanium(IV) into VPI-5 framework was studied by elemental and thermogravimetric analyses, combined with X-ray Absorption Near Edge Structure (XANES) spectroscopy and UV-VIS absorption spectroscopy. We found that titanium(IV) incorporated in TiVPI-5 isomorphously substitutes framework aluminium on octahedral sites and that it is not present in the structure in the form of TiO2 anatase. In situ IR measurements of pyridine adsorption/desorption were used to check the presence of catalytically active centres in the product resulting from titanium incorporation into the VPI-5 framework. Weak Lewis and Brønsted acid sites were found in small amounts in the calcined product TAPO-8