Isomorphous substitution of framework atoms by titanium in VPI-5 aluminophosphate molecular sieve

Extra-large pore aluminophosphate molecular sieve TiVPI-5 was synthesised h ydrothermally in the presence of di-n-butylamine and transformed by the cal cination process at 500 degreesC to a large pore TAPO-8. Incorporation of t itanium(IV) into VPI-5 framework was studied by elemental and thermogravime tric analyses, combined with X-ray Absorption Near Edge Structure (XANES) s pectroscopy and UV-VIS absorption spectroscopy. We found that titanium(IV) incorporated in TiVPI-5 isomorphously substitutes framework aluminium on oc tahedral sites and that it is not present in the structure in the form of T iO2 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 Bronsted acid sites were found in small amounts in the calcined product TAPO-8.