VAPO as catalyst for liquid phase oxidation reactions Part I: preparation, characterisation and catalytic performance Original Research Article

The preparation, characterisation and catalytic properties of vanadium containing aluminophosphate molecular sieves (type AEL and AFI) are described in this paper. The molecular sieves were prepared by post-synthesis treatment and hydrothermal procedures. Several parameters were varied: nature of the template, crystallisation procedure and vanadium content. Tri-propylamine appeared to be the best template for the preparation of VAPO-5: highly crystalline, homogeneous batches (crystallite size: 2×1×1 μm) with a maximum of about 2 wt% vanadium could be obtained in high yield (75–80%). Crystallographically pure VAPO-11 with a maximum of only 0.5 wt% of vanadium could be prepared. In VAPO the incorporation mode of vanadium gradually changes from tetra- to penta-coordinated when the amount of vanadium is increased. However the formation of vanadium pentoxide could not be detected. The vanadium containing molecular sieves were used as catalyst for the oxidation of allylic and secondary alcohols by tert-butyl hydroperoxide in the liquid phase. Compared with a homogeneous catalyst, bis(2,4-pentandionato)-oxovanadium(IV) (VO(acac)2), the activity of vanadium containing molecular sieves is a factor 3–100 times lower. The activity of VAPO becomes higher when the vanadium content is increased. The decomposition rate of the peroxide is influenced by the pore structure, whereas no other effects on the selectivity are found.