Oxidation capabilities of BEA isomorphously substituted with molybdenum, vanadium and titanium: an explorative study

Abstract

With titanium, vanadium and molybdenum isomorphously substituted zeolite BEA were prepared via a post-synthesis gas phase modification of the boron containing analogue. The materials were characterised with XRD, ICP AES, 29 Si MAS NMR, ESR, DRIFT, nitrogen sorption and TG/DSC. The redox behaviour of the materials was investigated, using the oxidation of 1-pentanol and 2-pentanol and the epoxidation of allylic alcohol, 1-octene, cyclohexene, cyclooctene and cyclododecene with TBHP as test reactions. The materials were inactive in the oxidation of 1-pentanol and for the epoxidation of allylic alcohol. 2-Pentanol could be converted selectively to 2-pentanone. All materials were active and selective catalysts in olefin epoxidations. Especially the molybdenum containing material was found to be highly active, with a yield of cyclohexene oxide based on TBHP of up to 100%. In contrast with the vanadium and the molybdenum containing materials the titanium containing material showed a pore size effect. The catalysts could be recycled at least two times. However, after each recycle the vanadium and molbydenum containing materials suffered a decrease in activity. Leaching experiments, in which the catalyst was removed from the solution, showed that [Ti]-BEA did not leach, in contrast to [V]-BEA and [Mo]-BEA. Leaching could be confirmed with elemental analysis, after three reaction cycles the Si/Ti ratio remained constant, whereas for [V]- and [Mo]-BEA a decrease in the metal content was found.