Nature of active vanadium nanospecies in MCM-41 type catalysts for olefins oxidation

CHANQUIA CORINA M.; ANALI L. CÁNEPA; ELLIN L. WINKLER; ENRIQUE RODRÍGUEZ-CASTELLÓN; CASUSCELLI SANDRA G.; EIMER GRISELDA A.

MATERIALS CHEMISTRY AND PHYSICS

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2016 vol. 175 p. 172 - 179

0254-0584

A multi-technique physicochemical investigation including UVeVis-DRS, Raman spectroscopy, XPS, ESR and FTIRS with pyridine adsorption was performed to analyze the nature of different vanadium nanospecies present on MCM-41 type catalysts. By employing a direct hydrothermal synthesis, vanadium species were incorporated into siliceous structure mainly as tetrahedrally coordinated isolated Vdþ ions, which would be located inside the wall and on the wall surface of the mesoporous channels. The coexistence of both vanadium oxidation states V4þ and V5þ was also revealed. Acidity measurements permitted to infer about the majority presence of Lewis acid sites, which increase with vanadium content. The catalytic performance of these materials was evaluated in the reaction of a-pinene oxidation with H2O2. The highest intrinsic activity of the sample with lower V loading was attributed to the high dispersion and efficiency of the isolated Vdþ species that actuate as active sites. A mixture of reactionproducts arising from competitive processes of epoxidation and allylic oxidation was found.