Structure and catalytic properties of MgO-supported vanadium oxide in the selective oxidation of cyclohexane (original) (raw)

2010, Journal of Molecular Catalysis A-chemical

MgO-supported vanadium oxide catalysts with different vanadium loadings have been prepared by wet impregnation and grafting using ammonium metavanadate or VOCl 3 as precursor, respectively. The prepared catalysts have been characterized by several techniques such as XRD, FT-IR, DR-spectroscopy, BET, 51 V solid-state NMR, SEM and EDX. For comparison, three different phases of magnesium vanadate (meta-␤-MgV 2 O 6 , pyro-␣-Mg 2 V 2 O 7 , and ortho-Mg 3 V 2 O 8 ) have been synthesized as reference materials for the structural characterization. The catalytic activity of the prepared catalysts was evaluated for the liquidphase oxidation of cyclohexane as a model reaction to obtain cyclohexylhydroperoxide, cyclohexanol and cyclohexanone with PCA as co-catalyst. The results show that VO x /MgO catalysts containing isolated VO 4 species either impregnated or grafted do not show considerable activity in the oxidation process. In contrary, catalysts with higher vanadium loading, which contain ortho-Mg 3 V 2 O 8 , pyro-Mg 2 V 2 O 7 and V 2 O 5 phases as surface species show conversions up to 70% and TONs up to 34,700. Compared to previously studied support materials for this catalytic system the leaching behavior is significantly improved. (R. Pietschnig). the course of our investigations it occurred to us that the basicity of the support material has a substantial influence on the catalytic performance and moreover on the leaching rate which can be a substantial problem for supported vanadium oxide catalysts. These findings prompted us to consider rather basic support materials like MgO as support materials for vanadium oxide species, which to our knowledge have not been used for this purpose so far.

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