Structure and catalytic properties of MgO-supported vanadium oxide in the selective oxidation of cyclohexane

• Published in: Journal of molecular catalysis. A, Chemical Chemical, 2010-03, Vol.318 (1), p.51-59
• Main Authors: Aboelfetoh, Eman Fahmy, Fechtelkord, Michael, Pietschnig, Rudolf
• Format: Article
• Language: English
• Subjects: Catalysis; Chemistry; Cyclohexane oxidation; C–H activation; Exact sciences and technology; General and physical chemistry; MgO; Supported catalyst; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Vanadium
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2009.11.007

MgO-supported vanadium oxide catalysts have been prepared which contain ortho-Mg 3V 2O 8, pyro-Mg 2V 2O 7 and MgV 2O 5 phases as surface species and for higher loadings show good activity in the conversion of cyclohexane to cyclohexylhydroperoxide and improved leaching behavior. The prepared catalysts have been characterized by several techniques such as XRD, FT-IR, DR-spectroscopy, BET, 51V solid-state NMR, SEM and EDX. 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, 51V solid-state NMR, SEM and EDX. For comparison, three different phases of magnesium vanadate (meta-β-MgV 2O 6, pyro-α-Mg 2V 2O 7, and ortho-Mg 3V 2O 8) have been synthesized as reference materials for the structural characterization. The catalytic activity of the prepared catalysts was evaluated for the liquid-phase 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 3V 2O 8, pyro-Mg 2V 2O 7 and V 2O 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.