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A series of bimetallic mesostructured Co (V, Nb, La)-MCM-41 molecular sieves with high surface area and narrow pore-size distribution were obtained by direct hydrothermal synthesis using two different silica sources. Their catalytic activity was tested in the oxidation of styrene and benzene with hydrogen peroxide. Structural and textural properties of the fresh and used catalysts were studied by X-ray powder diffraction, nitrogen adsorption–desorption, TEM and SEM. The influence of the synthesis procedure, composition and metals molar ratio on the structure, catalytic activity and selectivity was discussed. The activity of bimetallic catalysts was compared with that of monometallic Co-, V-, Nb- and La-MCM-41 molecular sieves. It was found that more ordered hexagonal structure favors the selectivity to benzaldehyde and decreases the induction time of reaction. The introduction of V as the second metal ions into Co-MCM-41 decreases or increases sharply the activity in the oxidation of styrene and benzene, respectively. While the introduction of Nb showed an opposite tendency, suggesting that the combination of Co-V favors the oxidation of styrene and Co-Nb the oxidation of benzene and that the catalytic sites for oxidation of styrene and benzene are different. No benefic effect has been observed by incorporation of La into Co-MCM-41 neither in oxidation of styrene nor in oxidation of benzene. It was found that the benzaldehyde formation is structure sensitive. |
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