Super high selectivity of acrolein in oxidation of propene on molybdenum promoted hierarchical assembly of bismuth tungstate nanoflakes

• Hierarchical Bi2WO6 microspheres composed by well shaped nanoflakes are obtained.
• Surface modification of MoO3 dramatically enhances the catalyst as selective one.
• Acrolein selectivity can surpass ∼96% in oxidation of propene with high conversion.
• Cooperation between surface molybdena and n-type semiconductor Bi2WO6 is important.

The catalytic properties of well-defined hierarchically assembled Bi2WO6 nanoflakes with surface dispersed molybdena have been studied with selective oxidation of propene as probe reaction. The adsorption of oxygen causes the decrease in the conductivity of Bi2WO6, demonstrating its nation of n-type semiconductor. The adsorption of oxygen gains electrons from the conduction band of Bi2WO6 to produce oxygen species active for propene reaction at low temperatures, which, however, gives mainly COx as products. The modification by surface molybdena significantly inhibited the total oxidation reaction of propene over the Bi2WO6, while dramatically increased the conversion of propene and selectivity to acrolein simultaneously, without the formation of acrylic acid. The characterization of conductivity measurements, H2-TPR, O2-TPD, XPS and TPSR indicated that the thermally excited electrons from the Bi2WO6 were combined with surface dispersed molybdena and resulted in an extraordinary increase of selective oxidation performance. The unique effects of the hierarchically assembled Bi2WO6 nanoflakes on the catalytic property of molybdena were discussed and the mechanism of the catalyst for the selectively catalytic oxidation was proposed. The results are useful to design novel catalysts for important reactions with nano concepts.

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