The activity and selectivity in the oxidation of furan on unsupported and supported V2O5 catalysts were investigated in connection with the catalyst structure. It was found that the steady-state reaction rate at various concentrations of O2 was proportional to the amount of V5+O species in the catalyst, indicating that the surface VO plays the active oxygen species for the reaction. The specific activity of surface VO species, defined by the rate per surface VO, for unsupported V2O5 changed greatly with the surface structure of the catalyst: The fusion of V2O5 markedly decreased the specific activity, while the severe redox treatment of the fused catalyst increased it. This means that the furan oxidation on V2O5 catalysts is a structure-sensitive reaction. The specific activity of the surface VO species for the V2O5 TiO2 and V2O5 Al2O3 catalysts was smaller than that for the unsupported V2O5, indicating the retarding effect of the support on the activity. This is in contrast to the known promoting effect of TiO2 support on the activity. The selectivity to maleic anhydride was found to be determined by the number of V2O5 layers on support for both V2O5 TiO2 and V2O5 Al2O3 catalysts. When the number of V2O5 layers was 1 or 2, the selectivity was low, while it increased markedly with the increase in the number of V2O5 layers to 5, and attained a constant value above 5 layers. The change in the oxidation state of the catalyst did not affect the selectivity. These behaviors in the activity and selectivity in the furan oxidation were discussed in comparison with those in the benzene oxidation.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry