Methanol oxidation on vanadium oxide catalyst prepared by in situ activation of amorphous vanadium pentoxide precursor

Amorphous vanadium pentoxide was prepared using the sol-gel process and vanadyl triisobutoxide as precursor. The catalytic properties of this material for methanol oxidation to formaldehyde were investigated in the temperature range 300 to 520 K. At 520 K the initial activity of the amorphous V2O5 was very low. However, during in situ activation at this temperature the activity increased steadily and reached a steady-state value which was about 30 times higher than the initial activity of the amorphous V2O5 and also considerably higher than the activity of crystalline V2O5. X-ray diffraction indicated that upon exposure to methanol oxidation conditions the amorphous vanadia crystallized slowly and was partly reduced. These changes were accompanied by drastic alterations of the bulk and surface structure of the amorphous precursor as evidenced by electron microscopy. The final catalyst exhibiting steady-state activity consisted of crystalline V2O5 and V3O7. Partial reduction of the bulk was not observed with crystalline vanadia catalysts and appears to be characteristic for the amorphous vanadia. The results indicate that amorphous vanadia undergoes structural changes more easily than its crystalline counterpart and may thus be an interesting catalyst precursor.