Abstract: Metastable hexagonal molybdenum trioxide was successfully synthesized using molybdic acid as precursor via a facile hydrothermal treatment followed by calcination.The products were characterized X-ray diffraction（XRD），scanning electron microscopy（SEM），Fourier transform infrared spectroscopy（FT-IR），H2 temperature programmed reduction（H2- TPR），X-ray photoelectron spectroscopy（XPS），and Raman spectroscopy.The catalyst′s activity was evalued by the selective oxidation reaction of methanol to formaldehyde.Results indicated that the relatively pure hexagonal MoO3 catalysts confirmed by XRD，FT-IR，XPS，and Raman spectroscopy can be obtained at a hydrothermal reaction temperature of 60~120 ℃ and a calcination temperature of 150~350 ℃，respectively，and the resulting h-MoO3 presented a morphology of hexa-prism with a diameter from 1 to 10 micrometer and a slenderness ratio of 5~10.The synthesized h-MoO3 catalysts exhibited rather high low temperature reactivity for methanol oxidation to formaldehyde.

Key words: hydrothermal synthesis, h-MoO3, methanol, selective oxidation, formaldehyde