Effects of reduction conditions on the formation of porous MoOx from MoO3

Abstract

Effects of reduction conditions on the transformation of MoO 3 to MoO x with large specific surface area have been investigated. The average valence number of Mo was an important parameter to determine the specific surface area of MoO x , irrespective of the reduction conditions. Comparison of the specific surface areas at a certain average Mo valence, however, indicated that reduction at 773 K or below under a small H 2 flow rate was suitable for the formation of MoO x with large surface area. The MoO x possessed pores with diameters of 6–100 Å, and a good relationship was observed between the pore volume and the specific surface area. The reduction products were composed of the MoO x H y and/or Mo metal phases. The formation of Mo metal was suppressed under the reduction conditions suitable for the formation of large surface area MoO x . Reduction in the presence of H 2 O vapor was found to retard Mo metal formation, and to yield MoO x with large surface area even at a high temperature and a large H 2 flow rate. • H 2 reduction of Pt/MoO 3 yielded porous MoO x , of which the surface area was linearly corelated with the micropore volume. • The largest specific surface area of 370 m 2 /g was obtained by reduction under the controlled conditions. • H 2 O vapor was found to have both positive and negative effects on the specific surface area of H 2 -reduced Pt/MoO 3 .