Characterization of Mo Species Supported on SiO2 Modified with Be2+ and Mg2+

Two series of modified carriers (m.c.) have been prepared by doping silica with various amounts of Be²⁺ and Mg²⁺. The prepared m.c. have been used as supports for the preparation of supported Mo^(VI) oxide catalysts. The magnitude of interactions between SiO₂ and Be²⁺ or Mg²⁺ nitrates depends on the kind and content of the cation. After calcination at 600°C a greater fraction of cations remains on the support surface as well dispersed M(NO₂)₂ in the case of Mg²⁺ m.c. Concerning the Mo containing samples it was found that doping by Be²⁺ and Mg²⁺ causes a solid state transformation of octahedral Mo^(VI) to tetrahedral Mo^(VI). As before, the extent of the effect differs between Be²⁺ and Mg²⁺ and it varies with the content of cation. This effect has been attributed to the inhibition of the polymerization of monomeric Mo^(VI) species and/or to the formation of molybdate salts.