1987 年 8 巻 3 号 p. 186-191
Geometrical structures of vanadium oxide and niobium oxide clusters supported on silica and alumina are investigated by means of ab initio molecular orbital method. Optimized geometries are searched using the energy gradient technique. For the clusters supported on silica and alumina, mono-oxo and di-oxo structures are more stable respectively. Stabilization of the di-oxo structure is ascribed to the bond formation between the oxygen and aluminum atoms in the cluster. Bond lengths estimated by the above calculations are 1.56Å (1.77A) and 1.58Å (1.95Å) for V-O double (single) bond on silica and alumina, respectively, and 1.72Å (1.92Å) and 1.73Å (2.11Å) were obtained for Nb-O double (single) bond. Calculated values are compared with available data from EXAFS measurements, and good agreement, as a whole, is given for the systems examined here.