β(L)-Bi2Mo2O9: A new, highly active and selective, mild oxidation bismuth molybdate catalyst

A new bismuth molybdate, obtained by means of microwave-assisted hydrothermal synthesis, is described by the chemical formula: β(L)-Bi2Mo2O9, in accordance with its low crystallization temperature and transition to β-Bi2Mo2O9 at 532 °C. Its structure, solved ab initio using powder diffraction data, crystallizes in the monoclinic system (space group P21/c), with a = 8.11413(5), b = 8.54445(5), c = 13.43623(6) Å, and β = 123.5085(2)°. This phase has been tested as a catalyst for the oxidation of propene. It appears to be highly stable on stream, with a specific rate of propene conversion comparable to that of α-Bi2Mo3O12 and a slightly higher selectivity to acrolein. A possible active site for the abstraction of the first hydrogen from propene has been identified, by analogy with that proposed for α-Bi2Mo3O12 and seems to correspond to a molybdenyl Mo = O oxygen that is weakly coordinated to a neighboring Bi cation.