Structural aspects of the <i>M</i>1 and <i>M</i>2 phases in MoVNbTeO propane ammoxidation catalysts

Abstract

Abstract The structures of M 1 and M 2 in MoVNbTeO propane ammoxidation catalysts have been solved using a combination of TEM, neutron powder diffraction, and synchrotron X-ray powder diffraction. The unit cell of M 1 is Pba 2 (No. 32) with a = 21.134(2) Å, b = 26.658(2) Å, c = 4.0146(3) Å and Z = 4. The formula unit is Mo 7.8 V 1.2 NbTe 0.937 O 28.9 . The unit cell of M 2 is Pmm 2 (No. 25) with a = 12.6294(6) Å, b = 7.29156(30) Å, c = 4.02010(7) Å and Z = 4. The formula unit is Mo 4.31 V 1.36 Te 1.81 Nb 0.33 O 19.81 . Tellurium sites in hexagonal channels of both phases are displaced toward vanadium-occupied framework sites, whereas Te in the heptagonal channel of M 1 is near the channel center. The chemical topology resulting from oxidation states and Madelung site potentials presents active moieties for the ammoxidation of propane in M 1 and propene in M 2. EPR confirmed the presence of V 4+ and possibly Mo 5+ in M 1 and V 4+ in M 2.