Thermal Behavior, Crystal Structure, and Solid-State Transformation of Orthorhombic Mo–V Oxide under Nitrogen Flow or in Air

Orthorhombic Mo–V oxide is one of the most active solid-state catalysts for selective oxidation of alkane, and revealing its detailed structure is important for understanding reaction mechanisms and for the design of better catalysts. We report the single-crystal X-ray structure analysis of orthorhombic Mo–V oxide heated under a N2 flow; V is present in 6-membered rings with partial occupancy, similar to the structure reported by Trunschke’s group for orthorhombic Mo–V oxide heated under an Ar flow (Trunschke, ACS Catal. 2017, 7, 3061). Our previous paper (Ishikawa, J. Phys. Chem. C, 2015, 119, 7195) reported that V is not present in the 6-membered rings when orthorhombic Mo–V oxide is calcined in the presence of oxygen. Furthermore, Trunschke’s paper reported that V in the 6-membered rings moves to the surface of the crystals under oxidation reaction conditions in the presence of H2O. Our present results provide additional evidence for V migration in the 6-membered rings during heat treatment. We also report the differences in the thermal behaviors, ultraviolet–visible absorptions, N2 isotherms, and elemental analysis results of Mo–V oxide heated in air and under a N2 flow. Furthermore, we report the solid-state transformation of orthorhombic Mo–V oxide to tetragonal Mo–V oxide by controlled heat treatment.