Crystal structure and catalytic performance for direst oxidation of propylene to acrylic acid of MoVTeNbOx prepared by high-pressure hydrothermal synthesis

MoVTeNbO_x catalysts were prepared through a high-pressure hydrothermal method, in which the crystalline structure and properties of the catalysts were tuned by varying the system pressure (0-12.0 MPa). Results showed that the system pressure had a significant influence on the structure and catalytic performance of MoVTeNbO_x. Under 3.0 MPa, MoVTeNbO_x prepared possessed the highest content of M1 phase (90.6%) and V⁵⁺ content (60.7%), exhibiting a uniform short and thick needle-like morphology. Also, it showed excellent selectivity (79.1%) and yield (52.8%) to acrylic acid at the catalytic temperature of 380°C. However, under 4.4 and 11.6 MPa, the characteristic peaks of M1 shifted to a certain extent and the morphology changed from short and thick to slender. As a result, the V⁵⁺ content of M1 (001) plane decreased, resulting in a remarkable decline of the selectivity to acrylic acid. Moreover, DFT simulation results showed that the anti-bond orbital energy of V-O bond is the highest under 3.0 MPa, while further increase of pressure leads to obvious extrusion between atoms in the internal structure of MoVTeNbO_x. Moreover, it was clear that the lower the anti-bond orbital energy of V-O bond, the lower the selectivity to acrylic acid.