Mechanochemical Synthesis of Multicomponent Bismuth-Based Molybdate Catalysts for Propylene Ammoxidation to Produce Acrylonitrile

Abstract

Activities and structures of metal oxide catalysts significantly rely on the synthesis procedures and conditions. In this study, a novel solvent-free mechanochemical method was employed to prepare catalysts for the ammoxidation of propylene. Multicomponent oxide catalysts containing bismuth, iron, cobalt, and molybdenum were successfully synthesized using a ball mill mixer and zirconia jars without the use of nitric acid. The mechanochemically synthesized catalysts exhibited higher catalytic performance than traditional catalysts prepared by coprecipitation (CP) and rotary evaporation (RE) methods in propylene ammoxidation. The synergistic effect of the mechanochemical method was investigated using various analyses, such as inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). ICP-AES analysis revealed that the ball-mill-based catalysts contained metal elements in designated amounts more accurately than those prepared by the CP or RE methods. Propylene ammoxidation reactions with ball-milled catalysts showed a synergistic effect and improved acrylonitrile yield, especially at a 50:50 wt% ratio of Bi₂Mo₃O₁₂ to Fe_0.36Co_0.64MoO₄. Comprehensive analyses, including XRD, SEM–EDS, Raman spectroscopy, and XPS, support the conclusion that the improved performance of the mechanochemically synthesized catalysts can be attributed to the increased interaction between different phases prepared under mechanical forces, leading to a favorable change in the oxidation state of iron.