Different Mo-Bi Phase Coupled with Fe-Co for Propylene Oxidation to Acrolein

Industrial Bi-Mo-Fe-Co composites catalysts for propylene oxidation, are consist of two main components: Bi-Mo oxidate for propylene activation and Fe-Co oxidate for oxygen activation. But there are three different Bi-Mo crystalline phases, i.e., α-Bi₂Mo₃O₁₂, β-Bi₂Mo₂O₉, γ-Bi₂MoO₆, their role in catalytic oxidation process is unclear. In this paper, above three kinds of Bi-Mo phase are prepared at first, then coupled them respectively with Fe-Co oxidates by ball milling method to manufacture Cat-α, Cat-β, and Cat-γ. It is showed that their catalytic performance for propylene oxidation to acrolein, has the order of Cat-α > Cat-β > Cat-γ, and the Cat-α exhibit the best propylene conversion (90.1%) and highest acrolein selectivity (91.7%). The result shows that Cat-α exhibited a lower redox temperature, and possessed a high O_lattice content, which benefit to its excellent oxidant ability. Meanwhile, α-Bi₂Mo₃O₁₂ exhibit rich Co²⁺/Co³⁺ pairs in Cat-α, prompt oxygen migration efficiency, and had a low interaction with propylene confirmed by DFT calculation, which inhibited the excessive oxidation, benefits to acrolein yield. Our study provides a new insight over Bi-Mo catalyst for selective oxidation.