Insight into the role of metal support interface through the synergistic effect between Ag and α-Bi₂Mo₃O₁₂ support for the selective oxidation of propylene to acrolein

Pre-synthesized morphologically tailored size and shape selective silver nanoparticles (AgNPs) decorated on bismuth molybdate support (AgNPs/α–Bi₂Mo₃O₁₂) using simple wet impregnation method was employed. The prepared AgNPs/α-Bi₂Mo₃O₁₂ nanocatalysts were tested in the selective partial oxidation of propylene to acrolein reaction. The introduction of well-defined size and shape of AgNPs on α–Bi₂Mo₃O₁₂ is greatly promoted the strong metal support interactions (SMSI), creation of oxygen vacancies (O_v) and high propylene adsorption binding energy (calculated by DFT). The strong metal support interactions between Ag and α-Bi₂Mo₃O₁₂ is clearly elucidated by the high quality HRTEM and STEM–HAADF microscopic images. In addition, surface atomic molar ratio measured by XPS analysis determined the key redox properties of AgNPs/α–Bi₂Mo₃O₁₂ system and their influence on the overall catalytic efficiency in the oxidation of propylene via reduction of Mo⁶⁺ to Mo⁵⁺ initiated at low temperatures in Ag/α–Bi₂Mo₃O₁₂ system. The Mo reduction is further confirmed by the activated oxygen removal from the MoO₄^2– moieties after Ag incorporation on α–Bi₂Mo₃O₁₂. Thus, confirmed the oxidation reaction pathway follows a Mars–van–Krevelen process. Further, DFT calculations supported the propylene adsorption is more favorable over Ag/α–Bi₂Mo₃O₁₂ than bare α–Bi₂Mo₃O₁₂ support. The propylene oxidation performance over Ag/α–Bi₂Mo₃O₁₂ system was 5.5 times higher than bare α–Bi₂Mo₃O₁₂ support, probably due to an enabled strong metal support interaction and increased oxygen vacancies.