Tuning the Surface Mn/Al Ratio and Crystal Crystallinity of Mn–Al Oxides by Calcination Temperature for Excellent Acetone Low-Temperature Mineralization

Here, Mn–Al oxides with the strengthened synergistic effect of Mn and Al species were fabricated by facilely adjusting the calcination temperature with the hydrolysis-driven redox-precipitation method. Results demonstrated that the surface Mn/Al ratio and KMn₈O₁₆ phase can be effectively tamed under different calcination temperatures, which obviously alter the CO₂ selectivity, reaction rate, and stability of Mn–Al oxides for catalytic oxidation of acetone, among which the Mn₅Al-350 catalyst exhibits the best catalytic performance (90% of acetone converted at 159 °C) with CO₂ selectivity higher than 99.5%, mainly owing to its higher surface Mn/Al ratio and weaker Mn–O bond with more Mn³⁺ as compared to Mn₅Al-250, Mn₅Al-450, and Mn₅Al-550. Although a decrease in the consumption rate of acetic acid in the presence of 3.0 vol % H₂O leads to the slight reduction of acetone conversion and CO₂ yield, Mn₅Al-350 still exhibits a superior catalytic stability. The reaction intermediates including acetaldehyde, ethanol, acetic acid, and formic acid species before total mineralization are determined by proton transfer reaction–mass spectrometry, theoretical calculations, and in situ DRIFTS. Theoretical calculations also reveal that the p-orbital interaction of C with a certain anisotropy leads to a weak catalytic effect in the process of acetic acid decomposition as the rate-limiting step.