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 degrees 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.

Automated summary

The study fabricated Mn-Al oxides with strengthened synergistic effects of Mn and Al species by adjusting the calcination temperature. Different temperatures effectively controlled the surface Mn/Al ratio and KMn8O16 phase, leading to significant changes in CO2 selectivity, reaction rate, and stability for catalytic oxidation. Mn5Al-350 catalyst exhibited the best performance with a high CO2 selectivity and superior catalytic stability. Reaction intermediates and theoretical calculations provided insights into the reaction mechanism.