Tuning the Surface Mn/Al Ratio and Crystal Crystallinity of Mn–Al Oxides by Calcination Temperature for Excellent Acetone Low-Temperature Mineralization
Jian‐Rong Li, Jie Zheng, Kun Wu, Mengmeng He, Junyi Zhao, Yang Meng, Jun He, Hong-Yun Ren, Hang Xiao, Chi He
Abstract
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 KMn 8 O 16 phase can be effectively tamed under different calcination temperatures, which obviously alter the CO 2 selectivity, reaction rate, and stability of Mn–Al oxides for catalytic oxidation of acetone, among which the Mn 5 Al-350 catalyst exhibits the best catalytic performance (90% of acetone converted at 159 °C) with CO 2 selectivity higher than 99.5%, mainly owing to its higher surface Mn/Al ratio and weaker Mn–O bond with more Mn 3+ as compared to Mn 5 Al-250, Mn 5 Al-450, and Mn 5 Al-550. Although a decrease in the consumption rate of acetic acid in the presence of 3.0 vol % H 2 O leads to the slight reduction of acetone conversion and CO 2 yield, Mn 5 Al-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.