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

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.

Acetone Efficient Degradation under Simulated Humid Conditions by Mn–O–Pt Interaction Taming-Triggered Water Dissociation Intensification

“…The small peaks at around 970 cm –1 are assigned to the Si–O–Mn bonds, and the intensity of which increases with the increasing of CA/Mn from 0 to 6, while it decreases with the increasing of CA/Mn from 6 to 9, in consistent with the FT-IR results (Figure b). The Mn–O lattice stretching vibration of [MnO 6 ] octahedral is located at around 605 cm –1 , which is much lower than that of the other reported MnO x (632–648 cm –1 ). ,,, The downshift of these peaks indicates the easier escape of the defected lattice oxygen that exhibits the higher catalytic activity. , Figure c shows UV–vis absorption spectra. The absorbance peaks located at the range of 255–307 nm are ascribed to the ligand-to-metal charge transfer (LMCT) from the strong bonding of oxygen ligands to the Mn 3+ ions (O 2– -Mn 3+ ) .…”

“…The in situ DRIFTS experiments were carried out to investigate the intermediate species on the catalyst surface. The adsorbed acetone, formate, acetate, or adsorbed/deprotonated ethanol can be found in Figure S7 and Table S2. ,− Figure S7c,d demonstrates that the Mars-van-Krevelen mechanism can explain the reaction process. ,, In order to investigate the effect of H 2 O on the intermediate species, we studied the in situ DRIFTS spectra for Pt–Mn/KS-6CA and Pt–Mn/KS at 160 °C (Figure a,b). As shown in Figure a, the intensities of the peaks for acetone cannot be found.…”

“…Meanwhile, the peak intensity of the deprotonated ethanol species decreases slightly after adding 1 vol % H 2 O, but they completely vanish in the presence of 3 vol % H 2 O. Obviously, more H 2 O is involved in the catalytic oxidation of deprotonated ethanol, 38,39 which accelerates the consumption rate of deprotonated ethanol compared to its generation rate.…”

Hydroxyl-Decorated Pt as a Robust Water-Resistant Catalyst for Catalytic Benzene Oxidation

“…Volatile organic compounds (VOCs) are extensively used in industries such as petrochemicals, coatings, paint spraying, and pharmaceuticals, and they possess potential teratogenic and carcinogenic properties. , These compounds pose a significant risk to human health and contribute to the deterioration of atmospheric quality if not properly treated. , Therefore, the development of reliable methods to eliminate these toxic VOCs is urgently needed. − Currently, various end-of-pipe techniques, including adsorption, ozone oxidation, photocatalytic oxidation, thermal combustion, and catalytic oxidation, are commonly employed to address this issue. , Among these techniques, catalytic oxidation has gained considerable attention because of its relatively low operational temperature, minimal production of harmful byproducts, and high efficiency. , However, the research and development of robust catalysts remain a primary concern in this field. Based on numerous reports, precious metals and metal oxides are commonly used catalysts for VOC removal. , Precious metals, in particular, exhibit superior catalytic activity and stability, making them widely applicable in this context …”

“…5−7 Currently, various end-of-pipe techniques, including adsorption, ozone oxidation, photocatalytic oxidation, thermal combustion, and catalytic oxidation, are commonly employed to address this issue. 8,9 Among these techniques, catalytic oxidation has gained considerable attention because of its relatively low operational temperature, minimal production of harmful byproducts, and high efficiency. 10,11 However, the research and development of robust catalysts remain a primary concern in this field.…”