Accelerating the Low-Temperature Catalytic Oxidation of Acetone over Al-Substituted Mn–Al Oxides by Rate-Limiting Step Modulation

Abstract

In order to enhance the catalytic activity and improve the stability of Mn–Al oxides in acetone oxidation, it is interesting to have found that modulating and accelerating the rate-limiting step by Al substitution rather than just mixing of Mn and Al is crucial for hydrocarbon efficient catalytic destruction. Here, a series of Mn–Al oxides with different Al substitution ratios were prepared by a scalable and facile hydrothermal-redox strategy. The reaction rate, selectivity, and stability of the representative α-MnO2 catalyst in acetone oxidation can be remarkably promoted by simple replacing of the partial framework Mn with Al, which changes the rate-limiting step from acetic acid dissociation to ethanol decomposition accelerated by H2O molecules. Among them, MnAl0.5 displays the best catalytic performance with 90% of acetone converted at just 165 °C and a remarkable CO2 yield. DFT results suggest that the p y and p x orbitals of the O element take part in the formation of the carbonyl group when the intermediate of removing H* from ethanol reacts with the hydroxyl group of H2O. The d xz orbital of Mn with p-electron of Al plays a vital role in the rate-limiting step. The work provides new insights into engineering catalysts for industrial VOC efficient and economical mineralization.

Boosting the Catalytic Performance of Volatile Organic Compound Oxidation Over Platelike MnO2/CoAlO Catalyst by Weakening the Co–O Bond and Accelerating Oxygen Activation

“…peaks were assigned to the characteristic peaks of tetrahedral sites (Co 2+ −O). 35 22,38,39 The binding energy of O 1s on the MnO 2 /CoAlO-F catalyst shifted to lower energy in comparison to MnO 2 /CoAlO-P, while a similar phenomenon was observed on CoAlO-F and CoAlO-P (Figure 3b). This suggested that flowerlike MnO 2 / CoAlO-F (CoAlO-F) might possess more oxygen vacancies than platelike MnO 2 /CoAlO-P (CoAlO-P).…”

“…At 180 °C, more formate than acetate species were observed on MnO 2 /CoAlO-F. This suggested that more acetate species were converted into formate species, and this conversion rate was higher than the conversion rate of formate into CO 2 and H 2 O, which was ever reported by He et al (the energy barrier for the conversion of acetate to formate was lower than that of formate to CO 2 and H 2 O) . This was the reason that more formate species were formed on MnO 2 /CoAlO-F in comparison to acetate species.…”

“…Notedly, the peak intensity at the Co 2+ –O modes for MnO 2 /CoAlO-X became weak and even disappeared, suggesting that most of surface Co 2+ cations on MnO 2 /CoAlO-X were oxidized, consistent with the Co 2p XPS results. A distinct red shift of the MnO 2 Raman peaks was observed on MnO 2 /CoAlO-F in comparison to MnO 2 /CoAlO-P, suggesting that MnO 2 on MnO 2 /CoAlO-F had more oxygen vacancies. ,, …”

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

“…47 The peak at 1370 cm −1 is ascribed to the stretching vibration of � CH 3 . 20 The band at 1231 cm −1 is ascribed to the stretching vibration of the carbon framework from acetone on the catalyst surface. 47 The peaks at 1415 and 1346 cm −1 are assigned to the symmetrical stretching vibration of carboxylate at acetate and formate species, respectively.…”

“…The Al is not a part of the main active phase, and the key role of Al is to disperse the active phase and adsorb acetone. 17,20 Therefore, the single metal oxide phase with highly homogeneous dispersion of Al species in the Al-based materials fully exhibits their own activity and synergistic effect, which promotes efficient catalytic oxidation of acetone. Until now, the effects of composition ratio and crystal phase of the whole material on catalytic activity have been widely investigated for Al-based catalysts.…”