Crystalline-phase-dependent catalytic performance of MnO2 for aerobic oxidation reactions

Abstract

Knowledge of the catalytic performances of different crystalline phases of a material is vital for the development of superior catalysts. In this study, different phases of MnO 2 (α, β, γ, and δ) have been prepared by the oxidation of Mn 2+, and their catalytic performances were evaluated using the aerobic oxidation of benzyl alcohol to benzaldehyde as a model reaction. α-MnO 2 promoted the reaction to the highest yield. However, when the yields were normalized by the corresponding surface areas, δ-MnO 2 exhibited the highest specific activity and α-MnO 2 the lowest, indicating that the diverse microstructures resulting from the crystalline phase have a profound effect on catalytic performance. α-MnO 2 showed the highest catalytic stability, resulting from its unchanged composition and morphology after use. Informed by the experimental results, a possible reaction mechanism involving the Mars-van Krevelen process was proposed. This work provides useful information for the development of effective catalysts for aerobic oxidation.

An efficient and universal solar interfacial photothermal reactor toward liquid phase oxidation

“…It is well known that the benzyl alcohol thermal‐oxidation on MnO 2 ‐based catalysts follows the Mars–van Krevelen mechanism: benzyl alcohol is first oxidized by the surface lattice oxygen of the catalyst, and then oxygen vacancies generate on the surface of the catalysts, which are subsequently replenished by gas‐phase O 2 60–62 . Our group has demonstrated that cerium doping could improve the mobility of the surface lattice oxygen in the MnO 2 , thus accelerating the benzyl alcohol oxidation 41 .…”

“…benzyl alcohol is first oxidized by the surface lattice oxygen of the catalyst, and then oxygen vacancies generate on the surface of the catalysts, which are subsequently replenished by gas-phase O 2 . [60][61][62] Our group has demonstrated that cerium doping could improve the mobility of the surface lattice oxygen in the MnO 2 , thus accelerating the benzyl alcohol oxidation. 41 In this work, the enhancement of benzaldehyde generation rates in bulk solution at the same temperatures was quite evident upon solar irradiation (Figure 4D), especially at high temperatures, indicating that the excellent catalytic performance of respectively.…”

Room-temperature tandem conversion of cyclic alkenes into 1,2-diols using molecular oxygen and β-MnO2 heterogeneous catalyst

“…The MnO 2 nanocrystal is composed of a large amount of [MnO 6 ] octahedral units shared by the edges and corners, which gives rise to a variety of polymorphic forms, including α-type, δ-type, β-type, and γ-type. 26,27 It has been reported that the crystal phase of MnO 2 nanocrystal presented a significant influence on its catalytic performance. 28,29 To date, there are scarce reports about the application of MnO 2 as a heterogeneous catalyst for activating molecular oxygen in alkene epoxidation reactions.…”