Syntheses of Hierarchical MnO2viaH2O2Selectively Reducing KMnO4for Catalytic Combustion of Toluene

Preparation of Mn-Fe Oxide by a Hydrolysis-Driven Redox Method and Its Application in Formaldehyde Oxidation

Homogeneous distribution of Mn-Fe oxides (xMn1Fe) with different Mn/Fe ratios was synthesized by a hydrolysis-driven redox method, and their catalytic activities in HCHO oxidation were investigated. The results showed that HCHO conversion was significantly improved after doping iron due to the synergistic effect between manganese and iron. The 5Mn1Fe catalyst exhibits excellent catalytic activity, achieving >90% HCHO conversion at 80 °C and nearly 100% conversion at 100 °C. The physicochemical properties of catalysts were characterized by BET, XRD, H2-TPR, O2-TPD, and XPS techniques. Experimental results revealed that the introduction of Fe into MnO x resulted in a large surface area, a high ratio of Mn4+, abundant lattice oxygen species and oxygen vacancy, and uniform distribution of Mn and Fe, thus facilitating the oxidation of HCHO to CO2 and H2O.

The Controlled Synthesis of Birnessite Nanoflowers via H2O2 Reducing KMnO4 For Efficient Adsorption and Photooxidation Activity

Birnessite nanoflowers composed of layers have been proven to be the strongest adsorbent and oxidant in the surface environment. However, the current synthesis methods of birnessite nanoflowers are suffering from long reaction time and high reaction temperature. Based on these, this paper explores a new method for the rapid and controlled synthesis of layered manganese oxides. The method relies on the molar ratios of KMnO₄ and H₂O₂ redox reacting species to drive the production of birnessite nanoflowers under acidic conditions. The molar ratios of KMnO₄ and H₂O₂ are the key to the crystal structure of the as-prepared. It was found that when the molar ratios of KMnO₄ and H₂O₂ is from 1:1.25 to 1:1.90, the sample is birnessite nanoflowers, and when the ratio is increased to 1:2.0, the sample is a mixture of birnessite nanoflowers and feitknechtite nanoplates. Among the as-prepared samples, BF-1.85 (molar ratios of KMnO₄ and H₂O₂ is 1:1.85) shows the highest capacity for Pb²⁺ adsorption (2,955 mmol/kg) and greatest degradation efficiency of phenol and TOC. The method proposed herein is economical and controllable, and it yields products with high efficiency for the elimination of inorganic and organic pollutants.

Manganese vacancy-confined single-atom Ag in cryptomelane nanorods for efficient Wacker oxidation of styrene derivatives

Single-atom catalysts provide a pathway to elucidate the nature of catalytically active sites. However, keeping them stabilized during operation proves to be challenging. Herein, we employ cryptomelane-type octahedral molecular sieve nanorods featuring abundant manganese vacancy defects as a support, to periodically anchor single-atom Ag. The doped Ag atoms with tetrahedral coordination are found to locate at cation substitution sites rather than being supported on the catalyst surface, thus effectively tuning the electronic structure of adjacent manganese atoms. The resulting unique Ag–O–MnO_x unit functions as the active site. Its turnover frequency reaches 1038 h⁻¹, one order of magnitude higher than for previously reported catalysts, with 90% selectivity for anti-Markovnikov phenylacetaldehyde. Mechanistic studies reveal that the activation of styrene on the ensemble site of Ag–O–MnO_x is significantly promoted, which can accelerate the oxidation of styrene and, in particular, the rate-determining step of forming the epoxide intermediate. Such an extraordinary electronic promotion can be extended to other single-atom catalysts and paves the way for their practical applications.

Manganese vacancy-confined single-atom Ag in cryptomelane nanorods efficiently catalyses Wacker oxidation of styrene derivatives.

Enhanced photothermal catalytic degradation of toluene by loading Pt nanoparticles on manganese oxide: Photoactivation of lattice oxygen

Light-driven photothermocatalysis can provide enough energy to reach light-off temperature of VOCs on the surface of catalyst without auxiliary heat source. Herein, we synthesized noble-metal supported manganese oxide catalysts (xPt/MO) and studied their photothermal catalytic behavior of toluene degradation, where 1 Pt/MO (1 wt.% loading of Pt) and 2 Pt/MO (2 wt.% loading of Pt) exhibited more than 90 % of conversion and 70 % of mineralization under illumination of 200 mW/cm² light intensity with a value of 30,000 mL/(g·h) for weight hourly space velocity (WHSV), respectively. Comparison to pure MO, 1 Pt/MO owns a good photothermal catalytic stability for at least 60 h without obvious deactivation. The introduction of Pt promotes the crystallization of MO (verified by XRD and TEM analysis) and enhances the mobility of surface/sub-surface lattice oxygen (verified by O₂-TPD, H₂-TPR and CO consumption). It is proved that illumination not only supplies thermal energy to trigger the reaction of toluene oxidation but also further evoke more lattice oxygen on Pt/MO to participate in toluene decomposition.

Effect of a mixed precursor over monolith MnOx/La–Al2O3 catalyst for toluene oxidation

The MNMA catalyst prepared with a mixed precursor of Mn(NO₃)₂ and Mn(Ac)₂·4H₂O possesses more α-MnO₂ species and good dispersion and is more active for toluene oxidation.

Preparation of a Series of Pd@UIO-66 by a Double-Solvent Method and Its Catalytic Performance for Toluene Oxidation

This paper reports on the preparation, characterization, and catalytic properties of the Pd@UIO-66 for toluene oxidation. The samples are prepared by the double-solvent method to form catalysts with large specific surface area, highly dispersed Pd⁰ (Elemental palladium) and abundant adsorbed oxygen, which are characterized by X-ray Photoelectron Spectroscopy (XPS), Brunauer-Emmett-Teller (BET) and Transmission Electron Microscopy (TEM). The results show that as the Pd content increases, the adsorbed oxygen content further increases, but at the same time Pd⁰ will agglomerate and lose some active sites, which will affect its catalytic performance. While 0.2%Pd@UIO-66 has the highest concentration of Pd⁰, the result shows it has the best catalytic activity and the T₉₀ temperature is 210 °C.

Structure-Activity Relationship of Manganese Oxide Catalysts for the Catalytic Oxidation of (chloro)-VOCs

Manganese oxide catalysts, including γ-MnO2, Mn2O3 and Mn3O4, were synthesized by a precipitation method using different precipitants and calcination temperatures. The catalytic oxidations of benzene and 1,2-dichloroethane (1,2-DCE) were then carried out. The effects of the calcination temperature on the catalyst morphology and activity were investigated. It was found that the specific surface area and reducibility of the catalysts decreased with the increase in the calcination temperature, and both the γ-MnO2 and Mn3O4 were converted to Mn2O3. These catalysts showed good activity and selectivity for the benzene and 1,2-DCE oxidation. The γ-MnO2 exhibited the highest activity, followed by the Mn2O3 and Mn3O4. The high activity could be associated with the large specific surface area, abundant surface oxygen species and excellent low-temperature reducibility. Additionally, the catalysts were inevitably chlorinated during the 1,2-DCE oxidation, and a decrease in the catalytic activity was observed. It suggested that a higher reaction temperature could facilitate the removal of the chlorine species. However, the reduction of the catalytic reaction interface was irreversible.

Characterisation of hexagonal birnessite with a new and rapid synthesis method—comparison with traditional synthesis

The new synthesis method of birnessite with rapid, simple, and low cost characteristics proposed in this work can be applied to industry products. Bir-H₂O₂ have a better physicochemical characteristics than Bir-HCl using traditional synthesis.

A Novel Redox Precipitation to Synthesize Au-Doped α-MnO2 with High Dispersion toward Low-Temperature Oxidation of Formaldehyde

A novel method of redox precipitation was applied for the first time to synthesize a Au-doped α-MnO₂ catalyst with high dispersion of the Au species. Au nanoparticles (NPs) can be downsized into approximate single atoms by this method, thereby realizing highly efficient utilization of Au element as well as satisfying low-temperature oxidation of formaldehyde (HCHO). Under catalysis of the optimal 0.25% Au/α-MnO₂ catalyst, a polluted stream containing 500 ppm HCHO can be completely cleaned at 75 °C with the condition of a weight hourly space velocity (WHSV) of 60000 mL/(g h). Meanwhile, the catalyst retains good activity for removal of low-concentration HCHO (about 1 ppm) at ambient temperature with a high WHSV, and exhibits a high tolerance to water and long-term stability. Our characterization of Au/α-MnO₂ and catalytic performance tests clearly demonstrate that the proper amount of Au doping facilitates formation of surface vacancy oxygen, lattice oxygen, and charged Au species as an active site, which are all beneficial to catalytic oxidation of HCHO. The oxidation of HCHO over Au-doped α-MnO₂ catalyst obeys the Mars-van Krevelen mechanism as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy.