Preparation of metal-doped Cu-Mn/HTS-1 catalysts and their mechanisms in efficient degradation of toluene

Regulating the mobility of lattice oxygen on hollow cobalt-manganese sub-nanospheres for enhanced catalytic oxidation of toluene and o-xylene

Promoting lattice oxygen mobility of Co-based catalysts is crucial to making progress in catalytic oxidation technology. The addition of manganese, a transition metal with similar ionic radius to cobalt and variable valence, was supposed to enhance the mobility of lattice oxygen species of Co-based oxide. A range of hollow CoMnaOx sub-nanosphere catalysts with different Mn/Co ratios was synthesized via a template-sacrificed method, and the effects of different Mn/Co ratios on the structural properties of the catalysts and their catalytic performance for benzene series volatile organic compounds (VOCs) oxidation were investigated. Hollow CoMn2Ox sub-nanosphere exhibited good catalytic activity for oxidation of toluene (T90 = 265 °C) and o-xylene (T90 = 297 °C), as well as excellent recycling ability and water resistance. By adjusting the Mn/Co ratio, metal ions enter into the different tetrahedral or octahedral active sites. Compared with Co3O4, the desorption temperature of surface lattice oxygen on CoMn2Ox decreased by 110 °C. These results demonstrate that the addition of manganese can encourage the electron transfer on CoMnaOx, indicating that the introduction of the appropriate amount of manganese accelerates the activation of gas O2 and mobility of surface lattice oxygen species, thereby expediting the oxidation of benzene series VOCs.

Unravelling the nature of the active species as well as the Mn doping effect over gamma-Al2O3 catalyst for eliminating AsH3 and PH3

To investigate the enhancing effect of Mn on the performance of simultaneous catalytic oxidation of AsH3 and PH3 by CuO-Al2O3 in a reducing atmosphere under micro-oxygen conditions, Cu-Mn modified γ-Al2O3 catalysts were prepared. The characteristics of the catalysts showed that Mn reduced the crystallinity of the active CuO component, increased the number of oxygen vacancies and acidic sites on the catalyst surface, enhanced the mobility of surface oxygen, and the interaction between copper and manganese promoted the redox cycling ability of the catalysts and improved their oxidation performance, which increased the conversion frequency (TOF) by 2.54 × 10-2 to 3.07 × 10-2 sec-1. On the other hand, the introduction of Mn reduced the production of phosphate and As2O3 on the catalyst surface by 30.96% and 44.9%, which reduced the coverage and inerting of the active sites by phosphate and As2O3, resulting in an 8 hr (6 hr) improvement in the stability of PH3 (AsH3) removal.

Design of bifunctional ultrathin MnO2 nanofilm with laccase-like activity for sensing environmental pollutants containing phenol groups

Laccase-catalyzed oxidative reactions are increasingly examined as a reliable approach to environmental analysis and remediation, and it is urgent to widen metal category to compensate huge gap in the number of studies on copper- and non-copper laccase mimics. Herein, two-dimensional ultrathin MnO2 nanofilm (Mn-uNF) was designed via a chemical deposition and alkali etching process. Similar to Cu-laccase, Mn-uNF can oxidize phenols via a one-electron-transfer reaction of Mn(III) and accelerate the MnIII/MnIV state cycle through an unconventional oxygen reduction process. The excellent laccase-like performance of Mn-uNF can be ascribed to the abundant atomically dispersed Vo-assisted Mn(III) and surface -OH species, which was confirmed by characterizations and DFT calculation. Further, a facile dual-function colorimetric platform was designed for array sensing of o-, m-, and p-dihydroxybenzene isomers and one-step discrimination of tetracyclines containing phenol groups. These findings provide reasonable guidance for the design of a nanozyme with active Mn sites as a new family member of highly efficient copper-free laccase mimics.

Study on the synergy effect of MnOx and support on catalytic ozonation of toluene

MnO_x has received widespread attention in low-temperature catalytic oxidation of VOCs, however, the synergy effect of MnO_x and support on the VOCs catalytic ozonation were rarely studied. In this study, five different MnO_x/X (X: MCM-41, 13X, ZSM-5, HY, USY) were synthesized and found their support greatly affect the catalytic oxidation activity. MnO_x/MCM-41 presents the largest specific surface area, pore volume and unique surface morphology, and thereby provides more sites for MnO_x loading and VOCs adsorption. Moreover, MnO_x/MCM-41 presents a high proportion of Mn³⁺, which helps to enhance the ion exchange capability, and thus promotes the regeneration of oxygen vacancies. Furthermore, a part of Mn was proved to be introduced into the MCM-41 lattice, which can promote the electron transfer between the active components and the support, and thereby effectively improve the surface electronic properties of the catalyst. The toluene catalytic experiments showed that MnO_x/MCM-41 exhibited the best catalytic activity, presenting complete degradation of O₃ and VOCs at room temperature. In addition, 5 wt%MnO_x/MCM-41 exhibited better catalytic activity than other loading, and its higher surface oxygen species endowed it with strong water resistance and stability. In-situ DRIFTs indicated that toluene was initially oxidized into benzyl alcohol during the adsorption process, and then decomposed to intermediate products (benzaldehyde, phenolate, etc.) during the catalytic ozonation process, and finally oxidized to carbon dioxide. In conclusion, the supply of loading sites and the improvement of interfacial electron transfer are the manifestations of the synergy between the support and MnO_x, leading to the promotion of the catalytic ozonation of VOCs.

Promotional effects of calcination temperature and H2O on the catalytic activity of Al-substituted MnAlO catalysts for low-temperature acetone oxidation

In order to enhance the role of Al in the materials, Al-substituted MnAlO catalysts were synthesized via the hydrothermal-redox method at different calcination temperatures for acetone oxidation. There were Al-substituted α-MnO₂ and amorphous aluminum oxide existed with homogeneous dispersion of elements in the catalysts. The surface property, reaction rate, CO₂ yield and water resistance of MnAlO catalysts were greatly affected by calcination temperatures. MnAlO-450 catalyst exhibited the best catalytic performance (acetone conversion of 90% at 165 °C) with CO₂ yield higher than 99.7%, which was mainly related to the weaker Mn-O bond strength, lower temperature reducibility and abundant Lewis acid sites. The acetone conversion of MnAlO-450 increased by as much as 16% in the presence of 1 vol% H₂O compared to that in the absence of H₂O at T₅₀ (the temperature for 50% conversion of acetone). The acceleration consumption of ethanol as the main by-product by H₂O improved the catalytic performance. This work would shed light on the Al substitution based catalysts for OVOC oxidation with highly efficient and water resistance.

Efficient catalytic degradation of toluene at a readily prepared Mn-Cu catalyst: Catalytic performance and reaction pathway

Fabricating of economical transitional metal oxide-based materials with satisfied low-temperature catalytic performance and application perspective is still a challenge in deep degradation of VOCs. Here, Mn-Cu bimetallic oxides were facilely prepared by one-step hydrothermal-redox method, which displayed much higher catalytic activity in toluene oxidation than those synthesized by hydrolysis-driven redox-precipitation or co-precipitation approach. It is shown that the lattice defect and oxygen vacancy concentration over prepared materials can be tuned by controlling Cu/Mn molar ratio. Amongst, spinel structured MnCu_0.5 exhibited the highest catalytic activity, superior durability and water resistance in toluene total oxidation owing to abundant surface adsorbed oxygen species, excellent low-temperature reducibility, and high amounts of Cu⁺ and Mn³⁺. In detail, the reaction rate of MnCu_0.5 was over 9.0 times higher than that of MnCu_0.75, MnCu_0.75-P and MnCu_0.75-H₂O₂ at relative low temperature of 210 °C. The cyclic redox process with easier oxygen species mobility played a key role in the catalytic oxidation of toluene. Typical reaction intermediates as benzyl alcohol, benzaldehyde, benzene, phenol, and benzoquinone could be detected by PTR-MS, which further decomposed to acetone, ethanol, ketone, acetic acid, methanol, formaldehyde and acetaldehyde species by ring opening before total mineralization.