MCM-41 Supported Cu−Mn Catalysts for Catalytic Oxidation of Toluene at Low Temperatures

Mesoporous Silica MCM-41 from Fly Ash as a Support of Bimetallic Cu/Mn Catalysts for Toluene Combustion

The main outcome of this research was to demonstrate the opportunity to obtain a stable and well-ordered structure of MCM-41 synthesized from fly ash. A series of bimetallic (Cu/Mn) catalysts supported at MCM-41 were prepared via grinding method and investigated in catalytic toluene combustion reaction to show the material's potential application. It was proved, that the Cu/Mn ratio had a crucial effect on the catalytic activity of prepared materials. The best catalytic performance was achieved with sample Cu/Mn(2.5/2.5), for which the temperature of 50% toluene conversion was found to be 300 °C. This value remains in line with the literature reports, for which comparable catalytic activity was attained for 3-fold higher metal loadings. Time-on-stream experiment proved the thermal stability of the investigated catalyst Cu/Mn(2.5/2.5). The obtained results bring a valuable background in the field of fly ash utilization, where fly ash-derived MCM-41 can be considered as efficient and stable support for dispersion of active phase for catalyst preparation.

Recent advances in the routes and catalysts for ethanol synthesis from syngas

Ethanol, as one of the important bulk chemicals, is widely used in modern society. It can be produced by fermentation of sugar, petroleum refining, or conversion of syngas (CO/H₂). Among these approaches, conversion of syngas to ethanol (STE) is the most environmentally friendly and economical process. Although considerable progress has been made in STE conversion, control of CO activation and C-C growth remains a great challenge. This review highlights recent advances in the routes and catalysts employed in STE technology. The catalyst designs and pathway designs are summarized and analysed for the direct and indirect STE routes, respectively. In the direct STE routes (i.e., one-step synthesis of ethanol from syngas), modified catalysts of methanol synthesis, modified catalysts of Fischer-Tropsch synthesis, Mo-based catalysts, noble metal catalysts and multifunctional catalysts are systematically reviewed based on their catalyst designs. Further, in the indirect STE routes (i.e., multi-step processes for ethanol synthesis from syngas via methanol/dimethyl ether as intermediates), carbonylation of methanol/dimethyl ether followed by hydrogenation, and coupling of methanol with CO to form dimethyl oxalate followed by hydrogenation, are outlined according to their pathway designs. The goal of this review is to provide a comprehensive perspective on STE technology and inspire the invention of new catalysts and pathway designs in the near future.

Effects of the Reaction Parameters and Light Hydrothermal Aging for Catalytic Combustion of Propane over Co-Mn-Ce Catalyst

A composite oxides’ Co-Mn-Ce catalyst was synthesized by a coprecipitation method, and the experiment was carried out to study the effects of reaction parameters and light hydrothermal aging on propane combustion over the Co-Mn-Ce catalyst. The influence of reaction temperature, propane concentration, oxygen concentration, water vapor, and hydrothermal aging was studied during the catalytic combustion of propane. The propane conversion significantly decreased by 10% when the propane concentration increased at 300°C and then further decreased from 80% to 40% as water vapor concentration increased from 0 to 10 vol.%. In addition, water vapor also prolonged the time required to reach equilibrium. After hydrothermal treatment, the catalyst obtained the lowest oxidation capacity of propane. Furthermore, the results of in situ DRIFTs and O2 temperature programmed desorption (O2-TPD) demonstrated that there were fewer oxygen species after hydrothermal aging, and carbonates were the main intermediates formed during the catalytic oxidation of propane.

Mn(CeZr)Ox chelation-induced synthesis and its hydrothermal aging characteristics for catalytic abatement of toluene

In this work, Mn(CeZr)O_x was synthesized by using chelation-induced synergistic self-assembly strategy for the combustion of toluene. The physicochemical properties of the synthesized catalysts were characterized by XRD, ICP-MS, SEM, TEM, XPS and N₂ sorption. The Mn(CeZr)O_x catalyst with T₉₀ = 225 °C exhibited improved catalytic performance than the original MnO_x catalyst (T₉₀ = 260 °C) and had significant low-temperature activity. The relationship between catalyst activity and structure was analyzed. By substituting Ce and Zr elements into the hollow microspheres of MnO₂, oxygen vacancies were produced. The main factors affecting the catalytic activity of the catalyst and the reason why it remained high catalytic activity after a long period of hydrothermal treatment were discussed. After hydrothermal aging, the original pore structure of Mn(CeZr)O_x catalyst collapsed and the specific surface area decreased, but the overall crystallinity of the catalyst increased and the content of oxygen species in the lattice increased. The distribution of Mn and oxygen species on the catalyst surface changed significantly after hydrothermal treatment. The appropriate ratio of Mn⁴⁺ to Mn³⁺ and the ratio of lattice oxygen to adsorbed oxygen species are beneficial to the redox reaction cycle.

Catalytic removal of toluene over manganese oxide-based catalysts: a review

It is necessary to control the emissions of toluene, which is hazardous to both human health and the atmosphere environment and has been classified as a priority pollutant. Manganese oxide-based (Mn-based) catalysts have received increased attention due to their high catalytic performance, good physicochemical characteristic, availability in various crystal structures and morphologies, and being environmentally friendly and low cost. These catalysts can be classified into five categories, namely single manganese oxide, Mn-based composite oxides, Mn-based special oxides, supported Mn-based oxides, and Mn-based monoliths. This review focused on the recent progress on the five types of Mn-based catalysts for catalytic removal of toluene at low temperature and further systematically summarized the strategies improving catalysts, including improving synthetic methods, incorporating MnO_x with other metal oxides, depositing Mn-based oxides on proper supports, and tuning the supports. Moreover, the effect of coexisting components, the reaction kinetics, and the oxidation mechanisms toward the removal of toluene were also discussed. Finally, the future research direction of this field was presented.

Enhanced catalytic performance for VOCs oxidation on the CoAlO oxides by KMnO4 doped on facile synthesis

The MnO_x was immobilized on the CoAl mixed oxides (CoAlO) derived from hydrotalcites with various anions (CO₃^2-, Cl^-, NO₃^- and SO₄^2-) using the hydration and impregnation methods. The CoAlO oxides modified by KMnO₄ were calcined in air at 300 °C to obtain stable oxides, which could be used as catalysts for VOCs (acetone and ethyl acetate) oxidation. CoAlO with CO₃^2- and 30 h of hydration time (CoAlO-C-Mn-30) exhibited a promising catalytic activity (T₉₀ = 173 °C for acetone oxidation; T₉₀ = 175 °C for ethyl acetate), highly superior to CoAlO without KMnO₄ modification. The improvement in acetone and ethyl acetate catalytic oxidation was ascribed to the Co³⁺ and surface adsorbed oxygen species. The increase of Co³⁺ in the CoAlO-C-Mn-30 oxide thanked to the self-decomposition of KMnO₄ and reducibility of Co²⁺ in the CoAlO oxide during the hydration process. This was also confirmed by XRD and XPS characterization, which showed that Mn cations were enriched on the catalyst surface in the valences of +3 and +4. The catalytic activity of the catalyst remained unchanged in four cycles in the presence of 5.5 vol.% water vapor, which indicated a great potential for industrial application.

The Design of MnOx Based Catalyst in Post-Plasma Catalysis Configuration for Toluene Abatement

This review provides an overview of our present state of knowledge using manganese oxide (MnOx)-based catalysts for toluene abatement in PPC (Post plasma-catalysis) configuration. The context of this study is concisely sum-up. After briefly screening the main depollution methods, the principles of PPC are exposed based on the coupling of two mature technologies such as NTP (Non thermal plasma) and catalysis. In that respect, the presentation of the abundant manganese oxides will be firstly given. Then in a second step the main features of MnOx allowing better performances in the reactions expected to occur in the abatement of toluene in PPC process are reviewed including ozone decomposition, toluene ozonation, CO oxidation and toluene total oxidation. Finally, in a last part the current status of the applications of PPC using MnOx on toluene abatement are discussed. In a first step, the selected variables of the hybrid process related to the experimental conditions of toluene abatement in air are identified. The selected variables are those expected to play a role in the performances of PPC system towards toluene abatement. Then the descriptors linked to the performances of the hybrid process in terms of efficiency are given and the effects of the variables on the experimental outcomes (descriptors) are discussed. The review would serve as a reference guide for the optimization of the PPC process using MnOx-based oxides for toluene abatement.

Effect of Mn doping on the activity and stability of Cu–SiO2catalysts for the hydrogenation of methyl acetate to ethanol

A series ofxMn–Cu–SiO₂catalysts with different manganese contents were prepared by an ammonia-evaporation method for methyl acetate hydrogenation.

Rod-like CuMnOx transformed from mixed oxide particles by alkaline hydrothermal treatment as a novel catalyst for catalytic combustion of toluene

Rod-like copper manganese mixed oxides by alkaline hydrothermal treatment exhibit superior catalytic activity toward toluene combustion at 210 °C.