Low-temperature catalytic combustion of methane over MnO x –CeO2 mixed oxide catalysts: Effect of preparation method

Synergy effect of CuO on CuCo2O4 for methane catalytic combustion

Spinel oxides (AB₂O₄) have been widely studied as catalysts for methane combustion. Increasing attention was focused on the catalysis properties of the [B₂O₃] octahedron; however, the role of the [AO] tetrahedron in the catalytic activity was seldom discussed. Herein, a series of (CuO)_x–CuCo₂O₄ (x = 0, 0.1, 0.2) composite oxides were synthesized by a solvothermal method. The structure, morphology, and physicochemical properties of the as-synthesized samples were characterized by the XRD, SEM, BET, and XPS techniques. The results of the catalytic activity tests showed that the coexistence of CuO with CuCo₂O₄ can improve the catalytic activity. The XPS results demonstrated that there were remarkable Cu⁺ ions present in the composite oxides, which can cause increases in the number of oxygen vacancies on the surface of the catalysts. In addition, the redox of Cu⁺ and Cu²⁺ may improve the oxygen exchange capacity for methane oxidation.

CuO and CuCo₂O₄ exhibit a synergistic effect in catalyzing methane combustion, which increases the oxidation rate of methane on the surface of (CuO)_0.2–CuCo₂O₄ composite oxide and decreasing the methane combustion temperature.

Recovery of cathode materials from spent lithium-ion batteries and their application in preparing multi-metal oxides for the removal of oxygenated VOCs: Effect of synthetic methods

Due to the sustainable use of wastes, cathode materials of spent lithium-ion batteries are recovered and used as transition metal precursors to prepare metal oxides catalysts for the oxidation of VOCs. In this work, a series of manganese-based and cobalt-based metal oxides are synthesized via different preparation methods. Catalytic activities of the catalysts prepared are investigated through complete oxidation of oxygenated VOCs and the physicochemical properties of optimum samples are characterized. Evaluation results indicate that MnOx (SY) (HT) sample prepared via hydrothermal method and CoOx (GS) (CP) synthesized via co-precipitation method had better performance, because they have higher specific surface area, higher concentration of active oxygen species and high-valence metal ion, as well as better low-temperature reducibility compared to the other multi-metal oxides used in the study. In addition, TD/GC-MS results imply that further oxidation of by-products requires high reaction temperature during VOCs oxidation.

Methane Combustion Using Pd Deposited on CeOx-MnOx/La-Al2O3 Pellistors

Pd deposited on CeO_x-MnO_x/La-Al₂O₃ has been prepared as a sensitive material for methane (CH₄) detection. The effect of different amounts (1.25%, 2.5% and 5%) of Pd loading has been investigated. The as prepared materials were deposited on Pt microcoils using a drop-coating method, as a way of developing pellistors operated using a Wheatstone bridge configuration. By spanning the operating temperature range between 300 °C and 550 °C, we established the linearity region as well as the maximum sensitivity towards 4900 ppm of CH₄. By making use of the sigmoid dependence of the output voltage signal from the Wheatstone bridge, the gas surface reaction and diffusion phenomena have been decoupled. The pellistor with 5% Pd deposited on CeO_x-MnO_x/La-Al₂O₃ exhibited the highest selective-sensitivity in the benefit of CH₄ detection against threshold limits of carbon monoxide (CO), sulfur dioxide (SO₂) and hydrogen sulfide (H₂S). Accordingly, adjusting the percent of Pd makes the preparation strategies of pellistors good candidates towards CH₄ detection.

Promotional removal of oxygenated VOC over manganese-based multi oxides from spent lithium-ions manganate batteries: Modification with Fe, Bi and Ce dopants

In this work, cathode materials of spent lithium-ions manganate batteries are recovered as the precursor of manganese-based oxides catalysts and furthermore, different amount of Fe, Bi, Ce are introduced to modify their properties. A series of MnOx(MS)-X Fe, MnOx(MS)-X Bi and MnOx(MS)-X Ce samples with crystal phase of Mn₅O₈ are synthesized using combustion method and then the catalytic behavior and physicochemical properties of prepared catalysts are investigated. Compared to binary MnOx-5% Fe, MnOx-15% Bi and MnOx-10% Ce samples, multi MnOx(MS)-5% Fe, MnOx(MS)-15 Bi and MnOx(MS)-10% Ce catalysts display enhanced catalytic performance significantly in the removal of oxygenated VOC, which could be attributed to larger specific surface area, higher concentration of surface active oxygen species and Mn⁴⁺ ions and better reducibility at low temperature. In-situ DRIFTS results imply that main oxygen-containing functional groups such as carbonyl (-C=O), carboxyl (-COO), hydroxyl (-OH) can be observed during VOC oxidation and by comparison, it can be found that gas-phase O₂ plays a crucial role in facilitating the further oxidation of by-products into CO₂. In addition, TD/GC-MS results point out that the main by-products are formaldehyde; 2-propanol, 1-methoxy-; ethanol, 2-methoxy-, acetate; 2-ethoxyethyl acetate; acetic acid during VOC oxidation.

Bulk Versus Surface Modification of Alumina with Mn and Ce Based Oxides for CH4 Catalytic Combustion

This study presents the synthesis and characterization of lanthanum-modified alumina supported cerium–manganese mixed oxides, which were prepared by three different methods (coprecipitation, impregnation and citrate-based sol-gel method) followed by calcination at 500 °C. The physicochemical properties of the synthesized materials were investigated by various characterization techniques, namely: nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and H₂–temperature programmed reduction (TPR). This experimental study demonstrated that the role of the catalytic surface is much more important than the bulk one. Indeed, the incipient impregnation of CeO₂–MnO_x catalyst, supported on an optimized amount of 4 wt.% La₂O₃–Al₂O_3, provided the best results of the catalytic combustion of methane on our catalytic micro-convertors. This is mainly due to: (i) the highest pore size dimensions according to the Brunauer-Emmett-Teller (BET) investigations, (ii) the highest amount of Mn⁴⁺ or/and Ce⁴⁺ on the surface as revealed by XPS, (iii) the presence of a mixed phase (Ce₂MnO₆) as shown by X-ray diffraction; and (iv) a higher reducibility of Mn⁴⁺ or/and Ce⁴⁺ species as displayed by H₂–TPR and therefore more reactive oxygen species.

Preparation of a monolith MnOx–CeO2/La–Al2O3 catalyst and its properties for catalytic oxidation of toluene

The catalyst DP-MnCe prepared by the deposition–precipitation method has the best catalytic activity for toluene oxidation.

Sphere-Shaped Mn3O4 Catalyst with Remarkable Low-Temperature Activity for Methyl-Ethyl-Ketone Combustion

Mn₃O₄, FeMnO_x, and FeO_x catalysts synthesized via a solvothermal method were employed for catalytic oxidation of methyl-ethyl-ketone (MEK) at low temperature. Mn₃O₄ with sphere-like morphology exhibited the highest activity for MEK oxidation, over which MEK was completely oxidized to CO₂ at 200 °C, and this result can be comparable to typical noble metal loaded catalysts. The activation energy of MEK over Mn₃O₄ (30.8 kJ/mol) was much lower than that of FeMnO_x (41.5 kJ/mol) and FeO_x (47.8 kJ/mol). The dominant planes, surface manganese species ratio, surface-absorbed oxygen, and redox capability played important roles in the catalytic activities of catalysts, while no significant correlation was found between specific surface area and MEK removal efficiency. Mn₃O₄ showed the highest activity, accounting for abundant oxygen vacancies, low content of surface Mn⁴⁺ and strong reducibility. The oxidation of MEK to CO₂ via an intermediate of diacetyl is a reaction pathway on Mn₃O₄ catalyst. Due to high efficiency and low cost, sphere-shaped Mn₃O₄ is a promising catalyst for VOCs abatement.

A reusable material with high performance for removing NO at room temperature: performance, mechanism and kinetics

Removing NO from the air with a reusable material at room temperature is challenging.

Mesoporous Mn- and La-doped cerium oxide/cobalt oxide mixed metal catalysts for methane oxidation

New precious-metal-free mesoporous materials were investigated as catalysts for the complete oxidation of methane to carbon dioxide. Mesoporous cobalt oxide was first synthesized using KIT-6 mesoporous silica as a hard template. After removal of the silica, the cobalt oxide was itself used as a hard template to construct cerium oxide/cobalt oxide composite materials. Furthermore, cerium oxide/cobalt oxide composite materials doped with manganese and lanthanum were also prepared. All of the new composite materials retained the hierarchical long-range order of the original KIT-6 template. Temperature-programmed oxidation measurements showed that these cerium oxide/cobalt oxide and doped cerium oxide/cobalt oxide materials are effective catalysts for the total oxidation of methane, with a light-off temperature (T50%) of ∼400 °C observed for all of the nanostructured materials.

Flower-Like Mn-Doped CeO2Microstructures: Synthesis, Characterizations, and Catalytic Properties

Mn-doped CeO2flower-like microstructures have been synthesized by a facile method, involving the precipitation of metallic alkoxide precursor in a polyol process from the reaction of CeCl3·7H2O with ethylene glycol in the presence of urea followed by calcination. By introducing manganese ions, the composition can be freely manipulated. To investigate whether there was a hybrid synergic effect in CH4combustion reaction, further detailed characteristics of Mn-doped CeO2with various manganese contents were revealed by XRD, Raman, FT-IR, SEM, EDS, XPS, OSC, H2-TPR, and N2adsorption-desorption measurements. The doping manganese is demonstrated to increase the storage of oxygen vacancy for CH4and enhance the redox capability, which can efficiently convert CH4to CO2and H2O under oxygen-rich condition. The excellent catalytic performance of MCO-3 sample, which was obtained with the starting Mn/Ce ratios of 0.2 in the initial reactant compositions, is associated with the larger surface area and richer surface active oxygen species.