Search Results (118)

Metal–organic frameworks (MOFs) have become a hot topic in various research fields nowadays. And MOF-derived metal oxides prepared by the sacrificial template method have been widely applied as catalysts for pollutant removal. Accordingly, we prepared a series of MOF-derived MnO_x catalysts with diverse morphologies (rod-like, flower-like, slab-like) via the pyrolysis of MOF precursors, and the as-prepared MnO_x catalysts demonstrated superior performance compared to the one prepared using the co-precipitation method. MnO_x-II, with a flower-like structure, exhibited excellent activity for formaldehyde (HCHO) catalytic ozonation at room temperature, reaching complete HCHO conversion at O₃/HCHO of 1.5 and more than 90% CO₂ selectivity at an O₃/HCHO ratio of 2.5. On the basis of various characterization methods, it was clarified that the enhanced catalytic performance of MnO_x-II benefited from its larger BET surface area, abundant oxygen vacancies, better redox ability at lower temperature, and more Lewis acid sites. The H₂O resistance and stability tests were also conducted. Furthermore, DFT calculations substantiated the enhanced adsorption of HCHO and O₃ on oxygen vacancies, while in–situ DRIFTS measurements elucidated the degradation pathway of HCHO during catalytic ozonation through detected intermediates. Full article

A series of Cu-MnO_x/GF catalytic electrodes, with graphite felt (GF) pretreated via microwave modification as the catalyst carrier, were prepared under various hydrothermal conditions and characterized using X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, and Raman spectroscopy. The catalytic oxidation activity of catalytic Cu-MnO_x/GF electrodes toward toluene was evaluated in an all-solid-state electrocatalytic device under mild operating conditions. The evaluation results demonstrated that the microwave-modified catalytic electrode exhibited high electrocatalytic activity toward toluene oxidation, with Cu-MnO_x/700W-GF exhibiting significantly higher catalytic activity, indicating that an increase in catalyst loading capacity can promote the removal of toluene. Only CO₂ and CO were detected, with no other intermediates observed in the reaction process. Moreover, the catalytic effect was significantly affected by the relative humidity. The catalytic oxidation of toluene can be fully realized under a certain humidity, indicating that the conversion of H₂O to strongly oxidizing ·OH on the catalytic electrode is a key step in this reaction. Full article

The aim of this work was the preparation of ceramic monolithic catalysts for the catalytic oxidation of gaseous mixture of benzene, toluene, ethylbenzene and o-xylene BTEX. The possibility of using zirconium dioxide (ZrO₂) as a filament for the fabrication of 3D-printed ceramic monolithic carriers was investigated using fused filament fabrication. A mixed manganese and iron oxide, MnFeO_x, was used as the catalytically active layer, which was applied to the monolithic substrate by wet impregnation. The approximate geometric surface area of the obtained carrier was determined to be 53.4 cm², while the mass of the applied catalytically active layer was 50.3 mg. The activity of the prepared monolithic catalysts for the oxidation of BTEX was tested at different temperatures and space times. The results obtained were compared with those obtained with commercial monolithic catalysts made of ceramic cordierite with different channel dimensions, and with monolithic catalysts prepared by stereolithography. In the last part of the work, a kinetic analysis and the modeling of the monolithic reactor were carried out, comparing the experimental results with the theoretical results obtained with the 1D pseudo-homogeneous and 1D heterogeneous models. Although both models could describe the investigated experimental system very well, the 1D heterogeneous model is preferable, as it takes into account the heterogeneity of the reaction system and therefore provides a more realistic description. Full article

The production of formic acid (FA) from lignocellulose and its derived sugars represents a pivotal upgrading reaction in biorefinery. This work prepared a Mn-Mo doped carbon nanotube composite catalyst for the catalytic oxidation of glucose into FA in an O₂ atmosphere, under extremely low Mn (3.27%) and Mo (0.40%) loading conditions, displaying a comparable performance with the traditional vanadium-based catalyst suffering from toxicity issues. It was confirmed that the doping of Mo led to the formation of MnMoO_X and increased the contents of low-valence Mn species (Mn²⁺ + Mn³⁺), lattice oxygen (O_latt), and surface adsorbed oxygen (O_ads) based on various characterization methods, such as XRD, XPS, TEM and ICP, which were beneficial to improve the catalytic performance. The maximum FA yield of 58.8% could be achieved over Mn₉Mo₁O_X@MWCNT after reaction for 6 h at 140 °C, which was far more than that obtained with undoped MnO_X@MWCNT (14.5%) at the identical conditions. Glyoxylic acid and arabinose were identified as two main intermediates, suggesting that the transformation of glucose into FA over Mn₉Mo₁O_X@MWCNT involved two different paths. This work proved that manganese-based catalyst was a green alternative for upgrading lignocellulose via catalytic oxidation. Full article

Chemical–structural characteristics of three differently synthesized research-benchmark Mn-Na-W-O_x/SiO₂ catalysts for the Oxidative Coupling of Methane (OCM) were systematically studied in this research. XRD, EDX, ICP-OES, and SEM/FIB-SEM techniques, as well as Carrier Gas Hot Extraction (CGHE) and high-temperature XRD analyses, were performed to explain the functional features of the studied catalysts, in particular, the features affecting the quantity and quality of the interactions of oxygen and methane with the catalyst surface and with other molecular and radical species. These enable tracking the potential for the oxygen activation and dynamic transformation of the solid-state chemistry on the surface and sub-surface of these Mn-Na-W-O_x/SiO₂ catalysts. These catalysts were synthesized, respectively, via the sol–gel synthesis method (Cat₁) and the incipient wetness impregnation of the non-structured silica support (Cat₂) and structured SBA-15 silica support (Cat₃), under different sets of temperatures and gas compositions. The catalysts with the homogenous distribution of active components, namely Cat₁ and Cat₃, showed similar trends in terms of their dynamic interaction with oxygen species. They also showed higher levels of crystallinity of the active materials and higher catalytic selectivity towards ethane and ethylene. An explanation is given as to how the structural characteristics of the catalysts on the nanometer–micrometer scale contribute to these. The gained knowledge will be crucial in the selection and treatment of the support and developing a proper synthesis approach for the ultimate goal of designing a selective OCM catalyst. Full article

A metal-doped modified CO oxidation catalyst with strong adsorption and water resistance for coalbed methane was prepared by the CO precipitation method. The CO ablation characteristics were tested, and the Cu Mn catalyst synthesized by metal Ce doping achieved an instantaneous ablation efficiency of 80% when in contact with CO at room temperature. By analyzing the surface crystal structure and pore characteristics, as well as by testing the ablation properties, it was found that the CO oxidation catalyst synthesized by Ce had the best effect at a precipitation temperature of 70 °C. A water-resistant CO oxidation catalyst was synthesized by adding polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). After storage at a relative humidity of 90%, it still had a CO adsorption rate of about 85%. The water-resistant CO oxidation catalyst prepared with polyvinyl alcohol (PVA) as an additive had a higher content of CeO₂ crystal nuclei, and the PVA-added CO oxidation catalyst had the best ablation characteristics. In the evaluation of the water-resistant steam ablation process, the CuMnO_x-Ce-PVA catalyst showed a significant increase in intermediate products during the stress process under water vapor conditions and a decrease in the peak value of the catalyst’s binding to water, and the catalyst has a particular inhibitory influence on the adsorption of water molecules on its surface. Due to its outstanding water resistance, the catalyst was able to retain good ablation characteristics. Full article

With the rapid growth of the sauce-flavored liquor industry, the treatment of wastewater has become an increasingly critical challenge. This study seeks to assess the catalytic oxidation efficacy of Mn₂Cu₂O_x/Al₂O₃ catalysts in the degradation of organic pollutants present in sauce-flavored liquor wastewater, while also elucidating the mechanisms underpinning their performance. Mn₂Cu₂O_x/Al₂O₃ catalysts were synthesized, and their physicochemical properties were thoroughly characterized using advanced techniques such as Brunauer–Emmett–Teller (BET) analysis, N₂ sorption isotherm analysis, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Moreover, the key active species involved in the catalytic oxidation process, including hydroxyl radicals (•OH) and superoxide anion radicals (•O₂⁻), were identified through hydroxyl radical quenching experiments employing tertiary butyl alcohol (TBA). The contribution of these free radicals to enhancing the ozone catalytic oxidation performance was also systematically evaluated. Based on both experimental data and theoretical analyses, the Mn₂Cu₂O_x/Al₂O₃ catalysts demonstrate remarkable catalytic activity and stability, significantly reducing chemical oxygen demand (COD) levels in wastewater. Furthermore, the catalysts are capable of activating oxygen molecules (O₂) during the reaction, producing reactive oxygen species, such as •O₂⁻ and •OH, which are potent oxidizing agents that effectively decompose organic pollutants in wastewater. The proposed catalysts represent a highly promising solution for the treatment of sauce-flavored liquor wastewater and lays a solid foundation for its future industrial application. Full article

K/MnO_x catalysts on MnO₂ and Fe₃O₄ supports were synthesized and compared for the deep oxidation of cyclohexane. The presence of potassium (K) on the catalysts enhanced the catalytic activity compared to catalysts with similar composition but without K. Interestingly, the lowest loading of K/MnO_x used in this study (0.63 mmoles/g support) performed better than those with higher loadings. The presence of K on the catalysts increased water adsorption, decreased the extent of sintering, and inhibited changes in crystal phase of the catalyst support, as evidenced by TGA, XRD, and BET surface area analyses. The XRD profiles of the catalysts showed mixed crystal phases of MnO_x and FeO_x species, and EPR results support the presence of mixed valence states of Fe and Mn. The activation energies for MnO_x-supported catalysts and FeO_x-supported catalysts were approximately 50 kJ/mole and 53 kJ/mole, respectively. Full article

Manganese-based oxides with good redox properties exhibit high soot oxidation activity. To further enhance their catalytic performance, introducing additional metal elements into manganese-based oxides is considered an effective approach. Herein, two rare earth elements (Sm and Ce)-modified MnO_x catalysts were prepared by the co-precipitation method. The synthesized MnO_x catalyst primarily consists of the Mn₃O₄ phase, with trace amounts of Mn₅O₈. The addition of Sm or Ce maintains the predominance of the Mn₃O₄ phase, increases the proportion of Mn₅O₈, and enhances the redox properties, thereby boosting the catalytic activity for NO and soot oxidation. Notably, the coexistence of Sm and Ce achieves optimal soot oxidation activity, with T₁₀ reaching 306 °C. Comprehensive physicochemical characterization elucidates the underlying structure–performance relationships of these catalysts. Full article

In this work, ceramic monolithic catalyst carriers based on zirconium dioxide (ZrO₂) were produced using fused filament fabrication (FFF). The active catalyst components were deposited on the resulting carriers using the wet impregnation method. The activity of the prepared monolithic catalysts was evaluated by catalytic oxidation of a mixture of aromatic volatile organic compounds: benzene, toluene, ethylbenzene, and o-xylene (BTEX). The efficiency of the prepared monolithic catalysts was investigated as a function of the geometry of the monolithic carrier (ZDP, Z, and M) and the chemical composition of the catalytically active component (MnFeO_x, MnCuO_x, and MnNiO_x) during the catalytic oxidation of BTEX compounds. The mechanical stability of the catalyst layer and the dimensional stability of the 3D-printed monolithic catalyst carriers were investigated prior to the kinetic measurements. In addition, thorough characterization of the commercial ZrO₂-based filament was carried out. The results of the efficiency of the prepared monolithic catalysts for the catalytic oxidation of BTEX showed that the 3D-printed model M, which contained MnFeO_x as the catalytically active component, was the most successful catalyst for the oxidation of BTEX compounds. The mentioned catalyst enables the catalytic oxidation of all components of the BTEX mixture (>99% efficiency) at a temperature of 177 °C. Full article

Four differently shaped monolithic catalyst supports were made using 3D printing technology. Two catalytically active mixed oxides, MnFeO_x and MnCuO_x, were applied to the monolithic supports using the impregnation technique. Catalysts were characterized using an adhesion test, field emission scanning electron microscopy, X-ray diffraction, and Raman spectroscopy in a manner similar to the density functional theory model. Excellent mechanical stability of the catalyst layer was obtained, with catalyst mass loss under 2% after 30 min of ultrasound exposure. SEM analysis revealed that the catalyst layer was rough but homogeneous in appearance and ~6 μm thick. The presence of double oxides—FeMnO₃ and CuMn₂O₄—as well as single oxides of Mn, Fe, and Cu was established via XRD and Raman spectroscopy. Additional theoretical calculations of Raman spectra for FeMnO₃ and CuMn₂O₄ were performed in order to aid in the interpretation of Raman spectra. The catalytic activity of the prepared catalysts for the catalytic oxidation of a gaseous mixture of benzene, toluene, ethylbenzene, and o-xylene (BTEX) was investigated. The monolithic support with the most complex shape and, consequently, the greatest surface area proved to enable the highest efficiency, while both catalysts performed well having similar conversions. Full article

In this work, the origin of the synergetic effect in mixed Mn_xCo_3-xO₄ oxides with the spinel structure in the CO oxidation reaction was tested. A series of Mn_xCo_3-x oxide catalysts were synthesized by the coprecipitation method with further calcination at 600 °C and varying manganese content from x = 0 to x = 3. The catalysts were characterized using XRD, TEM, N₂ adsorption, TPR, EXAFS, and XPS. The catalytic activity of Mn_xCo_3-x oxide catalysts was tested in CO oxidation reactions. The addition of manganese to cobalt oxide results in the formation of mixed Mn-Co oxides based on a cubic or tetragonal spinel structure, a change in microstructural properties, such as surface area and crystal size, as well as local distortions and a decrease in the surface concentration of Co ions and Co in the octahedral sites in spinel structure; it also decreases catalyst reducibility. For all catalysts, the activity of CO oxidation decreases as follows: Mn_0.1Co_2.9 > Co₃O₄~Mn_0.3Co_2.7 > Mn_0.5Co_2.5 > MnO_x > Mn_0.7Co_2.3 > Mn_0.9Co_2.1~Mn_1.1Co_1.9~Mn_2.5Co_0.5 > Mn_2.9Co_0.1 > Mn_1.7Co_1.3 > Mn_2.1Co_0.9 > Mn_1.3Co_1.7~Mn_1.5Co_1.5~Mn_2.3Co_0.7. The Mn_0.1Co_2.9 catalyst displays the best catalytic activity, which is attributed to its small crystal size and the maximum surface ratio between Co³⁺ and Co²⁺. A further increase in the manganese content (x > 0.3) provokes drastic changes in the catalytic properties due to a decrease in the cobalt content on the surface and in the volume of mixed oxide, changes in the oxidation states of cations, and structure transformation. Full article

The conversion of NO_x and the yield of N₂O during NH₃-SCR-DeNO_x below 473 K over TiO₂-supported transition metal oxide catalysts with equal loading of 20 wt.-% decreases in the following order of the supported oxides: MnO_x > CuO_x > CoO_x > FeO_x > NiO_x > CeO_x. The storage capacity for NH₃, characterized by the acid site density of the catalyst, is not directly correlated with the catalytic activity. Rather, the temperature range for the reduction of the supported transition metal oxides as determined by TPR-H₂ is the main governing factor for high NH₃-SCR-DeNO_x activity, especially in the temperature range below 473 K. At the same time, oxidation temperature range and the density of Lewis acid sites govern the formation of N₂O. The decomposition of NH₄NO₃ as an intermediate in the NH₃-SCR-DeNO_x reaction is determined by the redox property of TMO-based catalysts, which further influences both the windows of the decomposition temperature and the yield of N₂O. The correlation between the redox properties and the activity for NH₃-SCR-DeNO_x was confirmed for a series of MnO_x-CeO_x/TiO₂-SiO₂ mixed transition metal oxide catalysts as a promising combination of the less active and more selective CeO_x with less selective and highly active MnO_x. The linear correlation between reduction temperature range and the NH₃-SCR-DeNO_x activity indicates that the found relation can be transferred to other supported transition metal-containing catalysts for low-temperature NH₃-SCR-DeNO_x. Full article

Rice husk, a byproduct of rice production, poses significant environmental challenges due to disposal issues, while the emission of volatile organic compounds into the atmosphere further exacerbates these concerns. This study addresses both problems by exploring the potential of texturally enhanced SiO₂, derived from Uruguayan rice husk, as a catalytic support for manganese oxides in the combustion of volatile organic compounds. SiO₂ was synthesized from rice husk ash using a sustainable, acid-free pretreatment method, yielding a notably high silica purity of 96.5%—a level comparable to or exceeding previously reported values, highlighting the high silica quality inherent in Uruguayan rice husk. The catalytic activity was evaluated using acetone as a model volatile organic compound, achieving up to 90% conversion with 30 wt.% manganese oxide at 300 °C, with CO₂ as the primary product. Furthermore, a 24 h stability test demonstrated consistent performance, maintaining a conversion rate of around 95.6 ± 2.5%. These findings suggest that high-purity SiO₂ derived from Uruguayan rice husk, with its sustainability benefits, offers an effective solution for acetone removal when supporting an active phase such as manganese oxides, addressing both rice husk disposal and volatile organic compound emissions. Full article

Formaldehyde (HCHO) is known as one of the important indoor organic pollutants. How to remove and decompose the low concentration of formaldehyde at room temperature is important for indoor environments. Catalytic ozonation is an efficient method to thoroughly remove HCHO at room temperature, with high efficiency and few byproducts. A series of MnO_x/γ-Al₂O₃ catalysts were prepared in this work via the impregnation method and treated with different reagents (acid, alkali, and H₂O₂) to evaluate their catalytic activity for HCHO removal. The results showed that MnAl-II (acid treatment) performed well in activity tests, reaching a nearly 100% HCHO conversion at an O₃/HCHO of 2.0 and attaining a CO₂ selectivity of above 95% at an O₃/HCHO of 3.0 at 30 °C, with almost no ozone residual existing. The larger specific surface area, abundant oxygen vacancies, and higher number of acid sites contributed to the excellent performance of MnAl-II. Stability and H₂O resistance tests of MnAl-II were also conducted. To reveal the intermediate product formation and further investigate the reaction mechanism of HCHO ozonation, in-situ DRIFTS measurement was carried out combined with DFT calculations. Full article