Search Results (47)

In zinc electrowinning, industrial Pb-Ag anodes have inherent limitations, including high oxygen evolution overpotential and rapid corrosion. This study constructs Ti-Ti₂N-PbO₂-CeMnO_x composite anodes to overcome these shortcoming, Electrochemical characterization revealed enhanced performance with a reduced overpotential (725 mV 50 mA cm⁻²) and lower Tafel slope (102.92 mV dec⁻¹) in the standard zinc electrowinning electrolyte, indicating faster oxygen evolution kinetics compared to commercial benchmarks. Analysis of the XPS test revealed an increase in the content of Mn³⁺, which helps enhance the OER catalytic activity of the electrode. The Ti/Ti₂N/α/β-PbO₂-CeMnO_x (abbreviation: CMO) composite anode exhibited superior corrosion resistance with an extended service life of 53 h under accelerated polarization at 2 A cm⁻². This durability enhancement is attributed to the combined effects of the Ti₂N interlayer and CMO incorporation, which effectively mitigate anode degradation through passivation inhibition. The developed fabrication strategy enables the production of dimensionally stable anodes (DSAs) with balanced electrocatalytic activity and operational stability, showing promising potential for industrial zinc electrowinning applications. 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

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

Poor selectivity is one of the main bottlenecks restricting the development of metal oxide semiconductor (MOS) sensors. In this paper, using hydrogen cyanide (HCN) as the target gas, CeMnOx as the catalytic layer material and Pt@SnO₂ as the gas-sensitive layer material, we have proposed a scheme to improve the selectivity of a catalytic layer/gas-sensitive layer-laminated MOS sensor under dynamic temperature modulation. We tested HCN and 12 kinds of battlefield environment simulation gases, and the results showed that the CeMnOx/Pt@SnO₂ sensor, under the condition of temperature dynamic modulation (a constant temperature of 400 °C for the gas-sensitive layer and a variable temperature of room temperature to 400 °C for the catalytic layer; the heating and cooling rates were 200 °C/s, the highest temperature was maintained for 2 s, and the lowest temperature was maintained for 2 s), distinct characteristic peaks appeared on the G-T curves of the resistance response to HCN only. The quantification of the characteristic peaks was performed by peak heights, and the peak height of 5 mg/m³ HCN was obtained up to 0.104, while the peak heights of the other gases at the same concentration were up to 0.034. The peak height of HCN was significantly higher than that of other gases, which verified the high selectivity of the sensor for HCN. Meanwhile, the sensor also showed good sensitivity, response/recovery time, stability and anti-interference for HCN under the above temperature dynamic modulation. This work provides an important reference for the selectivity improvement of MOS sensors for HCN. 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

Batch heterogeneous catalytic ozonation experiments were performed using commercial and synthesized nanoparticles as catalysts in aqueous ozone. The transferred ozone dose (TOD) ranged from 0 to 150 μM, and nanoparticles were added in concentrations between 0 and 1.5 g L⁻¹, with all experiments conducted at 20 °C and a total volume of 240 mL. A Ce-doped TiO₂ catalyst (1% molar ratio of Ce/Ti) was synthesized via the sol–gel method. Response surface methodology (RSM) was applied to identify the most significant factors affecting the removal of selected pharmaceuticals, with TOD emerging as the most critical variable. Higher TOD resulted in greater removal efficiencies. Furthermore, it was found that the commercially available metal oxides α-Al₂O₃, Mn₂O₃, TiO₂, and CeO₂, as well as the synthesized CeTiO_x, did not increase the catalytic activity of ozone during the degradation of ibuprofen (IBF) and para-chlorobenzoic acid (pCBA). Carbamazepine (CBZ) and diclofenac (DCF) are compounds susceptible to ozone oxidation, thus their complete degradation at 150 μM transferred ozone dose was attained. The limited catalytic effect was attributed to the rapid consumption of ozone within the first minute of reaction, as well as the saturation of catalyst active sites by water molecules, which inhibited effective ozone adsorption and subsequent hydroxyl radical generation (^●OH). Full article

Three MnCeTiO_x catalysts with the same composition were prepared by conventional co-precipitation (MCT-C), reverse co-precipitation (MCT-R), and parallel co-precipitation (MCT-P), respectively, and their low-temperature SCR performance for de-NO_x was evaluated. The textural and structural properties, surface acidity, redox capacity, and reaction mechanism of the catalysts were investigated by a series of characterizations including N₂ adsorption and desorption, XRD, SEM, XPS, H₂-TPR, NH₃-TPD, NO-TPD, and in situ DRIFTs. The results revealed that the most excellent catalytic performance was achieved on MCT-R, and more than 90% NO_x conversion can be obtained at 100–300 °C under a high GHSV of 80,000 mL/(g_cat·H). Furthermore, MCT-R possessed optimal tolerance to H₂O and SO₂ poisoning. The excellent catalytic performance of MCT-R can be attributed to its larger BET specific surface area; higher contents of Mn⁴⁺, Ce³⁺, and adsorbed oxygen species; and more adsorption capacity for NH₃ and NO. Moreover, in situ DRIFTs results indicated that the NH₃-SCR reaction follows simultaneously the Langmuir–Hinshelwood and Eley–Rideal mechanisms at 100 °C. By adjusting the adding mode during the co-precipitation process, excellent low-temperature de-NO_x activity of MCT-R can be obtained simply and conveniently, which is of great practical value for the preparation of a MnCeTiO_x catalyst for denitrification. Full article

In view of the flue gas characteristics of cement kilns in China, the development of low-temperature denitrification catalysts with excellent anti-poisoning performance has important theoretical and practical significance. In this work, a series of MnCeO_x@TiO₂ and tourmaline-containing MnCeO_x@TiO₂-T catalysts was prepared using a chemical pre-deposition method. It was found that the MnCeO_x@TiO₂-T2 catalyst (containing 2% tourmaline) exhibited the best low-temperature NH₃-selective catalytic reduction (NH₃-SCR) performance, yielding 100% NO_x conversion at 110 °C and above. When 100–300 ppm SO₂ and 10 vol.% H₂O were introduced to the reaction, the NO_x conversion of the MnCeO_x@TiO₂-T2 catalyst was still higher than 90% at 170 °C, indicating good anti-poisoning performance. The addition of appropriate amounts of tourmaline can not only preferably expose the active {001} facets of TiO₂ but also introduce the acidic SiO₂ and Al₂O₃ components and increase the content of Mn⁴⁺ and O_α on the surface of the catalyst, all of which contribute to the enhancement of reaction activity of NH₃-SCR and anti-poisoning performance. However, excess amounts of tourmaline led to the formation of dense surface of catalysts that suppressed the exposure of catalytic active sites, giving rise to the decrease in catalytic activity and anti-poisoning capability. Through an in situ DRIFTS study, it was found that the addition of appropriate amounts of tourmaline increased the number of Brønsted acid sites on the catalyst surface, which suppressed the adsorption of SO₂ and thus inhibited the deposition of NH₄HSO₄ and (NH₄)₂HSO₄ on the surface of the catalyst, thereby improving the NH₃-SCR performance and anti-poisoning ability of the catalyst. Full article

In recent decades, with the rapid development of the inorganic synthesis and the increasing discharge of pollutants in the process of industrialization, hollow-structured metal oxides (HSMOs) have taken on a striking role in the field of environmental catalysis. This is all due to their unique structural characteristics compared to solid nanoparticles, such as high loading capacity, superior pore permeability, high specific surface area, abundant inner void space, and low density. Although the HSMOs with different morphologies have been reviewed and prospected in the aspect of synthesis strategies and potential applications, there has been no systematic review focusing on the structures and compositions design of HSMOs in the field of environmental catalysis so far. Therefore, this review will mainly focus on the component dependence and controllable structure of HSMOs in the catalytic elimination of different environmental pollutants, including the automobile and stationary source emissions, volatile organic compounds, greenhouse gases, ozone-depleting substances, and other potential pollutants. Moreover, we comprehensively reviewed the applications of the catalysts with hollow structure that are mainly composed of metal oxides such as CeO₂, MnO_x, CuO_x, Co₃O₄, ZrO₂, ZnO, Al₃O₄, In₂O₃, NiO, and Fe₃O₄ in automobile and stationary source emission control, volatile organic compounds emission control, and the conversion of greenhouse gases and ozone-depleting substances. The structure–activity relationship is also briefly discussed. Finally, further challenges and development trends of HSMO catalysts in environmental catalysis are also prospected. Full article

Manganese oxide-cerium oxide supported on titanate nanotubes (i.e., MnCe/TiNTs) were prepared and their catalytic activities towards NH₃-SCR of NO were tested. The results indicated that the MnCe/TiNT catalyst can achieve a high NO removal efficiency above 95% within the temperature range of 150–350 °C. Even after exposure to a HCl-containing atmosphere for 2 h, the NO removal efficiency of the MnCe/TiNT catalyst maintains at approximately 90% at 150 °C. This is attributed to the large specific surface area as well as the unique hollow tubular structure of TiNTs that exposes more Ce atoms, which preferentially react with HCl and thus protect the active Mn atoms. Moreover, the abundant OH groups on TiNTs serve as Brønsted acid sites and provide H protons to expel Cl atom from the catalyst surface. The irreversible deactivation caused by HCl can be alleviated by H₂O. That is because the dissociated adsorption of H₂O on TiNTs forms additional OH groups and relieves HCl poisoning. Full article

Cu-SSZ-39 zeolite with an AEI structure exhibits excellent hydrothermal stability and can be a potential alternative to Cu-SSZ-13 zeolite SCR catalysts for NO_x removal in diesel vehicles. However, the inferior low-temperature performance of Cu-SSZ-39 leads to substantial NO_x emissions during the cold-start period, impeding its practical application. In this study, Ce-Mn oxide-modified Cu-SSZ-39 catalysts (CeMnO_x/Cu-SSZ-39) and references (CeO₂/Cu-SSZ-39 and MnO_x/Cu-SSZ-39) were prepared by the ion-exchange of Cu ions followed by impregnation of the oxide precursors, with the aim of enhancing the NH₃-SCR performance at low temperatures. The modified catalysts exhibited improved low-temperature activity and hydrothermal stability compared to the unmodified counterpart. In particular, CeMnO_x/Cu-SSZ-39 showed the highest activity among the three catalysts and achieved NO_x conversions above 90% within the temperature range of 180 °C to 600 °C, even after undergoing hydrothermal aging at 800 °C. Experimental results indicated that the synergistic effect between Ce and Mn in CeMnO_x improves the redox properties and acidity of the catalyst due to the presence of Ce³⁺, Mn⁴⁺, and abundant adsorbed oxygen species, which facilitate low-temperature SCR reactions. Furthermore, the interaction of CeMnO_x with Cu-SSZ-39 stabilizes the zeolite framework and hinders the agglomeration of Cu species during the hydrothermal aging process, contributing to its exceptional hydrothermal stability. The kinetics and NO oxidation experiments demonstrated that CeMnO_x provides access to fast SCR reaction pathways by oxidizing NO to NO₂, resulting in a significant increase in low-temperature activity. This study provides novel guidelines for the design and preparation of Cu-SSZ-39 zeolite with outstanding SCR performance over a wide temperature range. Full article

Structure–performance relationships in functional catalysts allow for controlling their performance in a wide range of reaction conditions. Here, the structural and compositional peculiarities in CTAB-templated CeO₂-ZrO₂-MnO_x catalysts prepared by co-precipitation of precursors and their catalytic behavior in CO oxidation and soot combustion are discussed. A complex of physical–chemical methods (low-temperature N₂ sorption, XRD, TPR-H₂, Raman, HR TEM, XPS) is used to elucidate the features of the formation of interphase boundaries, joint phases, and defects in multicomponent oxide systems. The addition of Mn and/or Zr dopant to ceria is shown to improve its performance in both reactions. Binary Ce-Mn catalysts demonstrate enhanced performance closely followed by the ternary oxide catalysts, which is due the formation of several types of active sites, namely, highly dispersed MnO_x species, oxide–oxide interfaces, and oxygen vacancies that can act individually and/or synergistically. Full article

With the increasing stringency of environmental protection regulations, reducing the severe pollution caused by soot particles from diesel vehicle exhaust has become a widespread concern. Catalytic purification technology is currently an efficient method for eliminating soot particles, which needs to develop high-activity catalysts. This work uses a two-step hydrothermal method to synthesize MnO_x/CeO₂ nanosphere catalysts, which have synergistic effects between manganese and cerium, and have high reactive oxygen species. Among them, the MnCe-1:4 catalyst represents the optimal catalytic activity, and the values of T₁₀, T₅₀, and T₉₀ are 289, 340, and 373 °C, respectively. On account of their simple synthetic procedure and low cost, the prepared MnO_x/CeO₂ nanosphere catalysts have good prospects for practical applications. Full article

Dry reforming of methane with ratio CH₄/CO₂ = 1 is studied using supported Ni catalysts on SBA-15 modified by CeMnO_x mixed oxides with different Ce/Mn ratios (0.25, 1 and 9). The obtained samples are characterized by wide-angle XRD, SAXS, N₂ sorption, TPR-H₂, TEM, UV–vis and Raman spectroscopies. The SBA-15 modification with CeMnO_x decreases the sizes of NiO nanoparticles and enhances the NiO–support interaction. When Ce/Mn = 9, the NiO forms small particles on the surface of large CeO₂ particles and/or interacts with CeO₂, forming mixed phases. The best catalytic performance (at 650 °C, CH₄ and CO₂ conversions are 51 and 69%, respectively) is achieved over the Ni/CeMnO_x/SBA-15 (9:1) catalyst. The peculiar CeMnO_x composition (Ce/Mn = 9) also improves the catalyst stability: In a 24 h stability test, the CH₄ conversion decreases by 18 rel.% as compared to a 30 rel.% decrease for unmodified catalyst. The enhanced catalytic stability of Ni/CeMnO_x/SBA-15 (9:1) is attributed to the high concentration of reactive peroxo (O⁻) and superoxo (O₂⁻) species that significantly lower the amount of coke in comparison with Ni-SBA-15 unmodified catalyst (weight loss of 2.7% vs. 42.2%). Ni-SBA-15 modified with equimolar Ce/Mn ratio or Mn excess is less performing. Ni/CeMnO_x/SBA-15 (1:4) with the highest content of manganese shows the minimum conversions of reagents in the entire temperature range (X(CO₂) = 4–36%, X(CH₄) = 8–58%). This finding is possibly attributed to the presence of manganese oxide, which decorates the Ni particles due to its redistribution at the preparation stage. Full article

Ce-MnO_x composite oxide catalysts with different proportions were prepared using the coprecipitation method, and the CO-removal ability of the catalysts with the tested temperature range of 60–140 °C was investigated systematically. The effect of Ce and Mn ratios on the catalytic oxidation performance of CO was investigated using X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), H₂ temperature programmed reduction (H₂-TPR), CO-temperature programmed desorption (CO-TPD), and in situ infrared spectra. The experimental results reveal that under the same test conditions, the CO conversion rate of pure Mn₃O₄ reaches 95.4% at 170 °C. Additionally, at 140 °C, the Ce-MnO_x series composite oxide catalyst converts CO at a rate of over 96%, outperforming single-phase Mn₃O₄ in terms of catalytic performance. With the decrement in Ce content, the performance of Ce-MnO_x series composite oxide catalysts first increase and then decrease. The Ce MnO_x catalyst behaves best when Ce:Mn = 1:1, with a CO conversion rate of 99.96% at 140 °C and 91.98% at 100 °C. Full article