Search Results (5)

Activated carbon has shown good catalytic performance in water treatment, but its wide application is limited by its high price. Activated coke exhibits functional groups and is low-cost. However, there is limited research on activated coke as a catalyst. In our previous study, powdered activated coke (PAC) exhibited good catalytic performance in NH₃-N treatment with ozonation. Increasing nitrogen selectivity is the key to harmless degradation of NH₃-N, which has received little attention. In this paper, manganese-loaded powdered coke (Mn–PAC) was prepared, aiming to further improve the nitrogen selectivity. Under the same conditions, the PAC/O₃ system achieved 92.16% NH₃-N removal and 49.46% nitrogen selectivity, while the Mn–PAC/O₃ system achieved almost 100% NH₃-N removal and 79.31% N₂ selectivity. When Mn–PAC was reused for the sixth time, the system achieved about 70% and 46% NH₃-N removal and N₂ selectivity, both of which were about 10% higher than those of PAC. Complex redox and synergistic interactions existed in the Mn–PAC/O₃ system. The Mn–PAC surface contains reactive sites such as C=C, C=O, π–π bonds, ArOH, and various MnO_x. These components collectively facilitate ozone decomposition into ·OH, ·O₂⁻, and ¹O₂. The ¹O₂ may play a significant role in converting NH₃-N to N₂. Full article

Transition metal oxides (e.g., MnO_x) can effectively promote the redox reactions of heavy metal ions through abundant valence changes. However, relatively few studies have been conducted on the application of MnO_x for the detection of Cd²⁺ without pre-enrichment conditions. For this reason, in this study, MnO_x was grown in situ on a carbon cloth substrate by one-step electrodeposition. The effect of the valence composition of MnO_x and its variation on the Cd²⁺ without pre-enrichment detection performance was systematically investigated. The morphology, structure, and chemical composition of the materials were fully characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that the deposition of MnO_x not only significantly increased the active surface area of the electrodes but also facilitated electron transfer through the valence transition of Mn²⁺/Mn³⁺↔Mn³⁺/Mn⁴⁺. The detection of Cd²⁺ in water samples can be successfully achieved without pre-enrichment, and the electrode has good stability and reproducibility. This study provides a new design idea for applying MnO_x electrodes in Cd²⁺ detection without pre-enrichment and provides a reference for further optimization of electrochemical sensors. Full article

The promotional effect of potassium (~1.25 wt%) on a Co/MnO_x catalyst was studied for samples prepared by the impregnation method in the steam reforming of ethanol (SRE) process at 420 °C for a H₂O/EtOH molar ratio of 12/1. The catalysts were characterized using physicochemical methods to study their textural, structural, and redox properties. The XRD studies revealed that, during the treatment of both cobalt-based catalysts under a hydrogen atmosphere at 500 °C, Co⁰ and MnO phases were formed by the reduction in Co₃O₄ and Mn₂O₃/Mn₃O₄ phases, respectively. Potassium doping significantly improved stability and ability for the C–C bond cleavage of the Co/MnO_x catalyst. The enhancement of activity (at ~25%) and selectivity to hydrogen (at ca. 10%) and the C1 product, mainly carbon dioxide (at ~20%), of the Co/MnO_x catalyst upon potassium doping was clarified by the alkali promoter’s impact on the reducibility of the cobalt and manganese oxides. The microscopic observations revealed that fibrous carbon deposits are present on the surface of Co/MnOx and KCo/MnOx catalysts after the SRE reaction and their formation is the main reason these catalysts deactivate under SRE conditions. However, carbon accumulation on the surface of the potassium-promoted catalyst was ca. 12% lower after 18 h of SRE reaction compared to the unpromoted sample. Full article

Pt nanoparticles and a CeMnO_x composite were loaded on the surface of the natural diatomite material to generate the Pt/CeMnO_x/diatomite using the redox precipitation and impregnation methods. The physicochemical properties of the catalysts were characterized by means of various techniques. The catalytic properties and resistance to H₂O and SO₂ of the catalysts were measured for the oxidation of typical volatile organic compounds (i.e., toluene and ethyl acetate). Among all of the as-prepared samples, Pt/CeMnO_x/diatomite exhibited the highest catalytic activity: the temperatures (T_90%) at a toluene or ethyl acetate conversion of 90% were 230 and 210 °C at a space velocity (SV) of 20,000 mL g⁻¹ h⁻¹, respectively, and the turnover frequency (TOF_Pt) at 220 °C was 1.04 μmol/(g_cat s) for ethyl acetate oxidation and 1.56 μmol/(g_cat s) for toluene oxidation. In particular, this sample showed a superior catalytic activity for ethyl acetate oxidation at low temperatures, with its T_50% being 185 °C at SV = 20,000 mL g⁻¹ h⁻¹. In addition, the Pt/CeMnO_x/diatomite sample possessed good sulfur dioxide resistance during the toluene oxidation process. In the presence of SO₂, some of the SO₂ molecules were adsorbed on diatomite, which protected the active sites from being poisoned by SO₂ to a certain extent. The pathways of ethyl acetate and toluene oxidation over Pt/CeMnO_x/diatomite or Pt/CeMnO_x were as follows: The C–C and C–O bonds in ethyl acetate are first broken to form the CH₃CH₂O* and CH₃CO* species or toluene is first oxidized to benzaldehyde and benzoic acid, and all of these intermediates are then converted to CO₂ and H₂O. This work can provide a strategy to develop efficient catalysts with high catalytic activity, durability, low cost, and easy availability under actual working conditions. Full article

Advanced oxidation processes (AOPs) are technologies to degrade organic pollutants to carbon dioxide and water with an eco-friendly approach to form reactive hydroxyl radicals. Photocatalysis is an AOP whereby TiO₂ is the most adopted photocatalyst. However, TiO₂ features a wide (3.2 eV) and fast electron-hole recombination. When Mn is embedded in TiO₂, it shifts the absorption wavelength towards the visible region of light, making it active for natural light applications. We present a systematic study of how the textural and optical properties of Mn-doped TiO₂ vary with ultrasound applied during synthesis. We varied ultrasound power, pulse length, and power density (by changing the amount of solvent). Ultrasound produced mesoporous MnO_x-TiO₂ powders with a higher surface area (101–158 m² g⁻¹), pore volume (0-13–0.29 cc g⁻¹), and smaller particle size (4–10 µm) than those obtained with a conventional sol-gel method (48–129 m² g⁻¹, 0.14–0.21 cc g⁻¹, 181 µm, respectively). Surprisingly, the catalysts obtained with ultrasound had a content of brookite that was at least 28%, while the traditional sol-gel samples only had 7%. The samples synthesized with ultrasound had a wider distribution of the band-gaps, in the 1.6–1.91 eV range, while traditional ones ranged from 1.72 eV to 1.8 eV. We tested activity in the sonophotocatalytic degradation of two model pollutants (amoxicillin and acetaminophen). The catalysts synthesized with ultrasound were up to 50% more active than the traditional samples. Full article