Search Results (11)

Global municipal solid waste (~2B tons/year) affects sustainability, as landfill and incineration face persistent leachate contamination, demanding effective management to advance water recycling and circular economies. Accelerated investigation of hybrid biocatalytic ozonation systems is imperative to enhance contaminant removal efficiency for stringent discharge compliance. This study investigates the catalytic ozonation effects of γ-Al₂O₃-based catalysts loaded with different metals (Cu, Mn, Zn, Y, Ce, Fe, Mg) on the biochemical effluent of landfill leachate. The catalysts were synthesized via a mixed method and subsequently characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Pseudo-second-order kinetics revealed active metal loading’s impact on adsorption capacity, with Cu/γ-Al₂O₃ and Mg/γ-Al₂O₃ achieving the highest Q_e (0.85). To elucidate differential degradation performance among the catalysts, the ozone/oxygen gas mixture was introduced at a controlled flow rate. Experimental results demonstrate that the Cu/γ-Al₂O₃ catalyst, exhibiting optimal comprehensive degradation performance, achieved COD and TOC removal efficiencies of 84.5% and 70.9%, respectively. UV–vis absorbance ratios revealed the following catalytic disparities: Mg/γ-Al₂O₃ achieved the highest aromatic compound removal efficiency; Ce/γ-Al₂O₃ excelled in macromolecular organics degradation. EEM-PARAFAC analysis revealed differential fluorophore removal: Cu/γ-Al₂O₃ exhibited broad efficacy across all five components, while Mg/γ-Al₂O₃ demonstrated optimal removal of C2 and C4, but showed limited efficacy toward C5. These findings provide important insights into selecting catalysts in practical engineering applications for landfill leachate treatment. This study aims to elucidate catalyst formulation-dependent degradation disparities, guiding water quality-specific catalyst selection to ultimately enhance catalytic ozonation efficiency. Full article

Cu-containing and Ce-modified OMS-2 catalysts were prepared at various calcination temperatures using the hydrothermal method and tested for low-temperature CO oxidation. The structure, chemical compositions, and physical–chemical properties of the catalysts were characterized using XRD, N₂ physisorption, XRF, Raman spectroscopy, SEM, high-resolution TEM with EDX, TPR-H₂, and XPS. The incorporation of Cu into the Ce-OMS-2 sample facilitated the transformation of pyrolusite into cryptomelane, as confirmed by Raman spectroscopy data. In the light-off mode, the Cu/Ce-OMS-2-300 and Cu/OMS-2 samples exhibited higher activity in low-temperature CO oxidation (T₉₀ = 115 and 121 °C, respectively) compared to sample Cu/Ce-OMS-2-450. After a long-run stability test, the Cu/Ce-OMS-X samples demonstrated excellent performance: the T₈₀ increased by 16% and 7% for the samples calcined at 300 °C and 450 °C, respectively, while the T₈₀ for the Cu/OMS-2 increased by 40%. The Cu/OMS-2 and Cu/Ce-OMS-2-300 samples were found to have an increased content of nanodispersed copper sites on their surfaces. These copper sites contributed to the formation of the Cu²⁺-O-Mn⁴⁺ interface, which is responsible for the CO oxidation. The presence of Ce³⁺ in the catalyst was found to increase its stability in the presence of water vapor due to the higher reoxidation ability in comparison with Ce-free sample Cu/OMS-2. Full article

The development and characterization of synthesis techniques for oxide materials based on ceria is a subject of extensive study with the objective of their wide-ranging applications in pursuit of sustainable development. The present study demonstrates the feasibility of controlled synthesis of Ce_1−xM_xO_2−δ (M = Fe, Ni, Co, Mn, Cu, Ag, Sm, Cs, x = 0.0–0.3) in combustion reactions from precursors comprising glycine, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and cellulose as organic components. Controlled synthesis is achieved by varying the composition of the precursor, the type of organic component, and the amount of organic component, which allows for the influence of the generation of high-density electrical charges and outgassing during synthesis. The intensity of charge generation is quantified by measuring the value of the precursor–ground potential difference. It has been demonstrated that an increase in the intensity of charge generation results in a more developed morphology, which is essential for the practical implementation of ceria as a catalyst to enhance contact with gases and solid particles. The maximum value of the potential difference, equal to 68 V, is obtained during the synthesis of Ce_0.7Ni_0.3O_2−δ with polyvinyl alcohol in stoichiometric relations, which corresponds to a specific surface area of 21.7 m² g⁻¹. A correlation is established between the intensity of gas release for systems with different organic components, the intensity of charge generation, morphology, and the value of the specific surface area of the samples. Full article

A series of M(x)CoCeMgAlO mixed oxides with different transition metals (M = Cu, Fe, Mn, and Ni) with an M content x = 3 at. %, and another series of Fe(x)CoCeMgAlO mixed oxides with Fe contents x ranging from 1 to 9 at. % with respect to cations, while keeping constant in both cases 40 at. % Co, 10 at. % Ce and Mg/Al atomic ratio of 3 were prepared via thermal decomposition at 750 °C in air of their corresponding layered double hydroxide (LDH) precursors obtained by coprecipitation. They were tested in a fixed bed reactor for complete methane oxidation with a gas feed of 1 vol.% methane in air to evaluate their catalytic performance. The physico-structural properties of the mixed oxide samples were investigated with several techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), elemental mappings, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction under hydrogen (H₂-TPR) and nitrogen adsorption–desorption at −196 °C. XRD analysis revealed in all the samples the presence of Co₃O₄ crystallites together with periclase-like and CeO₂ phases, with no separate M-based oxide phase. All the cations were distributed homogeneously, as suggested by EDX measurements and elemental mappings of the samples. The metal contents, determined by EDX and ICP-OES, were in accordance with the theoretical values set for the catalysts’ preparation. The redox properties studied by H₂-TPR, along with the surface composition determined by XPS, provided information to elucidate the catalytic combustion properties of the studied mixed oxide materials. The methane combustion tests showed that all the M-promoted CoCeMgAlO mixed oxides were more active than the M-free counterpart, the highest promoting effect being observed for Fe as the doping transition metal. The Fe(x)CoCeMgAlO mixed oxide sample, with x = 3 at. % Fe displayed the highest catalytic activity for methane combustion with a temperature corresponding to 50% methane conversion, T₅₀, of 489 °C, which is ca. 40 °C lower than that of the unpromoted catalyst. This was attributed to its superior redox properties and lowest activation energy among the studied catalysts, likely due to a Fe–Co–Ce synergistic interaction. In addition, long-term tests of Fe(3)CoCeMgAlO mixed oxide were performed, showing good stability over 60 h on-stream. On the other hand, the addition of water vapors in the feed led to textural and structural changes in the Fe(3)CoCeMgAlO system, affecting its catalytic performance in methane complete oxidation. At the same time, the catalyst showed relatively good recovery of its catalytic activity as soon as the water vapors were removed from the feed. Full article

Ba_1−xCe_xMnO₃ (BM-Ce_x) and Ba_1−xLa_xMn_0.7Cu_0.3O₃ (BMC-La_x) perovskite-type mixed oxides were synthesized using the sol–gel method adapted for aqueous media with different values of x (0, 0.1, 0.3, 0.6) to estimate the effect of the degree of the partial substitution of Ba by Ce or La on the structure and properties that are relevant for their use as catalysts for gasoline direct injection (GDI) soot oxidation. The samples were deeply characterized by ICP-OES, XRD, XPS, N₂ adsorption, H₂-TPR, and O₂-TPD, and their potential as catalysts for soot oxidation has been analyzed in various scenarios that replicate the exhaust conditions of a GDI engine. By comparing the catalytic performance for soot oxidation of the two tested series (BM-Cex and BMC-Lax) and in the two conditions used (100% He and 1% O₂ in He), it could be concluded that (i) in the absence of oxygen in the reaction atmosphere (100% He), BMC-La_0.1 is the best catalyst, as copper is also able to catalyze the soot oxidation; and (ii) if oxygen is present in the reaction atmosphere (1% O₂/He), BM-Ce_0.1 is the most-active catalyst as it presents a higher proportion of Mn(IV) than BMC-La_0.1. Thus, it seems that the addition of an amount of Ce or La higher than that corresponding to x = 0.1 in Ba_1−xCe_xMnO₃ and Ba_1−xLa_xCu_0.3Mn_0.7O₃ does not allow us to improve the catalytic performance of BM-Ce_0.1 and BMC-La_0.1 for soot oxidation in the tested conditions. Full article

The effects of four distinct zinc species (ZnCl₂, Zn(NO₃)₂, ZnSO₄, and ZnCO₃) on a Mn-Ce co-doped CuX (MCCX)catalyst were investigated and contrasted in the low-temperature NH₃-SCR process. Aqueous solutions of ZnCl₂, Zn(NO₃)₂, ZnSO₄, and ZnCO₃ were used to poison the catalysts. The catalytic activity of all catalysts was assessed, and their physicochemical properties were studied. There was a notable drop trend in catalytic activity in the low temperature range (200 °C) after zinc species poisoning on MCCX catalyst. Interestingly, ZnSO₄ and ZnCO₃ on MCCX catalyst had more serious effect on catalytic activity than Zn(NO₃)₂ and ZnCl₂ from 150 °C to 225 °C, in which NO conversion of the MCCX-Zn-S and MCCX-Zn-C catalysts dropped about 20–30% below 200 °C compared with the fresh MCCX catalyst. The zeolite X structure was impacted by Zn species doping on the MCCX catalyst, and the Zn-poisoned catalysts had less acidic and lower redox ability than fresh Mn-Ce/CuX catalysts. Through the results of in situ DRIFTS spectroscopy experiments, all catalysts were governed by both Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanisms, and the possible mechanism for poisoning the Mn-Ce/CuX catalyst using various zinc species was revealed. Full article

In this work, soot oxidation was conducted over a series of Mn-X/γ-Al₂O₃ (M = Ce, Co and Cu) binary catalysts in a dielectric barrier discharge reactor. The soot conversion in the plasma–catalytic system was in the order of Mn/γ-Al₂O₃ (57.7%) > Mn-Co/γ-Al₂O₃ (53.9%) > Mn-Ce/γ-Al₂O₃ (51.6%) > Mn-Cu/γ-Al₂O₃ (47.7%) during the 30 min soot oxidation process at 14 W and 150 °C. Meanwhile, the doping of Ce, Co and Cu slightly improved the CO₂ selectivity of the process by 4.7% to 10.3% compared to soot oxidation over Mn/γ-Al₂O₃.It is worth to note that the order of CO₂ selectivity was in the opposite order with soot oxidation rate. The effects of discharge power, oxygen content in the carrier gas and reaction temperature on plasma–catalytic soot oxidation was systematically analyzed. The catalyst characterizations, including N₂ adsorption–desorption, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction by H₂ and temperature-programmed desorption of O_2, were conducted to illustrate the reaction mechanisms of plasma–catalytic soot oxidation and reaction pathways. Full article

To improve the catalytic performance of an active layered double hydroxide (LDH)-derived CuCeMgAlO mixed oxide catalyst in the total oxidation of methane, it was promoted with different transition-metal cations. Thus, two series of multicationic mixed oxides were prepared by the thermal decomposition at 750 °C of their corresponding LDH precursors synthesized by coprecipitation at constant pH of 10 under ambient atmosphere. The first series of catalysts consisted of four M(3)CuCeMgAlO mixed oxides containing 3 at.% M (M = Mn, Fe, Co, Ni), 15 at.% Cu, 10 at.% Ce (at.% with respect to cations), and with Mg/Al atomic ratio fixed to 3. The second series consisted of four Co(x)CuCeMgAlO mixed oxides with x = 1, 3, 6, and 9 at.% Co, while keeping constant the Cu and Ce contents and the Mg/Al atomic ratio. All the mixed oxides were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with X-ray energy dispersion analysis (EDX), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption at −196 °C, temperature-programmed reduction under hydrogen (H₂-TPR), and diffuse reflectance UV-VIS spectroscopy (DR UV-VIS), while thermogravimetric and differential thermal analyses (TG-DTG-DTA) together with XRD were used for the LDH precursors. The catalysts were evaluated in the total oxidation of methane, a test reaction for volatile organic compounds (VOC) abatement. Their catalytic performance was explained in correlation with their physicochemical properties and was compared with that of a reference Pd/Al₂O₃ catalyst. Among the mixed oxides studied, Co(3)CuCeMgAlO was found to be the most active catalyst, with a temperature corresponding to 50% methane conversion (T₅₀) of 438 °C, which was only 19 °C higher than that of a reference Pd/Al₂O₃ catalyst. On the other hand, this T₅₀ value was ca. 25 °C lower than that observed for the unpromoted CuCeMgAlO system, accounting for the improved performance of the Co-promoted catalyst, which also showed a good stability on stream. Full article

CuO-based catalysts are usually used for CO oxidation owing to their low cost and excellent catalytic activities. In this study, a series of metal oxide (La₂O₃, Fe₂O₃, PrO₂, Sm₂O₃, and MnO₂)-doped CuO-based catalysts with mesoporous Ce_0.8Zr_0.2O₂ support were simply prepared by the incipient impregnation method and used directly as catalysts for CO catalytic oxidation. These mesoporous catalysts were systematically characterized by X-ray powder diffraction (XRD), N₂ physisorption, transmission electron microscopy (TEM), energy-dispersed spectroscopy (EDS) mapping, X-ray photoelectron spectroscopy (XPS), and H₂ temperature programmed reduction (H₂-TPR). It was found that the CuO and the dopants were highly dispersed among the mesoporous framework via the incipient impregnation method, and the strong metal framework interaction had been formed. The effects of the types of the dopants and the loading amounts of the dopants on the low-temperature catalytic performances were carefully studied. It was concluded that doped transition metal oxides could regulate the oxygen mobility and reduction ability of catalysts, further improving the catalytic activity. It was also found that the high dispersion of rare earth metal oxides (PrO₂, Sm₂O₃) was able to prevent the thermal sintering and aggregation of CuO-based catalysts during the process of calcination. In addition, their presence also evidently improved the reducibility and significantly reduced the particle size of the CuO active sites for CO oxidation. The results demonstrated that the 15CuO-3Fe₂O₃/M-Ce80Zr20 catalyst with 3 wt. % of Fe₂O₃ showed the best low-temperature catalytic activity toward CO oxidation. Overall, the present Fe₂O₃-doped CuO-based catalysts with mesoporous nanocrystalline Ce_0.8Zr_0.2O₂ solid solution as support were considered a promising series of catalysts for low-temperature CO oxidation. Full article

The adsorption of NO, NH₃, H₂O, and SO₂ gaseous molecules on different transition metal oxides was studied based on density function theory (DFT), and three better-performing transition metal elements (Fe, Co, and Ce) were selected. Cu–Mn/SAPO-34 catalysts were prepared by impregnation method and then modified by the selected transition metals (Fe, Co, and Ce); the SO₂ resistance experiments and characterizations including Brunner−Emmet−Teller (BET), X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM), and thermal gravity analysis (TG)-differential thermal gravity (DTG) before and after SO₂ poisoning were conducted. The results showed that the deactivation of the Cu–Mn/SAPO-34 catalyst is ascribed to the deposition of lots of ammonium sulfates on the surface, depositing on the active sites and inhibiting the adsorption of NH₃. After the modification of Fe, Co, and Ce oxides, the SO₂ resistance of the modified Cu–Mn/SAPO-34 catalyst was significantly enhanced due to the less formation of ammonium sulfates. Among all these modified Cu–Mn/SAPO-34 catalysts, the Cu–Mn–Ce/SAPO-34 exhibited the highest SO₂ resistance owing to the decreased decomposition temperature and the trapper of ceria for capturing SO₂ to form Ce(SO₄)₂, further inhibiting the deposition of ammonium sulfates. Full article

Cu-Mn-Ce@γ-Al₂O₃ was prepared by incipient wetness impregnation and used to catalyze ozonation in a coal chemical wastewater-biotreated effluent. The preparation factors that considerably affected the catalytic performance of Cu-Mn-Ce@γ-Al₂O₃, specifically metal oxide loading percentage, calcination temperature, and calcination time, were examined. The catalyst was characterized by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, and Brunauer-Emmett-Teller analysis. The optimal catalytic ozonation operating parameters, such as ozone dosage, catalyst dosage, pH, and reaction time, were also investigated. Results showed that an optimized catalyst consisted of 17.0% CuO, 3.0% MnO₂, and 2.0% CeO₂ (wt.%). The optimal calcination temperature and calcination time were 600 °C and 5 h. The optimal catalytic ozonation operating parameters, including ozone dosage, catalyst dosage, pH, and reaction time, were 7, 80.0 mg/L, 20.0 mg/L, 7 and 50 min, respectively. The COD removal of biotreated effluent increased to 61% under these optimal operating conditions. Meanwhile, ozonation alone resulted in only 20% removal. This work proposes the use of easily available Cu-Mn-Ce@γ-Al₂O₃ catalyst and might drive the advancement of catalytic ozonation for chemical wastewater purification. Full article