Search Results (154)

Nitrogen oxides (NO_x) emissions pose environmental and health risks. Selective catalytic reduction (SCR) is effective for NO_x removal, and using CO as a reductant can eliminate both NO_x and CO. This study explores CuCe catalysts on SiO₂, Al₂O₃, and TiO₂ for CO-SCR. Results show catalytic activity relates to the synergy between lattice oxygen and CuCe species. TiO₂ enhances this interaction, promoting Cu⁺ and lattice oxygen for NO adsorption and dissociation. The CuCe/TiO₂ catalyst achieves 100% NO conversion at 300 °C and 40.2% at 100 °C, indicating excellent low-temperature performance. These findings are valuable for developing efficient SCR catalysts. Full article

The Dongping manganese (Mn) deposit, located within the Lower Triassic Shipao Formation of the Youjiang Basin, is one of South China’s most significant sedimentary Mn carbonate ore deposits. To resolve longstanding debates over its metallogenic pathway, we conducted integrated sedimentological, mineralogical, and geochemical analyses on three drill cores (ZK5101, ZK0301, and ZK1205) spanning the Mn ore body. X-ray diffraction and backscatter electron imaging reveal that the ores are dominated by kutnohorite, with subordinate quartz, calcite, dolomite, and minor sulfides. The low enrichment of U/Al, V/Al, and Mo/Al, as well as positive Ce anomalies, consistently suggest that Mn, in the form of oxides, was deposited in an oxic water column. Carbon isotope compositions of Mn carbonate ores (δ¹³C_VPDB: −2.3 to −6.1‰) and their negative correlation with MnO suggest that Mn carbonate, predominantly kutnohorite, show a diagenetic reduction in pre-existing Mn oxides via organic-matter oxidation in anoxic sediments pore waters. Elemental discrimination diagramms (Mn-Fe-(Co+Ni+Cu) × 10 and Co/Zn vs. Co+Cu+Ni) uniformly point to a hydrothermal Mn source. We therefore propose that hydrothermal fluids supplied dissolved Mn²⁺ to an oxic slope-basin setting, precipitating initially as Mn oxides, which were subsequently transformed to Mn carbonates during early diagenesis. This model reconciles both the hydrothermal and sedimentary-diagenetic processes of the Dongping Mn deposit. Full article

Petrological knowledge on weathering processes controlling the mobility of chemical elements is still limited in the dry tropical zone of Cameroon. This study aims to investigate the mobility of major and trace elements during rhyolite weathering and soil formation in Mobono by understanding the mineralogical and elemental vertical variation. The studied soil was classified as Cambisols containing mainly quartz, K-feldspar, plagioclase, smectite, kaolinite, illite, calcite, lepidocrocite, goethite, sepiolite, and interstratified clay minerals. pH values ranging between 6.11 and 8.77 indicated that hydrolysis, superimposed on oxidation and carbonation, is the main process responsible for the formation of secondary minerals, leading to the formation of iron oxides and calcite. The bedrock was mainly constituted of SiO₂, Al₂O₃, Na₂O, Fe₂O₃, Ba, Zr, Sr, Y, Ga, and Rb. Ce and Eu anomalies, and chondrite-normalized La/Yb ratios were 0.98, 0.67, and 2.86, respectively. SiO₂, Al₂O₃, Fe₂O₃, Na₂O, and K₂O were major elements in soil horizons. Trace elements revealed high levels of Ba (385 to 1320 mg kg⁻¹), Zr (158 to 429 mg kg⁻¹), Zn (61 to 151 mg kg⁻¹), Sr (62 to 243 mg kg⁻¹), Y (55 to 81 mg kg⁻¹), Rb (1102 to 58 mg kg⁻¹), and Ga (17.70 to 35 mg kg⁻¹). LREEs were more abundant than HREEs, with LREE/HREE ratio ranging between 2.60 and 6.24. Ce and Eu anomalies ranged from 1.08 to 1.21 and 0.58 to 1.24 respectively. The rhyolite-normalized La/Yb ratios varied between 0.56 and 0.96. Mass balance revealed the depletion of Si, Ca, Na, Mn, Sr, Ta, W, U, La, Ce, Pr, Nd, Sm, Gd and Lu, and the accumulation of Al, Fe, K, Mg, P, Sc, V, Co, Ni, Cu, Zn, Ga, Ge, Rb, Y, Zr, Nb, Cs, Ba, Hf, Pb, Th, Eu, Tb, Dy, Ho, Er, Tm and Yb during weathering along the soil profile. Full article

The Qieliekeqi siderite deposit, located in the Tashkurgan block of western Kunlun, is a carbonate-hosted iron deposit with hydrothermal sedimentary features. This study integrates whole-rock geochemistry, stable isotopes, and zircon U–Pb–Hf data to investigate its metallogenic evolution. Coarse-grained siderite samples, formed in deeper water, exhibit average Al₂O₃/TiO₂ ratios of 29.14, δEu of 2.69, and δCe of 0.83, indicating hydrothermal fluid dominance with limited seawater mixing. Banded samples from shallower settings show an average Al₂O₃/TiO₂ of 17.07, δEu of 3.18, and δCe of 0.94, suggesting stronger seawater interaction under oxidizing conditions. Both types are enriched in Mn, Co, and Ba, with low Ti and Al contents. Stable isotope results (δ¹³C_PDB = −6.0‰ to −4.6‰; δ¹⁸O_SMOW = 16.0‰ to 16.9‰) point to seawater-dominated fluids with minor magmatic and meteoric contributions, formed under open-system conditions at avg. temperatures of 53 to 58 °C. Zircon U–Pb dating yields an age of 211.01 ± 0.82 Ma, with an average εHf(t) of −3.94, indicating derivation from the partially melted ancient crust. These results support a two-stage model involving Late Cambrian hydrothermal sedimentation and Late Triassic magmatic overprinting. Full article

This study evaluates the wear and corrosion resistance of the Cu-50Ni-5Al alloy reinforced with CeO₂ nanoparticles for potential use as anodes in molten carbonate fuel cells (MCFCs). Cu–50Ni–5Al alloys were synthesized, with and without the incorporation of 1% CeO₂ nanoparticles, by the mechanical alloying method and spark plasma sintering (SPS). The samples were evaluated using a single scratch test with a cone-spherical diamond indenter under progressive normal loading conditions. A non-contact 3D surface profiler characterized the scratched surfaces to support the analysis. Progressive loading tests indicated a reduction of up to 50% in COF with 1% NPs, with specific values drop-ping from 0.48 in the unreinforced alloy to 0.25 in the CeO₂-doped composite at 15 N of applied load. Furthermore, the introduction of CeO₂ decreased scratch depths by 25%, indicating enhanced wear resistance. The electrochemical behavior of the samples was evaluated by electrochemical impedance spectroscopy (EIS) in a molten carbonate medium under a H₂/N₂ atmosphere at 550 °C for 120 h. Subsequently, the corrosion products were characterized using X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the CeO₂-reinforced alloy exhibits superior electro-chemical stability in molten carbonate environments (Li₂CO₃-K₂CO₃) under an H₂/N₂ atmosphere at 550 °C for 120 h. A marked reduction in polarization resistance and a pronounced re-passivation effect were observed, suggesting enhanced anodic protection. This effect is attributed to the formation of aluminum and copper oxides in both compositions, together with the appearance of NiO as the predominant phase in the materials reinforced with nanoparticles in a hydrogen-reducing atmosphere. The addition of CeO₂ nanoparticles significantly improves wear resistance and corrosion performance. Recognizing this effect is vital for creating strategies to enhance the material’s durability in challenging environments like MCFC. Full article

The use of different nanoparticles (NPs) is increasing in a wide variety of everyday products. Nevertheless, most studies concerning NP risk assessment have evaluated exposure scenarios involving a single kind of NP. A stepwise study distinguishing between the effects resulting from exposure to one kind of NP and those resulting from different co-exposure scenarios to ${\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{CeO}}_2$ NPs at concentrations below acute toxicity was conducted with different analytical techniques. As a starting point, WST-1 viability assays were performed to assess whether the chosen exposure concentrations resulted in any acute loss of viability, which would hamper further insight into the cellular response to NP exposure. Then, data on NP dissolution and uptake were obtained via single-particle inductively coupled plasma–mass spectrometry (spICP-MS) and microwave-assisted ICP-MS. Additionally, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed to check for differences in the biological response to the exposure scenarios at the single-cell level. It was found that the proposed combined techniques provide insight into changes in biological responses as well as cellular metal contents among the exposure scenarios. In this work, a comprehensive tiered analytical strategy for evaluating the biological responses to challenging exposure scenarios is provided. The results highlight the necessity of selecting situations more closely resembling real life—including concentrations below acute toxicity and potential interactions due to multiple NPs—when estimating potential health risks. These findings thus provide a foundation and an incentive for further research into the complex processes leading to the observed effects. Full article

Carbonaceous shale has garnered significant interest as a viable alternative source of rare earth elements (REEs) besides conventional REE-bearing ores. This study characterized rare earth element + Yttrium+ Scandium (REYs) enrichment in the 11 core samples of carbonaceous shale (7) and coal (4) collected from Arnot Mine. Major elements of the studied carbonaceous shale (CS) and coal showed high amounts of SiO₂, Al₂O₃, and Fe₂O₃, indicating a high content of aluminosilicate and iron-rich minerals. The plots Na₂O + K₂O against SiO₂ suggested alkali granite, granite, and granodiorite provenance sources for the studied shale and coal. The samples showed enrichment in low and heavy rare elements crystallized from a low potassium tholeiitic and medium calc-alkaline magma based on the plots of La_N/Yb_N and K₂O vs. SiO₂. The mineralogical and maceral analysis revealed the dominant presence of kaolinite (15%–45%), and it was suggested as the cation exchange site resulting from the isomorphous substitution of Al³⁺ for Si⁴⁺. Additionally, siderite was suggested as one of the REY hosts due to the Fe³⁺ site forming a complex with the REE³⁺ ions. Furthermore, the samples were classified as lignite to sub-bituminous coal category with dominant minerals including kaolinite, quartz, and siderite. The outlook coefficient (Coutl) of REY in CS revealed a promising area for economically viable, having two enrichment types, including low (La, Ce, Pr, Nd, and Sm) and heavy (Ho, Er, Tm, Yb, and Lu). The Eu_N/Eu_N* and Ce_N/Ce_N* ratio for the current studied samples exhibited a weak negative to no anomaly, and most of the studied samples were characterized by distinctive positive Gd anomalies derived from sediment source regions weathered from alkali granite, granite, and granodiorite provenance formed from a low potassium tholeiitic and medium calc-alkaline magma. Full article

Zirconolite is a wasteform that can immobilize Pu. Herein, zirconolites comprising Ce as a Pu simulant and Al as a charge compensator of Ce/Pu were synthesized by sintering raw CaO, ZrO₂, TiO₂, CeO₂, and Al₂O₃ powder mixtures at 1400 °C in static air. The reduction behavior and phase transformation of zirconolites during their heat treatment in an Ar–H₂ gas flow were investigated. In pure and Ce–Al co-doped zirconolite compositions, 2M-zirconolite and small amounts of perovskite were obtained after sintering. In contrast, 2M-, 4M-zirconolite and relatively large amounts of perovskite were obtained in Ce-doped zirconolite composition. All zirconolite compositions first underwent reduction at ~1050 °C by forming a small domain of perovskite phase. Ce–Al co-doped zirconolite showed a smaller fraction of phase transformation in perovskite than Ce-doped zirconolite, indicating the advantage of using a charge compensator to prevent perovskite formation. Full article

Nanoparticles of GdAlO₃:Ce were synthesized with sodium dodecylbenzene sulfonate (SDBS) as the dispersant and ammonia as the precipitant by co-precipitation reaction to prepare precursors under different conditions. The phase composition of the precursors and the particle morphology were characterized by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The excitation and emission spectra of the resultant samples were analyzed using a photoluminescence spectroscope (PL). The results showed that the as-prepared, well-dispersed, nano-sized GdAlO₃:Ce powder displayed spherical morphology at the initial concentration of metallic salt in liquor of 0.3 mol/L; the synthesized temperature was 0 °C, and it was calcined at 1300 °C for 2 h. The relative intensity of the photoluminescence peak had the maximum value when the Ce³⁺ dopant content was 0.9 mol% (mole fraction). The concentration quench occurred when the Ce³⁺ dopant content exceeded 0.9 mol%, and the peak of the excitation spectrum appeared at a wavelength of 381 nm. Full article

Geochemical proxies are a reliable tool in deciphering the paleoenvironment and diagenetic alteration in carbonate rock units. The Lower Cretaceous Yamama Formation (LCYF) is an important carbonate unit of the Saudi Arabia region which has been studied in detail to evaluate the paleoenvironment and diagenetic alteration through geochemical studies. This study presents new data on petrography, stable isotopes, and trace and rare-earth elements to enhance our understanding on paleoenvironments, redox conditions, and paleosalinity during the deposition of these carbonate units. Field studies show that the formation is composed of thick-to-thin-bedded limestone. Petrographic studies show that the formation is mostly composed of mudstone, wackestone, packstone, and grainstone facies. The stable isotopic values of carbon (δ¹³C V-PDB = +0.58‰ to +2.23‰) and oxygen (δ¹⁸O V-PDB = −6.38‰ to −4.48‰) are directly within the range of marine signatures. CaCO₃’s dominance over SiO₂ and Al₂O₃ indicates minimal detrital contribution during the LCYF precipitation. The REE pattern suggests coeval marine signatures which include (i) a slight LREE depletion compared to HREEs (av. Nd/Yb_N = 0.70), (ii) negative Ce anomalies (av. Ce/Ce* = 0.5), and (iii) a positive La anomaly (av. La/La* = 1.70). Micritic limestone has low Hf (bdl to 0.4 µg/g), Sc (bdl to 2.5 µg/g), and Th (bdl to 0.8 µg/g) content, which suggests negligible detrital influence. The Ce content of different facies (Ce = 1u.80 to 12.85 µg/g) suggests that their deposition took place under oxic to dysoxic conditions. However, there is moderate variation during the deposition of MF-I, with higher Ce values as compared to MF-II, MF-III, and MF-IV, which suggests that the deposition of MF-I mostly took place in anoxic to dysoxic conditions. Full article

Methane and carbon dioxide, the primary contributors to global warming, are now at critical levels, threatening the extinction of numerous organisms on our planet. In this regard, dry reforming of methane reactions have gained considerable attention because of the conversion capacity of CH₄ and CO₂ into synthetic/energy-important syngas (H₂ and CO). Herein, a molecular sieve (CBV3024E; SiO₂/Al₂O₃ = 30) with ZSM-8-type pore architect, is utilized as the support for the active site of Ni and Ce promoters. Catalysts are characterized by surface area and porosity, X-ray diffraction study, Raman and infrared spectroscopy, thermogravimetry analysis, and temperature-programmed reduction/desorption techniques. A total of 2 wt.% ceria is added over 5Ni/CBV3024E to induce the optimum connectivity of aluminum in the silicate framework. NiO residing in these porous cages are mostly under “prominent interaction with support” which is reduced easily into metallic Ni as the active sites for DRM reactions. The active sites over 5Ni2Ce/CBV3024E remain stable during the DRM reaction and achieve ~58% H₂ yield after 300 min TOS at 42,000 mL/(g_cat.h) GHSV and ~70% H₂ yield after 20 h at 26,000 mL/(g_cat.h) GHSV. The high activity after a longer time stream justifies using CBV3024E molecular sieves as the support and ceria as the promoter for Ni-based catalyst towards the DRM reaction. Full article

The accumulation of greenhouse gasses (CH₄ and CO₂) results in an increase in the temperature of the atmosphere. The conversion of greenhouse gasses into chemicals and fuels with high added value benefits not only the environment but also energy development. A promising and well-studied process is the reforming of methane, where CH₄ and CO₂ are converted into syngas (CO and H₂). However, catalysts hinder the development of the process. In this paper, we investigate the conversion of CH₄ and CO₂ into syngas using a thermal conversion method. The catalysis performance was evaluated by reforming methane. Ni-based catalysts were prepared by different methods. All prepared catalysts were characterized (XRD, HRTEM et al.), and the process of reforming carbon dioxide–methane was carried out in a fixed bed reactor under atmospheric pressure and a high temperature. Ni(M) @CeO₂ is one of the most popular options due to the role of CeO₂. The deposition of coke in Ni-based catalysts was investigated. Full article

Recently, ceramic–carbonate membrane reactors have been proposed to selectively separate CO₂ at elevated temperatures and to valorize this pollutant gas by coupling a catalyzed reaction. This work explores using a membrane reactor to perform the oxidative reforming of propane by taking advantage of the CO₂- and O₂-permeating properties of a LiAlO₂/Ag–carbonate membrane. The fabricated membrane showed excellent permeation properties, such as CO₂/N₂ and O₂/N₂ selectivity, when operating in the 725–850 °C temperature range. The membrane exhibited remarkable stability during the long-term permeation test under operating conditions, exhibiting minor microstructural and permeation changes. Then, by packing a Ni/CeO₂ catalyst, the membrane reactor arrangement showed efficient syngas production, especially at temperatures above 800 °C. A hydrogen-rich syngas mixture was obtained by the contributions of the oxidative reforming and cracking reactions. Specific issues observed regarding the membrane reactor’s performance are attributed to the catalyst that was used, which experienced significant poisoning by carbon deposition during the reaction, affecting syngas production during the long-term test. Thermodynamic calculations were performed to support the experimental results. Full article

This study aims to investigate the depositional environment, sediment sources, and elemental occurrence of Upper Paleozoic coal in the Renjiazhuang Mining District, Western Ordos Basin. Furthermore, SEM-EDX, optical microscope (OM), ICP-AES, ICP-MS, and AAS were used. Compared with hard coal of the world, M3 coals were enriched in Ga, Li, Zr, Be, Ta, Hf, Nb, Pb, and Th, M5 coals were enriched in Li (CC = 10.21), Ta (CC = 6.96), Nb (CC = 6.95), Be, Sc, Ga, Hf, Th, Pb, Zr, In, and REY, while M9 coals were enriched in Li (CC = 14.79), Ta (CC = 5.41), Ga, W, Hf, Nb, Zr, Pb, and Th. In addition, minerals were mainly composed of kaolinite, dolomite, pyrite, feldspar, calcite, and quartz, locally visible minor amounts of monazite, zircon, clausthalite, chalcopyrite, iron dolomite, albite, fluorite, siderite, galena, barite, boehmite, and rutile. In addition, maceral compositions of M3 coals and M9 coals were dominated by vitrinite (up to 78.50%), while M5 coals were the main inertite (up to 76.26%), and minor amounts of liptinite. REY distribution patterns of all samples exhibited light REY enrichment and negative Eu anomalies. The geochemistry of samples (TiO₂ and Al₂O₃, Nb/Y and Zr × 0.0001/TiO₂ ratios, and REY enrichment types) indicates that the sediment sources of samples originated from felsic igneous rocks. Indicator parameters (TPI, GI, VI, GWI, V/I, Sr/Ba, Th/U, and Ce_N/Ce_N*) suggest that these coals were formed in different paleopeat swamp environments: M3 coal was formed in a lower delta plain and terrestrial (lacustrine) facies with weak oxidation and reduction, and M5 coal was formed in a terrestrial and dry forest swamp environment with weak oxidation–oxidation, while M9 coal was formed in a seawater environment of humid forest swamps and the transition from the lower delta plain to continental sedimentation with weak oxidation and reduction. Statistical methods were used to study the elemental occurrence. Moreover, Li, Ta, Hf, Nb, Zr, Pb, and Th elements were associated with aluminosilicates, and Ga occurred as silicate. Full article