Amount Of Cerium Research Articles

Selective cerium removal by thermal treatment of mixed rare earth oxalates or carbonates obtained from non-purified rare earth sulphate liquor

One of the world́s most abundant of all the rare earth elements (REE) is cerium. It represents about 50 wt% of total REE content in the main rare earth minerals used industrially (monazite and bastnaesite). However, cerium is not a valuable product if compared with the other REE. In the most current pyro-hydrometallurgical processes routes, a high amount of cerium goes to the rare earth liquor, incurring in high operational and capital costs in the solvent extraction step used in the separation of each individual rare earth element. In this context, this study evaluates the use of thermal treatment for rare earth oxalates and carbonates and also hydrochloric acid leaching of calcination products for selective separation of cerium from other REE. This investigation also sheds light on the mechanisms involved in the processes proposed. For this purpose, mixed rare earth and cerium oxalates, also mixed rare earth and cerium carbonates were used as precursors. The mixed rare earth salts used in the experiments were generated from a non-purified rare earth sulphate liquor. The results indicated that the minimum required temperature to fully decompose the mixed rare earth oxalates, cerium oxalate, mixed rare earth carbonates and cerium carbonate to their respective rare earth oxides (REE2O3) or CeO2, was 1100 °C, with 1 h of residence time. In the experiments carried out with mixed rare earth oxalates, Ce3+ was not fully oxidized to Ce4+, it formed a mixture of Ce2O3 and CeO2 represented by Ce4O7, which was completely dissolved in the hydrochloric acid solution (37 wt%). Therefore, in such case, cerium was not selectively removed from the mixed rare earth oxalates by thermal treatment and hydrochloric acid leaching. On the other hand, the Ce3+ presented in the composition of the pure cerium oxalate or carbonate was fully oxidized to Ce4+ (CeO2) under the same condition of calcination. As expected, CeO2 was not dissolved by the hydrochloric acid solution (37 wt%). It was concluded that mixed rare earth carbonates generated Ce0.60Nd0.40O1.80 (Ce1-xNdxO2-x/2, x = 0.40) when calcined under the same condition. This crystalline structure was not also dissolved by hydrochloric acid solution (37 wt%). As a result, a process flowsheet was proposed to remove cerium selectively from a rare earth ore.

Evidence of the coexistence of multivalence cerium oxide nano-particles in a sodium borate glass

A sodium borate glass containing both trivalent cerium oxide and tetravalent cerium oxide states nano particles of 2–5 nm in size was successfully prepared by doping the glass with varying amounts of cerium (IV) oxide with. X-ray absorption spectroscopy measurement was used to determine the coexistence of the multivalent state of cerium oxide in the borate glass. Significant changes in the trivalent and tetravalent cerium oxide concentrations were observed when the glass was melted using different melting parameters and different raw materials. Glass made with borax that contained of 0.05mols of CeO2 and melted at 1100 °C for 3 h had the highest concentration of trivalent cerium oxide. Transmission electron micrographs confirmed the release of trivalent Ce2O3 and tetravalent CeO2 nanoparticles from the glassy matrix. Fourier transform Infrared measurements suggest that the CeO2 in the glass acts as both a glass-former and glass modifier.

Structural/texture evolution of CaO/MCM‐41 nanocatalyst by doping various amounts of cerium for active and stable catalyst: Biodiesel production from waste vegetable cooking oil

Structural/texture evolution of CaO/MCM‐41 nanocatalyst by doping various amounts of cerium for active and stable catalyst: Biodiesel production from waste vegetable cooking oil

Influence of cerium on the microstructure and mechanical properties of an as-cast and Q&T steel

ABSTRACTIn the present work the influence of Cerium on the microstructure and the mechanical properties of a cast, quenched and tempered GS33NiCrMo744 steel is analysed. The study shows that the addition of cerium to the steel melt results in an increase of the number of CeS dispersoids with a size between 0.5 and 3.0 µm. The CeS dispersoids change the solidification morphology and the as-cast microstructure because as a nucleating agent for ferrite. Furthermore, a part of the cerium remains dissolved in the steel. The width of the columnar zone in 25 mm thick castings diametrically correlates with the amount of cerium. Furthermore, the secondary dendritic arm spacing (SDAS) has a tendency to decrease. The tensile strength of these cerium treated and then quenched and tempered (Q&T) steels increases with the number of cerium-containing dispersoids. However, samples with a wall thickness of 75 mm do not show this behaviour.

Methyl N-phenyl carbamate synthesis over Zn/Al/Ce mixed oxide derived from hydrotalcite-like precursors.

Methyl N-phenyl carbamate (MPC) is an important intermediate for the green synthesis of methylene diphenyl diisocyanate (MDI) as well as many other important products. In the present work, Zn/Al/Ce mixed oxides derived from hydrotalcite-like precursors were employed as effective and recoverable heterogeneous catalyst for MPC synthesis via DMC aminolysis. Zn/Al/Ce hydrotalcite-like precursors prepared via coprecipitation method and the resulting catalysts were characterized by means of XRD, BET, SEM and XPS. Strong interactions within the Zn/Al/Ce mixed oxides were observed via the addition of appropriate amount of cerium. The mixed oxides containing 2.5% cerium showed high DMC aminolysis activity giving aniline conversion of 95.8%, MPC selectivity of 81.6% and MPC yield of 78.2%. Moreover, as a heterogeneous catalyst, it also exhibited superiorities of easy recovery and recyclable stability for MPC synthesis.

Plasma-enhanced dispersion of Cr2O3 over ceria-doped MCM-41 nanostructured catalyst used in CO2 oxidative dehydrogenation of ethane to ethylene

Abstract A series of chromium oxide catalysts supported on the mesoporous Ce-MCM-41 molecular sieves with different (Si/Ce) molar ratios have been synthesized by hydrothermal/impregnation method and compared with the catalysts treated by plasma energy. The effect of Si/Ce molar ratio on the catalytic activity of Cr/MCM-41 nanocatalysts in dehydrogenation of ethane with CO2 was examined. The nanocatalysts were characterized by XRD, FESEM, EDX, TEM, BET and FTIR analysis. According to the results obtained by XRD analysis, by increasing the amounts of ceria in the support the content of α-Cr2O3 phase decreased. Also, the results of FESEM analysis indicates that particle size decreased by increasing ceria content and more uniform morphology achieved. Actually, the better characteristic properties and catalytic activity obtained when the molar ratio of Si/Ce was considered 25. On the other hand utilization of plasma energy in catalyst treatment developed a catalyst with better dispersion of chromium oxide and more uniform morphology and smaller particle size compared to the untreated catalyst. This nanocatalyst remains stable after 300 min time on stream reaction and 62.3% of ethylene yield achieved on it at 700 °C.

Synthesis of ZnO Nanosheets Morphology by Ce Doping for Photocatalytic Activity

Pure and gradient amounts of cerium (Ce)-doped zinc oxide (ZnO) were synthesized by a co-precipitation method and then their photocatalytic activities were inspected. X-ray diffractometer patterns of the pure and Cedoped ZnO nanostructures exhibit hexagonal wurtzite crystal structure. Field emission scanning electron microscopic images show that the ZnO nanospindel morphology is changed into two-dimensional (2D) polar surface-oriented nanosheets by a cerium doping level up to 0.06 mol.%. The red-shift in the near band edge emission and strong defect states emissions (blue and green) are observed in ZnO with respect to the Ce doping level. From the detailed photocatalytic experiments, the maximum methylene blue dye degradation, 86.9%, is observed on the 0.06 mol.% Ce-doped ZnO photocatalyst. The eventual conclusion is that the edges of the (001) crystallographic facet attach to each other to form a ZnO nanosheet morphology at a specific ratio of Ce doping that serves as a good photocatalyst for methylene blue dye degradation.

Catalytic decomposition of methane over rare earth metal (Ce and La) oxides supported iron catalysts

The concurrent production of carbon oxides-free hydrogen and crystalline carbon by the thermocatalytic decomposition of methane is advantageous for environmental and energy catalysis. In the present work, rare earth metal oxide-supported iron catalysts were effectively prepared via a simple co-precipitation method, and their catalytic activity for methane decomposition was evaluated for the first time. The structural, textural and redox properties of the prepared catalysts were characterized using different analytical methods. The powder X-ray diffraction patterns of the catalysts indicated the presence of CeO2 and Fe2O3 as different phases in the fresh Fe/CeO2 catalyst and La(OH)3, Fe2O3, and LaFeO3 as different phases in the fresh Fe/La2O3 catalysts. However, large amounts of cerium and lanthanum orthoferrites were identified in the reduced samples. The nitrogen sorption analysis indicated the presence of a mesoporous texture due to the homogeneous aggregation of catalyst particles. The catalysts showed high catalytic activity and stability for methane decomposition, and no deactivation was observed for a period of 360 min of time on stream. A maximum hydrogen yield of 66 ± 1% was observed for both of the catalysts at 800 °C. However, the Fe/CeO2 catalyst showed high catalytic stability, where the highest initial and final hydrogen yield was found to be almost constant for the Fe/CeO2 catalyst. However, a substantial drop in the hydrogen yield was noticed for the Fe/La2O3 catalyst during the course of the reaction. The improved surface stabilization and fine dispersion of iron nanocrystals on the ceria matrix made it highly active and stable compared to the lanthanum-based catalyst for the methane decomposition reaction. The encapsulation of metallic iron by carbon deposited on the Fe/La2O3 catalyst could be responsible for the low catalytic stability. Multi-walled carbon nanotubes with different shapes were deposited on the catalysts with respect to the support material. A set of spiral-shaped multi-walled carbon nanotubes with a double helical-shaped chain-like structure were deposited on the Fe/La2O3 catalyst, that is rarely formed in methane decomposition. The nanocarbon deposited on the Fe/CeO2 catalyst exhibited a high degree of crystallinity and graphitization, as shown by the Raman spectroscopy.

Earth-abundant transition metal oxides with extraordinary reversible oxygen exchange capacity for efficient thermochemical synthesis of solar fuels

Efficient storage of solar and wind power is one of the most challenging tasks still limiting the utilization of the prime but intermittent renewable energy sources. The direct storage of concentrated solar power in renewable fuels via thermochemical splitting of water and carbon dioxide on a redox material is a scalable approach with up to 54% solar-to-fuel conversion efficiency. Despite progress, the search for earth-abundant materials that can provide and maintain high H2 and CO production rates over long period of high-temperature cycles continues. Here, we report a strategy to unlock the use of manganese, the 12th most abundant element in the Earth's crust, for thermochemical synthesis of solar fuels, achieving superior thermochemical stability, oxygen exchange capacity, and up to seven times higher mass-specific H2 and CO yield than cerium dioxide. We observe that incorporation of a small fraction of cerium ions in the manganese (II,III) oxide crystal lattice drastically increases its oxygen ion mobility, allowing its reduction from oxide to carbide during methane partial oxidation with simultaneous Ce exsolution. High CO2 and H2O splitting rates are achieved by re-oxidation of the carbide to manganese (II) oxide with simultaneous reincorporation of the cerium ions. We demonstrate that the oxide to carbide reaction is highly reversible achieving remarkable CO2 splitting rates over 100 thermochemical cycles of methane partial oxidation and CO2 splitting, and preserving the initial oxygen exchange capacity of 0.65 molOmolMn−1 and 89% of the fuel production rates. Due to this extraordinarily high reversible oxygen exchange capacity, the 3% Ce-doped manganese oxide achieves an average mass-specific CO yield for CO2 splitting of 17.72 mmolCO g−1, which is significantly higher than that previously achieved in thermochemical redox cycles. More generally, these findings suggest that incorporation of small soluble amounts of cerium in earth-abundant transition metal oxides like manganese oxide is a powerful approach to enable solar thermochemical fuel synthesis.

Tailorable thermal expansion and hygroscopic properties of cerium-substituted Y2W3O12 ceramics

A new series of cerium-substituted Y2W3O12 ceramics were first fabricated with the goal of tailoring the thermal expansion and reducing the hygroscopicity. Influence of cerium substitution on the structure, hygroscopicity and thermal expansion property of Y2W3O12 ceramics were investigated using XRD, FESEM, HRTEM, XPS, TGA and TMA. Results indicate that the Y3+ can partly be substituted by Ce3+ in Y2-xCexW3O12 ceramics and increasing substitution of Y3+ in Y2W3O12 by Ce3+ results in the crystal structure change from orthorhombic to monoclinic. Single-phase Y2-xCexW3O12 ceramics can be synthesized in the range of 0.0 ≤ x ≤ 0.25 with an orthorhombic Y2W3O12-type crystal structure and 1.0 < x ≤ 2.0 with monoclinic Ce2W3O12-type crystal structure, respectively. As the amount of substituted cerium increases, the hygroscopic phenomenon of Y2-xCexW3O12 is significantly promoted, meanwhile the coefficient of thermal expansion gradually decreases. The linear coefficient of thermal expansion of Y2-xCexW3O12 ceramics can be adjusted from −13.094 × 10−6 K−1 to 2.327 × 10−6 K−1 by changing the substituted amount of cerium. Moreover, Y0.25Ce1.75W3O12 does not absorb moisture in air and shows almost zero thermal expansion from 182 °C to 700 °C and its coefficient of thermal expansion is tested to be −0.820 × 10−6 K−1. This low thermal expansion Y0.25Ce1.75W3O12 material may have great potential applications in manufacturing precision device in many fields.

One-Step FSP Synthesis of Nanocrystalline Fe/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and Fe-Ce/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Catalyst for CO&lt;sub&gt;2&lt;/sub&gt; Hydrogenation Reaction

Nanocrystalline Fe/Al2O3and Fe-Ce/Al2O3catalysts doped with various amounts of cerium were prepared using the one-step flame spray pyrolysis (FSP) technique. The characterization of the catalysts was measured by several methods such as X-ray diffraction, nitrogen physisorption and hydrogen temperature programmed reduction (H2-TPR) techniques. The results revealed that the FSP-made catalyst exhibited the characteristic pattern of FeAl2O4phase without any phases of aluminum or iron oxide. In addition, cerium (Ce) dopant did not alter crystal structure at low content. However, 7 wt% content of cerium dopant resulted in the formation of ceria (CeO) and iron oxide (Fe2O3) phase. The catalytic performance of the FSP-made catalyst was tested in carbon dioxide hydrogenation for selective production of long chain hydrocarbon, and was compared to conventional impregnation-made catalysts. In the comparison, the FSP-made catalyst exhibited lower catalytic activity but possessed a higher long chain hydrocarbon selectivity. After doping with Ce, the catalytic activity was improved while the hydrocarbon selectivity was decreased and shifted to the short chain hydrocarbon product. In the case of conventional-made catalysts, the activity remained unchanged but the hydrocarbon selectivity was decreased. Among all catalysts, the FSP-made Fe-Ce/Al2O3catalyst with 3% Ce-promoted catalyst exhibited the best performance in terms of selectivity to long chain hydrocarbon.

Room temperature synthesis and enhanced photocatalytic property of CeO2/ZnO heterostructures

To achieve better photocatalytic performance, we proposed a facile solid-state reaction method to produce CeO2/ZnO heterostructures. Ceria and zinc oxide were synthesized simultaneously by thoroughly grinding the mixture of zinc acetate dihydrate, cerium nitrate hexahydrate and sodium hydroxide. The morphology of the as-prepared heterostructures varies dramatically as different amount of ceria was introduced in the composition. The photocatalytic performance of CeO2/ZnO heterojunctions was 4.6 times higher than that of pure ZnO. The enhanced photocatalytic activity could be ascribed to that more electrons and holes could transport to the surface of catalysts and react with the pollution due to the extended light-responsive range, accelerated migration, increased specific surface area and suppressed recombination of photogenerated carriers.

Ultrasound assisted green synthesis of cerium oxide nanoparticles using Prosopis juliflora leaf extract and their structural, optical and antibacterial properties

Abstract Cerium oxide nanoparticles (CONPs) were prepared using ultrasound assisted leaf extract of Prosopis juliflora acting as a reducing as well as stabilizing agent. The synthesized CONPs were characterized by ultraviolet-visible absorption spectroscopy (UV-Vis), particle size analyzer (PSA), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). From the UV-Vis analysis, the optical band gap of the prepared CONPs (Eg = 3.62 eV) was slightly increased as compared to the bulk ceria (Eg = 3.19 eV). The phytochemicals in the extract reduced the particle size to 3.7 nm ± 0.3 nm, as it is evident from the PSA. FT-IR results confirmed the Ce-O stretching bands by showing the peaks at 452 cm-1. The Raman spectrumshowed a characteristic peak shift for CONPs at 461.2 cm-1. XRD analysis revealed the cubic fluorite structure of the synthesizednanoparticles with the lattice constant, a of 5.415 Å and unit cell volume, V of 158.813 Å3. XPS signals were used to determine the concentration of Ce3+ and Ce4+ in the prepared CONPs and it was found that major amount of cerium exist in the Ce4+ state. HRTEM images showed spherical shaped particles with an average size of 15 nm. Furthermore, the antibacterial activity of the prepared CONPs was evaluated and their efficacies were compared with the conventional antibiotics using disc diffusion assay against a set of Gram positive (G+) bacteria (Staphylococcus aureus, Streptococcus pneumonia) and Gram negative (G-) bacteria (Pseudomonas aeruginosa, Proteus vulgaris). The results suggested that CONPs showed antibacterial activity with significant variations due to the differences in the membrane structure and cell wall composition among the two groups tested.

Fluidized bed oxidative dehydrogenation of ethane to ethylene over VOx/Ce-γAl2O3 catalysts: Reduction kinetics and catalyst activity

Cerium-doped γ-Al2O3 (Ce-γAl2O3) catalyst supports are prepared with various amounts of cerium (0.2–5wt.%). An excess solvent impregnation method is used to saturate the vanadium (5wt%) on the cerium-modified supports. The XRD and FTIR characterization techniques indicate the presence of crystalline CeO2 phase, and amorphous VOx phases on the γAl2O3. Raman analysis shows the coexistence of poly-vanadate and mono-vanadate species. BET analysis reveals a high surface area for the synthesized catalysts with a type-IV adsorption isotherm. TPR/TPO analyses show that VOx/Ce-γAl2O3 catalysts are very active and stable over repeated reduction/oxidation cycles. The stability/purity of the synthesized catalyst is also confirmed by TGA analysis. NH3-TPD characterization shows mild acidity while the TPR kinetics predicts lower activation energy for reduction. Oxidative dehydrogenation (ODH) of ethane experiments are developed over VOx/Ce-γAl2O3 catalysts under gas-phase oxygen-free conditions in a fluidized CREC Riser Simulator. Temperatures and residence times are varied between 450 and 600°C and 10–50s, respectively. A maximum ethylene selectivity of 87.9% with 10.0% ethane conversion is achieved at 550°C using the 1.0wt.% cerium-doped VOx/γ-Al2O3 catalyst. The successive ethane injections and subsequent catalyst regeneration show the stable redox characteristics of the prepared ODH catalysts.

Catalytic spectrophotometric determination of trace amount of cerium(IV)

Based on a property that in dilute hydrochloric acid hydrogen peroxide oxidizes Ponceau S to fade and cerium(IV) has a catalytic effect on the reaction, a new spectrophotometric method was developed for the determination of trace cerium(IV). At 450 nm, the cerium(IV) concentration presents a good linear relationship over the range of 0.08‒4 μg/mL with the fading degree ΔA. Its linear regression equation is ΔA = 0.0475c (μg/mL) + 0.0007, with a correlation coefficient of 0.9991. The detection limit of method is 0.05 μg/mL. The method has been successfully applied to the determination of cerium in water and molecular sieve samples with good results. The relative standard deviations of eleven determinations were 0.97‒1.11 and 0.19‒1.01%, respectively. The recoveries of standard additions were 99.4‒99.9 and 99.2‒101.0%, respectively. The reliability of this method was certified by parallel determination against the dibromo-p-chlorochlorophosphonazo spectrophotometry.

Electrical properties of scandia- and ceria-stabilized zirconia ceramics

Electrical properties of 10mol% Sc2O3 and 1mol% CeO2 stabilized zirconia (10Sc1CeSZ) ceramics are investigated at temperatures up to 1000K. Measurements are performed by combining 2- and 4-electrode methods with working frequencies of 10Hz to 10GHz and 10Hz to 2MHz, respectively. An advantage of 4-electrode method allows direct determination of contributions of grain and grain boundary conductivities to the total conductivity. These contributions at higher temperatures (when the responses of grain and grain boundary move to high frequencies) and permittivity are reliably measured by employing high frequency equipment. Obtained total conductivity values are found to be slightly higher, and activation energies lower than the vast majority of literature values. Dependence of character of distribution of charge carriers' relaxation times in ceramics grain on temperature is also estimated. It is found that grain conductivity values for 10Sc1CeSZ practically coincide with these for 10mol% Sc2O3 stabilized zirconia (10ScSZ) at 830K and higher temperatures. This indicates that an addition of 1mol% CeO2 to 10ScSZ practically has no effect on charge transport and dielectric properties of cubic 10ScSZ, though even such a small amount of ceria stabilizes cubic phase at 830K and lower temperatures.

Selective Oxidation of Cyclohexane Using Graphene Oxide‐Supported Ceria Nanocomposites with Exposed Active {1 0 0} Facets

AbstractThe present study is focused on the synthesis and characterization of ceria loaded graphene oxide (GO) and investigates their catalytic activity on vapor phase selective oxidation of cyclohexane. In this regards, we have synthesized various loading of CeO2 on GO with two different morphology includes nanocrystals and flower‐like, which designated as CeO2(x)/GO (where x= 0, 0.2, 0.4, 0.6, 0.8 and 1.0 wt.%). The physico‐chemical properties of the materials were extensively studied with help of XRD, N2 adsorption desorption (BET), DRUV‐Vis, HRSEM, HRTEM, H2‐TPR and XPS techniques. The crystalline nature of materials were analyzed by XRD, pure ceria shows high crystalline size about 15. 3 nm compared to others. Surface area of synthesized materials has been obtained with help of N2 adsorption desorption analysis, pure ceria and graphene oxide shows surface area about 93 and 574 m2/g, respectively. XPS and DRUV‐Vis spectra were confirms the presence of enormous Ce3+ ions in the lattice. The presence of nanocrystals and flower‐like morphology of CeO2(x)/GO were confirmed by HRSEM images. HRTEM images were clearly illustrated that the presence of dominant active {1 0 0} facets in flower‐like CeO2/GO than that of nanocrystalline morphology. The catalytic activity of materials has been evaluated on selective oxidation of cyclohexane using air as a green oxidant. The key reaction parameters were varied to study the stability, activity and selectivity of the catalysts. The activity of the catalysts is correlated with their physico‐chemical properties, and these results concluded that suitable amount of ceria and it's flower‐like morphology on GO is essential for selective oxidation of cyclohexane at low temperature (180 °C) compared to nanocrystalline morphology. Hence, flower‐like CeO2(0.4)/GO is a most suitable catalyst for high conversion (90%) of cyclohexane into cyclohexanone with 74% selectivity due to occurrence of enormous {1 0 0} facet and Ce3+.

Structure of active cerium sites within bioactive glasses

AbstractThe inclusion of small amounts of cerium within the matrix of bioactive glasses, a class of materials used for bone tissue reparation and regeneration, adds a very important antioxidant property. In this work we investigate the local structure around cerium ions in cerium oxide doped bioactive phosphosilicate and silicate glasses, by X‐ray absorption fine structure at the Ce K‐edge, combined with classical molecular dynamics (MD) simulations. The local structure of the active Ce sites results significantly different from the one in bulk cerium oxide phases. A contracted Ce–O first shell distance with respect to bulk oxides is detected, in full agreement with the results of MD simulations. The cerium environment in the glass matrix at different stages of the reaction with H2O2 does not show significant modifications, in spite of the very high catalytic activity. The accurate description of the active Ce sites within bioactive glasses reported in this work is an important step toward an atomic scale understanding of the material functionalities.

Investigation on the cation location, structure and performances of rare earth-exchanged Y zeolite

A series of Y zeolites exchanged with different amount of cerium and lanthanum cations were investigated. Comprehensive routine analysis tools including X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), X-ray diffraction (XRD) and Py-Fourier transform infrared spectroscopy (Py-FTIR) were used to identify the cation location, and the result was verified via XRD Rietveld study. The results revealed that almost all the RE cations in RE-4, most cations in RE-8 to RE-14 and part of cations in RE-16 were located in the sodalite cage. The AlIV/(AlV+AlVI) values revealed by 27Al MAS NMR spectra, the silicon aluminum ratio of the framework (SARF) values deduced from 29Si MAS NMR spectra and XRD, and hydroxyl amount were reasonably in accordance with the location and content of rare earth cations. The hydrothermal stability derived from in situ XRD investigation and catalyst activity provided by micro-activity test manifested that samples RE-8 to RE-14 exhibited better performances than RE-4 and RE-16, among which RE-12 had the best properties. The phenomena were interpreted by the cation location and structural properties.

CO2 reforming of methane over Ni/ZnAl2O4 catalysts: Influence of Ce addition on activity and stability

The catalytic performance of Ni supported on Ce-promoted ZnAl2O4 was evaluated in methane dry reforming. The effect of different nominal loadings of cerium (3, 5 and 7 wt%) in the activity, product yield and stability was studied. Ce presented a promote effect in catalytic activity, product yield and especially in stability. However the catalytic performance was considerably influenced by the amount of cerium. SEM images presented smaller particles and TPR profiles revealed stronger active phase/support interaction by Ce addition which led to increasing methane conversion and decreasing coke deposition. Although high amount of Ce was not in favor of its promoting effect due to aggregation of CeO2 on the catalyst surface. Among the catalysts investigated, the optimal catalytic activity and stability was achieved over the sample with 5 wt% of cerium.