Ce Zr Research Articles

Novel compounds of cerium binary alloys from high-throughput first-principles calculations

We report on a comprehensive study of 19 binary systems of cerium (Ce) and 4d or 5d transition metals involving high-throughput first-principles calculations. For Ce–Y, Ce–Zr, Ce–Nb, Ce–Mo, Ce–Hf, Ce–Ta, Ce–W, and Ce–Re, the computations and experiments agree that no compounds can form. However, for Ce–Tc and Ce–Au, the computations predict that stable compounds can form, although none have yet been synthesized experimentally. Regarding other possible systems, in addition to known compounds, a few dozen as-yet unreported compounds are predicted. For some systems, our calculations also identify novel crystalline structures with higher energetic stabilities compared to the corresponding experimentally reported structure at some particular compositions. According to the electronic-structure calculations, there is definite hybridization between the 4d or 5d electron states of the transition metals (i.e., with Tc, Ru, Rh, Pd, Os, Ir, and Pt) and the 4f electron states of Ce, whereas it is much weaker in Ce–Ag, Ce–Cd, Ce–Au, and Ce–Hg. Moreover, the elastic properties of these compounds are given. This systematic study offers new data for Ce-based alloys and will guide future studies of these important systems.

Development of thermodynamic databases in the system U–Zr–Ce–Cs–Fe–B–C–I–O–H for application to simulating phase equilibria in severe nuclear accidents

ABSTRACTIn case of severe nuclear accidents involving melt down of nuclear fuels at high temperatures, it is of considerable importance to accurately evaluate the highly-volatizing behavior of fission products (FPs) over multicomponent debris. Particularly, cesium (Cs)- and iodine (I)- bearing chemical species are regarded as notable FPs. In the present work, the authors have generated original thermodynamic databases for the system U–Zr–Ce–Cs–Fe–B–C–I–O–H featuring Cs- as well as I-bearing subsystems, which are contained in oxide, iodide, and metal (including borides and carbides) sub-databases. It has been confirmed that the phase diagrams calculated by the present set of the databases reproduce the corresponding literature data well in various kinds of subsystems of the above multicomponent system. The present set of databases has subsequently been applied to simulate phase equilibria and volatizing behavior of Cs- and I-including species, respectively, in multicomponent debris under specific temperature and atmospheric conditions corresponding to severe nuclear accidents.

Promotion effects of Ce added Fe–Zr–K on CO2 hydrogenation to light olefins

Microspherical and uniform Fe–Zr–Ce–K catalysts were prepared by the microwave assisted precipitation followed by impregnation and promoted CO2 hydrogenation toward advantageous synthesis of light olefins. The reducibility, surface basicity and surface atom composition of the catalysts was tuned as the Ce content was varied. The ceria spacer restrained the growth of the Fe2O3 crystallite. Ce addition weakened the interaction between Fe species and zirconia and the reduction of the Fe species became easier. On 35Fe–7Zr–1Ce–K at 320 °C and 2 MPa, the conversion of CO2 and the selectivity of C2–C4 olefins were 57.34 and 55.67%, respectively. The ratio of olefin/paraffin was 7. The selectivity of CO and C5+ hydrocarbons were 3 and 15.87%, respectively. The enhanced performance is attributed to intensified bifunctional activity toward CO hydrogenation as well as the reverse water–gas shift reaction.

Tailored metastable Ce-Zr oxides with highly distorted lattice oxygen for accelerating redox cycles.

Ceria-based catalysts are widely used in oxidation or oxidation-reduction reactions in the field of environmental science. Their catalytic functions are determined by their ability to exchange oxygen species with oxidants. The enhancement of oxygen release is desired since it is often the rate-determining step in redox cycles. Herein, we developed a lattice oxygen distortion method to enhance oxygen activation by quenching the Ce-Zr oxide nanoparticles formed from an extremely high temperature. This process can ensure the formation of solid solutions as well as avoiding atomic rearrangement during calcination, retaining the lattice oxygen at a metastable and disordered state without vacancies. Reduction, vacuum or metal deposition will easily induce oxygen release accompanied by vacancy creation. The metastable oxides can provide about 19 times more oxygen vacancies than traditional ones in a CO atmosphere. CO oxidation rates increased with increasing Zr content from 25 to 75% and achieved a new level, which is attributed to the acceleration of oxygen circulation via promoting oxygen release and supplying plenty of oxygen vacancies for redox cycles. This strategy is expected to be applied in the design and fabrication of improved oxygen storage materials.

Methane dry reforming over Ni catalysts supported on Ce–Zr oxides prepared by a route involving supercritical fluids

AbstractCe0.5Zr0.5O2mixed oxides were prepared in a flow reactor in supercritical isopropanol with acetylacetone as a complexing agent. Variation of the nature of the Zr salt and the temperature of synthesis affected the phase composition, morphology and specific surface area of oxides. X-ray diffraction and Raman spectroscopy studies revealed formation of metastable t” and t’ phases. Oxides are comprised of agglomerates with sizes depending on the synthesis parameters. Loading NiO decreases the specific surface area without affecting X-ray particle sizes of supports. Such sintering was the most pronounced for a support with the highest specific surface area, which resulted in the lowest surface content of Ni as estimated by X-ray photoelectron spectroscopy and in the formation of flattened NiO particles partially embedded into the support. The catalytic activity and stability of these samples in the dry reforming of methane were determined by the surface concentration of Ni and the morphology of its particle controlled by the metal-support interaction, which also depends on the type of catalyst pretreatment. Samples based on ceria-zirconia oxides prepared under these conditions provide a higher specific catalytic activity as compared with the traditional Pechini route, which makes them promising for the practical application.

Phosphate Functionalization of CeO2–ZrO2 Solid Solutions for the Catalytic Formation of Dimethyl Carbonate from Methanol and Carbon Dioxide

AbstractPhosphate surface groups on CeO2–ZrO2 solid solutions were generated by treating Ce–Zr–hydroxide precursors with phosphoric acid. In the catalytic formation of dimethyl carbonate (DMC) from methanol and CO2, the performance of the P‐modified samples was markedly affected relative to that of the unmodified ones: Phosphate treatment caused remarkable changes in the phase composition, acid–base properties, and the ability to form monodentate methoxy intermediates. The DMC yield (1.6 %) was successfully improved from 0.24 to 1.6 % by phosphate modification of CeO2–ZrO2 (Ce/Zr=4.7, P/Zr=0.13) and by performing the reaction at 170 °C and 6.5 MPa for 1 h.

The Synthesis of Ce1 – xZr x O2 Oxides in Supercritical Alcohols and Catalysts for Carbon Dioxide Reforming of Methane on Their Basis

The effect of the features of starting zirconium compounds on the solvothermal synthesis of mixed Ce–Zr oxides in a flow reactor using ethanol and isopropanol as a supercritical medium was studied. The phase composition and structural properties of the synthesized samples were investigated using X-ray diffraction analysis (XRD) and Raman spectroscopy. The morphology and textural properties were studied by transmission electron microscopy (TEM) and thermal desorption of nitrogen. It was found that the use of zirconium oxychloride or acetate as the starting substances results in the formation of a mixture of phases enriched with cerium or zirconium, whereas the use of zirconium butoxide with acetylacetone as a complexing agent allows obtaining a homogeneous solid solution. The catalytic properties of the synthesized oxides with supported Ni were tested in methane dry reforming (MDR). The catalyst containing a single-phase oxide synthesized in the presence of acetylacetone exhibited much higher activity, selectivity and coking stability.

Geochronology and geochemistry of the granitoids and ore – forming age in the Xiaoyao tungsten polymetallic skarn deposit in the Jiangnan Massif tungsten belt, China: Implications for their petrogenesis, geodynamic setting, and mineralization

The Xiaoyao tungsten polymetallic skarn deposit in the eastern Jiangnan Massif of Yangtze Block is located at the contact between a granodiorite pluton and Sinian–Cambrian limestone. The intrusions in the tungsten-rich district comprise the Xiaoyao and other granodiorite plutons and granite porphyry dikes. The age determinations by LA–ICP–MS U–Pb dating of zircons indicate that the granodiorite formed at 149.4±1.1Ma, whereas the granite porphyry was emplaced at 133.2±0.7Ma. Re–Os dating of molybdenite from the skarn orebodies yielded a weighted average age of 148.7±2.3Ma (n=5). These ages indicate that the tungsten mineralization is temporally related to the granodiorite. The granodiorites are metaluminous (A/CNK=0.86–0.98) and in the high-K calc-alkaline series. They contain hornblende and have a negative correlation between P2O5 and SiO2, indicating that they are typical I-type intrusions. The granite porphyries exhibit high alkali contents (Na2O+K2O=7.97–9.53%), elevated FeOT/(FeOT+MgO) ratios (0.83–0.94), high concentrations of Zr, Nb, Ce, and Y, and high Zr saturation temperatures (average of 812°C); thus, they are geochemically similar to A-type intrusions. The initial 87Sr/86Sr and εNd(t) values range respectively from 0.7074 to 0.7083 and from −7.9 to −1.3 for the granodiorite, and from 0.7008 to 0.7083 and from −6.3 to −4.7 for the granite porphyry. In addition, two-stage Nd model ages (T2DM) of 1.0–1.6Ga for the granodiorite and 1.3–1.4Ga for the granite porphyry indicate that the Proterozoic crustal rocks of the Shangxi Group could have contributed to the Xiaoyao magmas. The rhenium contents of the molybdenite grains vary from 32 to 136ppm, suggesting that the molybdenum was derived mainly from a mixture of mantle and crustal sources. Based on the new geochemical data and regional geological investigations, we propose that the Late Jurassic mineralization-related I-type granodiorite was derived from the Neoproterozoic Shangxi metamorphic rocks with some additional input of mantle material. The magmatism was triggered by asthenospheric upwelling induced by slab tearing during oblique subduction of the paleo-Pacific plate beneath the South China Block.

Effect of addition of elements on two-glass-forming ability of Zr–Ce–Co–Cu immiscible alloys

ABSTRACTThe effects of Al element addition and partial substitution of Ce with La, Pr, and Nd on the two-glass-forming ability of the phase-separating Zr–Ce–Co–Cu alloy system have been studied. The distribution of the additions in the two coexistent immiscible liquids was analysed thermodynamically. The results indicate that Al almost equally distributes in the two liquids, whereas the elements La, Pr, and Nd are predominantly found in the Ce–Cu-rich liquid. X-ray diffraction analysis reveals that these additions obviously enhance the two-glass-forming ability of the coexisting liquids. This work presents a strategy for improving the two-glass-forming ability of immiscible alloys to obtain phase-separated bulk metallic glasses.

In Situ Study of the Oxygen-Induced Transformation of Pyrochlore Ce2Zr2O7+x to the κ-Ce2Zr2O8 Phase

Temporary storage of oxygen in a solid catalyst is imperative for many important industrial oxidation reactions in the gas phase, for instance the post-treatment of automotive exhaust gas. A peculiar mixed Ce–Zr (1:1) oxide, the ordered κ-Ce2Zr2O8 phase, is a promising catalytic material exhibiting an extraordinarily high oxygen storage capacity (OSC) and high thermal and chemical stability. We elucidate the temperature-dependent transformation between the pyrochlore pyr-Ce2Zr2O7 and κ-Ce2Zr2O8 phase upon oxygen uptake by in situ X-ray diffraction, X-ray absorption, and in situ Raman spectroscopy, providing insights into the electronic and structural changes on the atomic level, which are at the heart of the extraordinarily high OSC. We demonstrate that the Ce3+ concentration can be followed during transformation in situ by Raman spectroscopy of the electronic spin flip in the f-shell of Ce3+. The catalytic activity of the κ-Ce2Zr2O8 phase was investigated without an additional active component such as no...

Effect of Cs-Ce-Zr Catalysts/Soot Contact Conditions on Diesel Soot Oxidation.

Cs–Ce–Zr catalysts with various weight ratios are prepared by the sol–gel method in this paper. The main crystalline phases were identified by X-ray diffraction. The activities of catalysts during soot combustion were tested by thermogravimetric and differential scanning calorimetry. The contact conditions of soot/catalysts (sintered at 450 and 380 °C, respectively, under loose and tight contact conditions) were observed by scanning electron microscopy to study the effect of contact conditions on catalytic activity, and it was determined that the catalytic activities under tight contact conditions are superior to those under loose contact conditions. However, the soot oxidation rate speeds up after the peak temperature of about 450 °C under loose contact conditions, which is due to the fact that the contact condition is enhanced by melting CsNO3. The soot onset ignition temperature is lower for the catalysts with more Cs content under loose contact conditions. The minimum gaps of the soot onset ignition temperature and soot oxidation rates under the two contact conditions are 32 and 7 °C, which shows that the gap of catalytic activities under the respective contact conditions can be decreased by the formation of different crystalline phases.

Petrology, geochemistry and zircon U–Pb geochronology of the Jurassic porphyry dykes in the Dehua gold field, Southeast China: Genesis and geodynamics

The widespread tectonic and magmatic events in Southeast China during the Mesozoic were accompanied by large‐scale metallogenesis. Here, we investigate the petrology, geochemistry, and zircon U–Pb age of the porphyry dykes in relation to the gold mineralization at Dongyang deposit in the Fujian Province. The geochemical data show silica‐rich and Mg‐ and Ca‐poor A‐type granite affinity for the dykes. The rocks have high concentrations of Light Rare Earth Elements (LREE) and Large Ion Lithophile Elements (LILE) and relatively low contents of Heavy Rare Earth Elements (HREE) and High Field Strength Element (HFSE). They display (La/Yb)N and (La/Sm)N values in the range of 5.7 to 31.4 and 6.0 to 8.3, respectively, with negative anomalies of Ba, Nb, Ta, Sr, Zr, Eu, and Ti and positive Ce anomaly. The source magma for the dykes was derived from a mixture of partially melted Al‐rich crustal material, with an input of mantle components. We present sensitive high‐resolution ion microprobe zircon U–Pb data from the dykes, which show emplacement ages in the range of 158 to 162 Ma, coinciding with the onset of the Yanshanian magmatism in Southeast China. Integrating the data obtained from studies on geology, geochronology and petro‐geochemistry, we suggest that the dykes played role in controlling the gold mineralization, and the magmatism and gold mineralization are the response of continental lithosphere thinning in Southeast China triggered by the subduction of the ancient Pacific Ocean Plate.

Simultaneous NO x and Particulate Matter Removal from Diesel Exhaust by Hierarchical Fe-Doped Ce-Zr Oxide.

Particulate matter and NOx emissions from diesel exhaust remains one of the most pressing environmental problems. We explore the use of hierarchically ordered mixed Fe–Ce–Zr oxides for the simultaneous capture and oxidation of soot and reduction of NOx by ammonia in a single step. The optimized material can effectively trap the model soot particles in its open macroporous structure and oxidize the soot below 400 °C while completely removing NO in the 285–420 °C range. Surface characterization and DFT calculations emphasize the defective nature of Fe-doped ceria. The isolated Fe ions and associated oxygen vacancies catalyze facile NO reduction to N2. A mechanism for the reduction of NO with NH3 on Fe-doped ceria is proposed involving adsorbed O2. Such adsorbed O2 species will also contribute to the oxidation of soot.

Characterization of Ce (1−x) Zr x O 2 yellow nanopigments synthesized by a green sol-gel method

Abstract In this paper, we report on the synthesis of Ce (1−x) Zr x O 2 yellow nanopigments (NPs) by a simple green sol-gel method, using gelatin as the stabilization and polymerization agent. Thermogravimetric analysis (TGA) was employed to obtain the optimum gel calcination temperature. The synthesized Ce (1−x) Zr x O 2 powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), UV–vis spectroscopy and CIE-L * a * b * measurement. The XRD patterns of the samples calcined at 600 °C revealed the formation of the desired crystal structures without any secondary phases, confirmed by Raman analysis. The TEM images indicated that the pigments' particle shapes are almost spherical with average particle size of about 8 nm. It was found that by increasing Zr +4 concentrations the absorption edge of the produced NPs have a red-shift. The produced NPs had brilliant yellow colour, derived from CIE-L * a * b * coordinates.

Methanation of Carbon Dioxide over Ni–Ce–Zr Oxides Prepared by One-Pot Hydrolysis of Metal Nitrates with Ammonium Carbonate

Ni–Ce–Zr mixed oxides were prepared through one-pot hydrolysis of mixed metal nitrates with ammonium carbonate for CO2 methanation. The effects of Ce/Zr molar ratio and Ni content on catalysts’ physical and chemical properties, reduction degree of Ni2+, and catalytic properties were systematically investigated. The results showed that Zr could lower metallic Ni particle sizes and alter interaction between Ni and supports, resulting in enhancements in the catalytic activity for CO2 methanation. The Ni–Ce–Zr catalyst containing 40 wt % Ni and Ce/Zr molar ratio of 9:1 exhibited the optimal catalytic properties, with 96.2% CO2 conversion and almost 100% CH4 selectivity at a low temperature of 275 °C. During the tested period of 500 h, CO2 conversion and CH4 selectivity over Ni–Ce–Zr catalyst kept constant under 300 °C.

Comparative Study of Ammonia‐fueled Solid Oxide Fuel Cell Systems

AbstractSeveral solid oxide fuel cell (SOFC) systems can be considered for the NH3 utilization. In this study, the catalytic activity and long‐term stability of the NH3 decomposition reactor with the Ni/Y2O3‐based catalysts and the autothermal NH3 cracker with the Co–Ce–Zr composite oxide catalyst were investigated. Moreover, the NH3 decomposition reactor and the autothermal NH3 cracker were combined with the SOFC stack and their performances of the stack were compared to those fueled with NH3 and H2/N2. The power output of each SOFC stack was over 200 W. Moreover, it was demonstrated that the direct NH3‐fueled SOFC stack was stable for 1,000 h at 770 °C without significant degradation.

Mesoporous cerium–zirconium oxides modified with gold and copper – synthesis, characterization and performance in selective oxidation of glycerol

Au–Cu interaction on Ce–Zr oxides leads to the increase of activity in glycerol oxidation and selectivity to glyceric acid.

The NO oxidation performance over Cu/Ce0.8Zr0.2O2 catalyst

The Cu-doped Ce0.8Zr0.2O2 (CZ) catalyst was investigated in terms of its NO oxidation activity, structure and surface characteristics. The Cu/CZ catalyst with 6 wt% Cu loading and 550°C calcination temperature of CZ support showed the best catalytic performance, and over 50% NO conversion was obtained in a wide temperature range (250–370°C). Moreover, this catalyst showed good resistance to H2O and SO2. The dispersion of CuO species on the smaller crystallite size CZ support was favorable for NO adsorption. The Cu–Ce–Zr solid solution provided the sites of oxygen vacancies, prompted the formation of active oxygen, which in sum improved the oxidation activity of NO.

Catalytic Oxidation of CO and Soot over Ce-Zr-Pr Mixed Oxides Synthesized in a Multi-Inlet Vortex Reactor: Effect of Structural Defects on the Catalytic Activity.

In the present work, ceria, ceria-zirconia (Ce = 80 at.%, Zr = 20 at.%), ceria praseodymia (Ce = 80 at.%, Pr = 20 at.%) and ceria-zirconia-praseodymia catalysts (Ce = 80 at.%, Zr = 10 at.% and Pr = 10 at.%) have been prepared by the multi-inlet vortex reactor (MIVR). For each set of samples, two inlet flow rates have been used during the synthesis (namely, 2 ml min−1 , and 20 ml min−1) in order to obtain different particle sizes. Catalytic activity of the prepared materials has been investigated for CO and soot oxidation reactions. As a result, when the catalysts exhibit similar crystallite sizes (in the 7.7–8.8 nm range), it is possible to observe a direct correlation between the Ov/F2g vibrational band intensity ratios and the catalytic performance for the CO oxidation. This means that structural (superficial) defects play a key role for this process. The incorporation of Zr and Pr species into the ceria lattice increases the population of structural defects, as measured by Raman spectroscopy, according to the order: CeO2 < Ce80Zr20 < Ce80Zr10Pr10 < Ce80Pr20. On the other hand, the presence of zirconium and praseodymium into the ceria lattice does not have a direct beneficial effect on the soot oxidation activity for these catalysts, in contrast with nanostructured ones (e.g., Ce–Zr–O nanopolyhedra, Ce–Pr–O nanocubes) described elsewhere (Andana et al. Appl. Catal. B 197: 125–137, 2016; Piumetti et al., Appl Catal B 180: 271-282, 2016).

Highly dispersed silica-supported ceria–zirconia nanocomposites: Preparation and characterization

Ternary CeO2–ZrO2/SiO2 nanocomposite oxides were synthesized by a liquid-phase method and subjected to thermal treatment at 550 °C. The physicochemical characterization of the obtained nanosized systems was carried out by various techniques, namely: X-ray diffraction (XRD), nitrogen adsorption–desorption, Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). The XRD measurements revealed the presence of cubic phase Zr0.4Ce0.6O2 in CZS1 (CeO2:ZrO2:SiO2 = 3:10:87) and CZS2 (CeO2:ZrO2:SiO2 = 10:10:80) samples. The crystallinity of this phase slightly increased with increasing ceria content in nanocomposites. Raman spectra indicated the presence of oxygen vacancies in the case of CZS2 and an absence displacement of oxygen ions from their normal lattice positions in both of the samples. XPS data indicated a significant quantity of Ce3+ ions present in the composites, which is greater in the CZS2 composite. In the case of CZS systems the TEM–HRTEM results showed well-dispersed nanosized Zr–Ce–oxides over the surface of amorphous SiO2. All the characterization techniques revealed that silica does not form any compounds with the dispersed Zr–Ce-oxides. The prepared materials were tested in catalytic reaction of CO oxidation in the presence of H2 and it was shown that CZS2 system had better performance than CZS1 one.