Higher Ce Content Research Articles

An investigation of the factors influencing the activity of Cu/Ce xZr 1− xO 2 for methanol synthesis via CO hydrogenation

An investigation was carried out to identify the effects of incorporating Ce into ZrO 2 on the catalytic activity and selectivity of Cu/Ce x Zr 1− x O 2 for the hydrogenation of CO to methanol. A series of Ce x Zr 1− x O 2 solid solutions was synthesized by forced hydrolysis at low pH. The resulting catalysts were characterized to determine the structure of the mixed oxide phase, the H 2 and CO adsorption capacities of the catalyst, and the reducibility of both oxidation states of both Cu and Ce. The methanol synthesis activity goes through a maximum at x = 0.5 , and the activity of 3 wt% Cu/Ce 0.5Zr 0.5O 2 catalyst is four times higher than that of 3 wt% Cu/ZrO 2 when tested at total pressure of 3.0 MPa and temperatures between 473 and 523 K with a feed containing H 2 and CO (H 2/CO=3). The maximum in methanol synthesis activity is paralleled by a maximum in the hydrogen adsorption capacity of the catalyst, an effect attributed to the formation of Ce 3+ O(H) Zr 4+ species by dissociative adsorption of H 2 on particles of supported Cu followed by spillover of atomic H onto the oxide surface and reaction with Ce 4+ O Zr 4+ centers. In situ infrared spectroscopy shows that formate and methoxide groups are the primary adspecies present on Cu/Ce x Zr 1− x O 2 during CO hydrogenation. The rate-limiting step for methanol synthesis is the elimination of methoxide species by reaction with Ce 3+ O(H) Zr 4+ species. The higher concentration of Ce 3+ O(H) Zr 4+ species on the oxide surface, together with the higher Brønsted acidity of these species, appears to be the primary cause of the four-fold higher activity of 3 wt% Cu/Ce 0.5Zr 0.5O 2 relative to 3 wt% Cu/ZrO 2.

Formation of Superoxochromium(III) by a Novel Mechanism

The reduction of chromate ion by l-cysteine in near-neutral aqueous solutions was studied by u.v.–vis spectroscopy. The rate constants for the formation, decomposition and redox degradation of a CrVI thioester intermediate (both in the absence and in the presence of dissolved O2) were determined by the use of a nonlinear least-squares regression to fit the experimental data to a double-exponential integrated rate law. Superoxochromium(III), CrOO2+, could be observed as a long-lived intermediate by the use of u.v. difference spectroscopy (peaks at 238 and 292 nm). The effects of several reaction variables on the yield of the intermediate CrOO2+ were studied. A striking result was that the yield decreased as the concentration of dissolved O2 increased. In the presence of phosphate buffer, the yield showed a maximum at pH 6.8. Formation of CrOO2+ was suppressed by the additives Mn2+, H2O2, d-ribose, 2-deoxy-d-ribose and a high concentration of Ce3+, whereas a low concentration of the latter enhanced its appearance. A novel mechanism for the formation of CrOO2+ from CrVI and l-cysteine (involving the intramolecular formation of an O–O bond) is proposed, and the possible routes for the decay of this intermediate are discussed. This novel mechanism might offer new insights into the redox chemistry of chromate ions.

Thermoelectric Properties of Nano-structure Controlled Sm2−xCexCuO4 Thin Films

ABSTRACTSm2−xCexCuO4 (SCCO) is well known as an n-type superconductor with large physical anisotropies. In order to enhance the thermoelectric conversion performance, we have prepared the SCCO epitaxial films and controlled a crystallographic orientation, a carrier concentration and an introduction of nano-structures. The SCCO films and nano-structures consisting of CeO2 were fabricated using pulsed laser deposition method on SrTiO3 single crystalline substrates. Due to the orientation control and the optimization of carrier concentration, a low resistivity and a high Seebeck coefficient were achieved, and a power factor (PF) reached 1.14×10−3 W/mK2 at 323 K in the SCCO film with x × = 0.02. In addition, we measured the nano-structural effect on the PF of SCCO films. As a result, the PF showed a maximum in the film on a certain shape of the nano-structures. We speculate that the low resistivity was achieved by a formation of high Ce concentration layer near the interface between film and nano-structure.

Lanthanum, cerium, praseodymium and yttrium in waters in an upland acidic and acid sensitive environment, mid-Wales

Abstract. The less than 0.45 mm filterable lanthanum (La), cerium (Ce), praseodymium (Pr) and yttrium (Y) concentrations in rainfall, cloud water, stream and groundwater in the upper River Severn catchments of mid-Wales are presented, based on up to ten years of weekly data. Results show that for rainfall, there is enrichment in the rare earth (RE) elements, especially under conditions of small volume of catch. However, within the correlations, there is a 'forked' relationship, with one line of high La, Ce and Pr with low Y, corresponding to clear pollutant events and the other with relatively low La, Ce and Pr and higher Y to background conditions. Cloud water and stream waters show a simpler relationship indicating two types of source. Cloud, stream and ground water show no split in pattern, with singular linear relationships between the rare La, Ce, Pr and Y. However, in many cases the monitoring of the streams and groundwaters post-dates the rainfall period with high pollutant Ce inputs. RE element concentrations vary systematically, in general decreasing with increasing volume of catch for cloud-water. For the streams, occasionally, there are relatively high Ce and La concentrations (up to about a tenth the maximum in rainfall), which occur in the same year as the corresponding high values in rainfall. Apart from these anomalous periods, RE element concentrations increase with decreasing pH and increasing aluminium concentrations; RE elements are mobilised under acidic conditions. The river waters are particularly enriched in Y relative to La, Ce and Pr, both in terms of average concentrations and values normalised to standard continental shales. The RE element level in the streams is variable and seems to be linked to the main soil types within the catchment; gleys in particular show higher concentrations than their peat and podzolic counterparts. On average, groundwaters are enriched in the RE elements relative to the stream but the link with pH and aluminium observed in the stream is much weaker.

Magnetostriction of Ce xTb 1− xFe 2 compounds

In this paper, the magnetostriction of Ce x Tb 1− x Fe 2 compounds was investigated using a standard strain gauge technique, and the intrinsic magnetostriction of Ce x Tb 1− x Fe 2 compounds was derived from fitting the (4 4 0) peak of the X-ray diffraction pattern. It is found that the magnetostriction of Ce x Tb 1− x Fe 2 compounds decreases slowly with increasing Ce content at low Ce content, while decreases sharply at high Ce content. X-ray diffraction analysis shows that the intrinsic magnetostriction decreases with the Ce concentration increasing in Ce x Tb 1− x Fe 2 compounds, and the Ce ion contributes to the magnetostriction.

Analysis of Tradescantia pallida plant exposed in different sites for biomonitoring purposes

Comparisons were made between the results obtained for elements accumulated by Tradescantia pallidaplant exposed in sites with different pollution levels: Cerqueira Cesar and Congonhas districts, considered polluted areas of Sao Paulo city, and Caucaia do Alto county, considered a non polluted site. Statistical test applied to the results indicated that plant samples from polluted areas presented higher concentrations of Ba, Ce, Cr, Co, Fe, La, Sb and Sc than those found for ones from a non-polluted site. Discriminant analysis applied to the results obtained revealed three groups of results corresponding to sites with different levels of pollution.

Contribution of the atmospheric emissions of Spanish ceramics industries

Contaminating industrial emissions produced by the ceramics industries (including frit and enamel production) can be divided into dust emissions and emissions produced in high temperature activities. Processes of accumulation and precipitation on the substratum, of compounds enriched in certain elements used in this type of industry can occur. The objective of the present work was to identify the contribution of the emissions of the ceramics industries to the atmospheric particulate that is susceptible to depositing on vegetation and accumulating in the substratum. Samples obtained from high volume collectors were studied. Two zones were considered: zone A, a high volume collector located in the municipalities adjacent to the companies that were the object of the study; and zone B, a high volume collector further away from the said companies and adjacent to a power station and a refinery. The analysis techniques were X-ray diffraction, scanning electron microscopy (SEM), and ICP-MS. The results obtained by means of the X-ray diffraction technique showed a high percentage of clays in the samples, minerals used as raw materials (K-Ba feldspar, zircon silicate), indications of high temperature phases, as well as a background noise characteristic of material of low crystallinity. The SEM analysis confirmed the presence of vitreous particles, which are crystalline phases at high temperature typical of the production of a large variety of frits. The results obtained in the chemical analysis demonstrate that (a) the influence of the frits and enamel production on the high concentrations of Zr, Cu and Ce obtained in zone type A compared with zone B; (b) the affect of clays used as raw materials in the ceramics industry can be demonstrated by the high concentrations of Fe, Al and Mg. The weekly evolution showed two series of elements, a characteristic group of dust emissions and another group of tracers from high temperature processes.

Characterization of Ce 1− xZr xO 2 thin films prepared by pyrolytic spray technique

It was demonstrated that spray pyrolysis can be used to prepare Ce 1− x Zr x O 2 thin films with x between 0 and 1. The composition of these films was determined by electron probe microanalysis (EPMA), and the crystalline structure by X-ray diffraction (XRD) and Raman spectroscopy (RS). Cyclic voltammetry (CV) was performed in an electrolyte of propylene carbonate with 1 M LiClO 4. Films with high Zr content were incapable of charge exchange of Li + ions. In the contrast, films with high Ce content were found to be able to insert/extract large charge densities of Li + ions. They also remained transparent during Li + intercalation.

High-Precision, Simultaneous Analysis of Pt, Pd, and Rh in Catalytic Converter Samples by Carius Tube Dissolution and Inductively Coupled Plasma Atomic Emission Spectroscopy with Charge-Injection Device Detection

A robust method of analysis that uses multichannel array detector technology is presented for high-precision, accurate measurement of Pt, Pd and Rh in catalytic converters. Catalytic converter samples, National Institute of Standards and Technology (NIST) reference standards, and a fresh converter sample are dissolved and analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Complete dissolution of sample sizes up to 2 g of NIST reference standards is achieved with the use of high-pressure, high-temperature carius tubes. Carius tube dissolution of a modern catalytic converter sample is found to be incomplete because of the presence of higher concentrations of Ce, Ni, and Zr. For this sample, the addition of FeCl3 increases the dissolving power of the carius tube for base metals and noble metals, particularly Rh. Although interference problems are encountered in samples bearing high concentrations of Fe, use of a high-resolution ICP-AES system alleviated these problems. Precise quantitation of Pt, Pd, and Rh is accomplished by using the method of standard additions, with high accuracy and a precision of 1–2% RSD (relative standard deviation). This analysis also confirmed the values determined by NIST by using isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) for standard reference materials (SRMs) 2556 and 2557.

Palladium based catalysts for exhaust aftertreatment of natural gas powered vehicles and biofuel combustion

Hydrothermally aged (1000/850°C, 12/16 h) Pd-Ce-supported alumina catalysts with high and low Ce content were prepared and tested in conversion of gas mixtures simulating the emissions from natural gas (NG) driven vehicles and biofuel combustion. The test procedure contained lean and rich light-off activity tests, stationary and oscillating lambda sweeps, space velocity tests as well as runs with sulphur poisoning. The catalysts exhibited high conversion of the model pollutants. In the oscillating lambda sweep experiments, the Pd-Ce/Al 2O 3 with high Ce loading showed high activities in conversion of CH 4 and CO at lean λ values up to 1.04. Ageing under the reactants flow as well as hydrothermal treatment of the catalysts resulted in improved catalytic activities in terms of light-off temperatures of the model pollutants. This activation was believed to be a result of both Cl-release from the surface as well as restructuring of the Pd-particles. Interaction of Pd-Ce or Al-Ce induced at high temperature was also believed to affect the activation. Addition of 5 ppm of SO 2 into the gas mixture of simulated emissions from biofuel combustion raised the T 50% of CH 4 by approximately 100°C. SO 2-TPD experiments were used to correlate the catalytic activity to S-poisoning. The catalysts were characterised by H 2-adsorption, XPS, FTIR, SO 2-/NO-/O 2-TPD, XRD, XRF and N 2-physisorption.

Geochemistry of Rare Earth Elements and Thorium in Sediments and Ferromanganese Nodules of the Atlantic Ocean

The behavior of rare earth elements (REE) and Th is studied along the west–east transect at 22°N across the Atlantic Ocean. It is shown that both REE and Th contents, relative to Al (the most lithogenic element), increase toward the pelagic region. The increasing trend becomes more complicated due to variations in the content of biogenic carbonate that serves as a diluting component in sediments. The REE composition varies symmetrically relative to the Mid-Atlantic Ridge (MAR) emphasizing a weak hydrothermal influence on sediments of the ridge axis, although the well-known criteria for hydrothermal contribution, such as Al/(Al + Mn + Fe) and (Fe + Mn)/Ti, do not reach critical values. Variations in the REE content and composition allowed us to distinguish the following five sediment zones in the transect: (I) terrigenous sediments of the Nares abyssal plain; (II) pelagic sediments of the North American Basin; (III) carbonate ooze of the MAR axis; (IV) pelagic sediments of the Canary Basin; and (V) terrigenous clay and calcareous mud of the African continental slope and slope base. Ferromanganese nodules of the hydrogenetic type with extremely high Ce (up to 1801 ppm) and Th (up to 138 ppm) contents occur in pelagic sediments. It is ascertained that P, REE, and Th concentrations depend on Fe content in Atlantic sediments. Therefore, one can suggest that only a minor amount of phosphorus is bound in bone debris. The low concentration of bone debris phosphorus is a result of relatively high sedimentation rates in the Atlantic, as compared with those in pelagic regions of the Pacific.

Evolution of a post-batholith dike swarm in central coastal Queensland, Australia: arc-front to backarc?

A swarm of felsic and mafic dikes cuts a Late Carboniferous–Permian batholith called the Urannah Suite in central coastal Queensland. Late Permian–Triassic westward thrusting (Hunter–Bowen Orogeny) exposed this mid-crustal Suite and the crosscutting dikes, thus enabling examination of dikes that range in age from syn- to post-batholithic. Although both mafic and felsic dikes have the same dominant northerly strike, field, geochronologic and geochemical examination reveal that the swarm is composite; felsic dikes are older (285 Ma) and geochemically and isotopically distinct from mafic dikes (∼273–229 Ma). Dike compositions are compared to those of the host plutonic rocks, and to volcanic rocks the same age as the dikes. Whereas the felsic (older) dikes are compositionally similar to their host granites (initial 87 Sr/ 86 Sr>0.7045 ), the mafic (younger) dikes are isotopically (Sr, Nd, Pb) less radiogenic. Moreover, several different types of mafic dikes are evident based on geochemistry; most of these have mixed characteristics in terms of tectonic classification. All but two dikes of basalt and basaltic andesite composition classify as `with-in plate' on Ti–Zr–Y tectonic classification plots. Many of the basalts have high TiO 2 contents (1.5–3.0 wt.%). Most of these have REE and spider diagram patterns like calc-alkaline tholeiites, the exceptions being a few alkali basalts recognized by their alkali content, and high Ti, Ce, Nb and Zr contents. When put into the context of all plutonic rocks in the area (late Paleozoic and Mesozoic), these dikes record a transition at ∼280 Ma, after which time, all magmatism in the region is less isotopically evolved (initial 87 Sr/ 86 Sr=0.7033–0.7044 ). A model of slab retreat and hinge movement to the east in the latest Permian explains the change of geochemical signature from arc-front to backarc at about 280 Ma.

Photoluminescence, and scintillation/thermoluminescence yields of several Ce 3+ and Eu 2+ activated borates

Powder samples of the borates YBO 3 : Ce 3+ , GdBO 3 : Ce 3+ , Li 6 Y( BO 3) 3 : Ce 3+ , LaB 3 O 6 : Ce 3+ , GdB 3 O 6 : Ce 3+ , LaMgB 5 O 10 : Ce 3+ , YMgB 5 O 10 : Ce 3+ , CaLaB 7 O 13 : Ce 3+ , CaLaB 7 O 13 : Eu 2+ , Ca 4 YO( BO 3) 3 : Ce 3+ and CaYOBO 3 : Eu 2+ were studied. The photoluminescence properties of Ce 3+ in these compounds are discussed and some of them are reported for the first time. The scintillation light yield of the orthoborates YBO 3 : Ce 3+ , GdBO 3 : Ce 3+ , ScBO 3 : Ce 3+ and YAl 3 B 4 O 12 : Ce 3+ is of the order of 10,000 pho/MeV. The light yield due to Ce 3+ in the other borates is an order of magnitude lower. In LaB 3 O 6 : Ce 3+ and LaMgB 5 O 10 : Ce 3+ a broad emission band, attributed to self-trapped exciton (STE) emission, is observed under X-ray excitation. The STE light yield of LaB 3 O 6 : Ce 3+ (0.05%) is 8000 pho/MeV and it is quenched at higher Ce concentrations. Thermoluminescence measurements show that none of these materials has a potential to be utilized as a thermal neutron storage phosphor.

Energy transfer between Ce 3+ and Eu 2+ in SrAl 12O 19:Ce x3+,Eu 0.012+ (x = 0.01–0.09)

The influence of the Ce 3+ concentration on the cathodoluminescence (CL) characteristics of SrAl 12O 19:Ce x 3+,Eu 0.01 2+ (x = 0.01–0.09) was studied. At 1 mol% cerium in SrAl 12O 19:Ce x 3+,Eu 0.01 2+ (x = 0.01), two broad emission bands centered at 320 nm and at about 400 nm were observed. The intensity of Ce 3+ emission at 320 nm decreased as the Ce 3+ concentration increased, whereas the intensity of the emission band at 400 nm increased with increasing Ce 3+ concentration at fixed Eu 2+ concentration. At low concentration of Ce 3+ (x = 0.1–0.5), the Ce 3+ emission intensity decreased with the Eu 2+ emission intensity being enhanced due to the energy transfer from Ce 3+ to Eu 2+. In high concentrations of Ce 3+ (x = 0.07, 0.09), the cross-relaxation processes between nearest Ce 3+ ions led to the diminishing intensity of Ce 3+ emission, because of the limited energy acceptors, i.e., Eu 2+ ions, which resulted in a single emission band at about 400 nm.

Effect of Ce Substitution on the Properties of Tl-Based Superconductors

Samples with nominal composition (Tl{sub 0.5}Pb{sub 0.5})Sr{sub 2{minus}x}Ce{sub x}Ca{sub 2}Cu{sub 3}O{sub y} were prepared with x in the range 0 to 0.5, to investigate the role of charge carrier concentration on the superconducting properties of Tl-based materials. The behavior of the normal state resistivity with temperature showed that as x changes from 0 to 0.2, the material moves towards optimally doped state. For higher Ce content the normal state resistivity versus temperature, started deviating from linearity. The onset transition temperature increased gradually by about 6 K as x was increased from 0 to 0.2. The zero resistance transition temperature rapidly decreased for samples with x > 0.2. Furthermore, XRD analysis revealed that Ce enters the structure of both Tl-1223 and Tl-1212. These results are discussed in terms of controlling the hole concentration in the CuO{sub 2} planes through Ce{sup 4+} replacement of Sr{sup 2+}.

On the magnetic and valence properties of CeMgY compounds

The structural and magnetic properties of a series of novel compounds in the ternary CeMgY system have been studied by X-ray diffraction. SQUID magnetometry and XAS spectroscopy. The crystal structures of the compounds Ce0.34Y0.67Mg2 and Ce0.49Y0.51Mg4.7 have been refined by the Rietveld technique. Magnetic data are consistent with a tripositive ground state 2F52 for the cerium atom. The XAS measurements confirm this result. Crystal field effects are apparent in the magnetic data at temperatures below about 50 K in the compounds with higher Ce concentration.

Rare earth elements and plant growth: III. Responses of corn and mungbean to low concentrations of cerium in dilute, continuously flowing nutrient solutions.

Abstract Corn (Zea mays cv. Hycorn 82) and mungbean (Vigna radiata cv. Berken) plants were grown for 16 d in dilute nutrient solutions containing constant cerium (Ce) concentrations from 0 to 1.31 μM. Corn root growth was increased approx. 2 fold at Ce concentrations 0.63 μM. However, the total dry matter production of corn was not significantly increased by Ce addition. With mungbean, the addition of as little as 0.19 μM Ce to the nutrient solution caused significant reductions in the dry weight of root (26%), shoot (48%) and total plant (44%). The youngest leaves of mungbean plants in the treatments containing 0.63 μM Ce displayed symptoms of manganese (Mn) deficiency. These leaves contained deficient Mn concentrations (5 mg/kg). Tissue concentrations of other nutrients in mungbean and all essential elements in corn were within ranges where healthy growth would be expected. The concentrations of Ce measured in the roots and shoots of mungbean were higher than in corn. Roots of both species accumulated much higher concentrations of Ce than the shoots. Cerium accumulated in the oldest leaves of both plant species. These patterns of distribution were similar to those reported previously for lanthanum.

Growth of Bi 2Sr 2Ca 1− xCe xCu 2O y single crystals from eutectic melts

Bi 2Sr 2Ca 1− x Ce x Cu 2O y single crystals with in-plane dimensions up to 8 × 8 mm 2 were successfully grown by spontaneous nucleation from eutectic melts. For x ⩽ 0.8, all the grown crystals possess the pure 2212 phase. However, when x = 1.0, the crystal is of pure 2201 phase with c = 24.662 A ̊ . The value of c of the crystals decreases with increasing Ce concentration. Upon Ce doping, the T onset c value reaches a maximum of 90 K for x = 0.1 and drops rapidly at higher Ce concentration.

The electronic structure of stoichiometric and reduced CeO 2 surfaces: an XPS, UPS and HREELS study

The influence of Ce 3+-related defects on the electronic structure of stoichiometric CeO 2 surfaces is studied by means of detection angle-dependent XPS, UPS and HREELS. Argon sputtering and hydrogen exposure at elevated temperatures lead to high concentrations of Ce 3+ at surface and subsurface sites. The latter are identified by the binding energies of the Ce 3d core levels, additional emissions of C4f 1-derived electronic states in the band gap, and characteristic changes in the electronic transitions from occupied into empty electronic states in the valence band region. UPS is found to show in particular a high sensitivity for intrinsic surface point defects, even if small concentrations are adjusted in the order of XPS and HREELS detection limits by high-temperature treatment of the CeO 2 surfaces under UHV conditions or by hydrogen exposure at medium temperatures

Dense Kondo states in Pd-Ce intermetallic compounds under high pressure

The electrical resistivity of Pd-Ce intermetallic compounds, Pd 5Ce 3, Pd 4Ce, has been measured under high pressures up to 10 GPa. It is found that the resistivity increases with the external pressure for all these intermetallics. The increase is due to the dense Kondo effect. Intermetallics with a higher concentration of Ce have a greater ratio of the resistivity-increase to pressure. However, a high-pressure X-ray diffraction experiment showed that the compressibility of the intermetallics is the same. These results suggest that the influence of pressure on the dense Kondo effect depends not only upon the Ce concentration but also on the local environment of Ce.