Lanthanum Content Research Articles

Effect of lanthanum content on the thermophysical properties and near-infrared reflection properties of lanthanum-cerium oxides

A series of lanthanum-cerium oxides with different lanthanum content were synthesized by low-temperature solid-state method, and the effect of lanthanum content on the thermal conductivity and near-infrared reflectance of lanthanum-cerium oxide ceramics was systematically investigated. The results indicated that the thermal conductivity of lanthanum-cerium oxide ceramics decreased significantly with the increase of lanthanum content, which was mainly due to the non-negligible phonon scattering caused by the increased point defects in the structure. Lanthanum-cerium oxide ceramics with different lanthanum content had high near-infrared reflectivity (82%) between 1200 and 2200 nm. The lanthanum-cerium oxide ceramics prepared in this work has lower thermal conductivity and higher near-infrared reflectivity, which has broad application prospects in the field of high-temperature energy saving as thermal insulation material.

Залежність структури ливарних сплавів системи Al-Ni-La від їх хімічного складу

The peculiarities of cast Al-Ni-La alloys structure formation depending on the content and ratio of the main components are analyzed in the work. It is shown, that so far the studied system has been considered mainly for the creation of amorphous materials. At the same time, Al-Ni and Al-La systems have phase diagrams that allow us to consider double and triple alloys of these systems to create promising creep-resistant alloys for casting. At the same time, the peculiarities of their structure formation in this context were not determined. Samples with different contents of nickel and lanthanum were prepared for research and analyzed how each of the elements, their number and ratio affect the formation of their structural-phase state. It is shown, that low nickel content of about 2 wt. % and lanthanum up to 5 wt. % eutectic is formed like thin almost monolithic intermetallic plates. As the number of components increases and, accordingly, the number of eutectics increases, the dispersion of its components increases. The analysis of the alloy structure dependence due to studied system on their chemical composition showed that, most likely, during the formation of the eutectic, Al11La3 particles, which may have the form of nanosized fibers, are formed first of all. It should be noted that at the eutectic content of lanthanum in the alloys no primary-formed Al11La3 particles were found. This may indicate that nickel shifts the eutectic concentration of lanthanum toward higher values. At the same time, at the hypoeutectic concentration of lanthanum and the hypereutectic concentration of nickel, some Al11La3 formations were outside the regions of the main eutectic with nickel aluminide. Such questions necessitate further studies of the aluminum angle of the triple state diagram of the Al-Ni-La system. Keywords: Al-Ni-La system, creep-resistant cast aluminum alloys, structure, eutectic.

Effect of lanthanum content on microstructure and mechanical properties of Al–5Mg–2Si-0.6Mn alloy in squeeze casting

The effect of Lanthanum content on the microstructure and mechanical properties of Al–5Mg–2Si-0.6Mn alloy in squeeze casting was studied. The microstructure of the alloy was characterized by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The mechanical properties of the alloy were tested by tensile testing machine. The results show that the rare earth Lanthanum has a significant effect on the secondary dendrite spacing and the volume fraction of α-Al + Mg2Si eutectic phase, both of which increase at first and then decrease with the increase of Lanthanum. When the content of Lanthanum is 0.05 wt.%, the maximum volume fraction of eutectic phase is 45.09%. When the content of Lanthanum is 0.05 wt.%, the minimum secondary dendrite spacing is 25.85 μm. When the addition of Lanthanum is more than 0.2 wt.%, the bulk LaAlSi phase is formed in the alloy, which is not coherent with the matrix, which reduces the mechanical properties of the alloy. When the addition of Lanthanum is 0.1 wt.%, the microstructure and mechanical properties of the alloy are the best. The ultimate tensile strength, yield strength and elongation of the alloy reached the maximum, which were 274 MPa, 197.2 MPa and 5.7%, respectively.

Galvanic interaction between different grinding media and galena (1 0 0) surface and its influence on galena flotation behavior: A DFT study

Galena has different electrostatic potentials from grinding medium. Collision and friction occur between them in the grinding process, which lead to electron transfer and charge redistribution on galena surface, affecting surface oxidation and galena recovery. In this paper, the galvanic interaction between galena and eight different grinding media including low carbon steel (carbon content 0.1 wt%), medium carbon steel (carbon content 0.3 wt%), high carbon steel (carbon content 0.9 wt%), and grinding medium containing 0.1 wt% Ce, 0.1 wt% La, 0.1 wt% Y, 4.6 wt% Cr, or 1.5 wt% Mn has been studied using DFT method. The effects of those galvanic interactions on the surface structure, surface activity and adsorption of oxygen and xanthate molecules on galena surface have been investigated. The results show that the adsorption of oxygen and xanthate molecules on the surface of galena is the strongest with medium carbon steel (carbon content is 0.3 wt%), followed by low carbon steel and high carbon steel. In addition, compared with the grinding media containing chromium, cerium, yttrium and manganese, the grinding medium containing lanthanum (lanthanum content is 0.1 wt%) is more conducive to the adsorption of oxygen and xanthate molecules on the surface of galena.

Dielectric and piezoelectric properties of PLZT x/40/60 (x = 5; 12) ceramics

The paper presents the results of studies of the structure, piezoelectric and dielectric properties of lead zirconate-titanate ceramics modified with lanthanum of various concentrations (PLZT). It was found that with an increase in the La content, the grain size and the average domain size increase. The PLZT 12/40/60 samples contain both labyrinth-like and periodic domains, as well as different lateral sizes from several hundred nanometers to 3 microns in diameter. It was found that the piezoelectric response signal increases with increasing domain sizes in samples with a high lanthanum content. The fact of the existence of areas on surface of PLZT x/40/60 ceramics having an internal displacement field is established, as evidenced by the asymmetry of the remnant piezoelectric hysteresis loops along the voltage axis. In the samples PLZT 5/40/60 and PLZT 12/40/60, a significant dispersion of the permittivity ε(f) and a maximum of the tangent of the dielectric loss angle were observed in the frequency range from 105 to 106 Hz. This is due to the presence of ionic relaxation polarization, as is the case in ionic dielectrics. It is established that the value of the dielectric constant increases markedly with increasing La, which confirms the occurrence of a rigid unipolar state in the PLZT 12/40/60 ceramic grains. In the samples under study, an increase in the tangent of the dielectric loss angle is observed at low frequencies of the measuring field, which is associated with the contribution of conductivity to tg δ. The dependences of the dielectric loss factor ε” on the dielectric permittivity ε’are constructed. They have the form of Cole-Cole diagrams, which indicates the presence of a relaxation time spectrum, while it was found that the spectrum width in PLZT 5/40/60 samples is about two times less than in PLZT 12/40/60 samples.

Study on the Preparation of Al2O3/Al-15Si-4Mg composite material

In this research, microstructure refinement treatment was carried out by adding different content of lanthanum to Al-15Si-4Mg alloy. The effect of heat treatment process on the alloy after metamorphism was studied, and the optimal performance matrix was selected for A12O3/Al composite research. The results show that La has good metamorphism effect on Al-15Si-4Mg alloy. With the increase of La metamorphic agent content, the eutectic silicon structure was obviously refined. When the La content reached 1wt.%, the refining effect was the best. The hardness of the alloy was 111HBS. When the optimum amount of La was 1wt.%, the XRD phase and EDS spectrum analysis show that the alloy without modification was mainly composed of Al, Si and Mg2Si, and the metamorphic alloy also forms a rich La phase. The mechanical properties can be significant improved by the heat treatment process. After the heat treatment, the acicular structure of the eutectic silicon structure became smooth and smooth, which reduced the splitting effect on the aluminum matrix. The hardness was 113HBS. The toughness of the material can be significantly improved by the heat treatment process. The sample with 1wt.% La was selected as the matrix of the A12O3/Al composite. A12O3 Al was prepared by liquid sintering method and no rich La phase but MgAl2O4 was found near the interface which is well reactivate wetted.

Microstructure, magnetic, and dielectric interplay in NiCuZn ferrite with rare earth doping for magneto-dielectric applications

The homogeneous conglomerate of ferrite oxide samples with increasing concentration of Neodymium and Lanthanum in the steps 0.02 with the chemical formula Ni0.6Cu0.2Zn0.2Fe2-x(Nd0.5La0.5)xO4 (0 ≤ x ≤ 0.10) were achieved by novel citric acid-metal nitrate sol–gel auto-ignition method. The nano-regime crystallites products were achieved by using Ni, Cu, Zn, La, Nd and Fe nitrates and keeping the metal nitrate to citrate ratio 1:1. The products of ensured recipe in the form of chemical formula resulted in precursor powders were calcined for removal of desiccated impurities. The ready blends were subjected to an exhaustive examination with distinctive characterizations. The completion of the reaction and phase formation temperature was confirmed by thermal analysis and structural confirmations were received by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectra. The analytics regarding the local symmetry in crystalline solids and understandings about the ordering phenomenon were discussed with the support of FTIR spectra. The diffractograms contributed to the corroboration that the powders obtained were bearing single phase and spinel structure. Evaluation of TEM and DLS confirms fine particle nature of the particles. SEM analysis and EDAX indicated that the samples were having dense, homogeneous and expected stoichiometric cation ratios. The neodymium and lanthanum content influenced the measured saturation magnetization negatively and coercivity positively. The heightened values in electrical conductivity, high ε′ and low dielectric losses in combination with high saturation magnetization, low coercivity, observed in the present samples make them prospect candidate for microwave and electromagnetic shielding applications.

Вплив магнію на високотемпературну структурно-фазову стабільність сплавів системи Al-Ni-La

The paper considers a relevance of the Al-Ni-La system cast alloys development as promising materials for application at elevated temperatures. The influence of magnesium on the structural-phase characteristics of alloys-representatives with a nickel content of about 2% wt. and lanthanum - about 5,5 and 11,5% wt. were studied in the cast condition and after annealing at 425 ° C for 5 hours. It is shown, that the addition of magnesium in the amount of 0,6 wt%. to alloys with a lanthanum content of 5,5 % wt. helps to increase the size of the lanthanum-containing eutectic component in the cast state, but stimulates its grinding after annealing. Since doubling the lanthanum content, magnesium has almost no effect on the structure of the eutectic in the cast state, but intensifies the process of changing its structure during annealing. In this case, the size of the eutectic components is almost unchanged and can be compared with an undoped alloy. Increasing the magnesium content twice to 1,2% wt. in the alloy with a lanthanum content of 11% wt. leads to a noticeable enlargement of Al11La3 intermetallics. After annealing, this structural component retains the characteristics of a fibrous structure and at the same time increases in size by about half. The magnesium content in the eutectic zones and in the solid solution hardly changes after annealing. The obtained data indicate the possibility of using magnesium as an additional alloying element of cast heat-resistant alloys of the Al-Ni-La system, which is able to simultaneously contribute to their strengthening both under normal conditions and at elevated temperatures. In this case, magnesium, in the amount of about 0,6% wt., also helps to preserve the fine structure of the eutectic components at high temperatures. Keywords: Al-Ni-La, Al-Ni-La-Mg, alloying, structural stability, heat resistance.

Lanthanum Diffusion in Fluorapatite at 400 °C, 50 MPa and 4–16 wt %

Apatite is an important carrier of rare earth elements (REEs) and phosphorite is a potential REEs resource. However, the influence of hydrothermal fluids on the migration and enrichment of REE in apatite remains controversial. The experimental study of the interaction between REE-bearing fluid and apatite is one of the essential ways to understand the chemical behavior of rare earth elements in apatite. In this study, we conducted the fluid–mineral reaction experimental study (at 400 °C, 50 MPa and 4–16 wt %) between high lanthanum (La) content hydrothermal solution and low REE content to reveal the influence of different salinities on the diffusion of rare earth elements in fluorapatite. Based on in situ geochemical analyses of experimental products, we show that the diffusion coefficients of La in fluorapatite are between 3.24 × 10−15 and 5.88 × 10−15 m2/s. The salinity of the fluid has a great influence on the diffusion coefficient, with the increase of salinity, the diffusion coefficient increase.

Phosphate-lanthanum coated sewage sludge biochar improved the soil properties and growth of ryegrass in an alkaline soil

The reclamation of alkaline soils remains challenging while the application of biochar has been proposed as a viable measure to rehabilitate soil fertility. The objective of the current pot study was to evaluate the efficacy of various P-La modified sewage sludge biochars (SSBC, La-SSBC, SSBC-P, La-SSBC-P) on soil phosphate-retention and ryegrass (Lolium perenne L.) growth in an alkaline soil (excess CaCO3). The results revealed that germination percentage, plant dry biomass, plant height, and the total amount of P in the ryegrass leaves were significantly (P < 0.05) improved under La-SSBC-P treatment as compared to other treatments. La-SSBC-P treatment significantly altered the chemical characteristics of post-harvest alkaline soil, such as pH, electrical conductivity (EC), cation exchange capacity (CEC), soil organic matter (SOM), limestone (CaCO3), phosphate, and lanthanum contents. In comparison to the SSBC treatment, soil available phosphorous (AP) contents under La-SSBC-P were enhanced by 6.7 times after loading biochar with P and La (La-SSBC-P). After the plantation of ryegrass, concentration of lanthanum in the soil was negligible. The contents of CaCO3 reduced by 76.2% after La-SSBC-P biochar treatment, compared to the cultivated control. This phenomenon clearly indicated that lanthanum was reduced due to the precipitation with limestone, which was proposed based on the data of X-ray diffraction (XRD) analysis. Overall, results showed that the P-loaded lanthanum decorated biochar (La-SSBC-P) could be used as a potential substitute for P-fertilizer under the experimental conditions. However, field experiments are required to confer the efficiency of La-SSBC-P as P fertilizer in different soils.

Resistive grain boundary and double-diffused potential barrier formation for delayed dielectric relaxation in SrBi1.98La0.02Nb-TaO9 material

In present work, doping modified SrBi1.98La0.02Nb2-xTaxO9; x = 0.0–2.0 in steps of 0.5 (SBLNT) matrix is investigated for typical potential barrier formation yielding delayed dielectric relaxation and repair of weak ferroelectric character due to deterioration post microwave synthesis. Unit cell regularizes to tetragonal character on doping tantalum compared to dominant orthorhombic nature of undoped SrBi1.98La0.02Nb2O9 SBLN sample. Regular decrease in c-axis strain in the presence of fix lanthanum content is due to increased electrostatic repulsion along a-b plane on doping tantalum. Strong correlation between 4f-electrons of tantalum and intense sp3-hybridization between Ta(4f)-O(2p) electrons is discussed as a major cause for holding any unbound charge without participating in conduction. Complex impedance and modulus spectroscopy both confirm growth of highly resistive grain boundaries in sample with 50% tantalum doping. Poled and unpoled ferroelectric hysteresis loops for all samples indicate rise in ferroelectric hardness on increase in tantalum doping besides decreasing pore-size.

Structural and microstructural features of lead‐free BNT–BT thin films: Nanoscale electromechanical response analysis

AbstractThe structural, microstructural, and electromechanical properties have been investigated at the nanoscale, as a function of the lanthanum concentration, in Bi0.506Na0.46Ba0.08–3x/2LaxTiO3 (x = 0, 2 and 3 at %) (BNLBT–x) lead‐free thin films. The structural characterization, investigated from X‐ray diffraction and Raman spectroscopy, confirmed the formation of the perovskite structure and suggests the coexistence of both antiferroelectric (tetragonal) and ferroelectric (rhombohedral) phases. The surface morphology, characterized by atomic force microscopy, has shown a dense and crack‐free nanostructured surface for all the studied compositions, noting that the increase in the lanthanum content promoted a decrease in both the grain size and surface roughness. PFM imaging analyses have evidenced the ferroelectric domain structure over the surface, as well as the presence of non–piezoelectric regions attributed to the antiferroelectric phase. PFM spectroscopy measurements revealed a reliable switching behavior for locally probed ferroelectric domains, yielding a noticeable local piezoactivity, which indeed shows to increase with the increase in the doping content. The static domain wall was also analyzed in terms of the nanoscale domain structure, and the obtained dimensionality indicated a local electric field‐induced structural disorder. The clear local piezo/ferroelectric nature highlighted on the studied materials underlines the potential for applications of the BNLBT–x films for their integration into advanced electronic nanodevices.

Phase pure synthesis of lanthanum doped bismuth ferrite nanostructures for the adsorption of doxorubicin

The improper disposal of pharmaceutical effluents, hospital sewage, wastes, and domestic drugs are the typical sources of emerging organic contamination (EOC). The untreated doxorubicin (DOX) effluent being released into the environment has harmful influence on human health. In this study, the lanthanum substituted bismuth ferrite nanoparticles with pure rhombohedral phase were prepared via facile co-precipitation technique, wherein the influence of La3+ ion substitution on structural, optical, and electrical properties of BiFeO3 (BFO) nanoparticles was investigated. Lanthanum content increment did not widely impact the structural properties but a systematic decrease in bandgap with increasing concentration of La3+ ion content was observed. DOX was treated with Bi1−xLaxFeO3 to investigate adsorption activity, where the kinetic modelling of isotherms and intraparticle diffusion showed that the adsorption of DOX followed the multi-layered heterogeneous adsorption mechanism. The BFO nanoparticles exhibited the highest adsorption efficiency of about 93% for DOX in the aqueous solution. The electrostatic interaction between DOX and BFO nanoparticles along with substantial diffusion at porous sites was the probable degradation mechanism of DOX. To assess the reusability merit, BFO were reused up to 4 times as an absorbent for DOX adsorption. Phase pure BFO can efficiently remove the DOX from aqueous medium and provide a cost-effective and eco-friendly solution to deal with EOC of water.

Adaptation, restoration and collapse of anammox process to La(III) stress: Performance, microbial community, metabolic function and network analysis

During the mining of rare earth mineral, the use of lanthanum-containing fertilizers, and the disposal of lanthanum-containing electronic products, the content of lanthanum (La(III)) in typical ammonia wastewater with low carbon to nitrogen ratio is increasing day by day. Here, effects of La(III) on anammox process in performance, microbial community structure, metabolic function, and microbial co-occurrence network were investigated. The results shown that the nitrogen removal efficiency was declines briefly and then gradually recovers after low dosage (1–5 mg/L) La(III) treatment and the decrease to low level (24.25 ± 1.74%) under high La(III) dosage (10 mg/L). La(III) in the range of 1–5 mg/L significantly promoted the relative abundance of Anammoxoglobus (0.024% to 9.762%). The blocking of key metabolic pathways was confirmed to cause the breakdown of anammox by PICRUSt. Furthermore, network analysis revealed that lack of cooperation bacteria limits the activity of Anammoxoglobus.

Equilibrium content of lanthanum in metal under the slag of СаО – SiO&lt;sub&gt;2&lt;/sub&gt; – La&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; – 15 % Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; – 8 % MgO system

Thermodynamic modeling results of lanthanum equilibrium content in metal under the slag of CaO – SiO2– La2О3– Al2O3– MgO system corresponding to chemical composition of 16 points of local simplex plan are presented using the HSC 8.03 Chemistry (Outokumpu) software package in combination with the simplex planning lattice method. In the work, slag is represented by CaO – SiO2– La2O3– – 15 % Al2O3– 8 % MgO oxide system in a wide range of chemical composition for temperatures of 1550 and 1650 °C, and metal contains 0.06 % C, 0.25 % Si, 0.05 % Al (in this expression and hereinafter in mass.%). The results of mathematical modeling are shown graphically in the form of composition - equilibrium content diagrams of lanthanum. There is significant effect of slag basicity on the lanthanum equilibrium content in metal. An increase in slag basicity from 2 to 5 at temperature of 1550 °C leads to an increase in the lanthanum equilibrium content from 0.2 ppm in the region of lanthanum oxide concentration of 1 – 5 % to 7 ppm in the region of increased concentration of lanthanum oxide to 4 – 7 %, hence the increase in slag basicity favorably affects development of lanthanum reduction. Increase in metal temperature also has positive effect on lanthanum reduction process. As temperature rises to 1650 °C, the lanthanum equilibrium content in metal increases from 0.2 ppm in the region of lanthanum oxide concentration of 1 – 3 % to 12 ppm in the region of increased concentration of lanthanum oxide to 4 – 7 %. In diagrams of chemical composition of slag containing 56 – 61 % CaO, 12 – 14 % SiO2and 4 – 7 % La2O3, the lanthanum content in metal at level of 7 – 12 ppm is ensured in temperature range from 1550 to 1650 °C. Therefore, there can be confirmed a decisive role of slag basicity, concentration of lanthanum oxide and temperature factor in development of lanthanum reduction from slags of the studied oxide system by aluminum dissolved in metal.

Equilibrium Content of Lanthanum in Metal under the Slag of CaO–SiO2–La2O3–15% Al2O3–8% MgO System

Equilibrium Content of Lanthanum in Metal under the Slag of CaO–SiO2–La2O3–15% Al2O3–8% MgO System

The Evolution of Microstructure, Mechanical Properties and Fracture Behavior with Increasing Lanthanum Content in AZ91 Alloy

AZ91 alloy is a widely applied commercial magnesium alloy due to its good castability, balanced mechanical properties and acceptable price, and lanthanum alloying has been proven to be one of the most effective methods to further improve its mechanical properties. Therefore, we reveal the evolution of microstructure, mechanical properties and fracture behavior with increasing lanthanum content in AZ91 alloy in this study. The magnesium matrix was significantly refined by lanthanum content, and this effect became more evident with increasing addition of lanthanum. The presence of Al3La precipitates significantly reduced the grain mobility and suppressed the formation of Mg17Al12 discontinuous precipitates along the grain boundaries. The rheo-cast alloys exhibited improved and balanced tensile strength and ductility after aging treatment. The fracture type of AZ91-La alloys could be classified as ductile fracture due to the presence of less quasi-cleavage planes and more dimples with a mixture of tear ridges and micropores. Due to the fully refined microstructure and the balanced mechanical properties, the AZ91–1.0La (mass%) alloy presented the greatest potential for industrial applications among the three studied AZ91-La alloys.

Influences of La3+ ion substitution on dielectric, susceptibility and permeability properties of Mg–Zn ferrite nanoparticles

Nanoparticles of lanthanum-substituted magnesium zinc ferrites with general formula Mg0.6Zn0.4La2yFe2−2yO4 (where y = 0.0, 0.05, 0.1, 0.15, 0.20 and 0.25) were prepared by employing co-precipitation (wet chemical) method. Phase formation was evaluated by X-ray diffraction analysis. Scanning electron microscopic analysis revealed interlocked nanoparticles exhibiting grain size varies between 300 and 95 nm. Initial permeability (µi) and Curie temperature (TC) decrease with lanthanum content. The synthesized lanthanum-substituted Mg–Zn ferrite nanoparticles displayed single-domain ferromagnetic behaviour below Curie temperature TC and superparamagnetic cluster above TC. The effects of lanthanum substitution on structural, electrical and magnetic properties of Mg–Zn ferrites were studied. The present investigation revealed that lanthanum substitution and content have great influence on the structural, electrical and magnetic properties of Mg–Zn ferrites.

Unravelling Crystal Superstructures and Transformations in the La6–xMoO12−δ (0.6 ≤ x ≤ 3.0) Series: A System with Tailored Ionic/Electronic Conductivity

Crystalline La6-xMoO12-δ materials with different lanthanum/molybdenum ratios (0.6 ≤ x ≤ 3.0) have been prepared via a freeze-drying precursor route. The influence of the lanthanum content, sintering temperature and cooling rate on the phase existence range and polymorphism was evaluated. Lanthanum rich compounds present three different polymorphs: a cubic (disordered) fluorite and two complex rhombohedral superstructures related to the fluorite. For the first time, the structural resolution of these rhombohedral superstructures, 7×7×1 and 5×5×1, has been successfully accomplished by neutron pow-der diffraction and transmission electron microscopy studies. As the La/Mo ratio decreases, the cubic symmetry is stabilized, although a phase transformation from cubic to monoclinic occurs at a low cooling rate. Impedance spectroscopy measure-ments under different atmospheres (dry and wet N2 and 5% H2-Ar) show that all materials exhibit mixed proton-electronic conductivity. The n-type electronic conductivity is attributed to Mo6+ reduction and increases for those phases with lower lanthanum content, i.e. for quenched samples, from 5 mS cm-1 for La5.4MoO11.1 to 9.5 mS cm-1 for La4MoO9 at 700 oC in very reducing and wet conditions, which are significantly better than the values published to date for mixed lanthanum tungstates/molybdates. This make these materials potential candidates for hydrogen separation membranes.

Thiophene HDS on La-Modified CoMo/Al2O3 Sulfided Catalysts. Effect of Rare-Earth Content

Alumina-lantana (2.5, 5, 7.5 and 10 wt% La) mixed oxides of suitable texture to be applied as supports of catalysts for hydrodesulfurization of FCC naphtha-range oil-derived distillates were prepared by rare-earth pore-filling impregnation through corresponding nitrate. Co, Mo and P were deposited on binary carriers by one-pot simultaneous impregnation method used during commercial hydrotreating catalysts preparation. Materials were characterized by N2 physisorption, XRD, SEM–EDS, adsorbed CO2 FTIR (basicity measurements), Raman and UV–vis spectroscopies. Sulfided catalysts were studied by chemical composition (EDAX) and HR-TEM. In general, amount and strength of surface basic sites increased with rare-earth content in binary carriers at 5 wt% and higher. Deposited molybdates dispersion augmented with lanthanum content in carriers. However, progressively increasing rare-earth loading on supports was detrimental on gas-phase thiophene HDS (523–563 K, steady-state fixed-bed plug-flow reactor operating at atmospheric pressure). Hardly sulfidable tetrahedral Mo species could be originated by decomposition of heteropolymolybdates originally present in one-pot acidic (pH ~ 1.9) Co–Mo–P solutions by impregnating at basic conditions in pores of La-modified carriers. At isoconversion (~ 10%) rare-earth containing sulfided CoMo catalysts had decreased yield to fully saturated n-butane as to the material supported on pristine alumina.