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Rare Earth Oxides and Their Applications

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Energy Materials".

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 16048

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Prof. Dr. Ginesa Blanco

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Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain
Interests: heterogeneous catalysis; lanthanoid oxides; X-ray photoelectron spectroscopy; nanoparticles
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Dear Colleagues,

Rare earth elements, according to the IUPAC recommendations, comprise a group of 17 elements, Sc, Y and the lanthanoids (from La to Lu). In principle, the term “rare” suggests that they are rather scarce elements, although they are actually more abundant in the Earth’s crust that some much better known elements. Thus, their abundance varies from 66 ppm in the case of Ce (an abundance similar to that of Cu or Zn) to less than 0.5 ppm in Tm (more abundant that Cd or Se). The term “rare” seems to be applied in the sense of “strange” or “extraordinary”, rather than “scarce”. For these reasons, it is not surprising the huge number of applications that all these elements have, both in bulk production industry or in minor volume applications. It has to be taken into account, as well, that most of the rare earth-containing materials with industrial applications are either oxides, or they are obtained from oxides. Regarding the bulk and mature industry applications of rare earth oxides, their use in catalysts formulations (such as in three way automotive catalysis), in glass-related industries (glass making, decolouring or colouring, glass polishing and other related applications), and permanent magnets manufacturing account for almost 70% of rare earth oxides usage. Other important industrial applications concern the metallurgy industry (used as additives in Fe or Al metal alloys), ceramics (specially in the case of Y), lighting-related applications (in the form of phosphors), as battery alloy components, or in solid oxide fuel cells, amongst others. Additionally, but not less important, there are lower scale applications, such as biomedical uses of nanoparticulated systems containing rare earth oxides for cancer treatment or as tumoral detection markers, or as sunscreens cosmetics for skin protection.

The aim of this Special Issue is to cover many of the above-mentioned applications, with a special focus on new developments for existing applications as well as the emergence of new and innovative ones. It is my pleasure to invite you to submit a manuscript to this Special Issue. Full papers, communications, and reviews will be welcome.

Prof. Ginesa Blanco
Guest Editor

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Keywords

Rare earth oxides
Lanthanoids
Applications

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Research

19 pages, 4240 KiB

Open AccessArticle

Thermocatalytic CO₂ Conversion over a Nickel-Loaded Ceria Nanostructured Catalyst: A NAP-XPS Study

by Adrián Barroso-Bogeat, Ginesa Blanco, Juan José Pérez-Sagasti, Carlos Escudero, Eric Pellegrin, Facundo C. Herrera and José María Pintado

Materials 2021, 14(4), 711; https://doi.org/10.3390/ma14040711 - 03 Feb 2021

Cited by 8 | Viewed by 3173

Abstract

Despite the increasing economic incentives and environmental advantages associated to their substitution, carbon-rich fossil fuels are expected to remain as the dominant worldwide source of energy through at least the next two decades and perhaps later. Therefore, both the control and reduction of CO₂ emissions have become environmental issues of major concern and big challenges for the international scientific community. Among the proposed strategies to achieve these goals, conversion of CO₂ by its reduction into high added value products, such as methane or syngas, has been widely agreed to be the most attractive from the environmental and economic points of view. In the present work, thermocatalytic reduction of CO₂ with H₂ was studied over a nanostructured ceria-supported nickel catalyst. Ceria nanocubes were employed as support, while the nickel phase was supported by means a surfactant-free controlled chemical precipitation method. The resulting nanocatalyst was characterized in terms of its physicochemical properties, with special attention paid to both surface basicity and reducibility. The nanocatalyst was studied during CO₂ reduction by means of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). Two different catalytic behaviors were observed depending on the reaction temperature. At low temperature, with both Ce and Ni in an oxidized state, CH₄ formation was observed, whereas at high temperature above 500 °C, the reverse water gas shift reaction became dominant, with CO and H₂O being the main products. NAP-XPS was revealed as a powerful tool to study the behavior of this nanostructured catalyst under reaction conditions. Full article

(This article belongs to the Special Issue Rare Earth Oxides and Their Applications)

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26 pages, 5714 KiB

Open AccessArticle

Tuning the Integration Rate of Ce(Ln)O₂ Nanoclusters into Nanoparticulated ZrO₂ Supports: When the Cation Size Matters

by Adrián Barroso-Bogeat, Iván Daza Raposo, Ginesa Blanco and José María Pintado

Materials 2020, 13(12), 2818; https://doi.org/10.3390/ma13122818 - 23 Jun 2020

Cited by 1 | Viewed by 2069

Abstract

Three nanostructured catalysts with low total rare earth elements (REEs) content (i.e., 15 mol.%) were prepared by depositing CeO₂ or Ln³⁺-doped CeO₂ (Ln³⁺ = Y³⁺ or La³⁺; Ln/Ce = 0.15) on the surface of ZrO₂ nanoparticles, as nanometre-thick, fluorite-type clusters. These samples were subjected to successive reduction treatments at increasing temperatures, from 500 to 900 °C. A characterisation study by XPS was performed to clarify the diffusion process of cerium into the bulk of ZrO₂ crystallites upon reduction to yield Ce_xZr_1−xO_2−δ surface phases, and the influence of the incorporation of non-reducible trivalent REE cations, with sizes smaller (Y³⁺) and larger (La³⁺) than Ce⁴⁺ and Ce³⁺. For all nanocatalysts, a reduction treatment at a minimum temperature of 900 °C was required to accomplish a significant cerium diffusion. Notwithstanding, the size of the dopant noticeably affected the extent of this diffusion process. As compared to the undoped ZrO₂-CeO₂ sample, Y³⁺ incorporation slightly hindered the cerium diffusion, while the opposite effect was found for the La³⁺-doped nanocatalyst. Furthermore, such differences in cerium diffusion led to changes in the surface and nanostructural features of the oxides, which were tentatively correlated with the redox response of the thermally aged samples. Full article

(This article belongs to the Special Issue Rare Earth Oxides and Their Applications)

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13 pages, 4075 KiB

Open AccessArticle

Photocatalytic Degradation of Diclofenac Using Al₂O₃-Nd₂O₃ Binary Oxides Prepared by the Sol-Gel Method

by José Eduardo Casillas, Jorge Campa-Molina, Francisco Tzompantzi, Gregorio Guadalupe Carbajal Arízaga, Alejandro López-Gaona, Sandra Ulloa-Godínez, Mario Eduardo Cano and Arturo Barrera

Materials 2020, 13(6), 1345; https://doi.org/10.3390/ma13061345 - 16 Mar 2020

Cited by 18 | Viewed by 2380

Abstract

This paper reports the sol-gel synthesis of Al₂O₃-Nd₂O₃ (Al-Nd-x; x = 5%, 10%, 15% and 25% of Nd₂O₃) binary oxides and the photodegradation of diclofenac activated by UV light. Al-Nd-based catalysts were analyzed by N₂ physisorption, XRD, TEM, SEM, UV-Vis and PL spectroscopies. The inclusion of Nd₂O₃ in the aluminum oxide matrix in the 10–25% range reduced the band gap energies from 3.35 eV for the γ-Al₂O₃ to values as low as 3.13–3.20 eV, which are typical of semiconductor materials absorbing in the UV region. γ-Al₂O₃ and Al-Nd-x binary oxides reached more than 92.0% of photoconverted diclofenac after 40 min of reaction. However, the photocatalytic activity in the diclofenac degradation using Al-Nd-x with Nd₂O₃ contents in the range 10–25% was improved with respect to that of γ-Al₂O₃ at short reaction times. The diclofenac photoconversion using γ-Al₂O₃ was 63.0% at 10 min of UV light exposure, whereas Al-Nd-15 binary oxide reached 82.0% at this reaction time. The rate constants determined from the kinetic experiments revealed that the highest activities in the aqueous medium were reached with the catalysts with 15% and 25% of Nd₂O_3, and these compounds presented the lowest band gap energies. The experimental results also demonstrated that Nd₂O₃ acts as a separator of charges favoring the decrease in the recombination rate of electron-hole pairs. Full article

(This article belongs to the Special Issue Rare Earth Oxides and Their Applications)

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0 pages, 2781 KiB

Open AccessArticle

Liquid Regions of Lanthanum-Bearing Aluminosilicates

by Yandong Li, Tongsheng Zhang, Yefeng Feng, Chengjun Liu and Maofa Jiang

Materials 2020, 13(2), 450; https://doi.org/10.3390/ma13020450 - 17 Jan 2020

Cited by 7 | Viewed by 2848 | Correction

Abstract

The Al₂O₃-SiO₂, La₂O₃-Al₂O₃, and La₂O₃-SiO₂ binary phase diagrams were estimated by Redlich–Kister expression. La_4.67Si₃O₁₃ (=La_4.67(SiO₄) [...] Read more.

The Al₂O₃-SiO₂, La₂O₃-Al₂O₃, and La₂O₃-SiO₂ binary phase diagrams were estimated by Redlich–Kister expression. La_4.67Si₃O₁₃ (=La_4.67(SiO₄)₃O) was introduced to improve the existing phase diagrams. The Al₂O₃-SiO₂-La₂O₃ ternary phase diagram extrapolated by Kohler method was optimized. Then, the liquidus of Al₂O₃-SiO₂-La₂O₃ system at 1600 °C was compared with Al₂O₃-SiO₂-RE₂O₃ (RE = Rare Earth Elements) systems and experimental results in other literature. The high temperature experiments were conducted in the tube furnace at 1500 °C. Then the field emission scanning electron microscope (FE-SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) were employed to verify the calculated liquid region and precipitates phase at 1500 °C. Moreover, the liquidus of binary systems were compared with FactSage results and experiments. The optimized ternary phase diagram shows the relatively reliable region of liquid phase, and it is significant to the seal glass of solid oxide fuel cells and other fields being related to RE containing silicates. Full article

(This article belongs to the Special Issue Rare Earth Oxides and Their Applications)

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16 pages, 2770 KiB

Open AccessFeature PaperArticle

Improved NO_x Storage/Release Properties of Ceria-Based Lean NO_x Trap Compositions with MnO_x Modification

by Marcos Schöneborn, Thomas Harmening, Javier Giménez-Mañogil, Juan Carlos Martínez-Munuera and Avelina García-García

Materials 2019, 12(13), 2127; https://doi.org/10.3390/ma12132127 - 02 Jul 2019

Cited by 4 | Viewed by 3647

Abstract

Ceria/spinel-based lean NO_x trap compositions with and without barium were modified with MnO_x via incipient wetness impregnation. The effect of the MnO_x layer on the aged materials (850 °C) as to the NO_x storage and release properties was investigated via NO_x adsorption (500 ppm NO/5% O₂/balance N₂) carried out at 300 °C in a dual-bed with a 1% Pt/Al₂O₃ catalyst placed upstream of the samples to generate sufficient amounts of NO₂ required for efficient NO_x storage. Subsequent temperature programmed desorption (TPD) experiments were carried out under N₂ from 300 °C to 700 °C. The addition of MnO_x to the barium free composition led to a slightly reduced NO_x storage capacity but all of the ad-NO_x species were released from this material at significantly lower temperatures (ΔT ≈ 100 °C). The formation of a MnO_x layer between ceria/spinel and barium had a remarkable effect on ageing stability as the formation of BaAl₂O₄ was suppressed in favour of BaMnO₃. The presence of this phase resulted in an increased NO_x storage capacity and lower desorption temperatures. Furthermore, NO_x adsorption experiments carried out in absence of the Pt-catalyst also revealed an unexpected high NO_x storage ability at low NO₂/NO ratios, which could make this composition suitable for various lean NO_x trap catalysts (LNT) related applications. Full article

(This article belongs to the Special Issue Rare Earth Oxides and Their Applications)

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