Trivalent‐Intermediate Valent Cerium Ordering in Ce2RuZn4

The new intermetallic cerium compound Ce₂RuZn₄ was synthesized from the elements in a sealed tantalum tube in a water‐cooled sample chamber of an induction furnace. Ce₂RuZn₄ crystallizes with a new structure type: P4/nmm, Z = 2, a = 719.6(1), c = 520.2(1) pm, wR2 = 0.0816, 273 F² values and 15 variables. The structure contains two crystallographically independent cerium atoms: Ce1 with CN 16 (12 Zn + 4 Ce) and Ce2 with CN 14 (2 Ru + 8 Zn + 4 Ce). Based on the interatomic distances the two sites can be assigned to trivalent Ce1 and intermediate valent Ce2. The trivalent‐intermediate valent cerium ordering is underlined by magnetic susceptibility measurements. Ce₂RuZn₄ shows modified Curie‐Weiss behaviour in the temperature range 10–290 K with an experimental magnetic moment of 2.57(1) μ_B per formula unit. Thus only half of the cerium atoms are trivalent in Ce₂RuZn₄. A remarkable feature of the Ce₂RuZn₄ structure are short Ce2–Ru distances of 260 pm. The crystal chemistry of Ce₂RuZn₄ is discussed.     

Einkristalle des Cer(III)‐Borosilicats Ce3[BSiO6][SiO4]

Single Crystals of the Cerium(III) Borosilicate Ce₃[BSiO₆][SiO₄] Colorless, lath‐shaped single crystals of Ce₃[BSiO₆]‐ [SiO₄] (orthorhombic, Pbca; a = 990.07(6), b = 720.36(4), c = 2329.2(2) pm, Z = 8) were obtained in attempts to synthesize fluoride borates with trivalent cerium in evacuated silica tubes by reaction of educt mixtures of elemental cerium, cerium dioxide, cerium trifluoride, and boron sesquioxide (Ce, CeO₂, CeF₃, B₂O₃; molar ratio 3 : 1 : 3 : 3) in fluxing CsCl (700 °C, 7 d) with the glass wall. The crystal structure contains eight‐ (Ce1) and ninefold coordinated Ce³⁺ cations (Ce2 and Ce3) surrounded by oxygen atoms. Charge balance is achieved by both discrete borosilicate ([BSiO₆]^5– ≡ [O₂BOSiO₃]^5–) and ortho‐silicate anions ([SiO₄]^4–). The former consists of a [BO₃] triangle linked to a [SiO₄] tetrahedron by a single vertex. The anions form layers in [001] direction alternatingly built up from [BSiO₆]^5– and [SiO₄]^4– groups while Ce³⁺ cations are located in between.     

Catalytic Hydrogenation of Acetic Acid to Acetaldehyde: Synergistic Effect of Bifunctional Co/Ce‐Fe Oxide Solid Solution Catalysts

The large‐scale industrial production of acetic acid (HAc) from carbonylation of methanol has enabled intense research interest from direct hydrogenation of HAc to acetaldehyde (AA). Herein, a series of cerium‐iron oxide solid solution supported metallic cobalt catalysts were prepared by modified sol‐gel method and were applied in gas‐phase hydrogenation of HAc to AA. A synergistic effect between the hydrogenation metal cobalt and Ce‐Fe oxide solid solution is revealed. Specifically, oxygen vacancies provide the active sites for adsorption of HAc, while highly uniformly dispersed metallic Co adsorbs H₂ and activates the reduction of HAc into AA. Moreover, the metallic Co can also assist the cyclical conversion between Fe³⁺/Fe²⁺ and Ce³⁺/Ce⁴⁺ on the surface of Ce_1‐xFe_xO_2‐δ supports. The unique effect substantially enhances the ability of the support material to rapidly capture oxygen atoms from HAc. It is found that the catalyst of 5% Co/Ce_0.8Fe_0.2O_2‐δ with the highest concentration of oxygen vacancy presents the best catalytic performance (i.e. acetaldehyde yield reaches 49.9%) under the optimal reaction conditions (i.e. 623 K and H₂ flow rate = 10 mL/min). This work indicates that the Co/Ce‐Fe oxide solid solution catalyst can be potentially used for the selective hydrogenation from HAc to AA. The synergy between the metallic Co and Ce_1‐xFe_xO_2‐δ revealed can be extended to the design of other composite catalysts.     

Electronic structure,magnetic properties,and mixed valence character of Ce2Ni3Si5 from first principles calculations

Cerium intermetallic compounds exhibit anomalous physical properties such as heavy fermion and Kondo behaviors. Here, an ab initio study of the electronic structure, magnetic properties, and mixed valence character of Ce₂Ni₃Si₅ using density functional theory (DFT) is presented. Two theoretical methods, including pure Perdew–Burke–Ernzerhof (PBE) and PBE + U , are used. In this study, Ce³⁺ and Ce⁴⁺ are considered as two different constituents in the unit cell. The formation energy calculations on the DFT level propose that Ce is in a stable mixed valence of 3.379 at 0 K. The calculated electronic structure shows that Ce₂Ni₃Si₅ is a metallic compound with a contribution at the Fermi level from Ce 4f and Ni 3d states. With the inclusion of the effective Hubbard parameter (U _eff), the five valence electrons of 5 Ce³⁺ ions are distributed only on Ce³⁺ 4f orbitals. Therefore, the occupied Ce³⁺ 4f band is located in the valence band (VB) while Ce⁴⁺ 4f orbitals are empty and Located at the Fermi level. The calculated magnetic moment in Ce₂Ni₃Si₅ is only due to cerium (Ce³⁺) in good agreement with the experimental results. The U _eff value of 5.4 eV provides a reasonable magnetic moment of 0.981 for the unpaired electron per Ce³⁺ ion. These results may serve as a guide for studying present mixed valence cerium‐based compounds. © 2017 Wiley Periodicals, Inc.     

Preparation and Characterization of the Antibacterial Zn2+ or/and Ce3+ Loaded Montmorillonites

A series of modified montmorillonites including Zn²⁺ loaded montmorillonite (Zn/MMT), Ce³⁺ loaded montmorillonite (Ce/MMT) and Zn²⁺‐Ce³⁺ loaded montmorillonites (Zn‐Ce/MMT) were prepared by an ion‐exchange reaction, and characterized using X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The specific surface areas, zeta potentials and antibacterial activity of the modified montmorillonites were also investigated. Zinc and cerium were proved to be present as bivalent zinc state and trivalent cerium state in the modified montmorillonites. For the modified montmorillonites, the d₀₀₁ basal spacings increased and the particles were formed of irregular shapes. The antibacterial activity of the modified montmorillonites was enhanced with the increase of specific surface areas and zeta potentials, and Zn²⁺‐Ce³⁺ loaded montmorillonites displayed obvious synergistic antibacterial effect. When Zn/Ce atomic ratio was 1.24, the Zn‐Ce/MMT showed high antibacterial efficiency and broad‐spectrum antibacterial activity, possessing the MIC against Escherichia coli, Staphylococcus aureus, Candida albicans and Mucor of 1500, 1000, 2000 and 3000 mg·L^?1, respectively.     

Syntheses and Crystal Structures of Hydrated Ternary Cerium Sulfates: Mixed‐valence K5Ce2(SO4)6·H2O and K2Ce(SO4)3·H2O

A new chemical and structural interpretation of K₅Ce₂(SO₄)₆·H₂O ( I ) and a redetermination of the structure of K₂Ce(SO₄)₃·H₂O ( II ) is presented. The mixed‐valent compound I crystallizes in the space group C2/c with a = 17.7321(3), b = 7.0599(1), c = 19.4628(4) Å, β = 112.373(1)° and Z = 4. Compound I has been discussed earlier with space group Cc. In the structure of I , there are pairs of edge sharing cerium polyhedra connected by sulfate oxygen atoms in the μ₃ bonding mode. These cerium dimers are linked through edge and corner sharing sulfate bridges, forming layers. The layers are joined by potassium ions which together with the water molecules are placed between the layers. No irregularity in the distribution of the Ce^III and Ce^IV to cause the lost of a crystallographic center of symmetry was detected. We suggest that the charge exerted by the extra f¹ electron for every cerium dimer is delocalized over the Ce1–O₂–Ce2 moiety in a non‐bonding mode. As a result, the oxidations state of each cerium ion is a mean value between III and IV at each atomic position. Compound II crystallizes in the space group C2 with a = 20.6149(2), b = 7.0742(1), c = 17.8570(1) Å, β = 122.720(1)° and Z = 8. The hydrogen atoms have been located and the absolute structure has been established. Neither hydrogen atom positions nor anisotropic displacement parameters were given in the previous reports. In compound II , the cerium polyhedra are connected by edge and corner sharing sulfate groups forming a three‐dimensional network. This network contains Z‐shaped channels hosting the charge compensating potassium ions.     

Assembly of 3‐D Network Structures Containing Oxydiacetate and CeIII or CeIV

Reaction of CeCl₃·7H₂O with Na₂(oda) (oda = O(CH₂CO₂)₂^2— oxydiacetate) in a 2:3 ratio gives the neutral cerium(III) complex [Ce₂(oda)₃(H₂O)₃]·9H₂O ( 1 ). Treatment of a 1:3 mixture of CeCl₃·7H₂O and H₂oda in water with 4 molar equivalents of NaOH also gives 1 but, with a larger excess of NaOH, the tri‐sodium salt Na₃[Ce(oda)₃]·9H₂O ( 2 ) is isolated. Formation of a tri‐ammonium analogue of 2 can be achieved by neutralisation of an aqueous solution of CeCl₃·7H₂O and H₂(oda) in a 1:3 ratio by NH₄OH, giving (NH₄)₃[Ce(oda)₃]·7H₂O ( 3 ). Use of the cerium(IV) reagent (NH₄)₂[Ce(NO₃)₆] with Na₂(oda) results in reduction to cerium(III) under ambient conditions and isolation of 1 . However, in the absence of light this reaction yields crystals of the novel cerium(IV) heterobimetallic [Ce(oda)₃Na₄(NO₃)₂] ( 4 ). Each of these complexes exhibit a 3‐D network structure having a common nine‐coordinate [Ce(oda)₃]^n— (n = 2 or 3) subunit, irrespective of the oxidation state of cerium. In 1 , six [Ce(oda)₃]^3— anions are connected, through bridging bidentate carboxylates, to a second Ce³⁺ site further coordinated by three water molecules. In contrast, the ammonium salt 2 , displays isolated [Ce(oda)₃]^3— anions, devoid of further carboxylate bonding, but enmeshed within a network of hydrogen‐bonded NH₄⁺ cations and water molecules. The remarkable structure of 4 consists of infinite 2‐D sheets of [Na₂(NO₃)]⁺ pillared by [Ce(oda)₃]^2— units, the connectivity arising by multidentate nitrate and carboxylate bridging.     

Visualization of Heterogeneous Oxygen Storage Behavior in Platinum‐Supported Cerium‐Zirconium Oxide Three‐Way Catalyst Particles by Hard X‐ray Spectro‐Ptychography

The cerium density and valence in micrometer‐size platinum‐supported cerium–zirconium oxide Pt/Ce₂Zr₂O_x (x=7–8) three‐way catalyst particles were successfully mapped by hard X‐ray spectro‐ptychography (ptychographic‐X‐ray absorption fine structure, XAFS). The analysis of correlation between the Ce density and valence in ptychographic‐XAFS images suggested the existence of several oxidation behaviors in the oxygen storage process in the Ce₂Zr₂O_x particles. Ptychographic‐XAFS will open up the nanoscale chemical imaging and structural analysis of heterogeneous catalysts.     

Bright Photoluminescence of [{(Cp )2Ce(μ‐Cl)}2]: A Valuable Technique for the Determination of the Oxidation State of Cerium

The synthesis and photoluminescence properties of the bright‐yellow organocerium complex [{(Cp )₂Ce(μ‐Cl)}₂] (Cp =1,3‐di(tert‐butyl)cyclopentadienyl) are presented. This coordination compound exhibits highly efficient photoluminescence within the yellow‐light wavelength range, with a high internal quantum yield of 61(±2) % at room temperature. The large red shift is attributed to the delocalizing ability of the aromatic ligands, whilst its quantum yield even makes this compound competitive with Ce³⁺‐activated LED phosphors in terms of its photoluminescence efficiency (disregarding its thermal stability). A bridging connection between two crystallographically independent Ce³⁺ ions is anticipated to be the reason for the highly efficient photoluminescence, even up to room temperature. The emission spectrum is characterized by two bands in the orange‐light range at both 10 K and room temperature, which are attributed to the parity‐allowed transitions 5d¹(²D_3/2)→4f¹(²F_7/2) and 5d¹(²D_3/2)→4f¹(²F_5/2) of Ce³⁺, respectively. The photoluminescence spectra were interpreted in relation to the structure and vibrational modes of the coordination compound. The spectra and optical properties indicate that trivalent cerium ions are the dominant species in the ground state, which also resolves an often‐encountered ambiguity in organocerium compounds. This result shows that photoluminescence spectroscopy is a versatile tool that can help elucidate the oxidation state of Ce in such compounds.     

Synergistic effect of doping and defect in achieving white light emission and oxygen reduction catalysis in Ce1-xSmxPO4

Multifunctional materials owing to their efficacy to perform more than one job have attracted the attention of global materials science community to resolve the issue of material crunch and reduce the work load. Here, in this work, we have demonstrated the suitability of CePO₄:Sm³⁺ (CPOS) phosphor for white light luminophore and oxygen reduction catalyst. Raman spectroscopy confirmed the stabilization of monoclinic phase for CPOS. White light emission with correlated color temperature (CCT) favoring cool white feature in CPOS is endowed by inefficient host to dopant energy transfer (HDET). X-ray photoelectron spectroscopy (XPS) suggested presence of both Ce³⁺ and Ce⁴⁺ in CPOS with later in lower fraction. XPS results also showed the presence of surface oxygen in CPOS which along with mixed oxidation state of cerium on the surface may be aiding CPOS to work as electrocatalysts for oxygen reduction reaction (ORR). The best electrocatalytic performance was achieved with 1.0% Sm doped sample which has higher concentration of oxygen associated with Ce (IV) on the surface.     

Metal–metal charge transfer and interfacial charge transfer mechanism for the visible light photocatalytic activity of cerium and nitrogen co-doped TiO2

Nanosized cerium and nitrogen co-doped TiO₂ (Ce–TiO_2?xN_x) was synthesized by sol gel method and characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), FESEM, Fourier transform infrared, N₂ adsorption and desorption methods, photoluminescence and ultraviolet–visible (UV–vis) DRS techniques. PXRD analysis shows the dopant decreases the crystallite sizes and slows the crystallization of the titania matrix. XPS confirm the existence of cerium ion in +3 or +4 state, and nitrogen in ?3 state in Ce–TiO_2?xN_x. The modified surface of TiO₂ provides highly active sites for the dyes at the periphery of the Ce–O–Ti interface and also inhibits Ce particles from sintering. UV–visible DRS studies show that the metal–metal charge transfer (MMCT) of Ti/Ce assembly (Ti⁴⁺/Ce³⁺ → Ti³⁺/Ce⁴⁺) is responsible for the visible light photocatalytic activity. Photoluminescence was used to determine the effect of cerium ion on the electron–hole pair separation between the two interfaces Ce–TiO_2?xN_x and Ce₂O₃. This separation increases with the increase of cerium and nitrogen ion concentrations of doped samples. The degradation kinetics of methylene blue and methyl violet dyes in the presence of sol gel TiO₂, Ce–TiO_2?xN_x and commercial Degussa P25 was determined. The higher visible light activity of Ce–TiO_2?xN_x was due to the participation of MMCT and interfacial charge transfer mechanism.     

Ordered mesoporous SBA‐15 functionalized with yttrium(III) and cerium(III) complexes: Towards active heterogeneous catalysts for oxidation of sulfides and preparation of 5‐substituted 1H‐tetrazoles

Mesoporous SBA‐15 was synthesized and modified with 3‐chloropropyltrimethoxysilane and then used in immobilization of creatinine groups, which were employed to introduce Y³⁺ and Ce³⁺ to give rise to two novel yttrium and cerium catalysts: SBA‐15@Creatinine@M (M = Y and Ce). The structures of the SBA‐15@Creatinine@M catalysts were determined using various techniques. These catalysts offered outstanding catalytic performances in the oxidation of sulfides to sulfoxides and in the preparation of 5‐substituted 1H‐tetrazoles. An important characteristic of the SBA‐15@Creatinine@M catalysts is that they are very stable without a considerable decrease in their catalytic performance lasting seven cycles.     

Electrochemically controlled multistability of ultrathin films of double-decker cerium phthalocyaninates

The spectral and electrochemical properties of Langmuir-Blodgett (LB) films of homoleptic double-decker cerium bis-[tetra-15-crown-5]-phthalocyaninate Ce[R₄Pc]₂ and its heteroleptic analog [Pc]Ce[R₄Pc] were studied. It was shown that during formation of Langmuir monolayers upon contact of both complexes solutions with water subphase the metal center with valent state IV in the solution transforms into one with the valent state III in the monolayer. Upon cyclic compression-expansion of these monolayers, orientation-induced reversible intramolecular transfers of electron from 4f orbital of cerium ion to the phthalocyanine macrocycle (compression) and in reverse direction (expansion) occur in a planar supramolecular system. Scheme of reversible electrochemical transformations occurring in ultrathin films of double-decker cerium crown-phthalocyaninates, one of which is associated with the Ce⁺³/Ce⁺⁴ redox-transition of metal center of the complex, was proposed and substantiated using the results of spectro-electrochemical investigations. It was shown that one of these transformations is associated with the Ce⁺³/Ce⁺⁴ redox transition of metal center of the complex and upon change of metal center oxidation state its size changes, and, consequently, the distance between the decks of the complex also changes. This change in the distance can lead to a substantial (13–15%) modulation of the linear size of molecular assemblies with a large number of molecules in stack. On the basis of this effect the supramolecular device that can perform mechanical work can be developed. Using surface plasmon resonance technique we have demonstrated that a step change in electrode potential in region of 200–1000 mV induces a corresponding optical response reflected in a step change of the resonance angle. High operation speed and reversibility of switching between stable states can serve as a basis for development of optoelectronic switching systems.     

Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 67 Erstmalige parametrische Analyse des Absorptionsspektrums einer Molekülverbindung des CeIIIμ: Tris(η5‐tetramethylcyclopentadienyl)cer

Electronic Structures of Organometallic Complexes of f Elements. 67 First Parametric Analysis of the Absorption Spectrum of a Molecular Compound of Ce^IIIμ: Tris(η⁵‐tetramethylcyclopentadienyl)cerium(III) The absorption spectra (in the IR/NIR/Vis/UV range) of Ce(C₅Me₄H)₃ ( 1 ) and La(C₅Me₄H)₃ ( 2 ) were recorded at room and low temperatures. From the spectra obtained, two alternative closely related crystal field (CF) splitting patterns of 1 could be derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian. The fact that the difference of the experimental energies of the barycenters of CF levels of the multiplets ²F_7/2 and ²F_5/2 is larger than in the gaseous free Ce³⁺ ion (“anti”‐relativistic nephelauxetic effect) could be explained by coupling effects of these multiplets via the CF, resulting in lower spin‐orbit coupling parameters than in the case of the gaseous free Ce³⁺ ion. The experimentally derived CF splitting pattern of 1 is compared with the predictions of previous non‐relativistic SW‐Xα and relativistic DV‐Xα calculations.     

Synthesis,Structure, and Photoluminescence Properties of Novel KBaSc2(PO4)3:Ce3+/Eu2+/Tb3+ Phosphors for White‐Light‐Emitting Diodes

A series of novel KBaSc₂(PO₄)₃:Ce³⁺/Eu²⁺/Tb³⁺phosphors are prepared using a solid‐state reaction. X‐ray diffraction analysis and Rietveld structure refinement are used to check the phase purity and crystal structure of the prepared samples. Ce³⁺‐ and Eu²⁺‐doped phosphors both have broad excitation and emission bands, owing to the spin‐ and orbital‐allowed electron transition between the 4f and 5d energy levels. By co‐doping the KBaSc₂(PO₄)₃:Eu²⁺ and KBaSc₂(PO₄)₃:Ce³⁺ phosphors with Tb³⁺ ions, tunable colors from blue to green can be obtained. The critical distance between the Eu²⁺ and Tb³⁺ ions is calculated by a concentration quenching method and the energy‐transfer mechanism for Eu²⁺→Tb³⁺ is studied by utilizing the Inokuti–Hirayama model. In addition, the quantum efficiencies of the prepared samples are measured. The results indicate that KBaSc₂(PO₄)₃:Eu²⁺,Tb³⁺ and KBaSc₂(PO₄)₃:Ce³⁺,Tb³⁺ phosphors might have potential applications in UV‐excited white‐light‐emitting diodes.     

New Structure Type among Octahydrated Rare‐Earth Sulfates, β‐Ce2(SO4)3·8H2O,and a new Ce2(SO4)3·4H2O Polymorph

Syntheses, crystal structures and thermal behavior of two new hydrated cerium(III) sulfates are reported, Ce₂(SO₄)₃·4H₂O ( I ) and β‐Ce₂(SO₄)₃·8H₂O ( II ), both forming three‐dimensional networks. Compound I crystallizes in the space group P2₁/n. There are two non‐equivalent cerium atoms in the structure of I , one nine‐ and one ten‐fold coordinated to oxygen atoms. The cerium polyhedra are edge sharing, forming helically propagating chains, held together by sulfate groups. The structure is compact, all the sulfate groups are edge‐sharing with cerium polyhedra and one third of the oxygen atoms, belonging to sulfate groups, are in the S–Oμ₃–Ce₂ bonding mode. Compound II constitutes a new structure type among the octahydrated rare‐earth sulfates which belongs to the space group Pn. Each cerium atom is in contact with nine oxygen atoms, these belong to four water molecules, three corner sharing and one edge sharing sulfate groups. The crystal structure is built up by layers of [Ce(H₂O)₄(SO₄)]_nⁿ⁺ held together by doubly edge sharing sulfate groups. The dehydration of II is a three step process, forming Ce₂(SO₄)₃·5H₂O, Ce₂(SO₄)₃·4H₂O and Ce₂(SO₄)₃, respectively. During the oxidative decomposition of the anhydrous form, Ce₂(SO₄)₃, into the final product CeO₂, small amount of CeO(SO₄) as an intermediate species was detected.     

Real‐time Probing the Formation of [M(2,2‐bipyridine)2(NO3)3] (M = Ce,La, Tb) Complexes and Influence of Synthesis Parameters

Despite the strong technological importance of lanthanide complexes, their formation processes are rarely investigated. This work is dedicated to determining the influence of synthesis parameters on the formation of [Ce(bipy)₂(NO₃)₃] as well as Ce³⁺‐ and Tb³⁺‐substituted [La(bipy)₂(NO₃)₃] (bipy = 2,2′‐bipyridine) complexes. To this end, we performed in situ luminescence measurements, synchrotron‐based X‐ray diffraction (XRD) analysis, infrared spectroscopy (IR), and measured pH value and/or ion conductivity during their synthesis process under real reaction conditions. For the [Ce(bipy)₂(NO₃)₃] complex, the in situ luminescence measurements initially presented a broad emission band at 490 nm, assigned to the 5d→4f Ce³⁺ ions within the ethanolic solvation shell. Upon the addition of bipy, a red shift to 700 nm was observed. This shift was attributed to the changes in the environment of the Ce³⁺ ions, indicating their desolvation and incorporation into the [Ce(bipy)₂(NO₃)₃] complex. The induction time was reduced from 8 to 3.5 min, by increasing the reactant concentration by threefold. In contrast, [La(bipy)₂(NO₃)₃] crystallized within days instead of minutes, unless influenced by high Ce³⁺ and Tb³⁺ concentrations. Monitoring and controlling the influence of the reaction parameters on the structure of emissive complexes is important for the development of rational synthesis approaches and optimization of their structure‐related properties like luminescence.     

Silicotungstic acid modified Ce‐Fe‐Ox catalyst for selective catalytic reduction of NOx with NH3: Effect of the amount of HSiW

The HSiW(x)/Ce‐Fe catalysts were used to research the effect of silicotungstic acid contents on the catalytic activity in the selective catalytic reduction of NO_x with NH₃. Doping different contents of silicotungstic acid affected surface species and redox property as well as the catalytic activity. With the increasing amount of HSiW (x = 5%, 10% and 20%), the redox reaction between Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺ enhanced, which could improve the ratio of Ce³⁺ and Fe³⁺. And then, more Ce³⁺ increased the ratio of chemisorbed oxygen (O_α). Besides, the type and strength of acid sites over HSiW(_x)/Ce‐Fe was affected by the HSiW contents. These factors facilitated the catalytic performance. Thus, the NO_x conversion of HSiW(x)/Ce‐Fe(x = 20%) was higher than 90%, which maintained in a wide temperature range between 200 and 400 °C.     

Trivalent‐Intermediate Valent Cerium Ordering in CeRuSn – A Static Intermediate Valent Cerium Compound with a Superstructure of the CeCoAl Type

New equiatomic stannide CeRuSn was synthesized from the elements by arc‐melting. CeRuSn was investigated by X‐ray powder and single crystal diffraction: C2/m, a = 1156.1(4), b = 475.9(2) and c = 1023.3(4) pm, β = 102.89(3)°, wR2 = 0.0466, 1229 F² values and 38 variables. CeRuSn adopts a superstructure of the monoclinic CeCoAl type through a doubling of the subcell c axis. In the superstructure two crystallographically independent cerium sites occur. Based on the interatomic distances the two sites can be assigned to trivalent Ce2 and intermediate valent Ce1. This trivalent‐intermediate valent cerium ordering is underlined by magnetic susceptibility measurements χ_m(T): below 150 K χ_m, measured with decreasing temperature, follows a Curie‐Weiss law χ_m = C_m/(T–θ_p) giving C_m = 0.38 emuK/mol as Curie constant per CeRuSn mol; a value showing that only half of the cerium atoms are trivalent in CeRuSn (C_m = 0.807 emuK/mol for one free Ce³⁺ ion). A remarkable feature of the CeRuSn structure are the short Ce1–Ru1 (233 pm) and Ce1–Ru2 (246 pm) distances. The crystal chemistry of CeRuSn is discussed on the basis of a group‐subgroup scheme.     

Sol–gel synthesis and optical behavior of Mg–Ce–O nano-crystallites

The Mg–Ce–O powder are shown to contain periclase-type MgO and/or fluoride-type cerium oxide (CeO₂) depending upon the composition (x) defined by Ce/(Ce + Mg) atomic ratio. Lattice contraction of pariclase phase of MgO (average crystallite size ~8.8 nm) at Ce content of ‘x’ = 0.20 in comparison to pure MgO (crystallite size ~9.5 nm) has been realized due to oxygen vacancy formation. The optical band gap values of CeO₂ varies (3.0–3.2 eV) due to oxygen vacancy formation in CeO₂ phase, crystallite size and/or Ce³⁺/Ce⁴⁺ ratio. Further, the addition of Ce has shown to reduce the physisorption and chemisorption of water significantly as reflected by (1) suppression of related absorption peaks and (2) absence of magnesium hydroxide, Mg(OH)₂, bands in Fourier transform infrared spectra.