Catalytic combustion of toluene on Pt/Al2O3 and Pd/Al2O3 catalysts with CeO2,CeO2-Y2O3 and La2O3 as coatings

CeO₂,La₂O₃,and CeO₂-Y₂O₃ oxides were coated on the surface of spherical granular AI₂O₃(3-5 mm)through impregnation method,and proved as better supports of Pd and Pt catalysts.The influences of rare earth metal doping on the adsorption rates of Pd and Pt ions,as well as the catalytic performance,were investigated.Results show that the H₂PtCl₆·6H₂O adsorption rates of the Al     

Highly dispersed CeO2–x nanoparticles with rich oxygen vacancies enhance photocatalytic performance of g-C3N4 toward methyl orange degradation under visible light irradiation

CeO₂/g-C₃N₄ photocatalysts have attracted tremendous attention in the photocatalytic degradation of organic pollutants. The design and construction of highly active CeO₂/g-C₃N₄ photocatalysts without harsh conditions are still challenging. Herein, highly dispersed CeO_2–x nanoparticles with rich oxygen vacancies were successfully precipitated on the surface of g-C₃N₄ under mild conditions. The fabricated CeO_2–x/g-C₃N₄ exhibits remarkable activity and stability for photocatalytic degradation of MO pollutant. The optimal rate constant of MO degradation over CeO_2–x/g-C₃N₄ is about 0.031 min^?1, which is three times higher than that of g-C₃N₄. A negligible activity decrease is observed after three cycling runs. The enhanced catalytic performance can be ascribed to the excellent dispersion of CeO_2–x with rich oxygen vacancies that benefit O₂ adsorption and visible light absorption. In addition, the proper band alignment between CeO_2–x and g-C₃N₄ is conducive to the highly efficient separation of photogenerated electron–hole pairs.     

A novel ceria hollow nanosphere catalyst for low temperature NOx storage

In this work, a highly active CeO₂ catalyst with hollow nanosphere morphology for low temperature NO_x storage was prepared by a surfactant-assisted solvothermal reaction. The physicochemical properties of ceria samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption–desorption, H₂-temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS). The as-prepared CeO₂ nanosphere possesses excellent NO oxidation capacity, smaller mesopores, better reducibility and more surface Ce³⁺ content. Compared with CeO₂ with nanorod and nanoparticle morphologies, CeO₂ nanosphere shows better intrinsic low temperature NO_x trapping performance, with a wide operating temperature window (150–300 °C), high NO_x adsorption capacity (NAC, 640–745 μmol/g) and high NO_x storage capacity (NSC, 250–350 μmol/g). Two reaction pathways are speculated for NO_x adsorption on CeO₂ nanosphere, including “nitrate route” and “nitrite route”. The thermally unstable surface nitrites formed on the CeO₂ nanosphere allow ceria to release more NO_x during the desorption process. The present work provides a new ceria morphology for NO_x traps, which may become a potential excellent NO_x storage material.     

Design and synthesis of Fe-Ce-O@C with efficient photocatalytic activity

Fe-Ce-OH@AR14 was obtained via the adsorption of acid red 14(AR14) on Fe-Ce-OH prepared by the codeposition of cerium nitrate hexahydrate,ferric nitrate nonahydrate,and ammonia,and then Fe-Ce-O@C with high photocatalyic efficiency was synthesized by the calcination of Fe-Ce-OH@AR14 in N₂.For comparison,Fe-Ce-O was also prepared by the calcination of Fe-Ce-OH in N₂.The obtained materials were characte rized by X-ray diffraction(XRD),Raman,X-ray photoelectron spectroscopy(XPS...     

Transition metal doping effect and high catalytic activity of CeO2–TiO2 for chlorinated VOCs degradation

A series of transition metals (Fe, Co, Ni, Cu, Cr and Mn)-doped CeO₂–TiO₂ catalysts were prepared by the sol–gel method and applied for the catalytic removal of 1,2-dichloroethane (DCE) as a model for chlorinated VOCs (CVOCs). The various characterization methods including X-ray diffraction (XRD), N₂ adsorption–desorption, UV-Raman, NH₃ temperature-programmed desorption (NH₃-TPD) and H₂ temperature-programmed reduction (H₂-TPR) were utilized to investigate the physicochemical properties of the catalysts. The results show that doping Fe, Co, Ni or Mn can obviously promote the activity of CeO₂–TiO₂ mixed oxides for DCE degradation, which is related to their improved texture properties, acid sites (especially for strong acidity) and low-temperature reducibility. Particularly, CeTi–Fe doped with moderate Fe exhibits excellent activity for 1,2-dichloroethane (DCE) degradation, giving a T_90% value as low as 250 °C. More importantly, only trace chlorinated byproducts were produced during the low-temperature degradation of various CVOCs (dichloromethane (DCM), trichloroethylene (TCE) and chlorobenzene (CB)) over CeTi–Fe1/9 catalyst with high durability.     

Slow magnetic relaxation in a 3D dysprosium(III)-fluoro-oxalate framework containing zig-zag [Dy–F]n chains

Dysprosium complexes based on [F–Dy] or near-linear [F–Dy–F] unit are of great concern in the field of single-molecule magnets due to their large magnetic anisotropy. Here, the crystal structure and the magnetic relaxation dynamics were reported for a three-dimensional (3D) metal–organic framework (MOF): [DyF(C₂O₄)(H₂O)₂]_n·2nH₂O (1), which is the unique MOF containing zig-zag [Dy–F]_n chains. Magnetic susceptibility characterization reveals that 1 is one of the few 3D MOFs which show slow magnetic relaxation under zero dc field. And the effective energy barrier of 72 K for 1 is also higher than most Dy-based 3D MOFs. The diamagnetic ion dilution study shows that the ferromagnetic exchange couplings mainly transmitted by F^? bridges in 1 contribute little to the energy barrier, but effectively suppress the quantum tunneling process and result in a smooth hysteresis loop with no waist-restricted step.     

Removal of organic pollutants by lanthanide-doped MIL-53(Fe) metal-organic frameworks:Effect of dopant type in magnetite precursor

A series of undoped and lanthanide doped MIL-53(Fe)/Ln-Fe₃O₄(Ln=La,Nd,or Gd) metal-organic frameworks(MOFs) were prepared by the solvothermal method.All prepared samples were characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),Brunauer-Emmett-Teller(BET) measurements,scanning electron microscopy(SEM),and thermal analysis.XRD and FT-IR results ascertain the successful MOF formation for all prepared samples.MIL-53(Fe)/La-Fe₃O_...     

Synthesis of two lanthanide clusters LnIII4 (Gd4 and Dy4) with [2 × 2] square grid shape: Magnetocaloric effect and slow magnetic relaxation behaviors

Two isostructural tetranuclear lanthanide clusters named [Ln₄(L)₄(CH₃O)₄]·CH₃OH (Ln = Gd(III) for 1, Dy(III) for 2, H₂L = N′-(2-hydroxy-3-methoxybenzylidene)-6-(hydroxymethyl) picolinohydrazide) were successfully isolated by using a polydentate Schiff based ligand and Ln(III) nitrate salts. The structures of 1 and 2 were characterized by X-ray structural analyses, they are held by four double deprotonated ligands L²⁻. In them all the lanthanide ions are eight-coordinated and distributed over four vertices of a parallelogram, presenting a Ln₄ cluster with a strict [2 × 2] square grid pattern. The details of magnetic analysis show that 1 displays weak anti-ferromagnetic exchange between neighboring Gd(III) ions through carboxylate oxygen and methanol oxygen ligand atoms. Furthermore, 1 exhibits significant magnetocaloric effect with the maximum entropy change –ΔS_m value of 28.5 J/(kg·K) for ΔH = 7.0 T at 2.0 K. For compound 2, remarkable slow magnetic relaxation behaviors are observed in the presence of zero magnetic field with τ₀ = 1.02 × 10⁻⁶ s and energy barrier ΔE/k_B = 43.24 K.     

Ln3+ (Ln = Eu,Dy) - doped Sr2CeO4 fine phosphor particles: Wet chemical preparation,energy transfer and tunable luminescence

The Sr₂CeO₄:Ln³⁺ (Ln = Eu, Dy) fine phosphor particles were prepared by a facile wet chemical approach, in which the consecutive hydrothermal-combustion reaction was performed. The doping of Ln³⁺ into Sr₂CeO₄ has little influence on the structure of host, and the as-prepared samples display well-crystallized spherical or elliptical shape with an average particle size at about 100–200 nm. For Eu³⁺ ions-doped Sr₂CeO₄, with the increase of Eu³⁺-doping concentration, the blue light emission band with the maximum at 468 nm originating from a Ce⁴⁺ → O²⁻ charge transfer of the host decreases obviously and the characteristic red light emission of Eu³⁺ (⁵D₀→⁷F₂ transition at 618 nm) is enhanced gradually. Simultaneously, the fluorescent lifetime of the broadband emission of Sr₂CeO₄ decreases with the doping of Eu³⁺, indicating an efficient energy transfer from the host to the doping Eu³⁺ ions. The energy transfer efficiency from the host to Eu³⁺ was investigated in detail, and the emitting color of Sr₂CeO₄:Eu³⁺ can be easily tuned from blue to red by varying the doping concentration of Eu³⁺ ions. Moreover, the luminescence of Dy³⁺-doped Sr₂CeO₄ was also studied. Similar energy transfer phenomenon can be observed, and the incorporation of Dy³⁺ into Sr₂CeO₄ host leads to the characteristic emission of ⁴F_9/2 → ⁶H_15/2 (488 nm, blue light) and ⁴F_9/2 → ⁶H_13/2 (574 nm, yellow light) of Dy³⁺. The Sr₂CeO₄:Ln³⁺ fine particles with tunable luminescence are quite beneficial for its potential applications in the optoelectronic fields.     

One-step solution combustion synthesis of micro-nano-scale porous Cu/CeO2 with enhanced photocatalytic properties

The Cu/CeO₂ nanoporous composite material was prepared via a one-step and energy-saving method of solution combustion synthesis(SCS).The phase composition,surface morphology and optical characteristics of Cu/CeO₂ were studied.The results show that the SCS products are composed of cubic fluorite CeO₂ and Cu.Due to the generation and escape of gas during the synthetic reaction,the SCS CeO₂ shows porous structure,in which the mesopores(diameter 10-17 nm) ...     

Association of a terpyridine ligand with lanthanide and copper(II) nitrates

Reactions between the 1,3-bis(6-methylpyridin-2-yl)pyridine ligand L, C₁₇H₁₅N₃ and Ln^III (1a, 1b, 1c, 1d) or a mixture of Ln^III and Cu^II nitrates (2a, 2b, 2c, 2d) resulted in a series of respectively novel mono- and heterodinuclear complexes, where Ln^III=Sm (a), Eu (b), Tb (c), Dy (d). The compounds were characterized by elemental analysis, ESI-MS and IR spectra, furthermore we obtained crystals of [H₂L][Eu(NO₃)₅] (1b) and [CuL₂][Eu(NO₃)₅] (2b) suitable for XRD characterization. In the crystal structures the Eu ions are 10-coordinated with quite a narrow range of Eu-O distances which are between 0.2436 and 0.2556 nm. In 1b the ligand molecule is protonated in both terminal rings, and the N-H groups are involved in the N-H···O hydrogen bonds with the same oxygen atom of one of the nitro groups. These hydrogen bonds connect the ions in 1b into the complex which is the principal building block of the structure. In 2b the [CuL₂]²⁺ counterions are present; the Cu is octahedrally coordinated by all nitrogen iatoms of two L molecules which are therefore almost perpendicular to each other. The electrostatic interactions between the charged species are in both cases the main driving force of the crystal packing.     

Influences of CeO2 morphology on enhanced performance of electro-Fenton for wastewater treatment

As a kind of rare-earth oxide, CeO₂ has been considered as a great potential material for its abundant oxygen vacancies and catalysis activity in wastewater treatment. In this study, three ceria samples with different morphological structure were prepared, and their effect on contaminates degradation in electro-Fenton (E-Fenton) system was investigated. It is found that the morphology of CeO₂ has great influence on promoting the performance of E-Fenton process. The rod-like CeO₂ (R–CeO₂) induced E-Fenton system shows higher azo dye X3B removal and mineralization rates than cubs (C–CeO₂) and octahedrons (O–CeO₂), and the degradation kinetic rate constants are 0.28, 0.169 and 0.181 min^?1 respectively, already surpass that of the blank one (0.120 min^?1). The H₂O₂ generation capacity of R–CeO₂ induced E-Fenton system is also superior to the others, and the corresponding Faraday current efficiency even increases to 166.2% at 2.5 min. Characterizations by scanning-transmission electron microscopy (STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), Raman spectroscopy were conducted to disclose the mystery behind this phenomenon. The results indicate that the difference of surface oxygen vacancy density in different shaped CeO₂ acts as a magic driving force for the accelerated oxygen reduction, and then leads to the enhanced degradation efficiency of E-Fenton system. This work provides a new insight into the development and application of rare-earth elements based catalyst in E-Fenton technology.     

Catalytic thermal decomposition of ammonium perchlorate by a series of lanthanide EMOFs

Given their unique and excellent properties,metal-organic frameworks(MOFs) materials have been used in many scientific fields.EMOFs use energetic materials as ligands,which can provide part of the energy for the system while catalyzing ammonium perchlorate.The energetic material 1.1’-dihydroxyazotetrazole(H₂AzTO),as a high-energy nitrogen-rich material,was selected as a ligand.Five kinds of La³⁺,Ce³⁺,Pr³⁺,Nd³⁺,and Sm³⁺ lanthanide ...     

Synthesis of pyrrolidinyl-ethylene fluorenyl rare-earth metal complexes and catalysis for 2-vinylpyridine polymerization

The metathesis reaction between pyrrolidinyl-ethylene fluorenyl lithium salts with in situ prepared cationic rare-earth metal dialkyl species [Ln(CH₂SiMe₃)₂(THF)_x][BPh₄] afford efficiently the corresponding constrained-geometry complexes L¹Ln(CH₂SiMe₃)₂(L¹=FluCH₂CH₂NC₄H₈,Ln=Y(1a),Lu(1b),Sc(1c)) and L² Ln(CH₂SiMe₃     

Application of three Ln(Ⅲ)-coordination polymers in fields of luminescence,antibacteria and detection of Fe3+ and 4-nitrophenol

Three lanthanide-based coordination polymers(Ln-CPs) with layered structure,{[La₂(L)₃(DMF)(H₂O)₃]·H₂O}_n(1),{[Eu₂(L)₃(DMF)₂(H₂O)]·(H₂O)}_n(2){Tb₂(L)₃(DMF)₂(H₂O)]·H₂O}n(3) were successfully synthesized from H₂L(N,N’-bis(4-carbozylbenzyl)aniline).Remarkably,compound 3 has extremely high sensitivity to 4-n...     

Constructing a high concentration CuO/CeO2 interface for complete oxidation of toluene: The fantastic application of spatial confinement strategy

In this paper,CeO₂ substrate was prepared by the sol-gel method,further CuO was introduced by adding the copper complexes with chelating agents into the sol-gel precursors of CeO₂,in which different chelating agents(β-cyclodextrin,glucose and trimesic acid) were tried.This synthesis method helps the CuO species to disperse very uniformly in the CeO₂ substrates.When the amount of copper oxide is up to33 mol%,the CuO/CeO₂ samples can still maintain a hig...     

CeO2-x modified Ru/γ-Al2O3 catalysts for ammonia decomposition reaction

Developing high-performance ammonia decomposition catalysts for preparing CO_x-free hydrogen shows great practical significance.Herein,CeO₂ is used as a promoter to modulate the metal-support interaction to enhance the catalytic performance of Ru/Al₂O₃ catalysts.A series of 1Ru/xCe-10AI(x=0.5,1,or 3)catalysts was prepared by a facile colloidal deposition method.We find that the optimized 1 Ru/1Ce-10Al catalyst exhibits excellent activity for the decompo...     

Enhancing low-temperature NH3-SCR performance of Fe–Mn/CeO2 catalyst by Al2O3 modification

In the work, supported catalysts of FeO_x and MnO_x co-supported on aluminum-modified CeO₂ was synthesized for low-temperature NH₃-selective catalytic reduction (NH₃-SCR) of NO. Impressively, the SCR activity of the obtained catalyst is markedly influenced by the adding amount of Al and the appropriate Ce/Al molar ratio is 1/2. The activity tests demonstrate that Fe–Mn/Ce1Al2 catalyst shows over 90% NO conversion at 75–250 °C and exhibits better SO₂ resistance compared to Fe–Mn/CeO₂. Fe–Mn/Ce1Al2 shows the expected physicochemical characters of the ideal catalyst including the larger surface and increased active reaction active sites by controlling the amount of Al doping. Also, the better catalytic activity is well correlated with the present advantaged surface adsorption oxygen species, Mn⁴⁺ species, Ce³⁺ species and the enhanced reducibility of Fe–Mn/Ce1Al2, which is superior to the Fe–Mn/CeO₂ catalyst. More importantly, we further demonstrate that the amount and strength of surface acid sites are improved by Al-doping and more active intermediates (monodentate nitrate) is generated during NH₃-SCR reaction. This work provides certain insight into the rational creation of simple and practical denitration catalyst environmental purification.     

Improvement in the Mechanical Properties of Silicon Nitride Ceramic in High-Temperature Deformation Processes

Studies have been made on the changes in structure and properties of sintered materials: Si₃N₄ - 5 mass% Y₂O₃ - 2 mass% Al₂O₃, Si₃N₄ - 5 mass% Y₂O₃ - 5 mass% Al₂O₃, and Si₃N₄ - 40 mass% TiN on deformation in a high-pressure chamber of toroid type (pressure 4–5 GPa, temperature 1000–1600 °C), and also by direct extrusion with degrees of reduction of 55 and 72% (temperature 1750–1850 °C, pressure on the plunger 20–30 MPa). After pressure-chamber treatment, the materials have elevated mechanical characteristics: HV₁₀ ≈ 16.7 GPa, K_Ic up to 8.4 MPa · m^1/2 for the system Si₃N₄ - Y₂O₃ - Al₂O₃; and HV₁₀ ≈ 16.9 GPa, K_Ic up to 9.4 MPa · m^1/2 for Si₃N₄ - TiN. A structure feature is the small size of the coherent-scattering regions: 51 nm for Si₃N₄ and 65 nm for TiN in the system Si₃N₄ - TiN, and 33 nm for specimens in the system Si₃N₄ - Y₂O₃ - Al₂O₃. High-temperature extrusion results in a structure with β-Si₃N₄ grains elongated along the deformation direction. The anisotropic structure has K_Ic values in directions perpendicular to and parallel to the direction of extrusion of 11.5–12.0 MPa · m^1/2 and 7.5–7.8 MPa · m^1/2, respectively. The hardness after extrusion becomes 16.0 GPa.     

Effect of CuO species and oxygen vacancies over CuO/CeO2 catalysts on low-temperature oxidation of ethyl acetate

The catalytic oxidation of ethyl acetate(EA) was studied over CuO/CeO₂ catalysts which were prepared by ball milling with different precursors(copper oxide,cerium acetate,cerium dioxide,copper acetate and cerium hydroxide).The CuO/CeO₂ catalyst(O-A) prepared with copper oxide and cerium acetate as precursors shows very high catalytic activity that 100% EA conversion is achieved at low temperature of 220℃.It is found that specific surface area(112.8 m²/g),particle...