TiO2 Supported Nano-Au Catalysts Prepared Via Solvated Metal Atom Impregnation for Low–Temperature CO Oxidation

The Ce _x Ti_1?x O₂ mixed oxides at different mole ratios (x=0.1–1.0) were prepared by co-precipitation of TiCl₄ and Ce(NO₃)₃. The structural and reductive properties of the Ce _x Ti_{1? x} O₂ were affected by calcination temperature. At x=0.1–0.3, CeTi₂O₆ phase was formed and mainly as amorphous after calcination at 650°C. At x=0.3, only CeTi₂O₆ was formed after calcination at 750°C and CeTi₂O₆ crystallized completely after calcination at 800°C. TPR analyses showed that the amount of H₂ consumption by Ce _x Ti_1?xO₂ (650°C) (except x=0.1) was greater than that by single CeO₂, and the valence of CeO₂was the lowest (+3.18) at x=0.3. CuO/Ce_0.3Ti_0.7O₂ was prepared by the impregnation method and catalytic properties were examined by means of a GC micro-reactor NO+CO reaction system, BET, TPR, XRD, XPS and NO-TPD. It was found that CuO/Ce_0.3Ti_0.7O₂ calcined at 650°C had the highest activity in NO+CO reaction with 100% NO conversion at reaction temperature of 300°C, and at 650°C Ce_0.3Ti_0.7O₂just began to crystallize. The catalytic activities were largely affected by the pre-treatment conditions. At low reduction temperature (100°C), CuO species was difficult to reduce. When high degree of reductions took place, both CuO species and Ce_0.3Ti_0.7O₂ reduced and thus a part of CuO species on the support surface would be covered. The XPS and NO-TPD analyses showed that CuO/Ce_0.3Ti_0.7O₂ had four NO absorption centers (Cu⁺, Cu²⁺(I), Cu²⁺(II) and Ce³⁺). The CuO species involving in NO+CO reaction included Cu²⁺(I) and Cu⁺, and CeO₂ species (Ce³⁺ and Ce⁴⁺).     

The Effects of P-Poisoning of CexZr1−xO2 on the Transient Oxygen Storage and Release Kinetics

The present work reports on the investigation of the effects of chemical poisoning of Ce_xZr_1?xO₂ solids by phosphorous (P) on the kinetics of oxygen storage and release (OSR) of the thus derived P-contaminated solids, as a function of Ce_xZr_1?xO₂ solid composition (x = 0.3, 0.5 and 0.7) for the first time. Phosphorous deposition on the surface of Ce_xZr_1?xO₂ particles followed by calcination in air at 850 °C forms nano-crystals of CePO₄, which lead to a drastic decrease in the population of surface and subsurface reactive and mobile oxygen species due to the formation of P–O–Ce bonding. The concentration (μmol/g) of exchangeable ¹⁶O in the solid with ¹⁸O from the gas phase was found to increase, and the degree of reduction in the Oxygen Storage Capacity (OSC) to decrease with increasing Ce content in the Ce_xZr_1?xO₂ solid after P-poisoning. The increase in the Ce content of Ce_xZr_1?xO₂ makes its OSR properties more resistant against P-poisoning due to the increasing number of poison-free Ce atoms, which are able to participate in the Ce³⁺ ? Ce⁴⁺ redox cycle.     

Chemical Removal of CeO2 Segregated on the Surface of CeO2–ZrO2 Binary Oxides for Improvement of OSC

A chemical treatment to remove residual CeO₂ phase on CeO₂–ZrO₂ (CZ) solid solution was carried out. A CZ was treated by H₂O₂ for the reduction of Ce⁴⁺ to Ce³⁺ and then HNO₃ for the dissolution of Ce³⁺ compounds (H–CZ). H₂-TPR, TEM-EDX and XPS analyses revealed the removal of CeO₂ phase and the homogeneous distribution of Ce species. About 20% improvement in oxygen storage capacity (OSC) of H–CZ was confirmed at 773 K by the weight measurements under H₂/N₂ and air atmospheres, indicating that the HNO₃/H₂O₂ treatment was effective to avoid the deterioration of the OSC by segregated CeO₂ on the CZ binary oxides.     

Ce Dispersed Al-MCM-41: A Photocombinate for Phenol Degradation Activity

Al-MCM-41 supported ceria samples of various cerium content (0.2, 0.3, 0.5, 0.8 and 3.0 wt.%) were prepared by impregnation and are characterized by BET, XRD, UV–VIS DRS, XPS and ESR techniques. At lower cerium contents the DRS clearly shows a blue shift of 50 nm in the absorbtion edge of CeO₂ indicating the size quantization and high dispersion of cerium particles. The XPS analyses of Ce–Al-MCM-41 samples revealed the interaction of cerium with Al-MCM-41 in Ce³⁺ state and at higher loadings in Ce^3+/4+ states. ESR studies also further substantiated this observation. These catalysts when subjected to photo degradation activity of phenol, 0.3 wt.% Ce–Al-MCM-41 is showing maximum degradation among all the catalysts tested. The present study highlights that cerium at lower loadings is in +3 oxidation state and is dispersed highly showing good photocatalytic activity in comparison with pure ceria.     

Perovskite structure and low frequency relaxor- like- dielectric response of (Sr,Ce)TiO3 solid solution

Phase composition, structure stability, cations valance state, and relaxor-like-dielectric behavior of Sr_(1–3/2x)Ce_xTiO₃ (SCT, x = 0.3, 0.4) solid solution were investigated systematically. The Sr_(1–3/2x)Ce_xTiO₃ samples appear to be single phase within the detection limits of the technique, whereas the solid solution exhibits the higher angle doublet and triplet peak splitting associated with (200) and (321). X-ray photoelectron spectroscopy (XPS) analysis showed that the Ce substitution induces change in the cations valance state upon oxygen vacancies formation. The system exhibits features of low-frequency dependent relaxor-like-dielectric behavior rather than sharp frequency-independent anomalies. Besides this, two kind of relaxations were detected in the temperature range ≥ 350 °C. According to the electric modulus and ac conductivity analysis, the relaxor-like-dielectric behavior results from the long-range conduction associated with ionized vacancies and mixed state of Ti^3+/4+ and Ce^3+/4+ cations.     

Catalytic combustion of volatile aromatic compounds over CuO-CeO<Subscript>2</Subscript> catalyst

Ce_1?x Cu _x O₂ oxide solid solution catalysts with different Ce/Cu mole ratios were synthesized by the one-pot complex method. The prepared Ce_1?x Cu _x O₂ catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H₂ temperature-programmed reduction (H₂-TPR). Their catalytic properties were also investigated by catalytic combustion of phenyl volatile organic compounds (PVOCs: benzene, toluene, xylene, and ethylbenzene) in air. XRD analysis confirmed that the CuO species can fully dissolve into the CeO₂ lattice to form CeCu oxide solid solutions. XPS and H²-TPR results indicated that the prepared Ce_1?x Cu _x O₂ catalysts contain abundant reactive oxygen species and superior reducibility. Furthermore, the physicochemical properties of the prepared Ce_1?x Cu _x O₂ catalysts are affected by the Ce/Cu mole ratio. The CeCu₃ catalyst with Ce/Cu mole ratio of 3.0 contains abundant reactive oxygen species and exhibits superior catalytic combustion activity of PVOCs. Moreover, the ignitability of PVOCs is also affected by the respective physicochemical properties. The catalytic combustion conversions of ethylbenzene, xylene, toluene, and benzene are 99%, 98.9%, 94.3%, and 62.8% at 205, 220, 225, and 225 °C, respectively.     

Ceria-based Catalysts for the Production of H2 Through the Water-gas-shift Reaction: Time-resolved XRD and XAFS Studies

Hydrogen is a potential alternate energy source for satisfying many of our energy needs. In this work, we studied H₂ production from the water-gas-shift (WGS) reaction over Ce_1?x Cu _x O₂ catalysts, prepared with a novel microemulsion method, using two synchrotron-based techniques: time-resolved X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). The results are compared with those reported for conventional CuO _x /CeO₂ and AuO _x /CeO₂ catalysts obtained through impregnation of ceria. For the fresh Ce_1?x Cu _x O₂ catalysts, the results of XAFS measurements at the Cu K-edge indicate that Cu is in an oxidation state higher than in CuO. Nevertheless, under WGS reaction conditions the Ce_1?x Cu _x O₂ catalysts undergo reduction and the active phase contains very small particles of metallic Cu and CeO_2?x . Time-resolved XRD and XAFS results also indicate that Cu^δ+ and Au^δ+ species present in fresh CuO _x /CeO₂ and AuO _x /CeO₂ catalysts do not survive above 200 °C under the WGS conditions. In all these systems, the ceria lattice displayed a significant increase after exposure to CO and a decrease in H₂O, indicating that CO reduced ceria while H₂O oxidized it. Our data suggest that H₂O dissociation occurred on the O_vacancy sites or the Cu–O_vacancy and Au–O_vacancy interfaces. The rate of H₂ generation by a Ce_0.95Cu_0.05O₂ catalyst was comparable to that of a 5 wt% CuO _x /CeO₂ catalyst and much bigger than those of pure ceria or CuO.     

Catalytic performances of NiO–CeO2 for the reforming of methane with CO2 and O2

Ce_1−xNi_xO₂ oxides with x varying from 0.1 to 0.5 were prepared by precipitation and characterized by XRD, TPR and XPS techniques. Three kinds of Ni phases co-exist in Ce_1−xNi_xO₂ catalysts: (1) aggregated NiO on the support CeO₂, (2) highly dispersed NiO with a strong interaction with CeO₂ and (3) Ni atoms incorporated into the CeO₂ lattice that forms the solid solution. For the reforming of methane with CO₂ and O₂, the Ce_1−xNi_xO₂ oxides prepared by precipitation are superior catalysts, which had a high catalytic activity and thermal stability, especially Ce_0.8Ni_0.2O₂. The catalytic activity is affected by the Ni dispersion on the surface of the catalyst. The Ni–CeO₂ solid solution formed by the Ni species incorporated into CeO₂ promotes the capability of coking resistance.     

Entropy-stabilized metal-CeOx solid solutions for catalytic combustion of volatile organic compounds

Doped Ceria with abundant oxygen vacancies exhibits enhanced performance in heterogeneous oxidation. In principle, doping 50 mol% divalent cations (such as: Cu²⁺, Zn²⁺, and Mg²⁺) into CeO₂ lattice would produce an exceptional catalyst with maximum active oxygen species. However, the huge size gap between Ce (IV) and divalent metal cations obstructs its synthesis. Here, we utilize the theory of increasing configurational entropy with five metal dopants to lower the Gibbs-free energy, and successfully incorporate 50 mol% divalent metal cations into CeO₂ lattice. This unique doping environment endows Ce_0.5Zn_0.1Co_0.1Mg_0.1Ni_0.1Cu_0.1O_x two features: (a) Abundant active oxygen species for excellent performance in volatile organic compounds catalytic oxidation; (b) Bring multi reactive sites, which enable the simultaneous combustion of carbon monoxide, propylene and toluene. Moreover, the increased entropy value makes Ce_0.5Zn_0.1Co_0.1Mg_0.1Ni_0.1Cu_0.1O_x an ultra-stable catalyst in both thermal and hydrothermal conditions (e.g., Working >200 hr in water-resistance experiment).     

Promotion effect and mechanism of MnOx doped CeO2 nano-catalyst for NH3-SCR

MnO_x-CeO₂ (denoted as Mn–Ce) nanorod and MnO_x-CeO₂ nanooctahedra catalysts were synthesized by the hydrothermal method and were used for selective catalytic reduction of NO with NH₃. The catalytic performance tests showed that the NO removal efficiency of CeO₂ catalysts was obviously improved after loading MnO_x. The structure and properties of catalysts had been characterized by SEM、TEM、XRD、BET、XPS、H₂-TPR、NH₃-TPD and in situ DRIFTS. It was found that Mn–Ce catalyst were of uniform core-shell structure, higher concentrations of Mn⁴⁺ and Ce³⁺, better reducibility, the increase of weak acid sites. The results of in situ DRIFTS indicated that the NH₃-SCR reaction should obey the E–R mechanism. Moreover, the promotion effect and mechanism of MnO_x doped CeO₂ was demonstrated, which improved the catalytic activity of Mn–Ce catalysts.     

Structural,dielectric, and piezoelectric properties of Ce-doped Bi7Ti4.2Ta0.3W0.5O21 intergrowth ferroelectric ceramics

The Bi_7-xCe_xTi_4.2Ta_0.3W_0.5O₂₁ (BTTW-BITT-xCe, x = 0.05, 0.10, 0.15, 0.20) ceramics were studied as potential materials for high-temperature applications. The microstructure, dielectric, piezoelectric and ferroelectric properties of Ce doped BTTW-BITT samples were analyzed in detail. The results indicated that an appropriate amount of Ce ion doping could inhibit the growth of grains, suppress the relaxation peak, reduce high-temperature dielectric losses, and greatly improve the piezoelectric activities. The optimal ceramics was obtained at x = 0.15, which possessed a maximum piezoelectric constant of d₃₃ = 23.4 pC/N, a high Curie temperature of 713 °C, a loss value of 6% at 500 °C, and a favorable thermal stability of d₃₃ = 21.1 pC/N (90% of the initial value) at 500 °C. This result indicates that BTTW-BITT-0.15Ce has great potential for applications in the high temperature fields. In addition, XPS results showed that there were two Ce valences states, Ce³⁺ and Ce⁴⁺present in the BTTW-BITT-xCe ceramics.     

Analysis of Sb-doped ceria: Magnetism,conductivity, dielectric,specific heat and optical properties

We report on magnetism, charge transport, dielectric properties and specific heat of Ce_1−xSb_xO₂ ceramics sintered at 1650 ^∘C with a final antimony content of 0 ≤ x ≤ 0.0017. In contrast to other donor dopants, such as Nb, Ta, U and W, charge compensation of antimony in Ce_1−xSb_xO₂ does not involve the formation of the Ce³⁺ ions as revealed by the magnetic susceptibility data. Therefore, we conclude that antimony is mainly present as Sb³⁺ ion and acts as an acceptor dopant in Ce_1−xSb_xO₂. This conclusion is also supported by a very low electrical conductivity of the Sb-doped ceria that shows an activation energy E_σ ∼ 0.97 eV. This activation energy is close to that observed in oxygen conducting acceptor-doped ceria and is significantly higher than the typical E_σ ∼ 0.1–0.3 eV values reported for n-type CeO₂. Below 10 K, both an anomaly in the dielectric loss and a small specific heat surplus in Sb-doped ceria indicate a low-energy dipolar relaxation probably associated with a local dynamics of the off-centered Sb³⁺ point defects.     

Structure and electrical properties of Ce-modified Ca1-xCexBi2Nb1.75(Cu0.25W0.75)0.25O9 high Curie point piezoelectric ceramics

Ca_1-xCe_xBi₂Nb_1.975(Cu_0.25W_0.75)_0.025O₉ (CBNCW-xCe: x = 0.00, 0.02, 0.04, 0.06, and 0.09) lead-free piezoelectric ceramics with improved piezoelectric properties were prepared by the traditional solid-state reaction method. The effects of CeO₂ doping on the microstructure and electrical properties were investigated in detail. XRD patterns and Rietveld refinement show that the crystal structures of the samples transform from the orthorhombic phase into the pseudotetragonal phase and that the lattice distortion is weakened. Raman and XPS spectra indicate that Ce ions exist with +3 and + 4 valences in the air sintered ceramics, in which Ce⁴⁺ replaces Nb⁵⁺, causing the weakened NbO₆ octahedral vibration of torsional and tensile and an increase in oxygen vacancies in the doped ceramics. When x = 0.04, it shows excellent comprehensive properties with a high d₃₃ value of 18.1 pC/N, a T_c value of 900 °C, and a ρ_dc value of 2.8 × 10⁵ Ω cm at 500 °C. Our results suggest that the CBNCW-0.04Ce ceramic is a promising candidate in high-temperature piezoelectric applications.     

Low-Temperature Combustion of CH4 over CeO2–MO x Solid Solution (M = Zr4+, La3+, Ca2+, or Mg2+) Promoted Pd/γ–Al2O3 Catalysts

The catalytic behavior of Pd (2 wt%) catalysts supported on γ-Al₂O₃ and promoted with CeO₂ ? MO _x (M = Zr⁴⁺, La³⁺, Ca²⁺, or Mg²⁺) solid solution was investigated for methane combustion. The results demonstrated that Pd/γ-Al₂O₃CeO₂ MO _x catalysts can be effective for the low-temperature catalytic combustion of methane and are comparable in activity to other conventional catalysts for this reaction. The XPS and XRD results indicated that an enhanced mobility of lattice oxygen induced by the perturbation of Ce–O lattice was responsible for an increased catalytic performance during oxidation reaction. The most active sites in the catalyst system involve contacts between Pd and the CeO₂–MO _x mixed oxide component. Meanwhile, pre-treatment conditions have significant effect on the catalytic activity in methane combustion.     

Low-Temperature Water Gas Shift Reaction on Combustion Synthesized Ce1−x Pt x O2−δ Catalyst

Catalytic activity of Pt²⁺ ion substituted CeO₂ synthesized by solution combustion method was tested for low-temperature water gas shift reaction in H₂ rich steam reformate. XPS studies show that Pt is dispersed as ions and there is no change in Pt oxidation state after the reaction. CO conversion is found to be maximum at 200 °C over Ce_1?x Pt _x O_2?δ catalysts without any methanation. The values of rate are 1.86 and 4.66 μmol/g/s at 125 and 150°C respectively with a dry gas flow rate of 6 Lh^?1 over 2% Pt/CeO₂.     

High-performance inductive couplers based on novel Ce3+ and Co2+ ions co-doped Ni-Zn ferrites

High-performance inductive couplers require Ni-Zn ferrites of high saturation magnetization, Curie temperature, permeability and application frequency. However, for inductive couplers some of these properties run against each other in one ferrite. To balance these requirements, in this work, novel Ni-Zn ferrite ceramics co-doped by Ce³⁺ and Co²⁺ ions with chemical formula Ni_0.4Zn_0.5Co_0.1Ce_xFe_2-xO₄ (x = 0–0.06) were designed and fabricated by a molten salt method. For the acquired ferrites, both Ce³⁺ and Co²⁺ ions could come into the lattices. The initially doped Co²⁺ ions would cause a slightly decreased grain size and dramatically reduced the specimen densification, but the further added Ce³⁺ ions could effectively inhibit the density reduction, while the grain size continues to dwindle. The additional Ce³⁺ ions would generate a foreign CeO₂ phase in the acquired specimens. The sole doping of Co²⁺ ions would aggrandize the saturation magnetization of ferrites, but the introduction of Ce³⁺ ions would cause its decrease. However, with an appropriate doping level, the Ce³⁺ and Co²⁺ ions co-doped ferrites could preserve a relatively high saturation magnetization, while the Curie temperature and cut-off frequency of the ferrites are dramatically augmented, although the permeability would be somewhat reduced. The as-acquired ferrites were simulated to apply in inductive couplers, revealing that the devices manufactured by the Ni_0.4Zn_0.5Co_0.1Ce_xFe_2-xO₄ ferrites had significantly high maximum operating frequency, compared with that of the one manufactured by pure Ni_0.5Zn_0.5Fe₂O₄ ferrite.     

Water�CGas Shift and CO Methanation Reactions over Ni�CCeO2(111) Catalysts

X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO₂(111) surfaces. Upon adsorption on CeO₂(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500?C800 K) leads to partial reduction of the ceria substrate with the formation of Ni²⁺ species that exists as NiO and/or Ce_1?xNi_xO_2?y. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species on CeO₂(111) which are clearly distinguishable from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce⁺³ cations, CO dissociates on the surface at 300 K forming NiC_x compounds that may be involved in the formation of CH₄ at higher temperatures. At medium and large Ni coverages (>0.3 ML), the Ni/CeO₂(111) surfaces are able to catalyze the production of methane from CO and H₂, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (<0.3 ML), the Ni/CeO₂(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water?Cgas shift reaction.     

Arsenate and arsenite adsorbents composed of nano-sized cerium oxide deposited on activated alumina

Cerium oxide composited activated alumina was prepared and used as arsenate and arsenite adsorbents by oxidation of cerium chloride in H₂O₂ solution. The preparation conditions affected arsenic adsorption capabilities in the Al₂O₃–CeO₂. Efficient adsorption of arsenic was achieved when CeO₂ was deposited on 6.0 g of powdered activated alumina at 0.01 M Ce³⁺ concentration and H₂O₂/Ce = 0.5. The arsenic adsorption was particularly enhanced in the presence of the nano-size CeO₂ on the Al₂O₃ support, obeying the Langmuir adsorption isotherm model with maximum adsorption capacities of 13.6 and 10.5 mg/g, respectively, for arsenate and arsenite.     

The Effect of CeO2 on the Hydrodenitrogenation Performance of Bulk Ni2P

Bulk Ni₂P and CeO₂-containing bulk Ni₂P (Ce?CNi₂P(x), where x represents the Ce/Ni atomic ratio) were prepared by a co-precipitation method followed by an in situ H₂ temperature-programmed reduction procedure. The catalysts were characterized by XRD, CO chemisorption, TEM, N₂ adsorption?Cdesorption, XPS and X-ray absorption spectroscopy (XAS). Their hydrodenitrogenation performances were studied using quinoline (Q) and decahydroquinoline as the model compounds. Both the hydrogenation and C?CN bond cleavage activities of Ni₂P were improved by the introduction of CeO₂. CeO₂ mainly accelerated the denitrogenation of Q to propylcyclohexane rather than to propylbenzene. XRD and XPS measurements revealed that the Ce species in Ce?CNi₂P(x) were mainly in the oxide form and both Ce⁴⁺ and Ce³⁺ species coexisted on the surface of the catalysts. Addition of CeO₂ significantly decreased the particle size of Ni₂P, resulting in increased specific surface areas and CO uptakes, possibly due to the strong interaction between the Ce species and Ni₂P. At a Ce/Ni atomic ratio higher than 0.25, segregation of CeO₂ took place. XAS results of the passivated catalysts showed that CeO₂ not only affected the oxidability of Ni₂P but also led to the formation of metallic Ni. The promoting effect of CeO₂ was discussed by considering the electronic interactions between Ce species and Ni₂P as well as the presence of the amorphous Ni and low valence Ce³⁺ species.     

Enhanced piezoelectric properties and low electrical conductivity of Ce-doped Bi7Ti4.5W0.5O21 intergrowth piezoelectric ceramics

New types of Ce-doped Ce_xBi_7-xTi_4.5W_0.5O₂₁ (BTW-BIT-xCe) Aurivillius intergrowth ceramics with high Curie temperatures were synthesized to improve the piezoelectric performances as well as the conduction behaviour, and these ceramics exhibit great potential for high-temperature lead-free piezoelectric applications. The crystal structure, electrical properties and conduction behaviour of BTW-BIT-xCe samples were analysed thoroughly. The XRD patterns combined with Rietveld refinements of the patterns showed that the crystal structure transformed from orthorhombic structure towards pseudo-tetragonal structure with increasing CeO₂ dopant, indicating that a higher symmetry was obtained. The dielectric properties of Ce-doped samples were improved, accompanied by a significant drop in the dielectric loss and a slight decreased Curie temperature (705 °C–683 °C). An enhanced piezoelectric constant d₃₃ of 25.3 pC/N was obtained in BTW-BIT-0.12Ce, which may be attributed to a common decrease in the electrical conductivity and coercive field. Besides, a low electrical conductivity of 2 × 10^-6 S/cm at 540 °C was achieved in the same component owing to a decreased concentration of the oxygen vacancies, which was verified by analyses on XPS spectra. The above results indicate that Ce-doped BTW-BIT samples have great development potential for high temperature piezoelectric applications.