Dopant-Induced Modification of Active Site Structure and Surface Bonding Mode for High-Performance Nanocatalysts: CO Oxidation on Capping-free (110)-oriented CeO2:Ln (Ln = La–Lu) Nanowires

Triple-shelled CuO/CeO2 hollow nanospheres derived from metal–organic frameworks as highly efficient catalysts for CO oxidation

Through a metal–organic framework engaged strategy, triple-shelled CuO/CeO₂-8% hollow nanospheres are fabricated as superior nanocatalysts for CO oxidation with excellent catalytic activity and cyclic stability.

Selectively creating oxygen vacancies on PrCe/SiO2 catalysts for the transformation of a furfural–acetone adduct into a functionalized 1,3-diene

Oxygen vacancies were selectively created on PrCe/SiO₂ for efficient transformation of a furfural–acetone adduct into a functionalized 1,3-diene.

Doping effect of Sm on the TiO2/CeSmOx catalyst in the NH3-SCR reaction: structure–activity relationship, reaction mechanism and SO2 tolerance

A good balance between the redox properties and surface acidity induces the high activity of the Sm doped TiO₂/CeO₂ catalyst.

Oxygen Vacancies Enhanced CeO2:Gd Nanoparticles for Sensing a Tumor Vascular Microenvironment by Magnetic Resonance Imaging

The specific characteristics of the tumor vascular microenvironment such as microvascular permeability and water diffusion have been demonstrated to play essential roles in the evaluation of infiltration of tumors. However, at present, there are few contrast agents (CAs) for magnetic resonance imaging to enhance the sensitivity for acquiring this vital information. Herein, we develop Gd-doped (CeO₂:Gd) nanoparticles as CAs to detect the tumor vascular microenvironment with high sensitivity. The lattice oxygen vacancies on the surface of CeO₂:Gd nanoparticles could bind considerable water molecules to improve the r₁ value, achieving an excellent dynamic contrast-enhanced perfusion weighted imaging performance for the measurement of microvascular permeability. Diffusion limiting of water molecules by oxygen vacancies of CeO₂:Gd nanoparticles further enhances the diffusion-weighted magnetic resonance imaging signal in vitro and in vivo. Excitingly, the strategy is not only essential for obtaining tumor vascular microenvironment information but also offers a way for further research in the design of magnetic resonance CAs.

A Rational Design of the Sintering-Resistant Au-CeO₂ Nanoparticles Catalysts for CO Oxidation: The Influence of H₂ Pretreatments

The redox pretreatment of samples is one of the crucial ways of altering the catalytic properties of the supported noble metal materials in many heterogeneous reactions. Here, H₂-reducing pretreatment is reported to enhance the thermal stability of Au-CeO₂ catalysts prepared by the deposition–precipitation method and calcination at 600 °C for CO oxidation. In order to understand the improved activity and thermal stability, a series of techniques were used to characterize the physico-chemical changes of the catalyst samples. H₂ pretreatment may lead to: (i) a strong metal–support interaction (SMSI) between Au nanoparticles (NPs) and CeO₂, evidenced by the particular coverage of Au NPs by CeO₂, electronic interactions and CO adsorption changes. (ii) the production of surface bicarbonates which can accelerate CO oxidation. As a result, the H₂ pretreatment makes the Au NPs more resistant to sintering at high temperature and enhances the CO oxidation activity. Furthermore, this reduction pretreatment strategy may provide a potential approach to enhance the thermal-stability of other supported noble metal catalysts.

Design of Porous/Hollow Structured Ceria by Partial Thermal Decomposition of Ce-MOF and Selective Etching

Metal-organic frameworks (MOFs) have been widely used to prepare corresponding porous metal oxides via thermal treatment. However, high temperature treatment always leads to obtained metal oxides with a large crystallite size, thus decreasing their specific surface area. Different from the conventional complete thermal decomposition of MOFs, herein, using Ce-MOF as a demonstration, we choose partial thermal decomposition of MOF, followed by selective etching to prepare porous/hollow structured ceria because of the poor stability of Ce-MOF under acidic conditions. Compared with the ceria derived from complete thermal decomposition of Ce-MOF, the as-prepared ceria is demonstrated to be a good support for copper oxide species during the CO oxidation catalytic reaction. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H₂-TPR) analysis revealed that the as-prepared ceria is favorable for strengthening the interaction between the ceria and loaded copper oxide species. This work is expected to open a new, simple avenue for the synthesis of metal oxides from MOFs via partial thermal decomposition.

A Simple Descriptor to Rapidly Screen CO Oxidation Activity on Rare-Earth Metal-Doped CeO2: From Experiment to First-Principles

Ceria (CeO₂) is an attractive catalyst because of its unique properties, such as facile redoxability and high stability. Thus, many researchers have examined a wide range of catalytic reactions on ceria nanoparticles (NPs). Among those contributions are the reports of the dopant-dependent catalytic activity of ceria. On the other hand, there have been few mechanistic studies of the effects of a range of dopants on the chemical reactivity of ceria NPs. In this study, we examined the catalytic activities of pure and Pr, Nd, and Sm-doped CeO₂ (PDC, NDC, and SDC, respectively) NPs on carbon monoxide (CO) oxidation. Density functional theory (DFT) calculations were also performed to elucidate the reaction mechanism on rare-earth (RE)-doped CeO₂(111). The experimental results showed that the catalytic activities of CO oxidation were in the order of CeO₂ > PDC > NDC > SDC. This is consistent with the DFT results, where the reaction is explained by the Mars-van Krevelen mechanism. On the basis of the theoretical interpretation of the experimental results, the ionic radius of the RE dopant can be used as a simple descriptor to predict the energy barrier at the rate-determining step, thereby predicting the entire reaction activity. Using the descriptor, a wide range of RE dopants on CeO₂(111) were screened for CO oxidation. These results provide useful insights to unravel the CO oxidation activity on various oxide catalysts.

Structural Evolutions and Crystal Field Characterizations of Tm-Doped YAlO3: New Theoretical Insights

The recent renaissance of the use of rare-earth-doped yttrium orthoaluminate as an ideal laser material has generated significant interest; however, the unique structural features underlying many of its outstanding optical properties still require elucidation. To solve this intriguing problem, we performed a systematic first-principles study; the results of the study reveal a new stable phase for Tm³⁺-doped YAlO₃ (YAP), of monoclinic Pm symmetry, with an 80-atom per unit cell. An unbiased CALYPSO structure search indicates that the Tm³⁺ impurity ion tends to substitute the position of Y³⁺ in the YAP crystal lattice. Electronic band structure calculations reveal that the insulated behaviors of YAP are significantly eliminated after doping the impure Tm³⁺ ions, as evidenced by the minor energy gap of about 0.4 eV, which is close to the band gap energy of a 2 μm emitter source. On the basis of our developed crystal-field theory method, the 4f¹² electronic structures and energies of Tm³⁺ ions in the YAP crystal are calculated. The theoretical results indicate that the electric-dipole-induced transition ³H₄ → ³H₅ is mainly responsible for producing the light wave at approximately 2.3 μm. The present results provide an essential understanding of the rare-earth-ion-doped lasing materials and serve as a practical tool for further exploration of such materials.

Pressure Regulations on the Surface Properties of CeO2 Nanorods and Their Catalytic Activity for CO Oxidation and Nitrile Hydrolysis Reactions

Surface properties of nanoscale CeO2 catalysts in terms of the surface Ce(3+) fraction and concentration of oxygen vacancy can affect their catalytic performance significantly. Continual adjustment on surface properties of CeO2 with the morphological preservation has not been realized by synthetic methods. The revisited studies show that surface properties of CeO2 nanorods can be effectively regulated by synthetic pressures while the rodlike morphology is well-preserved. Such phenomena are ascribed to the contact possibility between Ce(3+) species and dissolved O2, which is balanced by the rapidly increased and gradually saturated dissolution/recrystallization rate of Ce(OH)3 and linearly increased concentration of dissolved O2 with the increase of total air pressure or partial pressure of O2. Surface-property-dependent catalytic activity of CeO2 nanorods synthesized under various pressures was also demonstrated in two benchmark reactions-catalytic oxidation of CO and hydrolysis of nitrile. Such a finding of the pressure regulation on the reducible metal oxides provides an effective approach to rationally design novel catalysts for specific reactions, where ceria are supports, promoters, or actives.

Hydrophilic CeO2 nanocubes protect pancreatic β-cell line INS-1 from H2O2-induced oxidative stress

Oxidative stress plays a key role in the occurrence and development of diabetes. With their unique redox properties, CeO2 nanoparticles (nanoceria) exhibit promising potential for the treatment of diabetes resulting from oxidative stress. Here, we develop a novel preparation of hydrophilic CeO2 nanocubes (NCs) with two different sizes (5 nm and 25 nm) via an acetate assisted hydrothermal method. Dynamic light scattering, zeta potential measurements and thermogravimetric analyses were utilized to investigate the changes in the physico-chemical characteristics of CeO2 NCs when exposed to in vitro cell culture conditions. CCK-8 assays revealed that the CeO2 NCs did not impair cell proliferation in the pancreatic β-cell line INS-1 at the highest dose of 200 μg mL(-1) over the time scale of 72 h, while being able to protect INS-1 cells from H2O2-induced cytotoxicity even after protein adsorption. It is also noteworthy that nanoceria with a smaller hydrodynamic radius exhibit stronger antioxidant and anti-apoptotic effects, which is consistent with their H2O2 quenching capability in biological systems. These findings suggest that nanoceria can be used as an excellent antioxidant for controlling oxidative stress-induced pancreatic β-cell damage.

Solution synthesis protocols for shaping mixed valent oxide crystalline particles as robust catalytic materials

Recent progress in the solution based shape controlled synthesis of several typical mixed valent oxides which have been used as highly efficient catalytic nanomaterials in some heterogeneous and photocatalytic reactions has been reviewed.

First-principle study of CO adsorption and oxidation on Sm-doped CeO2(111) surface

The surface properties and CO oxidation on Sm doped CeO₂(111) have been studied systematically by using the DFT+U method to reveal the influence of Sm on the catalytic performance of CeO₂(111).

Nanocrystalline alumina-supported ceria–praseodymia solid solutions: structural characteristics and catalytic CO oxidation

The synergistic effect between ceria–praseodymia and alumina support is responsible for the efficient CO oxidation activity of the catalyst owing to the enhanced surface area, oxygen vacancy concentration, and active oxygen species formation.

Solubility product difference-guided synthesis of Co3O4–CeO2 core–shell catalysts for CO oxidation

Co₃O₄–CeO₂ core–shell catalysts are successfully fabricated by an ion exchange procedure between Co(CO₃)_0.35Cl_0.2(OH)_1.1 nanorods and Ce³⁺ aqueous solution, followed by a calcination step.

Facile and Mild Strategy to Construct Mesoporous CeO2-CuO Nanorods with Enhanced Catalytic Activity toward CO Oxidation

CeO2-CuO nanorods with mesoporous structure were synthesized by a facile and mild strategy, which involves an interfacial reaction between Ce2(SO4)3 precursor and NaOH ethanol solution at room temperature to obtain mesoporous CeO2 nanorods, followed by a solvothermal treatment of as-prepared CeO2 and Cu(CH3COO)2. Upon solvothermal treatment, CuO species is highly dispersed onto the CeO2 nanorod surface to form CeO2-CuO composites, which still maintain the mesoporous feature. A preliminary CO catalytic oxidation study demonstrated that the CeO2-CuO samples exhibited strikingly high catalytic activity, and a high CO conversion rate was observed without obvious loss in activity even after thermal treatment at a high temperature of 500 °C. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H2-TPR) analysis revealed that there is a strong interaction between CeO2 and CuO. Moreover, it was found that the introduction of CuO species into CeO2 generates oxygen vacancies, which is highly likely to be responsible for high catalytic activity toward CO oxidation of the mesoporous CeO2-CuO nanorods.

Anchoring High-Concentration Oxygen Vacancies at Interfaces of CeO(2-x)/Cu toward Enhanced Activity for Preferential CO Oxidation

Catalysts are urgently needed to remove the residual CO in hydrogen feeds through selective oxidation for large-scale applications of hydrogen proton exchange membrane fuel cells. We herein propose a new methodology that anchors high concentration oxygen vacancies at interface by designing a CeO2-x/Cu hybrid catalyst with enhanced preferential CO oxidation activity. This hybrid catalyst, with more than 6.1% oxygen vacancies fixed at the favorable interfacial sites, displays nearly 100% CO conversion efficiency in H2-rich streams over a broad temperature window from 120 to 210 °C, strikingly 5-fold wider than that of conventional CeO2/Cu (i.e., CeO2 supported on Cu) catalyst. Moreover, the catalyst exhibits a highest cycling stability ever reported, showing no deterioration after five cycling tests, and a super long-time stability beyond 100 h in the simulated operation environment that involves CO2 and H2O. On the basis of an arsenal of characterization techniques, we clearly show that the anchored oxygen vacancies are generated as a consequence of electron donation from metal copper atoms to CeO2 acceptor and the subsequent reverse spillover of oxygen induced by electron transfer in well controlled nanoheterojunction. The anchored oxygen vacancies play a bridging role in electron capture or transfer and drive molecule oxygen into active oxygen species to interact with the CO molecules adsorbed at interfaces, thus leading to an excellent preferential CO oxidation performance. This study opens a window to design a vast number of high-performance metal-oxide hybrid catalysts via the concept of anchoring oxygen vacancies at interfaces.

Engineering the defect state and reducibility of ceria based nanoparticles for improved anti-oxidation performance

Due to their excellent anti-oxidation performance, CeO2 nanoparticles receive wide attention in pharmacological application. Deep understanding of the anti-oxidation mechanism of CeO2 nanoparticles is extremely important to develop potent CeO2 nanomaterials for anti-oxidation application. Here, we report a detailed study on the anti-oxidation process of CeO2 nanoparticles. The valence state and coordination structure of Ce are characterized before and after the addition of H2O2 to understand the anti-oxidation mechanism of CeO2 nanoparticles. Adsorbed peroxide species are detected during the anti-oxidation process, which are responsible for the red-shifted UV-vis absorption spectra of CeO2 nanoparticles. Furthermore, the coordination number of Ce in the first coordination shell slightly increased after the addition of H2O2. On the basis of these experimental results, the reactivity of coordination sites for peroxide species is considered to play a key role in the anti-oxidation performance of CeO2 nanoparticles. Furthermore, we present a robust method to engineer the anti-oxidation performance of CeO2 nanoparticles through the modification of the defect state and reducibility by doping with Gd(3+). Improved anti-oxidation performance is also observed in cell culture, where the biocompatible CeO2-based nanoparticles can protect INS-1 cells from oxidative stress induced by H2O2, suggesting the potential application of CeO2 nanoparticles in the treatment of diabetes.

Glutamine-assisted synthesis of Cu-doped CeO2 nanowires with an improved low-temperature CO oxidation activity

Glutamine (GLN)-assisted Cu-doped CeO₂ nanowires exhibit an outstanding performance for CO oxidation and can completely convert CO at 90 °C.

Solvothermal synthesis of 1D nanostructured Mn2O3: effect of Ni2+ and Co2+ substitution on the catalytic activity of nanowires

In this paper, cation modified one dimensional Mn₂O₃ nanowires were synthesized via a solvothermal synthesis and calcination free from the template-assisted method.

High oxygen storage capacity and enhanced catalytic performance of NiO/NixCe1−xO2−δ nanorods: synergy between Ni-doping and 1D morphology

NiO/Ni-doped ceria nanorods have been synthesized. Their unique structure combines specific composition and 1D morphology, which provide great improvements in their physical chemical properties.

High-performance ZnCo₂O₄@CeO2₂₄ core@shell microspheres for catalytic CO oxidation

In this paper, we report a self-assembly method to synthesize high-quality ZnCo2O4@CeO2 core@shell microspheres with tunable CeO2 thickness. ZnCo2O4 spheres were first synthesized as the core, followed by a controlled CeO2 shell coating process. The thickness of CeO2 shell could be easily tuned by varying the feeding molar ratio of Ce/Co. Transmission electron microscope (TEM) images and scanning transmission electron microscope (STEM) image have identified the core@shell structure of these samples. In CO oxidation tests these ZnCo2O4@CeO2 core@shell microspheres exhibited promising catalytic performance, and the catalytic activity of the best sample is even close to the traditional noble metal-CeO2 system, attaining 100% CO conversion at a relatively low temperature of 200 °C. Cycling tests confirm their good stability of these core@shell microspheres besides activity. Their high catalytic performance should be attributed to the core@shell structure formation, and moreover further H2-temperature-programmed reduction (TPR) results revealed the possible synergistic effects between the two components of ZnCo2O4 and CeO2.

Autocatalytic oxidization of nanosilver and its application to spectral analysis

The stable yellow nanosilver (AgNP) and blue nanosilver (AgNPB) sols were prepared by the NaBH₄ procedure. The new nanocatalytic reaction of AgNP-NaCl-H₂O₂ was investigated by surface plasmon resonance (SPR) absorption, resonance Rayleigh scattering (RRS), surface-enhanced Raman scattering (SERS) and scanning electron microscope (SEM) techniques. The autocatalytic oxidization of Ag on AgNP surface by H₂O₂ was observed firstly and the AgNP/AgCl nanoparticles were characterized. The [Ag⁺] from AgNP is different to the Ag⁺ from AgNO₃ that adsorb on the AgNP surface. An autocatalytic oxidization mechanism was proposed to explain experimental phenomena. The relationship between the SPR absorption peaks and the RRS peaks of AgNPB was studied, and three characteristic RRS peaks called as out-of-plane quadrupole, out-of-plane dipole and in-plane dipole RRS peaks were observed firstly. Using AgNP as nanoprobe, a simple, sensitive and selective RRS method was developed for assay of H₂O₂ in the range of 2.0 × 10⁻⁸-8.0 × 10⁻⁵ mol/L.

Mesoporous CeO2 nanoparticles assembled by hollow nanostructures: formation mechanism and enhanced catalytic properties

In this paper, novel hierarchically mesoporous CeO₂ nanoparticles assembled by hollow nanocones were prepared through a facile solvothermal strategy using Ce(HCOO)₃ as the precursor.