Promoting effect of ceria on the physicochemical and catalytic properties of CeO2–ZnO composite oxide catalysts

Cobalt Element Effect of Ternary Mesoporous Cerium Lanthanum Solid Solution for the Catalytic Conversion of Methanol and CO2 into Dimethyl Carbonate

A citric acid ligand assisted self-assembly method is used for the synthesis of ternary mesoporous cerium lanthanum solid solution doped with metal elements (Co, Zr, Mg). Their textural property was characterized by X-ray diffraction, transmission electron microscopy, N₂ adsorption-desorption, X-ray photoelectron spectroscopy and TPD techniques, and so on. The results of catalytic testing for synthesis of dimethyl carbonate (DMC) from CH₃OH and CO₂ indicated that the DMC yield reached 316 mmol/g on Ce-La-Co solid solution when the reaction temperature was 413 K and the reaction pressure was 8.0 MPa. It was found that Co had synergistic effect with La and Ce, doping of Co on the mesoporous Ce-La solid solution was helpful to increase the surface area of the catalyst, promote CO₂ adsorption and activation, and improve the redox performance of solid solution catalyst. The conversion of Co²⁺ to Co³⁺ resulted in the continuous redox cycle between Ce⁴⁺ and Ce³⁺, and the oxygen vacancy content of the catalyst was increased. Studies have shown that the catalytic performance of Ce-La-Co solid solution is positively correlated with oxygen vacancy content. On this basis, the reaction mechanism of DMC synthesis from CO₂ and CH₃OH on the catalyst was speculated.

Synthesis, Crystallography, Microstructure, Crystal Defects, Optical and Optoelectronic Properties of ZnO:CeO2 Mixed Oxide Thin Films

We report the synthesis and characterization of pure ZnO, pure CeO2, and ZnO:CeO2 mixed oxide thin films dip-coated on glass substrates using a sol-gel technique. The structural properties of as-prepared thin film are investigated using the XRD technique. In particular, pure ZnO thin film is found to exhibit a hexagonal structure, while pure CeO2 thin film is found to exhibit a fluorite cubic structure. The diffraction patterns also show the formation of mixed oxide materials containing well-dispersed phases of semi-crystalline nature from both constituent oxides. Furthermore, optical properties of thin films are investigated by performing UV–Vis spectrophotometer measurements. In the visible region, transmittance of all investigated thin films attains values as high as 85%. Moreover, refractive index of pure ZnO film was found to exhibit values ranging between 1.57 and 1.85 while for CeO2 thin film, it exhibits values ranging between 1.73 and 2.25 as the wavelength of incident light decreases from 700 nm to 400 nm. Remarkably, refractive index of ZnO:CeO2 mixed oxide-thin films are tuned by controlling the concentration of CeO2 properly. Mixed oxide-thin films of controllable refractive indices constitute an important class of smart functional materials. We have also investigated the optoelectronic and dispersion properties of ZnO:CeO2 mixed oxide-thin films by employing well-established classical models. The melodramatic boost of optical and optoelectronic properties of ZnO:CeO2 mixed oxide thin films establish a strong ground to modify these properties in a skillful manner enabling their use as key potential candidates for the fabrication of scaled optoelectronic devices and thin film transistors.

Catalytic Steam Reforming of Bio-Oil-Derived Acetic Acid over CeO2-ZnO Supported Ni Nanoparticle Catalysts

The steam reforming of bio-oil-derived acetic acid over the developed Ni/CeO₂-ZnO nanoparticle catalysts for hydrogen production was studied. The correlations of CeO₂ to ZnO mass ratio (CZMR) and nickel loading with the properties and performances of Ni/CeO₂-ZnO catalysts were explored. The H₂, CO, and potential H₂ yields followed a Gaussian normal distribution with increasing the CZMR. An exponential function equation was established to correlate the H₂, CO, and potential H₂ yields with Ni loading. As the CZMR increased from 0 to 1/3, the H₂ yield increased from 57.8 to 69.4%, with a growth rate of 20.1%. Further, on increasing the CZMR from 1/3 to 3, the H₂ yield decreased by 37.6%. The CO yield showed a similar trend for the H₂ yield on increasing the CZMR, which first increased to a peak value, then started to decrease rapidly and finally stabilized. The yield of H₂ increased significantly from 20.6 to 73.5%, with the increase of nickel loading from 0 to 15%. Further, on increasing the nickel loading from 15 to 25%, the H₂ yield increased by only 5.8%. With the CZMR of 1/3 and the nickel loading of 15%, the selectivities of H₂ and CO were as high as 91.6 and 42.3%, respectively.

Cerium-Oxide-Nanoparticle-Decorated Zinc Oxide with Enhanced Photocatalytic Degradation of Methyl Orange

Cerium-oxide-nanoparticle-decorated zinc oxide was successfully prepared using a simple one-pot hydrothermal technique with different weight% Ce doping. It was found that an increase in Ce doping has an effect on the optical energy band-gap tunability. Ce dopant provides electron trapping on Ce/ZnO nanocomposites and also acts as a surface defect generator during hydrothermal processing. Additionally, a bi-metal oxide heterojunction forms, which acts as a charge separator to obstruct charge recombination and to increase the photodegradation performance. It was found that the methyl orange (MO) degradation performance improved with an increase in Ce doping. The decomposition of MO went from 69.42% (pristine ZnO) to 94.06% (7% Ce/ZnO) after 60 min under fluorescent lamp illumination.

Mesoporous Ce-doped ZnO hollow microspheres for oxidation of 1,2-dichlorobenzene

ZnCe5 microspheres exhibited excellent activity in o-DCB oxidation due to the enhanced reducibility and high concentration of surface active oxygen.

A hybrid nanocomposite of CeO2–ZnO–chitosan as an enhanced sensing platform for highly sensitive voltammetric determination of paracetamol and its degradation product p-aminophenol

A highly selective electrochemical sensor was fabricated based on CeO₂–ZnO–chitosan hybrid nanocomposite modified electrode and was successfully applied for the determination of PAR in pharmaceutical formulations.

Ce(3+)-ion-induced visible-light photocatalytic degradation and electrochemical activity of ZnO/CeO2 nanocomposite

In this study, pure ZnO, CeO2 and ZnO/CeO2 nanocomposites were synthesized using a thermal decomposition method and subsequently characterized using different standard techniques. High-resolution X-ray photoelectron spectroscopy measurements confirmed the oxidation states and presence of Zn(2+), Ce(4+), Ce(3+) and different bonded oxygen species in the nanocomposites. The prepared pure ZnO and CeO2 as well as the ZnO/CeO2 nanocomposites with various proportions of ZnO and CeO2 were tested for photocatalytic degradation of methyl orange, methylene blue and phenol under visible-light irradiation. The optimized and highly efficient ZnO/CeO2 (90:10) nanocomposite exhibited enhanced photocatalytic degradation performance for the degradation of methyl orange, methylene blue, and phenol as well as industrial textile effluent compared to ZnO, CeO2 and the other investigated nanocomposites. Moreover, the recycling results demonstrate that the ZnO/CeO2 (90:10) nanocomposite exhibited good stability and long-term durability. Furthermore, the prepared ZnO/CeO2 nanocomposites were used for the electrochemical detection of uric acid and ascorbic acid. The ZnO/CeO2 (90:10) nanocomposite also demonstrated the best detection, sensitivity and performance among the investigated materials in this application. These findings suggest that the synthesized ZnO/CeO2 (90:10) nanocomposite could be effectively used in various applications.

Novel magnetically separable ZnO/AgBr/Fe3O4/Ag3VO4 nanocomposites with tandem n–n heterojunctions as highly efficient visible-light-driven photocatalysts

In the present work, novel magnetically separable ZnO/AgBr/Fe₃O₄/Ag₃VO₄ nanocomposites with different weight percentages of Ag₃VO₄ were successfully prepared.

Structure-property-composition relationships in doped zinc oxides: enhanced photocatalytic activity with rare earth dopants

In this paper, we demonstrate the use of continuous hydrothermal flow synthesis (CHFS) technology to rapidly produce a library of 56 crystalline (doped) zinc oxide nanopowders and two undoped samples, each with different particle properties. Each sample was produced in series from the mixing of an aqueous stream of basic zinc nitrate (and dopant ion or modifier) solution with a flow of superheated water (at 450 °C and 24.1 MPa), whereupon a crystalline nanoparticle slurry was rapidly formed. Each composition was collected in series, cleaned, freeze-dried, and then characterized using analytical methods, including powder X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller surface area measurement, X-ray photoelectron spectroscopy, and UV-vis spectrophotometry. Photocatalytic activity of the samples toward the decolorization of methylene blue dye was assessed, and the results revealed that transition metal dopants tended to reduce the photoactivity while rare earth ions, in general, increased the photocatalytic activity. In general, low dopant concentrations were more beneficial to having greater photodecolorization in all cases.

Photocatalytic Degradation of Organic Dyes Using ZnO/CeO2 Nanocomposite Material under Visible Light

Nanorods of ZnO/CeO2 were synthesized by thermal decomposition method. The decomposition temperature and formation of composite material were confirmed by the thermogravimetric analysis (TGA) before the synthesis process. The prepared samples were characterized by different techniques. The structural and morphological properties of ZnO/CeO2 nanorods were confirmed by X-ray diffraction (XRD) and high resolution scanning electron microscopy (HR-SEM). The chemical composition and specific surface area analysis were done by energy dispersive X-ray spectroscopy (EDX) and Brunauer–Emmett–Teller (BET) method. Further the catalyst was used for photocatalytic degradation of organic dye under visible light irradiation

High-throughput continuous hydrothermal flow synthesis of Zn-Ce oxides: unprecedented solubility of Zn in the nanoparticle fluorite lattice

High-throughput continuous hydrothermal flow synthesis has been used as a rapid and efficient synthetic route to produce a range of crystalline nanopowders in the Ce-Zn oxide binary system. High-resolution powder X-ray diffraction data were obtained for both as-prepared and heat-treated (850 degrees C for 10 h in air) samples using the new robotic beamline I11, located at Diamond Light Source. The influence of the sample composition on the crystal structure and on the optical and physical properties was studied. All the nanomaterials were characterized using Raman spectroscopy, UV-visible spectrophotometry, Brunauer-Emmett-Teller surface area and elemental analysis (via energy-dispersive X-ray spectroscopy). Initially, for 'as-prepared' Ce(1-x)Zn(x)O(y), a phase-pure cerium oxide (fluorite) structure was obtained for nominal values of x=0.1 and 0.2. Biphasic mixtures were obtained for nominal values of x in the range of 0.3-0.9 (inclusive). High-resolution transmission electron microscopy images revealed that the phase-pure nano-CeO(2) (x=0) consisted of ca 3.7 nm well-defined nanoparticles. The nanomaterials produced herein generally had high surface areas (greater than 150 m(2) g(-1)) and possessed combinations of particle properties (e.g. bandgap, crystallinity, size, etc.) that were unobtainable or difficult to achieve by other more conventional synthetic methods.

Ceria-based solid catalysts for organic chemistry

Ceria has been the subject of thorough investigations, mainly because of its use as an active component of catalytic converters for the treatment of exhaust gases. However, ceria-based catalysts have also been developed for different applications in organic chemistry. The redox and acid-base properties of ceria, either alone or in the presence of transition metals, are important parameters that allow to activate complex organic molecules and to selectively orient their transformation. Pure ceria is used in several organic reactions, such as the dehydration of alcohols, the alkylation of aromatic compounds, ketone formation, and aldolization, and in redox reactions. Ceria-supported metal catalysts allow the hydrogenation of many unsaturated compounds. They can also be used for coupling or ring-opening reactions. Cerium atoms can be added as dopants to catalytic system or impregnated onto zeolites and mesoporous catalyst materials to improve their performances. This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium-based catalysts very effective for a broad range of organic reactions.