XRD and UV-Vis diffuse reflectance analysis of CeO2-ZrO2 solid solutions synthesized by combustion method
TL;DR: A series of ceria-incorporated zirconia (Ce1−xZrxO2,x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route as discussed by the authors.
Abstract: A series of ceria-incorporated zirconia (Ce1−xZrxO2,x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route. The products were characterized by XRD and UV-Vis-NIR diffuse reflectance spectroscopy. The materials are crystalline in nature and the lattice parameters of the solid solution series follow Vegard’s law. Diffuse reflectance spectra of the solid solutions in the UV region show two intense bands at 250 and 297 nm which are assigned respectively to Ce3+ ← O2−and Ce4+ ← O2− charge transfer transitions. The two vibrational bands in 6960 cm−1 and 5168 cm−1 in the NIR region indicate the presence of surface hydroxyl groups on these materials.
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TL;DR: In this article, a mild urea hydrolysis based hydrothermal method through homogeneous nucleation at 413 K followed by calcination at 773 or 1173 K was used for nanoparticulate powders.
Abstract: Ce1-xZrxO2 (x = 0−0.8) nanoparticulate powders were prepared via a mild urea hydrolysis based hydrothermal method through homogeneous nucleation at 413 K followed by calcination at 773 or 1173 K. X...
263 citations
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TL;DR: In this paper, the catalytic properties of Au nanoclusters deposited on a 1-D nanorod and CeO2-nanoparticles have been investigated during CO oxidation at ambient temperatures.
Abstract: Catalytic properties of Au nanoclusters deposited on a one-dimensional CeO2 (1-D) nanorod and CeO2-nanoparticles have been investigated during CO oxidation at ambient temperatures. The kinetic data showed that the activity of Au catalysts could be remarkably improved by using CeO2-nanorods as support compared to the CeO2-nanoparticles. The measured specific rate and apparent activation energy (Ea) at 278 K were 4.02 molCO gAu−1 h−1 and 15.9 kJ mol−1, respectively, for the Au/CeO2-nanorods (Au-CR) catalyst, while those for the Au/CeO2-nanoparticles (Au-CP) catalyst were 0.15 molCO gAu−1 h−1 and 28.4 kJ mol−1, respectively. Characterization by X-ray diffraction (XRD), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV–Vis spectroscopy (DR UV–Vis) and in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) of CO adsorption reveal that the predominantly exposed {1 0 0}/{1 1 0}-dominated surface structures of ceria nanorods show great superiority for anchoring and dispersing of gold nanoclusters, which in turn leads to a higher reducibility and activity of the Au-CeO2 surface for CO oxidation. It is also confirmed that, arising from the strong metal–support interaction (SMSI), the presence of gold nanoclusters has a strong influence on the electronic state of the CeO2 substrates.
245 citations
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TL;DR: In this paper, x-ray diffraction, Rietveld refinement and Fourier transform infrared (FTIR) spectroscopy were used to characterize the body-centred cubic structure of doped and codoped Y2O3 nanophosphors.
Abstract: In this work, Eu-doped, Tb-doped and Eu, Tb-codoped Y2O3 nanophosphors were synthesized by the combustion synthesis method The prepared phosphors were characterized by x-ray diffraction (XRD), Rietveld refinement and Fourier transform infrared (FTIR) spectroscopy XRD studies and Rietveld refinement confirmed the body-centred cubic structure of doped and codoped phosphors FTIR studies also confirmed the formation of these compounds Thermal analysis results indicated that there was no phase transition for all the phosphors in the studied temperature range In the optical properties, diffuse reflectance (DR) and photoluminescence (PL) measurements were performed DR spectra were used to determine the bandgap and it increased in the doped and codoped samples due to the crystallite size effect A strong characteristic emission from Eu3+ and Tb3+ ions was identified and the influence of doping concentration and annealing temperature on PL properties was systematically studied Transfer of energy was observed from Tb3+ to Eu3+ ions in the codoped phosphor at room temperature
189 citations
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TL;DR: In this paper, the influence of calcination temperature from 773 to 1073 K on the structural features and catalytic behavior of the nanostructured Ce 0.7 Mn 0.3 O 2−δ (CM) solid solutions was thoroughly investigated.
Abstract: Noble metal-free nanostructured Ce 0.7 Mn 0.3 O 2−δ (CM) solid solutions were prepared by a simple, facile, and high yielding coprecipitation method from aqueous solutions of cerium and manganese nitrates. The influence of calcination temperature from 773 to 1073 K on the structural features and catalytic behaviour of the CM solid solutions has been thoroughly investigated. The synthesized materials were characterized using XRD, ICP-OES, BET surface area, TEM and HRTEM, UV–vis DRS, Raman, XPS, EPR, and H 2 -TPR techniques. The XRD results indicated that the samples calcined at various temperatures from 773 to 973 K did not show any diffraction peaks corresponding to manganese oxides and thereby ensured the formation of Ce 0.7 Mn 0.3 O 2−δ solid solution. However, the diffraction peak corresponding to Mn 2 O 3 was clearly observed at 1073 K due to the occurrence of phase segregation between Mn–oxide and ceria. The TEM and HRTEM observations showed the nanocrystalline nature of the solid solutions with a particle size in the range of ∼7–20 nm. The doping of Mn into the ceria lattice increased the concentration of structural oxygen vacancies, which are beneficial for oxidation reaction as revealed by UV–vis DRS and Raman results. XPS analysis confirmed that Ce and Mn exist in +4 or +3 and +3 or +2 oxidation states, respectively on the surface of the samples. The EPR studies showed the presence of isolated Mn 2+ and Mn 3+ species in different structural locations such as ceria-lattice defect sites, framework of Ce 4+ locations, interstitial locations, and at the surface of the ceria. H 2 -TPR measurements showed a pronounced enhancement in the reduction of ceria by manganese doping. Among the various catalysts examined, the CM catalyst calcined at 773 K exhibited superior CO oxidation activity at much lower temperature with T 50 = 390 K and 100% CO conversion at ∼470 K in comparison to pure ceria and MnO x . The observed remarkable enhancement in the reactivity for CO oxidation at lower temperatures has been attributed to a highly dispersed state of Mn 2+ /Mn 3+ in the ceria matrix, facile redox behaviour, and a synergistic Mn–Ce interaction.
187 citations
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TL;DR: In this paper, the catalytic activity of Ni/CeO 2 -Al 2 O 3 catalysts modified with noble metals (Pt, Ir, Pd and Ru) was investigated for the steam reform of ethanol and glycerol.
Abstract: The catalytic activity of Ni/CeO 2 –Al 2 O 3 catalysts modified with noble metals (Pt, Ir, Pd and Ru) was investigated for the steam reform of ethanol and glycerol. The catalysts were characterized by the following techniques: Energy-dispersive X-ray, BET, X-ray diffraction, temperature-programmed reduction, UV–vis diffuse reflectance spectroscopy and X-ray absorption near edge structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of CeO 2 dispersed on alumina. The promoting effect of noble metals included a decrease in the reduction temperatures of NiO species interacting with the support, due to the hydrogen spillover effect. It was seen that the addition of noble metal stabilized the Ni sites in the reduced state along the reforming reaction, increasing the ethanol and glycerol conversions and decreasing the coke formation. The higher catalytic performance for the ethanol steam reforming at 600 °C and glycerol steam reforming was obtained for the NiPd and NiPt catalysts, respectively, which presented an effluent gaseous mixture with the highest H 2 yield with reasonably low amounts of CO.
162 citations
References
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TL;DR: A survey of the use of cerium oxide and CeO2-containing materials as oxidation and reduction catalysts is presented in this paper, with a special focus on catalytic interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide.
Abstract: Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.
2,850 citations
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TL;DR: In this paper, a review of transfer reduction using hydrogen donors is presented, focusing mainly on those processes that can be effected by heterogeneous catalysis using molecules other than molecular hydrogen as the source of hydrogen.
Abstract: Reduction of organic compounds is important synthetically both in the laboratory and in industry. There are many methods of effecting reduction which may or may not lead to hydrogenation, but in this review only processes leading to the addition of hydrogen or replacement of a functional group by hydrogen will be considered. Further, this review will be concerned mostly with those processes that can be effected by heterogeneous catalysis using molecules other than molecular hydrogen as the source of hydrogen. Reduction of organic functional groups can be categorized into (i) addition of hydrogen to unsaturated groups as, for example, in the reduction of ketones to alcohols and (ii) addition of hydrogen across single bonds leading to cleavage of functional groups (hydrogenolysis). Removal of oxygen as a reductive process, as in the deoxygenation of oxiranes to alkenes, will not be discussed. Of all the methods available for addition of hydrogen to organic compounds, heterogeneous catalytic transfer reactions have been relatively underutilized. This lack of popularity can be traced to the relatively meager success of much of the earlier research which suggested that the technique was of only limited scope and could provide only modest yields of products. The early pioneering work by Braude' was largely ignored because of poor yields and long reaction times, but the situation has changed considerably following the appearance4 of a stimulating review and the introduction of greater catalyst loadings and different hydrogen donors.2 Another reason for the underutilization of transfer reduction has been the very successful exploitation of molecular hydrogen and hydrides for reduction of organic compounds. In comparison with catalytic reduction using molecular hydrogen, transfer reduction using hydrogen donors has real and potential advantages. Molecular hydrogen, a gas of low molecular weight and therefore high diffusibility, is easily ignited and presents considerable hazards, particularly on the large scale; the use of hydrogen donors obviates these difficulties in that no gas
791 citations
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TL;DR: In this article, the specific properties of dispersed and promoted ZrO 2 are presented for the photocatalytic total decomposition of water and a novel application for photocatalysis of water is presented.
Abstract: Examples of the application of ZrO 2 for catalysts and catalyst supports are reviewed. The specificity of the structure and the surface properties including the behavior of surface OH groups are introduced. The catalytic properties of dispersed and promoted ZrO 2 are presented. The novel application to the photocatalytic total decomposition of water is also presented.
492 citations
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TL;DR: In this article, the bases of IR spectroscopic methods for the characterization of the surface acidity, of the Lewis type and of the Bronsted type, of solid, simple and mixed oxides are briefly reviewed.
Abstract: The bases of IR spectroscopic methods for the characterization of the surface acidity, of the Lewis type and of the Bronsted type, of solid, simple and mixed oxides are briefly reviewed. The results are described and a systematization is proposed. The surface acidity is essentially associated with the ionicity/covalency of the element–oxygen bond, mainly affected by the size and charge of the cation.
416 citations
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TL;DR: In this article, the utilization of mechanical milling for the preparation of catalysts based on ceria structurally modified with zirconia is presented, and it is shown that room-temperature high-energy ball milling is an effective tool for the synthesis of nanophase CeO2−ZrO2solid solution in a wide composition range.
Abstract: The utilization of mechanical milling for the preparation of catalysts based on ceria structurally modified with zirconia is presented. It is shown that room-temperature high-energy ball milling is an effective tool for the synthesis of nanophase CeO2–ZrO2solid solution in a wide composition range. The use of combined X-ray diffraction analysis, Raman spectroscopy, and electron microscopy indicate that the milling process induces the formation of true solid solutions with a contraction of thecell parameter for cubic ceria following the introduction of Zr into the lattice. This, in turn, remarkably enhances the oxygen storage/transport and redox capacity compared to pure ceria and zirconia or to a simple mixture thereof. An unusual resistance to high-temperature cycling was also evidenced. These features were analyzed by the study of the reduction profile of dopedceria carried out by temperature-programmed reduction at different milling times. The oxygen storage capacity (OSC) of the catalysts was also evaluated;both the total and the kinetic accessible OSC indicated that the best composition is CexZr1−xO2withx > 0.5. This was correlated to the structural features and to the presence of a high concentration of ions with redox character (i.e., Ce4+ions) which favor oxygen mobility.
340 citations
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