Showing papers on "Cerium published in 2012"
TL;DR: In this paper, the effects of cerium precursors on the structure, surface state, reducibility and CO oxidation activity of mesoporous CuO-CeO2 catalysts were investigated.
Abstract: This work investigated the effects of cerium precursors [Ce(NO3)3 and (NH4)2Ce(NO3)6] on the structure, surface state, reducibility and CO oxidation activity of mesoporous CuO-CeO2 catalysts. The catalysts were characterized by TG–DTA, XRD, LRS, N2 adsorption–desorption, HRTEM, XPS, H2-TPR and in situ FT-IR. The obtained results suggested that the precursors exerted a great influence on the properties of CuO-CeO2 catalysts: (1) compared with the catalysts from Ce(III) precursor, the derived Ce(IV) precursor catalysts showed smaller grain size, higher BET surface area, narrower pore size distribution, whereas their reducibility and activities were not enhanced. (2) In contrast, the catalysts from Ce(III) precursor without excellent texture displayed high reducibility and activities for CO oxidation due to the high content of Ce3+, following the redox equilibrium of Cu2+ + Ce3+ ↔ Cu+ + Ce4+ shifting to right to form more stable Cu+ species, which was the origin of synergistic effect. The synergistic effect between copper and cerium was the predominant contributor to the improved catalytic activities of CuO-CeO2 catalysts, instead of structural properties.
327 citations
TL;DR: The research group has recently reported that silver nanoparticles (AgNPs) on a basic support of hydrotalcite (Ag/HT) catalyzed the chemoselective reductions of nitrostyrenes and epoxides to the corresponding anilines and alkenes when using alcohols or CO/H2O as a reducing reagent while retaining the reducible C=C bonds.
Abstract: The interaction of metals with ligands is the key factor in the design of catalysts and much effort has been devoted to the rational control of metal–ligand interactions in order to exploit catalytic properties. Quite sophisticated heterogeneous catalysts have been produced by controlling the size and shape of active metal species, and by screening and altering the composition of the supports. The supports can be considered as “macro ligands” for supported active metals, and the fine-tuning of the interactions between active metal species and supports is the most important factor through which high catalytic performance can be attained. Despite many intrinsic advantages of heterogeneous catalysts over homogeneous ones, such as their durability at high temperatures and reusability, the fine-tuning of metal–ligand interactions in heterogeneous catalysts is more difficult than in homogeneous catalysts, and remains a challenging objective. Our research group has recently reported that silver nanoparticles (AgNPs) on a basic support of hydrotalcite (Ag/HT) catalyzed the chemoselective reductions of nitrostyrenes and epoxides to the corresponding anilines and alkenes when using alcohols or CO/H2O as a reducing reagent while retaining the reducible C=C bonds. During the reductions, polar species of hydrides and protons were formed in situ at the interface of AgNPs/HT through a cooperative effect between the AgNPs and basic sites (BS) of HT, which were then exclusively active for the reduction of the polar functional groups (Figure 1). However, the use of H2 instead of alcohols or CO/H2O in our Ag catalyst system caused reductions of both the polar groups (nitro and epoxide) and the nonpolar C=C bonds. This nonselective reduction was due to the formation of nonpolar hydrogen species through the homolytic cleavage of H2 at the AgNPs surface, which is active for C=C bond reduction (Figure 2a).
249 citations
TL;DR: A series of Ce-incorporated SBA-15 mesoporous materials were synthesized through direct hydrothermal synthesis method and further impregnated with 12 wt.% Ni as mentioned in this paper.
248 citations
TL;DR: Evidence is obtained that cerium oxide nanoparticles (CeO(2) NPs) are able to scavenge nitric oxide radical in contrast to the superoxide scavenging properties which are correlated with an increased level of cerium in the 3+ state.
231 citations
TL;DR: In this paper, the authors employed ambient pressure X-ray photoelectron spectroscopy and electrochemical impedance spectrographs to quantify simultaneously the concentration of the reactive trivalent cerium ions on the surface and in the bulk of Sm-doped CeO2(100) in hundreds of millitorr of H2-H2O gas mixtures.
Abstract: Trivalent cerium ions in CeO2 are the key active species in a wide range of catalytic and electro-catalytic reactions. We employed ambient pressure X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy to quantify simultaneously the concentration of the reactive Ce3+ species on the surface and in the bulk of Sm-doped CeO2(100) in hundreds of millitorr of H2–H2O gas mixtures. Under relatively oxidizing conditions, when the bulk cerium is almost entirely in the 4+ oxidation state, the surface concentration of the reduced Ce3+ species can be over 180 times the bulk concentration. Furthermore, in stark contrast to the bulk, the surface’s 3+ oxidation state is also highly stable, with concentration almost independent of temperature and oxygen partial pressure. Our thermodynamic measurements reveal that the difference between the bulk and surface partial molar entropies plays a key role in this stabilization. The high concentration and stability of reactive surface Ce3+ over wide ranges of...
164 citations
TL;DR: In this article, the synthesis, characterization and catalytic behavior in the oxidative dehydrogenation of ethane of NiO−CeO2 mixed oxides were presented, which is the result of an increase in both catalytic activity and selectivity to ethylene.
136 citations
TL;DR: In this article, rare earth element cerium (Ce) with variable valence states Ce4/Ce3+ is doped in the TiO2 photoanode for dye-sensitized solar cells (DSSCs).
Abstract: Rare earth element cerium (Ce) with variable valence states Ce4+/Ce3+ is doped in the TiO2 photoanode for dye-sensitized solar cells (DSSCs). The anatase crystalline phase keeps unchanged, while the crystalline size decreases slightly after Ce doping. The Ce positively changes the conduction band minimum of TiO2 due to the unoccupied Ce-4f trap states in the band gap, and the Ce4+ is reduced to Ce3+ when electrons are injected in the photoanode. The cerium-doped photoanodes with special electrochemical properties severely influence the performance of DSSCs. Due to the increased electron injection, the small Ce content (0.05% and 0.1%) doped TiO2 photoanodes improve the performance of DSSCs which is optimized to 7.65% with Ce0.1% doping (1 sun, AM1.5) compared with the one with a pure TiO2 photoanode (7.2%). However, the Ce4+ states effectively trap electrons in the photoanode with further increase of Ce from 0.3 to 0.9%, which is confirmed by the charge extraction method and electrochemical impedance spec...
133 citations
TL;DR: In this article, the apparent turnover frequency (TOF) of the catalytic water oxidation by CAN with [IrIII(Cp*){4,4′-(OH)2-2,2′-bipyridine}(H2O)]2+, which acts as a precatalyst, gradually increased during the reaction to reach the highest value among the Ir complexes.
Abstract: Water oxidation by cerium(IV) ammonium nitrate, CAN, with [IrIII(Cp*)(4,4′-R2-2,2′-bipyridine)(H2O)]2+ (R = OH, OMe, Me or COOH) to evolve oxygen has been investigated together with the possible oxidation of the ligands by CAN. The apparent catalytic reactivity is highly dependent on the substituent R and the highest catalytic reactivity was obtained when R = OH. The apparent turnover frequency (TOF) of the catalyticwater oxidation by CAN with [IrIII(Cp*){4,4′-(OH)2-2,2′-bipyridine}(H2O)]2+, which acts as a precatalyst, gradually increased during the reaction to reach the highest value among the Ir complexes. In the second run, the apparent TOF value was the highest from the beginning of the reaction. 1H NMR and dynamic light scattering measurements for solutions after the first run indicated formation of insoluble nanoparticles, which exhibited a much higher catalytic reactivity as compared with iridium oxide prepared by a conventional method. The 4,4′-R2-2,2′-bipyridine ligand was also efficiently oxidized by CAN up to CO2 only when R = OH. TG/DTA and XPS measurements of nanoparticles produced after the water oxidation suggested that the nanoparticles were composed of iridium hydroxide with a small amount of carbonaceous residue. Thus, iridium hydroxide nanoparticles act as an excellent catalyst for the water oxidation by CAN.
130 citations
TL;DR: Cerium‐doped Titanium dioxide (TiO2) nanoparticles are prepared by sol‐gel method, making it efficient for visible light photocatalysis, and cerium doping decreases the effective band gap of TiO2 and increases the Urbach energy levels.
Abstract: Cerium-doped Titanium dioxide (TiO(2)) nanoparticles are prepared by sol-gel method. Doping shifts the UV absorption edge of TiO(2) to the visible region, making it efficient for visible light photocatalysis. Incorporation of cerium decreases the effective band gap of TiO(2) and increases the Urbach energy levels. At the dopant concentrations of 0.015 and 0.025 mol the luminescence intensity increases compared to undoped TiO(2); however, the luminescence is quenched at 0.035 mol. Quenching of luminescence indicates efficient separation of charge carriers. Undoped TiO(2) is showing poor performance in the photocatalytic degradation of methyl orange under visible light. However, on cerium doping its photoactivity is increased, and is drastically enhanced at 0.035 mol of cerium. Further increase in Ce(3+) doping level to 0.045 mol results in the reduction of the photodegradation of the dye. On UV irradiation, entire samples show good photocatalytic activity up to 30 min, but their efficiency decreases when irradiation time is increased to 45 min. Irradiation for longer time results in negative charging of the TiO(2) surface with migrating electrons. The negatively charged surface repels the OH(-) ion and O(2) molecule from adsorbing on its surface thus decreasing the availability of hydroxyl and superoxide radical for dye degradation.
125 citations
TL;DR: In this article, a hydrometallurgical process to recover rare earth and basemetals from spent NiMH batteries was described, where rare earths were recovered by selective precipitation with sodium hydroxide at pH less than 2 after leaching: in these conditions a precipitate composed of lanthanum and cerium sulphates are produced.
122 citations
TL;DR: In this paper, a new multifunctional mesoporous zeolite catalyst with cerium incorporated within the framework was reported, which showed a shift in selectivity from typical HZSM-5 products to valuable oxygenated chemicals (furans, ketones, aldehydes) during the catalytic fast pyrolysis of lignocellulosic biomass.
Abstract: We report the synthesis of a new multifunctional mesoporous zeolite catalyst with cerium incorporated within the framework. This catalyst shows a shift in selectivity from typical HZSM-5 products (benzene, toluene, and xylenes) to valuable oxygenated chemicals (furans, ketones, aldehydes) during the catalytic fast pyrolysis of lignocellulosic biomass. The cerium-incorporated hierarchical zeolite was synthesized using a dry-gel method followed by steam-assisted crystallization. The catalyst was characterized by X-ray diffraction (XRD), N2 physisorption, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), NH3 temperature-programmed desorption (NH3-TPD), diffuse reflectance FT-IR, and diffuse reflectance UV–Visible (UV–Vis) spectroscopy. The multifunctional catalyst was then studied in the catalytic fast pyrolysis of glucose (a carbohydrate model compound) at 600 °C. The new catalyst was compared with a mesoporous HZSM-5 catalyst with ...
TL;DR: A cost and time effective process was used to prepare the solid solutions BaCe x Zr (0.9− x ) Y 0.1 O (3− δ ) (0,≤ x ǫ ≥ 0.4) as mentioned in this paper.
TL;DR: A series of characterizations including TEM-EDS, XRD, FTIR, SO 2 ǫ+O 2 TPD, XPS, H 2 -TPR and NH 3 -TPD has been carried out to explore the mechanism of the promoting effect of Cu addition on the SO 2 -resistance of the Ce Ti oxide catalyst.
TL;DR: In this paper, high temperature thermal decomposition of ceria precursors including cerium acetylacetonate hydrate, cerium oleylamine, and cerium nitrate hexahydrate was used to yield near-spherical cerium oxide nanocrystals with diameters ranging from 3 to 10 nm.
Abstract: Nanocrystalline ceria is an interesting inorganic material for biological application that can exhibit antioxidant properties due to facile electron transfer between cerium(III) and cerium(IV). In this work, ceria nanocrystals with uniform and tunable size, surface chemistry, and variable cerium(III) content were formed via the high temperature thermal decomposition of ceria precursors including cerium acetylacetonate hydrate, cerium oleylamine, and cerium nitrate hexahydrate. When combined with organic acid and amine surfactants at temperatures between 260 and 320 °C, these cerium precursors decomposed to yield near-spherical cerium oxide nanocrystals with diameters ranging from 3 to 10 nm. For all shapes of nanocrystals, the smallest primary particle sizes had the most cerium(III) content. Both poly(acrylic acid)–octyl amine as well as oleic acid could be used to transfer the hydrophobic nanocrystals into water; acute in vitro toxicology studies revealed that even at high concentrations (e.g., 10 ppm) 3...
TL;DR: The results indicate that the toxicity of CeO2 NPs depend on the physical and chemical environment; and in a majority of the possible combinations of the nine parameters, non-lethal to the bacteria.
Abstract: Cerium oxide nanoparticles have found numerous applications in the biomedical industry due to their strong antioxidant properties. In the current study, we report the influence of nine different physical and chemical parameters: pH, aeration and, concentrations of MgSO4, CaCl2, KCl, natural organic matter, fructose, nanoparticles and Escherichia coli, on the antibacterial activity of dextran coated cerium oxide nanoparticles. A least-squares quadratic regression model was developed to understand the collective influence of the tested parameters on the anti-bacterial activity and subsequently a computer-based, interactive visualization tool was developed. The visualization allows us to elucidate the effect of each of the parameters in combination with other parameters, on the antibacterial activity of nanoparticles. The results indicate that the toxicity of CeO2 NPs depend on the physical and chemical environment; and in a majority of the possible combinations of the nine parameters, non-lethal to the bacteria. In fact, the cerium oxide nanoparticles can decrease the anti-bacterial activity exerted by magnesium and potassium salts.
TL;DR: In this article, structural and optical characterizations of doped and undoped ceria nanoparticles, synthesized using chemical precipitation, are carried out using transmission electron microscopy, X-ray diffractometry, optical absorption spectroscopy, and fluorescence spectrograms.
Abstract: The effect of lanthanides that have positive association energies with oxygen vacancies, such as samarium and neodymium, and the elements with negative association energies, such as holmium and erbium, on ionization state of cerium and, consequentially, the oxygen vacancy concentration in doped ceria nanoparticles are investigated in this article. Structural and optical characterizations of the doped and undoped ceria nanoparticles, synthesized using chemical precipitation, are carried out using transmission electron microscopy, X-ray diffractometry, optical absorption spectroscopy, and fluorescence spectroscopy. It is deduced that the negative association energy dopants decrease the conversion of Ce+4 into Ce+3 and, hence, scavenge the oxygen vacancies, evidenced by the observed increase in the allowed direct bandgap, decrease in the integrated fluorescence intensity, and increased the size of doped nanoparticles. The opposite trends are obtained when the positive association dopants are used. It is concluded that the determining factor as to whether a lanthanide dopant in ceria acts as a generator or scavenger of oxygen vacancies in ceria nanoparticles is the sign of the association energy between the element and the oxygen vacancies. The ability to tailor the ionization state of cerium and the oxygen vacancy concentration in ceria has applications in a broad range of fields, which include catalysis, biomedicine, electronics, and environmental sensing.
TL;DR: N nano-sizedManganese oxides are proposed as active catalysts for water oxidation in the reaction of some manganese complexes and cerium(IV) ammonium nitrate.
Abstract: According to UV-visible spectroscopy, X-ray diffraction spectrometry, dynamic light scattering, Fourier transform infrared spectroscopy, electron paramagnetic resonance spectroscopy, transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy, nano-sized manganese oxides are proposed as active catalysts for water oxidation in the reaction of some manganese complexes and cerium(IV) ammonium nitrate.
TL;DR: The nano-sized manganese oxide shows efficient catalytic activity toward water oxidation and the epoxidation of olefins in the presence of cerium(IV) ammonium nitrate and hydrogen peroxide, respectively.
Abstract: Nano-sized particles of manganese oxides have been prepared by a very simple and cheap process using a decomposing aqueous solution of manganese nitrate at 100 °C. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectrometry have been used to characterize the phase and the morphology of the manganese oxide. The nano-sized manganese oxide shows efficient catalytic activity toward water oxidation and the epoxidation of olefins in the presence of cerium(IV) ammonium nitrate and hydrogen peroxide, respectively.
TL;DR: CeO2 catalysts modified with earth alkaline metals (M = Mg, Ca, and Sr) were prepared by the citrate method in a M:Ce molar ratio of 1:1.
Abstract: CeO2 catalysts modified with earth alkaline metals (M = Mg, Ca, and Sr) were prepared by the citrate method in a M:Ce molar ratio of 1:1. Different analytical techniques including diffuse reflectance Ultraviolet–Visible (DR UV–vis) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and temperature programmed desorption of CO2 (TPD-CO2) were used for the characterization of the catalysts. The materials were tested in the oxidative coupling of methane (OCM). The results of calcined samples revealed that the charge transfer from cerium to oxygen ions is shifted when CeO2 is doped, indicating defects on the catalyst surface. A linear correlation was found between the amount of surface basic sites and the ratio of the oxygen species O2– and O22– to lattice oxygen. This behavior is crucial for the CH4 conversion and selectivity to C2H6 and C2H4 at 700 °C. Ca-doped CeO2 catalyst revealed the best performance in the OCM, which ...
TL;DR: In this article, the authors used 10.5 and 10.2% of Ni and 7.5% of Ce to produce 1,2-propanediol (1-2-PDO) as majority product.
Abstract: Metallic Ni (10 wt.%) supported on SBA-15 silica and promoted with cerium loading ranged between 2.5 and 10 wt.%, reduced at 723 K during 1 h, were used as catalysts in the hydrogenolysis of a glycerol aqueous solution (80 wt.%) at 473 K and 2.4 MPa of H 2 pressure. Whereas pure Ni catalyst mainly produces volatile products by C C hydrogenolysis reaction, the promoted cerium catalysts lead to the formation of 1,2-propanediol (1,2-PDO) as majority product. After 8 h of reaction the catalyst with 10 wt.% of Ni and 7.5 wt.% of Ce gives the maximum glycerol conversion and selectivity to 1,2-PDO, with yield of this substance of 24.2%/g of catalyst. The presence of cerium species is essential to produce 1,2-PDO. The effect of cerium oxide is to act as strong acid sites (TPD-NH 3 ), improve the metallic Ni dispersion (XRD, H 2 chemisorption and XPS) and to make more difficult their reduction (TPR). The stronger acidity suggests that the formation of acetol takes place easier in these catalysts and subsequently this intermediate is reduced by activated hydrogen from the nearby Ni metallic sites.
TL;DR: CeO2 nanocubes and truncated octahedra have been synthesized with different capping agents in the alkaline environment as mentioned in this paper, which may be due to the existence of more coordination of unsaturated cerium atoms and more active adsorption of dissociated oxygen species on the CeO2 surface.
Abstract: CeO2 nanocubes and CeO2 truncated octahedra have been synthesized with different capping agents in the alkaline environment. The CeO2 nanocubes present enhanced catalytic properties in CO catalytic oxidation, which may be due to the existence of more coordination of unsaturated cerium atoms and more active adsorption of dissociated oxygen species on the CeO2 (100) surface.
TL;DR: In this article, the authors developed a diagram showing the distribution as well as the relative amount of Ce(III)/Ce(IV) species in aqueous media as a function of the pH range.
TL;DR: In this article, the performance of manganese and cerium oxides synthesized by an exotemplating method was evaluated in the total oxidation of ethyl acetate, ethanol and toluene.
TL;DR: In this paper, the binary metal oxide, CuO CeO 2 /γ-Al 2 O 3, has been compared with the single oxide components CuO/γ-al 2 O3 and CeO2 /γ -Al 2O 3 for toluene total oxidation.
TL;DR: In this article, the corrosion protection of the AA2024 aluminum alloy in 0.01 M NaCl solutions of Ce(III and Ce(IV) ammonium nitrates was studied, and the inhibition efficiency was evaluated applying linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS).
TL;DR: In this article, different levels of cerium (Ce) doped-tin oxide (SnO2) nanomaterials are synthesized by a hydrothermal method in order to improve its sensor performance.
TL;DR: Cerium-doped MCM-41 (Ce-MCM41) was prepared by a hydrothermal method and its catalytic activity for ozonation of p-chlorobenzoic acid (p-CBA) in aqueous solution was studied as mentioned in this paper.
Abstract: Cerium-doped MCM-41 (Ce-MCM-41) was prepared by a hydrothermal method and its catalytic activity for ozonation of p-chlorobenzoic acid (p-CBA) in aqueous solution was studied. For comparison, cerium-loaded MCM-41 (Ce/MCM-41) was prepared by a dipping method. Ce-MCM-41 was characterized by the low and wide angle X-ray powder diffraction (XRD), nitrogen adsorption–desorption, transmission electron microscopy (TEM) and ultraviolet–visible diffuse reflection spectrum (UV–vis DRS). The results showed that the material retained the highly ordered mesopore structure of MCM-41 and had a surface area of 852 m2 g−1. Cerium was incorporated into the framework of MCM-41, locating at tetrahedrally coordinated sites. The cerium doping content, initial pH of aqueous solution and reaction temperature played important roles in catalytic ozonation of p-CBA. Under the chosen conditions (1.39 mg l−1 ozone dosage, 10 mg l−1 p-CBA solution and 1 g l−1 catalyst dosage), the high mineralization rate (86%) was achieved by Ce-MCM-41/O3 process at 60 min reaction time, only 52% by O3 alone. The combination of Ce-MCM-41 and O3 exhibited a significant synergetic effect. Ce-MCM-41 showed the better activity and stability than cerium-loaded MCM-41(Ce/MCM-41) during catalytic ozonation of p-CBA, its cerium leaching was greatly reduced (only 0.085 mg l−1) and below detection limit after being reused, compared with that of Ce/MCM-41 (0.44 mg l−1) with the presence of the same theoretical cerium content. TOC removal rate slightly decreased from 86% to 81% and kept stable after Ce-MCM-41 being re-utilized two times, which illustrated that Ce-MCM-41 was a kind of promising catalyst for ozonation of p-CBA. The addition of Ce-MCM-41 significantly improved ozone decomposition into HO in aqueous solution and reduced ozone concentration in equilibrium.
TL;DR: In this paper, the authors considered the thermochemical CO2 splitting via cerium-based mixed oxides and investigated the influence of the synthesis method, the Zr content in ZrxCe1−xO2, and the temperature of the CO2 reduction reaction.
TL;DR: In this paper, the authors showed that the Ce0.65Zr0.25RE0.1O2−δ (RE = Tb, Gd, Eu, Sm, Nd, Pr, and La) solid solutions were successfully prepared by the glycine-nitrate process and tested for CO oxidation activity.
Abstract: In this study, Ce0.65Zr0.25RE0.1O2−δ (RE = Tb, Gd, Eu, Sm, Nd, Pr, and La) solid solutions were successfully prepared by the glycine-nitrate process and tested for CO oxidation activity. The X-ray diffraction results confirmed the formation of complete Ce0.65Zr0.25RE0.1O2−δ solid solutions. The Raman spectroscopy measurements suggested the presence of oxygen vacancies due to defective structure formation and further evidenced the formation of solid solution. The high-resolution transmission electron microscopy observations showed the nanocrystalline nature of the solid solutions. From X-ray photoelectron spectroscopy analysis it was revealed that the cerium, terbium, and praseodymium are present in +3 and +4 oxidation states. The UV–vis diffuse reflectance spectroscopy indicated that the Pr3+ ions in the Ce0.65Zr0.25Pr0.1O2−δ system provoked a significant increase in the Ce3+ fraction on the surface. H2 temperature-programmed reduction measurements showed an enhanced surface reduction at much lower temper...