Cerium Incorporation Research Articles

Enhanced activity and stability of copper oxide/γ-alumina catalyst in catalytic wet-air oxidation: Critical roles of cerium incorporation

By successive impregnation method, the Ce-modified Cu-O/γ-Al2O3 catalyst was prepared and characterized using nitrogen adsorption-desorption, scanning electron microscopy energy dispersive X-ray analysis (SEM-EDS), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, and H2-Temperature programming reduction (H2-TPR). In catalytic wet-air oxidation (CWAO) process for the printing and dyeing wastewater (PDW), the effects of Ce addition on performance, mechanism and kinetics of the catalyst were investigated. The Ce addition increases the Brunauer-Emmett-Teller (BET) surface area and pore volume of the catalyst and makes the active components uniformly distributed on the catalyst surface. Formation of a stable CuAl2O4 solid solution by anchoring Cu onto the γ-Al2O3 crystal lattice leads to a significant decrease in metal leaching of the Ce-modified catalyst. The proportion of lattice oxygen in the catalyst substantially increases and the apparent activation energy of Cu-O/γ-Al2O3 catalyst decreases owing to Ce addition. Therefore, the catalytic activity and stability of the Ce-modified catalyst are considerably improved. The scavengers experiments identify the active species existed in the CWAO reaction system, with the order of reactivity: h+ > O2•− > H2O2 > HO•. This novel Cu-Ce-O/γ-Al2O3 catalyst has great potential in applications for treatment of concentrated organic wastewater due to its superior catalytic activity and improved stability.

Selective photodegradation of phenol in the presence of a commercial humic acid

Preferential oxidation of certain pollutants has been a major challenge in photocatalysis, since normal source water contains low concentrations of highly toxic substances along with high concentrations of natural organic matter. Pure TiO2 and doped with cerium (0.1 nominal at.%) by the sol–gel method under different conditions were synthesized. In one of the synthesis conditions, a nonionic surfactant was used as a pore-directing agent along with an acetic acid-based sol–gel route without addition of water molecules. The effect of the presence of a surfactant, the doping with cerium, the light absorption, the adsorption and the degradation of phenol and a commercial humic acid, as well as the structural properties of the synthesized materials, were investigated in this study.It can be demonstrated that by controlling the porous structure of TiO2, the access of large size natural organic matter to the TiO2 can be suppressed, thus improving the selective oxidation of small size target contaminants. Phenol as a target contaminant was successfully decomposed even in the presence of a commercial humic acid as competing natural organic matter. Under UV irradiation, highly porous catalysts prepared with polyoxyethylene (20) sorbitan monooleate surfactant exhibited a higher photocatalytic activity for the degradation of phenol in the presence of a commercial humic acid than the materials prepared without this surfactant. Under visible irradiation, the material prepared with the surfactant and doped with Ce presented the best performance, probably due to the red shift of the electronic absorption band induced by cerium incorporation to TiO2.

Micro- and mesoporous supports for CO2 methanation catalysts: A comparison between SBA-15, MCM-41 and USY zeolite

Mesoporous SBA-15 synthesized by two different methods and MCM-41 were used as supports for Ni and Ni-Ce catalysts applied in CO2 methanation reaction. The performances obtained for both materials were compared taking into account the differences in terms of textural properties, Ni species and reaction mechanism. Results were compared with the reported in the literature for a microporous USY zeolite. XRD, DRS UV–Vis, H2-TPR and TEM were used for the characterization of the samples. Catalytic tests were performed under the same conditions for all catalysts. Finally, FTIR Operando studies were carried out in order to establish differences from the mechanistically point of view as well as in terms of CO2 adsorption species for the different samples. Promising data was obtained with the Ni-based SBA-15 catalysts whatever the preparation method. Despite the greater Ni particles size, MCM-41 also reported interesting catalytic performances, so that presenting the highest TOF values among the catalysts studied. The good results obtained for the MCM-41 could be explained by the lower amount of non-reactive carbonyl species adsorbed on the Ni0 particles surface during the reaction as well as by the enhanced interaction between metal and support reflected in the calculated band gap values. All the results are comparable to the obtained using a HNaUSY zeolite with Si/Al=2.8as support. Cerium incorporation on Ni/mesoporous supports allowed enhancing the CO2 conversion, especially at lower temperatures, as already reported for the zeolite-based samples.

Soft Chemical Fabrication of Iron-Based Thin Film Electrocatalyst for Water Oxidation under Neutral pH and Structure-Activity Tuning by Cerium Incorporation.

Design of electrocatalysts for the fundamentally important oxygen evolution reaction can be greatly aided by systematic structure-activity tuning via composition variation. We have explored the iron-cerium system as they are the most abundant transition and rare earth metals, and also due to the mutualistic impact of their size and electronic attributes that can induce critical changes in the structure and electrochemical activity. Submicrometer thick films of a series of Fe(III)-Ce(III) phosphate(oxyhydroxide) (FeCePH) are fabricated using a soft chemical strategy involving surfactant-aided assembly, spin-coating, and mild thermal annealing. FT-IR, Raman, and X-ray photoelectron spectroscopies, chemical analysis, X-ray diffraction, and electron microscopy reveal the systematic structural, electronic, and morphological variation, on tuning the iron-cerium composition. Nitrogen adsorption-desorption studies show the surface area increasing and pore size distribution shrinking with the cerium content, indicating its structure-directing role. The electrocatalysis of water oxidation by FeCePH films on FTO-coated glass is studied in neutral pH conditions. The overpotential and Tafel slope decrease with increasing cerium content, reaching minima at the optimal Fe:Ce ratio of 1:0.5; the turnover frequency shows a corresponding increase and maximum. The trends are explained on the basis of the structural changes in the films, and the coupling of Ce3+/Ce4+ with Fe3+/Fe4+ that leads to active state regeneration. This study presents a rational strategy to tune the efficiency of easily fabricated transition metal-based electrocatalyst thin films through rare earth metal incorporation; it should prove useful in the design of cost-effective catalysts for water oxidation.

A strategy to increase phosphor brightness: Application with Ce3+-doped Gd3Sc2Al3O12

Y3Al5O12 (YAG) doped with Ce3+ ions is widely used as a phosphor for the generation of white light in LEDs. However, the material presents intrinsic drawbacks: (1) a yellow emission band lacking a red component, leading to a “cold” white light and (2) limited cerium incorporation (~ 3mol%), resulting in poor absorption and thus limiting the external quantum efficiency (EQE) of the LED device. In order to increase phosphor absorption and thus phosphor brightness, we propose here an original strategy based on the increase of Ce content in a phosphor compound, while preserving a high internal luminescence quantum yield. For this purpose, we introduce Ce3+-doped Gd3Sc2Al3O12 (GSAG: Ce). Gd3(1-x)Ce3xSc2Al3O12 polycrystalline samples were prepared through a solid-state microwave-assisted reaction, with x varying from 0 to 0.5; Ce3+ ions can be incorporated into the GSAG matrix with a concentration up to approximately x=0.18 (i.e. 18mol%) without the formation of a parasitic phase. The maximum emission wavelength is located at 573nm for a doping concentration of x=0.1, giving an orange feature to the emission. The internal luminescence quantum yield (Φ) is 52% for Ce concentration up to x=0.03. The EQE, which is proportional to the product of Φ by the Ce concentration when considering a thin transparent phosphor layer is predicted to be about 30% stronger when using GSAG doped with 10mol% Ce (x=0.1), with respect to YAG doped with 2mol% Ce (x=0.02).

Fluoride adsorption properties of cerium-containing bone char

This paper discusses the surface chemistry modification of bone char using cerium species and its role as fluoride adsorbent. Different doping routes for the cerium incorporation on bone char were assessed using two cerium precursors where the defluoridation performance of synthetized adsorbents was determined. Results showed that the bone char modified with Ce4+ showed better adsorption properties for fluoride removal than the adsorbent containing Ce3+. The best cerium-doped bone char showed up to 13.6mg/g for fluoride removal at pH 7 and 30°C, which was higher than those obtained for commercial bone chars and other adsorbents reported in the literature. This novel adsorbent may offer additional advantages for fluoride removal, including chemical stability to pH changes and potential antibacterial properties, than those obtained with metal-loaded adsorbents. Fluoride adsorption using this cerium-doped bone char was endothermic and could involve a physico-chemical mechanism based on electrostatic interactions and ion exchange with OH− groups from the adsorbent. In summary, this study provides new insights on the use and application of rare earth elements for the synthesis of adsorbents with enhanced properties for fluoride removal from water.

Catalytic performance of CeAPSO-34 molecular sieve with various cerium content for methanol conversion to olefin

A series of CeAPSO-34s with various cerium contents was synthesized and characterized by multiple techniques such as XRD, SEM, BET, 29Si MAS NMR, NH3-TPD and CO2-TPD. NH3-TPD spectra showed that a number of acid sites, especially those of strong acidity, is reduced with the increasing of Ce incorporation. Incorporation of metal ions gave rise to more silica-islands in the CeAPSO-34 framework. CO2-TPD showed that basic sites on the surface of modified samples are due to the presence of Ce-containing species incorporation into the framework of CeAPSO-34 molecular sieves. The performance of the catalysts was studied in methanol to olefin reactions at 425 °C under the atmospheric pressure. The results showed that the incorporation of cerium ions had great effects on the structure and acidity of the molecular sieves. All SAPO-34 and MeAPSO-34 molecular sieves were the very active and selective catalyst for light olefins production. Cerium incorporation improved the catalyst lifetime and favored the ethylene and propylene generation. However, an excess Ce content resulted in an inferior catalytic performance and stability. Therefore, there existed optimal cerium content for a specific SAPO-34.

Coral-like CeO2/NiO nanocomposites with efficient enzyme-mimetic activity for biosensing application

Development of nanomaterials-based enzymatic mimics has gained considerable attention in recent years, because of their low cost, high stability and efficiently catalytic ability. Here, CeO2 was successfully incorporated into the coral-like NiO nanostructures assembled by nanoflakes with high surface area, forming the coral-like CeO2/NiO nanocomposites. The morphology and composition of CeO2/NiO nanocomposites were characterized by XRD, SEM, element mapping and XPS. The results of characterization showed that cerium was highly dispersed in the coral-like NiO nanostructures. The peroxidase-like activity of CeO2/NiO nanocomposites was investigated, and they exhibited enhanced peroxidase-like activity in comparison to that of pure NiO or CeO2. The catalytic activity was dependent on the cerium content, and the optimal content was 2.5%. The enhanced catalytic activity of CeO2/NiO nanocomposites arised from their high ability of electron transfer because of cerium incorporation. The catalytic performance of CeO2/NiO nanocomposites was evaluated by steady-state kinetic, which showed that the CeO2/NiO nanocomposites exhibited higher affinity for the substrates and similar catalytic efficiency compared with natural peroxidase. Based on the efficient peroxidase-like activity, CeO2/NiO was used for H2O2 determination. The constructed colorimetric H2O2 sensor had fast response for only 5min, a wide linear range from 0.05 to 40mM and a low detection limit with 0.88μM. The CeO2/NiO nanocomposites were expected to have potential applications in clinical diagnosis and biotechnology as enzymatic mimics.

Effect of cerium incorporation on the structural and optical properties of CdS film

The effect of cerium incorporation on structural and optical properties of CdS film has been investigated. X-ray diffraction patterns of the CdS and CdS:10%Ce films showed the hexagonal wurtzite type polycrystalline structure and the planes (100), (002), (101), (100), (103), (112) are clearly indexed. The crystallinity of the CdS film deteriorated with cerium incorporation. Each Raman spectrum has three raman peaks around 112cm−1, 294cm−1 and 600cm−1. All the peaks were assigned to the Raman modes of CdS. Optical properties were obtained from absorption, transmittance and reflectance spectra of the films. CdS:10%Ce film is found relatively to be highly transparent in the visible and near infra-red regions compared to as-deposited CdS film. Urbach energy value of the CdS film increased with cerium incorporation.

Photodegradation of phenol using reconstructed Ce doped Zn/Al layered double hydroxides as photocatalysts

ZnAlCe layered double hydroxides (LDH) with different content of Ce (3.5, 5.0 and 10.0%mol) were successfully synthesized in one step by the co-precipitation technique. The partial incorporation of cerium into the layers of the material can be appreciated in the XRD diffraction patterns, showing some deformation in the crystallographic direction (110) of the ZnAlCe LDHs. In the samples calcined at 400°C, the UV–vis-DRS study showed a shift of the absorption edge toward the blue region of the spectra as a result of the cerium incorporation to the ZnAl LDH; the analysis of XPS confirms the co-existence of Ce4+ and Ce3+ in the ZnAlCe LDHs. The photodegradation and mineralization of phenol under UV irradiation was remarkably improved in the sample containing 5%mol of Ce. A mechanism where cerium in the layered material promotes the separation of the photogenerated electron–hole pairs is proposed. In this mechanism, Ce4+ acts as electron scavenger, facilitating the electron transfer toward adsorbed O2 and an accumulation of holes, increasing the generation of radicals OH.

Influence of Ce doping on structural and photoelectric properties of CuInS2 thin films

Cerium doped CuInS2 thin films were successfully fabricated by a powder metallurgy method. X-ray diffraction and scanning electron microscope measurements showed that the as-prepared CuIn1−xCexS2 samples are of good crystallinity and crystallize with chalcopyrite structure when sintering at 550 °C. The presence of Ce3+ in host material was conformed by X-ray photoelectron spectroscopy. Two subband photon absorption peaks were observed at 1710 nm (0.73 eV) and 1955 nm (0.63 eV) in the UV–Vis–NIR absorption spectrum. This behavior could suggest that an intermediate band forms in the forbidden band of CuInS2 semiconductor due to cerium incorporation. The optical bandgap of CuIn1−xCexS2 films was tuned in the range of 1.38 eV to 1.23 eV with increasing cerium content. And the electrical conductivity could be improved if doped moderate cerium content, especially x = 0.1.

Synthesis and characterization of Ce-incorporated CuInS2 chalcopyrites

CuInS2 thin films incorporating with cerium have been successfully fabricated by a powder metallurgy method. X-ray diffraction and scanning electron microscope measurements showed that the as-prepared CuIn1−xCexS2 samples crystallize with chalcopyrite structure at 250°C and the crystallinity and film compactness could be improved as annealing temperature rises. In the ultraviolet–visible–near infrared spectrum, two additional light absorption peaks were observed at 1690nm and 1930nm. The optical bandgaps of CuIn1−xCexS2 films decrease from 1.38eV to 1.34eV with increasing cerium content. These observed optical behaviors could suggest that an intermediate band forms in the forbidden band of CuInS2 semiconductor due to cerium incorporation. The position of intermediate band locates at 0.64eV below conduction-band bottom. This kind of rare-earth doped materials enhances long-wavelength absorption, which could be helpful for high-efficiency solar cells.

Effects of cerium incorporation on the catalytic oxidation of benzene over flame-made perovskite La1−xCexMnO3 catalysts

Perovskite-type La1−xCexMnO3 (x=0–10%) catalysts were prepared by flame spray pyrolysis and their activities during the catalytic oxidation of benzene were examined over the temperature range of 100–450°C. The structural properties and reducibility of these materials were also characterized by X-ray diffraction (XRD), N2 adsorption/desorption, H2 temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The incorporation of Ce was found to improve the benzene oxidation activity, and the perovskite in which x was 0.1 exhibited the highest activity. Phase composition and surface elemental analyses indicated that non-stoichiometric compounds were present. The incorporation of Ce had a negligible effect on the specific surface area of the perovskites and hence this factor has little impact on the catalytic activity. Introduction of Ce4+ resulted in modification of the chemical states of both B-site ions and oxygen species and facilitated the reducibility of the perovskite. The surface Mn4+/Mn3+ ratio was increased as a result of Ce4+ substitution, while a decrease in the surface-adsorbed O/lattice O (Oads/Olatt) ratio was observed. The relationship between the surface elemental ratios and catalytic activity was established to allow a better understanding of the process by which benzene is oxidized over perovskites.

Investigation of biodiesel production by HUSY and Ce/HUSY zeolites: Influence of structural and acidity parameters

In this work, activities of HUSY and Ce/HUSY zeolites were studied in transesterification cycles of soybean oil and ethanol to produce biodiesel. The characterization of the materials was performed by FT-IR, XRD, BET method and pyridine adsorption followed by thermal analyses. TG/DTG results indicated a decrease of acid sites for both samples after each reaction cycle. However, Ce/HUSY zeolite showed a superior stabilization of acidic sites after three catalytic cycles and intermediary activation procedures. Biodiesel production exhibited high conversion levels (>96%) for both zeolites in all transesterification cycles. Surface area and pore volume measurements evidenced that cerium incorporation reduced the number of acid sites by interacting with OH groups in the micropore and external area of the zeolitic surface. This interaction resulted in an acid and structural stability, which provided a better activity (99%) than HUSY (96%). The higher conversion values obtained by zeolites showed a final product with a different distribution when compared with the traditional transesterification process. The identification of free fatty acids, diethyl and glycerol ethers in the final products and the reduction of unsaturated compounds indicated that parallel reactions also occurred in the studied systems. Nonetheless, the biofuel produced showed high ester content and did not present changes in its calorific power.

Effects of Cerium and Aluminum in Cerium-Containing Hierarchical HZSM-5 Catalysts for Biomass Upgrading

We report the synthesis of multifunctional, hierarchical, cerium-containing HZSM-5 catalysts with various aluminum and cerium contents using a dry-gel, dual templating method. The catalysts were characterized by X-ray diffraction, N2 physisorption, scanning electron microscopy, diffuse reflectance UV–Visible spectroscopy, diffuse reflectance Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy, NH3 temperature programmed desorption and X-ray photoelectron spectroscopy. At low theoretical Si:Al ratios (15 and 20), the formation of amorphous silica–alumina materials was observed. However, at higher theoretical Si:Al ratios (30, 40, and 50), crystalline materials were formed. Furthermore, with Si:Al ratios of 50, cerium incorporation as high as 2.2 wt% was obtained using this procedure. To understand the role of aluminum and cerium in the catalyst, the crystalline materials were studied in the catalytic fast pyrolysis of glucose at 600 °C. The catalysts with cerium incorporated showed an increase in the production of oxygenated chemicals as well as CO, compared with their non-cerium containing analogs.

First-principles study of the electronic structure and optical properties of Ce-doped ZnO

Density functional theory calculations by using both generalized gradient approximation (GGA) method and the GGA with considering strong correlation effect (GGA+U) were performed to elucidate the effect of Ce-4f orbit on the electronic structure of ZnO. It is found that after the cerium incorporation, a new localized band appears between the valence and conduction bands, which corresponds to the majority spin of Ce-4f states. It is this localized band that constructs a bridge between the valence and conduction states, which will improve the optical performance of ZnO. ZnO:Ce is a degenerate semiconductor. The strong correlation effect is very important for the 4f orbit of the Ce atom in ZnO:Ce. The mismatch of the majority and minority spin for the Ce-4f, Ce-5d states and the spin-polarized holes in O-2p states induced by Ce doping leads to the presence of the magnetic order for ZnO:Ce. We also studied the band structure and optical properties of ZnO:Ce with lacking one electron and two electrons, respectively. With the deficiency of the electrons, the Fermi level moves downward. The magnetism disappears when the system lacks two electrons. The analysis of optical properties shows that ZnO:Ce is a promising dielectric material and has potential applications in optoelectric devices.

Characterization and synthesis of Ce-incorporated mesoporous molecular sieves under microwave irradiation condition

Ce-incorporated MCM-41 mesoporous molecular sieves (CeMCM-41) were synthesized by microwave irradiation method from sodium silicate and ammonium cerium (IV) nitrate precursors and using cetyltrimethyl ammonium bromide (CTAB) as template. The resulting samples were characterized by means of XRD, TEM, FT-IR, UV-Vis, XPS and N2 physical adsorption, respectively. The effect of the Si/Ce molar ratio on the textural properties of CeMCM-41 was investigated. The results reveal that the CeMCM-41 was successfully synthesized. The resultant mesoporous materials have specific surface areas in the range of 602–1,216 m2/g and pore sizes in the range of ca. 2.6–2.9 nm. The structural properties are related to the amount of cerium incorporation. The surface area and pore volume of the resulting CeMCM-41 were gradually reduced as the cerium content in the sample increased, and the mesoporous ordering diminished.

Oxidation of benzene over bimetallic Cu–Ce incorporated rice husk silica catalysts

Oxidation of benzene to phenol with 30% H 2O 2 in liquid-phase was carried out over a series of Cu–Ce incorporated rice husk silica catalysts using acetonitrile as solvent at 343 K under atmospheric pressure. Cu and Ce incorporated rice husk silica catalysts were prepared by the sol–gel technique using cetyltrimethyl ammoniumbromide as the template. These catalysts were labeled as RHA–10Cu5Ce, RHA–10Cu20Ce, and RHA–10Cu50Ce. TG/DTG analysis of the catalysts confirmed complete removal of the template at 773 K and all catalysts were X-ray amorphous even after 50 wt% cerium incorporation. The rate for benzene oxidation increased linearly with cerium incorporation and depended directly on H 2O 2 decomposition. The high activity and phenol selectivity observed under mild reaction conditions (343 K, atmospheric pressure) could be correlated to the enhanced textural properties such as the BET surface area (403–279 m 2 g −1) and large pore volume (0.90–0.54 m 3 g −1) of the catalysts. Conversion during catalytic performance followed the order RHA–10Cu50Ce > RHA–10Cu20Ce > RHA–10Cu5Ce while phenol selectivity followed the order RHA–10Cu20Ce > RHA–10Cu5Ce > RHA–10Cu50Ce. A redox mechanism between Cu 2+/Cu + and Ce 4+/Ce 3+ active centers on the silica surface was responsible for the high catalytic activity of 84% with 96% phenol selectivity given by RHA–10Cu20Ce.

Effect of the Si/Ce molar ratio on the textural properties of rare earth element cerium incorporated mesoporous molecular sieves obtained room temperature

Rare earth Ce-incorporated MCM-41 mesoporous molecular sieves (CeMCM-41) were synthesized via a direct and nonhydrothermal method at room temperature from sodium silicate and ammonium cerium (IV) nitrate as raw materials. Cetyltrimethyl ammonium bromide (CTAB) was used as a template. The resultant samples were characterized by means of powder X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance ultraviolet–visible spectroscopy (UV–vis) and N 2 physical adsorption, respectively. The effect of the Si/Ce molar ratio on the crystalline structure and textural properties of CeMCM-41 was also investigated. The experimental results show that ordered CeMCM-41 mesoporous molecular sieves were successfully synthesized at room temperature and the resultant mesoporous materials have specific surface areas in the range of 594–1369 m 2/g and average pore sizes in the range of ca. 2.5–2.8 nm. It has been found that the structural properties are strongly related to the amounts of cerium incorporation. When the cerium content increased in the samples, the intensity of the peak (1 0 0) was gradually reduced, and the surface area and structural regularity were diminished.

CO oxidation on Au nanoparticles supported on wormhole HMS material: Effect of support modification with CeO2

This paper describes the performance of Au catalysts supported on wormhole hexagonal mesoporous silica (HMS) for the CO oxidation reaction, and the effect of support modification with cerium on the catalysts for this reaction. Supports and catalysts were characterized by N2 adsorption–desorption, XRD, HRTEM, DRS UV–vis, TPR and XPS. The HMS material was prepared by the surfactant neutral S0I0 templating route, and its modification with cerium was performed by direct synthesis (Ce-HMS) and impregnation (Ce/HMS) methods. Gold was deposited via the deposition–precipitation method. After calcination at 573K for 3h, the Au nanoparticles with sizes in the range 3.8–4.9nm were formed. The smallest Au particles were formed on the Ce/HMS support with small crystals of CeO2 phase on its surface, as shown by XRD. In general, Ce-containing Au catalysts were found to be more active in CO oxidation than the Ce-free Au/HMS counterpart, with the direct synthesis method of the cerium incorporation being less effective than the impregnation method. The highest activity of the Au/Ce-HMS catalyst in CO oxidation was associated with its higher gold dispersion and larger degree of coverage of HMS by CeO2, thereby increasing the effectiveness of oxygen mobility.