Series Of Ce1 Research Articles

Enhancement mechanism of Y-doped Ce1−xYxO2 for photocatalytic-assisted chemical-mechanical polishing

Photocatalytic-assisted chemical-mechanical polishing (PCMP) is an ultra-precision machining method which combines photocatalytic technology with chemical-mechanical polishing (CMP) technology. CeO2 has unique physicochemical properties (tribological properties and photochemical oxidation activity) and is applied to industrial fields extensively. In this paper, a series of Ce1−xYxO2 nanoparticles with controlled size and shape were produced by the molten salt method. SEM images show that Ce1−xYxO2 nanoparticles are nearly spherical with a size of about 113–148 nm. Ion doping can adjust the defect concentration and further enhance the chemical activity of samples. XPS spectra show that doping is beneficial to improve the concentration of Ce3+ and oxygen vacancy. In this way, the photocatalytic activity of CeO2 nanoparticles can be improved. Quartz glasses were polished by synthetic Ce1−xYxO2 nanoparticle polishing solution, where x is the doping amount. The results show that the material removal rate (MRR) of Ce0.95Y0.05O2 abrasives in PCMP was increased by 34.5%. The PCMP mechanism of CeO2 nanoparticles is further discussed. Ultraviolet irradiation increased the reactive sites on the surface of Ce1−xYxO2 nanoparticles, making them have better chemical activity. The hydration layer and Ce-O-Si bond on the surface of quartz glass are formed more easily, thus improving the material removal rate.

Ce1−xSnxO2 Catalysts Prepared with Combustion Method for Catalytic Combustion of Ethyl Acetate

A series of Ce1−XSnXO2 (X = 0, 0.2, 0.3, 0.4, 0.5, 0.9, 1) catalysts were synthesized via the combustion method. The physical and chemical structures of the prepared catalysts were systematically characterized by XRD, BET, SEM, TEM, XPS, and TPR. The Ce1−XSnXO2 catalysts have higher catalytic activities than the mono-oxide catalysts, as there are synergistic effects between CeO2 and SnO2. The catalytic activities of the Ce1−XSnXO2 catalysts are dependent on the X for the catalytic combustion of ethyl acetate (EA). The Ce1−XSnXO2 (X < 0.5) catalysts show high catalytic performances. Meanwhile, the Ce0.8Sn0.2O2 and Ce0.7Sn0.3O2 catalysts display the highest catalytic performance, with T50 = 190 °C and T90 = 210 °C. More importantly, the Ce0.8Sn0.2O2 catalyst exhibits superior thermal and catalytic activity stability. It is found that the Ce1−XSnXO2 catalysts form solid solutions, as the X is <0.5. The reduction of Sn4+ species to Sn2+ is significantly promoted by the CeO2, which is an important factor attributed to the high catalytic activities of the solid solution Ce1−XSnXO2 catalysts. The catalytic activities of the Ce1−XSnXO2 catalysts exhibit a strong correlation to the surface atomic areas of Ce3+ and Oα (VO). In other words, the higher surface atomic areas of Ce3+ and Oα (VO) are, the higher the catalytic activities will have.

The influence of partial substitution of Ce with K in CeMO3 (M = Mn, Fe, Co, Ni, Cu) perovskite catalysts on soot combustion performance

A series of Ce1−xKxMO3 (M = Mn, Fe, Co, Ni, Cu, and x = 0, 0.1, 0.2, 0.3, 0.4) perovskite catalysts were synthesized by citrate sol-gel method, in which A-site element Ce was partially substituted with K. The results showed that the catalytic performance could be significantly improved by partially substituting of Ce with K in CeCoO3 catalyst for soot combustion. Ce0.8K0.2CoO3 perovskite catalyst exhibited a superior catalytic activity, and its corresponding T10, T50, T90 and SmCO2 were 326, 383, 426 °C and 98.6%, respectively. The characterization results indicated that K+ had been successfully incorporated in the perovskite crystal structure. Partially substituting of Ce with K resulted in an increase in specific surface area. It also resulted in the formation of Co4+ in the perovskite catalysts together with abundant presence of oxygen vacancies on the surface. Moreover, it was of great significance to facilitate the activation of lattice oxygen species. In situ DRIFTS result showed that NO2 produced by thermal decomposition of monodentate nitrate species played a key role in soot combustion process.

Ce1−xFexVO4 with Improved Activity for Catalytic Reduction of NO with NH3

A series of Ce1−xFexVO4 (x = 0, 0.25, 0.50, 0.75, 1) catalysts prepared by modified hydrothermal synthesis were used for selective catalytic reduction (SCR) of NOx with NH3. Among them, Ce0.5Fe0.5VO4 showed the highest catalytic activity. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction using H2 (H2-TPR), and temperature-programmed desorption of NH3 (NH3-TPD). The results indicated the formation of Ce-Fe-V-O solid solutions. The average oxidation states (AOS) of Ce, Fe, V, and O atoms changed obviously with the incorporation of Fe3+ into CeVO4, and the acidity of Ce0.5Fe0.5VO4 differs from that of CeVO4 and FeVO4. The presence of more acid sites and a sharp increase in active oxygen species in Ce0.5Fe0.5VO4 effectively improved the selective catalytic reduction (SCR) activity.

Selective Aerobic Oxidation of Vanillyl Alcohol to Vanillin Catalysed by Nanostructured Ce-Zr-O Solid Solutions

A series of Ce1 − x–ZrxO2 − δ (x = 0.2, 0.5, and 0.8) mixed oxides were prepared by coprecipitation method and explored for selective oxidation of vanillyl alcohol employing O2 and acetonitrile as the oxidant and solvent, respectively under base-free conditions. To ascertain the key factors responsible for vanillyl alcohol oxidation, the physicochemical properties of the synthesized catalysts were investigated by various characterization techniques namely, XRD, BET surface area, Raman, XPS, and H2-TPR. It was observed from this exercise that the catalytic activity dependents on the Ce:Zr mole ratio, which is related to the degree of reducibility of the catalyst. Interestingly, the catalytic activity is enhanced with the increase of Ce content in the Ce–Zr mixed oxide. Among the investigated catalysts, the Ce0.8Zr0.2O2 combination exhibited a high catalytic activity with ~ 98% conversion and ~ 99% selectivity to vanillin. Smaller crystallite size, large BET surface area, more number of oxygen vacancies, improved redox properties, and strong synergetic interaction are found to be the key factors to promote the oxidation ability of Ce0.8Zr0.2O2 catalysts towards vanillyl alcohol oxidation. Further, the influence of reaction parameters such as time, solvent, temperature, and oxygen pressure were also studied to optimize the catalytic process for vanillyl alcohol oxidation. As revealed by these studies, the high activity of Ce0.8Zr0.2O2 catalyst could be retained up to five cycles without appreciable loss in the activity and selectivity. Nanosized Ce0.8Zr0.2O2 catalyst exhibited an excellent catalytic activity and superior selectivity to vanillin in the liquid phase oxidation of vanillyl alcohol under ecofriendly conditions

Novel synthesis and photocatalytic performance of Ce1 − xZrxO2/silica fiber

A series of Ce1−xZrxO2/silica fiber composites were successfully synthesized via a carbon nanofiber (CNF) template-assisted alcohol-thermal procedure. The resulting samples were characterized by X-Ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet-visible (UV–vis) diffuse reflectance spectroscopy, Brunauer-Emmett-Teller (BET) apparatus, and Raman spectroscopy. Furthermore, their photocatalytic activities were evaluated by UV-light photocatalytic degradation of methylene blue (MB) solution. The results show that the photocatalytic degradation of MB was fairly effective for the as-prepared Ce1−xZrxO2/silica fiber samples. Particularly, with zirconium (Zr) doping, Ce0.75Zr0.25O2/silica fiber composites clearly exhibit enhanced photocatalytic efficiencies, compared with CeO2/silica fiber samples. The incorporation of Zr into the CeO2 lattice not only causes a decrease in particle size but also brings about an increase in BET specific area and UV absorption ability, which should be responsible for the enhanced photocatalytic performance.

Steam Reforming of Bio-Ethanol to Produce Hydrogen over Co/CeO2 Catalysts Derived from Ce1−xCoxO2−y Precursors

A series of Ce1−xCoxO2−y precursors were prepared by homogeneous precipitation using urea as a precipitant. The Co/CeO2 catalysts obtained from the Ce1−xCoxO2−y precursors were used for the steam reforming of ethanol to produce hydrogen. Co ions could enter the CeO2 lattices to form Ce1−xCoxO2−y mixed oxides at x ≤ 0.2 using the homogeneous precipitation (hp) method. CeO2 was an excellent support for Co metal in the steam reforming of ethanol because a strong interaction between support and metal (SISM) exists in the Co/CeO2 catalysts. Because Co/CeO2 (hp) prepared by homogeneous precipitation possessed a high BET surface area and small Co metal particles, Co/CeO2 (hp) showed a higher ethanol conversion than the Co/CeO2 catalysts prepared using the co-precipitation (cp) method and the impregnation (im) method. The selectivity of CO2 over Co/CeO2 (hp) increased with increasing reaction temperature at from 573 to 673 K, and decreased with increasing reaction temperature above 673 K due to the increase of CO formation. The carbonaceous deposits formed on the catalyst surface during the reaction caused a slow deactivation in the steam reforming of ethanol over Co/CeO2 (hp). The catalytic activity of the used catalysts could be regenerated by an oxidation-reduction treatment, calcined in air at 723 K and then reduced by H2 at 673 K.

Superior catalytic performance of non-stoichiometric solid solution Ce1 − xCuxO2 − δ supported copper catalysts used for CO preferential oxidation

A series of Ce1−xCuxO2−δ non-stoichiometric solid solutions and their supported copper catalysts CuO/Ce1−xCuxO2−δ (x=0, 0.005, 0.022, 0.043) were prepared by co-precipitation and deposition–precipitation, respectively. The CuO/Ce1−xCuxO2−δ catalysts show high performance for CO preferential oxidation (CO PROX). Multiple techniques of N2 sorption (BET), XRD, Laser Raman spectroscopy (LRS), HRTEM, H2-TPR, O2-TPO, N2O chemisorption and in-situ DRIFTS were used for catalyst characterization. The results of XRD, LRS and H2-TPR conformably indicate that a small amount of Cu2+ ions can be incorporated into the lattice of CeO2, forming non-stoichiometric solid solutions Ce1−xCuxO2−δ, which shows much better reducibility than pure CeO2. The supported CuO/Ce1−xCuxO2−δ catalysts exhibit remarkably enhanced activity for CO PROX as compared with CuO/CeO2, especially the catalyst CuO/Ce0.978Cu0.022O2−δ containing 15% Cu, which displays the best CO PROX performance, showing not only the lowest temperature (115°C) for CO total conversion, but also the 100% selectivity of O2 to CO2 at this temperature. Several aspects including the presence of more oxygen vacancies, the improved reducibility, and stronger capability for CO chemisorption of this catalyst account well for its superior performance for CO PROX. Based upon the in-situ DRIFTS study, it is revealed that Cu+ is the main active site for CO oxidation, while Cu0 is more active for H2 activation and oxidation.

Perovskite-Based Lean-Burn NO x Trap Catalysts Without Using Platinum Group Metals: K/LaCoO3/Ce1−x Zr x O2

A series of Ce1−x Zr x O2 (x = 0, 0.1, 0.2, 0.3) solid solution supported lean-burn NO x trap (LNT) catalysts K/LaCoO3/Ce1−x Zr x O2 were prepared by successive impregnation. After sulfation the supported perovsikte LaCoO3 was well maintained; reducing treatment partly destroyed the perovsikte, but it can be well recovered by re-oxidation treatment. Based on NO x storage and sulfur-resisting performance of the catalysts, the optimal atomic ratio of Zr in Ce1−x Zr x O2 support is x = 0.2. The catalyst K/LaCoO3/Ce0.8Zr0.2O2 exhibits much better NO x storage capacity than the Pt-based catalyst Pt/K/Ce0.8Zr0.2O2, which is highly related to its stronger capability for NO to NO2 oxidation. During NO x storage much larger amounts of nitrate and nitrite species were identified by in situ DRIFTS over perovskite-based catalysts than over Pt-based one. The H2-TPR results reveal that after deep sulfation little sulfur species were deposited on the catalyst K/LaCoO3/Ce1−x Zr x O2, showing strong sulfur-resisting ability. As a result, it is thought that the full replacement of Pt by perovskite LaCoO3 in the corresponding LNT catalysts is feasible.

Preparation of Ce1−x Fe x O2 solid solution and its catalytic performance for oxidation of CH4 and CO

A series of Ce1−x Fe x O2 (0 < x ≤ 0.5) catalysts were prepared by the co-precipitation method, and their catalytic performances were investigated for the total oxidation of CO and CH4 as model reactions. X-ray diffraction (XRD) and Raman spectroscopy results show that Ce1−x Fe x O2−δ solid solutions are formed with x ≤ 0.2. Ce0.9Fe0.1O2 solid solution presents superior catalytic performance for CH4 and CO oxidation, while Ce1−x Fe x O2 with x > 0.2 shows less active for CO and CH4 oxidation. The results of H2-temperature programmed reduction (H2-TPR), CH4-temperature programmed surface reaction (CH4-TPSR) and CO-TPSR reveal that, the surface oxygen of catalyst is relevant to CO oxidation, which was promoted by the oxygen vacancies formed in Ce–Fe–O solid solution, while the easier lattice oxygen migration property and the favorable reducibility of the catalysts is responsible for the promoted catalytic performance for CH4 oxidation.

Nanostructured Cu-Doped Ceria Obtained by Reverse Microemulsion Method as Catalysts for Incineration of Selected VOCs

A series of Ce1−x Cu x O2 (0 ≤ x ≤ 0.1) nanostructured oxide systems was prepared using a modified reverse microemulsion method. The thermal decomposition of the carbonate and hydroxide precursors into oxides systems was studied using thermal analysis methods (EGA-TGA/DTG/SDTA). The morphology and the structure of the samples were characterized by XRD and BET analysis as well as visualized by scanning electron microscopy (SEM). The morphology of the obtained nanoparticles depended on a kind of the precursors used. The copper substituted CeO2 materials formed mono phase solid solutions, which were catalytically active in the incineration of various VOC molecules (ethylene, methanol, acetone). The correlation between activity of the studied catalysts and copper content has been found.

Synthesis and Characterization of Ce1−xEuxO2−x/2 Mixed Oxides and Their Catalytic Activities for CO Oxidation

A series of Ce1−xEuxO2−x/2 mixed oxides was synthesized by coprecipitation. The solids were characterized by means of XRF, SBET, XRD, UV−vis, and Raman techniques, and their catalytic activities toward CO oxidation were tested. A solid solution, with CeO2 F-type structure, is formed for europium contents (measured as Eu2O3 by XRF) ≤20% wt. For higher contents, the solid solution is not formed, but a physical mixture is detected. The existence of oxygen vacancies in the solids with Eu2O3 contents between 3 and 17% wt was demonstrated by the presence of bands at 532 and 1275 cm−1 in their Raman spectra. The catalytic performances of the solids correlate with the amount of these punctual defects in the solid solution.

Synthesis and room-temperature ferromagnetism ofCeO2 nanocrystalswith nonmagnetic Ca2+ doping

This work initiates an investigation on the creation of room-temperatureferromagnetism in diamagnetic solid via a nonmagnetic doping.CeO2 is taken as a prototype compound. A series ofCe1−xCaxO2−δ solidsolutions with x = 0–0.25 were prepared by a solution combustion method using L-glutamic acid as the fuel. Samplecharacterization indicates that all as-prepared samples crystallized in a pure face-centeredcubic fluorite structure with crystallite sizes smaller than 10 nm. On increasing the dopantcontent, the crystallite size decreased from about 8 to 4 nm, while the lattice parameterincreased systematically. At room temperature, all samples are ferromagnetic admixed withan apparent diamagnetic component, as composed to a mixture of paramagnetic andantiferromagnetic behaviors or the absence of the ferromagnetism reported inthe literature (Bouaine et al 2007 J. Phys. Chem. C 111 2924–8; Ney et al 2008Phys. Rev. Lett. 100 157201) for magnetically doped semiconductors such asSn1−xCoxO2 and Zn1−xCoxO. The coercivity and saturation magnetization forx = 0 are110 Oe and 2.01 × 10−4 emu g−1, respectively, which slightly increased to 148 Oe and2.26 × 10−4 emu g−1 on increasing thedopant content to x = 0.10. Upon annealing the as-prepared samples at800 °C for 2 h,these magnetic parameters were weakened. This observation was interpreted in terms of the mixed valencestate of Ce3+/Ce4+ and the doping effects. Finally, the nature of the room-temperature ferromagnetism isdiscussed by taking into account the oxygen vacancies and defects at the surface/interfacesthat act as the electron and hole traps.

Au/Ce1−xZrxO2 as effective catalysts for low-temperature CO oxidation

The physico-chemical properties and activity of Ce-Zr mixed oxides, CeO2 and ZrO2 in CO oxidation have been studied considering both their usefulness as supports for Au nanoparticles and their contribution to the reaction. A series of Ce1−xZrxO2 (x=0, 0.25, 0.5, 0.75, 1) oxides has been prepared by sol–gel like method and tested in CO oxidation. Highly uniform, nanosized, Ce-Zr solid solutions were obtained. The activity of mixed oxides in CO oxidation was found to be dependent on Ce/Zr molar ratio and related to their reducibility and/or oxygen mobility. CeO2 and Ce0.75Zr0.25O2, characterized by the cubic crystalline phase show the highest activity in CO oxidation. It suggests that the presence of a cubic crystalline phase in Ce-Zr solid solution improves its catalytic activity in CO oxidation. The relation between the physico-chemical properties of the supports and the catalytic performance of Au/Ce1−xZrxO2 catalysts in CO oxidation reaction has been investigated. Gold was deposited by the direct anionic exchange (DAE) method. The role of the support in the creation of catalytic performance of supported Au nanoparticles in CO oxidation was significant. A direct correlation between activity and catalysts reducibility was observed. Ceria, which is susceptible to the reduction at the lowest temperature, in the presence of highly dispersed Au nanoparticles, appears to be responsible for the activity of the studied catalysts. CeO2-ZrO2 mixed oxides are promising supports for Au nanoparticles in CO oxidation whose activity is found to be dependent on Ce/Zr molar ratio.