Addition Of CeO2 Research Articles

Microstructure and Corrosion Behavior of Laser-Cladding CeO2-Doped Ni-Based Composite Coatings on TC4

Laser-cladding CeO2-doped Ni-based composite coatings were prepared on the surface of a titanium alloy, and the effects of CeO2 addition on the microstructure, microhardness, and corrosion resistance of the prepared coatings were studied. The results showed that TiC, NiTi, Ni3Ti, and Ti2Ni phases were formed on the prepared coatings. Moreover, the addition of CeO2 in laser-cladding coatings effectively refined the microstructure and reduced the number of cracks generated in the laser-cladding process. When the amount of CeO2 was 2%, the number of cracks in the laser-cladding coating was significantly reduced compared with that of 0%. When the content of CeO2 was 2% or 3%, the microhardness of laser-cladding coatings reached the maximum value. At the same time, it was found that the appropriate addition of CeO2 was helpful to improve the corrosion resistance of the laser-cladding coating. However, excessive CeO2 addition could reduce the corrosion resistance of the laser-cladding coating.

Structural Characteristic and Dielectric Properties of Zirconia Toughened Alumina

Zirconia toughened alumina (ZTA) has shown a great effect in the cutting tool application due to its high hardness and comparable fracture toughness. However, the capability of the materials to be applied in as the dielectric resonator antenna (DRA) is not being discussed in detail. In this study, an attempt is made to further explore the potential of ZTA to be applied in DRA. Various related characterization techniques were applied that is subjected to DRA properties. The addition of CeO2 (0 wt.% to 15 wt.%) on ZTA has been pressed into pellets shape and sintered at 1600 °C for 2 hours under pressureless conditions. Based on the XRD analysis, only corundum and yttria doped zirconia phases were present. Shift in position of the zirconia peaks was observed due to an existence of Ce2Zr3O10 phase. For the DRA measurement, ZTA with 10 wt.% CeO2 addition have resonated at 6.76 GHz which is suitable for X-band applications. Meanwhile the radiation pattern indicated the omnidirectional characteristic, which suggested that the signal could be received by this dielectric antenna in various positions. Therefore, ZTA- 10 wt.% CeO2 have high potential to be used as DRA that operates X-band frequency range applications.

Dielectric constant, dielectric loss and thermal conductivity of Si3N4 ceramics by hot pressing with CeO2–MgO as sintering aid

Dense silicon nitride ceramic was sintered by hot pressing at 1800 °C for 3 h under the uniaxial pressure of 40 MPa in N2 atmosphere using CeO2–MgO as sintering aid. In this study, the effect of the addition of CeO2–MgO on the sintering of silicon nitride ceramics was investigated. The equiaxed α-Si3N4 was transformed into a rod-shaped β-Si3N4 completely by using XRD and SEM analysis. The sample reached a maximum density of 98.2% and a high flexural strength (872 ± 65 MPa). The range of dielectric constant is 10.79–11.06 (12.4 GHz), and the dielectric loss is in the order of 10 E−3. The highest thermal conductivity achieved in all samples is 45.5 W/mK.

Ketonization of xylose over CeO2 to produce mono-functional ketones

Ketonization of biomass-derived oxygenates provides an efficient way for bio-oil upgrading. However, little information on the ketonization of oxygen-rich sugars has been reported, leaving the deep deoxygenation of biomass an unsolved challenge. To address the problem, this paper investigated the catalytic pyrolysis of xylose over nano-CeO2 using an analytical pyrolyzer. Results showed that upon the addition of CeO2, multi-functional oxygenated compounds from xylose pyrolysis were majorly reformed to mono-functional ketonic products, resulting in a 5-fold increase in peak area of ketones. Among them, acetone and 2-butanone presented the highest selectivity of 51% with the CeO2 to xylose ratio of 10:1 at the temperature of 600 °C. Meanwhile, the short-chain oxygenates, i.e. C2-C3 aldehydes and alcohols, had been converted into C3-C5 ketones, indicating an outstanding ability of chain-increasing over CeO2. Both the catalyst dosage and the pyrolysis temperature play a vital role during the ketonization process. The reaction mechanism was proposed according to the experimental results, in which three major reaction pathways were analyzed. This study demonstrates that ketonization of biomass-derived sugars is a promising method for oxygen removal and carbon chain increase, thus improving the bio-oil quality.

Effect of CeO2 on sintering behavior, crystallization, and properties of CaO-Al2O3-SiO2 glass–ceramics for packages

The effect of CeO2 on the sintering behavior, crystallization, and properties of CaO-Al2O3-SiO2 glass–ceramics was investigated. The result revealed that a small addition of CeO2 promotes the phase transformation from quartz to cristobalite. Moreover, the CeO2 dopant reduces the sintering activation energy and thus improves the densification of CAS system. Also, the activation energy of crystallization is decreased and the crystallinity is elevated due to the modification of CeO2. Thus, in the case of 1 wt% CeO2 doping, the flexural strength and Young’s modulus of CAS glass–ceramics are, respectively, enhanced to 205 MPa and 78 GPa, accompanied by the increase in coefficient of thermal expansion from 10.0 × 10–6/°C to 12.4 × 10–6/°C.

Effect of nano cerium oxide additive with tire oil blends on diesel engine combustion and emissions parameters with soot morphology analysis

ABSTRACT This article focused to analyze the effect of cerium oxide (CeO2) as an additive to distilled tire oil blends (DTO30) in diesel engine operation. The nano cerium oxide (morphology: spherical with a size of 20 nm) was added with proportions of 50 mg/L and 100 mg/L to the distilled tire oil blend. Addition of this CeO2 to tire oil blends tend to reduce emission, soot suspension time along with improved engine performance. The extraction of tire oil was carried out by thermal pyrolysis and distilled with a fractional distillation column apparatus. The diesel engine was tested and the results were analyzed based on performance, combustion and emission with soot morphology analysis using transmittance electron microscope (TEM). The results with CeO2 operations show that the brake thermal efficiency was increased up to 14% with 100 mg/L and brake specific fuel consumption was reduced significantly compared with DTO30 without CeO2. The cylinder pressure and heat release rate were reduced by shortening the ignition delay. Also the NOx, CO, and UHC were reduced between 15% and 22% with CeO2 additives compared to normal operations. Also, the reduction of soot particle has found up to 20% while using additives. In TEM morphology, the size of soot particulates was increased because its intensity to bind around the cerium oxide, the size was increased up to 200 nm to 300 nm than normal size.

Influence of CeO2 content on WC morphology and mechanical properties of WC/Ni matrix composites coating prepared by laser in-situ synthesis method

Improving the mechanical properties of metal matrix composites (MMCs) by the addition of a ceramic phase is one of the present studying hot spots. Understanding the morphology evolution rule of the ceramic phase during laser cladding is a critical issue to its wider industrial applications. In the present paper, different CeO2 contents with WC reinforced Ni matrix composite coatings were prepared by laser in-situ synthesis technology. The influence of CeO2 content on the WC morphology and the attendant mechanical properties was investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy disperse X-ray (EDX) spectroscopy, hardmeter and frictional tester. The result shows that the shape of WC particles has a close relation to the addition of rare earth oxide CeO2. Specifically, at first, with the increasing CeO2 additions, the aspect ratio of WC particles reaches the minimum value when 2 wt. % CeO2 is added. Then, the aspect ratio increases with further increasing CeO2 additions. In addition, the effect of CeO2 on macroscopic morphology of laser cladding coating and the mechanism of CeO2 on the morphology evolution of WC particle were investigated. Finally, microhardness and wear results show that the coating with 2 wt. % CeO2 has the best mechanical properties.

Catalysts for Methane Steam Reforming Reaction: Evaluation of CeO2 Addition to Alumina-Based Washcoat Slurry Formulation

The effect of the addition of CeO2 to alumina-based washcoat slurry formulation on the methane steam reforming (MSR) reaction was investigated. Five Al2O3-CeO2-based washcoat slurries, differing from each other in the Al2O3/CeO2 ratio (nominal ratio equal to ∞, 0.042, 0.087, 0.250, 0.667) were prepared, dried and calcined; the resulting powders were loaded with nickel as an active metal and the obtained catalysts were tested in MSR reaction. Five cylindrical silicon carbide (SiC) monoliths were washcoated with the prepared slurries and their mechanical resistance was evaluated through the ultrasound adherence test. The activity tests results highlighted the best performance in terms of methane conversion and hydrogen selectivity of the powder catalyst, with the Al2O3/CeO2 percentage nominal ratio equal to 0.042. A structured catalyst was finally prepared by loading a SiC monolith with the most active catalytic formulation and tested in MSR reaction. The performance of the structured catalyst was evaluated in terms of methane conversion and its stability was verified in a time-on-stream test, which allowed for the evaluation of the carbon formation rate; furthermore, its activity was characterized by the estimation of the kinetic parameters. The results highlighted the beneficial effect of ceria addition on the catalytic activity; moreover, compared with data of the literature, the calculated carbon formation rate demonstrated a good resistance of the catalyst to coke formation.

Effect of cerium oxide on preparation of high-density sintered magnesia from crystal magnesite

Sintered MgO was prepared by using MgO powder with different particle sizes by calcination of by crystal magnesite as the raw material and CeO2 powder as an additive. In addition, the effect of the CeO2 addition on the performance of the sintered MgO was investigated. The results showed that (i) the densification of the sintered MgO with a small amount of CeO2 addition appreciably promoted, (ii) the maximum bulk density reached 3.48gcm−3, and (iii) the apparent porosity was 0.35%. In the sintering process, the Ca2+ could approach into CeO2 lattices, forming O2− vacancy at CeO2 grains, which resulted in promoting the growth of CeO2 grains filling the pores between the MgO grains, and enhanced the densification of sintered MgO. In addition, the solid solution reaction limited the formation of silicate phase in MgO, improving the bonding degree between the MgO grains.

CeO2‐CrOy/γ‐Al2O3 redox catalyst for the oxidative dehydrogenation of propane to propylene

AbstractCeO2‐CrOy loaded on γ‐Al2O3 was investigated in this work for the oxidative dehydrogenation (ODH) of propane under oxygen‐free conditions. The ODH experiments of propane were conducted in a fluidized bed at 500°C‐600°C under 0.1 Mpa. The prepared catalyst was characterized by N2 adsorption‐desorption measurements, H2‐temperature‐programmed reduction, O2‐temperature‐programmed desorption, NH3‐temperature‐programmed desorption, x‐ray photoelectron spectroscopy, and x‐ray diffraction. The change in the selectivity of propylene resulted from the thermal cracking of the propane and the competition for lattice oxygen in the catalyst between propylene formation and propane and propylene combustion. Therefore, to achieve higher propylene yield in the industry, the reaction temperature should be 550°C‐575°C for the 17.5Cr‐2Ce/Al catalyst. The results of H2‐TPR (from 0.2218 mmol/g‐0.3208 mmol/g) revealed that the addition of CeO2 can enhance the oxygen capacity of CrOy. Compared with that for 17.5Cr/Al, the conversion can be enhanced from 22.4% to 28.5% and the selectivity of propylene can be improved from 72.2% to 75.9% for the 17.5Cr‐2Ce/Al catalyst. In addition, CeO2 can inhibit the evolution of lattice oxygen (O2−) to electrophilic oxygen species (O2−), causing the average COx (CO and CO2) selectivity to decrease from 9.64% to 6.31%.

Study of the use of a Pd–Pt-based catalyst for the catalytic combustion of storage tank VOCs

Catalytic combustion is a very cost-effective way to eliminate volatile organic compounds (VOCs). The components of the VOCs in storage tanks are complex, with alkanes, alkenes and aromatic hydrocarbons being the main components. The aromatic hydrocarbons are the most difficult organic compounds among the storage tank VOCs in terms of catalysing combustion, and they are easy to cause catalyst carbon deposition. In this work, the Pt/γ-Al2O3, Pd/γ-Al2O3, Pd–Pt/γ-Al2O3, Pd–Pt/CeO2/γ-Al2O3 and Pd–Pt/CeO2/γ-Al2O3–N catalysts were prepared using an incipient wetness impregnation method. The performances of the catalysts were investigated using toluene and a simulation of VOCs in gas in a storage tank as model reactants. The study found that Pt has a higher catalytic combustion activity than Pd for the alkanes in the VOC gas in the simulation storage tank, and Pd has a higher catalytic combustion activity than Pt for the alkenes and toluene in the VOC gas in the simulation storage tank. The Pt addition enhances the activity of Pd-based catalysts for VOC catalytic combustion, and the Pd–Pt active component has good active stability. The catalyst prepared by using Pd–Pt alone has a defect in that it exhibits an insufficient oxygen supply performance in the catalytic combustion process. The addition of CeO2 improves the oxygen supply performance of the Pd–Pt-based catalyst. In addition, the activity of the Pd–Pt/CeO2/γ-Al2O3–N catalyst prepared by reducing the validated amount of Pd–Pt is higher than that of a commercial catalyst.

Comparison of structural, physical and optical properties of Na2O-B2O3 and Li2O-B2O3 glasses to find an advantageous host for CeO2 based optical and photonic applications

This study focuses on alkali oxide (lithium and sodium) glasses with an aim to explore suitable host for cerium ions which will enhance the optical properties like UV blocking efficiency. Conventional melt quench method was employed for making these glasses. FTIR results show conversion of BO3 to BO4 units and development of CeO4 groups with addition of CeO2. The increase in density values (2.10 to 2.67 g/cm3 for sodium glasses and 2.04 to 2.75 g/cm3 for Lithium glasses) and decrease in band gap values (3.16 to 2.40 eV for sodium glasses and 3.28 to 2.08 eV for Lithium glasses) in both glass systems confirm the modifier role of CeO2. Hardness of lithium-based glasses (1366.91 Kg/mm2) at 4 mol% of CeO2 is higher than the glasses containing sodium (1007.21 Kg/mm2). The obtained values of refractive index and transmittance show better suitability of CeO2 incorporated lithium glasses in some optical applications.

Photocatalytic properties of the CeO2‐xTiO2 and TiO2‐xCeO2 (x = 10, 30, and 50 mol%) heterostructures obtained by a MAH

AbstractIn this work, CeO2‐TiO2 heterostructures were submitted to the microwave‐assisted hydrothermal (MAH) method at 140°C for 30 minute, and varying the CeO2 and TiO2 percentages as 10, 30, and 50 mol%. The heterostructures were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer‐Emmett‐Teller methodology (BET), and UV‐Vis diffuse reflectance spectroscopy (UV‐Vis). The photocatalytic properties were estimated varying the concentration of methylene blue (MB) dye. The diffractograms indicate the formation of TiO2 anatase and CeO2 phases, without the formation of secondary phases. TEM images indicate the formation of nanocubes and nanospheres for CeO2 and TiO2, respectively. BET analysis indicates that CeO2 has the largest surface area (62.80 m2.g−1), and TiO2‐10%CeO2 heterostructure has a low surface area (26.13 m2.g−1). The addition of TiO2 to CeO2 increases the photocatalytic activity from 32% to 80% for CeO2 and CeO2‐50%TiO2, respectively. In contrast, the addition of CeO2 significantly decreases the photocatalytic activity of TiO2 from 98.9% to 50% for TiO2 and TiO2‐50%CeO2, respectively. Reuse tests showed that the TiO2‐xCeO2 samples maintain the photocatalytic response in subsequent cycles while the CeO2‐xTiO2 samples have an increase in the response.

Adsorption Kinetics for CO2 Capture using Cerium Oxide Impregnated on Activated Carbon

Various metal oxides of CeO2, ZnO, and Co3O4 impregnated on activated carbon (AC) were synthesized to determine the CO2 capture efficiency and analyse with adsorption kinetics model. Batch kinetic studies showed that CeO2/AC is the most efficient adsorbent with an equilibrium time of 10 minutes that was needed to obtain adsorption capacity of 52.68 mg/g. CO2 adsorption at 30 °C exhibits the optimum temperature with only 6.53% loss in adsorption capacity after 5 cycles of CO2 adsorption-desorption. The CeO2 on AC was detected through X-ray diffraction and the scanning electron microscope image shows well-distributed CeO2 particles on AC surfaces. CO2 adsorption at 30 °C is best fitted with the pseudo-second-order kinetics with R2 = 0.9994 and the relative error between calculated and experimental adsorption capacity only 1.32%. The adsorption considering chemisorption is responsible for improving adsorption capacity. The addition of CeO2 on AC enhanced the adsorption capacity by providing active sites to attract CO2.

One-pot synthesis of CeO2/Mg-Al layered double oxide nanosheets for efficient visible-light induced photo-reduction of Cr(VI)

CeO2-modified Mg-Al layered double oxide (CeO2/Mg-Al LDO) nanosheets were prepared via a one-pot hydrothermal route for visible-light induced photocatalytic reduction of Cr(VI). The addition of CeO2 can enhance the visible light harvesting capacity and the separation of charge carriers of CeO2/Mg-Al composites due to the surface-defect structures of Ce(III)/Ce(IV) couple and oxygen vacancies. The photocatalytic activity of CeO2/Mg-Al is affected by CeO2 content, Cr(VI) concentration, co-existing inorganic ions, and initial pH value. Among these obtained composites, CeO2/Mg-Al-2 with a nominal Mg/Al molar ratio of 2:1 and CeO2 content of 6.0 wt% presents the best photocatalytic efficiency and stability. The removal efficiency of Cr(VI) in the CeO2/Mg-Al-2-assisted photocatalytic system is varied from 96.76% to 92.87% after five cycle times. The quenching behaviors of active species and the possible photocatalytic mechanism of CeO2/Mg-Al-2 were proposed for the conversion of Cr(VI) into Cr(III) in the visible light region.

Catalytic performance of Pd catalyst supported on Zr:Ce modified mesoporous silica for methane oxidation

Catalytic oxidation of methane is critical for exhaust after-treatment systems where cold-start emissions and lean combustion still pose serious challenges. In this work, the effect of support materials on the complete catalytic oxidation of methane over palladium is studied in dry and wet conditions. A series of metal oxides (CeO2, ZrO2, n-SiO2) and mixed metal oxides (Zr0.65Ce0.35O2, Zr0.33Ce0.33/n-Si0.33O2, Zr0.66Ce0.17/n-Si0.17O2) supported Pd catalysts were synthesized, characterized and tested for methane oxidation. Pd/n-SiO2 was found to be highly active catalyst with the lowest initial (T10%) and final (T100%) conversion temperatures as compared to Pd supported on CeO2 and ZrO2. Methane combustion over mixed oxide supports, prepared with different ratios of Zr:Ce:Si, showed improved catalytic performance. Catalyst with equal ratios of Zr:Ce:Si (Pd/Zr0.33Ce0.33/n-Si0.33O2) showed similar performance to that of Pd/n-SiO2 with approximately ~8 (±2) °C higher light-off temperature. Additionally, cyclic wet (8 vol% H2O) and dry reactions were performed to evaluate the hydrothermal stability and activity regeneration when switching from wet to dry conditions. Optimal addition of ZrO2 and CeO2 to n-SiO2 resulted in higher stability of palladium catalyst over wide ranges of temperatures (350–600 °C). Catalysts were characterized by various analytical techniques, including TEM, XRD, XRF, N2-BET, O2-TPD, and CO chemisorption. TEM results demonstrate that mixed oxide support stabilized Pd nanoparticles, and n-SiO2 encapsulation prevented sintering and deactivation. Activity tests and characterization results demonstrate overall superior catalytic properties of Pd supported on Zr0.33Ce0.33/n-Si0.33O2. This catalyst can be quite promising for practical applications due to its high activity for total methane oxidation and excellent thermal stability.

Electrodeposition of Novel Nano-Composite Coatings of Niw Containing SiC and CeO2 with Outstanding Tribological Properties and Corrosion Performance

A special electrodeposition process utilizing a well-designed reversed pulse (RP) current waveform and specially formulated bath chemistry were used to produce nanostructured composite coating of nickel-tungsten (NiW) containing silicon carbide (SiC) and cerium oxide (CeO2). In this bath formulation, a specific type of propargyl derivative compound was used as a grain refiner due to its acetylene-type of bonding (i.e. -C≡C-H) at the end of its alkyl chain. This typical bond had a tendency to be adsorbed at high current density locations on the substrate being plated resulting in better control of nickel ion diffusion towards the cathode. Therefore, a uniform and defect-free deposit with mirror-finish surface was obtained. As well, this compound increased the nucleation sites for initiating of metal deposition on the surface of substrate resulting in the decrease in grain size of nickel. The resulting material demonstrated outstanding corrosion and tribological performances. It was found that the addition of SiC and CeO2 improved the corrosion performance of NiW. It was also found that the composite of NiW-SiC obtained by RP waveform, performed better in corrosion resistance compared to the same coatings deposited by DC waveform. The electrochemical corrosion tests including potentiodynamic polarization (PP) and cyclic potentiodynamic polarization (CPP) tests were used to evaluate the corrosion behaviors of the deposits. Following the PP tests, Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was used to investigate the various corrosion products on deposits. As well, tribological properties including hardness, and wear resistance of the deposits were investigated

Study on the effect of CeO2 for fabricating in-situ TiB2/A356 composites with improved mechanical properties

In this paper, in-situ 5 wt% TiB2/A356 composites were fabricated via a salts-metal exothermic reaction process. The effects of CeO2 on the microstructures and mechanical properties of the composites at both as-cast and T6 conditions were investigated. The results showed that the addition of CeO2 could significantly improve the dispersion of TiB2 particles, refine the α-Al grains and modify the coarse lamellar eutectic Si into fine fibrous and granular structures. The optimum addition level for dispersion, refinement and modification was 0.5 wt% CeO2. The values of YS, UTS and El pct of the composite with 0.5% CeO2 in T6 condition were 259 MPa, 307 MPa and 6.4%, which were 14.1%, 8.7% and 39.1% higher than those of the composite without CeO2. The YS enhancement of composite with 0.5 wt% CeO2 was mainly due to the improvement in dispersion of TiB2 particles in the matrix. The improved elongation of composite with 0.5 wt% CeO2 was mainly attributed to the improvement in dispersion of TiB2 particles, the grain refinement, and the modification of eutectic Si phase.

Detailed experimental investigation of the NOx reaction pathways of three-way catalysts with focus on intermediate reactions of NH3 and N2O

In this work possible reaction pathways of NOx were investigated for a three-way catalyst on a synthetic gas test bench with a focus on intermediately produced NH3 and N2O. NH3 formation during a typical lean-to-rich transient was verified. Further experiments were carried out in Ar atmosphere allowing to directly determine the N2 selectivity. It could be shown that the catalyst's oxygen storage capacity (OSC), which is implemented by addition of CeO2 to the washcoat material, plays a significant role and that NO can fill the oxygen storage in the absence of O2. Further, no nitrogen species were found to be stored. Also, intermediately produced NH3 was oxidized by stored oxygen with a high selectivity to N2. As soon as the OSC was fully exhausted, NH3 dissociated, leading to the formation of N2 and H2. The presence of side products and secondary emissions strongly depends on the actual operating conditions.

Development of phosphate glass and multi-phase titanate ceramic compositions for thermal treatment of irradiated nuclear fuel residues

The highly heterogeneous nature of UK legacy damaged and degraded spent nuclear fuels and so called, ‘orphan fuels’, prohibits the use of standard conditioning methods. An inventory of UK residual fuels yielded an account for three main fuel types: Magnox, AGR (advanced gas-cooled reactor) and MOx (mixed oxides). A series of glass and ceramic type host systems have been investigated for potential conditioning of these high uranium content spent fuel materials. Electron microscopy and powder X-ray diffraction techniques were used to characterise the prototypical wasteforms. Two sets of low-melt temperature phosphate glass compositions were trialled with additions of CeO2 to simulate the fluorite structure and large ionic radius of U in oxide fuels. Evolution of monazite-type phases at simulant oxide fuel loadings above 15 wt.% highlighted a potential development into a glass-ceramic hybrid assemblage. Investigation into the use of an alkoxide nitrate synthesis route for SYNROC-F type ceramic precursors has allowed for the demonstration of a sintered host pyrochlore phase containing up to ∼40 wt.% fuel simulant CeO2. Gas evolution has led to increased porosity at higher temperatures and longer sintering times, this may be mitigated by higher pre-calcination temperatures.