Addition Of Ceria Research Articles

Influence of Ce addition and Pt loading upon the catalytic properties of modified mesoporous PtTi-SBA-15 in total oxidation reactions

A series of PtCeTi-SBA-15 catalysts, with different concentrations of Pt (0.25 %, 0.5 %, 1.0 %), were synthesized. New Ti-SBA-15 material was obtained by direct synthesis and used as support in successive immobilization of Pt and Ce precursors, changing their order of addition. The characterization of the catalysts has been achieved taking an ensemble of techniques which showed preservation of the support porous structure, high dispersion of the amorphous metal oxides and Pt°, the formation of metal crystals for samples with 1wt% Pt and variation of Pt° content on surface in condition of ceria addition. The best conversion (100 %) was obtained in oxidation of hydrocarbons (CH4, C3H8 and C6H14) for the samples with 1% Pt and a significant diminish of activity was obtained for catalyst in which Ce was added on PtTi-SBA-15 sample. Differently of these, CO oxidation was totally irrespective of the catalyst composition.

Oxidation of Dichloromethane over Au, Pt, and Pt-Au Containing Catalysts Supported on γ-Al2O3 and CeO2-Al2O3.

Au, Pt, and Pt-Au catalysts supported on Al2O3 and CeO2-Al2O3 were studied in the oxidation of dichloromethane (DCM, CH2Cl2). High DCM oxidation activities and HCl selectivities were seen with all the catalysts. With the addition of Au, remarkably lower light-off temperatures were observed as they were reduced by 70 and 85 degrees with the Al2O3-supported and by 35 and 40 degrees with the CeO2-Al2O3-supported catalysts. Excellent HCl selectivities close to 100% were achieved with the Au/Al2O3 and Pt-Au/Al2O3 catalysts. The addition of ceria on alumina decreased the total acidity of these catalysts, resulting in lower performance. The 100-h stability test showed that the Pt-Au/Al2O3 catalyst was active and durable, but the selectivity towards the total oxidation products needs improvement. The results suggest that, with the Au-containing Al2O3-supported catalysts, DCM decomposition mainly occurs via direct DCM hydrolysis into formaldehyde and HCl followed by the oxidation of formaldehyde into CO and CO2.

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.

Hydrophobicity and wear resistance of ceria/PTFE composite coatings

For the purposes of investigating the effects of ceria content on the anti-icing, hydrophobicity, and antiwear performances of ceria/polytetrafluoroethylene (PTFE) composite coatings, ceria/PTFE composite coatings with ceria mass fractions of 0%, 1%, 3%, 5%, and 7% were prepared via one-step spraying method. The water contact angles (WCAs) on the composite coatings were measured via contact angle measuring device. The antiwear performance was characterized via ball-on-disk sliding tribo-tests. Experimental results show that the addition of ceria with a content of 5 wt% is the most effective to enhance hydrophobicity of the coatings, resulting from the coating surface structure, roughness, and intrinsic hydrophobicity of ceria. Moreover, the addition of ceria is helpful to the improvement of antiwear performances of PTFE composite coatings, when the content of ceria is 1–7 wt%. Ceria/PTFE composite coatings with a ceria content of 5 wt% show a wear rate of 0.388 × 10−4 mm3/Nm, which is 80.6% lower than that of PTFE coating without ceria (2.000 × 10−4 mm3/Nm).

Revealing the Li2O2 Nucleation Mechanisms on CeO2 Catalysts for Lithium‐Oxygen Batteries

AbstractThe addition of ceria (CeO2) nanoparticles to the cathode of a lithium‐oxygen battery results in increased capacity, lower overpotentials and better cyclability. To shed light on the mechanisms of this performance enhancement, we have investigated the early stages of Li2O2 nucleation at stoichiometric and reduced ceria surfaces by means of atomistic simulations based on density functional theory. Adsorption energies are stronger on ceria than on graphene, that is, nucleation mainly would take place on the oxide. The adsorption process of O2 is the one that determines the nucleation sites for the Li2O2 formation on the different CeO2 surfaces. The LiO2 intermediate is adsorbed at the O2 reduction sites. On the reduced (100) surface, the LiO2 tends to adsorb dissociatively, opening up the possibility to the formation of other species than the desired end‐product, Li2O2. On the contrary, optimal properties are found for the reduced (110) surface, which should therefore be the most active surface for Li2O2 nucleation among all low‐index surfaces of ceria. These findings could pave the route to produce better cathodes for Li‐oxygen batteries by the addition of carefully designed ceria nanoparticles, which maximizes the exposition of the most favorable facet.

Comparative Study of Strategies for Enhancing the Performance of Co3O4/Al2O3 Catalysts for Lean Methane Combustion

Spinel-type cobalt oxide is a highly active catalyst for oxidation reactions owing to its remarkable redox properties, although it generally exhibits poor mechanical, textural and structural properties. Supporting this material on a porous alumina can significantly improve these characteristics. However, the strong cobalt–alumina interaction leads to the formation of inactive cobalt aluminate, which limits the activity of the resulting catalysts. In this work, three different strategies for enhancing the performance of alumina-supported catalysts are examined: (i) surface protection of the alumina with magnesia prior to the deposition of the cobalt precursor, with the objective of minimizing the cobalt–alumina interaction; (ii) coprecipitation of cobalt along with nickel, with the aim of improving the redox properties of the deposited cobalt and (iii) surface protection of alumina with ceria, to provide both a barrier effect, minimizing the cobalt–alumina interaction, and a redox promoting effect on the deposited cobalt. Among the examined strategies, the addition of ceria (20 wt % Ce) prior to the deposition of cobalt resulted in being highly efficient. This sample was characterized by a notable abundance of both Co3+ and oxygen lattice species, derived from the partial inhibition of cobalt aluminate formation and the insertion of Ce4+ cations into the spinel lattice.

Mechanical Properties and Chemical Durability of Nafion/Sulfonated Graphene Oxide/Cerium Oxide Composite Membranes for Fuel-Cell Applications.

To improve both the mechanical and chemical durability of Nafion membranes for polymer electrolyte membrane fuel-cells (PEMFCs), Nafion composite membranes containing sulfonated graphene oxide (SGO) and cerium oxide (CeO2; ceria) were prepared by solution casting. The structure and chemical composition of SGO were investigated by FT-IR and XPS. The effect of the sulfonation, addition of SGO and ceria on the mechanical properties, proton conductivity, and chemical stability were evaluated. The addition of SGO gave rise to an increase in the number of sulfonic acid groups in Nafion, resulting in a higher tensile strength and proton conductivity compared to that of graphene oxide (GO). Although the addition of ceria was found to decrease the tensile strength and proton conductivity, Nafion/SGO/ceria composite membranes exhibited a higher tensile strength and proton conductivity than recast Nafion. Measurement of the weight loss and SEM observations of the composite membranes after immersing in Fenton’s reagent indicate an excellent radical scavenging ability of ceria under radical degradation conditions.

ZnO/CeO2 nanocomposite with low photocatalytic activity as efficient UV filters

In this study, we successfully synthesized ZnO/CeO2 composite nanoparticles for efficient ultraviolet (UV) filtering applications using a simple precipitation route. Various ratios of Ce/Ti, 2.5 at.%, 5 at.%, and 10 at.% were used to precipitate ceria onto commercial ZnO nanopowder at pH 9. The calculated mean crystallite sizes of the resultant nanocomposites were ~ 90 nm, ~ 79 nm, and ~ 41 nm for the 2.5 at.%, 5 at.% and 10 at.% ceria amounts, respectively. A stronger and more selective absorbance within the UV range was observed due to precipitation of a small amount of ceria to decorate the commercial ZnO surface. The photocatalyst results show that the addition of ceria, particularly with the precipitation amount increased up to 10 at.%, can effectively reduce crystal violet degradation by about 97% in a period of time from 0 to 30 min when exposed to ultraviolet light over 30 min or by around 99% under solar simulation for 30 min.

A study on the structure of tungsten by the addition of ceria: Effect of monomeric structure over W/Ce/TiO2 catalyst on the SCR reaction

In this study, we investigated the structural characteristics of catalysts and selective catalytic reduction (SCR) reaction activities depending on the Ce valence state and Ce content of the Ce/TiO2 support in order to examine the influence of the W structural characteristics of W/Ce/TiO2 catalyst on SCR reaction. Raman, X-ray photoelectron spectroscopy (XPS) and H2-temperature programmed reduction (H2-TPR) were performed in order to investigate the physicochemical characteristics of the catalyst·NH3-temperature programmed desorption (NH3-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) experiments were performed to investigate the reaction characteristics of the catalyst. As a result, SCR reaction activity was excellent when the W structure was present as monomeric W, and that this structure was formed by Ce2(WO4)3 compound, which was a binding species of WO42− monomeric W and Ce3+. In addition, the high Ce4+ ratio of the Ce/TiO2 increased the formation of monomeric W, which was found to be optimal when the loading of Ce was 10 wt%. Finally, the catalyst having the structure of monomeric W showed higher SCR reaction activity at low temperature because of increased NO adsorption and formation of unstable NOx adsorption species.

Complementary effect of ceria on the hydrogen oxidation kinetics on Ni - Ce0.8Sm0.2O2-δ anode

The paper illustrates the electrode kinetics studies results on Ni - Ce0.8Sm0.2O2-δ (Ni-SDC) anodes in a wet hydrogen atmosphere in the temperature range of 600–850°С by the electrochemical impedance spectroscopy before and after ceria addition to the anode. The addition of ceria to the anode by the solution impregnation technique is shown to result in the anode electrochemical activity growth by 10–24 times. An approach to the analysis of the impedance spectra based on the combination of the distribution of relaxation times method (DRT) and non-linear least squares method was verified. Based on data obtained from DRT functions, we found that the Ni-SDC anode reaction rate was limited by three processes, whereas the ceria-impregnated Ni-SDC anode electrode reaction rate was limited by two processes. The correlation of the DRT functions of both anodes demonstrated unambiguously that ceria addition to the Ni-SDC anode caused a significant decrease in the middle-frequency step of the electrode reaction, while the resistances of the other electrode reaction steps decreased less. Highly disperse ceria addition to the Ni-SDC anode was assumed to increase significantly the rate of reactions on the anode surface between the adsorbed species.

VO2(M)@CeO2 core-shell nanospheres for thermochromic smart windows and photocatalytic applications

Vanadium dioxide (VO2(M)) is a first order reversible thermochromic material which changes its phase at particular temperature and thus can be used as a thermochromic smart material for window coating. Similarly, the cerium dioxide (CeO2) is a well-known photo catalyst which can be applied on vanadium dioxide for self-cleaning. This paper reports a successful direct synthesis and detailed characterizations of core-shell VO2(M)@CeO2 spherical nanoparticles. In the core-shell nanoparticles, the vanadium dioxide core exhibits a solar light modulation property while cerium dioxide shell shows dye degradation through a facile photocatalytic process. Addition of ceria facilitates the VO2 (B) to VO2 (M) transformation and also improves its optical properties. With reduced transition temperature, the thermal stability was enhanced due to core –shell structure. To the extent of our knowledge, the synthesis of core-shell VO2@CeO2 nanoparticles is reported for the first time. The synthesized nanoparticles exhibited improved thermochromic and photocatalytic properties.

Reduced graphene oxide supported Ni-Ce catalysts for CO2 methanation: The support and ceria promotion effects

The reduced oxide graphene (RGO) supported Ni-based catalysts is prepared and modified with ceria (Ni-Ce/RGO) for CO2 methanation for the first time in the present work, and compared with the active carbon (AC) and γ-Al2O3 supported samples. The results show that the catalytic activity of the samples without ceria follow the order Ni/RGO > Ni/γ-Al2O3 > Ni/AC, vs. samples with ceria Ni-Ce/RGO > Ni-Ce/γ-Al2O3 > Ni-Ce/AC. The activities of all samples were greatly improved after ceria modification. The Ni-Ce/RGO works the best for CO2 methanation, which could reach the highest CO2 conversion of 84.5% and the highest methane yield of 83.0% at 350 °C with atmospheric pressure. The excellent catalytic performance of Ni-Ce/RGO could be attributed to the special support effect of RGO and the ceria promotion effect. The support effect of RGO could be attributed to its large surface area and surface oxygen-containing functional groups, which results in stable anchoring of the active metal. The addition of ceria promotes the Ni dispersion on the supports as well as to accelerate the positive reaction due to the oxygen vacancies of ceria.

Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NOx trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, which mainly consisted of three compounds: (i) Al2O3, (ii) Mg/Al2O3, and (iii) Mg/Ce/Al2O3 mixed with Pt, Pd, and Pt-Pd. A micro flow reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were employed in order to investigate the evolution and stability of the species formed during SO2 poisoning. The results showed that the addition of palladium and magnesium into the LNT formulation can be beneficial for the catalyst desulfation due mainly to the ability to release the sulfur trapped at relatively low temperatures. This was especially evident for Pd/Mg/Al2O3 model catalyst, which demonstrated an efficient LNT desulfation with low H2 consumption. In contrast, the addition of ceria was found to increase the formation of bulk sulfate species during SO2 poisoning, which requires higher temperatures for the sulfur removal. The noble metal nature was also observed to play an important role on the SOx storage and release properties. Monometallic Pd-based catalysts exhibited the formation of surface palladium sulfate species during SO2 exposure, whereas Pt-Pd bimetallic formulations presented higher stability of the sulfur species formed compared to the corresponding Pt- and Pd-monometallic samples.

New Insights into Excellent Catalytic Performance of the Ce-Modified Catalyst for NO Oxidation

Diesel exhaust has recently become a severe problem, and diesel oxidation catalyst (DOC) installed in the diesel exhaust treatment system is used to reduce automobile pollution containing CO, hydrocarbons (HC), and NO. In this work, for the purpose of elucidating the effect of ceria addition on the catalytic performance of Pt-based DOC in CO, HC, and NO oxidation reactions, a range of catalysts were prepared by impregnation method. Among them, the Pt/15CeSA catalyst showed excellent catalytic activity, and its NO maximum conversion could reach 62%. The experimental results of X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) confirmed that the interface Pt–O–Ce–O–Al existed in the Pt/15CeSA catalyst. Besides, more oxygen vacancies were created at this interface, which were confirmed by oxygen temperature-programmed desorption (O2-TPD) and Raman spectroscopic experiments, resulting in an outstanding catalytic performance of Pt/15CeSA. It is expected our res...

Influence of MgO/CeO2 ratio on CO2-oxidative transformation of C2H6 to C2H4 over highly active and stable Cr/MgO(x)–CeO2(100−x) nanocatalysts

Cr/MgO(x)–CeO2(100−x) nanocatalysts were synthesized by a coprecipitation method and characterized by X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray (EDX) spectroscopy, diffuse reflectance spectroscopy (DRS), and Brunauer–Emmett–Teller (BET) analysis. The effect of ceria addition on their physicochemical characteristics was investigated, and the results were correlated with their catalytic performance in oxidative dehydrogenation of ethane. A decrease in the size of the metal particles was found when adding a suitable content of ceria to the support. Crystalline Cr2O3 was not found in the calcined samples, indicating good dispersion of Cr species on the support. All samples showed nanosized particles with uniform morphology, with the best surface morphology for the Cr/MgO(50)–CeO2(50) sample, on which the particle distribution mainly lay in the range of 40–60 nm. Variation of the amount of Ce in the support led to an enhancement of the Cr6+/Cr3+ ratio, with the highest value for the Cr/MgO(50)–CeO2(50) sample. This catalyst effectively dehydrogenated ethane to ethylene with CO2 at 700 °C even after 5 h on-stream, giving 42.76 % ethylene yield.

Effect of cerium content on textural and hydrodesulfurization performance for dibenzothiophene over a bulk Ni2P catalyst

A series of ceria promoted Ni2P catalysts were prepared and evaluated in dibenzothiophene hydrodesulfurization steam. These catalysts were characterized by X-ray diffraction, N2 adsorption–desorption, CO chemisorptions, and X-ray photoelectron spectroscopy. The results showed that the addition of ceria into the bulk Ni2P catalyst was conducive to the formation of the Ni2P phase and contributed to a higher surface area, leading to a better dispersion and smaller crystallite size of Ni2P particles. The CexNi2P catalysts showed higher dibenzothiophene hydrodesulfurization activity than Ni2P catalyst and the Ce0.09Ni2P catalyst showed the highest dibenzothiophene hydrodesulfurization activity. The Ce0.09Ni2P catalyst showed a dibenzothiophene hydrodesulfurization conversion of 94.5% at the reaction conditions of 320°C, 4.0 MPa, a H2/oil ratio of 500 (V/V), and a weight hourly space velocity of 8.0 h−1. The dibenzothiophene was mainly transformed through desulfurization pathway.

Influence of a novel doping of Zn-CeO2 + MnO2 on the physical properties of a deposited coating

Mild steel can be electroplated with Zinc to enhance the properties of its surface without changing the properties of the substrate. However, the properties of the coating can be improved by alloying the zinc with other metals. In this study, the influence of novel doping of ceria to a zinc-based bath that contains manganese oxide, on the physical properties of deposited coating was investigated. The mild steel was plated at a current density of 2A and pH of 4,3 using a DC rectifier. Ceria was added as a dopant to a zinc bath and the mild steel samples were plated with MnO2 variations of 5 and 10g/L under constant parameters. OPM was used for the characterization of the morphologies of the coatings. The microhardness characteristics of the obtained deposits were analyzed with the use of the Vickers indenter. The corrosion behavior was studied using linear potentiodynamic polarization method in 3.65% NaCl and 0.5M H2SO4 solution. According to the OPM obtained, the compactness and homogeneity of the coatings improved with the addition of ceria up to an optimum 5g/L concentration of MnO2. The results also show that ceria significantly improves the hardness of the coating. The addition of MnO2 has little effect on the hardness of the coating, and a concentration of MnO2 beyond the optimum level reduces the hardness properties. There was improved corrosion resistance of the coatings compared to mild steel and pure zinc coating with the increase in the admix concentration.

The promotion effect of ceria on high vanadia loading NH3-SCR catalysts

A high vanadia loading (5 wt%) catalyst was modified by ceria to improve the NH3-SCR performance. CeVO4 was generated after the addition of ceria to 5 wt% V2O5/TiO2, result not seen in the case of low-loading vanadia samples. CeVO4 presented stable Brønsted acid sites for NH3 adsorption and moderate redox sites for NH3 activation rather than polymeric VOx for the V-based catalyst. These properties effectively suppressed formation of N2O and NO (side reactions). Therefore, ceria preserved the low-temperature activity of V2O5/TiO2 and improved its high-temperature N2 selectivity. Furthermore, ceria promoted the resistance of V2O5/TiO2 to SO2 and H2O poisoning.

Enhanced flux-pinning performance of YBCO films derived from a fluorine-free sol-gel process with ceria addition

In this work, a facile and effective method which can significantly improve the flux-pinning performance of YBCO films was reported. YBCO/CeO2 composite films were prepared on LaAlO3 (LAO) single crystal substrates through a fluorine-free sol-gel approach with a certain amount of ceria addition. During the nucleation and growth of YBCO films, CeO2 reacted with the barium-contained phase in YBCO precursors to generate the nanosized BaCeO3 phase and thus the redundant Y2O3 and CuO phases remained, leading to the wrong stacking of Cu atoms to form the stacking faults of Cu-O planes, which has been demonstrated by XRD, TEM, SEM and EDS results. The variation of critical current density (Jc) and flux-pinning force (Fp) with the percentage of ceria addition was investigated, and the results show that YBCO film with the amount of 5 mol% of ceria addition exhibits the highest Jc and the strongest Fp at the same temperature and applied magnetic fields. In addition, the stacking faults effectively reduced the degree of dependency of Jc of YBCO film on the applied magnetic field especially at low temperature.

Syngas production from dry reforming of methane over ni/perlite catalysts: Effect of zirconia and ceria impregnation

Ni catalysts with nominal loadings ranging between 2.5 and 20 wt% were synthesized over perlite by wet impregnation, then filtered, washed and calcined at 500 °C. Chemical analyses performed by MP-AES revealed that the maximum Ni content loaded over perlite corresponded to ∼15 wt%. Therefore, for comparison reasons, a Ni(20 wt%)/perlite catalyst was prepared by wetness impregnation without performing any washing treatment. The so prepared catalysts were tested in methane dry reforming without performing any pre-treatment reduction. The catalytic performances were compared by increasing the temperature from 500 up to 800 °C under the reaction mixture composed of 15 vol% CH4 + 15 vol% CO2/N2. Ni(15 wt%)/perlite was the most active catalyst among the series of monometallic samples. The effect of co-impregnating perlite with Ni and Zr or Ni and Ce precursors in order to obtain catalysts with final composition, Ni(15 wt%), 10 and 20 wt% as Zr or Ce, perlite (75 or 65 wt%) was, then, investigated. Characterizations performed by XRD, BET, DRS and H2-TPR evidenced that the physico-chemical and reduction properties are influenced by the Ni content and by the presence of zirconia and ceria oxides. It is worth of noting the increased reducibility of NiO species promoted by zirconia and ceria addition. The catalytic activity in the dry reforming of methane was also affected by the presence of doping oxides, in terms of enhanced CH4 and CO2 conversions and higher H2/CO atomic ratios. Runs tests at 700 °C for 12 h were carried out and the spent catalysts were analysed by TGA and TEM. Over Ni(15 wt%)/perlite large amount of amorphous carbon grows on the surface blocking the active centres, while zirconia and ceria doping improved the resistance to carbon poisoning favouring growing of filamentous carbon residues in small amount.