Influence Of Ceria Research Articles

The influence of ceria on Cu/TiO2 catalysts to produce abundant oxygen vacancies and induce highly efficient CO oxidation

Ce and Cu species deposited on TiO2 can apparently provide a higher turnover frequency rate and lower activation energy than the Cu/TiO2 catalyst and the Ce and Cu species on SiO2 catalysts.

The effect of ceria and zirconia nanoparticles on the corrosion behaviour of cataphoretic epoxy coatings on AA6060 alloy

In this work an attempt was made to produce epoxy coating doped with ceria (CeO2) and/or zirconia (ZrO2) nanoparticles, in single step electrophoretric deposition process. Deposition was carried out on AA6060 cataforetically from epoxy resin suspension containing synthesized stable aqueous colloidal dispersions (sols) of CeO2 and ZrO2. The influence of ceria and zirconia nanoparticles on the physicochemical characteristics of epoxy coatings was evaluated by energy dispersive X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis and adhesion measurements, while their corrosion stability during immersion in 0.5 M NaCl solution was monitored by electrochemical impedance spectroscopy. All ceria and/or zirconia containing coatings showed better corrosion stability and adhesion than pure epoxy coating, while between doped epoxy coatings one with CeO2/ZrO2 exhhibited the greatest values of charge-transfer resistance due to synergetic effect of both types of added nanoparticles.

Measurement of Open Flame Temperature of Nano Particle Additive Dispersed Diesel Using Digital Interferometry

ABSTRACTThe present work investigates the influence of ceria (CeO2) and its mixed oxide nanoparticles (CeZrO2 and CeZrYO2) dispersed in diesel on flame temperature. Interferometric technique, a non-intrusive method, has been used for the measurement of flame temperature. Optical components were aligned to obtain the wedge fringes and digital image processing techniques were used to obtain the temperature distributions from the fringes. Nanofluids (nanoparticle dispersed diesel) were prepared by dispersing CeO2, CeZrO2, and CeZrYO2 nanoparticles at various dosing levels ranging from 5 ppm to 20 ppm, using a standard ultrasonic mixing process. Results show that for concentration of nanoparticle in diesel below 10 ppm, no significant variation in flame temperature was observed as compared to pure diesel. However, above 10 ppm, the maximum temperature increases drastically, especially for 20 ppm, and is proportional to the concentration of nanoparticles. The percentage enhancement in temperature was found to be high for the mixed oxide of ceria nanoparticles, as compared to diesel with ceria nanoparticle alone, and is due to the increase in the oxygen vacancies in the ceria lattice due to doping.

Influence of ceria and yttria on the protective properties of SiO2–Al2O3 coatings deposited by sol–gel method on FeCrAl alloy

Three-layer Y2O3, CeO2, SiO2–Al2O3 and SiO2–Al2O3–Y2O3–CeO2 coatings were deposited by sol–gel method on the FeCrAl alloy foil substrate. The protective properties of the coatings during high-temperature cyclic oxidation and the changes in the topography of the surface, the structure, and chemical composition of the FeCrAl alloy surface layer were examined. It has been shown that small additions of cerium and yttrium affect the morphology of the growing Al2O3 scale. After 10 oxidation cycles in air (T = 900 °C, t = 120 h, one cycle = 12 h), the smallest change in the mass of the samples was observed for Y2O3 and SiO2–Al2O3–Y2O3–CeO2 coatings with an appropriate yttrium and cerium content. The protection effectiveness of the coatings to that of uncoated substrate after 10 oxidation cycles ranges from 28 to 66 %. The oxidation scale thickness (h) and the designated value of the parabolic rate constant (kp) depended on the yttrium and cerium content in the coating.

CeO2 based coating for high temperature oxidation protection

This paper investigates the influence of ceria (CeO2) coating on high temperature oxidation behaviour of 2·25Cr–1Mo steel. The superficial coating of CeO2 powder was prepared for experimental investigation. The isothermal corrosion study of uncoated and coated specimens was carried out in air oxidation environment at 973 K for 8 h. The corrosion rate and reaction kinetics were studied and the post corroded scales were characterised in scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction. The results clearly indicate that CeO2 coated specimen improves the high temperature oxidation resistance than uncoated specimen. The improvement of oxidation resistance in presence of CeO2 coating can be attributed to the formation of fine grained oxide on the scale, changed mechanism of scale growth from outer cation migration to inner anion migration and enhancement of scale adhesion with the substrate. The detail mechanism of the oxidation of CeO2 coated and uncoated specimen was further discussed in this paper.

Influence of ceria on the NOx reduction performance of NOx storage reduction catalysts

Influence of ceria on the NOx storage and reduction behavior of NSR catalysts was investigated in a systematic manner over γ-Al2O3, Ba/Al, Ce/Al, Ba/Ce/Al, Pt/Al, Pt/Ce/Al and Ba/Pt/Ce/Al systems using BET, XRD, Raman spectroscopy and in situ FTIR. Although ceria promotion does not seem to have a substantial influence on the overall NOx storage capacity, it does have a clearly positive effect on the NOx reduction via H2(g) during catalytic regeneration under rich conditions which is associated with the enhancement in the total amount of activated hydrogen on the catalyst surface and lowering of the thermal threshold for hydrogen activation. A strong metal support interaction (SMSI) between Pt sites and the BaOx/CeOx domains leads to a complex redox interplay including oxidation of the precious metal sites, reduction of ceria, formation of BaO2 species as well as the formation of Pt–O–Ce interfacial sites on the Ba/Pt/Ce/Al surface. Ceria domains also act as anchoring sites for Pt species, limit their surface diffusion, enhance dispersion and hinder sintering at elevated temperatures. On the Ba/Pt/Ce/Al catalyst surface, reduction of the stored nitrates under relatively mild conditions via H2(g) initially leads to the formation of surface –OH and –NHx species and gas phase N2O, as well as the destruction of surface nitrate species, leaving bulk nitrates mostly intact. Reduction proceeds with the conversion of N2O(g) into N2(g) along with the partial loss of surface –OH and –NHx groups, dehydration and the loss of bulk nitrates.

NOx storage and reduction properties of model ceria-based lean NOx trap catalysts

Three kinds of model ceria-containing LNT catalysts, corresponding to Pt/Ba/CeO2, Pt/CeO2/Al2O3 and Pt/BaO/CeO2/Al2O3, were prepared for comparison with a standard LNT catalyst of the Pt/BaO/Al2O3 type. In these catalysts ceria functioned as a NOx storage component and/or a support material. The influence of ceria on the microstructure of the catalysts was investigated, in addition to the effect on NOx storage capacity, regeneration behavior and catalyst performance during lean/rich cycling. The Pt/Ba/CeO2 and Pt/BaO/CeO2/Al2O3 catalysts exhibited higher NOx storage capacity at 200 and 300°C relative to the Pt/BaO/Al2O3 catalyst, although the latter displayed better storage capacity at 400°C. Catalyst regeneration behavior at low temperature was also improved by the presence of ceria, as reflected by TPR measurements. These factors contributed to the superior NOx storage-reduction performance exhibited by the Pt/Ba/CeO2 and Pt/BaO/CeO2/Al2O3 catalysts under cycling conditions in the temperature range 200–300°C. Overall, Pt/BaO/CeO2/Al2O3 (which displayed well balanced NOx storage and regeneration behavior), showed the best performance, affording consistently high NOx conversion levels in the temperature range 200–400°C under lean-rich cycling conditions.

The influence of ceria and other rare earth promoters on palladium-based methane combustion catalysts

In this work we investigate the effect of ceria and other rare earths (La, Pr, Tb) on Pd–PdO transformation, which is strongly related to the catalytic activity of Pd-based catalysts for the combustion of methane at high temperature. Also the behavior of Pd on ZrO 2 and on yttria-stabilized zirconia is considered for comparison. The catalysts are characterized by XRD and BET surface area measurements. Pd–PdO transformation is studied by means of temperature programmed oxidation measurements and thermogravimetric analysis. Temperature programmed combustion experiments have been carried out in order to compare catalytic activity of different catalysts. The results show that rare earth oxides promote the onset of Pd re-oxidation upon cooling, that for ceria doped sample is reflected in an improvement in the catalytic activity.

Novel CeO2 promoted TiO2–ZrO2 nano-oxide catalysts for oxidative dehydrogenation of p-diethylbenzene utilizing CO2 as soft oxidant

The influence of ceria on structural and catalytic properties of TiO2–ZrO2 mixed oxide was investigated for oxidative dehydrogenation (ODH) of p-diethylbenzene (DEB) to p-divinylbenzene (DVB) utilizing CO2 as soft oxidant. The investigated catalysts were synthesized by coprecipitation and impregnation methods involving microwave treatment. Catalyst characterization was achieved using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), BET surface area and temperature programmed desorption/oxidation (TPD/TPO) methods. The XRD and TEM results revealed that the prepared samples are in nanocrystalline form with 10–20nm size. The presence of acid–base sites and their distribution was examined by NH3 and CO2 TPD measurements. The ceria promoted sample exhibited more number of acid sites. The TPO measurements revealed that CO2 dissociates over the reduced surface of the catalysts. Among various catalysts investigated, the microwave treated CeO2/TiO2–ZrO2 sample exhibited better conversion and a high product selectivity. The time-on-stream studies revealed that ceria promoted TiO2–ZrO2 catalysts exhibit higher stability for ODH of DEB.

Influence of ceria and nickel addition to alumina-supported Rh catalyst for propane steam reforming at low temperatures

Kinetic studies reveal that loading ceria and Ni onto alumina-supported Rh dramatically increases the propane reforming rates; adding CeO 2 promotes steam and propane adsorption and activation, while adding Ni mainly enhances C 3 H 8 adsorption and activation. The influence of ceria and nickel addition to alumina-supported Rh catalyst for steam reforming of propane at low temperatures has been studied by preparing and examining 2 wt%Rh/Al 2 O 3 , 2 wt%Rh/20 wt%CeO 2 –Al 2 O 3 , and 2 wt%Rh–5 wt%Ni/20 wt%CeO 2 –Al 2 O 3 . TPR characterization showed that adding ceria makes rhodium oxide easier to reduce and the presence of rhodium also makes ceria easier to reduce through Rh–Ce interaction, whereas the addition of Ni makes Rh 2 O 3 and ceria more difficult to reduce, likely due to Rh–Ni and Ce–Ni interactions. Adding ceria and nickel significantly improved the catalytic activity of Rh catalyst for propane conversion at 475 °C. Kinetic study at different temperatures (450–650 °C) indicated that the addition of ceria and Ni can greatly increase the propane reforming rates by lowering the activation energies from 67.6–68.8 kJ/mol for 2Rh/Al to 50.1–50.4 kJ/mol for 2Rh/20CeAl and to 42.1–42.5 kJ/mol for 2Rh5Ni/20CeAl. The feed steam/carbon molar ratios corresponding to maximum reaction rates at 475 °C increased from 2.0 for 2Rh/Al to 3.0 for 2Rh/20CeAl and 4.5 for 2Rh5Ni/20CeAl catalyst. A kinetic equation based on Langmuir–Hinshelwood model best fitting the experimental data was applied for the propane steam reforming over the Rh-based catalysts. Kinetic results at different partial pressures of propane and steam revealed that the addition of ceria could enhance the steam and propane adsorption, while the addition of Ni could significantly promote the propane adsorption, probably through working with Rh as propane adsorption sites.

RETRACTED: Influence of ceria on physicochemical, surface and catalytic properties of alumina supported manganese catalysts

RETRACTED: Influence of ceria on physicochemical, surface and catalytic properties of alumina supported manganese catalysts

Influence of ceria on the NO x storage/reduction behavior of lean NO x trap catalysts

The effect of La 2O 3-stabilized ceria incorporation on the functioning of fully formulated lean NO x trap catalysts was investigated. Monolithic catalysts were prepared, corresponding to loadings of 0, 50 and 100 g CeO 2/L, together with a catalyst containing 100 g/L of ceria–zirconia (Ce 0.7Zr 0.3O 2). Loadings of the other main components (Pt, Rh and BaO) were held constant. Catalyst evaluation was performed on a bench flow reactor under simulated diesel exhaust conditions, employing NO x storage/reduction cycles. NO x storage efficiency in the temperature range 150–350 °C was observed to increase with ceria loading, resulting in higher NO x conversion levels. At 150 °C, high rich phase NO x slip was observed for all of the catalysts, resulting from an imbalance in the rates of nitrate decomposition and NO x reduction. Optimal NO x conversion was obtained in the range 250–350 °C for all the catalysts, while at 450 °C high rich phase NO x slip from the most highly loaded ceria-containing catalyst resulted in lower NO x conversion than for the ceria-free formulation. N 2O was the major NO x reduction product at 150 °C over all of the catalysts, although low NO x conversion levels limited the N 2O yield. At higher temperatures N 2 was the main product of NO x reduction, although NH 3 formation was also observed. Selectivity to NH 3 decreased with increasing ceria loading, indicating that NH 3 is consumed by reaction with stored oxygen in the rear of the catalyst.

Influence of Ceria on Characterization of Films Prepared by Vapor Deposition of Quasicrystal

Films were prepared on the steel (Q235) by means of vacuum vapor deposition through Al65Cu20Fe15 quasicrystal powders. Influence of ceria on the microstructure and properties of films were studied. TEM, SEM and XRD were used to observe the microstructure and morphology of films. The hardness and the modulus of the film were tested by MTS. The results showed that the films were formed through directly vapor deposited by Al65Cu20Fe15 quasicrystal. The films were constituted of many phases such as CuAl2, AlCu3 and I (Al65Cu20Fe15) phase. The composition of films was decided by the technology of deposition. After adding cerium, the microstructure of films did not radically change, however the hardness and modulus of films varied with the increase of cerium. When the cerium content was 5 wt%, the hardness of films was more than 9.0 GPa. Furthermore, adding cerium could improve obviously the corrosion resistance of films.

Reduction of N2O by CO over Ceria-Modified Three-Way Pt−Rh Catalysts: Kinetic Aspects

This study reports an extensive kinetic investigation of the CO + N2O reaction which is a major reaction involved with automotive exhaust catalysts during the overall reduction of NO, particularly during the start of a cold engine. Steady-state rate measurements were performed between 217 and 250 °C on Pt−Rh/γ-Al2O3−CeO2 with partial pressures in the range (4.5−12.0) × 10-3 and (2.0−7.4) × 10-3 atm respectively for CO and N2O. Particular attention has been paid toward the influence of ceria on the catalytic performances of noble metals. A bifunctional mechanism is proposed involving the redox properties of ceria which correctly explains the beneficial effect of ceria on the reduction of N2O by CO in the absence of NO. However, subsequent comparisons with previous optimized kinetic and thermodynamic constants for the CO + NO reaction on the same catalyst suggest that the promotional effect of ceria is suppressed. When N2O and NO coexist in the gas phase, only noble metals are active near the light-off temp...

Kinetics of the CO+NO Reaction over Bimetallic Platinum–Rhodium on Alumina: Effect of Ceria Incorporation into Noble Metals

The influence of ceria on the kinetic behavior of noble metals in the reduction of NO by CO has been investigated at 120 and 300°C on a freshly prepared Pt–Rh/Al2O3–CeO2 catalyst, and on an aged catalyst after reaction for 16 h at 500°C, within pressure ranges of 2.3–9×10−3 atm for CO and 1.5–8×10−3 atm for NO, using a differential fixed-bed flow reactor. These two temperatures have been selected from temperature-programmed experiments because they correspond to two very different regimes of activity of noble metals with ceria. It has been found that a rate equation derived from a bifunctional mechanism involving reaction paths either on metal or on ceria can correctly fit rate measurements performed at 120°C. In contrast a conventional mechanism earlier proposed for modeling the CO+NO reaction on Pt–Rh/Al2O3 at 300°C, where only noble metals are involved, enables modeling of rate measurements at 300°C on Pt–Rh/Al2O3–CeO2, which suggests that the interaction between ceria and noble metals is suppressed at that temperature. The temperature dependency of the rate constants and equilibrium constants for NO and CO adsorption has been quantified in order to explain such changes in the kinetic behavior of Pt–Rh/Al2O3–CeO2.

Influence of Ceria and Lanthana Promoters on the Kinetics of NO and N2O Reduction by CO over Alumina-Supported Palladium and Rhodium

The kinetic parameters of the NO+CO and N2O+CO reactions over alumina-, ceria/alumina-, and lanthana/alumina-supported Rh and Pd were determined from 425 to 625 K. For NO+CO, the presence of ceria and lanthana affected activity, apparent activation energy, dinitrogen selectivity, and reaction orders to varying degrees over both Pd and Rh. The turnover frequency (based on H2 chemisorption) for the ceria-promoted Pd catalyst was at least an order of magnitude greater than those for all other catalysts. Lanthana-promoted Pd was the next most active catalyst. Changes in kinetic parameters indicated that both ceria and lanthana facilitated NO dissociation on both Pd and Rh, but the effect of ceria on Pd was the most profound. For N2O+CO, ceria promoted the reaction rate on both Pd and Rh whereas lanthana did not promote the reaction on either metal. The ceria-promoted Pd catalyst was again the most active. However, the turnover frequencies for the N2O+CO reaction were about an order of magnitude lower than those for the NO+CO reaction under similar conditions. The rare earth components had very little effect on the activation energies and reaction orders for the N2O+CO reaction. In situ infrared spectroscopy showed the presence of isocyanate surface species on Rh/Al2O3 but not on Pd/Al2O3, which suggested two different reaction mechanisms for the N2O+CO reaction. No synergistic effect on NOx reduction was observed for a Pd/Rh bimetallic sample.

Influence of Ceria on Pd Activity for the CO+O2 Reaction

The behavior of a series of palladium catalysts supported on alumina, ceria, and ceria/alumina for the CO+O2 reaction has been analyzed by a combination of electron transmission microscopy, infrared and electron paramagnetic resonance spectroscopies, and catalytic test studies. Ceria is shown to decrease the onset of the reaction by ca. 130 K due to an enhanced activation of both reactant molecules. Even at room temperature, ceria facilitates activation of CO by promoting the formation of metallic palladium and that of oxygen by the presence of reactive vacancies at the Pd–Ce interface. The optimum ceria promoting effect in the CO conversion is observed for palladium particles in contact with 3-dimensional ceria supported particles, which seem to be oriented by their interaction with alumina, and ascribed to the specific characteristics of the anionic vacancies located at the corresponding Pd–Ce interface. The bulk ceria support, however, induces an oxidation–deactivation process of palladium at medium and high reaction temperatures which hinders reaction between Pd-bonded CO and Ce-bonded oxygen at the Pd–Ce interface.

Influence of Ceria on the Thermally Durability of Pt/Rh Automotive Catalyst

Influence of Ceria on the Thermally Durability of Pt/Rh Automotive Catalyst

Influence of Ceria on the Dispersion and Reduction/Oxidation Behaviour of Alumina-Supported Copper Catalysts

A study using TEM combined with electron diffraction (ED), several spectroscopies (IR, ESR, XPS), and mass spectrometry-temperature programmed surface reaction of adsorbed NO is carried out on a Cu/CeOx/Al2O3catalyst and on similar specimens without Ce or Cu. TEM shows a preferential nucleation of the oxidized Cu phase on the ceria-rich regions, leading to a particle size in the Cu-containing phase smaller than that found in the Al2O3-supported system and decreasing the formation of the CuAl2O4spinel. The Cu–Ce interaction developed in the calcination treatment also gives significant stability against sintering of the metallic copper phase formed during H2reduction. After reduction, the Ce-containing sample shows higher resistance to reoxidation of the surface copper phase by NO to the Cu2+state (in comparison to Cu/Al2O3). On the basis of XPS-Ar+sputtering data, this may be related to partial coverage of the metallic Cu by reduced ceria in a way similar to that currently accepted for the SMSI effect; a capability of the Ce-containing support to stabilize the Cu+state may also contribute to this behaviour. This stable copper state appears in subsurface regions and is likely related to a new phase detected by TEM-ED and tentatively identified as a (Ce,Cu)–Al perovskite. The copper-cerium interaction affects also the reactivity of the catalyst towards NO, increasing (partly through a dissociative mechanism) the amount of adsorbed species which leads to low temperature NO and N2/N2O desorption, as well as shifting the decomposition temperatures of surface species containing N–N bonds (N2/N2O) formed upon NO adsorption. It is proposed that the addition of ceria may help to enhance the reductive elimination of NO by copper in automobile exhaust gases.

Influence of Ceria on the Structure and Catalytic Property of F-T Synthesis Fe/ZrO<sub>2</sub> Catalysts

Influence of Ceria on the Structure and Catalytic Property of F-T Synthesis Fe/ZrO<sub>2</sub> Catalysts