Structural Defects In Cerium Oxide Catalytic Support Studied by Pulsed Neutron Diffraction

1998 ◽  
Vol 549 ◽  
Author(s):  
E. Mamontov ◽  
T. Egami ◽  
R. Brezny
Keyword(s):  
Cerium Oxide ◽  
Fluorite Structure ◽  
Oxygen Storage ◽  
Structural Defects ◽  
Interstitial Oxygen ◽  
Storage Mechanism ◽  
Oxygen Ions ◽  
Catalytic Support ◽  
Automotive Catalytic Converters ◽  
Pulsed Neutron

AbstractWe studied the structure of coarse and nano-scale powders of CeO2 using pulsed neutron scattering. The diffraction data were analyzed using Rietveld refinement, and were also Fourier-transformed to obtain the pair-distribution function (PDF). The Frenkel type oxygen defects consisting of vacancies in the oxygen sublattice and oxygen ions in the octahedral interstitial sites of the fluorite structure were observed in cerium oxide for the first time. The interstitial oxygen ions were found to recombine with vacancies when the sample underwent thermal treatment at 1073 K. We suggest that these defects are directly involved in the oxygen storage mechanism of ceria used in automotive catalytic converters.

scholarly journals First of Its Kind Automotive Catalyst Prepared by Recycled PGMs-Catalytic Performance

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 942
Author(s):  
Anastasia Maria Moschovi ◽  
Mattia Giuliano ◽  
Marios Kourtelesis ◽  
Giovanna Nicol ◽  
Ekaterini Polyzou ◽  
...  
Keyword(s):  
Oxygen Storage Capacity ◽  
Catalytic Performance ◽  
Platinum Group Metals ◽  
Oxygen Storage ◽  
Small Scale ◽  
Gas Mixture ◽  
Oxidation Reactions ◽  
Fresh Catalyst ◽  
Metal Precursors ◽  
Automotive Catalytic Converters

The production of new automotive catalytic converters requires the increase of the quantity of Platinum Group Metals in order to deal with the strict emission standards that are imposed for vehicles. The use of PGMs coming from the recycling of spent autocatalysts could greatly reduce the cost of catalyst production for the automotive industry. This paper presents the synthesis of novel automotive Three-Way Catalysts (PLTWC, Pd/Rh = 55/5, 60 gPGMs/ft3) and diesel oxidation catalysts (PLDOC, Pt/Pd = 3/1, 110 gPGMs/ft3) from recovered PGMs, without further refinement steps. The catalysts were characterized and evaluated in terms of activity in comparison with benchmark catalysts produced using commercial metal precursors. The small-scale catalytic monoliths were successfully synthesized as evidenced by the characterization of the samples with XRF analysis, optical microscopy, and N2 physisorption. Hydrothermal ageing of the catalysts was performed and led to a significant decrease of the specific surface area of all catalysts (recycled and benchmarks) due to sintering of the support material and metal particles. The TWCs were studied for their activity in CO and unburned hydrocarbon oxidation reactions under a slightly lean environment of the gas mixture (λ > 1) as well as for their ability to reduce NOx under a slightly rich gas mixture (λ < 1). Recycled TWC fresh catalyst presented the best performance amongst the catalysts studied for the abatement of all pollutant gases, and they also showed the highest Oxygen Storage Capacity value. Moreover, comparing the aged samples, the catalyst produced from recycled PGMs presented higher activity than the one synthesized with the use of commercial PGM metal precursors. The results obtained for the DOC catalysts showed that the aged PLDOC catalyst outperformed both the fresh catalyst and the aged DOC catalyst prepared with the use of commercial metal precursors for the oxidation of CO, hydrocarbons, and NO. The latter reveals the effect of the presence of several impurities in the recovered PGMs solutions.

Electrical Conduction by Oxygen Ions in Cerium Oxide

1966 ◽  
Vol 44 (10) ◽  
pp. 3692-3696 ◽  
Author(s):  
E. L. Holverson ◽  
C. J. Kevane
Keyword(s):  
Cerium Oxide ◽  
Electrical Conduction ◽  
Oxygen Ions

Sol-Gel Precursors and the Oxygen Storage Capacity of PrOy-ZrO2 Materials

1997 ◽  
Vol 497 ◽  
Author(s):  
C. K. Narula ◽  
K. L. Taylor ◽  
L. P. Haack ◽  
L. F. Allard ◽  
A. Datye ◽  
...  
Keyword(s):  
Single Phase ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Fluorite Structure ◽  
Oxygen Storage Capacity ◽  
Oxygen Storage ◽  
Molar Ratio ◽  
Metal Nitrates ◽  
Temperature Programmed

ABSTRACTThe gels derived from mixtures of Pr(OiC3H7)3 and Zr(OiC3H7)4•iC3H7OH, upon hydrolysis and pyrolysis, furnish single-phase PrOy-ZrO2 materials crystallized in the fluorite structure. These materials can be coated onto high-surface-area γ-alumina powders or deposited onto dense α-alumina coupons in the form of thin films from a solution of parent alkoxides modified with 2,4-pentanedione in THF. The fluorite structure of the PrOy-ZrO2 in the films appears to be thermally stable in air up to 1200°C. Temperature-programmed-reduction (TPR) measurements show that the bulk PrOy-ZrO2 material with a Pr. Zr molar ratio of 1:1 can store and release oxygen while that with a molar ratio of 1:3 cannot.The precursors play an important role in determining phase composition of the resulting PrOy-ZrO2 material. A mixture of monoclinic and cubic or tetragonal phases was found in PrOy-ZrO2 prepared from a new single-source heterometallic alkoxide, Pr2Zr6(μ4-O)2(μ-OAc)6(μ-OiPr)10(OiPr)10, whereas a mixture of cubic and tetragonal phases was present in PrOy-ZrO2 made previously by coprecipitation from aqueous solutions of the metal nitrates.

Overview: Modification of Cerium Oxide in Three-Way Catalysts

2014 ◽  
Vol 575 ◽  
pp. 97-102 ◽  
Author(s):  
M. Nazri Abu Shah ◽  
S. Hanim Md Nor ◽  
Kamariah Noor Ismail ◽  
Abdul Hadi
Keyword(s):  
Thermal Stability ◽  
Rare Earth ◽  
Metal Oxides ◽  
Cerium Oxide ◽  
Storage Capacity ◽  
Rare Earth Metals ◽  
Oxygen Storage Capacity ◽  
Oxygen Storage ◽  
Alkaline Metals ◽  
Three Way Catalyst

An overview of modification of cerium oxide, CeO2which is employed in the three-way catalyst (TWCs) is presented in this article. The modifications of cerium oxide, CeO2incorporated with the metal oxides for the improvement of thermal stability, microstructure and oxygen storage capacity (OSC) are discussed. In view of that, the types of metal oxide are grouped into transition metals, rare earth metals, and alkaline metals and the effect of each group into cerium oxide, CeO2are elaborated.

Crystallography with a pulsed neutron source

1994 ◽  
Vol 209 (5) ◽  
Author(s):  
B. T. M. Willis
Keyword(s):  
Diffuse Scattering ◽  
Fluorite Structure ◽  
Good Resolution ◽  
High Flux ◽  
Thermal Diffuse Scattering ◽  
Neutron Sources ◽  
The Past ◽  
Pulsed Neutron ◽  
Thermal Diffuse ◽  
Pulsed Neutron Source

AbstractIn the past decade pulsed-neutron sources have become firmly established as being complementary to reactor sources for work in crystallography. We describe some of the special advantages of pulsed-neutron crystallography, such as the presence of a high flux of short-wavelength neutrons and the exceptionally good resolution for powder diffraction studies. A few examples are then given of how these advantages have been exploited in practice, including the measurement of thermal diffuse scattering in materials with the fluorite structure.

Structure and spectroscopic properties of (AA′)(BB′)O3 mixed-perovskite crystals

2005 ◽  
Vol 20 (12) ◽  
pp. 3329-3337 ◽  
Author(s):  
Dorota A. Pawlak ◽  
Masahiko Ito ◽  
Lukasz Dobrzycki ◽  
Krzysztof Wozniak ◽  
Masaoki Oku ◽  
...  
Keyword(s):  
Spectroscopic Properties ◽  
Regular System ◽  
Interstitial Oxygen ◽  
X Ray Diffraction ◽  
Absorption Bands ◽  
Space Groups ◽  
Oxygen Ions ◽  
Reducing Atmosphere ◽  
Lanthanum Strontium ◽  
Unit Cells

Five different mixed-perovskite (AA′)(BB′)O3 single crystals were grown, where A = La, Nd; A′ = Sr; B = Al, Ga; and B′ = Ta, Nb. The as-grown crystals were yellowish/brownish. After annealing in air, the coloration was more intense. Annealing in a reducing atmosphere decreased coloration. The crystals were investigated by transmission spectroscopy, electron spectroscopy for chemical analysis (ESCA), and single-crystal x-ray diffraction. Additional broad absorption bands in the transmission spectra were observed for the as-grown samples. They are in line with the changes of the shape of O(1s) ESCA peaks. Redundant interstitial oxygen ions were recognized as the reason for the crystal coloration. All structures were solved and refined in different space groups of the regular system. Some of the unit cells have a doubled lattice constant: (i) lanthanum strontium gallium niobate, Pm3m, 3.9323(5) Å, at 100 K, 3.9270(5) Å; (ii) neodymium strontium aluminum tantalate, Pm3m, 3.8353(4) Å; (iii) lanthanum strontium aluminum tantalate, Pn3m, 7.720(1) Å, annealed in reducing atmosphere, 7.708(1) Å; (iv) neodymium strontium aluminum niobate, Fm3m, 7.744(4) Å.

Cordierite-CeO2 Composite Ceramic: A Novel Catalytic Support Material for Purification of Vehicle Exhausts

2007 ◽  
Vol 280-283 ◽  
pp. 1075-1078 ◽  
Author(s):  
Z.M. Shi
Keyword(s):  
Oxygen Concentration ◽  
Storage Capacity ◽  
Ceramic Powder ◽  
Composite Ceramic ◽  
Oxygen Storage Capacity ◽  
Oxygen Adsorption ◽  
Oxygen Storage ◽  
Support Material ◽  
Catalytic Support ◽  
Catalytic Coating

Stable oxygen concentration in exhausts is a decisive factor in catalytic purification of the vehicle exhausts. Nanostructured CeO2 is generally added into catalytic coating on a ceramic support to adjust the oxygen concentration because it possesses a unique oxygen storage capacity (OSC). However, a small amount of CeO2 gets insufficient when the oxygen concentration fluctuates in a large range. In the present work, the cordierite-CeO2 composite ceramic with oxygen storage capacity was prepared for a support material of catalytic converters. The oxygen storage-release performance of the ceramics, including temperature of releasing oxygen, adsorption process of oxygen and the oxygen storage, was examined by a temperature-programmed gas chromatography. The composition of the ceramics was analyzed by an X-ray powder diffraction (XRD) and a scanning electron microscope (SEM) to validate the reliability of the ceramic as the support material with OSC. Results show that the ceramics consist of α-cordierite and CeO2 phases, the latter of which is uniformly dispersed throughout the cordierite matrix. The ceramic powder with 10-20wt% of CeO2 possesses the expected oxygen storage capacity. It is suggested that this novel cordierite-CeO2 composite ceramic is helpful of improving the purification effect of vehicle exhausts.

A Study on Oxygen Storage Capacity of Zirconium-Cerium-Oxide Nanoparticles

2013 ◽  
Vol 685 ◽  
pp. 123-127 ◽  
Author(s):  
Ajin C. Sajeevan ◽  
V. Sajith
Keyword(s):  
Cerium Oxide ◽  
Storage Capacity ◽  
Oxygen Storage Capacity ◽  
Oxygen Storage ◽  
Precipitation Method ◽  
Xrd Pattern ◽  
Harmful Emissions ◽  
Uv Visible ◽  
Co Precipitation

One of the methods for the reduction of harmful emissions from diesel engines such as hydrocarbon, soot and NOx is the use of fuel born catalyst Cerium oxide. The oxygen storage capacity of Cerium oxide can be improved by coating it with metal such as Zirconium. Zr – Ce-O nanoparticles were synthesized by Co-precipitation method in the present work. Dynamic Light scattering, XRD pattern and UV-Visible spectroscopy were used for characterization of the prepared samples. Thermo gravimetric studies were conducted to investigate the thermal decomposition of Zr-Ce-O nanoparticles. The oxygen storage capacity of Zr-Ce-O nanoparticles was analyzed using TPR analysis.

Polycrystalline Tetragonal Zirconia of the Form ZrO2: 3 mol% Re2O3 (Re-TZP) for Use in Oxygen Sensors: Synthesis, Characterization and Ionic Conductivity

2014 ◽  
Vol 798-799 ◽  
pp. 145-153
Author(s):  
R.A. Muñoz ◽  
Paola Cristina Cajas ◽  
J.E. Rodriguez ◽  
A.C. Rodrigues ◽  
Cosme R.M. Silva
Keyword(s):  
Tetragonal Zirconia ◽  
Chemical Species ◽  
Fluorite Structure ◽  
Face Centered Cubic ◽  
Oxygen Ions ◽  
Oxygen Ion ◽  
Oxygen Ion Conductors ◽  
Fluorite Type ◽  
Face Centered ◽  
Ion Conductors

Oxygen ion conductors of zirconia based ceramics are a class of materials with technological applications in several application areas: sensors of chemical species, oxygen pumps, solid oxide fuel cells among others [1]. For these applications, the zirconia must possess the fluorite type crystal structure, or close to it. Such oxides with this structure are the classic oxygen ion conductors [2]. The fluorite structure consists of a cubic lattice of oxygen ions surrounded by cations. The cations are arranged in a face centered cubic structure with anions occupying tetrahedral positions. This leads to an open structure with large empty octahedral interstices.

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