Potential rare-earth modified CeO2 catalysts for soot oxidation

Kamasamudram, Krishna; Bueno‐López, Agustín; Makkee, Michiel; Moulijn, Jacob A.

doi:10.1016/j.apcatb.2007.04.009

Cited by 110 publications

(54 citation statements)

References 21 publications

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“…[5,6] The effectiveness of CeO 2 as a catalyst is associated with its high oxygen storage capacity (OSC), i.e. the ability to absorb/release oxygen under oxidizing/reducing conditions, [7][8][9][10] and is related to the comparatively facile formation of O vacancies in CeO 2 .…”

Section: Introductionmentioning

confidence: 99%

“…Trivalent rare-earth cations have been shown to be effective for catalysis, [21] with La(III) being a promising candidate dopant. [6] It is generally considered that when CeO 2 is doped with a trivalent cation, such as La(III), two lattice Ce(IV) ions are replaced by the dopants and an O ion is removed to conserve the charge. [22,23] In Kröger-Vink notation, this is:…”

Section: Introductionmentioning

confidence: 99%

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The nature of oxygen states on the surfaces of CeO2 and La-doped CeO2

Keating

Scanlon

Watson

2014

Chemical Physics Letters

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The oxygen states on CeO 2 surfaces were investigated with DFT+U calculations. The results reveal the variable nature of the oxygen states, including the never before modelled intrinsic peroxide surface defect. Under O-rich conditions, the peroxide defects on the (100) and (110) surfaces is more stable than oxygen vacancies. On surfaces doped with La(III) it is found that under O-rich conditions the (100) and (110) surface will preferentially form peroxide ions in response to the presence of the dopants while the (111) surface prefers oxygen vacancies. Calculated shifts in core levels match experimental binding energies, further suggesting the presence of peroxide species.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The nature of oxygen states on the surfaces of CeO2 and La-doped CeO2

Keating

Scanlon

Watson

2014

Chemical Physics Letters

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“…However, in the Diesel soot combustion application, it is difficult to reach an agreement about which property is the most critical one, because the answer to this question depends on the experimental conditions used to perform the catalytic tests, that is, the soot-catalyst contact mode (loose or tight), the gas composition (only with O 2 or also with NOx), the nature of soot, the set of ceria catalysts compared, the type of reactor (TGA, flow reactor, etc. ), the prevailing combustion mechanism (NO 2 -assisted or active oxygen-assisted) and so on.However, some general conclusions can be drawn:-High surface area/small crystal size of ceria usually has a positive effect since there is more surface available to catalyze the oxidation of NO to NO 2 and more contact points with soot to transfer active oxygen.-In mixed oxides, the composition [23,25,27,36] loading depends on the dopant size and on its redox properties.-Most authors conclude that the surface properties are more important than those of the bulk [29,74]. For instance, the oxygen storage capacity, which involves bulk oxygen, seems to be only important in the absence or defect of gas-phase O 2 , but not in O 2 -rich environments [74].…”

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confidence: 99%

Diesel soot combustion ceria catalysts

Bueno‐López

2014

Applied Catalysis B: Environmental

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This review article summarizes the contents of the keynote lecture with the same tittle presented at the 7 th edition of the International Conference on Environmental Catalysis hold in Lyon (France) in September 2012. Different aspects of the ceria-catalyzed Diesel soot combustion reactions have been critically discussed, such as the high catalytic activity of ceria for Diesel soot combustion in comparison to some other potential catalysts, the potential ceria-catalyzed Diesel soot combustion mechanisms (the so-called NO 2 -assisted mechanism and the active oxygen mechanism) and the effect of ceria doping with suitable cations like those of Pr, La or Zr. Ceria must be doped in order to enhance thermal stability, but ceria doping also changes different physicochemical and catalytic properties of ceria. Zr-doping, for instance, has a double role on ceria as soot combustion catalyst: enhances ceria oxidation capacity of the adsorbed NOx species (positive effect) but stabilizes NO 2 on surface (negative effect). The surface properties of a ceria catalyst are usually more important than those of bulk: high surface area/small crystal size usually has a positive effect on the catalyst performance and, in mixed oxides, the surface composition also plays a role. The optimal dopant loading depends on the foreign cation being, for instance, around 5-10%, 20-30% and 50 mole % for La 3+ , Zr 4+ , and Pr 3+ / 4+ , respectively.Keywords: DPF regeneration; soot; ceria; doped-ceria; Diesel engine contamination. 2This review article summarizes the contents of the keynote lecture with the same tittle presented at the 7 th edition of the International Conference on Environmental Catalysis hold in Lyon (France) in September 2012. 1.-The problem.Soot particles are formed as undesired by-products in combustion process, being one of the main pollutants emitted by Diesel engines together with NOx, CO and unburned hydrocarbons [1]. Typical gas exhaust composition of a Diesel car, which is summarized in Table 1, is 30-80 ppm hydrocarbons, 200-1500 ppm CO, 300-1650 ppm NO (~ 0 ppm NO 2 ), 5-18% O 2 , > 2% H 2 O and > 2% CO 2 .Soot particles consist of a carbon nucleus with some inorganic material and adsorbed hydrocarbons, SO x , and water [2]. Figure 1 shows TEM images of a real soot sample. The single particles of few nanometers present an amorphous core surrounded by a graphitic shell, and such single particles agglomerate in larger entities with size typically in the range 0.1-10 µm [3].Several adverse effects on health have been attributed to soot. A fraction of these particles (the so-called PM-10, with size smaller than 10 m) can penetrate the respiratory tract and are deposited on lungs increasing cancer risk, asthma and bronchitis. The adsorbed hydrocarbons are mutagenic substances and SO x in contact with water form strong acid compounds.Diesel particle traps with different designs can be used for soot removal from gas streams, wall-flow monoliths being the most popular [3,4]. Figure 2 shows a commercial SiC Diesel Part...

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“…These observations can be explained as being due to desorption of O 2 from the ceria containing materials (and the concomitant formation of Ce 3+ ) [16][17][18][19][20][21][22][23]. Initially this O 2 (rather than leaving the system) reacted with the PM and formed CO 2 .…”

Section: Formation Of Ce 3+ -Co Species From Reaction Between Cexzr1-mentioning

confidence: 99%

“…The rationale behind the use of these materials in this reaction is related to the oxygen storage capacity of the catalysts. CeO 2 can desorb and re-adsorb O 2 through formation and consumption of a Ce 2 O 3 oxide [16][17][18][19][20]. The oxygen atoms involved in this process are active for promotion of various combustion and reforming reactions [21][22][23][24][25] and for this reason (as well as their ability to dampen excursions to overly fuel rich or fuel lean exhaust conditions) Ce (x) Zr (1-x) O 2 catalysts are used as supports in many catalytic formulations.…”

Section: Introductionmentioning

confidence: 99%

Attempts at an in situ Raman study of ceria/zirconia catalysts in PM combustion

Sullivan

Dulgheru

Atribak

et al. 2011

Applied Catalysis B: Environmental

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Publisher's statementThis is the author's version of a work that was accepted for publication in Applied Catalysis B: Environmental. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Applied Catalysis B: Environmental, 108-109 (1) Ce (x) Zr (1-x) O 2 catalysts with various Ce / Zr contents were studied using Raman spectroscopy under different gaseous atmospheres, at different temperatures and in the presence of a model soot.Catalysts with high concentrations of Zr fluoresced at elevated temperatures making analysis of their spectra impossible. This effect became even more pronounced at higher temperatures. CeO 2 and solid solutions with relatively low concentrations of Zr showed a red shift and a decrease in intensity of the characteristic F 2g peak at high temperatures under different atmospheres. The magnitude of the latter effect was higher under reducing atmospheres. These changes are reversible upon cooling, showing that they relate to a lattice expansion effect rather than any major chemical change to the material. In the presence of the model soot the Raman spectra of all materials was much decreased due to the absorption of the incident and scattered radiation by the soot particles. The presence of soot does not change the relative intensities or positions of the peaks in the spectra of the solid solutions. Evidence is shown for the production of a Ce 3+ -CO species following interaction between the soot and the surface at high temperature in an inert atmosphere.

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Potential rare-earth modified CeO2 catalysts for soot oxidation

Cited by 110 publications

References 21 publications

The nature of oxygen states on the surfaces of CeO2 and La-doped CeO2

The nature of oxygen states on the surfaces of CeO2 and La-doped CeO2

Diesel soot combustion ceria catalysts

Attempts at an in situ Raman study of ceria/zirconia catalysts in PM combustion

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