Thermally stable ceria–zirconia catalysts for soot oxidation by O2

Atribak, Idriss; Bueno‐López, Agustín; Garcı́a-Garcı́a, Avelina

doi:10.1016/j.catcom.2007.05.047

Cited by 143 publications

(104 citation statements)

References 15 publications

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“…Ceriabased catalysts are the most widely investigated [9][10][11]. Some simple transition metals or oxides also exhibit good catalytic activity and stability [12].…”

Section: Introductionmentioning

confidence: 99%

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

et al. 2016

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The effect of surface and bulk potassium promotion on the transition metal oxides (Mn, Fe, Co) catalytic activity in catalytic soot oxidation was investigated. The surface promotion was obtained via incipient wetness impregnation, whereas the bulk promotion-nanostructuration-was obtained via wet chemical synthesis or solid state reaction leading to mixed oxide materials. The introduction of potassium into the transition metal oxide matrix results in the formation of tunneled or layered structures, which enable high potassium mobility. The structure of the obtained materials was verified by powder X-ray diffraction and Raman spectroscopy and the catalytic activity in soot oxidation was determined by TPO-QMS and TGA. It was found that the surface promotion does not alter the metal oxide structure and leads to either enhancement (Mn, Fe) or deterioration (Co) of the catalytic activity. Simultaneously, the catalytic activity in soot combustion of the potassium structured oxides is strongly enhanced. The most active, cobalt oxide based catalyst significantly lowers the temperature of 50 % of soot conversion by *350°C comparing to the non-catalyzed process. The study allows for the establishment of rational guidelines for designing robust materials for DPF applications based on ternary metal oxides.

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“…Ceriabased catalysts are the most widely investigated [9][10][11]. Some simple transition metals or oxides also exhibit good catalytic activity and stability [12].…”

Section: Introductionmentioning

confidence: 99%

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

et al. 2016

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“…The redox properties of the Ce 3+/4+ couple and the capacity of cerium oxide to exchange oxygen with the gas phase are also behind the good catalytic performance of ceria-based materials as soot combustion catalysts, as it is discussed in the coming sections. catalysts, including pure oxides [10,11], platinum [12,13], copper [14][15][16][17][18][19], zinc [16] and cobalt [12] catalysts, perovskites [14,15,17,19], spinels [13,16], manganese catalysts with birnessite and cryptomelane structure [10,20], alkali [14,17] and alkali earth metals-containing catalysts [15,17,19] and pure and doped cerium oxides [21][22][23][24][25][26][27][28][29][30][31]. The catalysts whose results are included in Figure 3 are the most active that have been prepared of a particular composition.…”

Section: -Why Ceria Catalysts For Soot Combustion?mentioning

confidence: 99%

“…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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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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“…Intense research effort has been carried out during the last decade in order to replace Pt by cheaper active phases, cerium oxide being one of the most promising options [3][4][5]. Advances in the preparation of both pure and doped cerium oxides, including zirconium, praseodymium, lanthanum or yttrium, among other dopants in the parent oxide, have been reported for this application [3][4][5][6][7][8].…”

Section: -Introductionmentioning

confidence: 99%

Evidences of the Cerium Oxide-Catalysed DPF Regeneration in a Real Diesel Engine Exhaust

et al. 2013

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The active phase Ce 0.5 Pr 0.5 O 2 has been loaded on commercial substrates (SiC DPF and cordierite honeycomb monolith) to perform DPF regeneration experiments in the exhaust of a diesel engine. Also, a powder sample has been prepared to carry out soot combustion experiments at laboratory. Experiments performed in the real diesel exhaust demonstrated the catalytic activity of the Ce-Pr mixed oxide for the combustion of soot, lowering the DPF regeneration temperature with regard to a counterpart catalyst-free DPF. The temperature for active regeneration of the Ce 0.5 Pr 0.5 O 2 -containing DPF when the soot content is low is in the range of 500-550 ºC. When the Ce 0.5 Pr 0.5 O 2 -containing DPF is saturated with a high amount of soot, pressure drop and soot load at the filter reach equilibrium at around 360 ºC under steady state engine operation due to passive regeneration. The uncoated DPF reached this equilibrium at around 440 °C. Comparing results at real exhaust with those at laboratory allow concluding that the Ce 0.5 Pr 0.5 O 2 -catalysed soot combustion in the real exhaust is not based on the NO 2 -assisted mechanism but is most likely occurring by the active oxygen-based mechanism.

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Thermally stable ceria–zirconia catalysts for soot oxidation by O2

Cited by 143 publications

References 15 publications

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

Diesel soot combustion ceria catalysts

Evidences of the Cerium Oxide-Catalysed DPF Regeneration in a Real Diesel Engine Exhaust

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