Red–ox properties and phase composition of CeO2–ZrO2 and Y2O3–CeO2–ZrO2 solid solutions

Markaryan, G. L.; Ikryannikova, Larissa N.; Muravieva, G. P.; Turakulova, A. O.; Kostyuk, B. G.; Lunina, E. V.; Лунін, В. В.; Zhilinskaya, E. A.; Aboukaı̈s, Antoine

doi:10.1016/s0927-7757(98)00574-3

Cited by 84 publications

(41 citation statements)

References 19 publications

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Section: -Doped Ceria Better Than Barementioning

confidence: 99%

“…In these profiles, H 2 consumption must be attributed to the reduction of Ce 4+ to Ce 3+ , because La 3+ is a nonreducible cation. The H 2 reduction profile of pure ceria calcined at mild temperature (600 ºC in the example of Figure 14) typically presents two peaks, one of them at around 450 ºC, which is attributed to surface reduction, and another one at around 850 ºC, which is assigned to bulk reduction [72]. As observed in Figure 14, the surface reduction peak of pure ceria diminishes with calcination temperature duo to sintering, that is, because of crystal growth and surface area decrease.…”

mentioning

confidence: 99%

“…Typically, doped cerias do not show the surface and bulk reduction peaks but a broad band in a very wide range of temperature. This type of profile is a consequence of the high mobility of oxygen within the lattice [72], since once the surface oxygen is reduced bulk oxygen migrates rapidly to surface and the reduction continues.The effect of high temperature aging on doped cerias reducibility is not as dramatic as in bare ceria, as observed in Figure 14 for Ce 0.9 La 0.1 O 2 . The doped ceria catalyst keeps certain surface reducibility and good oxygen mobility between bulk and surface even after 1000 ºC calcination.…”

mentioning

confidence: 99%

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Diesel soot combustion ceria catalysts

Bueno‐López

2014

Applied Catalysis B: Environmental

392

243

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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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Section: -Doped Ceria Better Than Barementioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Diesel soot combustion ceria catalysts

Bueno‐López

2014

Applied Catalysis B: Environmental

392

243

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“…In literature it was reported one or two TPR peaks for pure CeO 2 depending on the temperature range where the TPR experiment is carried out. 23,28 Tang et al 23 have reported one peak around 430 °C, whereas Markaryan et al 28 have informed two peaks. The first one at 500 ºC was assigned to the surface Ce +4 reduction, and the second one at about 850 ºC was attributed to reduction of bulk Ce +4 .…”

Section: -26mentioning

confidence: 99%

Methanol steam reforming over Cu/CeO2 catalysts: influence of zinc addition

Tonelli¹,

Gorriz²,

Arrúa³

et al. 2011

Quím. Nova

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Recebido em 20/10/10; aceito em 17/3/11; publicado na web em 5/5/11Methanol steam reforming reaction was studied over Cu(5 wt.%)/CeO 2 with and without the presence of Zn. The Zn addition decreased the Cu +2 reducibility and increased the oxygen mobility of ceria. The main products were CO 2 and H 2 with small amount of CO. Selectivity to CO decreased with the Zn addition and it was lower at lower reaction temperatures and lower space velocities. At 230 ºC and W/F MeOH = 648 g min mol -1 selectivities to H 2 and to CO 2 were 100% on Zn/Cu/Ce. The catalytic results indicated that CO was mainly a secondary product formed from reverse water gas shift reaction.

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“…The H2-TPR profiles of doped ceria typically consist of a broad band centered around 500-550 ºC with a shoulder or tail at higher temperatures in some cases [34,35], and all profiles of Figure 5 show this shape. In this type of experiments the catalyst surface is reduced first at mild temperature, and once surface oxygen is depleted bulk oxygen is consumed.…”

Section: Catalysts Reducibility Studied By H 2 -Tprmentioning

confidence: 91%

Effect of the CeZrNd mixed oxide synthesis method in the catalytic combustion of soot

2015

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Ce0.64Zr0.27Nd0.09O δ mixed oxides have been prepared by three different methods (nitrates calcination, coprecipitation and microemulsion), characterized by N2 adsortion, XRD, H2-TPR, Raman spectroscopy and XPS, and tested for soot combustion in NOx/O2. The catalyst prepared by microemulsion method is the most active one, which is related to its high surface area (147 m 2 /g) and low crystallite size (6 nm), and the lowest activity was obtained with the catalyst prepared by coprecipitation (74 m 2 /g; 9 nm). The catalyst prepared by nitrates precursors calcination is slightly less active to that prepared by microemulsion but the synthesis procedure is very straightforward and surfactants or other chemicals are not required, being very convenient for scaling up and practical utilization. The high activity of the catalyst prepared by nitrates calcination can be attributed to the better introduction of Nd cations into the parent ceria framework than on catalysts prepared by coprecipitaion and microemulsion, which promotes the creation of more oxygen vacancies.

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Red–ox properties and phase composition of CeO2–ZrO2 and Y2O3–CeO2–ZrO2 solid solutions

Cited by 84 publications

References 19 publications

Diesel soot combustion ceria catalysts

Diesel soot combustion ceria catalysts

Methanol steam reforming over Cu/CeO2 catalysts: influence of zinc addition

Effect of the CeZrNd mixed oxide synthesis method in the catalytic combustion of soot

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