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Journal ArticleDOI

Soot oxidation via CuO doped CeO2 catalysts prepared using coprecipitation and citrate acid complex-combustion synthesis

01 Aug 2010-Catalysis Today (Elsevier)-Vol. 153, Iss: 3, pp 125-132
TL;DR: In this paper, a possible pathway of soot oxidation over Cu0.05Ce0.95-CA is proposed, based on the relationship of the performance and physicochemical features of catalysts, which pathway follows the mechanism associated with redox couple and oxygen spill over effect.
About: This article is published in Catalysis Today.The article was published on 2010-08-01. It has received 62 citations till now. The article focuses on the topics: Coprecipitation & Redox.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a series of MnOx-CeO2 catalysts with various Mn/(Mn+Ce) molar ratios were synthesized with citric acid complex method for O-vacancy study in soot catalytic combustion.
Abstract: Oxygen vacancy (O-vacancy) is essential in catalytic oxidation but little is known about its insight. Herein, a series of MnOx-CeO2 catalysts with various Mn/(Mn + Ce) molar ratios were synthesized with citric acid complex method for O-vacancy study in soot catalytic combustion. The samples were characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption, O2-temperature programmed desorption (O2-TPD), H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and in situ Raman spectroscopy. It has been shown that MnOx(0.4)-CeO2 catalyst presented more O-vacancies, thus exhibiting the highest catalytic activities and redox properties. With the utilization of in situ Raman, two types of O-vacancies, including Frenkel-type oxygen vacancy (F OV) and intrinsic oxygen vacancy (I OV), were clarified. Furthermore, the transform relation between F OV and I OV was found. Those two types of O-vacancies favored to the migration and transformation of active species, enhancing further the oxidation-reduction cycle and the catalytic activity for soot oxidation. In addition, Mn4+/Mn3+(Mn2+), Olatt, Osur and Ce4+/Ce3+ were believed to play important roles in soot oxidation. Finally, evolution of O-vacancies was proposed, which is of significance for soot catalytic oxidation.

355 citations

Journal ArticleDOI
TL;DR: In this paper, two different techniques (precipitation with ammonia and hydrothermal synthesis with ethylene glycol, both followed by autoclave aging) were employed for the synthesis of CeO2-ZrO2 mixed oxides on a 80-20-wt.% basis.
Abstract: Two different techniques (precipitation with ammonia and hydrothermal synthesis with ethylene glycol, both followed by autoclave aging) were employed for the synthesis of CeO2–ZrO2 mixed oxides on a 80–20 wt.% basis. Aging parameters, such as time and temperature, were systematically investigated in order to determine the optimal conditions to maintain high surface area and oxygen mobility of the prepared solids. Different loadings of nickel and cobalt (3, 6, 12 and 18 wt.%) were subsequently deposited via homogeneous deposition precipitation method. Calcined bimetallic catalysts were characterized by N2 adsorption–desorption, XRD, H2-TPR, TPO-TGA and FE-SEM methods, and tested for activity, selectivity and stability in the reforming of equimolar CH4–CO2 gas streams. During temperature programmed methane reforming tests, syngas with a H2/CO ratio between 0.3 and 0.79 was produced. Growth of carbon nanofilaments over the catalyst does not lead to deactivation, but can cause reactor plugging. Two conditions are vital and must be fulfilled simultaneously to avoid excessive carbon deposition: strong interaction between the NiCo bimetallic particles and CeZr support, which exists only at NiCo loadings up to 6 wt.%, as well as high oxygen mobility within the highly defective CeO2–ZrO2 crystalline lattice for timely carbon oxidation.

282 citations

Journal ArticleDOI
TL;DR: In this paper, the authors focus on the measurement of oxygen storage capacity (OSC), the effect of influencing factors, and the role of OSC in typical reactions that occur in automotive emission control like oxidation, NO reduction, water gas shift, and reforming reactions.

189 citations

Journal ArticleDOI
TL;DR: Based on the comparison of the activity, durability and cost-efficiency of different soot oxidation catalysts, four kinds of applicable ceria-based catalysts have been screened out, which are: (1) CexZr1-xO2 catalyst with high cerium content (x)

168 citations

Journal ArticleDOI
TL;DR: In this paper, surface species and oxygen vacancies were studied in MnO x (0.4)-CeO 2 catalysts for repeated soot oxidation in a 10% O 2 /Ar gas flow and showed favorable activity and satisfactory durability.
Abstract: Surface species and oxygen vacancies were studied in MnO x (0.4)-CeO 2 toward repeated soot oxidation. MnO x (0.4)-CeO 2 catalysts prepared by the citric acid complex method were repeatedly used in a 10% O 2 /Ar gas flow and showed favorable activity and satisfactory durability toward soot oxidation. X-ray diffraction (XRD), N 2 adsorption/desorption, Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and in situ visible/UV Raman characterization methods were utilized to investigate the structural features of fresh and reused catalysts. The irreversible conversion of high valence manganese species as well as the reduction of Frenkel-type oxygen vacancies and lattice oxygen could be clearly observed in the reused samples, which were associated with the slight deactivation. Spectators and participators were two existing forms of Frenkel-type oxygen vacancies. It was noteworthy that the participators almost fully regenerated after each reaction cycle, which ensured the ability to activate O latt in repeated soot oxidation process. Therefore, the catalysts maintained favorable activity and satisfactory durability, which was mainly because the relatively stable level of participators.

140 citations

References
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Journal ArticleDOI
TL;DR: A survey of the use of cerium oxide and CeO2-containing materials as oxidation and reduction catalysts is presented in this paper, with a special focus on catalytic interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide.
Abstract: Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

3,077 citations

Journal ArticleDOI
TL;DR: In this article, a series of La 3+ -doped CeO 2 catalysts (La 3+ loading between 5 and 50 wt%) have been studied for soot oxidation by O 2.

379 citations

Journal ArticleDOI
TL;DR: In this paper, rare-earth ion doping has been used to increase the surface area of rare earth-modified ceria (CeO 2 ) and rare earth modified ceria(CeReO x with Re-=La, Pr, Sm, Y) catalysts.
Abstract: Ceria (CeO 2 ) and rare-earth modified ceria (CeReO x with Re = La, Pr, Sm, Y) catalysts are prepared by nitrate precursor calcination and are characterised by BET surface area, XRD, H 2 -TPR, and Raman spectroscopy. Potential of the catalysts in the soot oxidation is evaluated in TGA with a feed gas containing O 2 . Seven hundred degree Celsius calcination leads to a decrease in the surface area of the rare-earth modified CeO 2 compared with CeO 2 . However, an increase in the meso/macro pore volume, an important parameter for the soot oxidation with O 2 , is observed. Rare-earth ion doping led to the stabilisation of the CeO 2 surface area when calcined at 1000 °C. XRD, H 2 -TPR, and Raman characterisation show a solid solution formation in most of the mixed oxide catalysts. Surface segregation of dopant and even separate phases, in CeSmO x and CeYO x catalysts, are, however, observed. CePrO x and CeLaO x catalysts show superior soot oxidation activity (100% soot oxidation below 550 °C) compared with CeSmO x , CeYO x , and CeO 2 . The improved soot oxidation activity of rare-earth doped CeO 2 catalysts with O 2 can be correlated with the increased meso/micro pore volume and stabilisation of external surface area. The segregation of the phases and the enrichment of the catalyst surface with unreducible dopant decrease the intrinsic soot oxidation activity of the potential CeO 2 catalytic sites. Doping CeO 2 with a reducible ion such as Pr 4+/3+ shows an increase in the soot oxidation. However, the ease of catalyst reduction and the bulk oxygen-storage capacity is not a critical parameter in the determination of the soot oxidation activity. During the soot oxidation with O 2 , the function of the catalyst is to increase the ‘active oxygen’ transfer to the soot surface, but it does not change the rate-determining step, as evident from the unchanged apparent activation energy (around 150 kJ mol −1 ), for the catalysed and un-catalysed soot oxidation. Spill over of oxygen on the soot surface and its subsequent adsorption at the active carbon sites is an important intermediate step in the soot oxidation mechanism.

288 citations

Journal ArticleDOI
TL;DR: In this paper, the authors have demonstrated the reasons why CeO2 becomes an active catalyst for diesel particulate (soot) abatement, which attracts recent worldwide attention in the development of clean diesel automobiles.
Abstract: The present work has demonstrated the reasons why CeO2 becomes an active catalyst for diesel particulate (soot) abatement, which attracts recent worldwide attention in the development of clean diesel automobiles. Four typical fluorite-type oxides, CeO2, ZrO2, Pr6O11, and a CeO2−ZrO2 solid solution have been studied as model catalysts for soot oxidation in conjunction with the redox property and the reactivity of solid oxygen species. It was found that the redox property measured in terms of oxygen storage/release capacity was not the sole determining factor for the observed catalytic activity decreasing in the order of CeO2 ≫ Pr6O11 ≈ CeO2−ZrO2 > ZrO2. The reactivity of oxygen species involved in the redox cycles would rather be important. The ESR measurement showed that admission of O2 to the pre-reduced CeO2 surface generated superoxide ions (O2−). Such reactive oxygen species were less abundant on CeO2−ZrO2 and were not detected on ZrO2 and Pr6O11. The labeled and unlabeled O2 pulse experiments demonst...

287 citations

Journal ArticleDOI
TL;DR: In this article, the structure and chemical environment of Cu in Cu/CeO2 catalysts synthesized by the solution combustion method have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, Xray photoelectron spectroscope (XPS), cyclic voltammetry (CV), and extended Xray fine structure (EXAFS).
Abstract: The structure and chemical environment of Cu in Cu/CeO2 catalysts synthesized by the solution combustion method have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and extended X-ray fine structure (EXAFS) spectroscopy. High-resolution XRD studies of 3 and 5 atom % Cu/CeO2 do not show CuO lines in their respective patterns. The structure could be refined for the composition Ce1-xCuxO2-δ (x = 0.03 and 0.05; δ ∼ 0.13 and 0.16) in the fluorite structure with 5−8% oxide ion vacancy. High-resolution TEM did not show CuO particles in 5 atom % Cu/CeO2. EPR as well as XPS studies confirm the presence of Cu2+ species in the CeO2 matrix. Redox potentials of Cu species in the CeO2 matrix are lower than those in CuO. EXAFS investigations of these catalysts show an average coordination number of 3 around the Cu2+ ion in the first shell at a distance of 1.96 A, indi...

278 citations