Insights into the redox properties of ceria-based oxides and their implications in catalysis

Aneggi, Eleonora; Boaro, Marta; Leitenburg, Carla de; Dolcetti, Giuliano; Trovarelli, Alessandro

doi:10.1016/j.jallcom.2004.12.113

Cited by 389 publications

(201 citation statements)

References 43 publications

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“…According to the catalysts screening compiled in Figure 3, ceria-base catalysts are among the most effective for soot combustion, and this has promoted an intense research activity during the last years on different ceria-based catalysts for Diesel soot combustion like, among others, ceria doped with Zr [25,[35][36][37][38], Fe [36,39], La [21,36,38], Pr [21,36], Sm [21,36], Tb [36], Cu [40][41][42], Mn [40,43], and Mo [44] and different compounds supported on ceria such as K/Ceria [34,45], Co/Ceria [45][46][47][48][49], Ba,K/Ceria [50,51], Cu-V/Ceria [52], Ag/Ceria [53,54] or Cu/Ceria [55].…”

Section: -Why Ceria Catalysts For Soot Combustion?mentioning

confidence: 99%

Diesel soot combustion ceria catalysts

Bueno‐López

2014

Applied Catalysis B: Environmental

395

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: -Why Ceria Catalysts For Soot Combustion?mentioning

confidence: 99%

Diesel soot combustion ceria catalysts

Bueno‐López

2014

Applied Catalysis B: Environmental

395

243

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“…The use of OSC components was first proposed by Ghandi et al in 1976. [4] Since the pioneering works of Yao and Yu Yao [2] and of Su et al, [5,6] many studies have been devoted to improving knowledge of the kinetics of OSC [7][8][9] and of the mechanisms implicated in surface and bulk oxygen mobility in ceria and related compounds, [10][11][12][13][14] with a special insight into CeZrO x oxides. [15][16][17][18][19] Oxygen diffusivity in these materials can be measured by 18 O/ 16 O isotopic exchange, [20][21][22] while oxygen species (e.g., superoxides, peroxides) that might be involved in the diffusion process can be investigated by electron spin resonance (ESR) [23][24][25][26][27] or FTIR.…”

Section: Introductionmentioning

confidence: 99%

Ceria‐Based Solid Catalysts for Organic Chemistry

Vivier¹,

Duprez²

2010

ChemSusChem

362

244

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Ceria has been the subject of thorough investigations, mainly because of its use as an active component of catalytic converters for the treatment of exhaust gases. However, ceria‐based catalysts have also been developed for different applications in organic chemistry. The redox and acid–base properties of ceria, either alone or in the presence of transition metals, are important parameters that allow to activate complex organic molecules and to selectively orient their transformation. Pure ceria is used in several organic reactions, such as the dehydration of alcohols, the alkylation of aromatic compounds, ketone formation, and aldolization, and in redox reactions. Ceria‐supported metal catalysts allow the hydrogenation of many unsaturated compounds. They can also be used for coupling or ring‐opening reactions. Cerium atoms can be added as dopants to catalytic system or impregnated onto zeolites and mesoporous catalyst materials to improve their performances. This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium‐based catalysts very effective for a broad range of organic reactions.

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“…Além dessa função reguladora de oxigênio, a presença de CeO 2 também evita que os catalisadores CTV percam a eficiência em altas temperaturas, pois ela inibe/ desloca as transições de fase de outros materiais como, por ex., do suporte de alumina 16,19,22 . A adição de íons lantânio, zircônia, BaO e SiO 2 à estrutura do CeO 2 pode contribuir para aumentar a quantidade de defeitos na rede cristalina e proporcionar ao CeO 2 maior capacidade para armazenar oxigênio 22,[27][28][29][30][31][32][33]35,38,[42][43][44][45] , melhorando o desempenho dos catalisadores CTV. Atualmente, o uso de CeO 2 neste tipo de catalisador é uma das principais aplicações tecnológicas deste elemento e tem consumido a maior parte do cério produzido mundialmente 4,6 .…”

Section: Catáliseunclassified

Cério: propriedades catalíticas, aplicações tecnológicas e ambientais

Martins¹,

Hewer²,

Freire³

2007

Quím. Nova

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Recebido em 13/11/06; aceito em 2/3/07; publicado na web em 25/10/07 CERIUM: CATALYTIC PROPERTIES, TECHNOLOGICAL AND ENVIRONMENTAL APPLICATIONS. Cerium based-compounds have great importance in a wide range of technological applications, such as: fuel cell devices development; metallurgic processes, petroleum refining; glass and ceramic production. Recently, its catalytic properties have been also explored for environmental applications, especially those to prevent or to control atmospheric and water pollution. Subjects covered in this work include a brief description of the fundaments of cerium catalytic properties and some relevant technological applications. Special attention is given to its photocatalytic activity and its ability to degrade pollutants. Recent results and future prospect about these applications are also evaluated.Keywords: lanthanide; catalysis; heterogeneous photocatalyst. INTRODUÇÃOO cério, elemento químico de número atômico 58, é um dos 15 elementos classificados como lantanídeos (La ao Lu), que juntamente com Sc e Y formam a família das Terras Raras. Cério é o mais abundante das Terras Raras. Sua abundância na crosta terrestre é da ordem de 60 ppm, o que o torna o 26º elemento em freqüência de ocorrência, sendo quase tão abundante quanto cobre e níquel. Apesar de o cério ser o lantanídeo de maior ocorrência, é encontrado em muitos minerais somente em níveis traço, sendo a bastinasita e monasita os minerais mais importantes como fonte de cério e suprem a maior parte da demanda mundial deste elemento [1][2][3][4][5][6] . Estes dois minerais, dependo da localidade dos depósitos, possuem cerca de 65-70% (bastinasita) e 49-74% (monasita) de terras céricas (La-Gd), sendo que, considerando-se a porcentagem de lantanídeos na bastinasita e monasita como 100%, a quantidade de CeO 2 corresponde a aproximadamente 49 e 47%, respectivamente 5 .O cério, que tem a configuração eletrônica [Xe]4f 1 5d 1 s 2 , é muito eletropositivo e suas interações são predominantemente iônicas devido ao baixo potencial de ionização (3,49 kJ mol -1 ) para a remoção dos três primeiros elétrons 1-3 . Assim como outros lantanídeos, o estado de oxidação mais estável deste elemento é o (+III). O cério trivalente tem propriedades semelhantes a outros íons lantanídeos com mesmo estado de oxidação 3,5 , com exceção da sua fácil oxidação para Ce 4+ e instabilidade em ar e água. Seus sais, em geral, mais estáveis que os de Ce 4+ , são pouco hidrolisáveis e muito utilizados como precursores para vários compostos de cério [1][2][3][4][5][6] . Diferentemente dos demais elementos dessa classe, o estado de oxidação (+IV) também é estável, principalmente em virtude da configuração eletrônica semelhante à de um gás nobre ([Xe]4f 0 ). Este elemento é o único lantanídeo, no estado tetravalente, estável em solução aquosa, porém a influência da carga maior e tamanho iônico menor faz com que os sais do íon Ce 4+ sejam hidrolisados em soluções aquosas com mais facilidade que o íon Ce 3+ e, em conseqüência disso, estas soluções são fortemente ác...

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Insights into the redox properties of ceria-based oxides and their implications in catalysis

Cited by 389 publications

References 43 publications

Diesel soot combustion ceria catalysts

Diesel soot combustion ceria catalysts

Ceria‐Based Solid Catalysts for Organic Chemistry

Cério: propriedades catalíticas, aplicações tecnológicas e ambientais

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