Pr-rich cerium-zirconium-praseodymium mixed oxides for automotive exhaust emission control

Fahed, Simon; Pointecouteau, Rémy; Aouine, M.; Boreave, Antoinette; Gil, Sonia; Meille, Valérie; Bazin, Philippe; Toulemonde, Olivier; Demourgues, Alain; Daturi, Marco; Vernoux, P.

doi:10.1016/j.apcata.2022.118800

Cited by 9 publications

(5 citation statements)

References 32 publications

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“…A previous study [ 13 ] reported a negative effect of very high Pr loadings on the ceria (concerning BET surface area and pore development) when the direct calcination method was employed. In fact, recent works by Frizon et al [ 18 ] and Fahed et al [ 19 ] reported that the insertion of high Pr loadings in mixed oxides (specifically CZ-mixed oxides) significantly decreased the specific surface area. The observation of the non-correlation between S BET and average crystal size (in spherical approximation; r(nm) = 3/(ρ·S BET )), where ρ is the compound density, was attributed to the fact that the particles were not spherical and the aggregation phenomena occurred, limiting the pore size (see Table 1 ).…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…For the deepest insight, some quantitative considerations will be provided now. Considering a mean oxygen density of 21.7 µmol O·m −2 in ceria-based oxides, according to the assumptions taken by Fahed et al [ 19 ] based on other authors [ 27 ], the oxygen emitted relative to the first peak (see values in parentheses of Table 4 ) only concerns surface oxygen species (or a fraction of them) for the two mixed oxides under study. Conversely, for the case of PrO 2 , more than the theoretical oxygen surface population (even though it is small due to its very low surface area) can be desorbed in this low range of temperature, proving evidence of the very high oxygen mobility at the surface/subsurface level for this catalyst.…”

Section: Resultsmentioning

confidence: 99%

“…These values indicate the amount of energy required to remove an electron from the respective 3D orbitals of cerium (Ce) and praseodymium (Pr) atoms [24]. Overall, the segregation of dopant cations at the surface and domain boundaries of ceria is an important aspect to consider when studying or utilizing ceria-based materials, as it can have significant implications on their properties and performance in various applications [19,25] Pr cations (Pr 3+ and Pr 4+ ) are incorporated into the cerium oxide lattice (and/or partially segregated at the particle's surface), as suggested by the comparison of the Ce/Pr surface values with the nominal ones. Therefore, the presence of nano-domains with different Ce/Pr compositions (indistinguishable by XRD and/or HR-TEM) cannot be excluded for the two mixed oxides.…”

Section: Structural and Textural Parametersmentioning

confidence: 99%

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Nanostructured Pr-Rich CexPr1-xO2-δ Mixed Oxides for Diesel Soot Combustion: Importance of Oxygen Lability

Mekki,

Grzybek,

Kotarba

et al. 2024

Nanomaterials

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Soot combustion experiments with 5%O2/He were conducted using model soot, and four distinct compositions of CexPr1-xO2-δ oxides of varying nominal cerium compositions (x = 0, 0.2, 0.3, and 1) were prepared. The catalyst samples were comprehensively characterized using techniques such as XRD, Raman spectroscopy, HR-TEM, N2 adsorption at −196 °C, XPS, O2-TPD, H2-TPR, and work function measurements. The Pr-rich compositions, ranging from Ce0.3Pr0.7O2-δ to PrO2-δ, resulted in a significant increase in the total evolved O2 amounts and enhanced catalyst reducibility. However, a decrease in the textural properties of the catalysts was noted, which was particularly important for the pure praseodymia under the synthesis route conducted. The catalytic activity was investigated under the two following contact modes of mixing between soot and catalyst: loose and tight. The results revealed that the catalytic performance is associated with the surface contact in tight contact mode and with the combination of surface/subsurface/bulk oxygen mobility and the BET surface area in loose contact mode. Notably, the temperatures estimated at 10% and 50% of the conversion (T10 and T50) parameters were achieved at much lower temperatures than the uncatalyzed soot combustion, even under loose contact conditions. Specifically, the 50% conversion was achieved at 511 °C and 538 °C for Ce0.3Pr0.7O2 and Ce0.2Pr0.8O2, respectively. While no direct correlation between catalytic activity and work function was observed, a significant relationship emerges between work function values and the formation of oxygen vacancies, whatever the conditions used for these measurements. On the other hand, the ability to generate a high population of oxygen vacancies at low temperatures, rather than the direct activation of gas-phase O2, influences the catalytic performance of Pr-doped ceria catalysts, highlighting the importance of surface/subsurface oxygen vacancy generation, which was the parameter that showed a better correlation with the catalytic activity, whatever the soot conversion value or the mode of contact considered.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Structural and Textural Parametersmentioning

confidence: 99%

See 2 more Smart Citations

Nanostructured Pr-Rich CexPr1-xO2-δ Mixed Oxides for Diesel Soot Combustion: Importance of Oxygen Lability

Mekki,

Grzybek,

Kotarba

et al. 2024

Nanomaterials

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show abstract

“…In the latter case, the fluorite structure of ceria forms a solid solution having the composition of Ce x Pr 1−x O 2−δ for 0.3 < x < 1. A similar strategy has been used with oxide solid solutions containing Ce, Pr, and Zr, wherein the presence of both Pr 3+ and Pr 4+ were observed [113]. This, combined with the multivalence of cerium and praseodymium, produces structural oxygen vacancies that can be accurately tuned by the presence of praseodymium to promote lattice oxygen mobility within the framework of the Mars-van Krevelen mechanism.…”

Section: Soot and Particulate Oxidation-diesel Engine Exhaust Emissio...mentioning

confidence: 99%

The Emergence of the Ubiquity of Cerium in Heterogeneous Oxidation Catalysis Science and Technology

Brazdil

2022

Catalysts

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Research into the incorporation of cerium into a diverse range of catalyst systems for a wide spectrum of process chemistries has expanded rapidly. This has been evidenced since about 1980 in the increasing number of both scientific research journals and patent publications that address the application of cerium as a component of a multi-metal oxide system and as a support material for metal catalysts. This review chronicles both the applied and fundamental research into cerium-containing oxide catalysts where cerium’s redox activity confers enhanced and new catalytic functionality. Application areas of cerium-containing catalysts include selective oxidation, combustion, NOx remediation, and the production of sustainable chemicals and materials via bio-based feedstocks, among others. The newfound interest in cerium-containing catalysts stems from the benefits achieved by cerium’s inclusion, which include selectivity, activity, and stability. These benefits arise because of cerium’s unique combination of chemical and thermal stability, its redox active properties, its ability to stabilize defect structures in multicomponent oxides, and its propensity to stabilize catalytically optimal oxidation states of other multivalent elements. This review surveys the origins and some of the current directions in the research and application of cerium oxide-based catalysts.

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On the Selection of Catalysts’ Support with High Oxygen Delivery Capacity for DRM Application: Interest of Praseodymium as Dopant of Ceria

Herráez-Santos,

Goma-Jiménez,

Yeste-Sigüenza

et al. 2024

Top Catal

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In the present work, a series of supports with varying compositions (ranging from pure CeO2 to pure PrO2-y) was designed to investigate their ability to release oxygen (with the concomitant formation of oxygen vacancies) under diverse reducing atmospheres: hydrogen (H2), helium (He), and in the presence of a carbonaceous substance that mimics eventual carbon deposits formed under practical reaction conditions (DRM). Oxygen vacancies were generated effectively in all three atmospheres (following the order He < H2 < carbon material). With regard to the influence of the composition, the capability to generate oxygen vacancies clearly increased with the Pr content, for whatever the conditions tested. Notably, the non-stoichiometry obtained with the support of pure praseodymia in both inert and reducing atmospheres is very remarkable, as it approaches the maximum non-stoichiometry value of the well-established theoretical Bevan cluster. This leads to consider this formulation as a very promising support for applications in catalysis and other fields where oxygen vacancies play a crucial role. Dry Reforming of Methane requires catalytic supports that possess highly mobile oxygen, enabling it to actively participate in the reactions step involved or potentially gasify undesirable carbon deposits generated during parallel reactions. Consequently, designing and elucidating the behavior of ceria-praseodymium-based supports with high reducibility and generation of oxygen vacancies (oxygen storage and release capacity) holds particular relevance in this context. Actually, the very preliminary results comparing two counterpart formulations (5%Ni/PrO2-y versus 5%Ni/Al2O3) already confirm the suitability of the choice of pure praseodymia in terms of activity, stability and very high selectivity towards H2 and CO, reaching a very close value to the ideal H2/CO ratio of 1.

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Pr-rich cerium-zirconium-praseodymium mixed oxides for automotive exhaust emission control

Cited by 9 publications

References 32 publications

Nanostructured Pr-Rich CexPr1-xO2-δ Mixed Oxides for Diesel Soot Combustion: Importance of Oxygen Lability

Nanostructured Pr-Rich CexPr1-xO2-δ Mixed Oxides for Diesel Soot Combustion: Importance of Oxygen Lability

The Emergence of the Ubiquity of Cerium in Heterogeneous Oxidation Catalysis Science and Technology

On the Selection of Catalysts’ Support with High Oxygen Delivery Capacity for DRM Application: Interest of Praseodymium as Dopant of Ceria

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