Pr-Doped CeO<sub>2</sub> Catalyst in the Prins Condensation–Hydrolysis Reaction: Are All of the Defect Sites Catalytically Active?

Zhang, Zhixin; Wang, Yehong; Lü, Jianmin; Zhang, Jian; Li, Mingrun; Liu, Xuebin; Wang, Feng

doi:10.1021/acscatal.7b04500

Cited by 67 publications

(63 citation statements)

References 73 publications

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“…It is commonly known that the catalytic reaction takes place at defect sites of these oxide catalysts . However, it is not always found a monotonous relation between the catalytic performance and the concentration of a certain kind of defect sites, such as oxygen vacancies, lattice distortion and defect generated Lewis acid/base sites, as well as metastable valence states of cations …”

Section: Introductionmentioning

confidence: 99%

Asymmetric Oxygen Vacancies: the Intrinsic Redox Active Sites in Metal Oxide Catalysts

et al. 2019

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stability in many important reactions, [1] especially in some redox reactions, such as CO oxidation, [2] water-gas shift (WGS) reaction, [3] selective catalytic reduction of NO x , [4] oxidation of volatile organic compounds (VOCs), [5] and soot combustion. [6,7] It is commonly known that the catalytic reaction takes place at defect sites of these oxide catalysts. [8] However, it is not always found a monotonous relation between the catalytic performance and the concentration of a certain kind of defect sites, such as oxygen vacancies, [9,10] lattice distortion [11] and defect generated Lewis acid/base sites, [12,13] as well as metastable valence states of cations. [14] As discussed by McFarland and Metiu, [15] heterogeneous catalytic reactions are run under steady-state conditions instead of at equilibrium. It is difficult to accurately describe the catalytic performance of oxide catalysts using the property parameters of as-prepared catalysts, which are more likely to be in thermodynamic equilibrium during the preparation process. For example, according to many reports, the redox properties of catalysts were believed to relate to the amount of oxygen vacancies (regarded as active sites) in oxide catalysts. However, the steady-state concentration of oxygen vacancies is related to the rate of vacancy formation and that of vacancy vanishing. In other words, a real active oxygen vacancy should have high abilities of adsorbing the reactant molecules and desorbing the product molecules, allowing molecules easy come, easy go. To keep a balance of these two opposite abilities, the local environment of the oxygen vacancy plays an important role.It has been well accepted that doping of low-valence dopants in oxides can create oxygen vacancies due to a charge compensation effect, [16,17] accompanied by improved oxygen activation ability, which is usually considered as the key factor in promoting catalytic activity for redox reactions. However, when the oxides are doped by same-valence or high-valence dopants, the effect of doping on their catalytic performance will become much more complicated. Fortunately, for most oxidation reactions catalyzed by metal oxides, the lattice oxygen atoms at/near the surface of oxides are the active species based on a generally accepted Mars− van Krevelen (MvK) mechanism. [18] Therefore, the bonding situations of these surface oxygen atoms should be the key factors affecting the catalytic performance.In the last few years, researchers have paid more attention to the chemical environment of oxygen vacancies, including To identify the intrinsic active sites in oxides or oxide supported catalysts is a research frontier in the fields of heterogeneous catalysis and material science. In particular, the role of oxygen vacancies on the redox properties of oxide catalysts is still not fully understood. Herein, some relevant research dealing with M 1 -O-M 2 or M 1 -□-M 2 linkages as active sites in mixed oxides, in oxide supported single-atom catalysts, and at metal/oxide interfaces of oxide supporte...

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Section: Introductionmentioning

confidence: 99%

Asymmetric Oxygen Vacancies: the Intrinsic Redox Active Sites in Metal Oxide Catalysts

et al. 2019

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“…The peak around 460 cm −1 was very close to the F 2g position of pure CeO 2 (465 cm −1 ) with little migration, indicating only a small part of Mg dopant has entered into CeO 2 lattice. Given that cubic MgO has no evident Raman activity, the peak around 600 cm −1 may be attributed to the lattice distortion (MO 8 ‐type complexes) of Ce 0.5 Mg 0.5 O x ‐500 52,53 . After increasing dopant species from 1 to 2, the peak of 460 cm −1 shifted to a lower wavenumber (~440 cm −1 ), which demonstrated that there were increased dopant concentration in the Ce 0.5 Cu 0.25 Mg 0.25 O x ‐500.…”

Section: Resultsmentioning

confidence: 99%

“…For CeO 2 ‐based material, the F 2g symmetric breathing mode of the O atoms around a Ce cation is dependent on the lattice structure of CeO 2 52 . Normally, doped cations smaller than Ce (IV) would cause the peak left shifting to a lower wavenumber, while higher doping level would enlarge this trend 52,53 . As for Ce 0.5 Mg 0.5 O x ‐500, a main peak located at 460 cm −1 (the F 2g mode vibration), while another peak around 600 cm −1 can also be observed.…”

Section: Resultsmentioning

confidence: 99%

Entropy‐stabilized metal‐CeO_x solid solutions for catalytic combustion of volatile organic compounds

et al. 2020

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Doped Ceria with abundant oxygen vacancies exhibits enhanced performance in heterogeneous oxidation. In principle, doping 50 mol% divalent cations (such as: Cu2+, Zn2+, and Mg2+) into CeO2 lattice would produce an exceptional catalyst with maximum active oxygen species. However, the huge size gap between Ce (IV) and divalent metal cations obstructs its synthesis. Here, we utilize the theory of increasing configurational entropy with five metal dopants to lower the Gibbs‐free energy, and successfully incorporate 50 mol% divalent metal cations into CeO2 lattice. This unique doping environment endows Ce0.5Zn0.1Co0.1Mg0.1Ni0.1Cu0.1Ox two features: (a) Abundant active oxygen species for excellent performance in volatile organic compounds catalytic oxidation; (b) Bring multi reactive sites, which enable the simultaneous combustion of carbon monoxide, propylene and toluene. Moreover, the increased entropy value makes Ce0.5Zn0.1Co0.1Mg0.1Ni0.1Cu0.1Ox an ultra‐stable catalyst in both thermal and hydrothermal conditions (e.g., Working >200 hr in water‐resistance experiment).

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“…S1a †). The diffraction peaks at 2q ¼ 28.7 , 33.2 , 47.5 , and 55.6 were corresponded to the crystal planes (111), (200), (220), and (311) of CeO 2 with the uorite-type structure 59 (Fig. S1b †).…”

Section: Resultsmentioning

confidence: 99%

Capping experiments reveal multiple surface active sites in CeO₂ and their cooperative catalysis

et al. 2019

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Pr-Doped CeO₂ Catalyst in the Prins Condensation–Hydrolysis Reaction: Are All of the Defect Sites Catalytically Active?

Cited by 67 publications

References 73 publications

Asymmetric Oxygen Vacancies: the Intrinsic Redox Active Sites in Metal Oxide Catalysts

Asymmetric Oxygen Vacancies: the Intrinsic Redox Active Sites in Metal Oxide Catalysts

Entropy‐stabilized metal‐CeO_x solid solutions for catalytic combustion of volatile organic compounds

Capping experiments reveal multiple surface active sites in CeO₂ and their cooperative catalysis

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Pr-Doped CeO2 Catalyst in the Prins Condensation–Hydrolysis Reaction: Are All of the Defect Sites Catalytically Active?

Cited by 67 publications

References 73 publications

Asymmetric Oxygen Vacancies: the Intrinsic Redox Active Sites in Metal Oxide Catalysts

Asymmetric Oxygen Vacancies: the Intrinsic Redox Active Sites in Metal Oxide Catalysts

Entropy‐stabilized metal‐CeOx solid solutions for catalytic combustion of volatile organic compounds

Capping experiments reveal multiple surface active sites in CeO2 and their cooperative catalysis

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Product

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Pr-Doped CeO₂ Catalyst in the Prins Condensation–Hydrolysis Reaction: Are All of the Defect Sites Catalytically Active?

Entropy‐stabilized metal‐CeO_x solid solutions for catalytic combustion of volatile organic compounds

Capping experiments reveal multiple surface active sites in CeO₂ and their cooperative catalysis