Reduction effect on cerium oxide catalysts doped with copper(<scp>II</scp>) ions. An electron paramagnetic resonance study

Kais, A. Abou; Bennani, Abdelrhani; Aissi, C. F.; Wrobel, G.; Guelton, M.

doi:10.1039/ft9928801321

Cited by 32 publications

(16 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This indicates partial reduction of monomeric Cu 2+ to Cu + while a certain part of Cu 2+ remains unreduced, in agreement with the results of Kais et al, who found that complete reduction of Cu 2+ in CeO 2 took place only above 500 °C. 111 Similar EPR spectra were measured for the Cat2 catalyst (Figure 10b).…”

Section: Table 1 Elemental Composition (Icp-oes) and Textural Charact...supporting

confidence: 71%

“…Additional lines with a hyperfine structure (hfs) sextet also observed in the signal of the bare support can be assigned to a tiny Mn 2+ impurity in this support. For the Cu-containing catalysts, two partly superimposed Cu 2+ EPR signals (labeled as A 1 and A 2 in Figure 9 111 It is known that the transition from the tetragonally distorted octahedral coordination to a square pyramidal and further to a square planar environment leads to a decrease in g || and a corresponding increase in A || due to an increase in the tetragonal distortion. 112,113 Therefore, the signal A 2 (g || = 2.300, g ⊥ = 2.058, A || = 288 MHz, and A ⊥ = 60 MHz) is related to isolated Cu 2+ ions in surface substitutional sites with a square-pyramidal symmetry.…”

Section: Table 1 Elemental Composition (Icp-oes) and Textural Charact...mentioning

confidence: 99%

“…112,113 Therefore, the signal A 2 (g || = 2.300, g ⊥ = 2.058, A || = 288 MHz, and A ⊥ = 60 MHz) is related to isolated Cu 2+ ions in surface substitutional sites with a square-pyramidal symmetry. 111,114 Increasing the Cu content leads to rising intensity and line width of the Cu 2+ signals A 1 and A 2 , which is caused by mutual interaction between paramagnetic Cu 2+ species. 114 Moreover, there is a superimposed broad signal around g = 2.17 in Cat2 and Cat3 due to the formation of small CuO x clusters.…”

Section: Table 1 Elemental Composition (Icp-oes) and Textural Charact...mentioning

confidence: 99%

See 2 more Smart Citations

Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO₂–TiO₂ Deciphered by Operando Spectroscopy

et al. 2021

View full text Add to dashboard Cite

Cu single-atom catalysts (SACs) supported on CeO 2 −TiO 2 were prepared by a sol−gel method and tested for CO oxidation between 120 and 350 °C. Operando and in situ spectroscopic methods including diffuse reflectance infrared Fourier transform (DRIFT), electron paramagnetic resonance (EPR), and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) combined with other basic characterizations were applied to identify active sites and to derive reliable structure−reactivity relationships. Rising the Cu content from 0.06 to 0.86 wt % resulted in a significant decrease of the Cu-mass normalized CO 2 formation rate from 690 to 310 μmol CO 2 •g Cu −1 •s −1 at 250 °C, which was attributed to the formation of the less active CuO x species. The catalysts showed high stability during time on stream for more than 1000 min with negligible agglomeration of Cu single sites. Spectroscopic results revealed that active sites are single Cu ions on the surface of highly dispersed ceria particles, shuttling between −Cu 2+ −O−Ce 4+ − and −Cu + −□−Ce 3+ − by supplying active oxygen for oxidation of CO to CO 2 . The highest concentrations of Cu single sites and O vacancies associated with Ce 3+ species correlated with the highest CO oxidation activity.

show abstract

Section: Table 1 Elemental Composition (Icp-oes) and Textural Charact...supporting

confidence: 71%

Section: Table 1 Elemental Composition (Icp-oes) and Textural Charact...mentioning

confidence: 99%

Section: Table 1 Elemental Composition (Icp-oes) and Textural Charact...mentioning

confidence: 99%

See 1 more Smart Citation

Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO₂–TiO₂ Deciphered by Operando Spectroscopy

et al. 2021

View full text Add to dashboard Cite

show abstract

“…With increasing Cu loading, the EPR spectra show signals characteristic of predominantly isolated Cu(II) species of an axial symmetry with g || > g ⊥ > g e (Fig. 2f) [37][38][39][40] , Supplementary Fig. 7; Supplementary Note 1; Supplementary Table 3), superimposed on a broader virtually isotropic line with 〈g〉 = 2.1 (signal B1).…”

Section: Resultsmentioning

confidence: 99%

“…The EPR spectra are representative for composite signals indicating atomic Cu(II) sites are in different coordination environments. The spectrum of 0.05 wt% CuO–CeO 2 , shows two resolved species with g || = 2.327, g ⊥ = 2.048, A || = 372 MHz, A ⊥ = 55 MHz and g || = 2.293, g ⊥ = 2.036, A || = 402 MHz, A ⊥ = 92 MHz (signals A1 and C1, respectively 37 – 40 , Supplementary Fig. 7 ; Supplementary Note 1; Supplementary Table 3 ), superimposed on a broader virtually isotropic line with 〈 g 〉 = 2.1 (signal B1).…”

Section: Resultsmentioning

confidence: 99%

Adsorption and activation of molecular oxygen over atomic copper(I/II) site on ceria

et al. 2020

View full text Add to dashboard Cite

Supported atomic metal sites have discrete molecular orbitals. Precise control over the energies of these sites is key to achieving novel reaction pathways with superior selectivity. Here, we achieve selective oxygen (O 2) activation by utilising a framework of cerium (Ce) cations to reduce the energy of 3d orbitals of isolated copper (Cu) sites. Operando X-ray absorption spectroscopy, electron paramagnetic resonance and density-functional theory simulations are used to demonstrate that a [Cu(I)O 2 ] 3− site selectively adsorbs molecular O 2 , forming a rarely reported electrophilic η 2-O 2 species at 298 K. Assisted by neighbouring Ce(III) cations, η 2-O 2 is finally reduced to two O 2− , that create two Cu-O-Ce oxo-bridges at 453 K. The isolated Cu(I)/(II) sites are ten times more active in CO oxidation than CuO clusters, showing a turnover frequency of 0.028 ± 0.003 s −1 at 373 K and 0.01 bar P CO. The unique electronic structure of [Cu(I)O 2 ] 3− site suggests its potential in selective oxidation.

show abstract

Preferential CO Oxidation on a Highly Active Cu Single Atom Catalyst Supported by Ce−TiO_x

et al. 2022

View full text Add to dashboard Cite

A heterogeneous single-atom catalyst (SAC) based on a tiny Cu loading (0.05 wt.%) supported on CeO 2 À TiO 2 (Ce/Ti = 0.18) shows very high Cu mass-normalized CO oxidation activity, 100 % selectivity for CO 2 between 60 and 100 °C and essentially no deactivation during 17 h on stream in the preferential oxidation of CO (PROX) at 120 °C. Based on state of the art, this catalyst is among the most active and PROX-selective catalysts. Employing a combination of ex-situ and operando methods, we infer that the isolated Cu single sites are incorporated with redox-active Cu 2 + À OÀ Ce 4 + .Cu + À &À Ce 3 + moieties connected by labile oxygen and are exposed on the surface of highly dispersed ceria. This high dispersion is promoted by TiO 2 which itself does not participate in redox steps during PROX, as Ti ions remain essentially tetravalent while Cu and Ce undergo reversible redox shuttles.

show abstract

Reduction effect on cerium oxide catalysts doped with copper(II) ions. An electron paramagnetic resonance study

Cited by 32 publications

References 25 publications

Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO₂–TiO₂ Deciphered by Operando Spectroscopy

Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO₂–TiO₂ Deciphered by Operando Spectroscopy

Adsorption and activation of molecular oxygen over atomic copper(I/II) site on ceria

Preferential CO Oxidation on a Highly Active Cu Single Atom Catalyst Supported by Ce−TiO_x

Contact Info

Product

Resources

About

Reduction effect on cerium oxide catalysts doped with copper(II) ions. An electron paramagnetic resonance study

Cited by 32 publications

References 25 publications

Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO2–TiO2 Deciphered by Operando Spectroscopy

Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO2–TiO2 Deciphered by Operando Spectroscopy

Adsorption and activation of molecular oxygen over atomic copper(I/II) site on ceria

Preferential CO Oxidation on a Highly Active Cu Single Atom Catalyst Supported by Ce−TiOx

Contact Info

Product

Resources

About

Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO₂–TiO₂ Deciphered by Operando Spectroscopy

Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO₂–TiO₂ Deciphered by Operando Spectroscopy

Preferential CO Oxidation on a Highly Active Cu Single Atom Catalyst Supported by Ce−TiO_x