Cu, Sm co-doping effect on the CO oxidation activity of CeO2. A combined experimental and density functional study

AlKhoori, Ayesha A.; Polychronopoulou, Kyriaki; Belabbes, Abderrezak; Vega, Lourdes F.; Sebastián, Víctor; Hinder, Steven J.; Baker, Mark; Zedan, Abdallah F.

doi:10.1016/j.apsusc.2020.146305

Cited by 70 publications

(41 citation statements)

References 116 publications

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“…%). 24 The latter can be ascribed partially to the beneficial role of microwave synthesis, which allows the thorough mixing of the constituents’ elements. The mean crystallite size of the solids was calculated using the Scherer equation, and this was found to be in the 8.8–16.4 nm range (see Table 1 ).…”

Section: Resultsmentioning

confidence: 99%

Design Aspects of Doped CeO₂ for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach

Polychronopoulou

AlKhoori

Efstathiou

et al. 2021

ACS Appl. Mater. Interfaces

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CO elimination through oxidation over highly active and cost-effective catalysts is a way forward for many processes of industrial and environmental importance. In this study, doped CeO 2 with transition metals (TM = Cu, Co, Mn, Fe, Ni, Zr, and Zn) at a level of 20 at. % was tested for CO oxidation. The oxides were prepared using microwave-assisted sol–gel synthesis to improve catalyst’s performance for the reaction of interest. The effect of heteroatoms on the physicochemical properties (structure, morphology, porosity, and reducibility) of the binary oxides M–Ce–O was meticulously investigated and correlated to their CO oxidation activity. It was found that the catalytic activity (per gram basis or TOF, s –1 ) follows the order Cu–Ce–O > Ce–Co–O > Ni–Ce–O > Mn–Ce–O > Fe–Ce–O > Ce–Zn–O > CeO 2 . Participation of mobile lattice oxygen species in the CO/O 2 reaction does occur, the extent of which is heteroatom-dependent. For that, state-of-the-art transient isotopic 18 O-labeled experiments involving 16 O/ 18 O exchange followed by step-gas CO/Ar or CO/O 2 /Ar switches were used to quantify the contribution of lattice oxygen to the reaction. SSITKA-DRIFTS studies probed the formation of carbonates while validating the Mars–van Krevelen (MvK) mechanism. Scanning transmission electron microscopy-high-angle annular dark field imaging coupled with energy-dispersive spectroscopy proved that the elemental composition of dopants in the individual nanoparticle of ceria is less than their composition at a larger scale, allowing the assessment of the doping efficacy. Despite the similar structural features of the catalysts, a clear difference in the O lattice mobility was also found as well as its participation (as expressed with the α descriptor) in the reaction, following the order α Cu > α Co > α Mn > α Zn . Kinetic studies showed that it is rather the pre-exponential (entropic) factor and not the lowering of activation energy that justifies the order of activity of the solids. DFT calculations showed that the adsorption of CO on the Cu-doped CeO 2 surface is more favorable (−16.63 eV), followed by Co, Mn, Zn (−14.46, −4.90, and −4.24 eV, respectively), and pure CeO 2 (−0.63 eV). Also, copper compensates almost three times more charge (0.37 e − ) compared to Co and Mn, ca. 0.13 e − and 0.10 e − , respectively, corroborating for its tendency to be reduced. Surface analysis (X-ray photoelectron spectroscopy), apart from the oxidation state of the elements, revealed a heteroatom–ceria surface interaction (O a species) of different extents and of d...

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Section: Resultsmentioning

confidence: 99%

Design Aspects of Doped CeO₂ for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach

Polychronopoulou

AlKhoori

Efstathiou

et al. 2021

ACS Appl. Mater. Interfaces

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“…Comparing calcined with sintered CSDCs, the [V Figure 9: e relative concentration of (a) extrinsic V . Another type of segregate mentioned in literature is the SmO 8 -type complex, which causes the presence of microdomains in the microstructure with a predominant metastable C-type phase [47]. In this study, the relative concentration of the SmO 8 -type complex, [SmO 8 ], is shown in Figure 9(d…”

Section: B) E [V ••mentioning

confidence: 63%

“…When calcined CSDC/CA is compared to calcined CSDC/TA, the Advances in Materials Science and Engineering average lattice parameter of calcined CSDC/CA is close to that of CSDC/TA, which may be due to more substitution of Cu + (0.074 nm) and/or Cu2 + (0.071 nm) into Ce4 + [46]. e crystallite sizes (D) are estimated from Scherrer's equation as follows [8,47]:…”

Section: Xrd Patternsmentioning

confidence: 91%

The Effect of Tartaric Acid and Citric Acid as a Complexing Agent on Defect Structure and Conductivity of Copper Samarium Co‐Doped Ceria Prepared by a Sol‐Gel Auto‐Combustion Method

Duangsa

Tangtrakarn

Mongkolkachit

et al. 2021

Advances in Materials Science and Engineering

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Copper samarium co-doped ceria (CSDC) (Cu0.01Sm0.19Ce0.80O2−δ) nanoparticles were synthesized via a sol-gel auto-combustion of metal nitrates without a complexing agent (DI) and with tartaric acid (TA) or citric acid (CA). The solid oxide formation of CSDC/DI corresponds to the endothermic stage, whereas that of CSDC/TA and CSDC/CA matches the exothermic stage caused by the decomposition of the metal cross-linking and carbon combustion. The cross-linking occurs more extensively in the CA case as more heat is released in CA than in the TA route. The as-synthesized morphology of CSDC/DI reveals both layered structures and small agglomerated particles, whereas CSDC/TA and CSDC/CA show dense xerogel and porous xerogel, respectively. The cubic fluorite structure for calcined CSDCs was confirmed by XRD. From Raman analysis, calcined CSDC/CA has the lowest amount of copper segregation and the highest relative total oxygen vacancy concentration [ V O • • ]total, whereas calcined CSDC/DI has the highest amount of copper segregation and the lowest [ V O • • ]total. For all samples, copper segregation promotes densification, albeit to varying degrees. The relative densities of CSDC/DI, CSDC/TA, and CSDC/CA pellets are 82.8 ± 2.4%, 95.5 ± 1.8%, and 97.8 ± 0.9%, respectively. The sintered CSDC/DI has the lowest density because some copper segregates and liquid copper in interparticle spaces could evaporate earlier than samples containing a complexing agent, whereas sintered CSDC/CA has the highest density because Cu could slowly diffuse from the Cu-Sm-Ce solid solution to grain boundary regions and then precipitate as CuO. The specific grain boundary conductivity is predominantly influenced by CuO along grain boundaries, which reduces specific grain boundary conductivity and increases the enthalpy of association (ΔHa) at 250–350°C; however, it rarely impacts total grain boundary conductivity at temperatures higher than 400°C. CSDC/CA has slightly higher total conductivity than CSDC/TA despite having more CuO segregation because it has higher density and V O • • .

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“…Atsushi Satsuma reported in his study of CO-oxidation over supported Pd catalyst, that titanium oxide contributes to oxygen supply and hence Mars-van Krevelen can be proposed as a more representative mechanism [ 60 ]. Mars-van Krevelen is the most prominent mechanism for CO oxidation over different catalysts, such as Cu/Pd-supported catalysts and ceria-based catalysts [ 24 , 26 , 60 ].…”

Section: Resultsmentioning

confidence: 99%

“…The analysis was done with diffractometer at a voltage of 30 kV and intensity of 20 mA with scanning speed of 0.025°/step/second. The average crystallite size was calculated using Scherrer equation

where D indicates the average crystallite size, K = 0.9 (shape factor), λ is the X-ray wavelength, θ is the X-ray reflection angle, and β is the full width at half-maximum (FWHM) of the diffraction peak (radians) [ 24 , 25 , 26 ]. Nitrogen adsorption and desorption isotherms were collected on ASAP 2460 pore size analyzer (Micromeritics, Norcross, GA, USA) (at 77 K) and recorded in the range of 0.05 to 1 relative pressure.…”

Section: Methodsmentioning

confidence: 99%

CO Oxidation at Near-Ambient Temperatures over TiO2-Supported Pd-Cu Catalysts: Promoting Effect of Pd-Cu Nanointerface and TiO2 Morphology

et al. 2021

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Significant improvement of the catalytic activity of palladium-based catalysts toward carbon monoxide (CO) oxidation reaction has been achieved through alloying and using different support materials. This work demonstrates the promoting effects of the nanointerface and the morphological features of the support on the CO oxidation reaction using a Pd-Cu/TiO2 catalyst. Pd-Cu catalysts supported on TiO2 were synthesized with wet chemical approaches and their catalytic activities for CO oxidation reaction were evaluated. The physicochemical properties of the prepared catalysts were studied using standard characterization tools including SEM, EDX, XRD, XPS, and Raman. The effects of the nanointerface between Pd and Cu and the morphology of the TiO2 support were investigated using three different-shaped TiO2 nanoparticles, namely spheres, nanotubes, and nanowires. The Pd catalysts that are modified through nanointerfacing with Cu and supported on TiO2 nanowires demonstrated the highest CO oxidation rates, reaching 100% CO conversion at temperature regime down to near-ambient temperatures of ~45 °C, compared to 70 °C and 150 °C in the case of pure Pd and pure Cu counterpart catalysts on the same support, respectively. The optimized Pd-Cu/TiO2 nanowires nanostructured system could serve as efficient and durable catalyst for CO oxidation at near-ambient temperature.

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Cu, Sm co-doping effect on the CO oxidation activity of CeO2. A combined experimental and density functional study

Cited by 70 publications

References 116 publications

Design Aspects of Doped CeO₂ for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach

Design Aspects of Doped CeO₂ for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach

The Effect of Tartaric Acid and Citric Acid as a Complexing Agent on Defect Structure and Conductivity of Copper Samarium Co‐Doped Ceria Prepared by a Sol‐Gel Auto‐Combustion Method

CO Oxidation at Near-Ambient Temperatures over TiO2-Supported Pd-Cu Catalysts: Promoting Effect of Pd-Cu Nanointerface and TiO2 Morphology

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Cu, Sm co-doping effect on the CO oxidation activity of CeO2. A combined experimental and density functional study

Cited by 70 publications

References 116 publications

Design Aspects of Doped CeO2 for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach

Design Aspects of Doped CeO2 for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach

The Effect of Tartaric Acid and Citric Acid as a Complexing Agent on Defect Structure and Conductivity of Copper Samarium Co‐Doped Ceria Prepared by a Sol‐Gel Auto‐Combustion Method

CO Oxidation at Near-Ambient Temperatures over TiO2-Supported Pd-Cu Catalysts: Promoting Effect of Pd-Cu Nanointerface and TiO2 Morphology

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Design Aspects of Doped CeO₂ for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach

Design Aspects of Doped CeO₂ for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach