The surface chemistry of some perovskite oxides

Crespin, M.; Hall, W. Keith

doi:10.1016/0021-9517(81)90171-8

Cited by 154 publications

(60 citation statements)

References 25 publications

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“…Since many catalytic processes include sequential oxidation and reduction cycles, we have also investigated the NO x adsorption behavior of the currently synthesized LaMnO 3 , Pd/LaMnO 3 , LaCoO 3 and Pd/LaCoO 3 samples upon their exposure to reducing conditions. It is known that treatment of Co and Mn-based perovskites with an aggressive reducing agent such as H 2 (g) at high enough temperatures may cause reversible or irreversible structural changes [6,43]. This was found to be particularly valid for LaCoO 3 , where Dacquin and Dujardin showed that destruction of the perovskite structure due to the two-step reduction of the B-site cation (via Co 3+ → Co +2 → Co 0 ) led to the formation of metallic Co and La 2 O 3 [44][45][46].…”

Section: No 2 Adsorption/desorption Behavior Of Perovskite Surfacesmentioning

confidence: 99%

Palladium doped perovskite-based NO oxidation catalysts: The role of Pd and B-sites for NOx adsorption behavior via in-situ spectroscopy

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Doğaç

Vovk

et al. 2014

Applied Catalysis B: Environmental

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a b s t r a c tPerovskite-based materials (LaMnO 3 , Pd/LaMnO 3 , LaCoO 3 and Pd/LaCoO 3 ) were synthesized, characterized (via BET, XRD, Raman spectroscopy, XPS and TEM) and their NO x (x = 1,2) adsorption characteristics were investigated (via in-situ FTIR and TPD) as a function of the nature of the B-site cation (i.e. Mn vs Co), Pd/PdO incorporation and H 2 -pretreatment. NO x adsorption on of LaMnO 3 was found to be significantly higher than LaCoO 3 , in line with the higher SSA of LaMnO 3 . Incorporation of PdO nanoparticles with an average diameter of ca. 4 nm did not have a significant effect on the amount of NO 2 adsorbed on fresh LaMnO 3 and LaCoO 3 . TPD experiments suggested that saturation of fresh LaMnO 3 , Pd/LaMnO 3 , LaCoO 3 and Pd/LaCoO 3 with NO 2 at 323 K resulted in the desorption of NO 2 , NO, N 2 O and N 2 (without O 2 ) below 700 K, while above 700 K, NO x desorption was predominantly in the form of NO + O 2 . Perovskite materials were found to be capable of activating N-O linkages typically at ca. 550 K (even in the absence of an external reducing agent) forming N 2 and N 2 O as direct NO x decomposition products. H 2 -pretreatment yielded a drastic boost in the NO oxidation and NO x adsorption of all samples, particularly for the Cobased systems. Presence of Pd further boosted the NO x uptake upon H 2 -pretreatment. Increase in the NO x adsorption of H 2 -pretreated LaCoO 3 and Pd/LaCoO 3 surfaces could be associated with the electronic changes (i.e. reduction of B-site cation), structural changes (surface reconstruction and SSA increase), reduction of the precious metal oxide (PdO) into metallic species (Pd), and the generation of oxygen defects on the perovskite. Mn-based systems were more resilient toward B-site reduction. Pd-addition suppressed the B-site reduction and preserved the ABO 3 perovskite structure.

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Section: No 2 Adsorption/desorption Behavior Of Perovskite Surfacesmentioning

confidence: 99%

Palladium doped perovskite-based NO oxidation catalysts: The role of Pd and B-sites for NOx adsorption behavior via in-situ spectroscopy

Say

Doğaç

Vovk

et al. 2014

Applied Catalysis B: Environmental

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“…Two major resistance changing processes occur at 470-550°C and 570-645°C, which correspond to the reduction in Co 3+ to Co 2+ and Co 2+ to Co 0 , where the resistance is first increased from 10 3 to 10 5 ⍀ and finally reaches 10 6 ⍀. Since the reduced metal Co should be in a highly dispersed state on a matrix composed of the oxide, 13 the high resistance of the reduced sample is the result of an absence of conductive Co-O layers in the crystal structure. Each resistance changing rate peak is split into two parts, indicating two slightly different reducing temperatures.…”

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confidence: 99%

PO 2 dependant resistance switch effect in highly epitaxial (LaBa)Co2O5+δ thin films

Liu

Collins

Liu

et al. 2010

Applied Physics Letters

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Giant resistance switching behavior in mixed conductive ͑LaBa͒Co 2 O 5+␦ epitaxial thin film were discovered in high temperature and reducing environments during the reduction and reoxidation process. A reproducible resistance response of over 99% was achieved in the films during a change of 4% H 2 / 96% N 2 to oxygen at temperature range of 400-780°C. The results indicate that at, low oxygen partial pressure, the extension of oxygen deficiency is an essential factor to the high temperature physical properties of ͑LaBa͒Co 2 O 5+␦ and demonstrates its potential application as a chemical sensor device for reducing environments at high temperature. © 2010 American Institute of Physics. ͓doi:10.1063/1.3484964͔Cobalt based perovskite oxides have received increasing attention in the past decade due to their high mixed ionicelectronic conductivity in chemical sensor and green energy device development.1,2 Recent studies indicate that oxygen deficient doped double perovskite cobaltates ͑LnBa͒Co 2 O 5+␦ ͑Ln= La, Pr, Gd͒ have excellent mixed ionic-electronic conductivity with a fast surface exchange coefficient. [3][4][5] In this family of compounds, the A-site cationic ordered arrangement is favored due to the large difference in Ba 2+ and rare earth ionic radii, except ͑LaBa͒Co 2 O 5+␦ ͑LBCO͒. In LBCO, the doped bivalent Ba 2+ is not only inducing plenty of oxygen deficiency but also structurally providing the capability to achieve the smallest oxygen deficiency in this family of compounds due to the very similar ionic radii between Ba 2+ and La 3+ . Therefore, LBCO provides a unique platform with the geometrical stabilized perovskite phase and a wide range of oxygen deficiency, which enables one to study the electrical conductivity, defect structures and stability at high temperature over a wide range of oxygen partial pressure.Up to now, studies on LBCO are only limited to the bulk polycrystalline samples for low temperature transport and magnetic properties.6-8 The high temperature physical properties of LBCO are rarely studied due to the structure failure of the bulk material in a reducing environment. Recently, we have fabricated epitaxial single crystalline LBCO thin films on ͑001͒ LaAlO 3 ͑LAO͒, enabling one to systematically study the electrical transport properties of LBCO under various environments. A reproducibly dramatic resistance change is observed as the LBCO film is exposed to oxidizing and reducing environment over a wide range of temperature. Especially, it is interesting to note that the re-oxidation of the LBCO film has a very short response time, suggesting that an exceedingly fast oxygen exchange rate occurs at the film surface.A KrF excimer pulsed laser deposition system with a wavelength of 248 nm was employed to deposit the ͑LaBa͒Co 2 O 5+␦ thin films on ͑001͒ LaAlO 3 substrates. An energy density of 2.0 J / cm 2 and a laser repetition rate of 5 Hz were adopted during film deposition. A high density, single phase, stoichiometric ͑LaBa͒Co 2 O 5+␦ target was purchased from Praxair Inc. The deposit...

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“…Co-and Fe-based perovskites can be decomposed to separate metal and metal oxide phases in reducing atmospheres [55,63,64]. Re-oxidation of separate metal/metal oxide phases has been observed to reproduce perovskites with large crystallite size [65]. Sintering of particles would decrease catalytic activity by lowering the number of surface sites.…”

Section: Figure 2 V-i Curves Andmentioning

confidence: 99%

“…Studies on stability of LSCF in reducing environments of CH 4 and CO 2 showed that presence of O 2 in the feed gas allowed LSCF to maintain its perovskite structure with the desired electronic-ionic conductivity [68,69]. Perovskites were found to demonstrate reversible redox behavior at temperatures below the sintering temperature of their decomposed phases [13,55,65]. Thus, periodic addition of low concentration of air into CH 4 fuel as well as a systematic study of operating temperature could be the options to further stabilize the perovskite on the anode.…”

Section: Figure 2 V-i Curves Andmentioning

confidence: 99%

La0.6Sr0.4Co0.2Fe0.8O3 Perovskite: A Stable Anode Catalyst for Direct Methane Solid Oxide Fuel Cells

Mirzababaei

Chuang

2014

Catalysts

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Direct methane solid oxide fuel cells, operated by supplying methane to a Ni/YSZ anode, suffer from degradation via accumulation of carbon deposits on the Ni surface. Coating a 40 µm thin film of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) perovskite on the Ni/YSZ anode surface decreased the amount of carbon deposits, slowing down the degradation rate. The improvement in anode durability could be related to the oxidation activity of LSCF which facilitates oxidation of CH 4 and carbon deposits. Analysis of the crystalline structure of LSCF revealed that LSCF was stable in the reducing anode environment under H 2 and CH 4 flow at 750 °C and retained its perovskite structure throughout the 475 h long-term stability test.

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The surface chemistry of some perovskite oxides

Cited by 154 publications

References 25 publications

Palladium doped perovskite-based NO oxidation catalysts: The role of Pd and B-sites for NOx adsorption behavior via in-situ spectroscopy

Palladium doped perovskite-based NO oxidation catalysts: The role of Pd and B-sites for NOx adsorption behavior via in-situ spectroscopy

PO 2 dependant resistance switch effect in highly epitaxial (LaBa)Co2O5+δ thin films

La0.6Sr0.4Co0.2Fe0.8O3 Perovskite: A Stable Anode Catalyst for Direct Methane Solid Oxide Fuel Cells

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