Catalysts

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3 pages, 164 KiB

Open AccessEditorial

Catalysis by Metals on Perovskite-Type Oxides

by Davide Ferri

Catalysts 2020, 10(9), 1062; https://doi.org/10.3390/catal10091062 - 15 Sep 2020

Cited by 2 | Viewed by 1726

Abstract

Perovskites are currently on everyone’s lips and have made it in high-impact scientific journals because of the revolutionary hybrid organic–inorganic lead halide perovskite materials for solar cells [...] Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

Research

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18 pages, 9015 KiB

Open AccessArticle

Reactive Grinding Synthesis of LaBO₃ (B: Mn, Fe) Perovskite; Properties for Toluene Total Oxidation

by Bertrand Heidinger, Sébastien Royer, Houshang Alamdari, Jean-Marc Giraudon and Jean-François Lamonier

Catalysts 2019, 9(8), 633; https://doi.org/10.3390/catal9080633 - 25 Jul 2019

Cited by 22 | Viewed by 5070

Abstract

LaBO₃ (B: Mn, Fe) perovskites were synthesized using a three-step reactive grinding process followed by a calcination at 400 °C for 3 h. The three successive steps are: (i) solid state synthesis (SSR); (ii) high-energy ball milling (HEBM); (iii) low-energy ball milling [...] Read more.

LaBO₃ (B: Mn, Fe) perovskites were synthesized using a three-step reactive grinding process followed by a calcination at 400 °C for 3 h. The three successive steps are: (i) solid state synthesis (SSR); (ii) high-energy ball milling (HEBM); (iii) low-energy ball milling (LEBM) in wet conditions. The impact of each step of the synthesis on the material characteristics was deeply investigated using physico-chemical techniques (X-ray diffraction (XRD), N₂-physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS)) and the catalytic performances of the synthesized materials were evaluated for the toluene total oxidation reaction. Starting from single oxides, microcrystalline perovskite phase, exhibiting negligible surface areas, is obtained after the SSR step. The HEBM step leads to a drastic reduction of the mean crystal size down to ~20 nm, along with formation of dense aggregates. Due to this strong aggregation, surface area remains low, typically below 4 m²·g⁻¹. In contrast, the second grinding step, namely LEBM, allows particle deagglomeration resulting in increasing the surface area up to 18.8 m²·g⁻¹ for LaFeO₃. Regardless of the perovskite composition, the performance toward toluene oxidation reaction increases at each step of the process: SSR < HEBM < LEBM. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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11 pages, 2803 KiB

Open AccessArticle

Catalytic Oxidation of NO over LaCo_1−xB_xO₃ (B = Mn, Ni) Perovskites for Nitric Acid Production

by Ata ul Rauf Salman, Signe Marit Hyrve, Samuel Konrad Regli, Muhammad Zubair, Bjørn Christian Enger, Rune Lødeng, David Waller and Magnus Rønning

Catalysts 2019, 9(5), 429; https://doi.org/10.3390/catal9050429 - 8 May 2019

Cited by 18 | Viewed by 7146

Abstract

Nitric acid (HNO₃) is an important building block in the chemical industry. Industrial production takes place via the Ostwald process, where oxidation of NO to NO₂ is one of the three chemical steps. The reaction is carried out as a [...] Read more.

Nitric acid (HNO₃) is an important building block in the chemical industry. Industrial production takes place via the Ostwald process, where oxidation of NO to NO₂ is one of the three chemical steps. The reaction is carried out as a homogeneous gas phase reaction. Introducing a catalyst for this reaction can lead to significant process intensification. A series of LaCo_1−xMn_xO₃ (x = 0, 0.25, 0.5 and 1) and LaCo_1−yNi_yO₃ (y = 0, 0.25, 0.50, 0.75 and 1) were synthesized by a sol-gel method and characterized using N₂ adsorption, ex situ XRD, in situ XRD, SEM and TPR. All samples had low surface areas; between 8 and 12 m²/g. The formation of perovskites was confirmed by XRD. The crystallite size decreased linearly with the degree of substitution of Mn/Ni for partially doped samples. NO oxidation activity was tested using a feed (10% NO and 6% O₂) that partly simulated nitric acid plant conditions. Amongst the undoped perovskites, LaCoO₃ had the highest activity; with a conversion level of 24.9% at 350 °C; followed by LaNiO₃ and LaMnO₃. Substitution of LaCoO₃ with 25% mol % Ni or Mn was found to be the optimum degree of substitution leading to an enhanced NO oxidation activity. The results showed that perovskites are promising catalysts for NO oxidation at industrial conditions. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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11 pages, 2482 KiB

Open AccessArticle

BaTi_0.8B_0.2O₃ (B = Mn, Fe, Co, Cu) LNT Catalysts: Effect of Partial Ti Substitution on NOx Storage Capacity

by Craig Aldridge, Verónica Torregrosa-Rivero, Vicente Albaladejo-Fuentes, María-Salvadora Sánchez-Adsuar and María-José Illán-Gómez

Catalysts 2019, 9(4), 365; https://doi.org/10.3390/catal9040365 - 18 Apr 2019

Cited by 2 | Viewed by 3000

Abstract

The effect of partial Ti substitution by Mn, Fe, Co, or Cu on the NOx storage capacity (NSC) of a BaTi_0.8B_0.2O₃ lean NOx trap (LNT) catalyst has been analyzed. The BaTi_0.8B_0.2O₃ catalysts were [...] Read more.

The effect of partial Ti substitution by Mn, Fe, Co, or Cu on the NOx storage capacity (NSC) of a BaTi_0.8B_0.2O₃ lean NOx trap (LNT) catalyst has been analyzed. The BaTi_0.8B_0.2O₃ catalysts were prepared using the Pechini’s sol–gel method for aqueous media. The characterization of the catalysts (BET, ICP-OES, XRD and XPS) reveals that: i) the partial substitution of Ti by Mn, Co, or Fe changes the perovskite structure from tetragonal to cubic, whilst Cu distorts the raw tetragonal structure and promotes the segregation of Ba₂TiO₄ (which is an active phase for NOx storage) as a minority phase and ii) the amount of oxygen vacancies increases after partial Ti substitution, with the BaTi_0.8Cu_0.2O₃ catalyst featuring the largest amount. The BaTi_0.8Cu_0.2O₃ catalyst shows the highest NSC at 400 °C, based on NOx storage cyclic tests, which is within the range of highly active noble metal-based catalysts. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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15 pages, 8307 KiB

Open AccessArticle

Perovskite-type LaFeO₃: Photoelectrochemical Properties and Photocatalytic Degradation of Organic Pollutants Under Visible Light Irradiation

by Mohammed Ismael and Michael Wark

Catalysts 2019, 9(4), 342; https://doi.org/10.3390/catal9040342 - 8 Apr 2019

Cited by 132 | Viewed by 9040

Abstract

Perovskite-type oxides lanthanum ferrite (LaFeO₃) photocatalysts were successfully prepared by a facile and cost-effective sol-gel method using La(NO)₃ and Fe(NO)₃ as metal ion precursors and citric acid as a complexing agent at different calcination temperatures. The properties of the [...] Read more.

Perovskite-type oxides lanthanum ferrite (LaFeO₃) photocatalysts were successfully prepared by a facile and cost-effective sol-gel method using La(NO)₃ and Fe(NO)₃ as metal ion precursors and citric acid as a complexing agent at different calcination temperatures. The properties of the resulting LaFeO₃ samples were characterized by powder X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (IR), transmission electron microscopy (TEM), N₂ adsorption/desorption and photoelectrochemical tests. The photoactivity of the LaFeO₃ samples was tested by monitoring the photocatalytic degradation of Rhodamine B (RhB) and 4-chlorophenol (4-CP) under visible light irradiation, the highest photocatalytic activity was found for LaFeO₃ calcined at 700 °C, which attributed to the relatively highest surface area (10.6 m²/g). In addition, it was found from trapping experiments that the reactive species for degradation were superoxide radical ions (O₂⁻) and holes (h⁺). Photocurrent measurements and electrochemical impedance spectroscopy (EIS) proved the higher photo-induced charge carrier transfer and separation efficiency of the LaFeO₃ sample calcined at 700 °C compared to that that calcined at 900 °C. Band positions of LaFeO₃ were estimated using the Mott-Schottky plots, which showed that H₂ evolution was not likely. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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16 pages, 5515 KiB

Open AccessArticle

Segregation of Nickel/Iron Bimetallic Particles from Lanthanum Doped Strontium Titanates to Improve Sulfur Stability of Solid Oxide Fuel Cell Anodes

by Patrick Steiger, Dariusz Burnat, Oliver Kröcher, Andre Heel and Davide Ferri

Catalysts 2019, 9(4), 332; https://doi.org/10.3390/catal9040332 - 3 Apr 2019

Cited by 3 | Viewed by 4189

Abstract

Perovskite derived Ni catalysts offer the remarkable benefit of regeneration after catalyst poisoning or Ni particle growth through the reversible segregation of Ni from the perovskite-type oxide host. Although this property allows for repeated catalyst regeneration, improving Ni catalyst stability towards sulfur poisoning [...] Read more.

Perovskite derived Ni catalysts offer the remarkable benefit of regeneration after catalyst poisoning or Ni particle growth through the reversible segregation of Ni from the perovskite-type oxide host. Although this property allows for repeated catalyst regeneration, improving Ni catalyst stability towards sulfur poisoning by H₂S is highly critical in solid oxide fuel cells. In this work Mn, Mo, Cr and Fe were combined with Ni at the B-site of La_0.3Sr_0.55TiO_3±δ to explore possible benefits of segregation of two transition metals towards sulfur tolerance. Catalytic activity tests towards the water gas shift reaction were carried out to evaluate the effect of the additional metal on the catalytic activity and sulfur stability of the Ni catalyst. The addition of Fe to the Ni perovskite catalyst was found to increase sulfur tolerance. The simultaneous segregation of Fe and Ni from La_0.3Sr_0.55Ti_0.95-xNi_0.05Fe_xO_3±δ (x ≤ 0.05) was investigated by temperature programmed reduction, X-ray diffraction and X-ray absorption spectroscopy and catalytic tests after multiple redox cycles. It is shown that catalytic properties of the active phase were affected likely by the segregation of Ni/Fe alloy particles and that the reversible segregation of Ni persisted, while it was limited in the case of Fe under the same conditions. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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7 pages, 2091 KiB

Open AccessArticle

On the Effects of Doping on the Catalytic Performance of (La,Sr)CoO₃. A DFT Study of CO Oxidation

by Antonella Glisenti and Andrea Vittadini

Catalysts 2019, 9(4), 312; https://doi.org/10.3390/catal9040312 - 30 Mar 2019

Cited by 13 | Viewed by 4332

Abstract

The effects of modifying the composition of LaCoO₃ on the catalytic activity are predicted by density functional calculations. Partially replacing La by Sr ions has benefical effects, causing a lowering of the formation energy of O vacancies. In contrast to that, doping [...] Read more.

The effects of modifying the composition of LaCoO₃ on the catalytic activity are predicted by density functional calculations. Partially replacing La by Sr ions has benefical effects, causing a lowering of the formation energy of O vacancies. In contrast to that, doping at the Co site is less effective, as only 3d impurities heavier than Co are able to stabilize vacancies at high concentrations. The comparison of the energy profiles for CO oxidation of undoped and of Ni-, Cu-m and Zn-doped (La,Sr)CoO₃(100) surface shows that Cu is most effective. However, the effects are less spectacular than in the SrTiO₃ case, due to the different energetics for the formation of oxygen vacancies in the two hosts. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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17 pages, 3081 KiB

Open AccessArticle

Fe-Doping in Double Perovskite PrBaCo_2(1-x)Fe_2xO_6-δ: Insights into Structural and Electronic Effects to Enhance Oxygen Evolution Catalyst Stability

by Bae-Jung Kim, Emiliana Fabbri, Ivano E. Castelli, Mario Borlaf, Thomas Graule, Maarten Nachtegaal and Thomas J. Schmidt

Catalysts 2019, 9(3), 263; https://doi.org/10.3390/catal9030263 - 14 Mar 2019

Cited by 25 | Viewed by 6022

Abstract

Perovskite oxides have been gaining attention for its capability to be designed as an ideal electrocatalyst for oxygen evolution reaction (OER). Among promising candidates, the layered double perovskite—PrBaCo₂O_6-δ (PBC)—has been identified as the most active perovskite electrocatalyst for OER in [...] Read more.

Perovskite oxides have been gaining attention for its capability to be designed as an ideal electrocatalyst for oxygen evolution reaction (OER). Among promising candidates, the layered double perovskite—PrBaCo₂O_6-δ (PBC)—has been identified as the most active perovskite electrocatalyst for OER in alkaline media. For a single transition metal oxide catalyst, the addition of Fe enhances its electrocatalytic performance towards OER. To understand the role of Fe, herein, Fe is incorporated in PBC in different ratios, which yielded PrBaCo_2(1-x)Fe_2xCo_6-δ (x = 0, 0.2 and 0.5). Fe-doped PBCF’s demonstrate enhanced OER activities and stabilities. Operando X-ray absorption spectroscopy (XAS) revealed that Co is more stable in a lower oxidation state upon Fe incorporation by establishing charge stability. Hence, the degradation of Co is inhibited such that the perovskite structure is prolonged under the OER conditions, which allows it to serve as a platform for the oxy(hydroxide) layer formation. Overall, our findings underline synergetic effects of incorporating Fe into Co-based layered double perovskite in achieving a higher activity and stability during oxygen evolution reaction. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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14 pages, 3180 KiB

Open AccessArticle

K-Modulated Co Nanoparticles Trapped in La-Ga-O as Superior Catalysts for Higher Alcohols Synthesis from Syngas

by Shaoxia Guo, Guilong Liu, Tong Han, Ziyang Zhang and Yuan Liu

Catalysts 2019, 9(3), 218; https://doi.org/10.3390/catal9030218 - 27 Feb 2019

Cited by 6 | Viewed by 2825

Abstract

Owing to the outstanding catalytic performance for higher alcohol synthesis, Ga-Co catalysts have attracted much attention. In view of their unsatisfactory stability and alcohol selectivity, herein, K-modulated Co nanoparticles trapped in La-Ga-O catalysts were prepared by the reduction of La_1−xK_x [...] Read more.

Owing to the outstanding catalytic performance for higher alcohol synthesis, Ga-Co catalysts have attracted much attention. In view of their unsatisfactory stability and alcohol selectivity, herein, K-modulated Co nanoparticles trapped in La-Ga-O catalysts were prepared by the reduction of La_1−xK_xCo_0.65Ga_0.35O₃ perovskite precursor. Benefiting from the atomic dispersion of all the elements in the precursor, during the reduction of La_1−xK_xCo_0.65Ga_0.35O₃, Co nanoparticles could be confined into the K-modified La-Ga-O composite oxides, and the confinement of La-Ga-O could improve the anti-sintering performance of Co nanoparticles. In addition, the addition of K modulated parts of La-Ga-O into La₂O₃, which ameliorated the anti-carbon deposition performance. Finally, the addition of K increased the dispersion of cobalt and provided more electron donors to metallic Co, resulting in a high activity and superior selectivity to higher alcohols. Benefiting from the above characteristics, the catalyst possesses excellent activity, good selectivity, and superior stability. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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Review

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38 pages, 2491 KiB

Open AccessFeature PaperReview

Perovskites as Catalysts in Advanced Oxidation Processes for Wastewater Treatment

by María Luisa Rojas-Cervantes and Eva Castillejos

Catalysts 2019, 9(3), 230; https://doi.org/10.3390/catal9030230 - 2 Mar 2019

Cited by 47 | Viewed by 8301

Abstract

Advanced oxidation processes (AOPs), based on the formation of highly reactive radicals are able to degrade many organic contaminants present in effluent water. In the heterogeneous AOPS the presence of a solid which acts as catalyst in combination with other systems (O₃ [...] Read more.

Advanced oxidation processes (AOPs), based on the formation of highly reactive radicals are able to degrade many organic contaminants present in effluent water. In the heterogeneous AOPS the presence of a solid which acts as catalyst in combination with other systems (O₃, H₂O₂, light) is required. Among the different materials that can catalyse these processes, perovskites are found to be very promising, because they are highly stable and exhibit a high mobility of network oxygen with the possibility of forming vacancies and to stabilize unusual oxidation states of metals. In this review, we show the fundaments of different kinds of AOPs and the application of perovskite type oxides in them, classified attending to the oxidant used, ozone, H₂O₂ or peroxymonosulfate, alone or in combination with other systems. The photocatalytic oxidation, consisting in the activation of the perovskite by irradiation with ultraviolet or visible light is also revised. Full article

(This article belongs to the Special Issue Catalysis by Metals on Perovskite-Type Oxides)

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