Sol–gel Synthesis of LaBO<Subscript>3</Subscript>/Attapulgite (B=Mn,Fe, Co,Ni) Nanocomposite for NH<Subscript>3</Subscript>-SCR of NO at Low Temperature

LaBO₃/attapulgite (ATP) (B=Mn, Fe, Co, Ni) composites were prepared by sol–gel method using citric acid as complex agent. The products were characterized by X-ray diffraction transmission electron microscopy, energy-dispersive spectroscopy, Battett–Emmett–Teller, fourier-transform infrared, H₂ temperature-programmed reduction and temperature-programmed desorption of NH₃ measurements. The catalytic activity of LaBO₃/ATP nanocomposites was evaluated via selective catalytic reduction of NO with NH₃ by fixed bed denitration equipment at low-temperature. The impact of the various B-site elements on the NO conversion was investigated. Results showed that the adsorption capacity of NH₃ played significant role in the low temperature denitrification process, and Mn was the best B-site element where LaMnO₃/ATP achieves 81% conversion of NO at 250 °C.     

Dry reforming of methane over LaNi1−yByO3±δ (B = Mg,Co) perovskites used as catalyst precursor

Perovskites LaNiO₃, LaNi_1−xMg_xO_3−δ and LaNi_1−xCo_xO_3−δ were synthesized by auto combustion method. TPR analysis reveled that Mg or Co substituted perovskites were more difficult to reduce. The perovskites were evaluated as catalyst precursors in the dry reforming of methane. Catalysts obtained by reduction of LaNiO₃ and LaNi_1−xMg_xO_3−δ perovskite had the highest catalytic activity for CO₂ reforming of CH₄ at 700 °C using drastic reaction conditions (10 mg of catalyst, a mixture of CH₄/CO₂ without dilution gas). Methane and carbon dioxide conversions were 57% and 67%, respectively, with a H₂/CO ratio equal to 0.47.The presence of cobalt leads to a decrease of the catalytic activity. This decreasing of activity may be attributed to the Co–Ni alloy formation. Computational calculations revealed that Ni atom cleaves the C–H atom while Co is not able to activate the CH₄ molecule. The interaction energy of CH₄ with the Ni and CO atom was 18 kcal/mol and 0.7 kcal/mol, respectively.The catalysts were characterized by TPR, TEM and in situ XRD.     

Physicochemical and electrocatalytic properties of LaNiO3 prepared by a low-temperature route for anode application in alkaline water electrolysis

LaNi_1–x Fe_xO₃ (x = 0, 0.25, 0.5) has been synthesized by the hydroxide solid solution precursor method for electrochemical characterization as oxygen anode in strongly alkaline medium. Studies were made at the oxide film, which was obtained by the oxide-slurry painting technique. The cyclic voltammetric study showed the formation of a diffusion-controlled quasireversible redox couple, Ni(ii)/Ni(iii), (E ⁰ - 430 ± 10 mV) at the oxide surface in 1 m KOH. The reaction was observed to follow approximately first-order kinetics in OH^– concentration. Values of the Tafel slope ranged between 59 and 86 mV decade^–1 with all the oxide film electrodes. The electrocatalytic activity was found to be greatest with the Ni/LaNi_0.75Fe_0.25O₃ electrode. A comparison was made between the electrocatalytic activities of LaNiO₃ prepared by the hydroxide solid solution precursor and by the hydroxide coprecipitation technique.     

Rare earth-first-row transition metal perovskites as catalysts for the autothermal reforming of hydrocarbon fuels to generate hydrogen

Perovskite oxides (ABO₃) containing rare earth elements on the A-site and first-row transition metal elements on the B-site were studied as catalysts for autothermal reforming of liquid hydrocarbon fuels to produce hydrogen for fuel cell systems. Experiments were conducted in a fixed bed microreactor at temperatures of 600–800 °C and gas-hourly space velocities (GHSV) ranging from 4600 to 28,000 h⁻¹ using 2,2,4-trimethylpentane (isooctane) as a surrogate fuel. We have found that the two binary oxides, LaNiO₃ and LaCoO₃, produced high yields of H₂, but were not structurally stable. These perovskites decomposed to La₂O₃ and Ni/NiO or Co/CoO under the reducing conditions present in the reformer. Three other binary oxides, LaCrO₃, LaFeO₃, and LaMnO₃, were structurally stable but significantly less active than LaNiO₃ and LaCoO₃. The partial substitution of chromium, iron, aluminum, gallium, or manganese on the B-site of LaNiO₃ to yield LaB_xNi_1−xO₃ was shown to improve the structural stability without a significant decrease in the H₂ yield. The effects of substituting rare earth elements for La and the substitution of alkaline earth elements on the A-site (La_1−yA_yB_xNi_1−xO₃) on catalyst performance and stability were also investigated. Finally, La_0.8Sr_0.2M_0.9Ni_0.1O₃ catalysts (where M = Cr, Mn, or Fe) were tested with a “benchmark fuel” mixture containing from 0 to 50 ppmw sulfur. These tests showed that using chromium as a stabilizing element in LaNiO₃ imparts the most sulfur tolerance.     

Promotion effect of Au on perovskite catalysts for the regeneration of diesel particulate filters

Four LaBO₃ perovskite catalysts (B = Cr, Mn, Fe and Ni), also supporting 2% by weight of gold, were prepared via the so-called Solution Combustion Synthesis (SCS) method, and characterized by means of XRD, BET, FESEM-EDS, TEM, O₂-TPD and CO-TPR analyses. The performance of these catalysts, in powder form, was evaluated towards the simultaneous oxidation of soot and CO. The 2 wt.% Au–LaNiO₃ showed the best performance with a peak carbon combustion temperature of 431 °C and a half CO conversion of 156 °C. The same nano-structured catalyst, deposited by in situ SCS directly over a SiC filter and tested on real diesel exhaust gases, fully confirmed the encouraging results obtained with catalyst powder.     

Preparation of nanoscale LaXO3 (X=Co,Mn, Ni) by rheological phase method for oxygen reduction reaction

The rheological phase method(RPM) is a simple and environmentally friendly synthesis method. In this work, nanoscale LaXO₃ (X = Co, Mn, Ni) series catalysts have been synthesized by RPM and their oxygen reduction reaction (ORR) have been investigated. The optimal calcination temperature of the RPM is lower than that of the solid-phase method, and the catalytic activity of the catalyst is also higher than that of solid-phase method, mainly because the products prepared by RPM have a nanoscale porous structure and a small amount of residual carbon. By comparing the differences among LaCoO₃, LaMnO₃, and LaNiO₃, the results show that the ORR activity of the catalyst is the strongest when the b-site element is Mn, and the calculated electron transfer number is 3.99, which is close to 4 electrons, indicating that the by-product generation is relatively small, and the kinetic current density reach 6.63 mA cm^?2. Both were higher than of LaCoO₃ and LaNiO₃. This work is expected to provide a new green synthesis method for non-noble metal catalyst perovskite oxygen reduction catalyst of LaCoO₃, LaMnO₃, and LaNiO₃.     

Synthesis of La1−xSrxMO3 (M = Mn,Fe, Co,Ni) nanopowders by alanine-combustion technique

La_1?xSr_xMO₃ (M = Mn, Fe, Co, Ni, x = 0–0.3) powders were obtained by solution combustion technique using metal nitrates and α-alanine. The as-prepared powders, resulted by the combustion reaction, were annealed at different temperatures to investigate the evolution of crystalline phases. For the strontium-doped lanthanum-based perovskites, higher annealing temperatures than for the corresponding pure lanthanum-based perovskites are needed to obtain single-phase compounds depending on M-site metal and strontium content. The oxide powders were investigated by FT-IR spectra, X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific area measurements. Based on our results we propose different mechanisms for La_1?xSr_xMO₃ (M = Mn, Fe, Ni, x = 0–0.3) obtaining, depending on the intermediary compounds formed in the combustion reaction or during the thermal treatment of the as-prepared powders.     

Parallel oxygen and chlorine evolution on Ru1−xNixO2−y nanostructured electrodes

Nanocrystalline materials with chemical composition corresponding to formula Ru_1−xNi_xO_2−y (0.02 < x < 0.30) were prepared by sol-gel approach. Substitution of Ru by Ni has a minor effect on the structural characteristics extractable from X-ray diffraction patterns. The electrocatalytic behavior of Ru_1−xNi_xO_2−y with respect to parallel oxygen (oxygen evolution reaction, OER) and chlorine (chlorine evolution reaction, CER) evolution in acidic media was studied by voltammetry combined with differential electrochemical mass spectrometry (DEMS). The DEMS data indicate a significant decrease of the over-voltage for chlorine evolution with respect to that of pure RuO₂. The oxygen evolution is slightly hindered. The increasing Ni content affects the electrode material activity and selectivity. The overall material's activity increases with increasing Ni content. The activity of the Ru-Ni-O oxides towards Cl₂ evolution shows a distinguished maximum for material containing 10% of Ni. Further increase of Ni content results in suppression of Cl₂ evolution in favor of O₂ evolution. A model reflecting the cation-cation interactions resulting from Ni-doping is proposed to explain the observed trends in electrocatalytic behavior.     

Phase Stabilization of a LaNiO3 Perovskite and the Electric Resistivity of its A/B-Site Substituted,Ni-Deficient La(Ni0.6Fe0.3)O3 Modifiers

Modified LaNiO₃ single phases of the A/B-site substituted La(Ni_0.6Fe_0.3)O₃ perovskites with A=Ag⁺, Pb²⁺, and Nd³⁺ and B=Mn³⁺ and Ga³⁺ sustaining at high process temperatures without decomposition were synthesized and their crystallinity, microstructure, and electrical resistivity were investigated. Electrical resistivity was used as an indicator to explore the response of single-phase La(Ni_0.6Fe_0.3)O₃ to the different A/B-site substitutions. The rationalized explanation for the variations of resistivity with substitutions was based on the band structure-related tolerance factor or by its two independent lattice distances: d_La−O and d_Ni−O.     

Methyl ethyl ketone combustion over La-transition metal (Cr, Co, Ni, Mn) perovskites

A series of LaBO₃ (B = Cr, Co, Ni, Mn) and La_0.9K_0.1MnO_3+δ perovskites have been prepared and tested as catalysts in the combustion of methyl ethyl ketone (MEK) at two concentration levels in air. Complete MEK conversion can be achieved for the most concentrated stream (1250 ppmv, WHSV = 425 h⁻¹) at temperatures between 270 °C (manganite) and 345 °C (chromite). Activity is governed by the nature of the cation in position B and related to reducibility, being comparable for manganite activity with that of the much more expensive Pt-supported catalysts. Doping with K of lanthanum manganite produces an increase in surface area, as well as the formation of non-stoichiometric oxygen and a greater proportion of Mn⁴⁺ on the surface. All these factors may have a role in increasing its activity for catalytic combustion. Catalytic results suggest a marked influence of MEK concentration on the combustion rate. MEK oxidation to CO₂ goes through acetaldehyde as intermediate product; methyl vinyl ketone and diacetyl (2,3-butanedione) were also formed, albeit in very low amounts. Nevertheless, acetaldehyde yield is zero at complete conversion, so the combustion of MEK can be carried out over these perovskite systems with 100% selectivity for CO₂.     

Effect of sulphur poisoning on perovskite catalysts prepared by flame-pyrolysis

ABO₃ perovskite-like catalysts are known to be sensitive to sulphur-containing compounds. Possible solutions to increase resistance to sulphur are represented by either catalyst bed protection with basic guards or catalyst doping with different transition or noble metals. In the present work La_(1−x)A^′_xCoO₃, La_(1−x)A^′_xMnO₃ and La_(1−x)A^′_xFeO₃, with A′ = Ce, Sr and x = 0, 0.1, 0.2, either pure or doped with noble metals (0.5 wt% Pt or Pd), were prepared in nano-powder form by flame-pyrolysis. All the catalysts were tested for the catalytic flameless combustion of methane, monitoring the activity by on-line mass spectrometry. The catalysts were then progressively deactivated in operando with a new procedure, consisting of repeated injection of some doses of tetrahydrothiophene (THT), usually employed as odorant in the natural gas grid, with continuous analysis of the transient response of the catalyst. The activity tests were then repeated on the poisoned catalyst. Different regenerative treatments were also tried, either in oxidising or reducing atmosphere.Among the unsubstituted samples, higher activity and better resistance to poisoning have been observed in general with manganites with respect to the corresponding formulations containing Co or Fe at the B-site. The worst catalyst showed LaFeO₃, from both the points of view of activity and of resistance to sulphur poisoning. La_0.9Sr_0.1MnO₃ showed, the best results, exhibiting very high activity and good resistance even after the addition of up to 8.4 mg of THT/g of catalyst. Interesting results were attained also by adding Sr to Co-based perovskites. Sr showed a first action by forcing Mn or Co in their highest oxidation state, but, in addition, it could also act as a sulphur guard, likely forming stable sulphates due to its basicity. Among noble metals, Pt doping proved beneficial in improving the activity of both the fresh and the poisoned catalyst.     

Synthesis and characterization of La0.75Sr0.25Cr0.9M0.1O3 perovskites as anodes for CO-fuelled solid oxide fuel cells

A series of La_0.75Sr_0.25Cr_0.9M_0.1O₃ (M = Mn, Fe, Co, Ni) perovskite compounds was synthesized by a modified citrate sol-gel route and employed as anode electrodes on YSZ electrolyte supported SOFC cells. Materials and anode electrodes were characterized for their chemical composition, crystal structure and film morphology. The electrochemical performance of the prepared anodes was evaluated in button cells under SOFC operation with CO/CO₂ mixtures in the temperature range of 900–1000 °C. It was shown that the performance of the perovskite materials in terms of maximum power density follows the sequence Fe > Ni > Co > Mn, based on the substitution cation into the B-site. No carbon deposition was observed under the operating conditions examined, even for prolonged (120 h) exposure to the reaction mixture.     

Oxidation of alkylaromatics to benzylic ketones using TBHP as an oxidant over LaMO3 (M = Cr, Co, Fe, Mn, Ni) perovskites

A series of LaMO₃ (M = Cr, Co, Fe, Mn, Ni) perovskites were synthesized by citrate precursor decomposition method and characterized by XRD technique. The catalytic activity of the synthesized perovskites was investigated for the oxidative functionalization of alkylaromatics to benzylic ketones using TBHP as an oxidant. Of various perovskites screened, LaCrO₃ exhibited remarkable catalytic activity providing the oxidation of alkylarenes selectively at the benzylic position. The LaCrO₃/TBHP catalytic system provides excellent yields of the desired ketones under solvent-free conditions and the catalyst can be successfully used up to six consecutive cycles with no significant loss in activity.     

Oxidation of alkylaromatics to benzylic ketones using TBHP as an oxidant over LaMO3 (M = Cr,Co, Fe,Mn, Ni) perovskites

A series of LaMO₃ (M = Cr, Co, Fe, Mn, Ni) perovskites were synthesized by citrate precursor decomposition method and characterized by XRD technique. The catalytic activity of the synthesized perovskites was investigated for the oxidative functionalization of alkylaromatics to benzylic ketones using TBHP as an oxidant. Of various perovskites screened, LaCrO₃ exhibited remarkable catalytic activity providing the oxidation of alkylarenes selectively at the benzylic position. The LaCrO₃/TBHP catalytic system provides excellent yields of the desired ketones under solvent-free conditions and the catalyst can be successfully used up to six consecutive cycles with no significant loss in activity.     

Effects of manganese substitution at the B-site of lanthanum-rich strontium titanate anodes on fuel cell performance and catalytic activity

Sr_0.4La_0.6Ti_1−xMn_xO_3−δ with rhombohedral structure has been investigated in terms of their electrochemical performance, redox stability, and electro-catalytic properties for solid oxide fuel cell anodes. The performance of Sr_0.4La_0.6Ti_1−xMn_xO_3−δ anodes for solid oxide fuel cells strongly depends on the Mn substitution at the B-site of the perovskites. Electrical conductivity of Sr_0.4La_0.6Ti_1−xMn_xO_3−δ increases with increasing Mn content. X-ray photoelectron spectroscopy analysis reveals that the amount of Mn³⁺ and Ti³⁺, which is an electronic charge carrier, increases with Mn doping. The reduced anode powders with high Mn/Ti ratio show oxygen storage capability and a low carbon deposition rate. Linear thermal expansion coefficients of Sr_0.4La_0.6Ti_1−xMn_xO_3−δ anodes range from 9.46×10⁻⁶ K⁻¹ to 11.3×10⁻⁶ K⁻¹. The maximum power densities of the single cell with the Sr_0.4La_0.6Ti_0.2Mn_0.8O_3−δ anode in humidified H₂ and CH₄ at 800 °C are 0.29 W cm⁻² and 0.24 W cm⁻², respectively.     

Synthesis,characterization, and catalytic activity of 4 mol % N,N′‐methylene bisacrylamide crosslinked poly(acrylic acid)–metal complexes

The metal‐ion complexation behavior and catalytic activity of 4 mol % N,N′‐methylene bisacrylamide crosslinked poly(acrylic acid) were investigated. The polymeric ligand was prepared by solution polymerization. The metal‐ion complexation was studied with Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) ions. The metal uptake followed the order: Cu(II) > Cr(III) > Mn(II) > Co(II) > Fe(III) > Zn(II) > Ni(II). The polymeric ligand and the metal complexes were characterized by various spectral methods. The catalytic activity of the metal complexes were investigated toward the hydrolysis of p‐nitrophenyl acetate (NPA). The Co(II) complexes exhibited high catalytic activity. The kinetics of catalysis was first order. The hydrolysis was controlled by pH, time, amount of catalyst, and temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 272–279, 2004     

The electrocatalytic behavior of Ru0.8Co0.2O2−x—the effect of particle shape and surface composition

The electrocatalytic activity of Ru_0.8Co_0.2O_2−x nanocrystals was studied using diffraction, microscopic and spectroscopic techniques to elucidate the role of particle shape and surface chemical composition in the electrocatalytic evolution of oxygen and chlorine. The prepared Ru_0.8Co_0.2O_2−x samples are of the rutile structure, their chemical composition, however, differs. The samples with the smallest particle size compensate for the Co doping by oxygen deficiency. The materials featuring bigger particle size show tendency to compensate for the presence of cobalt by higher valency of Ru. Regardless of the particle size or actual surface composition of the Ru_0.8Co_0.2O_2−x electrodes, the chlorine evolution precedes that of oxygen by ca. 100 mV. The Ru_0.8Co_0.2O_2−x electrodes retain high affinity to oxygen evolution once the reaction becomes possible. This behavior can be ascribed to a stabilization of the six-valent ruthenium, which represents the major intermediate for the oxygen evolution process, at the electrode surface due to the presence of di-valent and tri-valent cobalt. This effect precludes the possible effects of the particle shape and crystal edge distribution.     

NO reduction by CO over aluminate‐supported perovskites

Well crystallised La₂CuO₄ and LaMO₃ perovskites were studied in the CO + NO reaction. Whereas for LaMO₃ solids (M = Cr, Mn, Co and Ni) the activity decreased after reaction at 650 °C, the opposite was observed for LaFeO₃ and La₂CuO₄ leading to the most active catalysts. Their activity was even more enhanced when supported onto magnesium aluminate of 60 m² g⁻¹. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of A- and B-site doping on the properties of the system La2CoO4±δ

In the present paper the compounds LaSrCo_0.5M_0.5O_4±δ (M = Co, Fe, Mn, Ni) and La_1.4Sr_0.6Co_0.5M_0.5O_4±δ (M = Co, Ni) were prepared and characterised in order to elucidate the influence of strontium doping on A-site as well as doping with transition metals on B-site of the mixed conductor La₂CoO_4±δ. All the prepared oxides of this paper possessed the K₂NiF₄ structure, exhibited high electrical conductivity (>100 S/cm) and adequately low linear thermal expansion coefficient. Therefore, they are very promising materials for high temperature electrochemical applications.     

Oxidative coupling of methane over some titanates based perovskite oxides

A series of perovskites of the formula Ca_1–xSr_xTi_1–yM_yO_3– (M = Fe or Co,x = 0–1,y = 0–0.6 for Fe,y = 0–0.5 for Co) were prepared and tested as the catalyst for the oxidative coupling of methane. The catalysts were stable under the reaction conditions. The catalysts of high p-type and oxide ionic conductivity afforded the high selectivity. Some catalysts containing Co on B-sites are thermally unstable and decomposed to metal oxide components at high temperature, giving rise to synthesis gas production.