LaCo1−x Pd x O3 Perovskite-Type Oxides: Synthesis, Characterization and Simultaneous Removal of NO x and Diesel Soot

A series of naometric perovskite catalysts LaCo_1?x Pd _x O₃ (x = 0, 0.01, 0.03) were prepared via a solution combustion synthesis route using metal nitrates as oxidizers and urea as fuel. It is essential to add a certain amount of ammonia aqueous solution to Pd²⁺ ions solution in the catalyst preparation process. Homogeneous nanoparticles LaCo_1?x Pd _x O₃ catalysts with the sizes in the range of 68–122 nm were obtained and characterized by using of XRD, BET, H₂-TPR, XPS, SEM and TEM. Pd was successfully introduced into the LaCoO₃ perovskite lattices. Further information was obtained by using XPS upon the LaCo_0.97Pd_0.03O₃ (with NH₄OH) sample after H₂-TPR. The results revealed that surface Pd was reduced to the metallic state at the end of the first step in the H₂-TPR experiment, and some surface Co could be reduced to metallic Co simultaneously. The catalytic properties were investigated for simultaneous NO _x -soot removal reaction. The performance of LaCo_1?x Pd _x O₃ catalysts were greatly improved by the partial substitution of Pd. The maximum NO conversion into N₂ and the ignition temperature of soot are 32.8% and 265 °C, respectively.     

The Effect of Copper Substitution on La2Ni1−x Cu x O4 Catalysts Activity for Simultaneous Removal of NOx and Diesel Soot

A series of the La₂Ni_1?x Cu _x O₄ (0 ≤ x ≤ 1.0) perovskite-like complex oxide catalysts, prepared and characterized by XRD, H₂-TPR, O₂-TPD and XPS, and catalytic activity tests, proved to be effective in the simultaneous removal of NOx and soot. The results indicated that the catalysts show the single orthorhombic K₂NiF₄-like phase. The doping of Cu led to the increase of orthorhombic distortion and the decrease of capability to accommodate non-stoichiometric oxygen, as well as the increase of the reducibility of lattice oxygen, resulting in improving catalytic activities. The La₂Ni_0.4Cu_0.6O₄ catalyst showed the highest activity. The maximum conversion of nitrogen oxide to molecular nitrogen was 15.6% and the ignition temperature decreased from 440 to 246 °C, as compared with the uncatalyzed soot combustion reaction.     

Simultaneous Removal of NO x and Soot Over Pt–Ba/Al2O3 and Pt–K/Al2O3 DPNR Catalysts

The effect of NO _x storage on the soot combustion activity when alkaline- and alkaline/earth-containing model DPNR catalysts are used is investigated in this work. The influence of different experimental conditions (NO concentration, temperature, and particulate loading) is addressed and discussed in relation to the NO _x storage efficiency and soot oxidation activity as well.     

Sol–gel synthesis of La0.6Sr0.4CoO3−x and Sm0.5Sr0.5CoO3−x cathode nanopowders for solid oxide fuel cells

Nano-powders of La_0.6Sr_0.4CoO_3?x (LSC) and Sm_0.5Sr_0.5CoO_3?x (SSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) with La(Sr)Ga(Mg)O_3?x (LSGM) as the electrolyte, were synthesized by low-temperature sol–gel method using metal nitrates and citric acid. Thermal decomposition of the citrate gels was followed by simultaneous DSC/TGA methods. Development of phases in the gels, on heat treatments at various temperatures, was monitored by X-ray diffraction. Sol–gel powders calcined at 550–1000 °C consisted of a number of phases. Single perovskite phase La_0.6Sr_0.4CoO_3?x or Sm_0.5Sr_0.5CoO_3?x powders were obtained at 1200 °C and 1300 °C, respectively. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy. The average crystallite size of the powders was ～15 nm after 700 °C calcinations and slowly increased to 70–100 nm after heat treatments at 1300–1400 °C.     

Novel Type of Metal-Containing Polyimides for the Heck and Suzuki–Miyaura Cross-Coupling Reactions as Highly Active Catalysts

Novel palladium (II)-containing polyimides with exceptional catalytic properties for the Heck and Suzuki–Miyaura cross-coupling reactions were prepared from Pd(II)--bis(imine) complex and the corresponding dianhyrides. The glass transition temperatures (T _g ) of the polymers ranged from 169 to 241°C. The temperatures at which 10% weight loss occurred in air ranged from 415 to 579°C. Polyimides based on the palladium (II) complex were tested for catalytic activity in the Heck coupling reaction between styrene and several aryl halides and the Suzuki coupling reaction between phenylboronic acid and several aryl halides. The negative effects (e.g., expense, low reaction rates, air-sensitivity) experienced by using phosphines, particularly electron-rich phosphines, as catalysts in large scale applications is overcome by using polymer supported catalysis.     

Single-Crystalline La0.6Sr0.4CoO3-δ Nanowires/Nanorods Derived Hydrothermally Without the Use of a Template: Catalysts Highly Active for Toluene Complete Oxidation

Single-crystalline nanowires and nanorods of cubic perovskite-type La_0.6Sr_0.4CoO_3-δ oxides have been fabricated by a hydrothermal method and characterized by a number of analytical techniques. Compared to the polycrystalline La_0.6Sr_0.4CoO_3-δ catalyst, the single-crystalline materials exhibit much better catalytic activity for the complete oxidation of toluene. The excellent performance can be attributed to the distinct oxygen nonstoichiometry and single-crystalline structure of the materials.     

Preparation of La1?x Sr x CoO3 Oxide Electrode Material and its Influence on the Structure and Dielectric Performance of the Supported Ba1?x Sr x TiO3 Thin Films

Using the sol–gel method, La_1−x Sr _x CoO₃ (LSCO) electrode films were first fabricated on the Si (100) substrates, followed by the growth of Ba_1−x Sr _x TiO₃ (BST) thin films on the LSCO electrode film. The crystal structure and surface morphology of these films were characterized by XRD and SEM. The effects of Sr-doping and annealing temperature on the structure and electric resistivity of the LSCO films and the dielectric properties of the BST films were studied. Results show that the La_0.5Sr_0.5CoO₃ electrode annealed at 750 °C has the lowest electric resistivity, 1.1 × 10⁻³Ω cm. The relative permittivity of the La_0.5Sr_0.5CoO₃-supported BST films first increases and then decreases with Sr-doping. The relative permittivity of the BST film decreases while the dielectric loss increases with frequency. Among the studied BST films, Ba_0.5Sr_0.5TiO₃ has the largest relative permittivity and the smallest dielectric loss (95 and 0.1, respectively) when the frequency is 1 kHz.     

Reforming of Diesel Fuel for Hydrogen Production over Catalysts Derived from LaCo1−x M x O3 (M = Ru, Fe)

Catalysts derived from perovskite type oxides LaCo_1?x M _x O₃ (M = Ru or Fe, x = 0.2) synthesized by a modified citrate sol–gel method were tested in the oxidative reforming of diesel for hydrogen production. Physicochemical characterization of the samples revealed differences in the surface area, crystalline size, reducibility and relative distribution of the cobalt active phase on the surface of catalyst. These properties have important implications in the catalytic behaviour of the samples in the oxidative reforming of diesel. The increase in reducibility and metal exposition implies higher reforming activity as it was observed for the catalyst derived from LaCo_0.8Ru_0.2O₃.     

Synthesis and Characterization of Perovskite-Type Oxides La1−xMxCoO3 (M = Ce,Sr) for the Selective CO Oxidation (SELOX)

Perovskite-type oxides La_1?xM_xCoO₃ (M = Ce, Sr) were prepared by citrate method, characterized and evaluated in the selective CO oxidation (SELOX-CO). The insertion of low Cerium or Strontium content generated solids with a single phase related LaCoO₃ perovskite. For higher contents we observed segregation of CeO₂ and SrCO₃. The iso-structural substitution favors the formation of vacancies. The SELOX-CO showed 100 % CO conversion at 200 °C. Higher temperatures favored hydrogen oxidation and methanation.     

Acid Strength of H3PW x Mo12−x O40 and H6P2W x Mo18−x O62 Heteropolyacid Catalysts as a Probe of Acid Catalysis for 2-Propanol Conversion Reaction

Acid strength of H₃PW _x Mo_12?x O₄₀ (x = 0, 3, 6, 9, and 12) Keggin heteropolyacid (HPA) and H₆P₂W _x Mo_18?x O₆₂ (x = 0, 3, 9, 15, and 18) Wells-Dawson HPA catalysts was determined by NH₃-TPD measurements. Desorption peak temperature (acid strength) of H₃PW _x Mo_12?x O₄₀ and H₆P₂W _x Mo_18?x O₆₂ catalysts showed the same trend with respect to tungsten substitution, and increased with increasing tungsten substitution in both families of HPA catalysts. In order to correlate the acid strength with the acid catalysis of HPAs, vapor-phase 2-propanol conversion reaction was carried out as a model reaction. Yield for propylene (a product formed by acid catalysis of HPA) increased with increasing tungsten substitution and with increasing desorption peak temperature (acid strength) across both HPA families, regardless of the identity of HPA catalyst (without HPA structural sensitivity). The acid strength of H₃PW _x Mo_12?x O₄₀ and H₆P₂W _x Mo_18?x O₆₂ catalysts could be utilized as a probe of acid catalysis for 2-propanol conversion reaction.     

Effect of CeO2 and La2O3 on the Activity of CeO2−La2O3/Al2O3-Supported Pd Catalysts for Steam Reforming of Methane

The effect of the addition of CeO₂ or La₂O₃ on the surface properties and catalytic behaviors of Al₂O₃-supported Pd catalysts was studied in the steam reforming of methane. The FTIR spectroscopy of adsorbed CO and the Pd dispersion suggest the partial coverage of Pd⁰ by ceria or lanthana species. This could lead to the formation of an adduct MPd _x O (M = Ce or La) at the surface of the metal crystallites. The addition of ceria or lanthana resulted in an increase of the turnover rate and specific rate for steam reforming of methane. One possible explanation if that the Pd⁰*Pd^δ+O–M interfacial species (M = Ce or La) are oxidized by H₂O or CO₂, promoting the O* transfer to the metal surface. This could facilitate the removal of C* species from the metal surface, resulting in the increase of specific reaction rate and increase of the accessibility of CH₄ to metal active sites.     

Highly CO2RR activity and electrochemical performance of A-site deficient symmetrical electrode materials (La0.6Sr0.4)1−xFe0.8Ni0.2O3-δ for CO2 electrolysis

A-site deficient (La_0.6Sr_0.4)_1−xFe_0.8Ni_0.2O_3-δ (x = 0, 0.05, 0.1) perovskite oxide materials (LSFN100, LSFN95, and LSFN90) are evaluated as symmetrical electrode materials for CO₂ electrolysis. All three perovskite oxides display pure cubic perovskite structure. The introduction of A-site deficiency results in greater tendency of in-situ exsolution and stronger CO₂ adsorption capacity, which are verified by temperature-programmed reduction of H₂ and temperature-programmed desorption of CO₂. Furthermore, the current densities with LSNF90 symmetrical cell are 1.72, 1.18 and 0.72 A·cm⁻² under the applied voltage of 1.8 V at 850, 800 and 750 °C to electrolysis CO₂, respectively. Low polarization resistance of 0.186, 0.267 and 0.454 Ω·cm² is also observed under open circuit conditions at 850, 800 and 750 °C, respectively. A-site deficiency of perovskite materials reduces the activation energy of oxygen evolution reaction (OER) and carbon dioxide reduction reaction (CO₂RR). Symmetrical cell with LSFN90 electrode shows good electrochemical performance and long-term stability for CO₂ electrolysis.     

Effect of Mn-doping on the morphological and electrical properties of (Ba0·7Sr0.3) (MnxTi1−x)O3 materials for energy storage application

Lead-free (Ba_0·7Sr_0.3) (Mn_xTi_1?x)O₃ (x = 0.0, 1.0, 2.0, 4.0, 6.0, and 8.0%) ceramics were effectively synthesized by the sol-gel process. XRD and Raman spectroscopy confirm the single-phase perovskite structure with tetragonal symmetry, for all compositions. An in-depth analysis of the chemical composition and thermochemistry of the ceramics was carried out via FT-IR and TG-DTG. Morphological analyses of the samples revealed that doping Mn at higher concentrations suppresses the grain size and grain growth rate. The dielectric properties increased first and then decreased with increasing Mn content. The ferroelectric properties represented similar trend in polarization and energy storage efficiency as showed in dielectric properties. 2% Mn-doped sample exhibits the best dielectric and energy storage performance which is attributed to increased densification and grain size effects. Dielectric anomaly caused by defect dipole polarization was observed in temperature-dependent dielectric constant curves, for 6% and 8% Mn-doped samples. This study is helpful to establish the relationship between the structure, morphology, dielectric and ferroelectric properties of Mn substituted Ba_0·7Sr_0·3TiO₃ ceramics.     

The Chemical Evolution of the La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>CoO<Subscript>3−δ</Subscript> Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity

Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO₃ (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O₂ reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC.