Pechini Method Research Articles

Catalytic Steam Reforming of Natural Gas over a New Ni Exsolved Ruddlesden‐Popper Manganite in SOFC Anode Conditions

AbstractThe catalytic behavior of the new Ni exsolved Ruddlesden‐Popper (RP) manganite (La1.5Sr1.5Mn1.5Ni0.5O7) for the reforming reaction was studied. The material was synthesized by the Pechini method and reduced to induce the formation of two phases: n=1 RP structure LaSrMnO4 decorated with Ni nanoparticles. Ni impregnation on (La,Sr)2MnO4 ceramic support of similar composition was also prepared for comparison. The catalytic measurements were carried out in a reduction‐reaction process with low steam to carbon content (S/C=0.15) at 700, 800 and 850 °C. The exsolved material exhibits a better performance than the impregnated for the methane steam reforming reaction, especially at 850 °C with higher conversion and H2 production rate. However, in light alkane gas mixtures (CH4−C2H6 and CH4−C3H8), the behavior is affected due to the competition between reactions and low available metallic active sites, without affecting the H2 production. The exceptional overall results considering this new material as a promising anode material in a SOFC fed with Colombian natural gas.

Versatile by design: Hollow Co3O4 architectures for superior lithium storage prepared by alternative green Pechini method

Co3O4 open hollow structures were synthesized by a new green alternative of Pechini method that implies three simple steps: (i) an initial formation of Co2+- citric soluble coordination compounds, (ii) hydrothermal processing (180 °C) in the presence of fructose followed by (iii) air thermal processing of the as-obtained precursor. Benefiting from its exclusive structural features, this appealing hollow Co3O4 material demonstrated superior specific capacity, rate performance and cycling stability (specific capacity of 848 mA h g−1 at an applied C-rate of 0.5 C with a coulombic efficiency of 98% after 250 cycles) in comparison with multi-shelled hollow spheres obtained in the absence of citric acid (525 mA h g−1 with a coulombic efficiency of 97% recorded under the same conditions).

Spectroscopic and paramagnetic properties of LaAlO3 polycrystals doped with vanadium ions

We present a study of the optical and paramagnetic properties of the LaAlO3 compound doped with vanadium ions (1 wt%). LaAlO3 material is a trigonal perovskite of microsized powder, made with using the Pechini method. The excitation and emission spectra as well as the luminescence decay profile, of LaAlO3 polycrystals with the presence of V4+ ions, were measured and analyzed. The CIE chromatic coordinates, as well as the color rendering index together with the correlated color temperature, were estimated. We have also analyzed the electron paramagnetic resonance spectrum with the occurrence of vanadium(IV) ions.

Undoped tetragonal ZrO2 obtained by the Pechini method: thermal evaluation of tetragonal–monoclinic phase transition and application as catalyst for biodiesel synthesis

Zirconia (ZrO2) is a well-known polymorphic material, and the monoclinic phase of this compound is the most stable phase at room temperature. Nevertheless, tetragonal zirconia has been obtained at room temperature without doping using chemical synthesis methods. In the present work, tetragonal undoped ZrO2 was obtained by the Pechini method, and the tetragonal–monoclinic phase transition was evaluated by thermogravimetry, differential thermal analysis (DTA) and in situ high-temperature X-ray diffraction (HT-XRD). The tetragonal phase was obtained as the major phase after calcination at and below 800 °C, while most of the transition to the monoclinic phase took place during cooling at temperatures below 500 °C, as indicated by DTA and HT-XRD. The pure monoclinic phase was obtained after calcination at 1000 °C. Samples calcined at 600 and 1000 °C were sulphated and applied in the ethylic transesterification of soybean oil. No meaningful difference was observed in the activity, and high efficiency was attained for both catalysts for the reaction performed at 100 °C for 2 h.

Oxygen vacancy induced performance enhancement of toluene catalytic oxidation using LaFeO3 perovskite oxides

Surface oxygen vacancies have been demonstrated to be an important factor for volatile organic compounds (VOCs) catalytic oxidation. In this work, the oxygen vacancy over LaFeO3 perovskite oxides was tuned by the way of controlling A-site cation deficiency. The catalysts were synthesized through the Pechini method and investigated for the complete oxidation of toluene. Upon the strategy, the catalytic activity for the complete oxidation of toluene was enhanced obviously. The sample L0.90FO exhibited excellent catalytic performance, better than the stoichiometric sample LaFeO3 and commercial Fe2O3. Via analyzation of diversified characterization results, the introduction of A-site cation deficiency could affect the surface physicochemical properties to a certain extent, including enhanced oxygen vacancies, surface element valence state, and surface oxygen species content. Furthermore, through DFT calculation, the introduction of A-site cation deficiency could boost the formation of oxygen vacancies, consistent with the results of characterizations. Herein, the strategy of the introduction of A-site cation deficiency is one effective method to tune the surface oxygen vacancy which would benefit the catalytic performance of toluene catalytic oxidation.

Synthesis, Characterization and Phase Transition of Highly Porous γ -Alumina Nanoparticles

Alumina is an important metal oxide used in a wide range of applications. It is a challenge to synthesize stable γ-alumina nanoparticles because, γ-phase of alumina is not as stable as α phase of alumina. But γ-alumina owns a higher surface area making it a good candidate for many industrial applications such as catalyst, catalytic support for petroleum refining, absorbent, alcohol dehydration, catalytic reduction of automotive pollutants like NOx, CO and hydrocarbons. This research focuses on synthesis, characterization and study of phase identification of pure γ-alumina nanoparticles. Modified “Pechini method”(Danks, Hall, and Schnepp (2016); Huizar-Felix, Hernandez, de la Parra, Ibarra, & Kharisov, 2012; Naskar, 2010; Zaki, Kabel, & Hassan, 2012)was used for the synthesis. Transesterification of citrate and ethylene glycol makes a covalent polymer network with trapped Al atoms. Continuous stirring of the reaction mixture while maintaining an optimum temperature is an important factor affecting this reaction. Calcination was carried out at different temperatures to identify phase transitions of alumina nanoparticles. In order to further reduce the particle size and increase the surface area, reactant ratio of citric acid: aluminum acetate was modified to 1:1, volume of ethylene glycol was increased up to 90% of volume of the solution and Triton X was used as a surfactant. PXRD confirmed the pure γ-alumina phase (JCPDS No. 00-010-0425) in samples calcined at 900 °C. At 1000 °C γ-alumina is converted to α-alumina (JCPDS No. 00-083-2080). After the modifications, γ-alumina was identified at 700 °C. FTIR-ATR analysis shows peaks around 1127 cm-1 indicating the presence of Al-O-Al asymmetric bending modes and the peaks around 500 cm-1-750 cm-1 correspond to γ-AlO6 octahedral sites and 800 cm-1 correspond to AlO4 tetrahedral sites in γ alumina spinel structure. Resulted product of low temperature, pure γ-alumina nanoparticles will facilitate the industrial development in various applications.

Removal of Various Textile Dyes Using LaMn(Fe)O3 and LaFeMn0.5O3 Nanoperovskites; RSM Optimization, Isotherms and Kinetics Studies

Nano-perovskites of La with Mn or Fe cations were prepared by the Pechini method. The products were characterized by FT-IR, TGA/DTA, XRD, FESEM, BET, and AFM analysis. The degradation efficiency of an acidic solution of anionic, cationic and neutral azo or anthraquinone dyes was investigated in the presence of LaMn(Fe)O3 and LaFeMn0.5O3 nanoperovskites without any external reagents under dark. The results reveal that degradation efficiency follows the order of LaMnO3.125 > LaFeMn0.5O3 > LaFeO3. Compared with pure LaFeO3, the LaFeMn0.5O3 sample exhibits an enhanced adsorption capability and consequently catalytic performance. The key parameters such as catalyst type, dye initial concentration and reaction time on the degradation efficiency were optimized using response surface methodology (RSM) based on historical data design. The R2, F-value, and p-value of the fitted quadratic model were obtained 0.9822, 315.51, and smaller than 0.0001, respectively; showing the significance and adequacy of the model. The Langmuir and Freundlich isotherms were utilized to fit the experimental data. The kinetic of degradation have been investigated with the use of pseudo-first-order and -second-order models. The isotherm and kinetic results reveal that each type of dye adsorb differently and need to study separately. Finally, the proposed catalysts outperformed similar catalysts in the degradation of organic dyes.

Influence of Synthesis Routes on the Crystallography, Morphology, and Electrochemistry of Li2MnO3.

With the potential of delivering reversible capacities of up to 300 mAh/g, Li-rich transition-metal oxides hold great promise as cathode materials for future Li-ion batteries. However, a cohesive synthesis-structure-electrochemistry relationship is still lacking for these materials, which impedes progress in the field. This work investigates how and why different synthesis routes, specifically solid-state and modified Pechini sol-gel methods, affect the properties of Li2MnO3, a compositionally simple member of this material system. Through a comprehensive investigation of the synthesis mechanism along with crystallographic, morphological, and electrochemical characterization, the effects of different synthesis routes were found to predominantly influence the degree of stacking faults and particle morphology. That is, the modified Pechini method produced isotropic spherical particles with approximately 57% faulting and the solid-state samples possessed heterogeneous morphology with approximately 43% faulting probability. Inevitably, these differences lead to variations in electrochemical performance. This study accentuates the importance of understanding how synthesis affects the electrochemistry of these materials, which is critical considering the crystallographic and electrochemical complexities of the class of materials more generally. The methodology employed here is extendable to studying synthesis-property relationships of other compositionally complex Li-rich layered oxide systems.

One-pot-like facile synthesis of YBa2Cu3O7-δ superconducting ceramic: Using PVP to obtain a precursor solution in two steps

There are a variety of chemical routes used to produce advanced ceramic materials. The sol-gel-like methods are widely applied since the final samples present high stoichiometric and grain size homogeneity. However, with the search for sustainable practices, researchers have been worked in the so-called one-pot synthesis, where all the chemical reactions occur in a single vessel with low residue production. Thus, in this work, we used a one-pot-like synthesis adapted to produce YBa2Cu3O7-δ superconducting ceramic samples. One shows that, in two main steps, a polymer solution is prepared in a few hours, and after heat treatments, a single-phase material is obtained. It is shown that the one-pot-like samples can present a higher diamagnetic signal in comparison with specimens prepared by the well-known Pechini Method. With this work, we show that there are alternative routes to produce advanced ceramics with simple and secure methods, if we compare, e.g., with trifluoroacetate routes.

Influence of Al3+ co-doping on the spectral properties of europium doped Ca9Y(PO4)7.

A series of luminescent materials based on a calcium yttrium phosphate matrix doped with europium and different concentrations of aluminum ions (0, 5, 10% of mole) was synthesized using the Pechini method. A two-step strategy of synthesis was applied. Phase composition analysis and spectroscopic measurements were performed to characterize the obtained phosphors. The XRD patterns show that in all cases the obtained materials consist of a pure phase of Ca9Y(PO4)7. Emission spectra of the materials obtained after the first step of the synthesis consist of narrow bands attributed to 5D0–7FJ transitions in Eu3+ ions. Independently of the aluminum concentration, europium ions are incorporated into at least two different cationic sites. Considering the asymmetric ratio (R), the sites are characterized by the presence/absence of inversion symmetry. The emission intensity of Eu3+ introduced into the more symmetric site decreases with increasing aluminum concentration. The emission spectra of the materials after the reduction process are characterized by intensive broad bands located at 420 and 488 nm attributed to the d–f transitions in Eu2+; however, the line shape of the spectra depends on the aluminum concentration. Moreover, incorporation of aluminum ions causes the stabilization of the Eu3+ ions under a reductive atmosphere.

Enhanced magnetic and magnetodielectric properties of Al-doped gallium ferrite nanoparticles

In this work, a series of Ga1-xAlxFeO3 (x = 0, 0.1, 0.2, 0.5) nanoparticles was prepared by a modified Pechini method. The influence of Al doping at the Ga site on the structural, magnetic, and magnetodielectric (MD) properties of GaFeO3 nanoparticles was studied. The X-ray diffraction pattern analysis using the Rietveld refinement method indicated that all samples have an orthorhombic structure with Pc21n space group and the value of lattice parameters decrease systematically with increasing Al concentration. Interestingly, the magnetic characterization indicated that with increasing Al-content up to 0.5, the ferrimagnetic transition temperature (TC) increases from 310 to 350 K. It is also found that magnetic hysteresis curves measured below TC exhibit two-phase-like magnetic behavior consisting of hard and soft magnetic phases. Moreover, the simultaneous improvement of magnetic behavior and MD effect of Al-doped GaFeO3 samples are prominent candidates for the applications of room temperature multiferroic devices.

Kalsinasyon Sıcaklığının Modifiye Edilmiş Pechini Yöntemi ile Hazırlanan Perovskit Özelliklerine Etkisi

Perovskite type oxides which have the general formula as ABO 3 including both rare earth elements and 3d transition metals is gaining interest according to be utilized as such strategic materials because of their excellent catalytic, magnetic, electrical and optical properties. Along with perovskitic materials, lanthanum nickel oxide (LaNiO 3 -LNO) shows potential as a consequence of its electronic and catalytic properties in not only reactions like reforming, redox reactions but also in storage and conversion of energy or synthesis an electrode material. LNOs are widely prepared by methods like sol-gel, co-precipitation, solid state and Pechini. Among these methods, the Pechini method uses the common metal salts consisting of nitrates, acetates, chlorides, etc. as precursors and citric acid (CA) as a chelating agent of metal ions and ethylene glycol (EG) as a cross-linking agent to form a polymeric resin on molecular level and declines segregation of metal ions and ensures compositional homogeneity. This process can defeat most of the difficulties and disadvantages that frequently occur in the alkoxides related to sol−gel method. The present work attempts to scan the effect of calcination temperature on the physical properties of LaNiO 3 catalysts prepared by modified Pechini method without ethylene glycol. In order to lay out the physical properties, X-ray diffraction (XRD), scanning energy micoscopy (SEM), and N 2 adsorption/desorption techniques were used. The change with the temperature in the structure caused a decrease in surface area, pore volume and increase in pore size. XRD studies revealed that calcination of LNO at 700°C favored the formation of an almost homogeneous LaNiO 3 perovskite phase rather than calcination at 500°C. The study underlined that the preparation of the LNO by the modified Pechini method can be applied successfully with the temperature above 700°C without EG as a cross-linking agent.

Obtaining TiO2:CoFe2O4 nanocatalyst by Pechini method for diuron degradation and mineralization

This paper proposes the obtaining of TiO2:CoFe2O4 nanocatalyst aiming to study the efficiency of photocatalytic degradation and mineralization of diuron (DRN). Therefore, the required nanocatalysts were synthesized, and the concentration effect of cobalt spinel ferrite (CoFe2O4) on the properties of TiO2 was investigated. TiO2 and TiO2:CoFe2O4 were synthesized via the Pechini method, while CoFe2O4 was synthesized via the combustion method. The nanocatalysts were characterized by XRD with Rietveld refinement, BET, SEM, granulometric analyses, FTIR, and zeta potential and magnetic measurements. Photocatalytic activity was evaluated by quantification of the final concentration of DRN and total organic carbon. The environmental toxicity was analyzed by using CE50 test. Results showed that all of the nanocatalysts were successfully synthesized. Formation of the major phases, namely, anatase TiO2 and spinel, was observed. Increasing amounts of CoFe2O4 added to TiO2 increased the saturation magnetization of the nanocatalysts from 2.51 emu/g to 19.03 emu/g, which indicates that increasing concentrations of CoFe2O4 could improve the separability of the nanocatalyst from the system after application. The photocatalytic systems achieved 100% DRN degradation, and their mineralization efficiency increased with decreasing CoFe2O4 concentration. The combination of photolysis and photocatalysis improved the efficiency of mineralization. The developed photocatalytic treatment decreased the system toxicity and increased CE50 from 1.5% to 14%.

Relationship between oxygen desorption and the reduction features of Mn and Fe in perovskite-type SrFe1−xMnxO3−δ

Perovskite-type (ABO3) SrFe1−xMnxO3−δ specimens (0.1 ​≤ ​x ​≤ ​0.6) were prepared via the Pechini method. The Mn and Fe valences were determined by means of X-ray absorption fine structure spectroscopy and iodometry, and the average B valences and oxygen contents (3−δ) were calculated from the obtained valences. In perovskite SrFe1−xMnxO3−δ specimens, it was found that oxide ion vacancies existed on several octahedra. Thermogravimetry showed that the degree of oxygen desorption increased upon increasing the temperature but decreased at higher Mn contents, thereby indicating that Mn ions were not reduced in the obtained cubic perovskite phase. It was therefore considered that Fe ions were more easily reduced, and that the crystal structure was stable during oxygen desorption, thereby suppressing the reduction of Mn ions in the B-site mixed perovskite-type SrFe1−xMnxO3−δ.

Photodegradation of 4-chloropehol in aqueous media using LaBO3 (B = Fe, Mn, Co) perovskites: Study of the influence of the transition metal ion in the photocatalytic activity

Three LaBO3 (B = Fe, Mn, Co) perovskitas were synthesized by the Pechini method using as raw materials ethylene glycol, citric acid and nitrates of the metal ions. The precursors so obtained, underwent to heat treatment to 600 and 700 °C. The catalysts were characterized by XRD, physisorption of N2, UV–vis diffuse reflectance and TEM microscopy. The results showed materials that exhibit a pure perovskite phase, low specific surface area (6.6998-15.7117 m2/g) and band gap energies in the range of 0.606–2.90 eV. The catalytic activity of the synthesized perovskites was evaluated in the photodegradation of 4-chlorophenol in aqueous media. Although all the photocatalysts degraded more than 35 % of the organic pollutant, the Mn-containing sample showed the major photocatalytic activity with a degrade percentage of approximately 80 after two hours of reaction. Fluorescence tests suggest the generation of OH radicals as the oxidative species of the target pollutant.

Pairwise Parahydrogen Addition Over Molybdenum Carbide Catalysts

Herein, we have shown that the phase composition of molybdenum carbide catalysts has a pronounced effect on the pairwise hydrogen addition selectivity in the gas-phase propyne hydrogenation with parahydrogen. Molybdenum carbide catalysts were prepared using either the Pechini method or temperature-programmed reduction with CH4/H2 carburizing gas mixture. The structures of carbide catalysts were characterized by high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that molybdenum carbide prepared by the Pechini method predominantly contains a face-centered-cubic MoC1−x phase, while the TPR method yields a hexagonal-close-packed Mo2C phase. By varying the gas hourly space velocity of carburizing gas mixture, the defected phase can be produced. Computer modeling for XRD patterns was used to identify the phase composition of Mo2C catalysts. All the catalysts were found to be active in pairwise hydrogen addition; however the hcp-Mo2C phase exhibits a higher contribution of pairwise H2 addition providing ~ 150-fold proton NMR signal enhancement.

Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water

Gd2NiMnO6 (GNMO NSs) nanostructures were synthesized via a Pechini method using propylene glycol (PG) as alkaline agent and various acid solutions as stabilizing agents. Effect of temperature, time and stabilizing agent was investigated in order to reach the finest nanostructures. The morphology, structure and magnetic property of nanostructures examined by XRD, SEM, HRTEM, FTIR, BET and VSM techniques. The photocatalytic degradation ability of GNMO NSs for the removal of different dyes from wastewater was reported. The obtained adsorbent with porous structure not only displayed fast rate adsorption, greater capacity adsorption, and promising selectivity adsorption to various dyes but also presented convenient magnetic separation characteristic. Rapid decomposition of dye observed with a rate of degradation, more than 90 % within the initial 105min, which is qualified to the porous structure, great surface area (6.1735 m2g−1), narrow of pore size (˜106.09nm) assessed from adsorption-desorption isotherms analysis of N2 as well as outstanding electron accepting structures of the planned porous nanoparticles. Consequently, prepared nanocomposite indicated the great potential to be considered as an active and rapid magnetic adsorbent for the dye removal from wastewater.

PET depolimerization in supercritical ethanol conditions catalysed by nanoparticles of metal oxides

The depolymerization of the PET in supercritical conditions using ethanol and catalyzed by cobalt and nickel oxides was enough for the recovery of the DET monomer, allowing yields close to 100 % depolymerization. The formation of DET in the depolymerization process was characterized by 1H-NMR, DSC, FTIR, SEM, and HPLC. Cobalt oxide and nickel oxide were obtained through the Pechini method and characterized using DRX, SEM, and TEM. A factorial design 22 with a duplicate center point was applied to evaluate the reaction time and amount of the catalyst effects on yield. Through analysis of response surface methodology (RSM), the highest degree of PET conversion (%) was obtained in 90 min reaction time and a smaller amount of catalyst (10 mg) through analysis of response surface contour. The smaller quantity of catalyst was sufficient to accelerate the process of depolymerization reaching almost 100 % yield, obtaining the monomer DET as the main product.

Physical and mechanical properties of low, ultralow and no cement refractory castables containing MgO nanoparticles developed in situ by means of polymeric resins

Abstract The introduction of MgO nanoparticles developed in situ in the matrix of high-alumina low cement, ultra-low and no cement refractory castables was made by means of a low viscosity containing aqueous polymeric resin, produced by the Pechini method. The addition of the liquid resin to the castables played two roles: first to serve as a supplier of mixing water and second as a precursor of nanoparticles of MgO, which were formed in situ in the castables matrices during firing. The results confirmed the benefits brought by the developed in situ MgO nanoparticles on the refractory properties of the investigated castables.

Dispersion of multiferroic BiFeO3 nanoparticles in nematic liquid crystals

Dispersion of ferroelectric- and ferromagnetic nanoparticles in liquid crystals (LCs) is investigated in the last decades. Recently, doping multiferroic-BiFeO3 nanoparticles in the LCs has become of interest. These nanoparticles have coupled ferroelectric- and ferromagnetic properties at ambient temperature. In the present experiments, a nematic LC was doped with a low concentration of BiFeO3 nanoparticles, synthesized using a modified Pechini method. The particles were characterized and their dispersions in heptane with an added surfactant were used for doping of the LC. The measured dielectric constants in the doped LCs varied as compared to the pure LC. It was shown that the presence of a magnetic field in the cooling process (cooling down from isotropic to anisotropic phase) of the LC cells leads to a significant increase of dielectric anisotropy. Also, the transition temperature decreased in the nematic-isotropic transition temperature for the doped sample.