Citrate Method Research Articles

Sol-Gel Synthesis And Characterization Of New Inorganic Pigments Containing Oxides of Iron, Aluminum, Strontium and Silicate

A series of inorganic pigments containing iron, aluminum, strontium, and silicate were prepared by the sol-gel method using compounds with different structures and morphologies as starting materials. The synthesis of the compounds was carried out using the modified citrate method. All powders were placed in a muffle furnace and calcined in air at 1100°C for 6 hours. Powder samples containing Fe, Sr, Al and Si oxides were obtained. The structure and chemical composition of the synthesized five inorganic pigments were investigated comparatively by Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy (UV-vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Energy Distribution X-ray Analysis (EDX).

Citrate Mediated Europium-Based Detection of Oxytetracycline in Citrus Tissues.

Oxytetracycline (OTC) and streptomycin have been used for the control of several plant diseases and were recently permitted for the control of citrus greening disease, Huanglongbing. Consequently, sensitive and reliable methods are highly needed for the detection of OTC in citrus tissues. Herein, we studied the replacement of cetyltrimethylammonium chloride (CTAC) by citrate (Cit) as a sensitizing agent for the analysis of OTC in citrus tissues using the recently established europium (Eu) method. In addition, we determined the optimal conditions for the formation of the Eu-OTC-Cit ternary complex in tris buffer. Our results showed that the plant matrix significantly decreased the fluorescence intensity of the Eu-OTC-Cit complex even after the replacement of CTAC. Our investigations showed that phenols such as gallic acid degrade slowly at high pH and their degradation was enhanced in the presence of the (Eu+3) cation. To reduce the plant matrix interference, the sample extract was cleaned using solid-phase extraction (SPE). The OTC recoveries from spiked healthy and Candidatus Liberibacter asiaticus (CLas)-infected trees were 91.4 ± 7.8% and 82.4 ± 3.9%, respectively. We also used the citrate method to determine the level of OTC in trunk-injected trees. The level of OTC as measured using the Eu-OTC-Cit complex (117.5 ± 20.3 µg g−1 fresh weight “FWT”) was similar to that measured using Eu-OTC-CTAC complex (97.5 ± 14 µg g−1 FWT). In addition, we were able to visualize the OTC in citrus leaf extract, under ultraviolet light (400 nm), after it was cleaned with the SPE. Our study showed that the citrate can be successfully used to replace the harmful CTAC surfactant, which could also react with phenols.

Structural Changes of the Lipid Model Systems in the Presence of Enzymes or Silver Nanoparticles

This work aimed to study the interaction of silver nanoparticles (AgNP) and lipases with models of biological membranes based on natural phospholipid and cholesterol. The crude phosphatidylcholine from egg yolk (PCe1) and synthetic cholesterol (Chol) were obtained from Sigma-Aldrich. Porcine pancreatic lipase (PPL) was obtained by purification from the hog pancreas. AgNP dispersion was prepared by the well-known citrate method. Measurement of surface tension (ST) was carried out using a BPA-1P device. The equilibrium surface tension (eST) was obtained by calculating the ST-time isotherms using the ADSA program. The particle sizes were determined by the dynamic light scattering method. An addition of AgNPs led to a pronounced decrease in both ST and eST (whereas almost no changes occurred by lipase addition), and AgNPs destructed the large lipid particles. The average lipid particle diameter values changed drastically, whereas the effective particle diameter values were almost the same by lipase addition. Thus, the interactions of AgNPs or lipase with the mixture of natural phospholipid and cholesterol have had entirely different features. These effects are interesting for modeling the interactions of inorganic and organic compounds with biological membranes.

Integrative effect of citrate on Cr(Ⅵ) and total Cr removal using a sulfate-reducing bacteria consortium

In controlling toxic Cr(Ⅵ) pollution, the sulfate-reducing bacteria (SRB) method—a bioresource technology—is considered more sustainable and stable than synthetic technologies; however, its mechanisms of metal removal are unclear. This study investigated the mechanism of the use of citrate as a carbon source in an SRB bioreactor for Cr(Ⅵ) removal by disassemble or simulation approach. We show that citrate can mask toxicity, whereby the IC50 value (inhibitory concentration affecting 50% of the test population) of citrate was higher than that of lactate, and that citrate can also protect water systems from oxidation. The anti-oxidation rate of citrate ranged from 76.00% to 90.92%; whereas for citrate‒Cr(Ⅲ), the oxidation rate was only 0.185%–0.587%. Citrate can up-regulate microbial genes and functions, causing acetate and sulfide (NaFeS2) accumulation. Acetate addition promoted Cr adsorption by sulfide (mainly NaFeS2) and promoted sulfide sedimentation. Moreover, in addition to Cr(Ⅵ) reduction and Cr(Ⅲ)‒sulfide generation, the addition of sulfide promoted sedimentation; the correlation coefficient between the sedimentation coefficient and the sulfur content was r = −0.88877 at p < 0.01. Therefore, citrate had a systemic radiative effect on every aspect of the SRB‒citrate system model for Cr(Ⅵ) removal. In addition to the reduction in the former simple model, an integrative effect (including adsorption, sedimentation, and metabolism) was combined with NaFeS2 for Cr removal, which was regulated by the SRB‒citrate system. Exploration and understanding of these mechanisms promote SRB‒citrate methods to be wider implications in practice.

Solgel synthesis of Gd2O3:Nd3+ nanopowders and the study of their luminescent properties

The paper presents the results of the sol-gel synthesis of Gd2O3:Nd3+ nanopowders by the citrate method, as well as the study of their structure and luminescent properties. A technique for using two different organic stabilizers with different thermal stability in sol-gel synthesis has been proposed and tested. The luminescent properties of the obtained Gd2O3:Nd3+ powders have been studied in the ultraviolet and near infrared spectral regions. The citrate sol-gel method was used to synthesize the materials. Aqueous solutions of metal nitrates were used as the main initial components. Citric acid and polyvinylpyrrolidone were used as organic modifying components, playing a double role in the synthesis process, i.e. acting as stabilizers of forming nanoparticles in colloidal solutions and serving as a fuel additive in the process of heat treatment of materials. Infrared spectroscopy and differential thermal and thermogravimetric analyses were used to study the evolution of the structure of materials during synthesis. Crystalline Gd2O3:Nd3+ nanopowders were obtained by a low-temperature sol-gel method using citric acid and polyvinylpyrrolidone as stabilizers. The data of infrared spectroscopy and differential thermal and thermogravimetric analyses show that the formation of Gd2O3:Nd3+ nanoparticles begins at the stage of the crude gel and the evolution process develops during the drying and heat treatment of materials. It is shown that the use of two different organic stabilizers with different thermal stability provides stabilization of the forming Gd2O3:Nd3+ nanoparticles at different stages of synthesis in a wide temperature range. The luminescence spectra are observed in the UV spectral region under excitation of the synthesized nanopowders by radiation with a wavelength of 238 nm. They are determined by electronic transitions in the Gd2O3 crystalline matrix. The synthesized Gd2O3:Nd3+ nanopowders exhibit intense photoluminescence in the UV and near-IR spectral regions. The results can be used in the development of a technology for the synthesis of various composite phosphors, as well as in the creation of luminescent nanopowders for nanothermometry in medicine.

Dye-sensitized solar cell with plasmonic gold nanoparticles modified photoanode

The depletion of fossil fuel and environmental anxieties has led to a greater interest in renewable forms of energy. To a large extent, the most prevalent form of renewable energy presently is solar energy. The Dye-sensitized solar cell (DSSC) is a promising substitute for all too familiar silicon solar cells. DSSC uses dyes as light-harvesting pigments in the conversion of solar energy to electric energy. This study is about the fabrication of DSSC using a photoanode made up of TiO 2 fused with gold nanoparticles. Gold nanoparticles enhance the performance of DSSC due to the plasmonic effect. The gold nanoparticles were made by the citrate method and characterized using UV–visible spectroscopy and dynamic light scattering. The performance of the solar cells was accessed via photocurrent and photovoltage measurements. The solar-to-electric power efficiency of the solar cells with gold nanoparticles was found to be about 50% higher than those without gold nanoparticles.

Investigations on microstructure, electrical and magnetic properties of Ni–Zn–Ga spinel ferrites

Two spinel ferrite samples Ni0.7Zn0.3GayFe2–yO4 (y = 0.5, 1.0) were prepared by both ceramic and citrate methods. X-ray diffraction patterns indicated a single phase of cubic structure for all the samples that have a space group Fd-3m. Rietveld analysis using MAUD software for all samples showed that the lattice parameter (a) decreases, while oxygen parameter (U) and strain (ɛ) increase by increasing the amount of Ga. A marked increase in the frequency bands in both the tetrahedral and octahedral sites was observed in the vibrational frequency bands of Fourier transform infrared spectra. Mossbauer effect (ME) spectra recorded at room temperature for the bulk sample (prepared by ceramic method) with lower concentrations of Ga3+ (y = 0.5) consist of two Zeeman sextets. ME spectra for the other bulk sample (y = 1.0) and the two samples in nanoscale (prepared by citrate method) can be fitted by one and two doublets due to the paramagnetic and superparamagnetic behaviour, respectively. Vibrating sample magnetometer measurements showed that the saturation magnetization (Ms) obtained from the hysteresis loop is decreased by increasing Ga3+ concentration for all the samples. The coercivity (Hc) is inversely proportional to the particle size (D) for bulk samples. Nevertheless, Hc of the nanoscale samples enhanced by increasing the particle size. The size dependence of Hc is an indication of the superparamagnetic characteristics supported by ME. The ac electrical conductivity (ln $$ \sigma $$ ), dielectric constant (e′) and dielectric loss tangent (tan δ) were studied at different frequencies and temperatures for the investigated samples. The obtained results showed that the conductivity for all samples increases with increasing temperature in a behaviour similar to that of the most semi-conductor materials.

Microstructure and electrical properties of 3Y‐TZP/Al2O3 composite obtained using the citrate gel method

Abstract3Y‐TZP sinters with 1, 5, 10, and 15 mol% of Al2O3 were prepared using two different procedures from a 3‐YSZ powder synthesized via the citrate process. In the first procedure, alumina was introduced during synthesis via the citrate method. In the second one, the 3‐YSZ powder was impregnated with aluminum nitrate. All samples were sintered at 1773 K. The prepared composites were evaluated in terms of their microstructure, chemical and phase composition, and electrical properties. The total conductivity of the 3Y‐TZP/Al2O3 composite material, which contained primarily the tetragonal phase, was found to increase with temperature, and to decrease for reduced concentrations of alumina in 3Y‐TZP. In the case of the samples which had alumina introduced via impregnation, its higher content was not associated with significantly lower electrical conductivity. These samples generally exhibited higher conductivity than the samples to which alumina had been added via chemical synthesis.

Low-temperature synthesis of bismuth titanate by modified citrate amorphous method

Bismuth titanate is a lead-free piezoelectric ceramic with outstanding properties that strictly depend on the composition and microstructure. However, bismuth-based materials are difficult to synthesize due to bismuth volatilisation that causes secondary phases and stoichiometry deviations. In this work, we propose a low-temperature chemical route, i.e. a modified amorphous citrate method, that allows a reduction of thermal treatment temperature, when compared with solid-state or other chemical routes, to obtain single-phase bismuth titanate samples. Single-phase powders with particle size under 300 nm are produced by calcination at 700 °C, and prepared into homogeneous dense pellets (density above 95%), with only isolated pores. The pellets show two distinctive features in the electrical behaviours directly associated with their mica-like microstructure: planar oriented boundaries are responsible for oxygen conduction, while the bulk is dominated by electronic conductivity. The samples show a high dielectric constant, around 200 at room temperature, while maintaining a low loss factor. The pellets also achieved a maximum polarisation of 5.85 μC/cm2 and an inverse piezoelectric coefficient of 7.4 pm/V. The dielectric and piezoelectric properties obtained are comparable or superior to the state-of-the-art.

Novel Mn–Ce bi-oxides loaded on 3D monolithic nickel foam for low-temperature NH3-SCR de-NOx: Preparation optimization and reaction mechanism

This study explored the superior citrate method (CM) to synthesize Mn–Ce bi-oxides on 3D monolithic Ni-foam (NF) catalysts for the selective catalytic reduction of NO by NH3 (NH3-SCR). The 17 wt% Mn(7)Ce(3)Ox/NF (CM-17) catalyst shows the NOx conversion of 98.7% at 175 °C and 90% in the presence of 10 vol% H2O. It is revealed that the combination of surface-active oxygen (formed by high-level oxygen vacancies) and strongly oxidized Mn4+ species promots the Fast-SCR reactions, in which Mn4+ species play a leading role in NH3-SCR reaction, and the unsaturated Ni atoms and also Ce3+ species promote electron exchange and thus improve the redox performance. The coexistence mechanisms of Fast-SCR reactions and E-R pathways are observed over Mn-CeOx/NF catalyst, which may be promoted by the Brønsted sites at low temperature. In addition, the heat resistance, stability, 3D monolithic porous structure and excellent physical properties of foam nickel provide a unique growth substrates for catalysts preparation and reaction sites for NOx purification. Therefore, industrial application of Mn–Ce bi-oxides loaded on 3D monolithic is proposed to be achieved through reasonable preparation methods.

Size-dependent phase stability of silver nanoparticles

A comparative analysis of the structure of silver nanoparticles obtained by chemical synthesis (citrate method) and electrical explosion of wires is carried out. The structure, phase composition, lattice parameters of silver nanoparticles with sizes from 2 to 50 nm were studied by electron diffraction and high-resolution transmission electron microscopy. All silver nanoparticles obtained by the chemical method have only a cubic structure. Silver nanoparticles obtained by the physical method have cubic and hexagonal structures. The existence of the hexagonal phase under normal conditions is explained by the quenching effect. The lattice parameters of the cubic phase of Ag NPs within the experimental determination error (± 0.01 nm), synthesized by the chemical method and by the method electrical explosion of wires do not differ from each other.

Synthesis and characterization of the structural and magnetic properties of the Sm3-xGdxFe5O12(x = 0.0–1.0) garnets using solid-state reaction and citrate methods

The present work focused on synthesis and characterization of the new garnet-type materials with formula Sm3-xGdxFe5O12 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), using both the citrate and solid-state reaction methods. The influence of the substituting cation and the synthesis routes on the structural, morphological, and magnetic properties were evaluated by X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and 57Fe Mössbauer spectroscopy. The results showed that Gd3+ substitution allows obtaining single-phase materials, with cubic structure and space-group symmetry Ia3¯d (230). The Gd3+ substitution modified the magnetic response of the Sm3Fe5O12 garnet, generating a decrease of the saturation magnetization (Ms), coercive field (Hc), remaining magnetization (Mr), besides, the sample with x = 1.0 exhibited a Tcomp of ≈60 K. The citrate method allowed obtaining smaller particle sizes, leading to an increase of the Hc and Mr, and decreasing the Ms, this compared with the samples obtained by the solid-state reaction method. The ferrimagnetic behavior of the materials was confirmed by room temperature 57Fe Mössbauer spectroscopy, which showed the existence of magnetic hyperfine fields and Fe3+ in the different crystallographic sites. This work shows that the use of the citrate method allows obtaining garnets of high purity and with outstanding magnetic and crystalline properties, making them applicable for transformers and microwave switches production. On the other hand, the garnets were synthesized at lower temperatures (300 °C) and less time (18 h) than those used in the solid-state reaction method, decreasing the production costs.

The Role of Acidity in Terephthalic Acid Synthesis from Renewable Carbon Source

AbstractIn this study, manganese‐cobalt (MnCo) mixed oxide catalysts were prepared by two different routes: co‐precipitation and citrate method. The structures and properties of the mixed oxide catalysts were investigated by several techniques: nitrogen adsorption‐desorption isotherms, X‐ray diffraction, X‐ray photoelectron spectroscopy, SEM, FTIR and UV‐Vis spectroscopies, temperature‐programmed reduction with H2 (H2‐TPR) and temperature‐programmed desorption of NH3 (NH3‐TPD). Their catalytic performance was investigated in the liquid‐phase selective oxidation of naturally occurred p‐cymene to terephthalic acid, as an alternative to p‐xylene, a fossil derivative fuel component. Within this study, we demonstrate that the materials prepared by the co‐precipitation method present strong acid sites that boost the oxidation rate and allow oxidation of p‐cymene up to terephthalic acid. The co‐existence of a significant number of strong acid and centers in higher oxidation state (Co3+) are required for these materials to be selective.

Tertiary Ni0.7-xZn0.3MxFe2O4 (M=Mn, Co, and Cu) spinel ferrites: Electrical and dielectric properties

Three systems of polycrystalline Ni0.7-xZn0.3MxFe2O4 ferrite (M = Mn2+, Co2+, and Cu2+; x = 0.0, 0.1, 0.3, 0.5, and 0.7) have been prepared using the citrate method. The dc conductivity (σdc), ac conductivity (σac), dielectric constant (ε’), and dielectric loss (ε”) of Ni–Zn ferrite doped with Mn/Co/Cu ions have been thoroughly inspected. Variations in dc and ac conductivity for each ferrite series have been evaluated with temperature elevation from 293 up to 848 K and altered frequencies from 102 to 106 Hz. The conductivity for dc and ac displayed both metallic and semiconductor-like behavior with temperature. The magnitudes of activation energies (Eσ) are estimated and discussed for the three investigated systems from Arrhenius plots. Small polaron hopping between Fe3+ and Fe2+ ions is accountable for the conduction mechanism in existing systems. Moreover, the behavior of dielectric parameters with increasing Mn/Co/Cu concentrations has been evolved independently. The enhanced values of conductivity, dielectric constant, and small dielectric loss are attained in copper doped Ni–Zn ferrite compositions particularly at high concentrations. This is a very promising feature for high-frequency and power applications of ferrites.

Nonlinear optical properties of Ag nanoparticles with and without silicon dioxide shell

Abstract The features of a nonlinear optical response of the spherical silver nanoparticles with an average size of 20 nm and “core-shell” systems based on them (Ag@SiO2) synthesized using the citrate method in the field of nanosecond pulses of the second harmonic of Nd:YAG laser (532 nm) are studied. It is shown that the presence of a SiO2 shell blocks the saturable absorption that occurs due to the photodestruction of silver nanoparticles. The formation of a positive dynamic lens for the Ag@SiO2, which is not typical for the original silver nanoparticles, was detected. An assumption is made about the capture of photo-excited charge carriers by the SiO2 shell.

Green and Cost-Effective Synthesis of Metallic Nanoparticles by Algae: Safe Methods for Translational Medicine.

Metal nanoparticles (NPs) have received much attention for potential applications in medicine (mainly in oncology, radiology and infectiology), due to their intriguing chemical, electronical, catalytical, and optical properties such as surface plasmon resonance (SPR) effect. They also offer ease in controlled synthesis and surface modification (e.g., tailored properties conferred by capping/protecting agents including N-, P-, COOH-, SH-containing molecules and polymers such as thiol, disulfide, ammonium, amine, and multidentate carboxylate), which allows (i) tuning their size and shape (e.g., star-shaped and/or branched) (ii) improving their stability, monodispersity, chemical miscibility, and activity, (iii) avoiding their aggregation and oxidation over time, (iv) increasing their yield and purity. The bottom-up approach, where the metal ions are reduced in the NPs grown in the presence of capping ligands, has been widely used compared to the top-down approach. Besides the physical and chemical synthesis methods, the biological method is gaining much consideration. Indeed, several drawbacks have been reported for the synthesis of NPs via physical (e.g., irradiation, ultrasonication) and chemical (e.g., electrochemisty, reduction by chemicals such as trisodium citrate or ascorbic acid) methods (e.g., cost, and/ortoxicity due to use of hazardous solvents, low production rate, use of huge amount of energy). However, (organic or inorganic) eco-friendly NPs synthesis exhibits a sustainable, safe, and economical solution. Thereby, a relatively new trend for fast and valuable NPs synthesis from (live or dead) algae (i.e., microalgae, macroalgae and cyanobacteria) has been observed, especially because of its massive presence on the Earth’s crust and their unique properties (e.g., capacity to accumulate and reduce metallic ions, fast propagation). This article discusses the algal-mediated synthesis methods (either intracellularly or extracellularly) of inorganic NPs with special emphasis on the noblest metals, i.e., silver (Ag)- and gold (Au)-derived NPs. The key factors (e.g., pH, temperature, reaction time) that affect their biosynthesis process, stability, size, and shape are highlighted. Eventually, underlying molecular mechanisms, nanotoxicity and examples of major biomedical applications of these algal-derived NPs are presented.

Effect of copper dopant on microstructural and optical properties of NiTiO3 ilmenite materials synthesized by citrate method

In this work, the Ni1-xCuxTiO3 (0 ≤x ≤ 0.1) ilmenite materials were successfully synthesized using the citrate-gel method using nickel nitrate, copper nitrate and titanium (IV) isopropoxide as Ni, Cu, Ti sources and citric acid as complexing reagent. The evolution of the microstructural properties was investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Powder X-ray diffraction pattern confirms the formation of the ilmenite phase for all the samples. The particle size of the prepared samples substantially increased with increase of copper dopant content. The study of phonon vibration by Raman spectroscopy identified a change in structure of NiTiO3 due to Cu dopant. The optical properties with the Cu content was carried out using UV-vis absorption spectroscopy. The reduction of optical band gap from 2.31 eV to 1.99 eV was obtained for undoped NiTiO3 and 10 mol.% Cu dopant in NiTiO3, respectively. To evaluate the photocatalyst properties of NiTiO3, the photocatalytic degradation of congo red under visible light irradiation was carried out. Our results revealed that the copper dopant into NiTiO3 lattice promoted the increase of particle size, decrease of optical bandgap and enhancement of textile photodegradation.

Review on Polymeric Citrate Precursor and Sono-chemical Methods for the Synthesis of Nanomaterials

Background: he properties of materials depend on the way of construction and the arrangement of atoms and molecules. Therefore, it is very important to know synthesis methods for the preparation of novel materials as per their desired structure. The low-temperature synthesis methods, such as polymeric citrate precursor and sonochemical methods are efficient enough to control the preparation of novel nanoparticles with morphological differences that leads to the novel devices with desired technological performances. These methods are simple, very less expensive and are easy to handle to operate for the synthesis of nanoparticles as per the expected morphology and dimensions. Methods: Polymeric citrate precursor method, a chelate-based method involves the reaction between mixed cations with citric acid, and then these cations are cross-linked with the help of ethylene glycol for the esterification process. Gel composites were heated which burns the organic moieties leaving behind the nanoparticles, and burning gels becomes essential for the reduction of nanoparticles. The sonochemical method, on the other hand, uses ultrasonic the irradiation results. The acoustic cavitation and high intensity ultrasound has been exploited for the preparation of different series of nanoparticles. Results: Commonly known for polymeric citrate method as Pechini gel pyrolysis method gives the evidence of versatile and elegant method for the synthesis of nanoparticles. The sonochemical method provides an unusual route of nanoparticle fabrication without bulk and that too with low temperature and pressure or less reaction time. These two methods have better control for the desired shape morphology and size and provide many opportunities for the use of these prepared nanoparticles in various aspects of science and technology. Conclusion: Polymeric citrate precursor and sonochemical methods are efficient to reduce to promote desirable reaction conditions and reduce the metal ions for the fabrication of nanoparticles. The prepared nanoparticles by using such low-cost elegant methods are uniform with a small size distribution, reproducible with good yield as per the demanded applications.

Oxy-CO2 reforming of CH4 on Ni-based catalysts: Evaluation of cerium and aluminum addition on the structure and properties of the reduced materials

Perovskites with the structural formula La1-xCexNi1-yAlyO3 (x = 0 y = 0; x = 0.05 y = 0; x = 0.05 y = 0.2 and x = 0.05 y = 0.5) were studied in the dry methane reforming in presence of oxygen or Oxy-Dry (OD). The materials were synthetized by the amorphous citrate method and characterized by XRD, in situ XRD under hydrogen and reactional (OD) atmospheres, TPR-H2, XRF, TPSR-OD, TPSR−CH4, TEM, HRTEM and TPO techniques. The catalytic performance was evaluated during 16 h of reaction, with a [CH4/CO2/O2] ratio = 4:2:1, at 800 °C and spatial velocity of 210.000 NL.h−1.kgcat−1. The addition of aluminum and cerium promoted an increase in the catalyst resistance to carbon poisoning, however, the higher the aluminum content was, the lower the reducibility of the perovskites and the nickel particle size. The La0.95Ce0.05Ni0.5Al0.5O3 sample showed the best results, with a maximum CH4 and CO2 conversion of 85 % and 86 % respectively and the higher syngas yield (45 % for CO and 48 % for H2). This sample presented the lowest Ni° particle size and carbon deposition after 16 h time on stream. No sign of deactivation was found for all the studied catalysts, showing the superior properties of catalysts prepared through perovskite-like mixed oxides.

Physicochemical Properties of LaFeO3 Perovskite Prepared by Various Methods and Its Activity in the Oxidation of Hydrocarbons

LaFeO3 perovskites, obtained through co-precipitation of carbonates with (NH4)2CO3, co-precipitation of hydroxides with NaOH, citrate method, and through solid-state reaction using metal nitrates as precursors, were deposited on a heat-resistant foil support. Their physicochemical properties were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry and thermogravimetric analysis (DSC/TGA), and specific surface area measurements. DSC/TGA showed that phase transitions took place in the LaFeO3 perovskite up to 800–840 °C. Pure LaFeO3 perovskite phase was obtained only when the citrate method was used. The following decreasing order of methane and hexane oxidation activity at 700 °C was determined for the catalysts with the LaFeO3 perovskite obtained by different methods: citric acid > ammonium carbonate ∼ metal nitrates > sodium hydroxide. LaFeO3 catalysts obtained at 700 °C in the presence of citric acid or ammonium carbonate can be used as three-way automotive exhaust catalysts or as catalysts in environmental protection.