Citrate Sol Gel Method Research Articles

A study of microwave-enhanced catalytic degradation of benzene using Co-Mn metal oxides combined with numerical simulation

Microwave can enhance catalytic reaction and is a promising alternative to convention heating. Herein, microwave-enhanced catalytic degradation of benzene was investigated using Co-Mn metal oxides. Numerical calculation was employed to analyze the microwave-enhanced catalytic degradation. The catalysts were synthesized by conventional citrate sol-gel method. Then, the morphologies, elements distribution and chemical structure were characterized. Compared to conventional heating, the catalysts exhibit better activity and lower apparent activation energy under microwave heating, indicating that microwave enhance catalytic degradation of benzene. Mn1Co2 exhibits good catalytic performance under microwave heating. From the finite element simulation, it is found that the E-field distribution on the spherical particle catalyst is non-uniform, and the E-field intensity is about 1.9 × 104 V/m and 4.27 × 104 V/m at the catalyst particles and the contact position. The DFT calculation results show that the electron density of Mn-O bond decreases and the charge density of Co atom increases under E-field, which is conducive to the molecule activation and electron transfer. The density of states results demonstrate the microwave E-field leads to lower electron energy on the surface, resulting in enhanced catalytic reaction. Combined with the results of finite element calculation, the microwave enhancement effect is more pronounced at the catalyst contact point.

Investigation of Ba doping in A-site deficient perovskite Ni-exsolved catalysts for biogas dry reforming

This work presents the development of an A-site deficient La0.9−xBaxAl0.85Ni0.15O3 (x = 0, 0.02, 0.04, and 0.06) perovskite oxide catalyst for dry reforming of model biogas. The catalysts are prepared using a citrate sol-gel method and used for biogas dry reforming at 800 °C for feed ratios (CH4/CO2) of 1.5 and 2.0. The fresh and spent catalysts are analyzed using XRD, FTIR, TPD, XPS, FESEM, TEM, TPR, TGA-DTA, and Raman analysis. The XRD analysis exhibits the host perovskite oxide structure and the exsolved Ni phase for all prepared catalysts. The partial doping of Ba improves the metal support interaction and oxygen vacancies that enhance catalytic activity and stability, as revealed by the TPR and XPS analysis. The stability experiment on La0.9−xBaxAl0.85Ni0.15O3, for x = 0 catalyst resulted in reduced activity due to the catalyst deactivation by sintering, as confirmed by XRD and FE-SEM. Among all the catalysts studied, La0.84Ba0.06Al0.85Ni0.15O3 (LB6AN-15) exhibited the highest catalytic stability with CH4, and CO2 conversions are 60% and 93%, respectively, for 40 h time-on-stream due to the strong metal support interactions, high oxygen vacancies, and anti-sintering of exsolved Ni nanoparticles in biogas dry reforming.

Kinetic study of ethanol dry reforming using lanthanum copper perovskite

This paper reports the syngas production from ethanol dry reforming reaction for a greener and sustainable process. The aims were to delineate the effect of lanthanum-copper-based perovskite catalyst on the kinetics of the reaction at the temperatures spanning from 725 to 800 °C. The citric sol–gel method was employed to prepare the catalysts by using lanthanum and copper nitrate salts by mixing them based on equal mass of the metals in the desired perovskite structure. The reactions were tested in a tubular reactor using 0.1 of g catalyst between 125 and 160 µm of particle size, which was reduced in-situ by using hydrogen before the reaction. The reactants were mixed in a few carbon dioxide to ethanol molar ratios from 2.5 to 1 and entered the reactor at 1.43 min of space time under atmospheric pressure to ensure the negligibility of mass transport hindrance. At steady states, the products were sampled and analysed in a GC-TCD. The parameters of power law were obtained from reactant consumption against various feedstock flows with R2 > 96% based on differential reactor method. 44.2 kJ /mol of activation energy and other rate constants were obtained.

Hydrogen Production from Biogas: Development of an Efficient Nickel Catalyst by the Exsolution Approach

Hydrogen production from biogas over alumina-supported Ce1−xNixO2−x catalysts was studied in a temperature range of 600–850 °C with an initial gas composition of CH4/CO2/H2O of 1/0.8/0.4. To achieve a high and stable hydrogen yield, highly dispersed Ni catalysts were prepared through the exsolution approach. A solid solution of Ce1−xNixO2−x was firstly formed on the surface of Al2O3 and then activated in H2/Ar at 800 °C. The genesis and properties of the Ce1−xNixO2−x/Al2O3 catalysts were established using X-ray fluorescence analysis, thermal analysis, N2 adsorption, ex situ and in situ X-ray diffraction, Raman spectroscopy, electron microscopy, EDX analysis, and temperature-programmed hydrogen reduction. The performance of Ce1−xNixO2−x/Al2O3 catalysts in biogas conversion was tuned by regulation of the dispersion and reducibility of the active component through variation of content (5–20 wt.%) and composition (x = 0.2, 0.5, 0.8) of Ce1−xNixO2−x as well as the mode of its loading (co-impregnation (CI), citrate sol–gel method (SG)). For the 20 wt.% Ce1−xNixO2−x/Al2O3 catalyst, the rate of the coke formation decreased by a factor of 10 as x increased from 0.2 to 0.8. The optimal catalyst composition (20 wt.% Ce0.2Ni0.8O1.8/80 wt.% Al2O3) and preparation mode (citrate sol–gel method) were determined. At 850 °C, the 20 wt.% Ce0.2Ni0.8O1.8/Al2O3-SG catalyst provides 100% hydrogen yield at full CH4 conversion and 85% CO2 utilization.

Biogas dry reforming over Ni/LnOx-type catalysts (Ln = La, Ce, Sm or Pr)

Ni/LnOx-type catalysts (Ln = La, Ce, Sm or Pr, denoted as LNO, CNO, SNO and PNO, respectively) were prepared via a citrate sol-gel method, characterized, and evaluated for the dry reforming of biogas. For the calcined catalysts, the formation of LaNiO3 perovskite crystallites with high purity was observed in the case of La, whereas NiO-LnOx mixed oxides were obtained for the other lanthanides. The reduction treatment led to the formation of medium-sized (∼15 nm) and highly dispersed Ni nanoparticles in LNO following the decomposition of the LaNiO3 perovskite, in contrast to the other catalysts, where bigger Ni crystallites were formed (∼30 nm). As a result, LNO was shown to possess a higher catalytic activity in comparison to the other materials. Regarding the catalytic stability, LNO displayed a considerable activity loss followed by a high pressure drop due to reactor blockage, meaning that the use of Sm (Ni/Sm2O3) can be considered as an alternative strategy to restrict catalyst deactivation. As evidenced by the characterization of the spent catalysts, the deactivation for the most part can be attributed to the extensive coke deposition over the catalysts. The coke deposited was found to be both in the form of more disordered/amorphous carbon, as well as in the form of highly crystalline and multi-walled carbon nanotubes.

Sm2O3: Eu3+ sol-gel ceramics obtained by the citrate sol-gel method

Polvos cerámicos de Sm2O3 dopados y mezclados con europio se obtuvieron a partir de la formación de cloruros de europio y samario a través de la ruta sol-gel de citrato. Este trabajo reporta la influencia de los iones de europio en las propiedades estructurales y luminiscentes de las cerámicas Sm2O3:Eu3+ (coordenadas CIE) variando el Eu3+ de 10 a 50% mol. Las características químicas, estructurales y morfológicas fueron establecidas por FTIR y XRD, revelando la presencia de bandas vibratorias características Sm-O de estructura cúbica hasta 40 mol% Eu3+ y una mezcla de fases de Sm2O3 y Eu2O3 a partir de 50 mol% Eu3+. Se establecieron los valores de las coordenadas CIE y la emisión de color para cerámicas Sm2O3:Eu3+ (10, 20, 30, 40 y 50% mol), tanto para muestras con una sola fase como para la mezcla de fases.

Comprehensive analysis on the effect of ionic size and size disorder parameter in high entropy stabilized ferromagnetic manganite perovskite

A series of high entropy manganites, $(5{A}_{0.2}){\mathrm{MnO}}_{3}$, were prepared with varying the average ionic radius, $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$, and cationic size disorder, ${\ensuremath{\sigma}}^{2}$, on the $A$ site. All the samples were synthesized using the citrate sol-gel method. In all the compounds, the manganese valence was kept unaltered with reference to the conventional manganite ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_{3}$, which is ferromagnetic with ${T}_{C}\ensuremath{\sim}365$ K. The ratio of manganese valance is found to be unaltered as confirmed using x-ray photoelectron studies. The samples were characterized by powder x-ray diffraction, field-emission scanning electron microscopy (FE-SEM), energy dispersive x-ray analysis, elemental mapping, and magnetization measurements. These high entropy oxides show the variation in Curie temperature over a wide range from 85 to 273 K depending on the average $A$-site ionic radius, $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$. A drastic drop down in the ferromagnetic transition temperature of ${T}_{C}=365$ K for ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_{3}$ with $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}=1.2536\phantom{\rule{0.16em}{0ex}}\AA{}$ to ${T}_{C}=137\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for (${\mathrm{La}}_{0.2}{\mathrm{Nd}}_{0.2}{\mathrm{Gd}}_{0.2}{\mathrm{Sr}}_{0.2}{\mathrm{Ba}}_{0.2}$)${\mathrm{MnO}}_{3}$ of comparable $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}=1.2532\phantom{\rule{0.16em}{0ex}}\AA{}$ can be attributed to the high entropy and/or cationic size disorder effect. The variation of ${T}_{C}$ with $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$ for the whole series of high entropy manganites does not follow the expected linear behavior; rather, it follows opposite traces of the variation in ${\ensuremath{\sigma}}^{2}$ with $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$. However, ${T}_{C}$ shows almost linear behavior with ${\ensuremath{\sigma}}^{2}$ except for the sample with lowest $\ensuremath{\langle}{r}_{A}\ensuremath{\rangle}$. This result suggests that the local cationic disordering is more important than the average cationic size in ferromagnetic high entropy manganites. Unlike the conventional system in these high entropy oxides, the ferromagnetic state is not suppressed; only the length scale of the double exchange mediated long-range ferromagnetic interaction is transformed to localized ferromagnetic clusters without losing the ferromagnetic identity. The presence of multiple $A$-site cations in high entropy oxides results in a local deformation of the ${\mathrm{MnO}}_{6}$ octahedra. This possibly increases the carrier localization followed by reducing the length scale of the double exchange interaction.

Efficient photothermal catalytic oxidation of toluene by La1-xFexMnO3 with full spectrum response: The effects of Fe doping and photoactivation

Developing efficient photothermal catalysts with full spectrum response is one of the frontier topics in photothermal catalytic of VOCs. In this work, La1-xFexMnO3 (0 ≤ x ≤ 0.2) was synthesized via citrate sol-gel method. Under full spectrum illumination of 1.3 × 104 W/m2, La0.9Fe0.1MnO3 exhibited a more superior activity (86.7% toluene conversion and 84.6% CO2 yield). Through controlled experiments, not only the origin of photothermal activity, but the possible intrinsic drivers (Fe doping and photoactivation) of the enhanced activity were also revealed. Particularly, the mechanistic details of their facilitating reactions were thoroughly studied, where the improved mobility and activation of lattice oxygen played the primary role. Moreover, the co-effect of Fe doping and photoactivation on the resistance to complex gas components (SO2, H2O) and durability was systematically investigated. Eventually, the plausible pathways and mechanisms of toluene oxidation were proposed. This study provides a new insight into photothermal catalysts with full spectrum response for environmental remediation.

Enhanced activation of peroxymonosulfate for ofloxacin rapid degradation and inhibition of metal leaching on LaNi0.6Co0.4O3 stably anchored at ZnO

The citrate sol-gel method was used to synthesize LaNi0.6Co0.4O3 anchored at ZnO (LaNi0.6Co0.4O3/ZnO) for activation of peroxymonosulfate to degrade ofloxacin in simulated wastewater. LaNi0.6Co0.4O3 nanoparticles were uniformly and firmly dispersed on ZnO support during the synthesis process. LaNi0.6Co0.4O3/ZnO had a rapid catalytic rate with an efficiency of 90% in 10 min, which was higher than that of LaNi0.6Co0.4O3 (87.7%). Meanwhile, LaNi0.6Co0.4O3/ZnO significantly inhibited metal ion leaching compared to LaNi0.6Co0.4O3 (Ni leaching: 0.128 mg/L to 0.022 mg/L, Co leaching: 0.083 mg/L to 0.012 mg/L). The composite material maintained great cyclic stability with efficiency of 93% after 5 cycles. Based on electron paramagnetic resonance studies and the quenching experiments, SO4·−、·OH、·O2− and 1O2 were the main reactive oxygen species involved in the reaction. The degradation intermediates of ofloxacin were detected by ICP-MS to propose the possible degradation pathways. This work provides an insight for perovskite catalyst for the activation of PMS to treat pharmaceutical wastewater.

Tailoring the magnetic landscape in Al-doped LaMnO3: an experimental and computational perspective

We have reported the synthesis, structural and magnetic properties of LaAl x Mn1−x O3 (x = 0.05, 0.15, 0.25) in this article. We have synthesized these compounds through the Sol-gel citrate method and performed the Rietveld refinement of X-ray diffraction data to determine the lattice parameters. The surface elemental composition and oxidation states of LaAl0.25Mn0.75O3 are investigated using X-ray photoelectron spectroscopy (XPS) in a wide energy window of 0–1200 eV. The magnetic study shows the ferromagnetic transition of these materials. To understand the nature of magnetization from the experiments, we have studied the first principle density functional theory (DFT) and Monte-Carlo simulation. From the DFT calculations, we have confirmed the ferromagnetic structure in the ground state and studied the electronic structure of these materials. The Monte Carlo simulation has been done through the anisotropic Ising model to analyze the origin of magnetic phase transition. We have determined the anisotropy and the interaction constants from the DFT calculations. The double exchange interaction is mainly responsible for the ferromagnetic ground state.

Mn–Zr composite oxides as efficient catalysts for catalytic oxidation of vinyl chloride

Mn–Zr composite oxides with variable molar ratios of Mn/Zr were prepared by a citrate sol–gel method for catalytic oxidation of vinyl chloride. The structure–activity relationship was studied by numerous characterization and experimental approaches.

Structural, magnetic and optical properties of disordered double perovskite Gd2CoCrO6 nanoparticles.

We have synthesized disordered double perovskite Gd2CoCrO6 (GCCO) nanoparticles with an average particle size of 71 ± 3 nm by adopting a citrate sol-gel method to investigate their structural, magnetic, and optical properties. Rietveld refinement of the X-ray diffraction pattern showed that GCCO is crystallized in a monoclinic structure with space group P21/n, which is further confirmed by Raman spectroscopic analysis. The absence of perfect long-range ordering between Co and Cr ions is confirmed by the mixed valence states of Co and Cr. A Néel transition was observed at a higher temperature of TN = 105 K compared to that of an analogous double perovskite Gd2FeCrO6 due to a greater degree of magnetocrystalline anisotropy of Co than Fe. Magnetization reversal (MR) behavior with a compensation temperature of Tcomp = 30 K was also observed. The hysteresis loop obtained at 5 K exhibited the presence of both ferromagnetic (FM) and antiferromagnetic (AFM) domains. Super-exchange and Dzyaloshinskii-Moriya (DM) interactions between various cations via oxygen ligands are responsible for the observed FM or AFM ordering in the system. Furthermore, UV-visible and photoluminescence spectroscopy demonstrated the semiconducting nature of GCCO with a direct optical bandgap of 2.25 eV. The Mulliken electronegativity approach revealed the potential applicability of GCCO nanoparticles in photocatalytic H2 and O2 evolution from water. Due to a favorable bandgap and potentiality as a photocatalyst, GCCO can be a promising new member of double perovskite materials for photocatalytic and related solar energy applications.

EFFECT OF ERBIUM DOPING ON PHYSICAL PROPERTIES OF LaFeO3


 
 
 Multiferroic La1-xErxFeO3 (x= 0, 0.2, 0.4, 0.6, 0.8 and 1) successfully synthesized using auto combustion sol-gel citrate method. The crystalline structure examined by X-ray Diffraction (XRD) analysis is orthorhombic. Infrared (IR) active phonons for Erbium substitution in La1-xErxFeO3 studied at room temperature in frequency range 30-1000 cm-1 via Fourier transformed infrared (FTIR) spectroscopy. The experimental reflectivity spectra has been fitted using Lorentz oscillator model and obtain the parameter like damping factor, optical frequency as well as oscillator strength. Real and imaginary part of dielectric constant, optical conductivity, loss function and energy band gap in addition to transverse and longitudinal optical frequency modes have been calculated by these parameters. The frequency shift has been observed with doping concentration of Erbium in LaFeO3. Optical conductivity spectra are of semiconducting type. La1-xErxFeO3 is further characterized by UV- visible spectroscopy and electrical resistivity measurements. The optical spectrum of UV-Visible phenomena exhibits typical semiconductor behaviour. Investigation shows there is a drop in activation energy of samples if doped element Er increases. The electrical resistivity trend shows semiconducting behaviour of the sample which exhibit p-type polaronic conduction.
 
 

Effects of varying Sm3+ concentration on the structure, morphology and photoluminescence properties of the BaAl2O4 /CaAl2O4/Ca4Al6O13/Ca3Al2O6:x% Sm3+ (0 ≤ x ≤ 1.9) mixed phases using citrate sol-gel method

BaAl2O4/CaAl2O4/Ca4Al6O13/Ca3Al2O6:x% Sm3+ (0 ≤ x ≤ 1.9) (hereafter called BCCC:x% Sm3+) nanophosphors were successfully prepared by citrate sol-gel method. The structure, morphology and photoluminescence properties of the prepared nanophosphors were investigated. X-ray diffraction (XRD) indicated that the nanophosphors composed of the mixed phases of the hexagonal (CaAl2O4, BaAl2O4) and cubic (Ca4Al6O13, Ca3Al2O6) crystal structures. Scanning electron microscopy (SEM) revealed that doping influences the morphology of the prepared nanophosphor. High resolution transmission electron microscopy (HR-TEM) confirmed that the prepared phosphor particles are in the nanoscale range. Photoluminescence (PL) results showed emission peaks originating from the intrinsic defects within the BaAl2O4, CaAl2O4 and Sm3+ transitions. The optimum luminescence intensity was found at 0.7% Sm3+. Commission Internationale de l'éclairage (CIE) shows that the Sm3+ doped samples emitted the orange colour.

Facile synthesis of NdFeO3 perovskite for photocatalytic degradation of organic dye and antibiotic

In this study, a visible-light sensitive neodymium iron oxide (NdFeO3) perovskite nanostructure was fabricated via facile citrate sol–gel method to target the degradation of lomefloxacin (LMF) antibiotic and methylene blue (MB) dye. The as-synthesized catalyst were investigated employing various characterization techniques scuch as XRD, EDX, SEM, UV–vis and PL. The NdFeO3 photocatalyst demonstrates excellent photocatalytic activity of maximum 88 % and 95 % for the photodegradation of LMF (15 mg/L) and MB (15 mg/L) in 120 min under a visible light source (LED, 30 W). The current study provides an exciting technique for developing a NdFeO3 photocatalyst capable of high-performance LMF and MB detoxification.

Unravelling the synergism of catalytic oxidation and filtration in Co-Mn-oxide impregnated ceramic membrane for intensified degradation of recalcitrant micropollutant with peroxymonosulfate

In this study, catalytic ceramic membrane (CCM) impregnated with uniform and high purity Co-Mn-oxide was fabricated via citrate sol–gel method. It was applied to activate peroxymonosulfate (PMS) for degradation of sulfamethoxazole (SMX). Due to the synergistic effect between the two cations, the Co-Mn bimetallic oxides exhibited significantly higher catalytic activity in activating PMS and degrading organic pollutants in comparison to their single oxides. Minimum calcination temperature of 700 °C was required to form the highly activating Co-Mn-oxide while higher calcination temperature reduced its catalytic activity. The effect of catalyst loading and the SMX:PMS ratio was investigated, and excessive catalyst loading, and oxidant dosage were found to be detrimental to the SMX removal efficiency. The investigation revealed the importance of process parameters in achieving achieve optimal performance of CCM/PMS process, achieving low specific oxidant consumption of 1.2 M PMS M−1 TOC. The ratio between catalyst loading in CCM, oxidant concentration and pollutant concentration influenced the availability of active sites on the catalyst to activate oxidants in the process and the possibility of self-scavenging of the generated reactive oxidizing species (ROS). The role of various ROS generated and mechanism of activation of PMS by the catalyst was investigated through radical scavenging experiments and electron paramagnetic resonance (EPR) spectroscopy test. Co2+ can be regenerated from the Mn2+/Mn3+/Mn4+ redox conjugate triplet and concurrently activate PMS to generate ROS, significantly enhancing its catalytic performance. Additionally, based on LC-QTOF analysis, the intermediates, and the possible degradation pathway of SMX degradation in this hybrid process were determined. Overall, the investigation of CCM fabrication and hybrid process operation parameters could provide an insight in the hybrid process to intensify the oxidant utilization and pollutant removal.

Sol-gel synthesis and structural evolution in solid solutions of InGaZn1-xCoxO4 (0 ≤ x ≤ 1)

Complete solid solutions InGaZn1-xCoxO4 (0 ​≤ ​x ​≤ ​1) were synthesized via the citrate sol-gel method and structurally characterized by powder X-ray diffraction. All oxides adopt the LuFe2O4-type layered structure and crystallize in the space group R3¯m. The successful cationic doping can be first confirmed by the linear changes in a- and c-axes lengths, then investigated by careful Rietveld refinements. The Co2+-to-Zn2+ replacement induces the structural changes in the [MO]2 (M ​= ​Ga, Zn, Co) layers exclusively, where M locates in the trigonal bipyramidal (TBP) coordination. In detail, three M-Obasal bond exhibit a gentle expansion, and two apical M-O bonds show opposite variations (a minor expansion and a severe contraction) with an overall decreasing in length. Interestingly, the latter one is likely due to the so-favored AFM interactions between Co2+-Co2+ couples along edge-shared TBPs. The temperature-dependent magnetic susceptibility confirms the very strong AFM interactions, however no magnetic order can be established above 5 ​K.

Sol-Gel Materials for Electrochemical Applications: Recent Advances

This review article emphases on the modern approaches to the types of sol-gel materials that are beneficial for electrochemistry, monitored by a report of recent advances in the numerous fields of sol-gel electrochemistry. Modified electrodes for sensors and supercapacitors as well as anti-corrosion are described. Sol-gel synthesis expands the capabilities of technologists to obtain highly porous, homogeneous, and hybrid thin-film materials for supercapacitor electrode application. The widespread materials are transition metal oxides, but due to their low conductivity, they greatly impede the rate capability of electrochemical supercapacitors. The way to optimize their properties is the production of complex oxides or different composites. Among the new materials, a special place is occupied by perovskites and materials with an olivine-type structure, which can be easily obtained by the sol-gel method. The sol-gel coating process has demonstrated excellent chemical stability to advance the corrosion resistance of the various metal alloy substrates. Furthermore, the sol-gel process is a user-friendly technique for applying a hybrid sol-gel coating to provide corrosion resistance. The hybrid sol-gel coating technique is the most attractive, easy to prepare at a lower temperature, and has shown the potential to swap Cr-based coatings. The hybrid sol-gel coating has exhibited promising properties of adherent and uses chemically inert to enhance the corrosion resistance of the metal and alloys. Hence, this review article emphases on the recent advances and approaches in the sol-gel coating processes that influence the belongings of its hybrid sol-gel coating for protecting metal substrates and their alloys from corrosion. In addition, the author discusses the current problem and challenges of hybrid anti-corrosion sol-gel coatings. Metal oxides and composites based on them are actively used to create electrochemical sensors. They synthesized, including the anhydrous and citrate sol-gel methods. Such materials are widely used as glucose biosensors and harmful gas sensors.

One-pot synthesis of hard/soft SrFe10O19/x(Ni0.8Zn0.2Fe1.8Cr0.2O4) nanocomposites: Electrical features and reflection losses

Hard/soft (H/S) SrFe 10 O 19 / x(Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 ) ( x ≤ 2.5) nanocomposites (NCs) were manufactured using a one-pot citrate sol–gel method. The structural, dielectric, and microwave absorption features of the products were studied using X-ray diffractometry (XRD), scanning/transmission electron microscopy (SEM/TEM), dielectric spectroscopy, and network analysis. The measured XRD powder patterns confirmed the formation of H/S ferrite NCs without impurities. Both SEM and TEM images showed an accumulation of hexagonal and cubic particles. The dielectric and electrical properties of H/S SrFe 10 O 19 /x(Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 ) (x ≤ 2.5) NCs were systematically examined for applied voltage frequencies up to 3.0 MHz and measurement temperatures between 20 and 120 °C. The conduction mechanisms related to the dielectric constant, ac/dc conductivity, dissipation factor, and dielectric loss were studied for different compositional ratios. In general, the conductivity variations follows power-law rules with frequencies, largely depending on the compositional ratios of the NCs. The frequency-dependent variation of the dielectric constant in all NCs confirmed the typical dielectric distribution, which is largely dependent on the soft phase content (x). Most of the dielectric parameters of H/S SrFe 10 O 19 /x(Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 ) (x ≤ 2.5) NCs can be attributed to grain-to-grain boundaries based on conduction mechanisms, as in most compositional ferrites, which can be clarified using Koop's model. The reflection losses (K ref ) were calculated based on the measured electrodynamic parameters (permeability and permittivity vs. frequency). A nonlinear behavior is observed for K ref with an increase in x. When the soft magnetic phase, Ni 0.8 Zn 0.2 Fe 1.8 Cr 0.2 O 4 , increases from x = 0.0 to x = 2.5, reflection losses decrease from between −17.8 and −20.7 dB to between −0.7 and −9.9 dB, in the 2–10 GHz frequency range. This is attributable to the increasing reflected energy because of the increasing eddy currents, in turn caused by the increasing the electrical conductivity of the NCs.

Boosting propene oxidation activity over LaFeO3 perovskite catalysts by cobalt substitution

To develop robust and cost-effective catalysts for propene total oxidation, LaFe1−xCoxO3 (x = 0, 0.1, 0.2, 0.3, 1) perovskites were prepared via a citrate sol-gel method. XRD, FTIR and Raman analyses suggested that after cobalt substitution, the LaFeO3 structure was well maintained, whereas abundant lattice distortions were generated accompanied by weaker Fe−O bond. H2-TPR and O2-TPD results demonstrated that cobalt incorporation led to better reducibility and higher oxygen mobility of the oxides. The propene oxidation activity of the catalysts was found to increase with the cobalt content, which correlated well with the amount of surface-active oxygen species. The optimal catalyst LaFe0.8Co0.2O3 presented comparable activity to LaCoO3 at much lower cost. Moreover, it showed excellent cyclability (6 cycles) and stability (35 h), decent performance at high space velocity (24,0000 mL g–1 h–1) or in the presence of 5 vol% water, thereby being a promising candidate for industrial application.