Investigation on structure,thermodynamic and multifunctional properties of Ni–Zn–Co ferrite for Gd3+ substitution

This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni–Zn–Co ferrite tailored by Gd³⁺ substitution at the B-site replacing Fe³⁺ ions. The synthesized composition of Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) crystallized with a single-phase cubic spinel structure that belongs to the Fd$\bar{3}$m space group. The average particle size decreases due to Gd³⁺ substitution at Fe³⁺. Raman and IR spectroscopy studies illustrate phase purity, lattice dynamics with cation disorders and thermodynamic conditions inside the studied samples at room temperature (RT = 300 K). Ferromagnetic to paramagnetic phase transition was observed in all samples where Curie temperature (T_C) decreases from 731 to 711 K for Gd³⁺ substitution in Ni–Zn–Co ferrite. In addition, Gd³⁺ substitution reinforces to decrease the A-B exchange interaction. Temperature-dependent DC electrical resistivity (ρ_DC) and temperature coefficient of resistance (TCR) have been surveyed with the variation of the grain size. The frequency-dependent dielectric properties and electric modulus at RT for all samples were observed from 20 Hz to 100 MHz and the conduction relaxation processes were found to spread over an extensive range of frequencies with the increase in the amount of Gd³⁺ in the Ni–Zn–Co ferrite. The RLC behavior separates the zone of frequencies ranging from resistive to capacitive regions in all the studied samples. Finally, the matching impedance (Z/η₀) for all samples was evaluated over an extensive range of frequencies for the possible miniaturizing application.

This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni–Zn–Co ferrite tailored by Gd³⁺ substitution at the B-site replacing Fe³⁺ ions.     

Effects of calcination temperatures on the structure–activity relationship of Ni–La/Al2O3 catalysts for syngas methanation

A series of Ni–La/Al₂O₃ catalysts for the syngas methanation reaction were prepared by a mechanochemical method and characterized by thermogravimetric analysis (TG-DTA), X-ray fluorescence (XRF), X-ray diffraction (XRD), N₂ adsorption–desorption, H₂ temperature-programmed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS). The calcination temperatures (350–700 °C) had significant impacts on the crystallite sizes and interactions between NiO and Al₂O₃. The catalyst calcined at 400 °C (cat-400) showed a 12.1% Ni dispersion degree and the maximum bound state of NiO (54%) through the Gaussian fitting of H₂-TPR. Cat-400 also achieved the highest CO conversion, CH₄ selectivity and yield. Cat-400 exhibited good stability and catalytic activity in a lifetime testing of 200 h. The deactivation of cat-400 was mainly caused by carbon deposition according to the data from XRD, TG-DTG and XPS.

Calcination temperature affects the existing types of NiO, and the influence of the three NiO types on the catalytic activity of samples is bound type ≫ free type > combined type.     

Effect of specific surface area on syngas production performance of pure ceria in high-temperature thermochemical redox cycling coupled to methane partial oxidation

Specific surface area is a key parameter determining the rates of thermochemical redox reactions in metal oxides. We have experimentally investigated the effect of specific surface area on syngas production of pure ceria powders under two experiments such as a heating experiment without syngas production and an isothermal thermochemical redox cycling experiment using carbon dioxide splitting and methane partial oxidation. The specific surface area of ceria powders decreased relatively slowly during 50 hours of ceria powder heating without syngas production due to a combination of oriented attachment and grain-boundary diffusion. When cycled thermochemically, the specific surface area of ceria powders rapidly decreased only in the initial 10 minutes of reduction in the 1st cycle due to evaporation and condensation. A significant decrease of specific surface area during the initial stage of thermochemical ceria powder cycling is unavoidable even if temperatures as low as T = 1173 K are used in the reduction reaction coupled to methane partial oxidation.

Specific surface area is a key parameter determining the rates of thermochemical redox reactions in metal oxides.     

Magnetic and spectroscopic properties of Ni–Zn–Al ferrite spinel: from the nanoscale to microscale

This article presents the annealing effect on the structural, elastic, thermodynamic, optical, magnetic, and electric properties of Ni_0.6Zn_0.4Fe_1.5Al_0.5O₄ (NZFAO) nanoparticles (NPs). The samples were successfully synthesized by the sol–gel method followed by annealing of the as-synthesized at 600, 800, 900, 1050, and 1200 °C. This approach yielded the formation of a highly crystalline structure with crystallite size ranging from 17 nm to 40 nm. X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques, as well as energy disperse spectroscopy (EDS), Fourier transform infrared (FTIR) and Raman spectroscopy, were used in order to determine the structural and morphological properties of the prepared samples. Rietveld XRD refinement reveals that Ni–Zn–Al ferrite nanoparticles crystallize in inverse cubic (Fd$\bar{3}$m) spinel structure. Using FTIR spectra, the elastic and thermodynamic properties were estimated. It was observed that the particle size had a pronounced effect on elastic and thermodynamic properties. Magnetic measurements were performed up to 700 K. The prepared ferrite samples present the highest Curie temperature, which decreases with increasing particle size and which is consistent with finite-size scaling. The thickness of the surface shell of about 1 nm was estimated from size-dependent magnetization measurements using the core–shell model. Besides, spin resonance, magnetostriction, temperature coefficient of resistance (TCR), and electrical resistivity properties have been scientifically studied and appear to be different according to their size. The optical properties of synthesized NZFAO nanoparticles were investigated, and the differences caused by the particle sizes are discussed on the basis of the phonon confinement effect. This effect was also inspected by the Raman analysis. Tuning of the physical properties suggests that the Ni–Zn–Al ferrite samples may be promising for multifunctional diverse applications.

This article presents the annealing effect on the structural, elastic, thermodynamic, optical, magnetic, and electric properties of Ni_0.6Zn_0.4Fe_1.5Al_0.5O₄ (NZFAO) nanoparticles (NPs).     

Influence of neodymium substitution on structural,magnetic and spectroscopic properties of Ni–Zn–Al nano-ferrites

Ni_0.6Zn_0.4Al_0.5Fe_1.5−xNd_xO₄ ferrite samples, with x = 0.00, 0.05, 0.075 and 0.1, were synthesized using the sol–gel method. The effects of Nd³⁺ doping on the structural, magnetic and spectroscopic properties were investigated. XRD Rietveld refinement carried out using the FULLPROF program shows that the Ni–Zn ferrite retains its pure single phase cubic structure with Fd$\bar{3}$m space group. An increase in lattice constant and porosity happens with increasing Nd³⁺ concentration. FTIR spectra present the two prominent absorption bands in the range of 400 to 600 cm⁻¹ which are the fingerprint region of all ferrites. The change in Raman modes in the synthesized ferrite system were observed with Nd³⁺ substitution. The magnetization curves show a typical transition, at the Curie temperature T_C, from a low temperature ferrimagnetic state to a high temperature paramagnetic state. The saturation magnetization, coercivity and remanence magnetization are found to be decreasing with increasing the Nd³⁺ concentration.

The incorporation of Nd³⁺ in the Ni–Zn–Al ferrite spinel causes an improvement in magnetic parameters. Spectroscopic properties were discussed based on FTIR and Raman measurements and proved the purity and good crystallization of the samples.     

Correlation among the structural,electric and magnetic properties of Al3+ substituted Ni–Zn–Co ferrites

This study explored the structural, electrical, and magnetic properties of diamagnetic aluminium (Al³⁺) substituted nickel-zinc-cobalt (Ni–Zn–Co) mixed spinel ferrites, though the research on this area is in the infancy stage. Single-phase cubic spinel structures with the Fd$\bar{3}$m space group of the synthesized Ni_0.4Zn_0.35Co_0.25Fe_(2−x)Al_xO₄ (0 ≤ x ≤ 0.12) ferrite samples were confirmed by X-ray diffraction (XRD) analysis. The average particle size ranged from 0.67 to 0.39 μm. Selected area electron diffraction (SAED) patterns were indexed according to the space group Fd3m, representing the particle''s crystallinity. The optical band gaps ranged from 4.784 eV to 4.766 eV. Frequency-dependent dielectric constants and ac conductivity measurement suggested that the prepared ferrites were highly resistive. Relaxation times were reduced to a low value from 45.45 μs to 1.54 μs with the composition x. The Curie temperatures (T_c) were 615–623 K for all samples. Real part permeabilities (μ^/) were relatively stable up to an extended frequency range of 10⁶ Hz with relative quality factors (RQF) of around 10³. Tuning of the properties indicates that the fabricated ferrites may be promising for high-frequency electronic devices.

This study explored the structural, electrical, and magnetic properties of diamagnetic aluminium (Al³⁺) substituted nickel–zinc–cobalt (Ni–Zn–Co) mixed spinel ferrites, though the research on this area is in the infancy stage.     

Synthesis of Ni–Ag–ZnO solid solution nanoparticles for photoreduction and antimicrobial applications

ZnO is one of the most promising and efficient semiconductor materials for various light-harvesting applications. Herein, we reported the tuning of optical properties of ZnO nanoparticles (NPs) by co-incorporation of Ni and Ag ions in the ZnO lattice. A sonochemical approach was used to synthesize pure ZnO NPs, Ni–ZnO, Ag–ZnO and Ag/Ni–ZnO with different concentrations of Ni and Ag (0.5%, 2%, 4%, 8%, and 15%) and Ni doped Ag–ZnO solid solutions with 0.25%, 0.5%, and 5% Ni ions. The as-synthesized Ni–Ag–ZnO solid solution NPs were characterized by powdered X-ray diffraction (pXRD), FT-IR spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), UV-vis (UV) spectroscopy, and photoluminescence (PL) spectroscopy. Ni–Ag co-incorporation into a ZnO lattice reduces charge recombination by inducing charge trap states between the valence and conduction bands of ZnO and interfacial transfer of electrons. The Ni doped Ag–ZnO solid solution NPs have shown superior 4-nitrophenol reduction compared to pure ZnO NPs which do not show this reaction. Furthermore, a methylene blue (MB) clock reaction was also performed. Antibacterial activity against E. coli and S. aureus has inhibited the growth pattern of both strains depending on the concentration of catalysts.

The synergic effect of Ni and Ag in Ni–Ag–ZnO solid solutions has tuned the optoelectronic properties of ZnO for photoreduction reactions.     

Microstructure,friction and corrosion resistance properties of a Ni–Co–Al2O3 composite coating

Ni–Co–Al₂O₃ composite coatings were prepared by pulsed electrodeposition and electrophoresis–electrodeposition on aluminum alloy. The content of Al₂O₃ particles of the Ni–Co–Al₂O₃ composite coating prepared by electrophoresis–electrodeposition was significantly higher than the composite coating prepared by pulsed electrodeposition. The composite coating prepared by electrophoresis–electrodeposition exhibited a better anti-wear performance than that prepared by pulsed electrodeposition. The morphology, composition and microstructure of the composite coatings were determined by means of X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The hardness and friction properties of the samples were tested on the microhardness tester and the friction and wear loss tester respectively.

Ni–Co–Al₂O₃ composite coatings were prepared by pulsed electrodeposition and electrophoresis–electrodeposition on aluminum alloy.     

Effect of Re promoter on the structure and catalytic performance of Ni–Re/Al2O3 catalysts for the reductive amination of monoethanolamine

In this paper, Ni/Al₂O₃ catalysts (15 wt% Ni) with different Re loadings were prepared to investigate the effect of Re on the structure and catalytic performance of Ni–Re/Al₂O₃ catalysts for the reductive amination of monoethanolamine. Reaction results reveal that the conversion and ethylenediamine selectivity increase significantly with increasing Re loading up to 2 wt%. Ni–Re/Al₂O₃ catalysts show excellent stability during the reductive amination reaction. The characterization of XRD, DR UV-Vis spectroscopy, H₂-TPR, and acidity–basicity measurements indicates that addition of Re improves the Ni dispersion, proportion of octahedral Ni²⁺ species, reducibility, and acid strength for Ni–Re/Al₂O₃ catalysts. The Ni15 and Ni15–Re2 catalysts were chosen for in-depth study. The results from SEM-BSE, TEM, and CO-TPD indicate that smaller Ni⁰ particle size and higher Ni⁰ surface area are obtained in the reduced Ni–Re/Al₂O₃ catalysts. Results from in situ XPS and STEM-EDX line scan suggest that Re species show a mixture of various valances and have a tendency to aggregate on the surface of Ni⁰ particles. During reaction, the Ni⁰ particles on the Al₂O₃ support are stabilized and the sintering process is effectively suppressed by the incorporation of Re. It could be concluded that sufficient Ni⁰ sites, the collaborative effect of Ni–Re, and brilliant stability contribute to the excellent catalytic performance of Ni–Re/Al₂O₃ catalysts for the reductive amination of monoethanolamine.

Re promoters improve the catalyst performance and stability of Ni–Re/Al₂O₃ catalysts for the reductive amination of monoethanolamine.     

Facile construction of a flexible and wearable electrode based on the hierarchical structure of RGO-coated cotton fabric with amorphous Co–Ni–B alloy

As an emerging energy storage material, amorphous Co–Ni–B alloy was firstly introduced to construct the flexible supercapacitor electrode. To ensure the high electrochemical property, amorphous Co–Ni–B alloy and RGO sheets were combined to form the three-dimensional hierarchical structure on the surface of the cotton fabric, which was beneficial to enhance the electrochemical property. Notably, the preparation conditions of this amorphous Co–Ni–B/RGO/fabric electrode were facile and mild with room temperature and atmospheric pressure, thus avoiding serious damage to the textile fabric because of high temperature and harsh chemical reactions of most preparation methods. This flexible electrode exhibited an optimum specific capacitance of 313.9 F g⁻¹ at 5 mV s⁻¹ and good cycling stability with specific capacitance retention of 85.0% after 3000 cycles. Such special architecture bestowed this electrode with nice electrochemical property, in addition to great promising application in the supercapacitor field.

Schematic diagram of preparation process of amorphous Co–Ni–B/RGO/cotton fabric flexible electrode.     

Syngas production by bi-reforming methane on an Ni–K-promoted catalyst using hydrotalcites and filamentous carbon as a support material

Steam reforming of methane (SRM) and dry reforming of methane (DRM) are frequently used in the production of syngas; however, the bi-reforming of methane (BRM) is an interesting and alternative process. In this study, BRM was studied over MgO, a layered double hydroxide (LDH) phase that was destroyed between 600 °C and 900 °C during the reaction. It showed good sorption capacity for CO₂ at relatively low temperatures (<500 °C), with CO₂ adsorption being a pre-requisite for its catalytic conversion. Among the tested materials, the potassium-promoted LDH showed the highest activity, achieving a maximum CO₂ conversion of 75%. The results suggest that at high temperature, the electronic structure of the used materials influences the destabilization of the feed in the order of methane, water and carbon dioxide. K promotes the catalytic activity, compensates the presence of large Ni particle sizes originating from the high metal loading, and favors the formation of Mg–Al-spinel. K is known to be an electronic promoter that releases electrons, which flow to the active metal. This electron flow induces instability on the molecule to be converted, and most probably, also induces size variations on the respective active nickel metal. The influence of the operating conditions in the range of 300 °C to 900 °C on the conversion of the reactants and product distribution was studied. Accordingly, it was concluded that it is only possible to obtain molar ratios of hydrogen-to-carbon monoxide close to two at high temperatures, a pre-requisite for the synthesis of methanol.

A Ni phase dispersed in CO₂ is used with a K promoter in the BRM. The LDH support structure collapses at high temperatures, inducing large Ni crystal sizes, and disfavoring activity. The catalyst is compensated by the K promoter, and the formation of an Mg–Al-spinel.     

Synergistic effects of Ni–Fe alloy catalysts on dry reforming of methane at low temperatures in an electric field

Dry reforming of methane (DRM) is a promising reaction able to convert greenhouse gases (CO₂ and CH₄) into syngas: an important chemical feedstock. Several difficulties limit the applicability of DRM in conventional thermal catalytic reactions; it is an endothermic reaction that requires high temperatures, resulting in high carbon deposition and a low H₂/CO ratio. Catalysis with the application of an electric field (EF) at low temperatures can resolve these difficulties. Synergistic effects with alloys have also been reported for reactions promoted by the application of EF. Therefore, the synergistic effects of low-temperature DRM and Ni–Fe bimetallic catalysts were investigated using various methods and several characterisations (XRD, XPS, FE-STEM, etc.), which revealed that Ni–Fe binary catalysts show high performance in low-temperature DRM. In particular, the Ni_0.8Fe_0.2 catalyst supported on CeO₂ was found to carry out DRM in EF effectively and selectively by virtue of its bimetallic characteristics.

Dry reforming of methane (DRM) is a promising reaction able to convert greenhouse gases (CO₂ and CH₄) into syngas: an important chemical feedstock.     

Effect of reduction temperature on the structure and hydrodesulfurization performance of Na doped Ni2P/MCM-41 catalysts

The removal of sulfur compounds from petroleum is increasingly important because of the environmental pollution caused by sulfur compounds. In this work, Na doped Ni₂P/MCM-41 catalysts were successfully prepared, and their hydrodesulfurization (HDS) performances were assessed using dibenzothiophene (DBT) as a model molecule. Moreover, the effects of reduction temperature (450–600 °C) on the structure and HDS performance of the Ni₂P/Na-MCM-41 catalysts were studied. Results showed that: (a) the reduction temperature of the catalyst could be as low as 450 °C due to Na doping, which is about 200 °C lower than that of the conventional temperature-programmed reduction method (650–1000 °C); (b) increasing the reduction temperature lead to an increase in the diameter of Ni₂P particles, which was demonstrated by size distribution analysis; (c) the HDS performance of the Ni₂P/Na-M41-T catalysts increases with reduction temperature and 99.2% DBT conversion was observed for Ni₂P/Na-M41-600, whereas the hydrogenation route of the catalysts decreased with increasing the reduction temperature, which indicates the lower reduction temperature favored the direct desulfurization pathway (DDS).

The removal of sulfur compounds from petroleum is increasingly important because of the environmental pollution caused by sulfur compounds.     

In situ X-ray absorption spectroscopy study of CuO–NiO/CeO2–ZrO2 oxides: redox characterization and its effect in catalytic performance for partial oxidation of methane

In this work we analyze the effect of adding CuO to a NiO/Ce_0.9Zr_0.1O₂ oxide by in situ X-ray absorption near-edge structure XANES technique in Ce L3, Ni K and Cu K absorption edges in terms of sample reducibility and catalytic activity. The oxidation states of Ce, Ni and Cu cations are followed up during temperature programmed reduction (TPR) experiments in diluted hydrogen and during catalytic tests for partial oxidation of methane (POM) reaction. Redox behavior was correlated to conventional fixed bed reactor results. The effect of firing temperature, crystallite size, CeO₂–ZrO₂ support and the presence of Cu and/or Ni as an active phase is also analyzed. Results showed a beneficial effect of CuO addition in terms of Ce and Ni reduction. A stronger interaction of NiO species with the support was revealed upon analysis of XANES reduction profiles in sample NiO/ZDC in contrast to bimetallic CuO–NiO/ZDC sample. Reduction onset temperature was found to depend on Ni crystallite size, being markedly promoted when samples exhibited low values of crystallite size both in supported and non-supported CuO–NiO species. In situ catalytic experiments for partial oxidation of methane showed a clear interplay between the redox behavior from the Ce in the CeO₂–ZrO₂ support and the Ni from the active phase. Sample NiO/ZDC exhibited a continuous reduction of Ce cations in CH₄ : O₂ feed flow, carbon formation was detected in X-ray Powder Diffraction (XPD) patterns and Ni re-oxidation was found to take place, clear indications of catalyst deactivation. In contrast, sample CuO–NiO/Ce_0.9Zr_0.1O₂ displayed a slight re-oxidation of Ce and no re-oxidation of Ni altogether with the suppression of carbon formation.

In situ X-Ray Absorption (XAS) experiments in reducing atmospheres (H₂ and CH₄ : O₂) uncovered Ce, Ni and Cu redox interplay during catalytic experiments.     

Facile preparation of porous sheet–sheet hierarchical nanostructure NiO/Ni–Co–Mn–Ox with enhanced specific capacity and cycling stability for high performance supercapacitors

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination. The thermodynamic behavior was observed by TG/DTA. The chemical structure and composition, phase structure and microstructures were tested by XPS, XRD, FE-SEM and TEM. The electrochemical performance was measured by CV, GCD and EIS. The mechanism for formation and enhancing electrochemical performance is also discussed. Firstly, the precursors such as NiOOH, CoOOH and MnOOH grow on nickel foam substrates from a homogeneous mixed solution via chemical bath deposition. Thereafter, these precursors are calcined and decomposed into NiO, Co₃O₄ and MnO₂ respectively under different temperatures in a muffle furnace. Notably, NiO/Ni–Co–Mn–O_x on nickel foam substrates reveals a high specific capacity with 1023.50 C g⁻¹ at 1 A g⁻¹ and an excellent capacitance retention with 103.94% at 5 A g⁻¹ after 3000 cycles in 2 M KOH, its outstanding electrochemical performance and cycling stability are mainly attributed to a porous sheet–sheet hierarchical nanostructure and synergistic effects of pseudo-capacitive materials and excellent redox reversibility. Therefore, this research offers a facile synthesis route to transition metal oxides for high performance supercapacitors.

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination.     

A first-principles calculation of structural,mechanical, thermodynamic and electronic properties of binary Ni–Y compounds

The intermetallic compounds between rare earth (RE) elements and transition metal elements have been comprehensively researched due to their appealing magnetic, electronic, optical and thermal properties, in which Ni–Y alloys are one kind of important system. In this work, a systematic investigation concerned with structures, elastic, and thermodynamic properties of Ni₁₇Y₂, Ni₅Y, Ni₇Y₂, Ni₃Y, Ni₂Y, NiY, Ni₂Y₃ and NiY₃ in Ni–Y systems is implemented by means of first-principles calculations. NiY has the lowest formation enthalpy within −0.49 kJ per mol per atom. Ni₅Y has the largest bulk modulus, shear modulus and Young''s modulus of 181.71 GPa, 79.75 GPa and 208.70 GPa, respectively. Furthermore, the effects of different concentrations of yttrium on the mechanical and thermal properties of Ni–Y compounds are estimated by using the Voigt–Reuss method. The electronic density of states and chemical bonding between Ni and Y are key factors that determine mechanical and thermodynamic properties of these compounds. What''s more, results indicate that all compounds are dynamically stable as shown by the calculated phonon dispersions.

A systematic investigation concerned with structures, elastic, and thermodynamic properties of Ni₁₇Y₂, Ni₅Y, Ni₇Y₂, Ni₃Y, Ni₂Y, NiY, Ni₂Y₃ and NiY₃ in Ni–Y system.     

Insight on the effect of Ni and Ni–N co-doping on SnO2 anode materials for lithium-ion batteries

With the increased demand for high-rate performance Li-ion batteries, it is necessary to find available methods to improve the rate properties of SnO₂ electrodes. It is noteworthy that doping was considered to be a feasible means. The electronic structures and diffusion energy barriers of Ni-doped and Ni–N co-doped SnO₂ were calculated based on density functional theory. The results estimated that the energy gaps of Ni-doped and Ni–N co-doped SnO₂ are 1.07 eV and 0.94 eV, which both are smaller than the value of 2.08 eV of SnO₂. These exhibit that the conduction properties of SnO₂ can be enhanced by doping with the Ni or Ni–N atoms. Moreover, the diffusion properties of Li can also be improved by doping with Ni–N atoms due to the diffusion energy barrier of Li from the B to C point for Ni–N co-doped SnO₂ being 0.12 eV smaller than the value of 0.24 eV for the pristine SnO₂. Meanwhile, the diffusion energy barriers of Li along other pathways for Ni–N co-doped SnO₂ are almost the same as 0.24 eV for SnO₂. These results show that both the electronic and ionic conductivity of SnO₂ can be enhanced by Ni–N co-doping, which provides a theoretical explanation to promote the rate properties of SnO₂ by Ni–N co-doping as anode materials for Li-ion batteries.

Energy barriers of Li, where red, green and yellow curves represent diffusion energy barriers of Li in the pure, Ni-doped, and Ni–N co-doped SnO₂, respectively.     

Cerium–zirconium mixed oxide nanostructures for diesel soot oxidation: synthesis and effect of structure

Nanostructured materials have been used in several branches of science and technology. Particulate matter is one of the major air pollution concerns. In this work, nanorods and nanoparticles of Ce_0.8Zr_0.2O₂ (CZ) mixed oxides were prepared by different routes, and the use of an organic template was evaluated in diesel soot oxidation. The catalysts were characterized by several techniques including structural analysis (XRD, TEM, N₂ adsorption–desorption) and activity (TPR/MS, TPO/MS). A fast TPR/MS method is proposed to calculate hydrogen consumption that can be correlated to the oxygen storage capacity (OSC). It was demonstrated that CZ-nanorods with twice the amount of template in the syntheses (CZ-NRs-2X) were very active for soot oxidation with T_50% at 351 °C, and CO₂ and H₂O were the only oxidation products from Printex®-U (Evonik). This catalyst, reported for the first time, was subjected to up to three cycles and it showed fair activity, proving that this morphology is one of the best mixed oxides of CZ for oxidation.

Nanorods and nanoparticles of Ce_0.8Zr_0.2O₂ (CZ) mixed oxides were prepared by different routes and showed good activity for diesel soot oxidation.     

Effect of temperature and large guest molecules on the C–H symmetric stretching vibrational frequencies of methane in structure H and I clathrate hydrates

Large molecules such as 2-methylbutane (C₅H₁₂) or 2,2-dimethylbutane (C₆H₁₄) form structure H (sH) hydrates with methane (CH₄) as a help gas. In this study, the Raman spectra of the C–H symmetric stretch region of CH₄ enclathrated within various sH hydrates and structure I CH₄ hydrates were analyzed in the temperature range 137.7–205.4 K. Thermal expansions of these sH hydrate samples were also measured using powder X-ray diffraction. Symmetric stretch vibrational frequencies of CH₄ in host–water cages increased because of varying temperature, and the sizes of the host–water cages also increased; variation of CH₄ in small cages was less than in larger cages. Comparing the variations of the C–H symmetric stretching frequencies of CH₄ in gas hydrates with varying pressure and temperature, we suggest that the observed trend is caused by thermal vibrations of the CH₄ molecule in water cages.

Temperature effect on C–H symmetric stretching frequencies of CH₄ in water cages of sI and sH clathrate hydrates were clarified.