Synergistic effect of Pt or Pd and perovskite oxide for water gas shift reaction

The water gas shift (WGS) reaction over Pt and Pd catalysts supported on various perovskite oxides has been investigated at 573 K without catalyst pretreatment. The Pt and Pd catalysts on LaCoO₃ support showed high catalytic activity. Interaction between Pt or Pd and the support is considered to promote the WGS reaction: Pt/LaCoO₃ had high initial activity but deactivated immediately; Pd/LaCoO₃ was less active than Pt/LaCoO₃, but had superior stability. Catalysts were characterized using XRD, STEM, XPS, and H₂-temperature programmed reduction (TPR). Results of this study showed that reduction of the support decreased the CO conversion on Pt/LaCoO₃. On the other hand, Pd/LaCoO₃ showed stable activity for the WGS reaction. Therefore, Pd was added to Pt/LaCoO₃ for stabilizing the catalyst activity, and 0.5 wt.% Pd/1 wt.% Pt/LaCoO₃ catalyst showed higher activity and stability.     

Combination of photocatalytic and photoelectro-Fenton/citrate processes for dye degradation using immobilized N-doped TiO2 nanoparticles and a cathode with carbon nanotubes: Central composite design optimization

In this report, commercial TiO₂ nanoparticles were doped with nitrogen by a manual grinding method using urea. The prepared catalyst was characterized by X-ray diffraction (XRD), diffuse reflectance spectra (DRS), and transmission electron microscopy (TEM). N-doped TiO₂ was immobilized on ceramic plates by methyl tri-methoxy silane. Next, multi-walled carbon nanotubes (CNTs) were stabilized on carbon paper to fabricate the cathode. Scanning electron microscopy (SEM) was employed to confirm stabilization of the CNTs. The prepared cathode and immobilized catalyst were utilized for the degradation of C.I. Direct Red 23 (DR23) by the photoelectro-Fenton (PEF) process in the presence of citrate (Cit) combined with a photocatalytic process. The coupled PEF/Cit/N-TiO₂ process could be performed under visible light, not only due to the formation of iron–citrate complexes, but also because of the incorporation of nitrogen to the crystalline structure of TiO₂ and the generation of TiO₂ complexes with electrogenerated H₂O₂. Results demonstrated that the degradation efficiency of DR23 (20 mg/L) using the identical operational conditions, followed a decreasing order of: PEF/Cit/N-TiO₂ > PEF/Cit > PEF > EF > N-TiO₂. Eventually, a model was developed by the central composite design (CCD) method, describing the degradation efficiency as a function of the operational parameters.     

Microwave absorption study of carbon nano tubes dispersed hard/soft ferrite nanocomposite

Nickel substituted strontium hexaferrite, SrNi₂Fe₁₀O₁₉·(SrFe₁₂O₁₉/NiFe₂O₄) nanoparticles have been synthesized by low combustion method by citrate precursors using sol to gel (S–G) followed by gel to nano crystalline (G–N) conversion. The resulting ‘as-synthesized’ powder is heat treated (HT) at 800 and 1000 °C for 4 h in nitrogen atmosphere. The hysteresis loops show an increase in saturation magnetization from 27.443 to 63.706 emu/g with increasing HT temperatures. The multiwalled carbon nano tubes (CNTs) were synthesized by thermal decomposition of acetylene gas over iron-catalyst deposited on silicon wafer in the temperature range of 750–800 °C. A microwave absorbing medium is prepared by adding CNTs in the nickel substituted strontium hexaferrite nanoparticles. Addition of certain mass of CNTs improves the microwave absorption properties and wave band of SrFe₁₂O₁₉/NiFe₂O₄ absorbent. When 10 wt% CNTs is mixed with SrFe₁₂O₁₉/NiFe₂O₄ nanoparticles to fabricate a composite with 2 mm thickness, the maximum reflection loss reaches to ?36.817 dB at 9.292 GHz and ?10 dB bandwidth reaches 3.27 GHz.     

In situ hydrothermally synthesized mesoporous LaCoO3/SBA-15 catalysts: High activity for the complete oxidation of toluene and ethyl acetate

Mesoporous yLaCoO₃/SBA-15 (y = 10–50 wt%) catalysts were prepared and characterized for the combustion of toluene and ethyl acetate (EA). The results show that well-ordered mesoporous LaCoO₃/SBA-15 catalysts of high surface areas (338–567 m²/g) could be fabricated by a facile in situ method of hydrothermal treatment. The particles of perovskite-type LaCoO₃ were highly dispersed on the walls of pore channels. The ordered mesoporous structure and high dispersion of LaCoO₃ are beneficial to the adsorption and activation of toluene and EA molecules. We found that in terms of specific activity, the in situ fabricated 35LaCoO₃/SBA-15 and 40LaCoO₃/SBA-15 is, respectively, superior to 35LaCoO₃/SBA-15_imp (generated by incipient wetness impregnation method) and bulk LaCoO₃ (prepared by sol–gel method) in catalytic performance. Based on the above results, we conclude that the excellent performance can be attributed to the good dispersion of highly reducible LaCoO₃ species in yLaCoO₃/SBA-15.     

Thermal transport phenomena and limitations in heterogeneous polymer composites containing carbon nanotubes and inorganic nanoparticles

An Off-Lattice Monte Carlo model was developed to investigate effective thermal conductivities (K_eff) and thermal transport limitations of polymer composites containing carbon nanotubes (CNTs) and inorganic nanoparticles. The simulation results agree with experimental data for poly(ether ether ketone) (PEEK) with inclusions of CNTs and tungsten disulfide (WS₂) nanoparticles. The developed model can predict the thermal conductivities of multiphase composite systems more accurately than previous models by taking into account interfacial thermal resistance (R_bd) between the nanofillers and the polymer matrix, and the nanofiller orientation and morphology. The effects of (i) R_bd of CNT–PEEK and WS₂–PEEK (0.0232–115.8 × 10⁻⁸ m²K/W), (ii) CNT concentration (0.1–0.5 wt%), (iii) CNT morphology (aspect ratio of 50–450, and diameter of 2–8 nm), and (iv) CNT orientation (parallel, random and perpendicular to the heat flux) on K_eff of a multi-phase composite are quantified. The simulation results show that K_eff of multiphase composites increases when the CNT concentration increases, and when the R_bd of CNT–PEEK and WS₂–PEEK interfaces decrease. The thermal conductivity of composites with CNTs parallel to the heat flux can be enhanced ∼2.7 times relative to that of composites with randomly-dispersed CNTs. CNTs with larger aspect ratio and smaller diameter can significantly improve the thermal conductivity of a multiphase polymer composite.     

Fabrication and microwave absorption properties of magnetite nanoparticle–carbon nanotube–hollow carbon fiber composites

Absorbents with “tree-like” structures, which were composed of hollow porous carbon fibers (HPCFs) acting as “trunk” structures, carbon nanotubes (CNTs) as “branch” structures and magnetite (Fe₃O₄) nanoparticles playing the role of “fruit” structures were prepared by chemical vapor deposition technique and chemical reaction. Microwave reflection loss, permittivity and permeability of Fe₃O₄–CNTs–HPCFs composites were investigated in the frequency range of 2–18 GHz. It was proven that prepared absorbents possessed the excellent electromagnetic wave absorbing performances. The bandwidth with a reflection loss less than −15 dB covers a wide frequency range from 10.2 to 18 GHz with the thickness of 1.5–3.0 mm, and the minimum reflection loss is −50.9 dB at 14.03 GHz with a 2.5 mm thick sample layer. Microwave absorbing mechanism of the Fe₃O₄–CNTs–HPCFs composites is concluded as dielectric polarization and the synergetic interactions exist between Fe₃O₄ and CNTs–HPCFs.     

A simple approach for the synthesis of bi-functional Fe3O4@WO3 − x core–shell nanoparticles with magnetic-microwave to heat responsive properties

A facile direct precipitation method has been developed for the synthesis of multi-functional magnetic, microwave to heat responsive properties with Fe₃O₄ nanoparticles as the core and WO_3 − x as the shell. Transmission electron microscopy (TEM) images revealed that the obtained bi-functional nanoparticles had a core-shell structure and a spherical morphology. The average size was ~ 250 nm, and the thickness of the shell was ~ 15 nm. The X-ray diffraction (XRD) patterns showed that a cubic spinel structure of Fe₃O₄ core and the WO_3 − x shell were obtained. The nanoparticles showed both strong magnetic, and unique microwave to heat responsive properties, which may lead to development of nanoparticles with great potential for applications in drug targeting delivery, controlled release drug, photo- and microwave-thermal combination therapy and water treatment.     

Increased CNT growth density with an additional thin Ni layer on the Fe/Al catalyst film

Density of 3 × 10¹¹/cm² and diameter of CNTs of 9–12 nm were successfully controlled by using the multi-layered catalyst film consisting of an additional Ni layer on Fe/Al catalyst film. EDS analysis for the annealed catalyst films revealed that the increase of the density of Fe catalyst particles corresponded with the decrease of Ni in the films, which strongly suggested that the additional thin Ni layer on the Fe/Al multi-layered catalyst films prevented the fine Fe catalyst particles from agglomeration, resulting in the growth of high-density, and uniform diameter of CNTs.     

Co-production of hydrogen and multi-wall carbon nanotubes from ethanol decomposition over Fe/Al2O3 catalysts

The co-production of hydrogen and carbon nanotubes (CNTs) from the decomposition of ethanol over Fe/Al₂O₃ at different temperatures and feeding rates of ethanol was investigated systematically. The results indicated that Fe/Al₂O₃ was a quite active catalyst for the co-production of hydrogen and CNTs and that its activity and stability depended strongly on the Fe loading. Among all catalysts tested, 10 mol% Fe/Al₂O₃ was the most effective catalyst based on the ratio of hydrogen production, the total H₂ yield, and the quality of the CNTs formed. The efficiency of hydrogen production from ethanol decomposition over 10 mol% Fe/Al₂O₃ reached a maximum of ∼80% at 800 °C and the yield of CNTs with well-oriented growth and uniform diameter was 141%. In addition, the reaction of hydrogen and CNTs co-produced from ethanol decomposition was proposed.     

Microstructural features of nanocomposite of alumina@carbon nanotubes/alumina nanoparticles synthesized by a solvothermal method

The present study focuses on the synthesis of nanocomposite gamma alumina (γ-Al₂O₃), boehmite and multi- walled carbon nanotubes (MWCNTs) via a solvothermal procedure. The method is based on the ex situ filling of opened CNTs by liquid reactants. The microstructure and morphology of the synthesized nanocomposite Al₂O₃@CNTs/Al₂O₃ was characterized by high resolution transmission electron microscopy (HRTEM), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and N₂ adsorption–desorption analysis.Based on the experimental results, it was determined that the volume ratio of γ-Al₂O₃/MWCNTs and the surface tension of the solvent both greatly influence the morphology of the nanocomposite. The resultant MWCNTs were coated and filled by homogeneous and uniform boehmite and γ-Al₂O₃ layers and nanoparticles with thicknesses of 1–3 nm and diameters of 20–40 nm, when the volume ratio of γ-Al₂O₃/MWCNT_S is 1 and the surface tension of the solvent is approximately 26 mN m^?1 at 20 °C, far below the maximum value (100–200 mN m^?1) for MWCNT filling.     

Non-congruence of high-temperature mechanical and structural behaviors of LaCoO3 based perovskites

This paper presents the mechanical behavior of LaCoO₃ and La_0.8Ca_0.2CoO₃ ceramics under four-point bending in which the two cobaltites are subjected to a low stress of ∼8 MPa at temperatures ranging from room temperature to 1000 °C. Unexpected stiffening is observed in pure LaCoO₃ in the 700–900 °C temperature range, leading to a significant increase in the measured Young’s modulus, whereas La_0.8Ca_0.2CoO₃ exhibits softening from 100 °C to 1000 °C, as expected for most materials upon heating. Neutron diffraction, X-ray diffraction and micro-Raman spectroscopy are used to study the crystal structure of the two materials in the RT–1000 °C temperature range. Despite a detailed study, there is no conclusive evidence to explain the stiffening behavior observed in pure LaCoO₃ as opposed to the softening behavior in La_0.8Ca_0.2CoO₃ at high temperatures (above 500 °C).     

Catalytic activity of nanometer La1−xSrxCoO3 (x = 0, 0.2) perovskites towards VOCs combustion

Combustive oxidation of volatile organic compounds (VOCs), such as propyl alcohol, toluene and cyclohexane, were studied. The combustion was catalyzed by nanoparticles of La_1−xSr_xCoO₃ (x = 0, 0.2) perovskites prepared by a co-precipitation method. The results showed high activities of the perovskite catalysts. Compared to LaCoO₃, in particular, La_0.8Sr_0.2CoO₃ was much higher in catalytic ability. The total oxidation of VOCs followed the increasing order: cyclohexane < toluene < propyl alcohol. The T_99% of cyclohexane was 40 °C lower than that of toluene, which appeared to be determined by the bond strengths of the weakest C–H and C–C bonds. The 100-h stability experiments showed that La_1−xSr_xCoO₃ (x = 0, 0.2) perovskite was highly stable.     

Synthesis of Fe/Fe3C nanoparticles encapsulated in nitrogen-doped carbon with single-source molecular precursor for the oxygen reduction reaction

Ammonium ferric citrate (AFC) was used as a single-source molecular precursor to prepare Fe/Fe₃C nanoparticles encapsulated in nitrogen-doped carbon by pyrolysis in Ar atmosphere followed by acid-leaching. Comparative studies, using citric acid and ferric citrate as the precursors, indicated that the ammonia and ferric ion in AFC and the pyrolysis temperature affected the composition of iron species and the properties of carbon in AFC-derived materials. Above the pyrolysis temperature of 600 °C, the iron species were Fe/Fe₃C, and the carbon had a hollow graphitic nanoshell structure in AFC-derived materials. The specific surface area and content of nitrogen element decreased with increasing pyrolysis temperature. The AFC-derived material pyrolyzed at 600 °C had the optimal graphitization degree, specific surface area (489 m² g⁻¹) and content of nitrogen (1.8 wt.%), thus resulted in the greatest activity for oxygen reduction reaction among the AFC-derived materials pyrolyzed at different temperatures. The AFC-derived material pyrolyzed at 600 °C exhibited improved methanol-resistance ability compared with Pt/C catalyst.     

Catalytic removal of diesel soot particulates over K and Mg substituted La1 − xKxCo1 − yMgyO3 perovskite oxides

K and Mg substituted perovskite catalysts La_1 − xK_xCo_1 − yMg_yO₃ (x = 0–0.4, y = 0–0.2) for soot combustion were prepared by citric acid complexation and characterized by XRD, FT-IR, SEM, TEM, EDS, H₂-TPR, XPS and TG. Soot combustion was remarkably accelerated when K was introduced into LaCoO₃. Then Mg was doped into the K substituted LaCoO₃, soot combustion was further improved for the restrained growth of Co₃O₄ phase. K/Mg substitutions were responsible for enhancing activity of catalysts by improving reducibility as suggested by H₂-TPR studies. Among all the catalysts, La_0.6K_0.4Co_0.9Mg_0.1O₃ exhibited the highest activity.     

Evaluation of water treatment sludge as a catalyst for aqueous ozone decomposition

A new, novel, efficient, and stable green catalyst has been successfully used as a catalyst in aqueous ozone decomposition in acidic medium. The catalyst was characterized by using X-ray fluorescence (XRF), transmission electron microscope (TEM), scanning electron microscope (SEM), and X-ray diffraction (XRD) techniques. The sludge mainly consists of various metal and non-metal oxides. The effect of various experimental parameters such as catalyst loading, initial ozone concentrations, and various metal oxide catalysts on the decomposition of ozone was investigated. The decomposition of dissolved ozone was substantially enhanced by increasing the catalyst loading from 125 to 750 mg and by increasing the initial ozone concentration. The ozone decomposition efficiencies of Al₂O₃, SiO₂, TiO₂, Fe₂O₃, ZnO, and sludge have been studied and the efficiencies of these catalysts were found to be in the following order: ZnO ≈ sludge > TiO₂ > SiO₂ > Al₂O₃ ≈ Fe₂O₃. The catalytic stability was also investigated for up to four successive cycles and it was found that the catalyst was stable and ozone did not affect the catalyst morphology and its composition. However, the surface area of the catalyst increased after 1st cycle then it became stable. It was concluded that the sludge powder used in this study was a promising catalyst for aqueous ozone decomposition.     

A wall-coated catalytic capillary microreactor for the direct formation of hydrogen peroxide

The direct formation of hydrogen peroxide from H₂ and O₂ was successfully carried out in a capillary microreactor at room temperature and atmospheric pressure. A key element in sustaining the activity of the catalyst is the incarceration of the palladium nanoparticles in a cross-linkable amphiphilic polystyrene-based polymer, prepared following the protocol of Kobayashi [R. Akiyama, S. Kobayashi, J. Am. Chem. Soc. 125 (2003) 3412–3413]. The immobilization effectively reduced the leaching of palladium under acidic conditions. Applying the catalyst as a coating on the inner walls of a capillary enabled the sustained production of 1.1% hydrogen peroxide over at least 11 days. The highest catalyst utilization in a 2 mm capillary reactor was 0.54 mol_H2O2/h g_Pd. When the inner diameter of the reactor capillary was reduced to 530 μm, the rate was enhanced fourfold to 2.28 mol_H2O2/h g_Pd corresponding to a turnover frequency of 0.067 s^?1.     

Structural,magnetic, and textural properties of iron oxide-reduced graphene oxide hybrids and their use for the electrochemical detection of chromium

Superparamagnetic Fe₃O₄ nanoparticles were anchored on reduced graphene oxide (RGO) nanosheets by co-precipitation of iron salts in the presence of different amounts of graphene oxide (GO). A pH dependent zeta potential and good aqueous dispersions were observed for the three hybrids of Fe₃O₄ and RGO. The structure, morphology and microstructure of the hybrids were examined by X-ray diffraction, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, Raman and X-ray photoelectron spectroscopy. TEM images reveal lattice fringes (d₃₁₁ = 0.26 nm) of Fe₃O₄ nanoparticles with clear stacked layers of RGO nanosheets. The textural properties including the pore size distribution and loading of Fe₃O₄ nanoparticles to form Fe₃O₄–RGO hybrids have been controlled by changing the concentration of GO. An observed maximum (～10 nm) in pore size distribution for the sample with 0.25 mg ml^?1 of GO is different from that prepared using 1.0 mg ml^?1 GO. The superparamagnetic behavior is also lost in the latter and it exhibits a ferrimagnetic nature. The electrochemical behavior of the hybrids towards chromium ion was assessed and a novel electrode system using cyclic voltammetry for the preparation of an electrochemical sensor platform is proposed. The textural properties seem to influence the electrochemical and magnetic behavior of the hybrids.     

Low-temperature selective catalytic reduction of NO over MnOx/CNTs catalysts: Effect of thermal treatment condition

Carbon nanotubes (CNTs) supported manganese oxide catalysts were prepared through different thermal treatment routes and used for low-temperature selective catalytic reduction of NO with NH₃. The MnO_x/CNTs catalyst prepared by calcined the precursor in air at 300 °C showed lower NO conversions than that treated at 250 °C, while it showed higher NO conversions than the one calcined in nitrogen. BET, TGA, XRD and H₂-TPR results indicated that CNTs may impose effects on the oxidation state and redox ability of the manganese oxide and hence on the catalytic activity during the calcination process at given temperatures.     

Thermodynamics and regeneration studies of CO2 adsorption on multiwalled carbon nanotubes

Multiwalled carbon nanotubes (CNTs) were fabricated and modified by 3-aminopropyl-triethoxysilane (APTS) solutions to study thermodynamics and regeneration of CO₂ adsorption from gas streams. The CO₂ adsorption capacities of CNTs and CNT(APTS) decreased with temperature indicating the exothermic nature of adsorption process while the thermodynamic analysis gave low isosteric heats of adsorption, which are typical for physical adsorption. The cyclic CO₂ adsorption on CNT(APTS) showed that the adsorbed CO₂ could be effectively desorbed via thermal treatment at 120 °C for 25 min while the adsorbed CO₂ due to physical interaction could be effectively desorbed via vacuum suction at 0.145 atm for 30 min. If a combination of thermal and vacuum desorption was conducted at 120 °C and 0.145 atm, the time for effectively desorbing CO₂ could be further shortened to 5 min. The adsorption capacities and the physicochemical properties of CNT(APTS) were preserved during 20 cycles of adsorption and regeneration. These results suggest that the CNT(APTS) can be stably employed in prolonged cyclic operation and they are thus possibly cost-effective sorbents for CO₂ capture from flue gases.     

Template-free synthesis of mesoporous γ-alumina with tunable structural properties

Mesoporous γ-Al₂O₃ (MA) with agglomerated nanoparticles was successfully synthesized by using aluminum sulfate as inorganic Al resource, and hexamethylene tetramine (HMTA) as precipitant without using any surfactants, via a hydrothermal method. All the experimental processes experienced the hydrolysis, precipitation and calcination steps. The structural and morphological properties of uncalcined and calcined samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry differential thermal gravity (TG-DTG) and N₂ adsorption–desorption. The bulk density of the sample is 0.682 cm³  g⁻¹, and the specific surface area is 273.302 m² g⁻¹. The pore diameters (7.1 nm and 9.7 nm) indicate that a typical bimodal mesoporous structure was formed within MA. In order to tune the structural properties of MA, various kinds of inorganic aluminum sources and precipitating agents were employed to carry out contrast experiments, which leaded to regular variations in the specific surface area (200.898–273.302 m² g⁻¹), pore volume (0.121–1.327 cm³ g⁻¹) and pore size (3.7–35.9 nm). At the same time, the experimental results also demonstrated that the various kinds of Al resources and precipitants had no effects on the crystal structure of MA. However, the morphologies of samples, such as nanoparticles, short fibers, flower-like and block-shaped, can be controlled effectively. The present study provides a simple and effective approach for preparing MA, and the structural properties of MA can be controlled precisely by carefully choosing aluminum sources and precipitants. The approach of this work not only allows us to investigate the growth mechanism of the final product, but also reduces cost and the environmental pollution effectively than other template methods.