Synthesis of boron nitride nanotube films with a nanoparticle catalyst

Boron nitride nanotube（BNNT） films were synthesized by combining ball milling and thermal chemical vapor deposition（CVD） using nano-Fe3O4 as a catalyst. The as-produced BNNTs have a bamboo-like structure and have a diameter in the range of 50~200 nm with an average length of more than 40 mm.Moreover, BNNT nanojunction structures were synthesized. The structure and morphology of the BNNTs were characterized by XRD, SEM, TEM and HRTEM. The possible growth mechanism of BNNTs and BNNT nanojunction structures were proposed. Though the BNNT films were observed, out of our expectation,BNNTs with thin tube wall and small average diameter have not been achieved, and this could be mainly ascribed to the aggregation of the nanoparticle catalyst, resulting in greater catalyst particles during the process of BNNT growth. This result will provide a promising approach to obtain the desired shape of BNNTs and produce branched junctions of BNNTs.

PEO-b-P4VP/Yttrium Hydroxide Hybrid Nanotubes as Supporter for Catalyst Gold Nanoparticles

The adsorption of poly （ethylene oxide）-b-poly（4-vinylpyridine）（PEO-b-P4VP） micelles onto the surface of yttrium hydroxide nanotubes （YNTs） resulted in the hybrid nanotubes with a dense P4VP inner layer and a stretched PEO outer layer surrounding YNTs. The dense P4VP layer was further stabilized by the crosslinking using 1,4-dibromobutane as the crosslinker. Then, the crosslinked hybrid nanotubes （CHNTs） were used as a novel nano supporter for loading the catalyst gold nanoparticles （GNPs） within the crosslinked P4VP layer. The resultant GNPs/CHNTs （GNTs loaded on CHNTs） were applied to catalyze the reduction reaction of p-nitrophenol. The results indicate that this novel nano supporter has advantages such as good dispersity in the suspension, high capacity in loading GNPs （0.87 mmol/g）, high catalytic activity of the loaded GNPs （12.9 μmol-lmin-i）, and good reusability of GNTs/CHNTs.

Controlling the Diameter of Single-Walled Carbon Nanotubes by Improving the Dispersion of the Uniform Catalyst Nanoparticles on Substrate

To have uniform nanoparticles individually dispersed on substrate before single-walled carbon nanotubes(SWNTs)growth at high temperature is the key for controlling the diameter of the SWNTs.In this letter,a facile approach to control the diameter and distribution of the SWNTs by improving the dispersion of the uniform Fe/Mo nanoparticles on silicon wafers with silica layer chemically modified by 1,1,1,3,3,3-hexamethyldisilazane under different conditions is reported.It is found that the dispersion of the catalyst nanoparticles on Si wafer surface can be improved greatly from hydrophilic to hydrophobic,and the diameter and distribution of the SWNTs depend strongly on the dispersion of the catalyst on the substrate surface.Well dispersion of the catalyst results in relatively smaller diameter and narrower distribution of the SWNTs due to the decrease of aggregation and enhancement of dispersion of the catalyst nanoparticles before growth.It is also found that the diameter of the superlong aligned SWNTs is smaller with more narrow distribution than that of random nanotubes.

Correlation between catalytic activity of supported gold catalysts for carbon monoxide oxidation and metal–oxygen binding energy of the support metal oxides

The effect of a wide variety of metal oxide （MOx） supports has been discussed for CO oxidation on nanoparticulate gold catalysts. By using typical co‐precipitation and deposition–precipitation methods and under identical calcination conditions, supported gold catalysts were prepared on a wide variety of MOx supports, and the temperature for 50%conversion was measured to qualita‐tively evaluate the catalytic activities of these simple MOx and supported Au catalysts. Furthermore, the difference in these temperatures for the simple MOx compared to the supported Au catalysts is plotted against the metal–oxygen binding energies of the support MOx. A clear volcano‐like correla‐tion between the temperature difference and the metal–oxygen binding energies is observed. This correlation suggests that the use of MOx with appropriate metal–oxygen binding energies （300–500 kJ/atom O） greatly improves the catalytic activity of MOx by the deposition of Au NPs.

Development of Highly Effective Nanoparticle Spinel Catalysts for Aerobic Oxidation of Benzylic Alcohols

Spinel catalyst MnFe 1.8Cu 0.15Ru 0.05O 4 with particle size of about 42 nm is an effective heterogeneous catalyst for the oxidation of benzylic alcohols. The substitution of Fe for Cu improves its catalytic activity. Based on the characterization of BET, XPS and EXAFS, two factors influencing the structure and texture of the catalyst caused by the substitution of Cu for Fe may be assumed: physical factor responsible for the increasing of surface area; chemical factor responsible for the transformation of Ru-O bonds to Ru=O bonds. β-Elimination is considered to be an important step in the reaction.

Recent advances in high-loading catalysts for low-temperature fuel cells: From nanoparticle to single atom

Low-temperature fuel cells(LTFCs)are considered to be one of the most promising power sources for widespread application in sustainable and renew-able energy conversion technologies.Although remarkable advances have been made in the mass activity of catalysts,mass transport impedance needs to be urgently addressed at a well-designed membrane electrode assembly(MEA)scale.Increasing the loading of electrocatalysts is conducive to prepare thinner and more efficient MEAs owing to the resulting enhanced reactant permeability,better proton diffusion,and lower electrical resistance.Herein,recent progress in high-loading(≥40 wt.%)Pt nanoparticle catalysts(NPCs)and high-loading(≥2 wt.%)single-atom catalysts(SACs)for LTFC applications are reviewed.A summary of various synthetic approaches and support materials for high-loading Pt NPCs and SACs is systematically presented.The influences of high surface area and appropriate surface functionalization for Pt NPCs,as well as coordina-tion environment,spatial confinement effect,and strong metal-support interac-tions(SMSI)for SACs are highlighted.Additionally,this review presents some ideas regarding challenges and future opportunities of high-loading catalysts in the application of LTFCs.

Rational design of Fe-N-C electrocatalysts for oxygen reduction reaction:From nanoparticles to single atoms

As an alternative energy,hydrogen can be converted into electrical energy via direct electrochemical conversion in fuel cells.One important drawback of full cells is the sluggish oxygen reduction reaction(ORR)promoted by the high-loading of platinum-group-metal(PGM)electrocatalysts.Fe-N-C family has been received extensive attention because of its low cost,long service life and high oxygen reduction reaction activity in recent years.In order to further enhance the ORR activity,the synthesis method,morphology regulation and catalytic mechanism of the active sites in Fe-N-C catalysts are investigated.This paper reviews the research progress of Fe-N-C from nanoparticles to single atoms.The structure-activity relationship and catalytic mechanism of the catalyst are studied and discussed,which provide a guidance for rational design of the catalyst,so as to promote the more reasonable design of Fe-N-C materials.

A simple granulation technique for preparing high-porosity nano copper oxide(Ⅱ) catalyst beads

A simple and efficient method was developed for fabricating spherical granules of CuO catalyst via a three-step procedure. In the first step, copper oxide nanoparticles were synthesized by hydrothermal decomposition of copper nitrate solution under supercritical condition. Then, they were immobilized in the polymeric matrix of calcium alginate, and followed by high-temperature calcination in an air stream as the third step, in which carbonaceous materials were oxidized, to result in a pebble-type catalyst of high porosity. The produced CuO nanoparticles were characterized by transmission electron microscopy （TEM） that revealed an average size of 5 nm, X-ray diffractometry （XRD）, and thermo gravimetric （TG） analysis. The catalysts were further investigated by BET test for measurement of their surface area, and by temperature-programmed reduction analysis （H2-TPR） for determination of catalytic activity. The results demonstrated that immobilization of the CuO nanoparticle in the polymeric matrix of calcium alginate, followed by calcination at elevated temperatures, could result in notable mechanical strength and enhanced catalytic activity due to preservation of the high surface area, both valuable for practical applications.

Effects of synthesis methods on the performance of Pt + Rh/Ce_(0.6)Zr_(0.4)O_2 three-way catalysts

The 0.7 wt% Pt ＋ 0.3 wt% Rh/Ce0.6Zr0.4O2 catalysts were fabricated via different methods, including ultrasonic-assisted membrane reduction （UAMR） co-precipitation, UAMR separation precipitation, co-impregnation, and sequential impregnation. The catalysts were physico-chemically characterized by N2 adsorption, XRD, TEM, and Hz-TPR techniques, and evaluated for three-way catalytic activities with simulated automobile exhaust. UAMR co-precipitation- and UAMR separation precipitation- prepared catalysts exhibited a high surface area and metal dispersion, wide λ window and excellent conversion for NOx reduction under lean conditions. Both fresh and aged catalysts from UAMR- precipitation showed the high surface areas of ca. 60-67 m^2/g and 18-22 m^2/g, respectively, high metal dispersion of 41%-55%, and small active particle diameters of 2.1-2.7 nm. When these catalysts were aged, the catalysts prepared by the UAMR method exhibited a wider working window （△λ = 0.284--0.287） than impregnated ones （△λ = 0.065-0.115） as well as excellent three-way catalytic performance, and showed lower/so （169℃） and T90 （195℃） for NO reduction than the aged catalysts from impregnation processes, which were at 265 and 309℃, respectively. This implied that the UAMR-separation precipitation has important potential for industrial applications to improve catalytic performance and thermal stability. The fresh and aged 0.7 wt% Pt ＋ 0.3 wt% Rh/Ce0.6Zr0.4O2 catalysts prepared by the UAMR-separation precipitation method exhibited better catalytic performance than the corresponding catalysts prepared by conventional impregnation routes.

Stability and regeneration of metal catalytic sites with different sizes in Fenton-like system

Metal-based catalysts with different site sizes(e.g.,metal nanoparticles(NPs)and single atom catalysts(SACs))demonstrated outstanding catalytic activities in versatile Fenton-like reactions.However,the surface/structural instability is a critical issue,which will result in rapid passivation in Fenton-like reaction and fail in long-term operation.The catalytic stability of the catalysts with different metal sizes considering versatile peroxides(H_(2)O_(2),peroxymonosulfate(PMS),and peroxodisulfate(PDS))should be analyzed.In addition,strategies for catalyst regeneration and recyclability improvement are also important to realize the metal-based catalysts for practical applications.In this review,catalytic stability of catalysts with different metal sizes in the backgrounds of versatile peroxides and water matrixes in Fenton-like reactions were first evaluated.Regeneration of metal catalytic sites with different methods were also reviewed.Finally,major challenges and development of methods concerning the stability and regeneration of metal catalytic sites with different sizes were discussed to understand the future researches of metal catalytic sites in Fenton-like reactions.

Cerium and ruthenium co-doped La_(0.7)Sr_(0.3)FeO_(3-δ) as a high-efficiency electrode for symmetrical solid oxide fuel cell

Symmetrical solid oxide fuel cells(SSOFCs)could be alternative energy conversion devices due to their simple fabrication process and low cost.Herein,perovskite La_(0.6)Ce_(0.1)Sr_(0.3)Fe_(0.95)Ru_(0.05O3-δ)(LCSFR)was synthesized and evaluated as a high-performance electrode for SSOFCs based on the electrolyte of La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O_(3-δ)(LSGM).LCSFR retains their stable perovskite crystal structure in both reducing and oxidizing atmospheres,though a minor amount of LaSrFeO4 phase is present under reducing conditions.Morphology investigation shows that homogeneously dispersed Ru metallic nanoparticles are exsolved on the surface of LCSFR after being reduced.The polarization resistance(Rp)of LCSFR-CGO(Ce_(0.9)Gd_(0.1O2-δ))is about 0.11Ω·cm^(2)at 800℃in air,while the value of Rp for LCSFR-CGO in wet H_(2)(3%H_(2)O)increases up to 0.32Ω·cm^(2).The symmetrical LCSFR-CGOILSGMILCSFR-CGO cell demonstrates a performance with an open circuit potential(OCV)of 1.07 V and a maximum peak power density of 904 mW/cm^(2)at 800℃using wet H2 as the fuel.This high performance indicates that LCSFR is a candidate electrode for SSOFCs.

Nano palladium catalyzed C(sp^(3))-H bonds arylation by a transient directing strategy

Reported herein is the first example of heterogeneous palladium catalyzed C(sp^(3))-H bonds arylation by a transient-ligand-directed strategy.Using supported palladium(metallic state) na nopariticles as catalyst,a wide range of aryl iodides undergo the coupling with various o-methylbenzaldehyde derivatives to assemble a library of highly selective and functionalized o-benzylbenzaldehydes.The stability of the catalyst was easily recovered four runs without significant loss of activity.The XPS analysis of the catalyst before and after reaction indicated that the reaction might be carried out by a catalytic cycle starting with Pd~0.

CuS/RGO hybrid by one-pot hydrothermal method for efficient electrochemical sensing of hydrogen peroxide

In this study,a non-enzymatic hydrogen peroxide sensor was successfully fabricated on the basis of copper sulfide nanoparticles/reduced graphene oxide（CuS/RGO） electrocatalyst.Using thiourea as reducing agent and sulfur donor,CuS/RGO hybrid was synthesized through a facile one-pot hydrothermal method,where the reduction of GO and deposition of CuS nanoparticles on RGO occur simultaneously.The results confirmed that the CuS/RGO hybrid helps to prevent the aggregation of CuS nanoparticles.Electrochemical investigation showed that the as-prepared hydrogen peroxide sensor exhibited a low detection limit of 0.18μmol/L（S/N = 3）,a good reproducibility（relative standard deviation（RSD） of4.21%）,a wide linear range（from 3 to 1215 μmol/L） with a sensitivity of 216.9 μA L/mmol/cm-2 under the optimal conditions.Moreover,the as-prepared sensor also showed excellent selectivity and stability for hydrogen peroxide detection.The excellent performance of CuS/RGO hybrid,especially the lower detection limit than certain enzymes and noble metal nanomaterials ever reported,makes it a promising candidate for non-enzymatic H2O2 sensors.