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1.
Small ; 20(12): e2308193, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-37953460

RESUMO

Designing catalysts to proceed with catalytic reactions along the desired reaction pathways, e.g., CO2 methanation, has received much attention but remains a huge challenge. This work reports one Ru1Ni single-atom alloy (SAA) catalyst (Ru1Ni/SiO2) prepared via a galvanic replacement reaction between RuCl3 and Ni nanoparticles (NPs) derived from the reduction of Ni phyllosilicate (Ni-ph). Ru1Ni/SiO2 achieved much improved selectivity toward hydrogenation of CO2 to CH4 and catalytic activity (Turnover frequency (TOF) value: 40.00 × 10-3 s-1), much higher than those of Ni/SiO2 (TOF value: 4.40 × 10-3 s-1) and most reported Ni-based catalysts (TOF value: 1.03 × 10-3-11.00 × 10-3 s-1). Experimental studies verify that Ru single atoms are anchored onto the Ni NPs surface via the Ru1-Ni coordination accompanied by electron transfer from Ru1 to Ni. Both in situ experiments and theoretical calculations confirm that the interface sites of Ru1Ni-SAA are the intrinsic active sites, which promote the direct dissociation of CO2 and lower the energy barrier for the hydrogenation of CO* intermediate, thereby directing and enhancing the CO2 hydrogenation to CH4.

2.
Small ; 20(6): e2305715, 2024 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-37788910

RESUMO

Mesocrystals (MCs) with high-index facets may have superior catalytic properties to those with low-index facets and their nanocrystal counterparts. However, synthesizing such mesocrystal materials is still very challenging because of the metastability of MCs and energetic high-index crystal facets. This work reports a successful solvothermal method followed by calcination for synthesizing copper oxide-based MCs possessing a core-shell structure (denoted as Cu2 O@CuO HIMCs). Furthermore, these MCs are predominantly bounded by the high-index facets such as {311} or {312} with a high-density of stepped atoms. When used as catalysts in Si hydrochlorination to produce trichlorosilane (TCS, the primary feedstock of high-purity crystalline Si), Cu2 O@CuO HIMCs exhibit significantly enhanced Si conversion and TCS selectivity compared to those with flat surfaces and their nanostructured counterparts. Theoretical calculations reveal that both the core-shell structure and the high-index surface contribute to the increased electron density of Cu sites in Cu2 O@CuO HIMCs, promoting the adsorption and dissociation of HCl and stabilizing the dissociated Cl* intermediate. This work provides a simple method for synthesizing high-index faceted MCs and offers a feasible strategy to enhance the catalytic performance of MCs.

3.
Small ; 18(46): e2203658, 2022 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-36161498

RESUMO

Tuning the electronic structures of mesocrystals at the atomic level is an effective approach to obtaining unprecedented properties. Here, a lattice-confined strategy to obtain isolated single-site Sn atoms in CuO mesocrystals to improve catalytic performance is reported. The Sn/CuO mesocrystal composite (Sn/CuO MC) has ordered Sn-O-Cu atomic interfaces originated from the long-range ordering of the CuO mesocrystal itself. X-ray absorption fine structure measurements confirm that the positively charged Sn atoms can tune the electronic structure of the Cu atoms to some extent in Sn/CuO MC, quite different from that in the conventional single-atom Sn-modified CuO nanoparticles and nanoparticulate SnO2 -modified CuO mesocrystal catalysts. When tested for the Si hydrochlorination reaction to produce trichlorosilane, Sn/CuO MC exhibits significantly better performances than the above two catalysts. Theoretical calculations further reveal the electronic modification to the active Cu component and the induced improvement in HCl adsorption, and thus enhance the catalytic performance. This work demonstrates how to design efficient metal oxide mesocrystal catalysts through an electronic structure modification approach.

4.
Adv Mater ; 34(49): e2205703, 2022 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-36153834

RESUMO

The lack of efficient catalysts with a wide working temperature window and vital O2 and SO2 resistance for selective catalytic reduction of NO by CO (CO-SCR) largely hinders its implementation. Here, a novel Ir-based catalyst with only 1 wt% Ir loading is reported for efficient CO-SCR. In this catalyst, contiguous Ir atoms are isolated into single atoms, and Ir-W intermetallic nanoparticles are formed, which are supported on ordered mesoporous SiO2 (KIT-6). Notably, this catalyst enables complete NO conversion to N2 at 250 °C in the presence of 1% O2 and has a wide temperature window (250-400 °C), outperforming the comparison samples with Ir isolated-single-atomic-sites and Ir nanoparticles, respectively. Also, it possesses a high SO2 tolerance. Both experimental results and theoretical calculations reveal that single Ir atoms are negatively charged, dramatically enhancing the NO dissociation, while the Ir-W intermetallic nanoparticles accelerate the reduction of the N2 O and NO2 intermediates by CO.

5.
J Colloid Interface Sci ; 589: 198-207, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-33472146

RESUMO

As compared with conventional nanocrystal systems, Cu-based mesocrystals have demonstrated distinct advantages in catalytic applications. Here, we report the preparation of a novel architectural Cu2O@CuO catalyst system integrated with the core/shell and mesocrystal structures (Cu2O@CuO MC) via a facile solvothermal process followed by calcination. The formation mechanism of the Cu2O@CuO MC with hexapod morphology was deciphered based on a series of time-dependent experiments and characterizations. When applied as a Cu-based catalyst to produce trichlorosilane (TCS) via Si hydrochlorination reaction, the Cu2O@CuO MC exhibited a much higher Si conversion, TCS selectivity, and stability than the catalyst-free industrial process and the Cu2O@CuO catalyst with a core-shell nanostructure. The enhanced catalytic efficiency of the former is attributed to the collective effects from its quite rough surface for providing abundant adsorption sites, the ordered nanoparticle arrangement in the core and shell for generating strong synergistic effects, and the micrometer size for the improved structural stability. This work demonstrates a practical route for designing sophisticated architectural structures that combine several structural functions within one catalyst system and their catalysis applications.

6.
Chemistry ; 26(56): 12882-12890, 2020 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-32700801

RESUMO

To overcome the drawbacks of the structural instability and poor conductivity of SnO2 -based anode materials, a hollow core-shell-structured SnO2 @C@Co-NC (NC=N-doped carbon) composite was designed and synthesized by employing the heteroatom-doping and multiconfinement strategies. This composite material showed a much-reduced resistance to charge transfer and excellent cycling performance compared to the bare SnO2 nanoparticles and SnO2 @C composites. The doped heteroatoms and heterostructure boost the charge transfer, and the porous structure shortens the Li-ion diffusion pathway. Also, the volume expansion of SnO2 NPs is accommodated by the hollow space and restricted by the multishell heteroatom-doped carbon framework. As a result, this structured anode material delivered a high initial capacity of 1559.1 mA h g-1 at 50 mA g-1 and an initial charge capacity of 627.2 mA h g-1 at 500 mA g-1 . Moreover, the discharge capacity could be maintained at 410.8 mA h g-1 after 500 cycles with an attenuation rate of only 0.069 % per cycle. This multiconfined SnO2 @C@Co-NC structure with superior energy density and durable lifespan is highly promising for the next-generation lithium-ion batteries.

7.
RSC Adv ; 10(61): 37287-37298, 2020 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-35521249

RESUMO

Hydrotreatment is an effective upgrading technology for removing contaminants and saturating double bonds. Still, few studies have reported the hydro-upgrading of shale oil, with unusually high sulfur (13200 ppm) content, using the CoMo/Al2O3 catalyst. Here we report an extensive study on the upgrading of shale oil by hydrotreatment in a stirred batch autoclave reactor (500 ml) for sulfur removal and viscosity reduction. From a preliminary optimization of the reaction factors, the best-operating conditions were 400 °C, an initial H2-pressure of 5 MPa, and an agitation rate of 800 rpm, a catalyst-to-oil ratio of 0.1, and a reaction time of 1 h. We could achieve a sulfur removal efficiency of 87.1% and 88.2% viscosity reduction under the optimal conditions. After that, the spent CoMo/Al2O3 was repeatedly used for subsequent upgrading tests without any form of pre-treatment. The results showed an increase in the sulfur removal efficiency with an increase in the number of catalyst runs. Ultimately, 99.5-99.9% sulfur removal from the shale oil was achieved by recycling the spent material. Both the fresh and the spent CoMo/Al2O3 were characterized and analyzed to ascertain their transformation levels by XRD, TEM, TG, XPS, TPD and N2 adsorption analysis. The increasing HDS efficiency is attributed to the continuing rise in the sulfidation degree of the catalyst in the sulfur-rich shale oil. The light fraction component in the liquid products (IBP-180 °C) was 30-37 vol% higher than in the fresh shale oil. The product oil can meet the sulfur content requirement of the national standard marine fuel (GB17411-2015/XG1-2018) of China.

8.
Natl Sci Rev ; 7(3): 600-608, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-34692079

RESUMO

Single-atom catalysts are of great interest because they can maximize the atom-utilization efficiency and generate unique catalytic properties; however, much attention has been paid to single-site active components, rarely to catalyst promoters. Promoters can significantly affect the activity and selectivity of a catalyst, even at their low concentrations in catalysts. In this work, we designed and synthesized CuO catalysts with atomically dispersed co-promoters of Sn and Zn. When used as the catalyst in the Rochow reaction for the synthesis of dimethyldichlorosilane, this catalyst exhibited much-enhanced activity, selectivity and stability compared with the conventional CuO catalysts with promoters in the form of nanoparticles. Density functional theory calculations demonstrate that single-atomic Sn substitution in the CuO surface can enrich surface Cu vacancies and promote dispersion of Zn to its atomic levels. Sn and Zn single sites as the co-promoters cooperatively generate electronic interaction with the CuO support, which further facilitates the adsorption of the reactant molecules on the surface, thereby leading to the superior catalytic performance.

9.
J Nanosci Nanotechnol ; 15(1): 15-30, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-26328302

RESUMO

High capacity electrode materials are searched for commercial applications due to the increase in energy density and power density requirements for lithium-ion secondary cells. Silicon has triggered significant research effort because of its low Li-uptake potential and the high theoretical capacity. However, volume changes during cycling cause pulverization and capacity fade, which is an obstacle of the application of silicon as an anode. Here we present a review of research progress on silicon-based anode materials for lithium-ion batteries, focusing on the effects of the morphology and compound on the electrochemical properties. The reasons of poor cycle performance are discussed. It is pointed out that to control the huge volume change and solid electrolyte interface growth during cycling is an effective way to improve the cycle performance. Outlook for the future development of silicon-based composite anode materials for the application of silicon anodes are finally outlined.

10.
ACS Appl Mater Interfaces ; 7(11): 6300-9, 2015 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-25738385

RESUMO

The yolk-shell hollow structure of transition metal oxides has many applications in lithium-ion batteries and catalysis. However, it is still a big challenge to fabricate uniform hollow microspheres with the yolk bishell structure for mixed transition metal oxides and their supported or embedded forms in carbon microspheres with superior lithium storage properties. Here we report a new approach to the synthesis of manganese cobalt iron oxides/carbon (MnxCo1-xFe2O4 (0 ≤ x ≤ 1)) microspheres through carbonization of Mn(2+)Co(2+)Fe(3+)/carbonaceous microspheres in N2, which can be directly applied as high-performance anodes with a long cycle life for lithium storage. Furthermore, uniform hollow microspheres with a MnxCo1-xFe2O4 yolk bishell structure are obtained by annealing the above MnxCo1-xFe2O4/carbon microspheres in air. As demonstrated, these anodes exhibited a high reversible capacity of 498.3 mAh g(-1) even after 500 cycles for Mn0.5Co0.5Fe2O4/carbon microspheres and 774.6 mAh g(-1) over 100 cycles for Mn0.5Co0.5Fe2O4 yolk bishell hollow microspheres at the current density of 200 mA g(-1). The present strategy not only develops a high-performance anode material with long cycle life for lithium-ion batteries but also demonstrates a novel and feasible technique for designed synthesis of transition metal oxides yolk bishell hollow microspheres with various applications.

11.
Nanoscale ; 6(12): 6805-11, 2014 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-24827728

RESUMO

We report the preparation of Mn(0.5)Co(0.5)Fe2O4 (MCFO) nanoparticles highly dispersed within porous carbon microspheres as anodes for Li-ion batteries. In situ growth of MCFO nanoparticles (5-20 nm) on the surface of carbon black (CB) and graphitized carbon black (GCB) nanoparticles was conducted via a hydrothermal method to form MCFO-CB and MCFO-GCB composites, respectively, which were employed as building blocks to assemble MCFO-CB and MCFO-GCB porous microspheres (PM) with a size of 5-30 µm by the spray drying technique using sucrose as a binder, and followed by carbonization in N2 (labeled as MCFO-CB-PM and MCFO-GCB-PM, respectively). Compared with the pure MCFO, MCFO-CB, and MCFO-GCB, both MCFO-CB-PM and MCFO-GCB-PM showed a significantly improved electrochemical performance. This is attributed to their unique porous structure, in which, the abundant pores promote the diffusion of Li-ion and electrolyte solution, the microspherical morphology enhances the electrode-electrolyte contact, and the carbon substrates from CB (and GCB) and sucrose substantially prevent the aggregation of MCFO nanoparticles and buffer the volume change. Particularly, MCFO-GCB-PM exhibits the best rate performance and excellent cycling stability because of the high graphitization degree of GCB. This work opens up an effective route for large scale fabrication of metal oxide/carbon porous microspheres as anode materials for potential applications in the new generation of Li-ion batteries.

12.
Angew Chem Int Ed Engl ; 53(20): 5165-9, 2014 May 12.
Artigo em Inglês | MEDLINE | ID: mdl-24700513

RESUMO

Despite the promising application of porous Si-based anodes in future Li ion batteries, the large-scale synthesis of these materials is still a great challenge. A scalable synthesis of porous Si materials is presented by the Rochow reaction, which is commonly used to produce organosilane monomers for synthesizing organosilane products in chemical industry. Commercial Si microparticles reacted with gas CH3 Cl over various Cu-based catalyst particles to substantially create macropores within the unreacted Si accompanying with carbon deposition to generate porous Si/C composites. Taking advantage of the interconnected porous structure and conductive carbon-coated layer after simple post treatment, these composites as anodes exhibit high reversible capacity and long cycle life. It is expected that by integrating the organosilane synthesis process and controlling reaction conditions, the manufacture of porous Si-based anodes on an industrial scale is highly possible.


Assuntos
Carbono/química , Fontes de Energia Elétrica , Eletrodos , Lítio/química , Silício/química , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Análise Espectral Raman , Difração de Raios X
13.
Nanoscale ; 6(1): 371-7, 2014 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-24201898

RESUMO

We report the growth of linked silicon/carbon (Si/C) nanospheres on Cu substrate as an integrated anode for Li-ion batteries. The Si/C nanospheres were synthesized by a catalytic chemical vapor deposition (CCVD) on Cu substrate as current collector using methyltrichlorosilane as precursor, a cheap by-product of the organosilane industry. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermal gravimetry, Raman spectroscopy, nitrogen adsorption, inductively coupled plasma optical emission spectrometry, and X-ray photoelectron spectroscopy. It was found that the linked Si/C nanospheres with a diameter of 400-500 nm contain Si, Cu(x)Si, and Cu nanocrystals, which are highly dispersed in the amorphous carbon nanospheres. A CCVD mechanism was tentatively proposed, in which the evaporated Cu atoms play a critical role to catalytically grown Si nanocrystals embedded within linked Si/C nanospheres. The electrochemical measurement shows that these Si/C nanospheres delivered a capacity of 998.9, 713.1, 320.6, and 817.8 mA h g(-1) at 50, 200, 800, and 50 mA g(-1) respectively after 50 cycles, much higher than that of commercial graphite anode. This is because the amorphous carbon, Cu(x)Si, and Cu in the Si/C nanospheres could buffer the volume change of Si nanocrystals during the Li insertion and extraction reactions, thus hindering the cracking or crumbling of the electrode. Furthermore, the incorporation of conductive Cu(x)Si and Cu nanocrystals and the integration of active electrode materials with Cu substrate may improve the electrical conductivity from the current collector to individual Si active particles, resulting in a remarkably enhanced reversible capacity and cycling stability. The work will be helpful in the fabrication of low cost binder-free Si/C anode materials for Li-ion batteries.


Assuntos
Cobre/química , Fontes de Energia Elétrica , Lítio/química , Nanosferas/química , Carbono/química , Técnicas Eletroquímicas , Íons/química , Silício/química
14.
J Colloid Interface Sci ; 404: 16-23, 2013 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-23726283

RESUMO

CuCl microcrystals with different morphologies such as tetrahedra, etched tetrahedra, tripod dendrites, and tetrapods were synthesized using CuCl2⋅2H2O as the copper precursor in the mixed solvent of acetylacetone and ethylene glycol. The samples were characterized with X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and transmission electron microscope. Cu(C5H7O2)2 was identified as the key intermediate, and the morphology and structure of the CuCl microcrystals were highly dependent on the reaction time and temperature, as well as the volume of the solvents. The catalytic properties of these CuCl microcrystals were explored in the dimethyldichlorosilane synthesis via Rochow reaction. Compared to the commercial CuCl microparticles with irregular morphology and dense internal structure, the obtained CuCl microcrystals possessed regular morphology and different exposed crystal planes and showed much higher dimethyldichlorosilane selectivity and Si conversion via the Rochow reaction because of the enhanced formation of active CuxSi phase and gas transportation within the dendritic structure, demonstrating the significance of regular morphology of the copper-based catalysts in catalytic organosilane synthesis.

15.
J Nanosci Nanotechnol ; 13(2): 1530-4, 2013 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-23646676

RESUMO

We report the preparation and characterization of mesoporous hollow CuO (MPH-CuO) microspheres by thermal decomposition of hollow copper oxalate microspheres synthesized via the reaction of ammonium oxalate and copper chloride without using any template. The sample was characterized by Nitrogen adsorption, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The electrochemical performance of MPH-CuO microspheres as anode materials in Li-ion batteries was evaluated. It was found that the MPH-CuO microspheres possessed an average diameter of 2.5 microm, a pore size of 17.5 nm, and a BET surface area of 15.2 m2/g. Their shells were composed of CuO nanocrystals with a size of 17.9 nm. Compared with the dense CuO microspheres, the obtained MPH-CuO shows an enhanced electrochemical performance with a higher capacity of 599.4 mAh/g and a better cyclability (484 mAh/g after 15 cycles) because of its mesoporous hollow structure that provides quick intercalation and large accommodation of lithium ions together with short diffusion distance for lithium ions, suggesting a potential application in Li-ion batteries.

16.
Nanoscale ; 5(12): 5384-9, 2013 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-23652614

RESUMO

We report the preparation and characterization of amorphous silicon-carbon (Si-C) nanospheres as anode materials in Li-ion batteries. These nanospheres were synthesized by a chemical vapor deposition at 900 °C using methyltrichlorosilane (CH3SiCl3) as both the Si and C precursor, which is a cheap byproduct in the organosilane industry. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermal gravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that the synthesized Si-C nanospheres composed of amorphous C (about 60 wt%) and Si (about 40 wt%) had a diameter of 400-600 nm and a surface area of 43.8 m(2) g(-1). Their charge capacities were 483.6, 331.7, 298.6, 180.6, and 344.2 mA h g(-1) at 50, 200, 500, 1000, and 50 mA g(-1) after 50 cycles, higher than that of the commercial graphite anode. The Si-C amorphous structure could absorb a large volume change of Si during Li insertion and extraction reactions and hinder the cracking or crumbling of the electrode, thus resulting in the improved reversible capacity and cycling stability. The work opens a new way to fabricate low cost Si-C anode materials for Li-ion batteries.


Assuntos
Carbono/química , Fontes de Energia Elétrica , Lítio/química , Nanosferas/química , Silanos/química , Silício/química , Eletrodos , Gases/química , Íons/química , Nanosferas/ultraestrutura
17.
Bioresour Technol ; 137: 311-7, 2013 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-23591118

RESUMO

This work demonstrates the efficient hydrogenolysis of cellulose to C4-C7 alcohols and gas products (reaction 1) by coupling it with the reforming reaction of methanol (reaction 2) over bi-functional CuO-based catalysts. In this process, the CuO-based catalysts catalyze both the reactions 1 and 2, and the in situ regenerated H2 in the reaction 2 is used for the reaction 1. A series of CuO-MO/Al2O3 (M=Ce, Mg, Mn, Ni, Zn) catalysts were prepared by the co-precipitation method. Among these catalysts, CuO-ZnO/Al2O3 exhibited the highest activity to generate a high cellulose conversion of 88% and a high C4-C7 alcohols content above 95% in the liquid products. The CuO-ZnO/Al2O3 catalyst was stable under the reaction conditions and reusable after 4 runs. This work provides a cost-effective route to convert abundant renewable cellulose to liquid fuels.


Assuntos
Celulose/metabolismo , Metanol/metabolismo , Biocombustíveis , Catálise , Celulose/química , Cobre/química , Hidrogênio/química , Hidrogênio/metabolismo , Cinética , Metanol/química , Temperatura , Fatores de Tempo
18.
J Colloid Interface Sci ; 398: 185-92, 2013 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-23489612

RESUMO

We report the synthesis and characterization of the mesoporous manganese ferrite (MnFe2O4) microspheres as anode materials for Li-ion batteries. MnFe2O4 microspheres were synthesized by a facile solvothermal method using Mn(CH3COO)2 and FeCl3 as metal precursors in the presence of CH3COOK, CH3COOC2H5, and HOCH2CH2OH. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermal gravimetric, X-ray photoelectron spectroscopy, temperature programmed reduction, and temperature programmed oxidation. The synthesized mesoporous MnFe2O4 microspheres composed of nanoparticles (10-30 nm) were 100-500 nm in diameter and had surface areas between 60.2 and 86.8 m(2) g(-1), depending on the CH3COOK amounts added in the preparation. After calcined at 600°C, MnFe2O4 was decomposed to Mn2O3 and Fe2O3 mixture. The mesoporous MnFe2O4 microspheres calcined at 400°C showed a capacity of 712.2 mA h g(-1) at 0.2C and 552.2 mA h g(-1) at 0.8C after 50 cycles, and an average capacity fading rate of around 0.28%/cycle and 0.48%/cycle, much better than those of the samples without calcination and calcined at 600°C. The work would be helpful in the fabrication of binary metal oxide anode materials for Li-ion batteries.

19.
ACS Appl Mater Interfaces ; 4(3): 1295-302, 2012 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-22364243

RESUMO

Porous cubic Cu microparticles were synthesized by a facile solvothermal method using Cu(CH(3)COO)(2)·H(2)O as the Cu precursor and NaOH in a solution containing ethanol, ethylene glycol, and water. The synthesis conditions were investigated and a growth process of porous cubic Cu microparticles was proposed. The catalytic properties of the porous Cu microparticles as model copper catalysts for Rochow reaction were explored. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, temperature-programmed reduction, and nitrogen adsorption. It was found that the morphology and structure of the porous cubic Cu microparticles are highly dependent on the reaction time and temperature as well as on the amount of reactants added. Compared to the commercial Cu microparticles with irregular morphology and dense internal structure, porous cubic Cu microparticles show much higher dimethyldichlorosilane selectivity and Si conversion via Rochow reaction, which are attributed to the enhanced formation of active Cu(x)Si phase and gas transportation in the presence of the pore system within microparticles, demonstrating the significance of the pore structure of the copper catalysts in catalytic reactions of organosilane synthesis.

20.
ACS Appl Mater Interfaces ; 3(10): 3824-30, 2011 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-21919500

RESUMO

N-doped porous carbon nanospheres (PCNs) were prepared by chemical activation of nonporous carbon nanospheres (CNs), which were obtained via carbonization of polypyrrole nanospheres (PNs). The catalysts, PtRu and Pt nanoparticles supported on PCNs and Vulcan XC-72 carbon black, were prepared by ethylene glycol chemical reduction. Transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy were employed to characterize samples. It was found that PCNs containing N function groups possess a large number of micropores. Uniform and well-dispersed Pt and PtRu particles with narrow particle size distribution were observed. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that alloy catalyst (Pt(1)Ru(1)/PCN) possessed the highest catalytic activity and better CO tolerance than the other PtRu and Pt-only catalysts; PtRu nanoparticles supported on PCN showed a higher catalytic activity and more stable sustained current than on carbon black XC-72. Compared to commercial Alfa Aesar PtRu catalyst, Pt(1)Ru(1)/PCN reveals an enhanced and durable catalytic activity in methanol oxidation because of the high dispersion of small PtRu nanoparticles and the presence of N species of support PCNs.

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