Showing papers by "Changhai Liang published in 2010"

Nanostructured WCx/CNTs as highly efficient support of electrocatalysts with low Pt loading for oxygen reduction reaction

Abstract: Highly active Pt–WCx/carbon nanotube (CNT) electrocatalysts for the oxygen reduction reaction (ORR) have been developed by the combination of tungsten carbide with CNTs as electrocatalyst supports. The obtained WCx/CNT and Pt–WCx/CNT samples were characterized by XRD, TEM, XPS and electrochemical measurements. The results showed that nanostructured tungsten carbide particles on carbon nanotubes could be prepared by microwave-assisted thermolytic molecular precursor method, and the particle size of tungsten carbide increased with the increase of tungsten loading. The nanostructured WCx/CNTs showed electrocatalytic activity for oxygen reduction reaction. The deposition of Pt nanoparticles on the WCx/CNTs resulted in higher electrocatalytic activity for the oxygen reduction reaction and better immunity to methanol than Pt/CNT catalysts. The unique electrocatalytic properties of the novel Pt–WCx/CNT electrocatalyst were attributed to a synergistic effect between Pt, WCx and the CNTs. The findings also indicated that WCx/CNTs were efficient electrocatalyst supports that could reduce Pt usage while the same electrocatalytic properties were kept for the ORR in direct methanol fuel cells.

Microwave-Assisted Preparation of Mo2C/CNTs Nanocomposites as Efficient Electrocatalyst Supports for Oxygen Reduction Reaction

Abstract: Nanostructured Mo2C/CNTs composites have been synthesized by using a novel methodology of microwave-assisted thermolytic molecular precursor with Mo(CO)6 as single source precursor. Pt electrocatalysts supported on the Mo2C/CNTs composites were prepared by using the modified ethylene glycol method. The resulting Mo2C/CNTs and Pt−Mo2C/CNTs were characterized by inductively coupled plasma-optical emission spectroscopy, thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The rotating disk electrode experiments were used to measure electrocatalytic activity for oxygen reduction reaction. The results showed highly dispersed sphere-like Mo2C and Pt particles with 3−6 nm can be prepared upon CNTs by the above-mentioned methods. The formation process of Mo2C includes the following steps: decomposition of Mo(CO)6 precursor to the metallic Mo and CO, CO dismutation reaction, formation of the MoOxCy by the metallic Mo and CO, the MoOxCy carburiza...

A non-alkoxide sol–gel route to highly active and selective Cu–Cr catalysts for glycerol conversion

Abstract: A non-alkoxide sol–gel route to highly active and selective Cu–Cr catalysts for glycerol conversion is presented. The addition of propylene oxide to ethanol solutions of Cr(NO3)3·9H2O and Cu(NO3)2·3H2O resulted in the formation of transparent Cu–Cr gels. The resulting gels were converted to the Cu–Cr catalysts by atmospheric drying and calcination. The Cu–Cr catalysts are characterized by X-ray diffraction (XRD), N2 physisorption, temperature-programmed reduction (TPR), and transmission electron microscopy (TEM). The results show that the surface area of the Cu–Cr catalyst is adjusted by the hydrolysis conditions, Cu/Cr molar ratio, and treatment conditions (such as gas atmosphere and final temperature). For the sample with Cu/Cr = 0.5, the surface area of Cu–Cr xerogel can reach 94 m2/g and decreased to only 31 m2/g after calcination at 500 °C. The catalysts show significant catalytic activity and selectivity in glycerol conversion, i.e. above 52% conversion of glycerol and above 88% selectivity to 1,2-propanediol at 210 °C and 4.15 MPa H2 pressure. CuCr2O4 supported Cu catalysts are much more active than Cr2O3 supported Cu catalysts. This indicates a strong interaction between Cu and CuCr2O4 that is significantly improving the effectiveness of the catalyst for glycerol conversion.

Synthesis and Catalytic Properties for Phenylacetylene Hydrogenation of Silicide Modified Nickel Catalysts

Abstract: Interstitial silicide-modified nickel, with high selectivity in some hydrogenation reactions, had been produced by dissolving silicon atoms into the nickel lattices. The metallic nickel was obtained by reducing the as-prepared high surface area NiO, followed by modification of the bulk nickel through silification of silane/H2 at relatively low temperature and atmospheric pressure. The as-prepared materials were characterized by X-ray diffraction, magnetic measurements, X-ray photoelectron spectroscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and temperature-programmed reduction. The results show nickel silicide formation involves the following sequence as a function of increasing temperature: Ni (cubic) → Ni2Si (orthorhombic) → NiSi (orthorhombic) → NiSi2 (cubic). The insertion of Si atoms into the interstitial sites between Ni atoms resulted in a significant change in the unit cell lattice of nickel. All of the silicide-modified nickel materials were ferromagnetic at room ...

Cobalt Silicide Nanoparticles in Mesoporous Silica as Efficient Naphthalene Hydrogenation Catalysts by Chemical Vapor Deposition

Abstract: Cobalt silicide nanoparticles in mesoporous silica SBA-15 were successfully prepared by metal-organic chemical vapor deposition of a single-source precursor and were characterized by nitrogen physorption, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption, and transmission electron microscopy. The catalytic hydrogenation of naphthalene on the cobalt silicide nanoparticles in mesoporous silica was investigated in a fixed-bed reactor at 340 °C under 4.0 MPa hydrogen pressure. No cobalt silicide was observed in the mesoporous silica without calcination because of the hydrolysis of Co(SiCl3)(CO)4. Highly dispersed and evenly distributed cobalt silicide particles with diameters of 2−4 nm could be formed by adsorption and reduction of Co(SiCl3)(CO)4 in the mesoporous silica with calcination above 500 °C. The cobalt silicide loading in the mesoporous silica depended on both the amount of precursor provided and the amount of hydroxyl groups in the mesoporous silica. A 8.3% CoSi...

Naphthalene Hydrogenation over Silica Supported Nickel Phosphide in the Absence and Presence of N-Containing Compounds

Abstract: Silica supported nickel phosphide catalysts with initial Ni/P molar ratios from 0.5 to 2.0 and the sum of NiO and P 2 O 5 loadings from 10 to 40 wt % in their precursors have been prepared by the temperature-programmed reduction method and characterized by means of X-ray diffraction, N 2 physisorption, CO chemisorption, and pyridine adsorption with in situ Fourier transform-infrared (FT-IR) spectroscopy. Naphthalene hydrogenation was carried out at 340 °C and 4.0 MPa over the as-prepared Ni 2 P/SiO 2 catalysts. Mutual influences of naphthalene hydrogenation and quinoline hydrodenitrogenation were investigated under similar conditions. The catalyst with Ni/P = 1.25 and 30 wt % loading showed the complete naphthalene conversion as well as 92.1% of selectivity to decalin. It was observed that cis-decalin converted partly into trans-decalin under the studied conditions. Addition of quinoline into naphthalene hydrogenation obviously decreased naphthalene conversion and selectivity to decalin over the Ni 2 P/SiO 2 catalysts due to the strong adsorption of quinoline on active sites. The similar effects of the quinoline hydrogenated compounds on naphthalene hydrogenation were also observed over the Ni 2 P/SiO 2 catalysts. The addition of naphthalene had no effect on quinoline hydrogenation to tetrahydroquinoline but inhibited tetrahydroquinoline hydrogenation to decahydroquinoline. Naphthalene conversion over the Ni 2 P/SiO 2 catalyst in the presence of quinoline and dibenzothiophene decreased with the increase of their contents. It is noteworthy that naphthalene conversion could be recovered after the removal of quinoline while the hydrogenation activity could not in the case of dibenzothiophene.

A Facile and Controlled Route to Prepare an Eggshell Pd Catalyst for Selective Hydrogenation of Phenylacetylene

Abstract: Selective hydrogenation of phenylacetylene to styrene is an important industrial process in polystyrene production, because the polymerization catalysts are extremely sensitive to trace phenylacetylene in styrene feedstocks. Many efforts have been devoted to develop effective catalysts with satisfactory activity and selectivity to styrene. Supported Pd catalysts have been shown to be promising along these lines, although the catalysts must be modified by other transition metals to avoid complete hydrogenation of phenylacetylene to ethylbenzene. In the present case, we have tested the hypothesis that ethylbenzene formation can be suppressed by distributing active metals on the external surface of the support in the eggshell configuration. Many researchers have reported that eggshell catalysts are superior to uniform ones in some reactions, involving heat/ mass-transfer limitations. Iglesia et al. proposed a route to synthesize eggshell catalysts that involved support impregnation with a high viscosity liquid. In contrast, Ding et al. prepared Co/SiO2 catalysts with different distributions by reducing the capillary pressure. Other methods have also been developed, including spray method, metal organic chemical vapor deposition, and using porous hollow silica support. Unfortunately, several factors have limited the implementation of eggshell catalysts, including the long preparation period, high solvent cost, and difficulty in controlling the eggshell thickness. The controlled synthesis of the well-defined eggshell catalysts therefore still remains an important challenge. A facile and controlled route to synthesize the eggshell Pd/SiO2–Al2O3 catalysts is presented. The novel method involves CO reduction deposition of PdCl2 on SiO2–Al2O3 support at room temperature in ethanol aqueous solution. The as-prepared eggshell Pd catalyst exhibited a higher activity for converting phenylacetylene to styrene than a uniform one prepared by traditional incipient wetness impregnation. When the SiO2–Al2O3 support is added to the PdCl2-ethanol aqueous solution, a certain amount of palladium ions adsorb onto the oxide surface. After exposure to CO, the process of reduction can be expressed by the following [Equation (1)]:

Chemical vapor deposition of Fe(CO)4(SiCl3)2 for the synthesis of hydrogenation catalyst made of highly dispersed iron silicide particles on silica

Abstract: New iron silicides based hydrogenation catalysts have been prepared by organometallic chemical vapor deposition of Fe(CO)4(SiCl3)2 precursor on silica support. Fe(CO)4(SiCl3)2 was synthesized from Fe3(CO)12 and SiHCl3 at 120 °C, as confirmed by FTIR, 13C and 29Si NMR. The FeSi loadings have been varied by changing the amount of the precursor. XRD patterns only showed a diffraction peak due to silica, indicating that iron silicide particles were too small to be detected. TEM image showed that the lattice spacing of the particles was 0.2578 nm, which matched well with the lattice spacing 0.2591 nm of the FeSi (111) plane. TEM image showed that the size of iron silicide particles dispersed on the silica was about 3 nm. However, the so-prepared FeSi/SiO2 catalysts showed little catalytic activity in naphthalene hydrogenation. More studies would be needed to have a better understanding on how to improve the efficiency of these new catalysts.

A novel approach to synthesize highly selective nickel silicide catalysts for phenylacetylene semihydrogenation

Abstract: Nickel silicides (NiSi x ) have been prepared by carbon template for nanostructured NiO and further silicidization with SiH 4 /H 2 at relatively low temperature and atmospheric pressure. The results showed that the formation of nickel silicides involves the following sequence, Ni (cubic) → Ni 2 Si (orthorhombic) → NiSi (orthorhombic) → NiSi 2 (cubic), with increasing temperatures. The as-prepared nickel silicides showed above 92% selectivity to styrene in the semihydrogenation of phenylacetylene due to the electronic and geometrical effects derived from the addition of Si into Ni particles.

Microwave-assisted preparation of Mo2C/CNTs nanocomposites as an efficient support for electrocatalysts toward oxygen reduction reaction

Abstract: Nanostructured Mo 2 C/CNTs has been synthesized by microwave-assisted thermolytic molecular precursor method. Pt nanoparticles were deposited on the as-prepared Mo 2 C/ CNTs by using the modified ethylene glycol method. The samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrocatalytic activity toward ORR was measured through a thin-film rotating disk electrode. The results showed the particles size of Mo 2 C and Pt ranged from 3 to 6 nm. The formation process of Mo 2 C followed the sequence: Mo(CO) 6 → Mo → [Mo,O,C] → Mo 2 C → Mo 3 C 2 . The Pt-Mo 2 C/CNTs sample possessed higher ORR activity with a more positive onset potential in acid solution than that of Pt /CNTs under the same condition, which could be attributed to the synergistic effect among Pt, Mo 2 C and CNTs.