Characterizations and activities of the nano-sized Ni/Al2O3 and Ni/La-Al2O3 catalysts for NH3 decomposition

A series of nano-sized Ni/Al2O3 and Ni/La-Al2O3 catalysts that possess high activities for NH3 decomposition have been successfully synthesized by a coprecipitation method. The catalytic performance was investigated under the atmospheric conditions and a significant enhancement in the activity after the introduction of La was observed. Aiming to study the influence of La promoter on the physicochemical properties, we characterized the catalysts by N-2 adsorption/desorption, XRD, H-2-TPR, chemisorption and TEM techniques. Physisorption results suggested a high specific surface area and XRD spectra showed that nickel particles are in a highly dispersed state. A combination of XRD, TEM and chemisorption showed that Ni-0 particles with the average size lower, than 5.0 nm are always obtained even though the Ni loading ranged widely from 4 to 63 %. Compared with the Ni/Al2O3 catalysts, the Ni/La-Al2O3 ones with an appropriate amount of promoter enjoy a more open mesoporous structure and higher dispersion of Ni. Reduction kinetic studies of prepared catalysts were investigated by temperature-programmed reduction (TPR) method and the fact that La additive partially destroyed the metastable Ni-Al mixed oxide phase was detailed. (c) 2005 Elsevier B.V. All rights reserved.

Development and application of oxygen permeable membrane in selective oxidation of light alkanes

In this paper, oxygen permeable membrane used in membrane reactor for selective oxidation of alkanes will be discussed in detail. The recent developments for the membrane materials will be presented, and the strategy for the selection of the membrane materials will be outlined. The main applications of oxygen permeable membrane in selective oxidation of light alkanes will be summarized, which includes partial oxidation of methane (POM) to syngas and partial oxidation of heptane (POH) to produce H-2, oxidative coupling of methane (OCM) to C-2, oxidative dehydrogenation of ethane (ODE) to ethylene and oxidative dehydrogenation of propane (ODP) to propylene. Achievements for the membrane material developments and selective oxidation of light alkanes in membrane reactor in our group are highlighted.

Preparation and characterization of multi-walled carbon nanotubes supported PtRu catalysts for proton exchange membrane fuel cells

A series of PtRu nanocomposites supported on H2O2-oxidized multi-walled carbon nanotubes (MWCNTs) were synthesized via two chemical reduction methods - one used aqueous formaldehyde (HCHO method) and the other used ethylene glycol (EG method) as the reducing agents. The effects of the solvents (water and ethylene glycol) and the surface composition of the MWCNTs on the deposition and the dispersion of the metal particles were investigated using N-2 adsorption. TEM. ICP-AES. FTIR and TPD. The wetting heats of the MWCNTs in corresponding solvents were also measured. The characterizations suggest that combination of the surface chemistry of the MWCNTs with the solvents decides the deposition and the dispersion of the metal nanoparticles. These nanocomposites were evaluated as proton exchange membrane fuel cell anode catalyts for oxidation of 50 ppm CO contaminated hydrogen and compared with a commercial PtRu/C catalyst. The data reveal superior performances for the nanocomposites prepared by the EG method to those by the HCHO method and even to that for tile Commercial analogue. Structure performance relationship of the nanocomposites was also studied. (C) 2005 Elsevier Ltd. All rights reserved.

Development of a LCST membrane forming system for cellulose acetate ultrafiltration hollow fiber

A novel lower critical solution temperature (LCST) membrane forming system containing cellulose acetate (CA)/poly (vinyl pyrrolidone) (PVP 3 60K)/N-methyl-2-pyrrolidone (NMP)/1,2-propanediol with a weight ratio of 24.0:5.0:62.6:8.4 had been developed. CA hollow fiber ultrafiltration (UF) membranes were fabricated using the dry-wet spinning technique. The fibers were post-treated with a 200 mg/L hypochlorite solution over a period of 6 It at pH 7. The experimental results showed that water flux of a membrane decreased while retention increased with increasing CA concentration in a dope. It was concluded that the membrane pore size decreased with increasing CA concentration. The membrane fouling tendency for BSA was 3 times higher than that for PVP 24K. (C) 2004 Elsevier B.V. All rights reserved.

Improvement of direct methanol fuel cell performance by modifying catalyst coated membrane structure

A five-layer catalyst coated membrane (CCM) based upon Nation 115 membrane for direct methanol fuel cell (DMFC) was designed and fabricated by introducing a modified Nafion layer between the membrane and the catalyst layer. The properties of the CCM were determined by SEM, cyclic voltammetry, impedance spectroscopy, ruinous test and I-V curves. The characterizations show that the modified Nation layers provide increased interface contact area and enhanced interaction between the membrane and the catalyst layer. As a result, higher Pt utilization, lower contact resistance and superior durability of membrane electrode assembly was achieved. A 75% Pt utilization efficiency was obtained by using the novel CCM structure, whereas the conventional structure gave 60% efficiency. All these features greatly contribute to the increase in DMFC performance. The DMFC with new CCM structure presented a maximum power density of 260 MW cm(-2), but the DMFC with conventional structure gave only 200 mW cm(-2) under the same operation condition. (c) 2005 Elsevier B.V. All rights reserved.