Microcalorimetric studies of the iridium catalyst for hydrazine decomposition reaction

Microcalorimetric studies of H-2, NH3 and O-2 adsorption, as well as the NH3 decomposition activities evaluation were used to characterize the iridium catalysts for hydrazine decomposition with different supports (Al2O3, SiO,) and iridium contents (1.8, 10.8 and 22.1%). The higher H-2 chemisorption amounts on Ir/Al2O3 catalysts than those on the corresponding Ir/SiO2 counterparts revealed that the strong interaction of iridium and Al2O3 led to higher dispersion of iridium on Ir/Al2O3 catalysts than on Ir/SiO2 catalysts. The larger increase in strong H-2 adsorption sites on highly loaded Ir/Al2O3 than the corresponding Ir/SiO2 ones could be attributed to the interaction not only between iridium atoms but also between iridium and Al2O3. The microcalorimetric results for NH3 adsorption showed that no apparent chemisorption of NH3 existed on Ir/SiO2 catalysts while NH3 chemisorption amounts increased on Ir/Al2O3 catalysts with iridium loadings, which arose from the interaction of the catalysts support of Al2O3 With chloride anion. Both highly dispersed iridium active sites and chloride anion on Ir/Al2O3 catalysts could be beneficial to the intermediate NH3 decomposition in N2H4 decomposition. The similar O-2 plots of differential heat versus normalized coverage on Ir/Al2O3 and Ir/SiO2 catalysts could not be due to the metal-support interaction, but to the formation of strong Ir-O bond. (C) 2005 Elsevier B.V. All rights reserved.

A highly active palladium-phosphoramidite catalyst for the Suzuki cross-coupling of aryl bromides

A highly efficient palladium-catalyzed Suzuki coupling of aryl bromides with aiylboronic acids using phosphoramidite ligand 2c was developed. The phosphoramidite ligands are cost-effective and easily prepared from inexpensive, commercially available starting materials using a simple, efficient method. It represents an advance toward the discovery of low-cost catalyst systems for eventual availability. (c) 2005 Elsevier B.V. All rights reserved.

One-step synthesis of 2-pentanone from ethanol over K-Pd/MnOx-ZrO2-ZnO catalyst

A highly active and selective K-Pd/MnOx-ZrO2-ZnO catalyst for the one-step synthesis of 2-pentanone from ethanol is described. The possible reaction pathways for ethanol reaction over K-Pd/MnOx-ZrO2-ZnO catalyst were investigated by means of TPSR, CO2- and NH3-TPD techniques. The reactions were performed in a fixed bed continuous flow reactor. Complete conversion with high selectivity for 2-pentanone, was observed under 370 similar to 390degreesC, 2 similar to 4 MPa, GHSV = 8000 similar to 10,000 h(-1) and LHSV < 1.25 h(-1) conditions. Ethanol reactions over K-Pd/MnOx-ZrO2-ZnO catalyst showed that the catalyst could catalyze dehydrogenation. aldol. dehydration and hydrogenation reactions. Both acidic and basic properties are found on the surface of K-Pd/MnOx-ZrO2-ZnO catalyst, whose multifunctionality with the combination of basic, acid and metal sites may be responsible for the efficiency of the K-PdMnOx-ZrO2-ZnO catalyst. (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.