Structural and permeation kinetic correlations in PdCuAg membranes.

Addition of Ag is a promising way to enhance the H2 permeability of sulfur-tolerant PdCu membranes for cleanup of coal-derived hydrogen. We investigated a series of PdCuAg membranes with at least 70 atom % Pd to elucidate the interdependence between alloy structure and H2 permeability. Membranes were prepared via sequential electroless plating of Pd, Ag, and Cu onto ceramic microfiltration membranes and subsequent alloying at elevated temperatures.

Hydrogen-induced high-temperature segregation in palladium silver membranes.

Higher operation temperatures benefit H2 permeability and selectivity of metal membranes and they are interesting for e.g. water gas shift and steam reforming in membrane reactors.

Nanoscale heterogeneity in alkyl-methylimidazolium bromide ionic liquids.

High-energy x-ray diffraction measurements and atomistic molecular dynamics (AMD) numerical simulations have been carried out on 1-alkyl-3-methylimidazolium bromide ionic liquids, C(n)mimBr, with n = 2, 4, and 6. Excellent agreement between experiment and simulation is obtained, including the region of the low-Q peak that has proved problematic in previous work in the literature. In the partial structure analysis of the AMD results, a distinct peak develops at the leading edge of the ring-ring pair distribution function and shifts to lower r with increasing alkyl chain length, indicating that the preferential parallel and antiparallel alignment of neighboring cation rings plays a larger role with increasing chain length.

Structure of a prototypic ionic liquid: ethyl-methylimidazolium bromide.

High-energy X-ray diffraction measurements have been carried out on 1-ethyl-3-methylimidazolium bromide and complemented with molecular-dynamics simulations. Because the structure of the corresponding crystal is known, both the liquid and the crystal phases are simulated numerically. The liquid structure factor is dominated by an intense peak at 1.

Permeation hysteresis in PdCu membranes.

H 2 permeation hysteresis has been observed during cycling of a 3 mum thick supported PdCu membrane with approximately 50 atom % Pd through the fcc/bcc (face-centered cubic/body-centered cubic) miscibility gap between 723 and 873 K. Structural investigations after annealing of membrane fragments under H 2 at 823 K reveal retardation of the fcc(H) --> bcc(H) transition, which is attributed to the occurrence of metastable hydrogenated fcc PdCu(H) phases. The H(2) flux at 0.

CO2 decomposition over Pd membrane surfaces.

The interaction of pure CO 2 with a 3 microm thin, supported Pd membrane has been investigated between 473 and 773 K. Diagnostic H 2 permeation measurements indicate a reduction of the H 2 flux after CO 2 exposure at the lower and upper ends of this temperature range. Temperature-programmed oxidation and desorption in combination with scanning electron microscopy analyses reveal the dissociation of CO 2 above 523 K, yielding molecularly and/or dissociatively adsorbed CO below 623 K and nanoscopic carbon deposits above 723 K.

Segregation and H2 transport rate control in body-centered cubic PdCu membranes.

The H2 permeation of a supported 2 microm thick Pd48Cu52 membrane was investigated between 373 and 909 K at DeltaP=0.1 MPa. The initial H2 flux was 0.

Selenium/zeolite Y nanocomposites.

Confinement in molecular sieves is a promising strategy for fabricating nanostructured semiconductor assemblies with a highly uniform size and shape distribution. However, disorder effects often hamper the engineering of matrix-embedded cluster materials with specific properties. The host-guest interaction is a key factor for optimizing their structure, electronic characteristics, and stability.