A two-step synthesis for the preparation of single-phase and nanoparticulate GaPd and GaPd2 by coreduction of ionic metal-precursors with LiHBEt3 in THF without additional stabilizers is described. The coreduction leads initially to the formation of Pd nanop articles followed by a Pd-mediated reduction of Ga3+ on their surfaces, requiring an additional annealing step. The majority of the intermetallic particles have diameters of 3 and 7 nm for GaPd and GaPd2, respectively, and unexpected narrow size distributions as determined by disk centrifuge measurements. The nanoparticles have been characterized by XRD, TEM, and chemical analysis to ensure the formation of the intermetallic compounds. Unsupported nanoparticles possess high catalytic activity while maintaining the excellent selectivity of the ground bulk materials in the semihydrogenation of acetylene. The activity could be further increased by depositing the particles on alpha-Al2O3.
Phase equilibria in the palladium-rich part of the gallium–palladium system. The crystal structures of Ga3Pd7 and Ga1−xPd2+x
作者:Christoph Wannek、Bernd Harbrecht
DOI:10.1016/s0925-8388(00)01511-5
日期:2001.3
The phase relations between the palladium-rich phases of the gallium-palladium system are clarified by combining preparative methodologies with powder X-ray diffraction and thermochemical analyses. A modified phase diagram of the palladium-rich part of the system is presented. The structure of Ga3Pd7, decomposing peritectoidally at 881(2)degreesC, was determined by powder X-ray diffraction and refined by a Rietveld profile fit. Ga3Pd7 adopts a new structure type with monoclinic space group symmetry: C2/m, Z = 2, a = 1359.46(2) pm, b=405.510(5) pm, c=544.339(6) pm, beta =105.2219(7)degrees, wR(p) = 0.082. The structure can be seen as a strongly distorted, ordered variant of a respective GaxPd1-x fcc solid solution. It comprises two structural motifs: layers of columns of fused (GaPd6/2)(2) prisms are formally separated by equiatomic GaPd layers. The impact of the composition on the structure of Co2Si-type Ga1-xPd2+x was studied. There exists a symmetry relation between the cubic close-packed arrangement of atoms and the structures of the Co2Si-type branch of AB(2) phases with Pearson symbol oP12 and space group symmetry Pnma. (C) 2001 Elsevier Science B.V. All rights reserved.
Hydrogenation of palladium rich compounds of aluminium, gallium and indium
作者:H. Kohlmann
DOI:10.1016/j.jssc.2009.11.029
日期:2010.2
Palladium rich intermetallic compounds of aluminium, gallium and indium have been Studied before and after hydrogenation by powder X-ray diffraction and during hydrogenation by in situ thermal analysis (DSC) at hydrogen gas pressures up to 39 MPa and temperatures Lip to 700 K. Very weak DSC signals and small unit cell increases of below 1% for AlPd(2), AlPd(3), GaPd(2), Ga(5)Pd(13), ln(3)Pd(5), and InPd(2) suggest negligible hydrogen uptake. In contrast, for both tetragonal modifications of InPd(3) (ZrAl(3) and TiAl(3) type), heating to 523 K at 2 MPa hydrogen pressure leads to a rearrangement of the intermetallic structure to a cubic AuCu(3) type with an increase in unit cell Volume per formula unit by 3.6-3.9%. Gravimetric analysis suggests a composition InPd(3)H(approximate to 0.8) for the hydrogenation product. Very similar behaviour is found for the deuteration of InPd(3). (C) 2009 Elsevier Inc. All Fights reserved.