engleski

Physical properties of the InPd intermetallic catalyst

The InPd intermetallic compound is a candidate material for the use as a catalyst in the selective hydrogenation of alkynes. Due to structural reasons, the compound follows the site- isolation concept that assures high catalytic selectivity, whereas covalent bonding provides long-term stability of the material under the reaction conditions. To connect catalytic properties of the surface to the structural and electronic properties of the bulk, we have grown large monocrystals of the InPd phase by the Czochralski method and determined their electronic, thermal, magnetic and hydrogen- absorbing properties. By growing crystals from a high-temperature solution, we could crystallize a slightly off-stoichiometric In-rich composition In52.2Pd47.8, which contained a large concentration of constitutional defects in the lattice (Pd vacancies on the Pd sublattice) to retain the CsCl–type structure. The strongly inhomogeneously broadened 115In NMR spectrum and the high residual electrical resistivity confirmed the presence of constitutional defects in the InPd lattice. The InPd material did not absorb any hydrogen, as requested for a good hydrogenation catalyst material. The electrical and thermal conductivities of InPd were found typical metallic. The thermoelectric power and the Hall coefficient both show positive sign, revealing a predominantly hole-type conductor. The electronic density of states at the Fermi energy was determined from the low-temperature specific heat and the electronic specific heat coefficient has revealed that InPd is a free-electron-like intermetallic compound. Magnetic measurements have shown that InPd is a simple diamagnet. All results are compared to the GaPd intermetallic compound, which is considered as a prototype catalyst system obeying practically ideally the site-isolation concept.

transport properties; quasicrystals

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