hide
Free keywords:
-
Abstract:
The intermetallic phase InPd is a candidate material for the use as a
catalyst in the methanol steam reforming process. To study the
connection between the catalytic properties of the surface and the
structural and electronic properties of the bulk, we have grown single
crystals of the InPd phase by the Czochralski method and determined
their electronic, thermal, magnetic and hydrogen-absorption properties.
By growing crystals from a high-temperature solution, we could
crystallize a slightly off-stoichiometric In-rich composition
In1.04Pd0.96, which contained a significant amount of constitutional
defects in the lattice (Pd vacancies on the Pd sublattice) to retain the
CsCl-type structure. The strongly inhomogeneously broadened In-115 NMR
spectrum and the high residual (T -> 0) electrical resistivity confirmed
the presence of constitutional defects. Single crystals of InPd do not
absorb hydrogen, as requested for a good hydrogenation catalyst
material. Calculated electronic density of states (DOS) shows large
contribution of Pd(d) states at the Fermi level. Application of the
electron localizability indicator reveals ionic and multi-centre In Pd
interactions stabilizing the crystal structure. The electrical and
thermal conductivities of InPd show metallic character, whereas the
thermoelectric power and the Hall coefficient both show positive sign,
revealing that InPd is a predominant hole-type conductor. The calculated
electronic DOS at the Fermi energy is in a good agreement with the
experimental value determined from the low-temperature specific heat.
Magnetic measurements have shown that InPd is a diamagnet. All results
are compared to the chemically related intermetallic compound GaPd. The
active site-isolation concept for increased catalytic selectivity is
discussed in relation to the InPd and GaPd structures. (C) 2014 Elsevier
Ltd. All rights reserved.
