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Abstract

An unsupported Pd-rich GaPd2 sample in form of a thin film has been
prepared by alternating layer deposition of Pd and Ga metal and was
subsequently used as a structurally and chemically stable model system
to clarify the catalytic properties of the unsupported intermetallic
compound GaPd2 in methanol steam reforming (MSR). The sample revealed a
slightly Pd-richer GaPd2 bulk composition of Ga28Pd72, as evidenced by
EDX analysis, low-energy ion scattering, X-ray diffraction measurements,
and depth profiling by in situ X-ray photoelectron spectroscopy. The
latter additionally showed a high stability of GaPd2 both under methanol
and oxidative methanol steam reforming conditions. No active redox
chemistry of Ga species or other reaction-induced oxidative Ga surface
segregation has been detected during catalytic MSR reaction.
Corroborating these observations, corresponding catalytic experiments
under methanol steam reforming conditions revealed only a, in comparison
with elemental Pd, very small activity in methanol dehydrogenation (CO
formation rate at maximum 0.019 mbar min(-1); 0.08 site(-1)-s(-1)).
Unsupported thin film Pd-rich GaPd2 with the given surface and bulk
stoichiometry must therefore be considered a poor methanol steam
reforming/dehydrogenation catalyst. In oxidative steam reforming
experiments, only total oxidation without significant H-2 formation has
been observed. (C) 2013 Elsevier Inc. All rights reserved.