Intermetallic compounds in heterogeneous catalysis-a quickly developing field - PubMed (original) (raw)

Intermetallic compounds in heterogeneous catalysis-a quickly developing field

Marc Armbrüster et al. Sci Technol Adv Mater. 2014.

Abstract

The application of intermetallic compounds for understanding in heterogeneous catalysis developed in an excellent way during the last decade. This review provides an overview of concepts and developments revealing the potential of intermetallic compounds in fundamental as well as applied catalysis research. Intermetallic compounds may be considered as platform materials to address current and future catalytic challenges, e.g. in respect to the energy transition.

Keywords: acetylene semi-hydrogenation; complex metallic alloy; heterogeneous catalysis; intermetallic compound; methanol steam reforming; selective hydrogenation.

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Figures

Figure 1

Figure 1

Reaction network of the semi-hydrogenation of acetylene (a); _π_- and di-_σ_-bonded acetylene (b).

Figure 2

Figure 2

Unit cell of GaPd and coordination of palladium in GaPd (a). Density of states for elemental palladium as well as for GaPd (b).

Figure 3

Figure 3

Ga–Pd phase diagram [32, 33] (top) and coordination of the palladium atoms in intermetallic Ga–Pd compounds as well as the alloy Ga5Pd95 and elemental palladium (bottom, gallium atoms are blue, palladium atoms are red; mixed occupancy in the alloy is indicated by purple).

Figure 4

Figure 4

Electron localization function in Ga7Pd3, electron localizability indicator in GaPd and GaPd2 (from top) revealing covalent contributions to the chemical bonding in all compounds.

Figure 5

Figure 5

XPS spectra of the intermetallic compounds in comparison to elemental palladium: Pd3d5/2 core level spectra (a) and valence band spectra (b) (identical color code in both panels).

Figure 6

Figure 6

Temperature-dependent powder x-ray diffraction of GaPd in 50% H2 in helium (a). Results from PGAA for GaPd in pure hydrogen as well as under reactive conditions in comparison to elemental palladium (b).

Figure 7

Figure 7

(a) XPS spectra of the Pd 3d5/2 region of GaPd in UHV (left) and reactive atmosphere (400 K) (right). (b) Infrared spectra of CO adsorpt on a commercial 5% Pd/Al2O3 (left, arrows indicate falling partial pressure) and unsupported GaPd powder (right, the arrow indicates increasing partial pressure) revealing only isolated on-top adsorption on GaPd.

Figure 8

Figure 8

Conversion of acetylene (a) and selectivity to ethylene (b) for the intermetallic compounds Ga7Pd3, GaPd and GaPd2 in comparison to 5% Pd/Al2O3 and an unsupported Ga5Pd95 alloy (identical color code in both panels).

Figure 9

Figure 9

Crystal structure of Al13Fe4 highlighting the Fe–Al–Fe groups and their surroundings (a). Electronic density of states of Al13Fe4 (b).

Figure 10

Figure 10

DSC/TG of Al13Fe4 powder in 50% H2/He (a), XPS of the single-crystalline (010) surface: (b) Fe 2p in UHV and in situ in comparison to elemental iron foil and (c) depth profile of the Al 2p region corresponding to inelastic mean free paths of 6.6, 11.3 and 14.7 nm (top to bottom).

Figure 11

Figure 11

Comparison of several intermetallic catalysts to supported 5% Pd/Al2O3 and the unsupported substitutional alloy Ag80Pd20. The dashed line is a guide to the eye.

Figure 12

Figure 12

Composition dependent CO2 selectivity in MSR at different temperatures over unsupported ZnPd. Results from in situ ambient pressure XPS measurements are summarized at the bottom (IMC: intermetallic compound), revealing the presence of ZnO in the case of samples rich in Zn.

Figure 13

Figure 13

Two pathways for methanol steam reforming: the ZnPd/ZnO interface holds the active sites (a) or the reaction proceeds via spill-over of activated species from ZnPd and/or ZnO (b).

Figure 14

Figure 14

Different leaching behaviors of the quasicrystalline compound Al63Cu25Fe12 and the crystalline compound Al70Cu20Fe10, leading to different Cu morphologies after leaching (adapted with permission from [100]).

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