Complex intermetallic compounds such as transition metal (TM) aluminides are promising alternatives to expensive Pd-based catalysts, in particular for the semi-hydrogenation of alkynes or alkadienes. Here, we compare the gas-phase butadiene hydrogenation performances of o-Al 13 Co 4 (100), m-Al 13 Fe 4 (010) and m-Al 13 Ru 4 (010) surfaces, whose bulk terminated structural models exhibit similar cluster-like arrangements. Moreover, the effect of the surface orientation is assessed through a comparison between o-Al 13 Co 4 (100) and o-Al 13 Co 4 (010). As a result, the following room-temperature activity order is determined: Al 13 Co 4 (100) < Al 13 Co 4 (010) < Al 13 Ru 4 (010) < Al 13 Fe 4 (010). Moreover, Al 13 Co 4 (010) is found to be the most active surface at 110°C, and even more selective to butene (100%) than previously investigated Al 13 Fe 4 (010). DFT calculations show that the activity and selectivity results can be rationalized through the determination of butadiene and butene adsorption energies; in contrast, hydrogen adsorption energies do not scale with the catalytic activities. Moreover, the calculation of projected densities of states provides an insight into the Al 13 TM 4 surface electronic structure. Isolating the TM active centers within the Al matrix induces a narrowing of the TM d-band, which leads to the high catalytic performances of Al 13 TM 4 compounds.
Self-organized molecular films with long-range quasiperiodic order have been grown by using the complex potential energy landscape of quasicrystalline surfaces as templates. The long-range order arises from a specific subset of quasilattice sites acting as preferred adsorption sites for the molecules, thus enforcing a quasiperiodic structure in the film. These adsorption sites exhibit a local 5-fold symmetry resulting from the cut by the surface plane through the cluster units identified in the bulk solid. Symmetry matching between the C60 fullerene and the substrate leads to a preferred adsorption configuration of the molecules with a pentagonal face down, a feature unique to quasicrystalline surfaces, enabling efficient chemical bonding at the molecule-substrate interface. This finding offers opportunities to investigate the physical properties of model 2D quasiperiodic systems, as the molecules can be functionalized to yield architectures with tailor-made properties. KeywordsC60, self-assembly, quasiperiodic order, scanning tunneling microscopy, density functional theory, 5-fold symmetry Disciplines Materials Chemistry | Materials Science and Engineering CommentsReprinted with permission from ACS Nano 8 (2014) Q uasicrystals (QCs) were discovered in intermetallic compounds by D. Shechtman, Nobel Prize in Chemistry 2011. 1 They possess long-range order but no translational invariance. They are a special class of complex intermetallics, in the sense that their unit cell is of infinite dimension. QCs have a fascinating beauty associated with forbidden symmetries, like five-, 10-, or 12-fold rotational symmetries not found in periodic systems. Today, the field is very active, and QCs are being discovered in a broad range of systems. Hundreds of intermetallic compounds with quasiperiodic structures have been identified in phase diagrams. 2 But QCs are no longer restricted to intermetallics. Soft QCs are an emerging field in colloidal and supramolecular chemistry. 3,4 Perovskite oxide thin films with quasiperiodic structures have recently been identified, 5 and even water thin films have been predicted to adopt quasiperiodic structures under specific conditions. 6 In this article, we show that molecular films with long-range quasiperiodic order can also be grown by using clean QC surfaces as templates, thus extending the concept of QCs to an even wider materials field.Thorough investigations of QC surfaces in an ultra-high-vacuum environment have led to the conclusion that they are bulk terminated at specific planes. 7,8 For Al-based QCs, the selected terminations are dense Al-rich planes of the bulk structure separated by the largest interplanar distances corresponding to the lowest surface energy terminations. Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) images reveal both the long-range quasiperiodic order and local atomic configurations corresponding to cluster building blocks used to described the bulk structure that are truncated by the surface plane. 9À12 Such termin...
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