Facetting of a quasicrystalline approximant surface for stability and optimized catalytic performances Heterogeneous catalysis by intermetallics (K = 2) reciprocal space maps of o-Al13Co(010), where the facet4 represents a quickly growing field, which signal is clearly visible. The facet rods do not intercept each other contributed to innovative breakthroughs at the Bragg peaks of the orthorhombic structure (black circles), meaning that the facets do not present the o-Al13Co structure.4 in recent years. Quasicrystals and related Facets are therefore related to the monoclinic m-Al13Co structure,4 phases are promising compounds as catalysts, that coexists with o-Al13Co in the investigated sample. They are4 since their original structures could open consistent with a m-(-201) orientation. A total of 34 inequivalent crystal truncation rods of o-Al13Co(010) were extracted from4 new mechanisms for tuning the catalytic the measured region and compared to DFT-based simulations properties. Surface X-ray diffraction and using different surface structure models. A surface model was Density Functional Theory are used here to proposed (Fig. 2), which combines o-Al13Co(010) terraces and4 derive an atomistic model for the pseudo- m-AlCo(-201) facets. Facets substantially stabilize the system,13 4 with calculated surface energies in the range 1.19–1.31 J/m,2 twofold surface of the o-AlCo approximant. i.e. much lower than the ones of o-Al13Co(010) (1.66 J/m).24 13 4 Both surfaces exhibit surface Co atoms, which can be favorable The faceted and columnar surface structure is found very similar to the one of the adsorption and dissociation sites. twofold surface of the d-AlNiCo quasicrystal. FIGURE 1 Facets substantially stabilize the system and are a main factor for the AlCo catalytic413 performances. A few low-order approximants to decagonal quasicrystals have been shown to provide excellent activity and selectivity for alkene and alkyne hydrogenation [1]. It is the case for the Al13TM4 quasicrystalline approximants (TM = transition metal), for which the site isolation has been identified as an important factor for the catalytic performances toward butadiene hydrogenation. Among them, the pseudo-twofold surface of the orthorhombic o-Al13Co4 compound was revealed as the most active model catalyst at 110°C, even compared with the pseudo-tenfold orientation [2]. While the pseudo-tenfold surface has been extensively studied in the past years [3, 4], very few is known about the o-Al13Co(010)4 surface structure and properties. A combination of surface science FIGURE 2 techniques, including atomic force microscopy (AFM), scanning tunneling microscopy (STM) and surface x-ray diffraction (SXRD), combined with density functional theory (DFT) calculations, is used in this study to investigate the surface structure as well as the adsorption properties of o-Al13Co(010).4 SURFACE STRUCTURES After annealing at 700°C for 1 hour, STM and AFM analyses showed the presence of facets along the [100] direction of o-Al13Co. This4 was confirmed by low energy electron diffraction, where a (1x1) surface structure is mainly observed. A large part of the reciprocal was then collected during the SXRD exper ent tat was performed at SixS beamline. Figure 1 presents the in-plane and out-of-plane 26