Catalytic activation of a non-noble intermetallic surface through nanostructuration under hydrogenation conditions revealed by atomistic thermodynamics

Abstract

On the basis of DFT, we predict nanostructuration and subsequent catalytic activation of Al13Co4(100) under reaction conditions, while Al13Fe4(010) remains nanostructured.

Pseudo-2-Fold Surface of the Al13Co4 Catalyst: Structure, Stability, and Hydrogen Adsorption

“…STM images were simulated using the Tersoff-Hamann approximation. 61 The approach used to compute surface energies in this work is the typical symmetric slab model, 62,63 already used in our previous studies, 35,64 wherein a supercell of the crystal oriented to expose its (hk ) surface is generated, and atoms are removed from a portion of the supercell to create a vacuum (16 to 24Å thick symmetric slabs, void thickness 16Å). This set-up for surface modeling leads to surface energies converged within less than 2.0 mJ/m 2 .…”

“…11). Two surface models are available for the pseudo-tenfold surface: a dense Alrich flat plane, identified by a combination of surface science studies and DFT calculations (P 24 ), [32][33][34] and a highly corrugated model, keeping intact the Henleytype clusters at the surface (P 14 ), 24,35,46 build by a model), they turn up to be the most stable in the full range of allowed chemical potentials, with surface energies ranging from 1.19 J/m 2 (Co-rich potentials) to 1.31 J/m 2 (Al-rich potentials). Thus, they substantially contribute to stabilize the pseudo-twofold orientation over the pseudo-tenfold one.…”

“…The adsorption has been computed on specific points of regular grids covering the surfaces, using point densities of 1.0 pts.Å The energy landscape is quite contrasted on the different terminations considered here. Focusing on the pseudo-tenfold orientation -for which two surface models have been identified -the reaction conditions may indeed modify the Al-rich and relatively flat surface structure observed under ultra-high vacuum (P 24 model), in the form of highly cohesive clusters emerging from the bulk lattice (P 14 model), 35 to give rise to a nanostructured surface demonstrated to be more active. 24,35 Hydrogen is calculated to be quite weakly bound on the P 24 model (E ads > -0.23 eV), the most stable sites being located on Al-Al bridges above a subsurface Co atom, and slightly more strongly adsorbed on the P 14 model (E ads > -0.58 eV), the more stable sites being located on top of the Al "glue" atoms that connects the bipentagonal Al motif, or in the vicinity of protruding Co atoms.…”

“…Regardless of temperature, the o-Al 13 Co 4 (010) pseudo-twofold surface was found much more active than the o-Al 13 Co 4 (100) pseudo-tenfold orientation. While the pseudo-tenfold surface has been extensively studied these last years, [31][32][33][34][35] very few is known about the o-Al 13 Co 4 (010) peudo-twofold surface structure and properties. On the basis of surface science techniques, including Surface X-Ray Diffraction (SXRD), combined with Density Functional Theory (DFT) calculations, we derive a model at the atomic scale for the o-Al 13 Co 4 (010) faceted and columnar structure, analogous to the one of the twofold d-Al-Ni-Co surface.…”

Influence of Cr, Mn, Co and Ni Addition on Crystallization Behavior of Al13Fe4 Phase in Al-5Fe Alloys Based on ThermoDynamic Calculations

“…It has been reported that the monoclinic phases of Al13Co4 and Al13Fe4 possess similar crystallographic structures and may form a continuous solid-solution of Al13(Fe,Co)4 [28,48], which is not observed in the case of other transition metals. The experimental and theoretical studies revealed that the formation enthalpy of Al13Co4 is more negative than the Al13Fe4 phase [49]. This can be the reason for the lower formation enthalpy and a smaller volume of Al78(Fe23Co) phase than the Al78(Fe23M) phase (M = Cr, Mn On the other hand, the addition of Cr and Mn increased the formation enthalpy of the compound and decreased its stability.…”