Hydrogen adsorption on Fe50Ni50

S. SIMONETTI; F. REY SARAVIA; G. CANTO

Conferencia; The Energy & Materials Research Conference; 2012

Iron promoted nickel based catalyst has been developed for high yield hydrogen generation through ethanol reforming [1]. The reaction results show a remarkable improved durability in catalytic activity as well as selectivity. On the other hand, the perturbations in the electronic properties of the bimetallic surfaces are considered to be a contributory factor to the change in the catalytic action [2]. Investigations have reported that binary Fe-Ni catalysts decreased the reaction temperature and yielded 70-90 percent of hydrogen [3, 4]. In the present work, we have analyzed at theoretical level, the adsorption of hydrogen on the Fe50Ni50(111) surface by Atom Superposition and Electron Delocalization calculations [5]. Different sites on the surface were selected in order to establish the preferential H location and the optimum H-surface distance. The two most stable sites for H on Fe50Ni50(111) are those where H bonds on top Fe at 1.50 Å from the surface, and the H bonds on the Fe-Fe bridge site at 0.70 Å from the bimetallic surface.  We found that the minimum energy site corresponds to the H bonding on top Fe atom. The Fe-H interaction is formed and the bond is mainly due to the overlaps between the H s orbital with the Fe pz, s, dz2 and py orbitals. As a consequence, it is observed a local Fe-Fe bond weakening of 12 %. On the other hand, when the H is located on the Fe-Fe bridge site, the Fe-H interactions weaken the Fe-Fe nearest bonds to about 33% and the Fe-H interaction is mainly formed with participation of Fe pz, py, s and dyz orbitals. In general, after H adsorption, the Fe-Ni and Ni-Ni bonds are slightly affected. The Ni-H interaction is not evidence on the Fe50Ni50(111) surface.