Adsorption of CO on Ni/Cu(110) bimetallic surfaces

Abstract

The adsorption behavior of CO on bimetallic Ni/Cu͑110͒ surfaces has been studied experimentally by thermal-desorption spectroscopy and theoretically by density-functional theory ͑DFT͒ calculations. The bimetallic surfaces were produced either by evaporation of nickel or by decomposition of Ni͑CO͒ 4 on Cu͑110͒. Adsorption of CO at 180 K on such a bimetallic surface yields three new adsorption states with adsorption energies between that of CO on clean Cu͑110͒ and clean Ni͑110͒. The new desorption peaks from the bimetallic surface, designated as ␤ 1 -␤ 3 , can be observed at 250, 300, and 360 K, respectively. These new states are most pronounced when 1 2 monolayer of nickel is present on the copper surface. DFT calculations, using the Vienna ab initio simulation package code, were performed to identify the most probable Ni/Cu atomic arrangements at the bimetallic surface to reconcile with the experimental results. It turned out that CO adsorption on nickel dimers consisting of in-surface and adjacent subsurface atoms can best explain the observed experimental data. The result shows that CO adsorption is determined by local ͑geometric͒ effects rather than by long-range ͑electronic͒ effects. These findings should contribute to a better understanding of tailoring catalytic processes with the help of bimetallic catalysts.

Adsorption of CO onNi3Al(111)investigated using high-resolution photoemission spectroscopy and density functional theory

“…6,11 The adsorption of CO on Ni surfaces has also attracted significant interest theoretically. 14,[37][38][39][40][41][42][43][44] The overall agreement with experimental results are good for CO adsorption on the Ni͑111͒ and Ni͑110͒ surfaces. On the Ni͑111͒ surface, density functional theory ͑DFT͒ calculations predict CO to adsorb in the hollow sites at low coverages with only a small energy difference between the fcc and hcp hollow sites.…”

“…37 On the Ni͑110͒ surface the CO molecules have been found to preferentially bind to the short bridge sites, with a tilted CO axis in a ͑2 ϫ 2͒ structure, in agreement with experimental results. 38,40,41 Similar DFT investigations have not been reported for the CO/Ni͑100͒ system.…”

Tunability of the CO adsorption energy on a Ni/Cu surface: Site change and coverage effects

“…17,18 In general, a simulation cell contains n CO adsorbed molecules and we calculate the adsorption energy E ads of the first desorbing CO molecule, defined as the total energy difference between the cell with n CO molecules and the cell with (n 1) CO molecules plus the total energy of the free CO molecule. 34 Thus, the adsorption energy can vary according to the specific site, apart from the case of ϑ CO = 0.25 ML, where we use simulation cells containing only one adsorbed CO molecule. With this definition, the adsorption energy is negative for stable adsorption configurations.…”

“…15,16,32 The interaction of carbon monoxide with the bimetallic Ni/Cu(110) surface was already investigated by means of a combined experimental and theoretical approach based on TPD spectroscopy and DFT ab initio calculations. [33][34][35] Distinct desorption peaks (β i with i = 1, 2, 3) were identified at intermediate temperature between the features corresponding to CO desorption from pure Cu (α 1 -200 K) and from pure Ni (α-450 K). 33,34 The β i states were associated with CO adsorption geometries in which the molecule is bound to "mixed" sites, where both Ni and Cu atoms are present in the surface and/or subsurface layers.…”

“…[33][34][35] Distinct desorption peaks (β i with i = 1, 2, 3) were identified at intermediate temperature between the features corresponding to CO desorption from pure Cu (α 1 -200 K) and from pure Ni (α-450 K). 33,34 The β i states were associated with CO adsorption geometries in which the molecule is bound to "mixed" sites, where both Ni and Cu atoms are present in the surface and/or subsurface layers. The presence of these configurations was related to the Ni layer preparation recipes, which resulted in Ni-Cu intermixing.…”