Carbon monoxide chemisorption on Cu covered Ni(111) surfaces

Abstract

The adsorption of carbon monoxide on copper covered Ni (111) surfaces has been studied by high resolution electron energy loss spectroscopy (HREELS). CO is used to titrate the various adsorption sites present, yielding information about the structure and composition of the two metal species at the surface. The results show that CO adsorbs at locations which resemble the top and bridge sites of pure Cu(111) and Ni(111) surfaces, and on a new mixed Cu–Ni bridge site. For a Cu coverage greater than one monolayer, the CO HREEL spectra are very similar to those observed on the clean Cu(111) surface. For Cu coverages less than one monolayer, and deposition at 80 K, small Cu clusters and Cu islands are observed. For submonolayer Cu deposition at temperatures >300 K, a mixed Cu–Ni layer can be formed. The HREELS results for the mixed surface with low Ni concentration show that CO adsorbs on the Ni top sites first (at T<400 K), Cu top sites next (at T<150 K), and then a mixed Cu–Ni bridge site (at T<120 K). Strong evidence suggests that the mixed CuNi bridge site is occupied by depopulating the Ni–CO top-site species.

In situ IR spectroscopic studies of Ni surface segregation induced by CO adsorption on Cu–Ni/SiO2 bimetallic catalysts

“…53 A mixed Cu-Ni layer can be formed at 700 K as observed in Cu-Ni(111) systems. 41,54 But here the Cu atoms deposited at coverages less than 1.5 MLE mainly populate on the surface blocking CO adsorption as observed by CO TPD, which agrees with the Cu atoms segregating on the Cu-Ni bimetallic surface and form Cu over layers due to its lower surface free energy. 26,41,47,55,56 As we mentioned before, the active Ni sites on the monometallic 5 MLE Ni/SiO 2 are measured to be 1.7 MLE, which coincidently equals to the observed breaking point in the AES spectra.…”

“…32 CO has been used as a probe molecule to study the surface structure and composition of Cu-Ni bimetallic catalysts. 35,[40][41][42][43][44] In spite of extensive studies on Cu-Ni bimetallic catalysts, in situ studies on the interaction of CO with Cu-Ni bimetallic catalysts are still missing. Based on the large difference in bond strength between CO on Ni and Cu sites, possible surface segregation induced by CO adsorption can be expected, which is the key to understand CO involved reactions on Cu-Ni bimetallic catalysts, such as methanation of CO 30 and the water-gas-shift reaction on Cu-Ni bimetallic catalysts.…”

Mixed layer formation on the copper-deposited Ni(110) surface

“…For the Cu/Ni͑111͒ surface, the perturbed ␥␥ angular correlation ͑PAC͒ of 111 In ͑Ref. 17͒ and the x-ray photoelectron spectroscopy of CO titration 18,19 also showed no significant mixing of Cu into the Ni substrate even after annealing at 800 K. In contrast to these faces, photoelectron spectroscopy ͑PES͒ combined with ion scattering spectroscopy ͑ISS͒ for Cu/Ni͑110͒ exhibited significant Cu/Ni mixing even at room-temperature deposition. 20,21 Unlike the ͑111͒ and ͑001͒ faces, the arrangement of surface atoms of the Ni͑110͒ 1 ϫ 1 structure is relatively open and the coordination of the top layer atoms is smaller than other low-index faces.…”

Atomic Structure Optimization with Machine-Learning Enabled Interpolation between Chemical Elements

“…This is in agreement with the fact that the adsorption energy is larger on Ni(111) than on Cu(111) [50], and this overcomes the segregation energy of copper. Experimentally CO is observed to occupy top sites in Cu-Ni(111) alloy surfaces with mixing of the metal atoms [51], even though CO prefers hollow sites on pure Ni(111) and Cu(111) [50]. The effect of Ni atoms backsegregating to the surface exposed to CO has also been observed experimentally [52].…”