The influence of CO adsorption on the surface composition of cobalt/palladium alloys

Abstract

Segregation induced by the adsorption of gas phase species can strongly influence the composition of bimetallic surfaces and can therefore play an important role in influencing heterogeneous catalytic reactions. The addition of palladium to cobalt catalysts has been shown to promote Fischer Tropsch catalysis. We investigate the adsorption of CO onto bimetallic CoPd surfaces on Pd{111} using a combination of reflection absorption infrared spectroscopy and medium energy ion scattering. The vibrational frequency of adsorbed CO provides crucial information on the adsorption sites adopted by CO and medium energy ion scattering probes the surface composition before and after CO exposure. We show that cobalt segregation is induced by CO adsorption and rationalise these observations in terms of the strength of adsorption of CO in various surface adsorption sites.

Au–Rh Surface Structures on Rh(111): DFT Insights into the Formation of an Ordered Surface Alloy

“…These results reveal that there is a bimodal structure formation on two different lateral scales and shapes: (1) 2 ×1 ordered domains of 3×3 nm 2 embedded in an unordered phase; (2) elongated stripes of 3-4 nm width containing the 2×1 ordered domains and separated by surface regions where no ordering can be found. The 2×1 ordered structure found in our case is quite similar to the L1 0 phase of CuAu type structures which was also identified for CoPt, FePt, FePd and CoPd systems by STM and LEED methods 36 . In these latter cases, however, the ordered phase was also extended to the bulk region, so it was not restricted to the surface layer as we assumed in the above schematic model for the Au-Rh system.…”

“…reported a surface alloy ordering in the case of epitaxial growth of Co on Pd(111) and the formation of Co(50%)Pd(50%) surface alloy of p(2×1) registry. 36 They detected quite similar STM images at around 600 K annealing as was described for the Au/Rh(111) system in the temperature range of 650-1050K. 31…”

“…The issue is, what is the driving force of the ordering of the surface alloy phases and how frequent is this tendency by looking at the different material systems? Naturally, to the formation of an energetically more stable ordered (instead of a random) phase, it needs the 6/39 activation of atomic scale diffusion and exchange processes (kinetic factor) 6,7,9,11,[35][36][37] . Murdoch et al…”

Size and surface-energy dependence of the adsorption/desorption equilibrium in ethanol electro-oxidation by Pd-nanoparticles. Theory and experiment

“…The second was an explicit method, in which we used eqn (12) to calculate the value of the electron-transfer coefficient (a) directly in the modied Laviron equation to obtain the adsorption equilibrium constant (K eq ) and, nally, the calculation of the number of adsorbed molecules (G 0 ).…”

“…This adsorption depends directly on the intrinsic characteristics of the materials, their chemical compositions, their crystallographic arrays, their size, the concentrations of the species in the bulk dissolution, and on the surface-electrolyte interface. [9][10][11][12][13] The oxidation current depends on the number of adsorbed fuel molecules, and the adsorption of molecules on a surface is related to the energy associated with the electrochemical process. A useful theoretical model that takes into account such characteristics and describes the production of the oxidation current is the Laviron equation…”