Dissociation of Carbon Monoxide on the Rhenium(10-10) Surface

Abstract

We have studied the interaction of carbon monoxide with a Re(10-10) surface between 150 and 800 K by means of low-energy electron diffraction (LEED), temperature-programmed thermal desorption, and work function change (∆ ) measurements. We find two (temperature-dependent) interaction/reaction channels: At 200 K, CO forms molecular (R) states with binding energies between 95 and 118 kJ/mol. At a coverage of Θ CO ) 0.5, a c(2 × 2) LEED phase forms; for Θ CO > 0.5, a dim (2 × 3) structure is observed. The work function change of ∆ max ) +780 meV indicates negatively polarized adsorbed CO molecules. Exposure at 500 K exclusively yields dissociated CO as deduced from high-temperature desorption states (185 kJ/mol < E des < 210 kJ/mol), second-order reaction kinetics, and the formation of a sharp (1 × 2) LEED pattern at Θ CO ) 0.25 (Θ C + Θ O ) 0.50) associated with the least strongly bound 1 CO state. ∆ max amounts to merely +400 meV. Smaller CO coverages (0.125 < Θ < 0.16) give rise to a c(2 × 4) LEED structure. Upon heating, but prior to desorption, both superstructures undergo an order-disorder phase transition. Our results are discussed in terms of face specifities of CO dissociation, CO binding states, and structures and are compared with previous work on CO interaction/dissociation on related transition-metal surfaces.

Confined small-sized cobalt catalysts stimulate carbon-chain growth reversely by modifying ASF law of Fischer–Tropsch synthesis

“…The desorption quantity and desorption temperature of CO increased with the decrease of the crystallite sizes of cobalt. According to the literatures 41 , 42 , the desorbed CO is generated from the recombination of the C* and O* species adsorbed on the metal sites. The findings from CO-TPD/MS indicate that the smaller cobalt crystallites can more strongly adsorb the C* species compared with the larger ones, resulting in the higher desorption temperature.…”

Model Studies on CO Oxidation Catalyst Systems: Titania and Gold Nanoparticles

“…In Figure 6 a, we present a typical LEED pattern of the pg (22) phase with the characteristic missing spots in the (h AE 1/2, 0) directions, and in Figure 6 b, some recently obtained STM micrographs of our (011) films showing the expected real-space zig-zag structure [83] and allowing us to deduce the period lengths in [011] and [100] direction as~5,5 and~8,5 , respectively. We note that an analogous phase was reported by Beck et al [49] for a TiO 2 (011) single crystal and associated with a (2 1)-reconstructed (011) surface.…”

“…Concerning the overall amount of adsorbed CO, we can directly compare the CO-TD peak areas with those obtained in a previous study of the CO interaction with the Re(10-10) surface, where distinct LEED superstructures allowed a quantitative determination of the absolute CO coverage. [100] We obtain 8 10 17 m À2 for the saturation density of adsorbed CO on TiO 2 (011) [V sat = 0.4, related to the (2 1) unit mesh of the reconstructed surface]. This value is considerably lower than the CO coverage reported for the TiO 2 (110) surface (2.5 10 18 m 2 [88] ), whereby the difference is not unreasonable in view of the different surface structure of the two orientations.…”

Interaction of copper with the rhenium$(1 0\bar {1}0)$ surface

“…After appropriate bake-out an ultimate pressure as low as ∼1 × 10 −10 mbar could be achieved; during thin film deposition, the pressure did not rise to more than 6 × 10 −10 mbar, for it must be stressed that these pressure conditions are crucial in order to avoid spurious co-adsorption of reactive gases, carbon monoxide or water vapour in particular. Note that even traces of these gases can drastically affect the morphology of the deposit metal phases and their growth properties, as demonstrated in more detail elsewhere [34].…”