Adsorption and coadsorption of CO and H on ruthenium surfaces

The interaction of CO with the Ru(0001) surface at several coverages (11.1, 25.0, and 33.3%) was studied, as well as the interaction of CO with a stepped Ru(0001) surface. The preference for the adsorption site (atop vs. hcp) was analyzed with d. of states diagrams. Hydrogen layers can be densely packed; 1 ML could, in fact, correspond to >100% coverage, where 100% coverage would correspond to 1 adatom for each metal atom on the surface. Calcns. were made for 1 ML of adsorbed hydrogen ?300% coverage for 2 * 2 supercells. The H coadsorption with CO (2 * 2 (CO + nH), n = 1, 3, 4) is discussed for different adsorption sites. The lateral interaction H-CO is repulsive. Hads and COads prefer to form islands rather than mixed structures. CO is little influenced by coadsorption, except when 1 ML of at. hydrogen is preadsorbed. H is strongly affected by coadsorption. The H adsorption sites become highly asym. if H and CO share 1 metal atom

Hydrogen-assisted CO dissociation on FCC-Co{100} : DFT analysis and microkinetic interpretation

A comparative study of the direct and hydrogen assisted CO dissociation pathways have been performed using DFT on the FCC-Co{l00} surface. An interpretation of the calculated energies is afforded by using the microkinetic approach. These results are analysed in the broader context of the related { 111 } surface to obtain a picture of catalytic behavior on a hypothetical cobalt particle consisting of flat surfaces. This approach clearly shows that the hydrogen assisted CO dissociation mechanism is an important contributor to the CO activation mechanism during the first step of Fischer-Tropsch synthesis

Adsorption and decomposition of ethene and propene on Co(0001):the surface chemistry of fischer-tropsch chain growth intermediates

\u3cp\u3e(Graph Presented) Experiments that provide insight into the elementary reaction steps of C\u3csub\u3ex\u3c/sub\u3eH\u3csub\u3ey\u3c/sub\u3e adsorbates are of crucial importance to better understand the chemistry of chain growth in Fischer-Tropsch synthesis (FTS). In the present study we use a combination of experimental and theoretical tools to explore the reactivity of C\u3csub\u3e2\u3c/sub\u3eH\u3csub\u3ex\u3c/sub\u3e and C\u3csub\u3e3\u3c/sub\u3eH\u3csub\u3ex\u3c/sub\u3e adsorbates derived from ethene and propene on the close-packed surface of cobalt. Adsorption studies show that both alkenes adsorb with a high sticking coefficient. Surface hydrogen does not affect the sticking coefficient but reduces the adsorption capacity of both ethene and propene by 50% and suppresses decomposition. On the other hand, even subsaturation quantities of CO\u3csub\u3ead\u3c/sub\u3e strongly suppress alkene adsorption. Partial alkene dehydrogenation occurs at low surface temperature and predominantly yields acetylene and propyne. Ethylidyne and propylidyne can be formed as well, but only when the adsorbate coverage is high. Translated to FTS, the stable, hydrogen-lean adsorbates such as alkynes and alkylidynes will have long residence times on the surface and are therefore feasible intermediates for chain growth. The comparatively lower desorption barrier for propene relative to ethene can to a large extent be attributed to the higher stability of the molecule in the gas phase, where hyperconjugation of the double bond with σ bonds in the adjacent methyl group provides additional stability to propene. The higher desorption barrier for ethene can potentially contribute to the anomalously low C\u3csub\u3e2\u3c/sub\u3eH\u3csub\u3ex\u3c/sub\u3e production rate that is typically observed in cobalt-catalyzed FTS.\u3c/p\u3

Fundamental issues on practical Fischer–Tropsch catalysts : how surface science can help

The present article highlights the contribution of surface science and molecular modeling to the understanding of Fischer–Tropsch catalysis, in particular related to carbon-induced Co Fischer–Tropsch catalyst deactivation. The role of atomic and graphitic carbon in surface restructuring is discussed. Both forms of surface carbon stabilize surface roughness, while molecular CO promotes mobility of Co surface atoms. In a proposed chain growth mechanism on Co(0 0 0 1) chain elongation proceeds via alkylidyne + CH. The resulting acetylenic species is hydrogenated to alkylidyne, the route to further growth. (Cyclo-)polymerization of acetylenic species produces (aromatic) forms of polymeric surface carbon, a slow side reaction

CO adsorption on hydrogen saturated Ru(0001)

The interaction of CO with the Ru(0001)(1 x 1)H surface has been studied by density functional theory (DFT) periodic calculations and molecular beam techniques. The hydrogen (1 x 1) phase induces an activation barrier for CO adsorption with a minimum barrier height of 25 kJ mol(-1). The barrier originates from the initial repulsive interaction between the CO-4 sigma and the Ru-d(3z2-r2) orbitals. Coadsorbed H also reduces the CO adsorption energy considerably and enhances the site preference of CO. On a Ru(0001)(1 x 1)H surface, CO adsorbs exclusively on the atop position. (C) 2001 American Institute of Physic

Ethanol decomposition on Co(0001):C-O Bond scission on a close-packed cobalt surface

Recently there has been a renewed interest in Co-catalyzed Fischer- Tropsch synthesis (FTS) from natural gas, coal, and biomass, because it offers a realistic alternative to crude oil as a source of transportation fuels. Efforts to understand the FT mechanism on the atomic level have mainly focused on theoretical methods, whereas experimental surface science results have only had little impact on the understanding of the mechanism. An essential step in any FT mechanism is scission of the C-O bond. On a flat Co(0001) surface direct dissociation of the CO molecule is practically impossible at FTS conditions. We have found for the first time experimentally that the C-O bond can be broken at 350 K even on the relatively inert Co(0001) surface if a CxHy group and a hydrogen atom are attached to the C-end of the C-O moiety