Site Structure Sensitivity Differences for Dissociation of Diatomic Molecules

Shetty, SG Sharankumar; Santen, Rutger A. van

doi:10.1007/s11244-010-9516-6

Cited by 10 publications

(8 citation statements)

References 40 publications

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“…The large variation of CO dissociation barriers in magnitude of 1.43 eV (hcp) and 1.15 eV (fcc) suggests that CO dissociations are highly structure sensitive on both Ru phases. This is in good agreement with the result of diatomic molecules dissociation on transition-metal surfaces. ,,− Considering typical aqueous-phase FTS reaction conditions (393–443 K), an increase of the dissociation barrier by 0.1 eV means a decrease of the corresponding rate constant by more than 1 order of magnitude. As a result, we focus below the structures with CO dissociation barrier falling in the window of 0.94–1.39 eV only, which contains 14 of 18 different surface structures (Figure ).…”

Section: Resultssupporting

confidence: 86%

Chemical Insights into the Design and Development of Face-Centered Cubic Ruthenium Catalysts for Fischer–Tropsch Synthesis

et al. 2017

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Ruthenium is a promising low-temperature catalyst for Fischer-Tropsch synthesis (FTS). However, its scarcity and modest specific activity limit its widespread industrialization. We demonstrate here a strategy for tuning the crystal phase of catalysts to expose denser and active sites for a higher mass-specific activity. Density functional theory calculations show that upon CO dissociation there are a number of open facets with modest barrier available on the face-centered cubic (fcc) Ru but only a few step edges with a lower barrier on conventional hexagonal-closest packed (hcp) Ru. Guided by theoretical calculations, water-dispersible fcc Ru catalysts containing abundant open facets were synthesized and showed an unprecedented mass-specific activity in the aqueous-phase FTS, 37.8 mol·mol·h at 433 K. The mass-specific activity of the fcc Ru catalysts with an average size of 6.8 nm is about three times larger than the previous best hcp catalyst with a smaller size of 1.9 nm and a higher specific surface area. The origin of the higher mass-specific activity of the fcc Ru catalysts is identified experimentally from the 2 orders of magnitude higher density of the active sites, despite its slightly higher apparent barrier. Experimental results are in excellent agreement with prediction of theory. The great influence of the crystal phases on site distribution and their intrinsic activities revealed here provides a rationale design of catalysts for higher mass-specific activity without decrease of the particle size.

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Section: Resultssupporting

confidence: 86%

Chemical Insights into the Design and Development of Face-Centered Cubic Ruthenium Catalysts for Fischer–Tropsch Synthesis

et al. 2017

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“…Even lower barriers are found for direct CO dissociation on the Co(101̅0)B surface (B refers to the specific surface cut)where the activation barrier is only 68 kJ/mol, whereas the overall barrier for the hydroxycarbene (HCO) mechanism is 105 kJ/mol on the same surface. Other computational studies also indicate that the carbene mechanism is indeed the preferred route on stepped and corrugated metal surfaces such as ruthenium, ,− rhodium, and cobalt . An ideal active site for FTS should not only have low barriers for CO dissociation but also allow for a propagation cycle to take place that can sustain itself.…”

Section: Introductionmentioning

confidence: 99%

Reactivity of CO on Carbon-Covered Cobalt Surfaces in Fischer–Tropsch Synthesis

et al. 2014

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Tropsch synthesis is an attractive process to convert alternative carbon sources, such as biomass, natural gas, or coal, to fuels and chemicals. Deactivation of the catalyst is obviously undesirable, and for a commercial plant it is of high importance to keep the catalyst active as long as possible during operating conditions. In this study, the reactivity of CO on carbon-covered cobalt surfaces has been investigated by means of density functional theory (DFT). An attempt is made to provide insight into the role of carbon deposition on the deactivation of two cobalt surfaces: the closedpacked Co(0001) surface and the corrugated Co(112̅ 1) surface. We also analyzed the adsorption and diffusion of carbon atoms on both surfaces and compared the mobility. Finally, the results for Co(0001) and Co(112̅ 1) are compared, and the influence of the surface topology is assessed.

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“…It was proposed that the cleavage of either the C–O bond of the molecule itself (carbide mechanism) or its partially hydrogenated intermediates (via H-assisted mechanism) is responsible for the formation of these important precursor species on Ru, with the morphology of the surface dictating which pathway dominates . On stepped and corrugated surfaces, for example, temperature desorption spectroscopy (TDS), high-resolution electron energy loss spectroscopy (HREELS), infrared reflection–absorption spectroscopy (IRAS), and low-energy electron diffraction (LEED) studies indicate that the carbide mechanism was preferred with direct dissociation occurring in the temperature range of 300–500 K. − Subsequent density functional theory (DFT) studies based on model surfaces containing under-coordinated sites, such as steps, revealed that the molecule was tilted with both carbon and oxygen essentially interacting with metal atoms. − The activation of the C–O bond resulting from the enhanced interaction with the surface was thought to be responsible for the low barrier dissociation of the molecule.…”

Section: Introductionmentioning

confidence: 99%

Further Theoretical Evidence for Hydrogen-Assisted CO Dissociation on Ru(0001)

Alfonso

2013

J. Phys. Chem. C

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Extensive calculations based on spin-polarized density functional theory were carried out to examine how CH x are formed from the dissociation of CO on Ru(0001) in the presence of hydrogen. Common pathways, such as the direct CO dissociation and H-assisted route leading to HCO or COH, including alternative routes that involve the formation of HCOH and CH2O, were examined. The reaction energy and barrier for each elementary step were calculated. The calculations show that the carbide mechanism is not the main reaction pathway for the conversion of CO on Ru(0001). Complementary microkinetic simulations utilizing results from first-principles quantum mechanical calculations indicate that a branch starting from the hydrogenation of CO to HCOH (via COH intermediate) and subsequent C–O bond cleavage is more plausible.

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Site Structure Sensitivity Differences for Dissociation of Diatomic Molecules

Cited by 10 publications

References 40 publications

Chemical Insights into the Design and Development of Face-Centered Cubic Ruthenium Catalysts for Fischer–Tropsch Synthesis

Chemical Insights into the Design and Development of Face-Centered Cubic Ruthenium Catalysts for Fischer–Tropsch Synthesis

Reactivity of CO on Carbon-Covered Cobalt Surfaces in Fischer–Tropsch Synthesis

Further Theoretical Evidence for Hydrogen-Assisted CO Dissociation on Ru(0001)

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