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The factor dominating olefin to paraffin ratio in cobalt-catalyzed Fischer-Tropsch synthesis has been identified via experimental kinetic studies and theoretical calculations including the van der Waals interaction between the adsorbates and Co surfaces. The olefin to paraffin ratio for each carbon number is expressed as a function of adsorption energies of olefin and activation energies of hydrogenation steps. Density functional theory calculations on Co (0 0 0 1) surface were performed to provide a comprehensive fundamental insight for the chemistry governing the olefin to paraffin ratio. The calculated olefin to paraffin ratio decreases with chain length except for ethylene, which agrees well with the experimental results. The differences introduced to the adsorption energies of olefin by van der Waals functional are correlated with d-band center changes of the Co surface. The carbon number dependent adsorption energies of olefin, rather than the activation energies of their hydrogenation reactions, are the driven force for the carbon number dependent olefin to paraffin ratio. The insights may delineate a new blueprint for the rational design of catalysts with enhanced olefin to paraffin ratio. [ABSTRACT FROM AUTHOR]

During the last years it has been an increasing focus on fundamental studies of the Fischer-Tropsch synthesis (FTS). Steady-state isotopic transient kinetic analysis and first principles investigation have proven to be important methods in studying the reaction mechanism of FTS. The present contribution deals with recent progresses in understanding of the F-T mechanism on Co catalysts based on combined DFT calculations, in situ characterization, steady-state isotopic transient kinetic analysis and microkinetics. A brief outlook into future perspectives of the FTS for converting synthesis gas from different carbon sources to fuels and chemicals is also provided. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Highlights: [•] CO hydrogenation studied at methanation conditions, 483K, 1.85bar, H2/CO=3–10. [•] Integrated transient and steady-state modeling as a powerful tool for useful kinetic parameters. [•] Combining experiments and DFT investigations of kinetic isotopic effect. [•] Dominating CO activation pathway through hydrogen-assisted CO dissociation. [•] Two carbon pools and two corresponding reaction pathways for CH4 formation. [ABSTRACT FROM AUTHOR]

This work gives an insight into combined experimental and DFT study of water gas shift reaction on Ni catalysts at moderately elevated temperatures. The relative reactivity of surface adsorbed species O*, OH* and H* with CO* and their catalytic consequence in reaction mechanism and kinetics was studied. DFT investigation and microkinetic analysis pointed out that the favorable reaction pathway depends on the relative reactivity of O*, OH* and H* with CO* on the surface. It rationalizes the experimental observed changes in kinetics with hydrogen pressure. • Experimental and DFT study leads to WGS reaction mechanism insight on Ni catalyst. • It reveals dependency of the reaction mechanism and kinetics on hydrogen pressure. • Reaction pathway is dependent on relative reactivity of O*, OH* and H* with CO*. • DFT studies rationalize the experimental changes in kinetics with H 2 pressure. This paper presents a combined experimental and density functional theory study of the relative reactivity of surface species O*, OH*, and H* with CO* on nickel catalysts and their catalytic consequence in reaction mechanism and kinetics of water gas shift reaction. The kinetic study illustrates the hydrogen reaction order changes from 0.5 at relatively low hydrogen pressures to -1 at high hydrogen pressures. Detailed kinetic analysis indicated a hydrogen-induced change of the corresponding reaction pathway from hydrogen assisted CO activation to the redox mechanism with CO*+O* as a rate-determining step. The DFT investigation revealed that the surrounding surface H* atoms destabilize more significantly O* adsorption than H* adsorption, thus enhance more the reactivity of O* than H* towards reaction with CO* at high H* coverage. This kinetic study provides an insightful depiction for the future study of CO activation on other transition metals and the catalyst development for WGS reaction. [ABSTRACT FROM AUTHOR]

In this contribution, we combine density functional theory (DFT) calculations, experimental kinetic study and DFT-assisted analysis to elucidate the impact of the interface of monolayer Pt on the Ni surface on catalytic performance of steam methane reforming including carbon formation on core-shell (Ni@Pt) catalysts and compare it with Ni and Pt catalysts. We demonstrate that core-shell structured Ni@Pt significantly lowers the carbon formation without sacrificing much the activity. The DFT results demonstrate that the metal identity, core shell structure and support have significant impacts on the reaction mechanisms. The direct methane activation is energetically favorable reaction pathway on Ni, while the OH* assisted methane activation is the favorable pathway on Pt and Ni@Pt catalysts, where methane activation is the rate-determining step on all catalysts. We unambiguously reveal that the core-shell Ni@Pt catalyst modified the surface Pt electron density and shifted d -band center away from Fermi level compared to Ni(1 1 1) and Pt(1 1 1). It results in a strong basic surface OH* which actively reacts with CH x and thus enhances carbon formation resistance. Above all, Ni-core/Pt-shell particle could decouple the activity and carbon resistance to keep the activity and reduce carbon formation simultaneously in methane steam reforming. In addition, by taking into account the activation of steam on the support, the effective activation energy estimated from DFT-assisted analysis is well consistent with the experimental value on the both Ni and Ni@Pt catalysts, which could shed some light on building a bridge between experimental work and DFT-assisted kinetic study. [ABSTRACT FROM AUTHOR]