Size-dependent dissociation of carbon monoxide on cobalt nanoparticles.

In situ soft X-ray absorption spectroscopy (XAS) was employed to study the adsorption and dissociation of carbon monoxide molecules on cobalt nanoparticles with sizes ranging from 4 to 15 nm. The majority of CO molecules adsorb molecularly on the surface of the nanoparticles, but some undergo dissociative adsorption, leading to oxide species on the surface of the nanoparticles. We found that the tendency of CO to undergo dissociation depends critically on the size of the Co nanoparticles. Indeed, CO molecules dissociate much more efficiently on the larger nanoparticles (15 nm) than on the smaller particles (4 nm). We further observed a strong increase in the dissociation rate of adsorbed CO upon exposure to hydrogen, clearly demonstrating that the CO dissociation on cobalt nanoparticles is assisted by hydrogen. Our results suggest that the ability of cobalt nanoparticles to dissociate hydrogen is the main parameter determining the reactivity of cobalt nanoparticles in Fischer-Tropsch synthesis.

[1]  N. Kruse,et al.  Hydrocarbon chain lengthening in catalytic CO hydrogenation: evidence for a CO-insertion mechanism. , 2012, Journal of the American Chemical Society.

[2]  M. Rønning,et al.  Fischer–Tropsch synthesis: An XAS/XRPD combined in situ study from catalyst activation to deactivation , 2012 .

[3]  Im Ionel Ciobica,et al.  Hydrogen-assisted CO dissociation on the Co(211) stepped surface , 2012 .

[4]  J. Fierro,et al.  Catalytic effects of ruthenium particle size on the Fischer–Tropsch Synthesis , 2011 .

[5]  R. A. Santen,et al.  CO dissociation on Ru and Co surfaces : the initial step in the Fischer-Tropsch synthesis , 2011 .

[6]  Manos Mavrikakis,et al.  Kinetically Relevant Steps and H2/D2 Isotope Effects in Fischer−Tropsch Synthesis on Fe and Co Catalysts , 2010 .

[7]  Anders Holmen,et al.  Understanding the effect of cobalt particle size on Fischer-Tropsch synthesis: surface species and mechanistic studies by SSITKA and kinetic isotope effect. , 2010, Langmuir : the ACS journal of surfaces and colloids.

[8]  Manos Mavrikakis,et al.  CO activation pathways and the mechanism of Fischer–Tropsch synthesis , 2010 .

[9]  R. V. van Santen,et al.  Hydrogen induced CO activation on open Ru and Co surfaces. , 2010, Physical chemistry chemical physics : PCCP.

[10]  N. Kruse,et al.  DRIFTS/MS Studies during Chemical Transients and SSITKA of the CO/H2 Reaction over Co-MgO Catalysts , 2010 .

[11]  A. Jansen,et al.  Direct versus hydrogen-assisted CO dissociation. , 2009, Journal of the American Chemical Society.

[12]  P. Concepción,et al.  Cobalt particle size effects in Fischer–Tropsch synthesis: structural and in situ spectroscopic characterisation on reverse micelle-synthesised Co/ITQ-2 model catalysts , 2009 .

[13]  A. Cabot,et al.  Influence of the cobalt particle size in the CO hydrogenation reaction studied by in situ X-ray absorption spectroscopy. , 2009, The journal of physical chemistry. B.

[14]  J. Bitter,et al.  On the origin of the cobalt particle size effects in Fischer-Tropsch catalysis. , 2009, Journal of the American Chemical Society.

[15]  A. Borgna,et al.  Density Functional Theory Study of the CO Insertion Mechanism for Fischer−Tropsch Synthesis over Co Catalysts , 2009 .

[16]  Burtron H. Davis,et al.  Fischer–Tropsch Synthesis: Reaction mechanisms for iron catalysts , 2009 .

[17]  J. Nørskov,et al.  Structure Sensitivity of the Methanation Reaction: H2 induced CO dissociation on nickel surfaces , 2008 .

[18]  Oliver R. Inderwildi,et al.  Fischer−Tropsch Mechanism Revisited: Alternative Pathways for the Production of Higher Hydrocarbons from Synthesis Gas , 2008 .

[19]  Freek Kapteijn,et al.  Cobalt particle size effects in the Fischer-Tropsch reaction studied with carbon nanofiber supported catalysts. , 2006, Journal of the American Chemical Society.

[20]  B. Weckhuysen,et al.  In Situ X-ray Absorption of Co/Mn/TiO2 Catalysts for Fischer−Tropsch Synthesis , 2004 .

[21]  Hans Schulz,et al.  Short history and present trends of Fischer–Tropsch synthesis , 1999 .

[22]  G. Blyholder,et al.  Hydrogen-assisted dissociation of CO on a catalyst surface , 1991 .

[23]  Alexis T. Bell,et al.  Catalytic Synthesis of Hydrocarbons over Group VIII Metals. A Discussion of the Reaction Mechanism , 1981 .

[24]  H. Pichler,et al.  Neuere Erkenntnisse auf dem Gebiet der Synthese von Kohlenwasserstoffen aus CO und H2 , 1970 .