Influence of the Cobalt Particle Size in the CO Hydrogenation Reaction Studied by In Situ X-Ray Absorption Spectroscopy

Abstract

TitleInfluence of the cobalt particle size in the CO hydrogenation reaction studied by in situ X-ray absorption spectroscopy To whom correspondence should be addressed. E-mail: MBSalmeron@lbl.govThe influence of particle size in the carbon monoxide hydrogenation reaction has been studied using cobalt nanoparticles (NP) with narrow size distribution prepared by colloidal chemistry. The surfactant covering the NP after synthesis could be removed by heating to 200-270ºC in H 2 . Soft X ray absorption spectroscopy was performed in a gas flow cell under reaction conditions of H 2 and CO at atmospheric pressure. Flow of pure hydrogen at 350ºC removed the protecting surfactant layer and reduced the NP from oxidized to metallic. The NP remained metallic during the methanation reaction with their surface covered by CO. The methanation turnover frequency of silica supported NP was found to decrease with diameter below 10 nm, while the reaction activation energy was found to be independent of NP size. H-D exchange experiments indicated that it is the dissociation of H 2 that is responsible for the observed decrease in activity with size.2 KEYWORDS. Cobalt, nanoparticles, Fischer-Tropsch, X-ray absorption (XAS), in situ studies, soft xray spectroscopy, particle size dependence.

In situ soft X-ray absorption spectroscopy investigation of electrochemical corrosion of copper in aqueous NaHCO3 solution

“…The large absorption cross-section of most gases and liquids in this energy range requires the use of UHV instrumentation. However by using ultrathin membranes to separate the samples from the UHV environment, soft x-rays can be used for studies under real conditions, such as high-pressure gas and liquid environments [14][15][16][17][18][19][20][21].…”

Generalized kinetic model for iron and cobalt based Fischer–Tropsch synthesis catalysts: Review and model evaluation

“…Also Inverse H 2 -D 2 isotope effect supports H involvement in CO dissociation [59]. Most recently it was found that size-dependent dissociation of carbon monoxide on Co nano-particles is related to H-assisted CO dissociation [60,61].…”

X-ray spectroscopic and scattering methods applied to the characterisation of cobalt-based Fischer–Tropsch synthesis catalysts

“…Spectra are then acquired using the total electron yield method in which a drain current is measured between electrical ground and the sample (resulting from ejected electrons, and secondary electron emission from the sample). This method was adopted for studying model Co FTS catalysts at higher pressures by Salmeron et al in 2009 [90]. They were able to follow the reduction in hydrogen flow at 1 bar of 3 and 10 nm (average sized) nanoparticles using the Co L-edge by this technique, starting in both cases with octahedrally co-ordinated CoO, and observing the formation of metallic cobalt.…”