The steady state approximation is fundamental to the way we study catalytic processes; yet it limits the type of information we can gain from reactor experiments. Transient kinetic reactors – such as Chemical Transient Kinetics, Steady State Isotopic Transient Kinetic Analysis, and others – can probe kinetic and surface information that are inaccessible by steady-state measurements alone. As the field of heterogeneous catalysis moves toward a deeper understanding of fundamental surface processes, transient kinetic experiments will play an important role in contributing new, experimental reaction data.<br/>This presentation will focus on a chemical transient kinetics study of size controlled cobalt nanoparticles for the Fischer-Tropsch (FT) reaction (catalytic hydrogenation of CO to longer chain hydrocarbons). As FT synthesis is a complex, multi-pathed reaction having a large product distribution, controlling the selectivity is highly desirable to eliminate waste and unwanted products. Cobalt is commonly used as a catalyst for the FT reaction and it displays a rate dependence on the catalyst particle size. At particle sizes less than ~8nm, the turn over frequency (TOF) of Co catalysts decreases. To understand this phenomenon, colloidal chemistry is employed to prepare well-defined, size controlled, cobalt nanoparticles supported on silica as model catalysts.<br/>Results from atmospheric pressure transient studies (H2/CO = 2) will be presented and discussed in light of the observed size dependence of cobalt catalysts. Large Co nanoparticles (9.5nm) can support &gt;2 C atoms/Co surface site, while small Co particles (4.3nm) can support &lt;0.5 C atoms/Co surface site. In addition, the evolution of the product distribution at short timescales is evaluated in relation to the ‘build-up’ of carbon on the surface.

Size Controlled Co Nanoparticles for Fischer-Tropsch Synthesis: Transient Kinetics for Mechanistic Insight

253rd National Meeting (2017)

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