It is well established that metal oxides deposited onto the surface of Co nanoparticles influence their activity and selectivity for Fischer-Tropsch synthesis. Until recently, though, there was little evidence for the spatial relationship of the metal oxide and the Co and its effects on the chemisorption of CO. High-resolution elemental mapping by STEM-EDS has recently shown that depending on the composition of the metal oxide it may disperse either with preferential contact with the CO nanoparticles, as in the case of MnO, or non-preferential contact, as in the case of ZrO2. The effect of a metal oxide promoter on the activity and selectivity of Fischer-Trospch synthesis depends on the fraction of the surface of the Co nanoparticles covered and on the Lewis acidity of the metal cations comprising the metal oxide. In all cases, the presence of the metal oxide increase the FTS activity of Co, reduces the selectivity to CH4, and increases the selectivity to C5+ products. The enhance activity is ascribed to enhanced C-O bond cleavage at sites located along the metal oxide-metal perimeter of the metal oxide particles, whereas the shift to higher molecular weight products is ascribed to a decrease in the H/CO ratio in the adsorbed species on the Co surface. Experimental and theoretical evidence supporting these ideas will be presented. It will be demonstrated that quantum chemical calculations nicely support the qualitative interpretation deduced from the experimental results.

Influence of metal oxide promoters on Fischer Tropsch synthesis over Co

251st National Meeting (2016)

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