(569ee) Support Effects in Fischer-Tropsch Synthesis

In this work, we are developing a new generation of Fischer-Tropsch catalysts that is aimed to optimize the C₅₊ selectivity under ambient pressure condition by leveraging the electronic metal-support interaction (EMSI).

Our central hypothesis is that by using basic oxide supports, electron density can be injected into supported ruthenium (Ru) and cobalt (Co) nanoparticles, strengthening the binding of CO to the surface and driving the selectivity toward long-chain hydrocarbons and eliminating methanation.

For Co catalysts, we found that methane selectivity decreased from 35% to 17% over Co/SiO₂ and Co/MgAlO_x, respectively, with a concurrent increase in C₅₊ selectivity at atmospheric pressure and 493 K. Systematic decreases in the basicity of the support increased the methane selectivity and decreased the C5+ selectivity. These results are attributed to the stronger CO binding on the Co surface, as evidenced by higher CO desorption temperatures and a shift in the CO IR stretching frequency to higher wavenumbers on the basic supports.

Similarly, for Ru catalysts, the methane selectivity at differential conversion was about 35% lower over Ru/MgO compared to Ru/SiO₂. To probe the changes in the Ru d-band as a result of support basicity, we performed Ru L_III edge XANES, as the 2p to 4d transition is symmetry allowed. The spectra of the MgO-supported catalyst show a decreased density of holes in the 4d band of Ru, compared to that of the SiO₂-supported catalyst, consistent with electron donation from the basic support.