Understanding and Controlling Wax-Water Interactions in Pores of Fischer-Tropsch Synthesis Catalysts

University Of Florida, Gainesville FL

Investigators

Abstract

Fischer-Tropsch synthesis (FTS) is a chemical reaction that converts carbon monoxide and hydrogen into water, carbon dioxide, and hydrocarbons. This reaction is a critical and commercially relevant process for upgrading feedstocks such as natural gas (including shale gas resources), coal, and even biomass into useful chemicals and fuels. FTS is catalyzed by metal catalysts (e.g., iron, cobalt or ruthenium) and occurs within very small pores of inexpensive oxide supports (e.g., silica, alumina or titanium dioxide). This research project aims to unravel longstanding mysteries concerning the role of water in FTS catalysis and to leverage those discoveries to create new materials that can lead to more efficient and selective FTS catalysts. The outcomes of this research project will lead to improvements in converting natural gas, coal, and biomass into liquid fuels and chemicals. Furthermore, this project will leverage programs at the University of Florida and Ohio State University to support the involvement of K-12 and undergraduate students, with a focus on under-represented groups, in this research. The water formed during FTS has been shown to increase the rates of FTS as well as shift selectivities towards more desirable long-chain hydrocarbons. However, these promotional effects are not universal, as some studies have shown that water either has a minor impact on FTS rates or causes them to decrease. The effects of water depend on the pore size and hydrophilicity of the oxide support being used in a manner that suggests that water may condense within the pores of the support. These pores are filled with hydrophobic liquid hydrocarbons during FTS, and this hydrophobic environment may assist in capillary condensation of water by effectively reducing the pore size of the support. The first objective of this research project is to determine whether water is condensed within the pores of ruthenium-based FTS catalysts under industrially-relevant conditions by synthesizing and testing Ru catalysts on SBA-15 silica supports. Organosilane surface modifiers will be used to alter the pore size and hydrophobicity of the support. The second objective is to clarify the mechanistic role of water on carbon-oxygen bond activation and carbon-carbon bond formation pathways relevant to the rate and selectivity of FTS. DFT calculations will be performed to study water-assisted reaction pathways with and without extended water solvation networks. The results of this research project will provide additional evidence for the role of water during catalysis and determine whether the influence of water on reaction rates and mechanism requires condensed water phases or simply water vapor. The discovery that water is condensed within the pores of FTS catalysts at industrially-relevant conditions would provide a shift in our understanding of FTS and would have the potential to create new strategies for improving FTS catalyst reactivity, selectivity, and stability. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.