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

费托合成（FTS）是一种将一氧化碳和氢转化为水、二氧化碳和碳氢化合物的化学反应。该反应是将天然气（包括页岩气资源）、煤炭甚至生物质等原料升级为有用的化学品和燃料的关键和商业相关过程。FTS由金属催化剂（如铁、钴或钌）催化，发生在廉价氧化物载体（如二氧化硅、氧化铝或二氧化钛）的非常小的孔隙中。该研究项目旨在解开长期以来关于水在FTS催化中的作用的谜团，并利用这些发现来创造新的材料，从而产生更高效、更有选择性的FTS催化剂。这项研究项目的成果将导致天然气、煤炭和生物质转化为液体燃料和化学品的改进。此外，该项目将利用佛罗里达大学和俄亥俄州立大学的项目来支持K-12和本科生的参与，重点关注代表性不足的群体。在催化倒换过程中形成的水已被证明可以增加催化倒换的速率，并将选择性转向更理想的长链碳氢化合物。然而，这些促进作用并不是普遍的，因为一些研究表明，水要么对FTS率有轻微影响，要么导致它们下降。水的作用取决于孔隙大小和氧化物载体的亲水性，使用的方式表明水可以在载体的孔隙中凝结。在FTS过程中，这些孔隙中充满疏水液态烃，这种疏水环境可以通过有效地减小支架的孔径来帮助水的毛细凝结。本研究项目的第一个目标是通过在SBA-15二氧化硅载体上合成和测试Ru催化剂，确定在工业相关条件下，钌基FTS催化剂的孔隙内是否存在冷凝水。有机硅烷表面改性剂将用于改变载体的孔径和疏水性。第二个目标是澄清水在碳氧键活化和碳碳键形成途径中的机制作用，这些途径与FTS的速率和选择性有关。DFT计算将用于研究有或没有扩展的水溶剂化网络的水辅助反应途径。本研究项目的结果将为水在催化过程中的作用提供额外的证据，并确定水对反应速率和机理的影响是需要冷凝水相还是简单的水蒸气。在工业相关条件下，水在FTS催化剂的孔内凝结的发现将改变我们对FTS的理解，并有可能创造新的策略来提高FTS催化剂的反应性、选择性和稳定性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.