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

费托合成(FTS)是将一氧化碳和氢气转化为水、二氧化碳和碳氢化合物的化学反应。对于将天然气(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来说，这一反应是一个关键的、具有商业意义的过程。FTS由金属催化剂(例如，铁、钴或Ru)催化，并存在于廉价氧化物载体(例如，二氧化硅、氧化铝或二氧化钛)的非常小的孔中。该研究项目旨在揭开长期存在的关于水在FTS催化中的作用的谜团，并利用这些发现创造新的材料，从而导致更高效和更有选择性的FTS催化剂。这一研究项目的成果将促进将天然气、煤炭和生物质转化为液体燃料和化学品的工作。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和本科生参与这项研究，重点是代表性不足的群体。在FTS过程中形成的水已被证明提高了FTS的速率，并将选择性转移到更理想的长链烃上。然而，这些促进作用并不是普遍存在的，因为一些研究表明，水对FTS率的影响很小，或者会导致FTS率下降。水的影响取决于氧化物载体的孔大小和亲水性，其使用方式表明水可能在载体的孔内凝结。在FTS过程中，这些孔中充满了疏水的液态碳氢化合物，这种疏水环境可以通过有效地减小载体的孔径来帮助水的毛细凝聚。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催化剂来确定在工业相关条件下水是否凝聚在Ru基FTS催化剂的孔内。将使用有机硅烷表面改性剂来改变载体的孔径和疏水性。第二个目标是阐明水对碳-氧键活化的机理作用，以及与FTS的速率和选择性相关的碳-碳键的形成途径。将进行密度泛函计算来研究有无扩展水溶剂化网络的水辅助反应路径。这一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，并确定水对反应速度和机理的影响是需要凝聚的水相还是简单的水蒸气。在与工业相关的条件下，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NSF的法定使命，并通过使用基金会的智力优势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.