Chen Wei, Filot Ivo A W, Pestman Robert, Hensen Emiel J M
Laboratory of Inorganic Materials Chemistry, Schuit Institute of Catalysis, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
ACS Catal. 2017 Dec 1;7(12):8061-8071. doi: 10.1021/acscatal.7b02758. Epub 2017 Oct 16.
Fischer-Tropsch (FT) synthesis is one of the most complex catalyzed chemical reactions in which the chain-growth mechanism that leads to formation of long-chain hydrocarbons is not well understood yet. The present work provides deeper insight into the relation between the kinetics of the FT reaction on a silica-supported cobalt catalyst and the composition of the surface adsorbed layer. Cofeeding experiments of CH with CO/H evidence that CH surface intermediates are involved in chain growth and that chain growth is highly reversible. We present a model-based approach of steady-state isotopic transient kinetic analysis measurements at FT conditions involving hydrocarbon products containing up to five carbon atoms. Our data show that the rates of chain growth and chain decoupling are much higher than the rates of monomer formation and chain termination. An important corollary of the microkinetic model is that the fraction of free sites, which is mainly determined by CO pressure, has opposing effects on CO consumption rate and chain-growth probability. Lower CO pressure and more free sites leads to increased CO consumption rate but decreased chain-growth probability because of an increasing ratio of chain decoupling over chain growth. The preferred FT condition involves high CO pressure in which chain-growth probability is increased at the expense of the CO consumption rate.
费托（FT）合成是最复杂的催化化学反应之一，其中导致长链烃形成的链增长机制尚未得到充分理解。目前的工作更深入地洞察了二氧化硅负载钴催化剂上FT反应动力学与表面吸附层组成之间的关系。CH与CO/H的共进料实验表明，CH表面中间体参与链增长，并且链增长是高度可逆的。我们提出了一种基于模型的方法，用于在FT条件下进行稳态同位素瞬变动力学分析测量，所涉及的烃产物含有多达五个碳原子。我们的数据表明，链增长和解链速率远高于单体形成和链终止速率。微观动力学模型的一个重要推论是，主要由CO压力决定的自由位点分数对CO消耗速率和链增长概率有相反的影响。较低的CO压力和更多的自由位点会导致CO消耗速率增加，但链增长概率降低，这是因为链解耦与链增长的比例增加。优选的FT条件涉及高CO压力，其中链增长概率以CO消耗速率为代价而增加。
