CO activation pathways and the mechanism of Fischer-Tropsch synthesis
CO activation pathways and the mechanism of Fischer-Tropsch synthesis
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DOI：
10.1016/j.jcat.2010.04.012
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发表时间：
2010-06-15
影响因子：
7.3
通讯作者：
Iglesia, Enrique
中科院分区：
文献类型：
--
作者：
Ojeda, Manuel;Nabar, Rahul;Iglesia, Enrique
通过对典型的Fe和Co表面上化学吸附CO的基本步骤的动力学和理论分析，讨论了费托合成（FTS）中单体形成及其氧排斥途径的未解决的机理细节。这些研究为氢辅助CO活化作为主要的动力学和理论证据提供了实验和理论依据。在FTS实践的典型条件下对Fe和Co催化剂进行相关步骤。H-2和CO对FTS速率和氧排斥选择性（如H2O或CO2）的动力学效应和活化势垒和结合能的密度泛函理论估计与H辅助CO解离一致，但与先前接受的直接CO解离和化学吸附碳氢化基本步骤的动力学相关性不一致。H-辅助的CO解离以H2O形式除去O原子，而直接解离形成化学吸附的氧原子，其以CO2形式解吸。直接CO解离路线是次要的贡献者，单体形成的Fe和可能成为有利的在高温下碱促进的催化剂，但不是在Co催化剂，除去氧主要作为H2O，因为H-辅助CO解离路线的优势。实验和理论的结合使以前由单独的实验和理论研究所未解决的持久的机械问题得以澄清。(C)2010年爱思唯尔公司All rights reserved.
Unresolved mechanistic details of monomer formation in Fischer-Tropsch synthesis (FTS) and of its oxygen rejection routes are addressed here by combining kinetic and theoretical analyses of elementary steps on representative Fe and Co surfaces saturated with chemisorbed CO. These studies provide experimental and theoretical evidence for hydrogen-assisted CO activation as the predominant kinetically-relevant step on Fe and Co catalysts at conditions typical of FTS practice. H-2 and CO kinetic effects on FTS rates and oxygen rejection selectivity (as H2O or CO2) and density functional theory estimates of activation barriers and binding energies are consistent with H-assisted CO dissociation, but not with the previously accepted kinetic relevance of direct CO dissociation and chemisorbed carbon hydrogenation elementary steps. H-assisted CO dissociation removes O-atoms as H2O, while direct dissociation forms chemisorbed oxygen atoms that desorb as CO2. Direct CO dissociation routes are minor contributors to monomer formation on Fe and may become favored at high temperatures on alkali-promoted catalysts, but not on Co catalysts, which remove oxygen predominantly as H2O because of the preponderance of H-assisted CO dissociation routes. The merging of experiment and theory led to the clarification of persistent mechanistic issues previously unresolved by separate experimental and theoretical inquiries. (C) 2010 Elsevier Inc. All rights reserved.