Fe/Co催化剂在合成气转化领域的新进展:结构调控和性能强化

C1化学通常是指所有参与反应的分子都只含有一个碳原子, 是煤化学和天然气化学的核心, 其中合成气(CO + H2)转化是其中最重要的工业反应体系. 如今部分国家和地区, 由于能源结构调整和煤炭资源利用, 急需开发更清洁、更高效的绿色能源. 合成气转化作为煤炭间接液化技术中最重要的一个环节, 根据目标产物的不同已经发展了三个主要的反应体系: 传统的费托合成制备汽油、柴油和蜡等饱和碳氢化合物, 类费托合成制备以低碳烯烃、芳香化合物为主的不饱和碳氢化合物, 以及一步转化为高碳醇的含氧化合物.铁/钴作为两种主要的工业催化剂, 引起了研究者的广泛关注. 不同的产物对于催化体系的要求不同, 即使催化剂的组 成相同, 仍需对催化剂的结构进行大范围的调变和修饰. 而催化剂结构的改变可以通过载体的选择、助剂的修饰和活化条件的调控来改变催化剂中活性相的尺寸和分散度、活性位点的电子密度甚至获得新的活性物种. 通过对催化剂进行改性,我们可以有效的促进反应物的活化、削弱产物的吸附并最终获得目标产物. 与此同时, 反应条件的优化(温度和压力)、反应介质的转变和不同反应的耦合同样可以极大改变催化性能. 由此可见, 无论是直接对催化剂结构进行修饰还是间接的改变反应条件都可以有效的提升催化性能.高效催化剂的设计主要基于结构调控和新反应体系的建立, 本文系统地综述了铁/钴催化剂在合成气转化方面的三个重要反应和最新研究进展. 第一部分概述了费-托合成反应中关于铁活性物种的辨别与确认、对制备汽油和柴油的性能优化, 着重介绍了原位技术在该反应中的应用及对催化体系中构效关系的揭示. 第二部分讨论了制备烯烃和芳香化合物等不饱和碳氢化合物的催化剂结构设计, 总结了产物选择性(尤其是C2-C4烯烃选择性)的调控方法. 第三部分综述了近期报导的合成气直接转化为高碳醇的催化剂的研究进展, 包括制备方法、载体和助剂对于提升总醇和高碳醇选择性的影响. 最后, 本文探讨了该领域尚未解决的问题, 主要包括制备烯烃和高碳醇的性能仍距实际工业生产的指标相去甚远、在苛刻的反应条件下活性位点极难保持稳定的结构、以及反应体系的复杂性对于深入理解反应机理所造成的阻碍, 并从新型催化剂的制备、金属载体相互作用的调控、原位实验的探究等方面提出了可行的解决方案.

New development in Fe/Co catalysts: Structure modulation and performance optimization for syngas conversion

C1 chemistry is the essence of coal chemistry and natural gas chemistry. Catalytic methods to effi-ciently convert C1 molecules into fuels and chemicals have been extensively studied. Syngas (CO +H2) conversion is the most important industrial reaction system in C1 chemistry, and Fe and Co catalysts, two major industrial catalysts, have been the focus of fundamental research and industrial application. In the last decade, considerable research efforts have been devoted to discoveries con-cerning catalyst structure and increasing market demands for olefins and oxygenates. Since the development of efficient catalysts would strongly benefit from catalyst design and the establish-ment of a new reaction system, this review comprehensively overviews syngas conversion in three main reactions, highlights the advances recently made and the challenges that remain open, and will stimulate future research activities. The first part of the review summarizes the breakthroughs in Fischer-Tropsch synthesis regarding the optimization of activity and stability, determination of the active phase, and mechanistic studies. The second part overviews the modulation of catalytic struc-ture and product selectivity for Fischer-Tropsch to olefins (FTO). Catalysts designed to produce higher alcohols, as well as to tune product selectivity in C1 chemistry, are described in the third section. Finally, present challenges in syngas conversion are proposed, and the solutions and pro-spects are discussed from the viewpoint of fundamental research and practical application. This review summarizes the latest advances in the design, preparation, and application of Fe/Co-based catalysts toward syngas conversion and presents the challenges and future directions in producing value-added fuels.