基于原子层沉积法调控的Fe-Cu催化剂用于合成气直接制低碳醇的研究

The direct synthesis of higher alcohols (C2+-OH) as ultra clean fuels from coal derived synthesis gas (CO/H2) and Fischer-Tropsch reaction has become one of the strategies to solve the rapid depletion of oil resources and the environmental issues. Currently, the highly dispersed Fe-Cu based bimetallic catalysts usually suffered from phase separation during the reaction leading to the declined selectivity to higher alcohols. In this project, we are planning to introduce a controllable porous metal oxide overcoating by atomic layer deposition (ALD) method onto the surface of highly dispersed Fe-Cu bimetallic nanoparticles to immobilize them and prevent their phase separation in the reaction. To establish a suitable preparation and activation method of Fe-Cu based bimetallic catalysts with higher selectivity to higher alcohols, several activation procedures and active components introduction methods as well as the ratio of Fe/Cu are going to be investigated. Combined with well-designed characterization techniques and experimental means, the relationship between the catalytic performances, such as activity and selectivity, and the composition and distribution of active phases as well as their evolutions will be clarified. Further, the influence of the type, thickness and pore structure of ALD membrane on the evolution of active phases during the reaction will be illustrated. Based on the above mentioned concerns, Fe-Cu based bimetallic catalyst for higher alcohol synthesis with high activity, high selectivity to higher alcohols and high stability is expected to be obtained, and it will provide a strategy to solve the problem of phase separation induced catalytic performance degradation.

由煤基合成气（CO/H2）经费托合成直接制超清洁低碳醇燃料是解决石油资源枯竭和环境问题的重要途径。本项目针对高度分散的Fe-Cu双金属催化剂在反应中容易发生Fe、Cu相分离，从而导致低碳醇选择性下降的关键问题，探索采用原子层沉积（Atomic layer deposition, ALD）法在高度分散的Fe-Cu纳米颗粒表面可控地引入多孔氧化物膜层，达到固定纳米颗粒、抑制其在反应过程中发生相分离的目的。通过研究活性组分的引入方式、配比和活化方式，建立获得高选择性低碳醇的Fe-Cu催化剂的制备和活化方法；运用多种表征技术和实验手段，阐明反应过程中催化活性、选择性与活性相组成、分布及其演变之间的关系，探索ALD沉积膜的种类、厚度和孔结构等因素对活性相演变的影响，获得高活性、高选择性和高稳定性的Fe-Cu双金属催化剂。本项目研究将为解决催化剂因相分离而导致的催化性能下降提供解决方案和思路。

二氧化碳作为一种温室气体，其对全球的气候变化造成了严重的影响，它的排放已经引起了世界范围内的广泛关注。同时，二氧化碳也是一种可再生、可持续的碳资源。它的转化和利用能够缓解对煤、石油、天然气能化石资源的依赖。由于二氧化碳分子的化学稳定性和化学惰性，其单独的转化和利用需要消耗大量的能量。但当还原剂H2存在的时候，CO2的转化变得容易了。因此CO2加氢被用来生产各种化学品，如低碳烯烃、液体燃料、芳烃以及含氧化合物等。在这些反应中二氧化碳加氢制甲醇被广泛研究，因为甲醇不仅可以直接作为燃料使用，而且它是一种重要的平台化合物，可以用来制备烯烃、芳烃等。本项目围绕影响二氧化碳加氢反应路径的关键科学问题，系统研究了氧空位、粒径、金属-氧化物界面等对二氧化碳活化以及反应路径的影响。结果表明氧空位有利于二氧化碳的活化和转化，但氧空位的反应活性受限于氧空位的形成能。比较低的氧空位形成能虽然有利于氧空位数量的增加，但其单个反应活性并不高。因此，合适的氧空位形成能对于提高二氧化碳的转化率很重要，其中棒状CeO2暴露（110）和（111）晶面具有最高的二氧化碳活化能力。不同金属粒径对二氧化碳加氢的影响不同。对于Pd金属，小颗粒的Pd有利于形成甲酸盐中间体，进而有利于甲醇的形成；而大颗粒的Pd金属则有利于CO和甲烷的生成；而对于Cu金属，Cu-ZnO界面处有利于形成甲酸盐中间体，是生成甲醇的主要位点，而小颗粒的Cu则有利于形成COOH中间体，进而有利于CO的形成。无论是Pd还是Cu，金属-载体界面都是形成甲醇的主要位点，因为二氧化碳的加氢反应需要同时活化CO2和H2，而金属主要吸附和活化H2，载体则主要吸附和活化CO2。这些研究成果为进一步设计和开发高活性、高选择性的二氧化碳加氢催化剂提供了研究基础。