Insights into CO2 Hydrogenation: Tuning the Selectivity towards Alcohols by Investigating Ni-Fe Bimetallic Catalysts

大气中二氧化碳浓度的上升是当今社会最具挑战性的问题之一。鉴于正在发生的气候变化及其相关后果的日益认识，将二氧化碳转化为燃料和化学品成为一个高度相关的话题。在这里，二氧化碳在非贵重、丰富和相对廉价的金属催化剂上的加氢是一个重大进展。将温室气体二氧化碳转化为高附加值产品的关键之一是设计高效和选择性的催化剂。然而，在催化研究中，寻找更高效和更选择性的催化剂是一个持续的挑战。合理的催化剂设计要求对目前应用的催化剂和反应机理有基本的了解。只有结合各种分析方法才能得出这样的基本理解，因为每种方法都只提供特定的信息。此外，分析方法应在反应条件下现场应用，并结合几种原位方法来了解催化剂在实际工作条件下的情况。对于二氧化碳转化为甲烷，镍基催化剂因其高活性和选择性而受到普遍欢迎。然而，对于CO2加氢制醇，包括长链醇，目前还没有找到最优的催化剂材料。长链醇在工业和日常生活中的各种应用都需要长链醇作为燃料。在镍基催化剂上将二氧化碳加氢反应的选择性转向长链醇的一种可能性是利用镍的活性和铁的选择性将镍与另一种金属如铁结合起来。本项目的主要目的是通过应用Ni-Fe/SiO_2催化剂来调整二氧化碳加氢合成醇的选择性，并对这些催化剂的结构-功能相关性有一个基本的了解。将采用多方面的方法在不同的水平上深入了解这些双金属催化剂。通过这样做，各种分析方法将相互协同佐证。为了实现这一目标，该项目将建立在四个支柱上：催化剂的合成和评估、详细的结构表征、光谱学和基于X射线的光谱学。只有将所有四个支柱的预期结果结合在一起，才能阐明复杂的Ni-Fe/SiO_2催化剂的全貌。这将包括催化剂的成功合成和对所得到的结构及其演化的理解，反应机理，结构敏感效应，以及最终调节对醇的选择性的参数。最终，这种多方面的方法将能够推导出设计下一代双金属催化剂的一般指导方针，以便在二氧化碳加氢制备长链醇的过程中向前迈进一步。

Rising atmospheric CO2 concentration constitutes one of the most challenging problems of today’s society. In view of the proceeding climate change and increasing awareness of its associated consequences, CO2 conversion into fuels and chemicals became a highly relevant topic. Here, hydrogenation of CO2 over non-noble, abundant, and relatively inexpensive metal catalysts constitutes a major advance. One key to conversion of the greenhouse gas CO2 into value-added products is the design of efficient and selective catalysts.Yet, in catalysis research, seeking more efficient and selective catalysts is an ongoing challenge. Rational catalyst design requires a fundamental understanding of the currently applied catalysts and of the reaction mechanism. Such a fundamental understanding can only be deduced by combining various analysis methods, as each method only provides particular information. Additionally, the analysis methods should be applied in situ, under reaction conditions, and operando, by combining several in situ methods, to understand the catalysts under realistic working conditions.For CO2 conversion to methane, Ni-based catalysts are commonly desired due to their high activity and selectivity. However, for CO2 hydrogenation towards alcohols, including long-chain alcohols, the optimal catalyst material is not yet found. Long-chain alcohols are required for various applications in industry and daily life, like as fuels. One possibility to redirect the selectivity in CO2 hydrogenation towards long-chain alcohols over Ni-based catalysts is to combine Ni with another metal, e.g. Fe, by taking advantage of the activity of Ni and the selectivity of Fe in a combined fashion.The main objective of this project is to tune the selectivity in CO2 hydrogenation towards alcohols by applying Ni-Fe/SiO2 catalysts and to gain a fundamental understanding of structure-function correlations of these catalysts. A multifaceted approach will be applied for gaining insights into these bimetallic catalysts at different levels. By doing so, various analysis methods will synergistically corroborate each other. For achieving this, the project will be built up on four pillars: catalysts synthesis and evaluation, detailed structural characterization, light spectroscopy, and X-ray based spectroscopy. Only the combination of the expected results of all four pillars will allow to elucidate the whole picture of the complex Ni-Fe/SiO2 catalysts. This will comprise the successful catalysts synthesis and the understanding of resulted structures and their evolutions, the reaction mechanism, structure sensitive effects, and finally the parameters for tuning the selectivity towards alcohols. Eventually, this multifaceted approach will enable to deduce a general guideline to design next generation bimetallic catalysts for going one step forward in CO2 hydrogenation towards long-chain alcohols.