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

不断上升的大气二氧化碳浓度构成了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和对其相关后果的日益认识，将二氧化碳转化为燃料和化学品已成为一个高度相关的主题。在这里，在非贵重的、丰富的、相对便宜的金属催化剂上进行二氧化碳加氢是一项重大进展。将温室气体二氧化碳转化为增值产品的一个关键是高效和选择性催化剂的设计。然而，在催化研究中，寻找更高效、更有选择性的催化剂是一个持续的挑战。合理的催化剂设计需要对目前应用的催化剂和反应机理有基本的了解。这种基本的理解只能通过结合各种分析方法来推导，因为每种方法只提供特定的信息。此外，分析方法应在现场、反应条件和操作条件下应用，结合几种现场方法，以了解实际工作条件下的催化剂。对于二氧化碳转化为甲烷，通常需要镍基催化剂，因为它们具有高活性和选择性。然而，对于二氧化碳加氢生成醇类，包括长链醇类，目前还没有找到最佳的催化剂材料。长链醇在工业和日常生活中的各种应用都需要，比如作为燃料。利用Ni的活性和Fe的选择性，将Ni与另一种金属（例如Fe）结合，这是将Ni的活性和Fe的选择性结合起来的一种可能。本项目的主要目标是通过应用Ni-Fe/SiO2催化剂来调整CO2加氢对醇的选择性，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水平上深入了解这些双金属催化剂。这样，各种分析方法将相互协同，相互印证。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起来才能阐明Ni-Fe/SiO2复合催化剂的全貌。这将包括催化剂的成功合成和对结果结构及其演变的理解，反应机理，结构敏感效应，最后调整对醇的选择性的参数。最终，这种多方面的方法将能够推断出设计下一代双金属催化剂的一般指导方针，使二氧化碳加氢向长链醇的方向迈进一步。

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.